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Physicists observationally confirm Hawking’s black hole theorem for the first time

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There are certain rules that even the most extreme objects in the universe must obey. A central law for black holes predicts that the area of their event horizons — the boundary beyond which nothing can ever escape — should never shrink. This law is Hawking’s area theorem, named after physicist Stephen Hawking, who derived the theorem in 1971.

Fifty years later, physicists at MIT and elsewhere have now confirmed Hawking’s area theorem for the first time, using observations of gravitational waves. Their results appear today in Physical Review Letters .

In the study, the researchers take a closer look at GW150914, the first gravitational wave signal detected by the Laser Interferometer Gravitational-wave Observatory (LIGO), in 2015. The signal was a product of two inspiraling black holes that generated a new black hole, along with a huge amount of energy that rippled across space-time as gravitational waves.

If Hawking’s area theorem holds, then the horizon area of the new black hole should not be smaller than the total horizon area of its parent black holes. In the new study, the physicists reanalyzed the signal from GW150914 before and after the cosmic collision and found that indeed, the total event horizon area did not decrease after the merger — a result that they report with 95 percent confidence.

Their findings mark the first direct observational confirmation of Hawking’s area theorem, which has been proven mathematically but never observed in nature until now. The team plans to test future gravitational-wave signals to see if they might further confirm Hawking’s theorem or be a sign of new, law-bending physics.

“It is possible that there’s a zoo of different compact objects, and while some of them are the black holes that follow Einstein and Hawking’s laws, others may be slightly different beasts,” says lead author Maximiliano Isi, a NASA Einstein Postdoctoral Fellow in MIT’s Kavli Institute for Astrophysics and Space Research. “So, it’s not like you do this test once and it’s over. You do this once, and it’s the beginning.”

Isi’s co-authors on the paper are Will Farr of Stony Brook University and the Flatiron Institute’s Center for Computational Astrophysics, Matthew Giesler of Cornell University, Mark Scheel of Caltech, and Saul Teukolsky of Cornell University and Caltech.

An age of insights

In 1971, Stephen Hawking proposed the area theorem, which set off a series of fundamental insights about black hole mechanics. The theorem predicts that the total area of a black hole’s event horizon — and all black holes in the universe, for that matter — should never decrease. The statement was a curious parallel of the second law of thermodynamics, which states that the entropy, or degree of disorder within an object, should also never decrease.

The similarity between the two theories suggested that black holes could behave as thermal, heat-emitting objects — a confounding proposition, as black holes by their very nature were thought to never let energy escape, or radiate. Hawking eventually squared the two ideas in 1974, showing that black holes could have entropy and emit radiation over very long timescales if their quantum effects were taken into account. This phenomenon was dubbed “Hawking radiation” and remains one of the most fundamental revelations about black holes.

“It all started with Hawking’s realization that the total horizon area in black holes can never go down,” Isi says. “The area law encapsulates a golden age in the ’70s where all these insights were being produced.”

Hawking and others have since shown that the area theorem works out mathematically, but there had been no way to check it against nature until LIGO’s first detection of gravitational waves .

Hawking, on hearing of the result, quickly contacted LIGO co-founder Kip Thorne, the Feynman Professor of Theoretical Physics at Caltech. His question: Could the detection confirm the area theorem?

At the time, researchers did not have the ability to pick out the necessary information within the signal, before and after the merger, to determine whether the final horizon area did not decrease, as Hawking’s theorem would assume. It wasn’t until several years later, and the development of a technique by Isi and his colleagues, when testing the area law became feasible.

Before and after

In 2019, Isi and his colleagues developed a technique to extract the reverberations immediately following GW150914’s peak — the moment when the two parent black holes collided to form a new black hole. The team used the technique to pick out specific frequencies, or tones of the otherwise noisy aftermath, that they could use to calculate the final black hole’s mass and spin.

A black hole’s mass and spin are directly related to the area of its event horizon, and Thorne, recalling Hawking’s query, approached them with a follow-up: Could they use the same technique to compare the signal before and after the merger, and confirm the area theorem?

The researchers took on the challenge, and again split the GW150914 signal at its peak. They developed a model to analyze the signal before the peak, corresponding to the two inspiraling black holes, and to identify the mass and spin of both black holes before they merged. From these estimates, they calculated their total horizon areas — an estimate roughly equal to about 235,000 square kilometers, or roughly nine times the area of Massachusetts.

They then used their previous technique to extract the “ringdown,” or reverberations of the newly formed black hole, from which they calculated its mass and spin, and ultimately its horizon area, which they found was equivalent to 367,000 square kilometers (approximately 13 times the Bay State’s area).

“The data show with overwhelming confidence that the horizon area increased after the merger, and that the area law is satisfied with very high probability,” Isi says. “It was a relief that our result does agree with the paradigm that we expect, and does confirm our understanding of these complicated black hole mergers.”

The team plans to further test Hawking’s area theorem, and other longstanding theories of black hole mechanics, using data from LIGO and Virgo, its counterpart in Italy.

“It’s encouraging that we can think in new, creative ways about gravitational-wave data, and reach questions we thought we couldn’t before,” Isi says. “We can keep teasing out pieces of information that speak directly to the pillars of what we think we understand. One day, this data may reveal something we didn’t expect.”

This research was supported, in part, by NASA, the Simons Foundation, and the National Science Foundation.

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Researchers from MIT and other institutions have been able to observationally confirm one of Stephen Hawking’s theorems about black holes, measuring gravitational waves before and after a black hole merger to provide evidence that a black hole’s event horizon can never shrink, reports Caroline Delbert for Popular Mechanics . “This cool analysis doesn't just show an example of Hawking's theorem that underpins one of the central laws affecting black holes,” writes Delbert, “it shows how analyzing gravitational wave patterns can bear out statistical findings.”

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Are black holes time machines? Yes, but there’s a catch

Black holes form natural time machines that allow travel to both the past and the future. But don’t expect to be heading back to visit the dinosaurs any time soon.

At present, we don’t have spacecraft that could get us anywhere near a black hole. But, even leaving that small detail aside, attempting to travel into the past using a black hole might be the last thing you ever do.

What are black holes?

A black hole is an extremely massive object that is typically formed when a dying star collapses in on itself.

Like planets and stars, black holes have gravitational fields around them. A gravitational field is what keeps us stuck to Earth, and what keeps Earth revolving around the Sun.

As a rule of thumb, the more massive an object is, the stronger its gravitational field.

Earth’s gravitational field makes it extremely difficult to get to space. That’s why we build rockets: we have to travel very fast to break out of Earth’s gravity.

The gravitational field of a black hole is so strong that even light can’t escape it. That’s impressive, since light is the fastest thing known to science!

Incidentally, that’s why black holes are black: we can’t bounce light off a black hole the way we might bounce a torch light off a tree in the dark.

Stretching space

Albert Einstein’s general theory of relativity tells us matter and energy have a curious effect on the universe. Matter and energy bend and stretch space. The more massive an object is, the more space is stretched and bent around it.

A massive object creates a kind of valley in space. When objects come near, they fall into the valley.

That’s why, when you get close enough to any massive object, including a black hole, you fall towards it. It’s also why light can’t escape a black hole: the sides of the valley are so steep that light isn’t going fast enough to climb out.

The valley created by a black hole gets steeper and steeper as you approach it from a distance. The point at which it gets so steep that light can’t escape is called the event horizon.

Event horizons aren’t just interesting for would-be time travellers: they’re also interesting for philosophers, because they have implications for how we understand the nature of time .

Stretching time

When space is stretched, so is time. A clock that is near a massive object will tick slower than one that is near a much less massive object.

A clock near a black hole will tick very slowly compared to one on Earth. One year near a black hole could mean 80 years on Earth, as you may have seen illustrated in the movie Interstellar .

In this way, black holes can be used to travel to the future. If you want to jump into the future of Earth, simply fly near a black hole and then return to Earth.

If you get close enough to the centre of the black hole, your clock will tick slower, but you should still be able to escape so long as you don’t cross the event horizon.

Loops in time

What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.

Imagine taking a sheet of paper and joining the two ends to form a loop. That’s what a black hole seems to do to time.

This creates a natural time machine. If you could somehow get onto the loop, which physicists call a closed timelike curve, you would find yourself on a trajectory through space that starts in the future and ends in the past.

Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn cause things to happen in the past!

So, you’ve found a black hole and you want to use your trusty spaceship to go back and visit the dinosaurs. Good luck.

There are three problems. First, you can only travel into the black hole’s past. That means that if the black hole was created after the dinosaurs died out, then you won’t be able to go back far enough.

Second, you’d probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a particular time in the past, you’d need to exit the event horizon. That means travelling faster than light, which we’re pretty sure is impossible.

Third, and probably worst of all, you and your ship would undergo “ spaghettification ”. Sounds delicious, right?

Sadly, it’s not. As you crossed the event horizon you would be stretched flat, like a noodle. In fact, you’d probably be stretched so thin that you’d just be a string of atoms spiralling into the void.

So, while it’s fun to think about the time-warping properties of black holes, for the foreseeable future that visit to the dinosaurs will have to stay in the realm of fantasy.

Sam Baron , Associate Professor, Philosophy of Science, Australian Catholic University

This article is republished from The Conversation under a Creative Commons license. Read the original article .

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Black Holes, Relativity And Time Travel

May 19, 2013 James Miller Black Holes , Time Travel 0

Stories in which people have traveled through time and experienced the effects of time dilation have been around for centuries, with one of the earliest found in the ancient Indian epic the Mahabharata, in which King Revaita travels to another world only to find on his return entire ages have passed.

But is time travel really possible ? Certainly, as we all travel forward in time by one hour per hour, but can we actually go faster or slower than that rate? Scientists now realize we can after Albert Einstein shook the foundations of physics by demonstrating the flexible and relative nature of time .

An atomic clock placed on top of a mountain, for instance, will experience a weaker gravitational force and so go faster than one placed in a valley, in accordance with Einstein’s theory of General Relativity. Also, as predicted by Special Relativity, an atomic clock on an airplane would run slower than a stationary one back on Earth as time slows down as speed increases.

Time Travel and Special Relativity

Consider the equation: Speed = Distance ÷ Time .

Einstein’s theory of special relativity suggests nothing can travel faster than the speed of light, so as the speed of an object approaches the maximum limit set by the speed of light (c), the other variables in the equation start to change with distances becoming shortened relative to time which becomes lengthened.

It actually works out that for a person traveling at 99% the speed of light, time is stretched and slows down by a factor of roughly 7, such that a return journey to a star system 7 light-years away would take the astronaut 2 years to complete, while to an observer on Earth over 14 years would have passed. If, however, our astronaut was able to reach a speed equal to 99.999% the speed of light, then 1 year on board his craft would pass for every 223 years back on Earth.

Time Travel and General Relativity

In addition to speed affecting time, Einstein discovered that gravity, too, causes time to slow down, with the effect more pronounced near a massive object. Therefore, a black hole with its intense gravitational field could potentially provide a fantastic means to travel through time by getting close enough to its Event Horizon without being swallowed up. In principle, by maintaining this “safe” distance you could travel centuries into the future relative to outside observers, although for you just a few hours or days would seem to have elapsed.

Time Travel to The Past

All the scenarios discussed so far involve traveling to the future, but is time travel to the past possible? Yes, in theory at least, as general relativity does allow for a tunnel through space-time linking two distant points in time, which then form a circular time loop called a wormhole or Einstein-Rosen bridge . Similar to a black hole, a wormhole would have a massive gravitational field capable of bending space-time , but in contrast to a black hole’s single point singularity which collapses matter, a wormhole may have a central spinning singularity-shaped ring, known as a Kerr black hole . It may then be possible to pass through its “empty” middle to a white hole on the other side, from which matter is subsequently expelled.

That said, many scientists question the theory of stable, traversable wormholes which are able to be crossed in both directions. Further concerns about time travel to the past are thrown up by temporal paradoxes , such as the Grandfather Paradox , which seem to imply their own negation. Nevertheless, the principles involved in using closed timelike curves to travel and return to one’s own spacetime may be perplexing but still remain theoretically possible.

Famous Stephen Hawking theory about black holes confirmed

The areas of black holes are tied to the amount of disorder in the universe

The gravitational waves emitted by two black holes as they spiral into each other, shown in a simulation.

One of Stephen Hawking's most famous theorems has been proven right, using ripples in space-time caused by the merging of two distant black holes .

The black hole area theorem, which Hawking derived in 1971 from Einstein's theory of general relativity , states that it is impossible for the surface area of a black hole to decrease over time. This rule interests physicists because it is closely related to another rule that appears to set time to run in a particular direction: the second law of thermodynamics , which states that the entropy , or disorder, of a closed system must always increase. Because a black hole's entropy is proportional to its surface area, both must always increase.

According to the new study, the researchers' confirmation of the area law seems to imply that the properties of black holes are significant clues to the hidden laws that govern the universe. Oddly, the area law seems to contradict another of the famous physicist's proven theorems: that black holes should evaporate over extremely long time scale, so figuring out the source of the contradiction between the two theories could reveal new physics.

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"A black hole's surface area can't be decreased, which is like the second law of thermodynamics. It also has a conservation of mass, as you can't reduce its mass, so that's analogous to the conservation of energy," lead author Maximiliano Isi, an astrophysicist at the Massachusetts Institute of Technology, told Live Science. "Initially people were like 'Wow, that's a cool parallel,' but we soon realized that this was fundamental. Black holes have an entropy, and it's proportional to their area. It's not just a funny coincidence, it's a deep fact about the world that they reveal."

A black hole's surface area is set out by a spherical boundary known as the event horizon — beyond this point nothing, not even light, can escape its powerful gravitational pull. According to Hawking's interpretation of general relativity, as a black hole's surface area increases with its mass, and because no object thrown inside can exit, its surface area cannot decrease. But a black hole's surface area also shrinks the more it spins, so researchers wondered whether it would be possible to throw an object inside hard enough to make the black hole spin enough to decrease its area.

"You will make it spin more, but not enough to counterbalance the mass you've just added," Isi said. "Whatever you do, the mass and the spin will make it so that you end up with a bigger area."

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To test out this theory, the researchers analyzed gravitational waves, or ripples in the fabric of space-time, created 1.3 billion years ago by two behemoth black holes as they spiraled toward each other at high speed. These were the first waves ever detected in 2015 by the Advanced Laser Interferometer Gravitational-Wave Observatory (LIGO), a laser beam split into two 2,485-mile-long (4 kilometer) paths, and capable of detecting the slightest distortions in space-time by how they alter its path length.

By splitting the signal into two halves — before and after the black holes merged — the researchers calculated mass and the spin of both the two original black holes and the new combined one. These numbers, in turn, allowed them to calculate the surface area of each black hole before and after the collision.

"As they spin around each other faster and faster, the gravitational waves increase in amplitude more and more until they eventually plunge into each other — making this big burst of waves," Isi said. "What you're left with is a new black hole that's in this excited state, which you can then study by analyzing how it's vibrating. It's like if you ping a bell, the specific pitches and durations it rings with will tell you the structure of that bell, and also what it's made out of."

The surface area of the newly created black hole was greater than that of the initial two combined, confirming Hawking's area law with a more than 95% level of confidence. According to the researchers, their results are pretty much in line with what they expected to find. The theory of general relativity — where the area law came from — does a very effective job of describing black holes and other large scale objects.

The real mystery however, begins when we try to integrate general relativity — the rules of big objects — with quantum mechanics — those of the very small. Weird events start to take place, wreaking havoc on all of our hard and fast rules, and breaking the area law completely.

This is because black holes cannot shrink according to general relativity, but they can according to quantum mechanics. The iconic British physicist behind the surface area law also developed a concept known as Hawking radiation — where a a fog of particles are emitted at the edges of black holes through strange quantum effects. This phenomenon leads the black holes to shrink and, eventually, over a time period several times longer than the age of the universe, evaporate. This evaporation may happen over timescales long enough to not violate the area law in the short term, but that's small consolation for physicists.

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"Statistically, over a long period of time, the law is violated," Isi said. "It's like boiling water, you're getting steam evaporating from your pan, but if you only limit yourself to looking at the disappearing water inside of it, you might be tempted to say the entropy of the pan is decreasing. But if you take the steam into account too, your overall entropy has increased. It's the same with black holes and Hawking radiation."

With the area law established for short to medium time frames, the researchers' next steps will be to analyze data obtained from more gravitational waves for deeper insights that could be gleaned from black holes.

"I'm obsessed with these objects because of how paradoxical they are. They're extremely mysterious and confounding, yet at the same time we know them to be the simplest objects that exist," Isi said. "This, as well as the fact that they're where gravity meets quantum mechanics, makes them the perfect playgrounds for our understanding of what reality is."

The researchers published their findings May 26 in the Journal Physical Review Letters .

Originally published on Live Science.

Ben Turner is a U.K. based staff writer at Live Science. He covers physics and astronomy, among other topics like tech and climate change. He graduated from University College London with a degree in particle physics before training as a journalist. When he's not writing, Ben enjoys reading literature, playing the guitar and embarrassing himself with chess.

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14 March 2024

Do black holes explode? The 50-year-old puzzle that challenges quantum physics

Davide Castelvecchi

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Fifty years after Stephen Hawking’s seminal paper, it remains unclear what happens to information swallowed by black holes. Credit: EHT Collaboration

In hindsight, it seems prophetic that the title of a Nature paper published on 1 March 1974 ended with a question mark: “Black hole explosions?” Stephen Hawking’s landmark idea about what is now known as Hawking radiation 1 has just turned 50. The more physicists have tried to test his theory over the past half-century, the more questions have been raised — with profound consequences for how we view the workings of reality.

In essence, what Hawking, who died six years ago today, found is that black holes should not be truly black, because they constantly radiate a tiny amount of heat. That conclusion came from basic principles of quantum physics, which imply that even empty space is a far-from-uneventful place. Instead, space is filled with roiling quantum fields in which pairs of ‘virtual’ particles incessantly pop out of nowhere and, under normal conditions, annihilate each other almost instantaneously.

However, at an event horizon, the spherical surface that defines the boundary of a black hole, something different happens. An event horizon represents a gravitational point of no return that can be crossed only inward, and Hawking realized that there two virtual particles can become separated. One of them falls into the black hole, while the other radiates away, carrying some of the energy with it. As a result, the black hole loses a tiny bit of mass and shrinks — and shines.

Unexpected ramifications

The power of Hawking’s 1974 paper lies in how it combined basic principles from the two pillars of modern physics. The first, Albert Einstein’s general theory of relativity — in which black holes manifest themselves — links gravity to the shape of space and time, and is typically relevant only at large scales. The second, quantum physics, tends to show up in microscopic situations. The two theories seem to be mathematically incompatible, and physicists have long struggled to find ways to reconcile them. Hawking showed that the event horizon of a black hole is a rare place where both theories must play a part, with calculable consequences.

Science mourns Stephen Hawking’s death

And profoundly unsettling ones at that, as quickly became apparent. The random nature of Hawking radiation means that it carries no information whatsoever. As Hawking soon realized 2 , this means that black holes slowly erase any information about anything that falls in, both when the black hole originally forms and subsequently as it grows — in apparent contradiction to the laws of quantum mechanics, which say that information can never be destroyed. This conundrum became known as the black-hole information paradox.

It has since turned out that black holes should not be the only things that produce Hawking radiation. Any observer accelerating through space could, in principle, pick up similar radiation from empty space 3 . And other analogues of black-hole shine abound in nature. For example, physicists have shown that in a moving medium, sound waves trying to move upstream seem to behave just as Hawking predicted. Some researchers hope that these experiments could provide hints as to how to solve the paradox.

A scientific wager

In the 1990s, the black-hole information paradox became the subject of a celebrated bet. Hawking, together with Kip Thorne at the California Institute of Technology (Caltech) in Pasadena, proposed that quantum mechanics would ultimately need to be amended to take Hawking radiation into account. Another Caltech theoretical physicist, John Preskill, maintained that information would be found to somehow be preserved, and that quantum mechanics would be saved.

But in 1997, theoretical physicist Juan Maldacena, who is now at the Institute for Advanced Study in Princeton, New Jersey, came up with an idea that indicated Hawking and Thorne might be wrong 4 . His paper now has more than 24,000 citations, even more than the 7,000 or so times Hawking’s paper has been cited. Maldacena suggested that the Universe — including the black holes it contains — is a type of hologram, a higher-dimensional projection of events that occur on a flat surface. Everything that happens on the flat world can be described by pure quantum mechanics, and so preserves information.

Cosmologist Stephen Hawking reacts during a conversation on October 10, 1979 in Princeton, New Jersey.

Stephen Hawking worked on the black-hole information paradox throughout his life. Credit: Santi Visalli/Getty

At face value, Maldacena’s theory doesn’t fully apply to the type of Universe that we inhabit. Moreover, it did not explain how information could escape destruction in a black hole — only that it should, somehow. “We don’t have a concrete grasp of the mechanism,” says Preskill. Physicists, including Hawking , have proposed countless escape mechanisms, none of which has been completely convincing, according to Preskill. “Here it is, 50 years after that great paper, and we’re still puzzled,” he says. (Maldacena’s ideas were enough to change Hawking’s mind, however, and he conceded the bet in 2004.)

A quantum conundrum

Attempts to solve the information paradox have grown into a thriving industry. One of the ideas that has gained traction is that each particle that falls into a black hole is linked to one that stays outside through quantum entanglement — the ability of objects to share a single quantum state even when far apart. This connection could manifest itself in the geometry of space-time as a ‘wormhole’ joining the inside of the event horizon with the outside.

Entanglement is also one of the crucial features that make quantum computers potentially more powerful than classical ones. Moreover, in the past decade, the link between black holes and information theory has become only stronger, as Preskill and others have investigated similarities between what happens in holographic projections and the types of error-correction algorithm developed for quantum computers. Error correction is a way of storing redundant information that enables a computer — whether classical or quantum — to restore corrupted bits of information. Some researchers see quantum computation theory as the key to solving Hawking’s paradox. When creating a black hole, the Universe could be similarly storing several versions of its information — some inside the event horizon, some outside — so that the destruction of the black hole does not erase any history.

Hawking’s latest black-hole paper splits physicists

But other researchers think that the full resolution of the information paradox might have to wait until another big problem is solved — that of reconciling gravity with quantum physics. Hawking continued working on the problem almost up until his death, but with no clear outcome .

As for the title of Hawking’s paper, seeing actual black-hole explosions is a possibility that astronomers take seriously. Large black holes act like very cold bodies, but smaller ones are hotter, which makes them shrink faster; and the particles they shed should become more and more energetic, reaching a culmination when the black hole disappears. Hawking showed that ‘ordinary’ stellar-mass black holes, which form when massive stars collapse in on themselves at the end of their lives, take many times longer than the age of the Universe to get to this point. But, in principle, black holes with a range of smaller masses could have formed from random fluctuations in the density of matter during the first moments after the Big Bang. If a primordial black hole of the right mass were to fizzle into non-existence somewhere near the Solar System, it could be picked up by neutrino and γ-ray observatories.

Astronomers have not seen any black holes explode so far, but they are still on the lookout 5 . Such an observation would have certainly earned Hawking the Nobel Prize that eluded him all his life. As it is, the questions produced by his simple, inquisitive paper title look set to nourish the intersection between cosmology and physics for a good few years yet.

doi: https://doi.org/10.1038/d41586-024-00768-4

Hawking, S. W. Nature 248 , 30–31 (1974).

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Hawking, S. W. Phys. Rev. D 14 , 2460–2473 (1976).

Unruh, W. G. Phys. Rev. D 14 , 870–892 (1976).

Maldacena, J. Adv. Theor. Math. Phys. 2 , 231–252 (1998).

The IceCube Collaboration. In Proc. 36th International Cosmic Ray Conference (ICRC2019) Vol. 358, article 863 (2019).

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Are black holes time machines? Yes, but there's a catch

The Conversation

Topic: Astronomy (Space)

A NASA visualisation of a black hole shows it is neither black, nor a hole. ( Supplied: NASA's Goddard Space Flight Center/Jeremy Schnittman )

Black holes form natural time machines that allow travel to both the past and the future. But don't expect to be heading back to visit the dinosaurs any time soon.

At present, we don't have spacecraft that could get us anywhere near a black hole. But, even leaving that small detail aside, attempting to travel into the past using a black hole might be the last thing you ever do.

What are black holes?

A black hole is an extremely massive object that is typically formed when a dying star collapses in on itself.

Like planets and stars, black holes have gravitational fields around them. A gravitational field is what keeps us stuck to Earth, and what keeps Earth revolving around the Sun.

As a rule of thumb, the more massive an object is, the stronger its gravitational field.

Earth's gravitational field makes it extremely difficult to get to space. That's why we build rockets: we have to travel very fast to break out of Earth's gravity.

The gravitational field of a black hole is so strong that even light can't escape it. That's impressive, since light is the fastest thing known to science!

Incidentally, that's why black holes are black: we can't bounce light off a black hole the way we might bounce a torch light off a tree in the dark.

Stretching space

Albert Einstein's general theory of relativity tells us matter and energy have a curious effect on the universe. Matter and energy bend and stretch space. The more massive an object is, the more space is stretched and bent around it.

A massive object creates a kind of valley in space. When objects come near, they fall into the valley.

That's why, when you get close enough to any massive object, including a black hole, you fall towards it. It's also why light can't escape a black hole: the sides of the valley are so steep that light isn't going fast enough to climb out.

The valley created by a black hole gets steeper and steeper as you approach it from a distance. The point at which it gets so steep that light can't escape is called the event horizon.

Event horizons aren't just interesting for would-be time travellers: they're also interesting for philosophers, because they have implications for how we understand the nature of time .

Stretching time

When space is stretched, so is time. A clock that is near a massive object will tick slower than one that is near a much less massive object.

A clock near a black hole will tick very slowly compared to one on Earth. One year near a black hole could mean 80 years on Earth, as you may have seen illustrated in the movie Interstellar .

In this way, black holes can be used to travel to the future. If you want to jump into the future of Earth, simply fly near a black hole and then return to Earth.

If you get close enough to the centre of the black hole, your clock will tick slower, but you should still be able to escape so long as you don't cross the event horizon.

Loops in time

What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.

Imagine taking a sheet of paper and joining the two ends to form a loop. That's what a black hole seems to do to time.

Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn cause things to happen in the past!

Unfortunately, you'd probably have to cross the event horizon to get into the loop. ( Supplied: ESA/Hubble, ESO, M. Kornmesser )

So, you've found a black hole and you want to use your trusty spaceship to go back and visit the dinosaurs. Good luck.

There are three problems. First, you can only travel into the black hole's past. That means that if the black hole was created after the dinosaurs died out, then you won't be able to go back far enough.

Second, you'd probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a particular time in the past, you'd need to exit the event horizon. That means travelling faster than light, which we're pretty sure is impossible.

Third, and probably worst of all, you and your ship would undergo " spaghettification ". Sounds delicious, right?

Sadly, it's not. As you crossed the event horizon you would be stretched flat, like a noodle. In fact, you'd probably be stretched so thin that you'd just be a string of atoms spiralling into the void.

So, while it's fun to think about the time-warping properties of black holes, for the foreseeable future that visit to the dinosaurs will have to stay in the realm of fantasy.

Sam Baron is an Associate Professor in Philosophy of Science, Australian Catholic University. This piece first appeared on The Conversation .

Black Holes Could Work as Time Machines — If You Want to Die

Don’t expect to be heading back to visit the dinosaurs any time soon.

Nebula of paint and light on subject of art, design and creativity.

Black holes form natural time machines that allow travel to both the past and the future. But don’t expect to be heading back to visit the dinosaurs any time soon.

What are black holes?

A black hole is an extremely massive object that is typically formed when a dying star collapses in on itself.

Like planets and stars, black holes have gravitational fields around them. A gravitational field is what keeps us stuck to Earth, and what keeps Earth revolving around the Sun.

As a rule of thumb, the more massive an object is, the stronger its gravitational field.

Earth’s gravitational field makes it extremely difficult to get to space. That’s why we build rockets: we have to travel very fast to break out of Earth’s gravity.

The gravitational field of a black hole is so strong that even light can’t escape it. That’s impressive since light is the fastest thing known to science!

Incidentally, that’s why black holes are black: we can’t bounce light off a black hole the way we might bounce a torch light off a tree in the dark.

IN SPACE - APRIL 10: In this handout photo provided by the National Science Foundation, the Event Ho...

M87, the first black hole event horizon ever imaged by telescopes.

Stretching space

A massive object creates a kind of valley in space. When objects come near, they fall into the valley.

That’s why, when you get close enough to any massive object, including a black hole, you fall toward it. It’s also why light can’t escape a black hole: the sides of the valley are so steep that light isn’t going fast enough to climb out.

The valley created by a black hole gets steeper and steeper as you approach it from a distance. The point at which it gets so steep that light can’t escape is called the event horizon.

Event horizons aren’t just interesting for would-be time travelers: they’re also interesting for philosophers because they have implications for how we understand the nature of time .

Stretching time

When space is stretched, so is time. A clock that is near a massive object will tick slower than one that is near a much less massive object.

A clock near a black hole will tick very slowly compared to one on Earth. One year near a black hole could mean 80 years on Earth, as you may have seen illustrated in the movie Interstellar .

In this way, black holes can be used to travel to the future. If you want to jump into the future of Earth, simply fly near a black hole and then return to Earth.

If you get close enough to the center of the black hole, your clock will tick slower, but you should still be able to escape so long as you don’t cross the event horizon.

Loops in time

What about the past? This is where things get truly interesting. A black hole bends time so much that it can wrap back on itself.

Imagine taking a sheet of paper and joining the two ends to form a loop. That’s what a black hole seems to do to time.

Inside the loop, you would also find that cause and effect get hard to untangle. Things that are in the past cause things to happen in the future, which in turn causes things to happen in the past!

Kino. Zurueck In Die Zukunft, Back To The Future, Zurueck In Die Zukunft, Back To The Future, Christ...

Not as easy as hopping in a DeLorean ...

So, you’ve found a black hole and you want to use your trusty spaceship to go back and visit the dinosaurs. Good luck.

Second, you’d probably have to cross the event horizon to get into the loop. This means that to get out of the loop at a particular time in the past, you’d need to exit the event horizon. That means traveling faster than light, which we’re pretty sure is impossible.

Third, and probably worst of all, you and your ship would undergo “ spaghettification ”. Sounds delicious, right?

Sadly, it’s not. As you crossed the event horizon you would be stretched flat, like a noodle. In fact, you’d probably be stretched so thin that you’d just be a string of atoms spiraling into the void.

So, while it’s fun to think about the time-warping properties of black holes, for the foreseeable future that visit to the dinosaurs will have to stay in the realm of fantasy.

This article was originally published on The Conversation by Sam Baron at Australian Catholic University. Read the original article here .

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Physicists Observationally Confirm Hawking’s Black Hole Theorem For The First Time

An age of insights

Hawking and others have since shown that the area theorem works out mathematically, but there had been no way to check it against nature until LIGO’s first detection of gravitational waves .

Hawking, on hearing of the result, quickly contacted LIGO co-founder Kip Thorne, the Feynman Professor of Theoretical Physics at Caltech. His question: Could the detection confirm the area theorem?

Before and after

The team plans to further test Hawking’s area theorem, and other longstanding theories of black hole mechanics, using data from LIGO and Virgo, its counterpart in Italy.

This research was supported, in part, by NASA, the Simons Foundation, and the National Science Foundation.

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Can we time travel? A theoretical physicist provides some answers

Emeritus professor, Physics, Carleton University

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Time travel makes regular appearances in popular culture, with innumerable time travel storylines in movies, television and literature. But it is a surprisingly old idea: one can argue that the Greek tragedy Oedipus Rex , written by Sophocles over 2,500 years ago, is the first time travel story .

But is time travel in fact possible? Given the popularity of the concept, this is a legitimate question. As a theoretical physicist, I find that there are several possible answers to this question, not all of which are contradictory.

The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of thermodynamics or relativity . There are also technical challenges: it might be possible but would involve vast amounts of energy.

There is also the matter of time-travel paradoxes; we can — hypothetically — resolve these if free will is an illusion, if many worlds exist or if the past can only be witnessed but not experienced. Perhaps time travel is impossible simply because time must flow in a linear manner and we have no control over it, or perhaps time is an illusion and time travel is irrelevant.

a woman stands among a crowd of people moving around her

Laws of physics

Since Albert Einstein’s theory of relativity — which describes the nature of time, space and gravity — is our most profound theory of time, we would like to think that time travel is forbidden by relativity. Unfortunately, one of his colleagues from the Institute for Advanced Study, Kurt Gödel, invented a universe in which time travel was not just possible, but the past and future were inextricably tangled.

We can actually design time machines , but most of these (in principle) successful proposals require negative energy , or negative mass, which does not seem to exist in our universe. If you drop a tennis ball of negative mass, it will fall upwards. This argument is rather unsatisfactory, since it explains why we cannot time travel in practice only by involving another idea — that of negative energy or mass — that we do not really understand.

Mathematical physicist Frank Tipler conceptualized a time machine that does not involve negative mass, but requires more energy than exists in the universe .

Time travel also violates the second law of thermodynamics , which states that entropy or randomness must always increase. Time can only move in one direction — in other words, you cannot unscramble an egg. More specifically, by travelling into the past we are going from now (a high entropy state) into the past, which must have lower entropy.

This argument originated with the English cosmologist Arthur Eddington , and is at best incomplete. Perhaps it stops you travelling into the past, but it says nothing about time travel into the future. In practice, it is just as hard for me to travel to next Thursday as it is to travel to last Thursday.

Resolving paradoxes

There is no doubt that if we could time travel freely, we run into the paradoxes. The best known is the “ grandfather paradox ”: one could hypothetically use a time machine to travel to the past and murder their grandfather before their father’s conception, thereby eliminating the possibility of their own birth. Logically, you cannot both exist and not exist.

Read more: Time travel could be possible, but only with parallel timelines

Kurt Vonnegut’s anti-war novel Slaughterhouse-Five , published in 1969, describes how to evade the grandfather paradox. If free will simply does not exist, it is not possible to kill one’s grandfather in the past, since he was not killed in the past. The novel’s protagonist, Billy Pilgrim, can only travel to other points on his world line (the timeline he exists in), but not to any other point in space-time, so he could not even contemplate killing his grandfather.

The universe in Slaughterhouse-Five is consistent with everything we know. The second law of thermodynamics works perfectly well within it and there is no conflict with relativity. But it is inconsistent with some things we believe in, like free will — you can observe the past, like watching a movie, but you cannot interfere with the actions of people in it.

Could we allow for actual modifications of the past, so that we could go back and murder our grandfather — or Hitler ? There are several multiverse theories that suppose that there are many timelines for different universes. This is also an old idea: in Charles Dickens’ A Christmas Carol , Ebeneezer Scrooge experiences two alternative timelines, one of which leads to a shameful death and the other to happiness.

Time is a river

Roman emperor Marcus Aurelius wrote that:

“ Time is like a river made up of the events which happen , and a violent stream; for as soon as a thing has been seen, it is carried away, and another comes in its place, and this will be carried away too.”

We can imagine that time does flow past every point in the universe, like a river around a rock. But it is difficult to make the idea precise. A flow is a rate of change — the flow of a river is the amount of water that passes a specific length in a given time. Hence if time is a flow, it is at the rate of one second per second, which is not a very useful insight.

Theoretical physicist Stephen Hawking suggested that a “ chronology protection conjecture ” must exist, an as-yet-unknown physical principle that forbids time travel. Hawking’s concept originates from the idea that we cannot know what goes on inside a black hole, because we cannot get information out of it. But this argument is redundant: we cannot time travel because we cannot time travel!

Researchers are investigating a more fundamental theory, where time and space “emerge” from something else. This is referred to as quantum gravity , but unfortunately it does not exist yet.

So is time travel possible? Probably not, but we don’t know for sure!

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Astrophysicist says he has cracked the code for time travel

Can you imagine going back in time to visit a lost loved one? This heartwrenching desire is what propelled astrophysicist Professor Ron Mallett on a lifelong quest to build a time machine. After years of research, Professor Mallett claims to have finally developed the revolutionary equation for time travel.

The idea of bending time to our will – revisiting the past, altering history, or glimpsing into the future – has been a staple of science fiction for over a century. But could it move from fantasy to reality?

The inspiration: A father’s love and a classic novel

Professor Mallett’s obsession with time travel and its equation has its roots in a shattering childhood experience. When he was just ten years old, his father, a television repairman who fostered his son’s love of science, tragically passed away from a heart attack.

Devastated, the young Mallett sought solace in books. It was H.G. Wells’ The Time Machine that sparked a lifelong fascination.

Wells’ opening lines became his mantra: “Scientific people know very well that Time is only a kind of Space. And why cannot we move in Time as we move about in the other dimensions of Space?”

This profound question ignited Mallett’s scientific journey. He dedicated himself to understanding the nature of time, determined to find a way to revisit the past and see his beloved father once more.

Time travel equation in the hospital

Decades of research into black holes and Einstein’s theories of relativity led to the time travel equation.

While hospitalized for a heart condition, Mallett had a revelation. “It turns out that black holes can create a gravitational field that could lead to the creation of time loops that could allow us to go back in time,” he explained.

Imagine the fabric of spacetime as a river. While time usually flows in one direction, Mallett theorizes that the immense gravity of a spinning black hole can create whirlpools, where time twists back on itself.

The time machine blueprint

Mallett’s vision for a time machine centers on what he calls “an intense and continuous rotating beam of light” to manipulate gravity. His device would use a ring of lasers to mimic the spacetime-distorting effects of a black hole.

“Let’s say you have a cup of coffee in front of you. Start stirring the coffee with the spoon. It started to spin, right? That’s what a spinning black hole does,” explained Mallett.

“In Einstein’s theory, space and time are related to each other. That’s why it’s called space-time. So when the black hole spins, it will actually cause time to shift.”

“Eventually, a rotating beam of laser lights can be used as a kind of time machine and cause a time warp that will allow us to go back to the past,” said Mallett. Perhaps, what began as a son’s wish to see his father one last time might one day transform our understanding of time itself.

Challenges and limitations

The obstacles on the path from time travel equation to machine are immense. Mallett acknowledges the “galactic amounts of energy” needed to power such a device – energy levels far beyond our current capabilities.

The sheer size of a theoretical time machine is also unknown. While Mallett optimistically states, “I figured out how to do it. In theory, it is possible,” the reality is that he may not live to see the machine built.

Furthermore, Mallett’s theory comes with a significant constraint. “You can send information back, but you can only send it back to the point where you started operating the device.”

In this sense, the time machine is like a one-way message service to the past. You can’t travel to a point before the machine existed.

Mallet’s lifetime of dedication to time travel

Despite the daunting challenges, Mallett’s remarkable journey is a testament to the human spirit. Alongside his time travel research, he’s led a distinguished academic career, teaching physics at the University of Connecticut .

Now in his seventies, his work has been propelled by an unwavering belief in the possibility of the seemingly impossible.

Equation vs. reality of time travel

Whether Mallett’s time machine will ever transcend the realm of theory is uncertain. Skeptics point to the vast technological hurdles and potential paradoxes raised by tampering with time.

Yet, the mere possibility that science might one day unlock the secrets of temporal travel is enough to ignite the imagination. Could we rewrite our regrets, learn from past mistakes, or witness historical events firsthand?

Perhaps Professor Mallett’s greatest legacy won’t be a time travel equation itself, but the inspiration he provides – a reminder that audacious dreams and unrelenting curiosity have the power to push the boundaries of what we believe is possible.

Read more about Professor Mallett’s work here .

More about space-time

As discussed above, space-time, a concept that feels as vast and complex as the universe itself, forms the backbone of our cosmic understanding.

At its core, it blends the dimensions of space and time into a single four-dimensional continuum, challenging our perceptions of reality. This intertwined nature of space and time underpins everything from the motion of planets to the flow of time itself.

Einstein’s groundbreaking contribution

Albert Einstein, with his theory of relativity, revolutionized our understanding of space-time. He posited that space and time are not separate entities but are connected in a dynamic relationship affected by mass and energy.

This relationship implies that the presence of a massive object, like a planet or a star, can warp the fabric of space-time around it. It’s a concept that turns the notion of a flat, unchanging universe on its head, suggesting that the very structure of the cosmos is malleable.

The warp and weft of the cosmos

Imagine space-time as a vast sheet of fabric. When a heavy object sits on this fabric, it creates a dip or curve. This curvature is what we perceive as gravity.

Planets orbit stars not because they are being “pulled” in a straight line towards them, but because they are following the curved space-time geometry that these massive objects create.

This curvature of space-time is not just a theoretical concept; it’s observable and measurable, especially in the presence of extremely massive and dense objects, like black holes.

Gravitational waves: Echoes of cosmic events

One of the most compelling pieces of evidence for the theory of relativity and the dynamic nature of space-time comes from the detection of gravitational waves.

These waves are ripples in the fabric of space-time, generated by some of the most violent and energetic processes in the universe, such as colliding black holes.

Their discovery not only confirmed Einstein’s predictions but also opened a new window into observing cosmic events that were previously invisible to us.

Practical impact of space-time

While these concepts might seem distant from daily life, they have real-world applications, particularly in technology. The Global Positioning System (GPS), a technology integral to modern navigation, relies on an understanding of space-time.

Satellites orbiting Earth need to account for the effects of gravitational time dilation — a consequence of the curvature of space-time — to provide accurate location data to users on the ground.

In summary, space-time is a framework that shapes our understanding of the universe. From guiding the planets in their orbits to enabling precise navigation on Earth, its effects are both profoundly cosmic and surprisingly practical.

As we continue to explore and understand the intricacies of space-time, we edge closer to unraveling the mysteries of the cosmos, one gravitational wave at a time.

How black holes are linked to time travel

Playing a major role in Dr. Mallett’s time machine, black holes exert a gravitational pull so immense that not even light can escape their grasp. This intense gravity fundamentally alters the fabric of space-time around the black hole.

The stronger the gravity, the more pronounced these effects become, leading to what scientists call gravitational time dilation — a phenomenon where time itself warps, slowing down relative to an observer far from the gravitational pull.

Time dilation explained

At the heart of this phenomenon lies Albert Einstein’s theory of General Relativity, which posits that gravity is the result of masses warping the space-time around them.

In the vicinity of a black hole, this warping becomes so extreme that it significantly affects the flow of time.

An observer standing at a safe distance would perceive time to pass much slower for someone closer to the black hole.

This effect intensifies as one approaches the event horizon, the point of no return beyond which the gravitational pull becomes inescapable.

Boundary between time zones

The event horizon of a black hole marks a stark boundary in the universe, where time as we understand it undergoes a dramatic transformation.

To an external observer, objects approaching the event horizon appear to slow down and almost freeze in time, never quite crossing the threshold.

This illusion results from the light from those objects taking longer and longer to reach the observer as the objects move closer to the event horizon, due to the extreme gravitational pull affecting the light’s path.

Theoretical implications and observations

This warping of time around black holes is not just a theoretical curiosity. As Dr. Mallett explained previously in this article, it has practical implications for our understanding of the universe. For instance, it plays a crucial role in the behavior of binary systems where one star orbits a black hole.

Moreover, advancements in technology, such as precise atomic clocks and observations from space telescopes, have allowed scientists to measure these effects, further confirming the predictions of General Relativity.

In summary, black holes serve as natural laboratories for testing the limits of our understanding of physics, offering insights into the complex interplay between gravity and the fabric of space-time.

The phenomenon of time dilation near these cosmic behemoths challenges our notions of time and space, inviting us to explore beyond the boundaries of our current knowledge.

As we continue to observe and study these fascinating objects, we inch closer to unraveling the mysteries of the universe.

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Time travel: Is it possible?

Science says time travel is possible, but probably not in the way you're thinking.

time travel graphic illustration of a tunnel with a clock face swirling through the tunnel.

Albert Einstein's theory

General relativity and GPS
Wormhole travel
Alternate theories

Science fiction

Is time travel possible? Short answer: Yes, and you're doing it right now — hurtling into the future at the impressive rate of one second per second.

You're pretty much always moving through time at the same speed, whether you're watching paint dry or wishing you had more hours to visit with a friend from out of town.

But this isn't the kind of time travel that's captivated countless science fiction writers, or spurred a genre so extensive that Wikipedia lists over 400 titles in the category "Movies about Time Travel." In franchises like " Doctor Who ," " Star Trek ," and "Back to the Future" characters climb into some wild vehicle to blast into the past or spin into the future. Once the characters have traveled through time, they grapple with what happens if you change the past or present based on information from the future (which is where time travel stories intersect with the idea of parallel universes or alternate timelines).

Related: The best sci-fi time machines ever

Although many people are fascinated by the idea of changing the past or seeing the future before it's due, no person has ever demonstrated the kind of back-and-forth time travel seen in science fiction or proposed a method of sending a person through significant periods of time that wouldn't destroy them on the way. And, as physicist Stephen Hawking pointed out in his book " Black Holes and Baby Universes" (Bantam, 1994), "The best evidence we have that time travel is not possible, and never will be, is that we have not been invaded by hordes of tourists from the future."

Science does support some amount of time-bending, though. For example, physicist Albert Einstein 's theory of special relativity proposes that time is an illusion that moves relative to an observer. An observer traveling near the speed of light will experience time, with all its aftereffects (boredom, aging, etc.) much more slowly than an observer at rest. That's why astronaut Scott Kelly aged ever so slightly less over the course of a year in orbit than his twin brother who stayed here on Earth.

Related: Controversially, physicist argues that time is real

There are other scientific theories about time travel, including some weird physics that arise around wormholes , black holes and string theory . For the most part, though, time travel remains the domain of an ever-growing array of science fiction books, movies, television shows, comics, video games and more.

Scott and Mark Kelly sit side by side wearing a blue NASA jacket and jeans

Einstein developed his theory of special relativity in 1905. Along with his later expansion, the theory of general relativity , it has become one of the foundational tenets of modern physics. Special relativity describes the relationship between space and time for objects moving at constant speeds in a straight line.

The short version of the theory is deceptively simple. First, all things are measured in relation to something else — that is to say, there is no "absolute" frame of reference. Second, the speed of light is constant. It stays the same no matter what, and no matter where it's measured from. And third, nothing can go faster than the speed of light.

From those simple tenets unfolds actual, real-life time travel. An observer traveling at high velocity will experience time at a slower rate than an observer who isn't speeding through space.

While we don't accelerate humans to near-light-speed, we do send them swinging around the planet at 17,500 mph (28,160 km/h) aboard the International Space Station . Astronaut Scott Kelly was born after his twin brother, and fellow astronaut, Mark Kelly . Scott Kelly spent 520 days in orbit, while Mark logged 54 days in space. The difference in the speed at which they experienced time over the course of their lifetimes has actually widened the age gap between the two men.

"So, where[as] I used to be just 6 minutes older, now I am 6 minutes and 5 milliseconds older," Mark Kelly said in a panel discussion on July 12, 2020, Space.com previously reported . "Now I've got that over his head."

General relativity and GPS time travel

Graphic showing the path of GPS satellites around Earth at the center of the image.

The difference that low earth orbit makes in an astronaut's life span may be negligible — better suited for jokes among siblings than actual life extension or visiting the distant future — but the dilation in time between people on Earth and GPS satellites flying through space does make a difference.

Can wormholes take us back in time?

General relativity might also provide scenarios that could allow travelers to go back in time, according to NASA . But the physical reality of those time-travel methods is no piece of cake.

Wormholes are theoretical "tunnels" through the fabric of space-time that could connect different moments or locations in reality to others. Also known as Einstein-Rosen bridges or white holes, as opposed to black holes, speculation about wormholes abounds. But despite taking up a lot of space (or space-time) in science fiction, no wormholes of any kind have been identified in real life.

Related: Best time travel movies

"The whole thing is very hypothetical at this point," Stephen Hsu, a professor of theoretical physics at the University of Oregon, told Space.com sister site Live Science . "No one thinks we're going to find a wormhole anytime soon."

Primordial wormholes are predicted to be just 10^-34 inches (10^-33 centimeters) at the tunnel's "mouth". Previously, they were expected to be too unstable for anything to be able to travel through them. However, a study claims that this is not the case, Live Science reported .

The theory, which suggests that wormholes could work as viable space-time shortcuts, was described by physicist Pascal Koiran. As part of the study, Koiran used the Eddington-Finkelstein metric, as opposed to the Schwarzschild metric which has been used in the majority of previous analyses.

In the past, the path of a particle could not be traced through a hypothetical wormhole. However, using the Eddington-Finkelstein metric, the physicist was able to achieve just that.

Koiran's paper was described in October 2021, in the preprint database arXiv , before being published in the Journal of Modern Physics D.

Alternate time travel theories

While Einstein's theories appear to make time travel difficult, some researchers have proposed other solutions that could allow jumps back and forth in time. These alternate theories share one major flaw: As far as scientists can tell, there's no way a person could survive the kind of gravitational pulling and pushing that each solution requires.

Infinite cylinder theory

Astronomer Frank Tipler proposed a mechanism (sometimes known as a Tipler Cylinder ) where one could take matter that is 10 times the sun's mass, then roll it into a very long, but very dense cylinder. The Anderson Institute , a time travel research organization, described the cylinder as "a black hole that has passed through a spaghetti factory."

After spinning this black hole spaghetti a few billion revolutions per minute, a spaceship nearby — following a very precise spiral around the cylinder — could travel backward in time on a "closed, time-like curve," according to the Anderson Institute.

The major problem is that in order for the Tipler Cylinder to become reality, the cylinder would need to be infinitely long or be made of some unknown kind of matter. At least for the foreseeable future, endless interstellar pasta is beyond our reach.

Time donuts

Theoretical physicist Amos Ori at the Technion-Israel Institute of Technology in Haifa, Israel, proposed a model for a time machine made out of curved space-time — a donut-shaped vacuum surrounded by a sphere of normal matter.

"The machine is space-time itself," Ori told Live Science . "If we were to create an area with a warp like this in space that would enable time lines to close on themselves, it might enable future generations to return to visit our time."

Amos Ori is a theoretical physicist at the Technion-Israel Institute of Technology in Haifa, Israel. His research interests and publications span the fields of general relativity, black holes, gravitational waves and closed time lines.

There are a few caveats to Ori's time machine. First, visitors to the past wouldn't be able to travel to times earlier than the invention and construction of the time donut. Second, and more importantly, the invention and construction of this machine would depend on our ability to manipulate gravitational fields at will — a feat that may be theoretically possible but is certainly beyond our immediate reach.

Graphic illustration of the TARDIS (Time and Relative Dimensions in Space) traveling through space, surrounded by stars.

Time travel has long occupied a significant place in fiction. Since as early as the "Mahabharata," an ancient Sanskrit epic poem compiled around 400 B.C., humans have dreamed of warping time, Lisa Yaszek, a professor of science fiction studies at the Georgia Institute of Technology in Atlanta, told Live Science .

Every work of time-travel fiction creates its own version of space-time, glossing over one or more scientific hurdles and paradoxes to achieve its plot requirements.

Some make a nod to research and physics, like " Interstellar ," a 2014 film directed by Christopher Nolan. In the movie, a character played by Matthew McConaughey spends a few hours on a planet orbiting a supermassive black hole, but because of time dilation, observers on Earth experience those hours as a matter of decades.

Others take a more whimsical approach, like the "Doctor Who" television series. The series features the Doctor, an extraterrestrial "Time Lord" who travels in a spaceship resembling a blue British police box. "People assume," the Doctor explained in the show, "that time is a strict progression from cause to effect, but actually from a non-linear, non-subjective viewpoint, it's more like a big ball of wibbly-wobbly, timey-wimey stuff."

Long-standing franchises like the "Star Trek" movies and television series, as well as comic universes like DC and Marvel Comics, revisit the idea of time travel over and over.

Related: Marvel movies in order: chronological & release order

Here is an incomplete (and deeply subjective) list of some influential or notable works of time travel fiction:

Books about time travel:

A sketch from the Christmas Carol shows a cloaked figure on the left and a person kneeling and clutching their head with their hands.

Rip Van Winkle (Cornelius S. Van Winkle, 1819) by Washington Irving
A Christmas Carol (Chapman & Hall, 1843) by Charles Dickens
The Time Machine (William Heinemann, 1895) by H. G. Wells
A Connecticut Yankee in King Arthur's Court (Charles L. Webster and Co., 1889) by Mark Twain
The Restaurant at the End of the Universe (Pan Books, 1980) by Douglas Adams
A Tale of Time City (Methuen, 1987) by Diana Wynn Jones
The Outlander series (Delacorte Press, 1991-present) by Diana Gabaldon
Harry Potter and the Prisoner of Azkaban (Bloomsbury/Scholastic, 1999) by J. K. Rowling
Thief of Time (Doubleday, 2001) by Terry Pratchett
The Time Traveler's Wife (MacAdam/Cage, 2003) by Audrey Niffenegger
All You Need is Kill (Shueisha, 2004) by Hiroshi Sakurazaka

Movies about time travel:

Planet of the Apes (1968)
Superman (1978)
Time Bandits (1981)
The Terminator (1984)
Back to the Future series (1985, 1989, 1990)
Star Trek IV: The Voyage Home (1986)
Bill & Ted's Excellent Adventure (1989)
Groundhog Day (1993)
Galaxy Quest (1999)
The Butterfly Effect (2004)
13 Going on 30 (2004)
The Lake House (2006)
Meet the Robinsons (2007)
Hot Tub Time Machine (2010)
Midnight in Paris (2011)
Looper (2012)
X-Men: Days of Future Past (2014)
Edge of Tomorrow (2014)
Interstellar (2014)
Doctor Strange (2016)
A Wrinkle in Time (2018)
The Last Sharknado: It's About Time (2018)
Avengers: Endgame (2019)
Tenet (2020)
Palm Springs (2020)
Zach Snyder's Justice League (2021)
The Tomorrow War (2021)

Television about time travel:

Image of the Star Trek spaceship USS Enterprise

Doctor Who (1963-present)
The Twilight Zone (1959-1964) (multiple episodes)
Star Trek (multiple series, multiple episodes)
Samurai Jack (2001-2004)
Lost (2004-2010)
Phil of the Future (2004-2006)
Steins;Gate (2011)
Outlander (2014-2023)
Loki (2021-present)

Games about time travel:

Chrono Trigger (1995)
TimeSplitters (2000-2005)
Kingdom Hearts (2002-2019)
Prince of Persia: Sands of Time (2003)
God of War II (2007)
Ratchet and Clank Future: A Crack In Time (2009)
Sly Cooper: Thieves in Time (2013)
Dishonored 2 (2016)
Titanfall 2 (2016)
Outer Wilds (2019)

Additional resources

Explore physicist Peter Millington's thoughts about Stephen Hawking's time travel theories at The Conversation . Check out a kid-friendly explanation of real-world time travel from NASA's Space Place . For an overview of time travel in fiction and the collective consciousness, read " Time Travel: A History " (Pantheon, 2016) by James Gleik.

Join our Space Forums to keep talking space on the latest missions, night sky and more! And if you have a news tip, correction or comment, let us know at: [email protected].

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Vicky Stein is a science writer based in California. She has a bachelor's degree in ecology and evolutionary biology from Dartmouth College and a graduate certificate in science writing from the University of California, Santa Cruz (2018). Afterwards, she worked as a news assistant for PBS NewsHour, and now works as a freelancer covering anything from asteroids to zebras. Follow her most recent work (and most recent pictures of nudibranchs) on Twitter.

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Theoretically, particle physicists could link different corners of the Universe. | Image: Stockernumber2/Dreamstime

Teleportation and travelling forwards through time may be possible through wormholes, the bipolar black holes that link different regions of the universe. This is the conclusion drawn from a model created by Kyriakos Papadodimas of CERN and Rik van Breukelen of the University of Geneva. Instantaneous travel and travel into the future would become possible by travelling through a wormhole, and this completely free of the time dilation predicted by Einstein’s theory of relativity. It is, however, “a purely theoretical model that would only apply to an elementary particle, such as a photon”, adds van Breukelen.

With their model, the physicists have developed a new category of worm hole and describe – in theoretical terms – how information stored on a particle (e.g., using its electrical charge) could travel instantaneously to another part of space-time. “Wormholes are today still only theories”, says van Breukelen. “But, in principal, it would be possible to create an artificial black hole, by using a particle accelerator, for example, although it would have to be a billion kilometres long, the same distance the Earth travels around the sun in a year. So it’s an idea that’s theoretically possible, but also many millennia ahead of its time”.

Investigation into the phenomenon is advancing on two separate tracks: the Anti-de Sitter space (AdS n ), based on a quantum theory of gravitation, and the conformal field theory (CFT), a model of elementary particles that treats them as excitations of the fields of fundamental forces.

This work remains abstract in nature. There’s still a long way to go before computers can simulate the behaviour of particles travelling through a worm hole. “That will require quantum computers, which may not see the light of day for another 15 years. Even then, we’re still talking simulations, but it beats waiting 2,000 years”, says van Breukelen.

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But how does this relate to time travel?

But that's just time travel into the future, what about going back.

December 1, 2015

12 min read

Can Time Travelers Reach the Past via Wormholes?

Astronauts already skip ahead in time, but the laws of physics seem to forbid going backward—or do they?

By Tim Folger

The famous writer H. G. Wells published his first novel, The Time Machine , in 1895, just a few years before Queen Victoria's six-decade reign over the U.K. ended. An even more durable dynasty was also drawing to a close: the 200-year-old Newtonian era of physics. In 1905 Albert Einstein published his special theory of relativity, which upset Isaac Newton's applecart and, presumably to Wells's delight, allowed something that had been impossible under Newton's laws: time travel into the future. In Newton's universe, time was steady everywhere and everywhen. It never sped up. It never slowed down. But for Einstein, time was relative.

Time travel is not merely possible—it has already happened, though not exactly as Wells imagined. The biggest journey through time so far, according to J. Richard Gott, an astrophysicist at Princeton University, was taken by Sergei K. Krikalev. Over the course of his long career, which began in 1985, the Russian cosmonaut spent 803 days in space. As Einstein proved, time passes more slowly for objects in motion than for those at rest, so as Krikalev hurtled along at 17,885 miles an hour onboard the Mir space station, time did not flow at the same rate for him as it did on Earth. While in orbit, Krikalev aged 1/48 of a second less than his fellow earthlings. Put another way, he traveled 1/48 of a second into the future.

The time-travel effect becomes easier to see as distances stretch longer and speeds creep higher. If Krikalev left Earth in 2015 and made a round-trip to Betelgeuse—a star that is about 650 light-years from Earth—at 99.995 percent the speed of light, then by the time he returned to Earth he would be only 10 years older. Sadly, everyone he knew would be long dead because 1,000 years would have passed on Earth; it would be the year 3015. “Time travel to the future, we know we can do,” Gott says. “It's just a matter of money and engineering!”

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Jumping a few nanoseconds—or even a few centuries—into the future is relatively straightforward, practical challenges aside. But going backward in time is harder. Einstein's special theory of relativity forbade it. After another decade of work, Einstein unveiled his general theory of relativity, which finally lifted that restriction. How someone would actually travel back in time, however, is a vexing problem because the equations of general relativity have many solutions. Different solutions assign different qualities to the universe—and only some of the solutions create conditions that permit time travel into the past.

Whether any of those solutions describes our own universe is an open question, which raises even more profound puzzles: Just how much tweaking of fundamental physics would it take to allow backward time travel? Does the universe itself somehow prevent such journeys even if Einstein's equations do not rule them out? Physicists continue to speculate, not because they imagine time travel to the past will ever be practical but because thinking about the possibility has led to some surprising insights about the nature of the universe we live in—including, perhaps, how it came to be in the first place.

A new way of looking at time With his special theory of relativity, Einstein made time malleable in a way that must have pleased Wells, who presciently believed that we inhabit a universe in which three-dimensional space and time are knit together into a four-dimensional whole. Einstein arrived at his revolutionary results by exploring the implications of two fundamental ideas. First, he argued that even though all motion is relative, the laws of physics must look the same for everyone anywhere in the universe. Second, he realized that the speed of light must be similarly unchanging from all perspectives: if everyone sees the same laws of physics operating, they must also arrive at the same result when measuring the speed of light.

To make light a universal speed limit, Einstein had to jettison two commonsense notions: that all observers would agree on the measurement of a given length and that they would also agree on the duration of time's passage. He showed that a clock in motion, whizzing past someone at rest, would tick more slowly than a stationary clock at the person's side. And the length of a ruler moving swiftly by would shorten. Yet for anyone who was traveling at the same speed as the clock and ruler, the passage of time and the length of the ruler would appear normal.

At ordinary speeds, the time-and-space-distorting effects of special relativity are negligible. But for anything moving at a hefty fraction of the speed of light (relative to the observer), they are very real. For example, many experiments have confirmed that the decay rate of unstable particles called muons slows by an order of magnitude when they are traveling at close to the speed of light. The speeding muons, in effect, are minuscule time travelers—subatomic Krikalevs—hopping a few nanoseconds into the future.

Gödel's strange universe Those speedy clocks and rulers and muons are all racing forward in time. Can they be thrown into reverse? The first person to use general relativity to describe a universe that permits time travel into the past was Kurt Gödel, the famed creator of the incompleteness theorems, which set limits on the scope of what mathematics can and cannot prove. He was one of the towering mathematicians of the 20th century—and one of the oddest. His many foibles included a diet of baby food and laxatives.

Gödel presented this model universe as a gift to Einstein on his 70th birthday. The universe Gödel described to his skeptical friend had two unique properties. It rotated, which provided centrifugal force that prevented gravity from crunching together all the matter in the cosmos, and thus created the stability Einstein demanded of any cosmic model. But it also allowed for time travel into the past, which made Einstein deeply uneasy. In Gödel's cosmos, space travelers could set out and eventually reach a point in their own past, as if the travelers had completed a circuit around the surface of a giant cylinder. Physicists call these trajectories in spacetime “closed timelike curves.”

A closed timelike curve is any path through spacetime that loops back on itself. In Gödel's rotating cosmos, such a curve would circle around the entire universe, like a latitude line on Earth's surface. Physicists have concocted a number of different types of closed timelike curves, all of which allow travel to the past, at least in theory. A journey along any of them would be disappointingly ordinary, however. Through the portholes of your spaceship, you would see stars and planets—all the usual sights of deep space. More important, time—as measured by your own clocks—would tick forward in the usual way; the hands of a clock would not start spinning backward even though you would be traveling to a location in spacetime that existed in your past.

“Einstein was already aware of the possibility of closed timelike curves back in 1914,” says Julian Barbour, an independent theoretical physicist who lives near Oxford, England. As Barbour recalls, Einstein said, “My intuition strives most vehemently against this.” The curves' existence would create all kinds of problems with causality—how can the past be changed if it has already happened? And then there is the hoary grandfather paradox: What happens to a time traveler who kills Granddad before Granddad meets Grandma? Would the demented, now parentless traveler ever be born?

Fortunately for fans of causality, astronomers have found no evidence that the universe is rotating. Gödel himself apparently pored over catalogs of galaxies, looking for clues that his theory might be true. Gödel might not have devised a realistic model of the universe, but he did prove that closed timelike curves are completely consistent with the equations of general relativity. The laws of physics do not rule out traveling to the past.

An annoying possibility Over the past few decades cosmologists have used Einstein's equations to construct a variety of closed timelike curves. Gödel conjured an entire universe that allowed them, but more recent enthusiasts have warped spacetime only within parts of our universe.

In general relativity, planets, stars, galaxies and other massive bodies warp spacetime. Warped spacetime, in turn, guides the motions of those massive bodies. As the late physicist John Wheeler put it, “Spacetime tells matter how to move; matter tells spacetime how to curve.” In extreme cases, spacetime might bend enough to create a path from the present back to the past.

Physicists have proposed some exotic mechanisms to create such paths. In a 1991 paper, Gott showed how cosmic strings—infinitely long structures thinner than an atom that may have formed in the early universe—would allow closed timelike curves where two strings intersected. In 1983 Kip S. Thorne, a physicist at the California Institute of Technology, began to explore the possibility that a type of closed timelike curve called a wormhole—a kind of tunnel joining two different locations in spacetime—might allow for time travel into the past. “In general relativity, if you connect two different regions of space, you're also connecting two different regions of time,” says Sean M. Carroll, a colleague of Thorne's at Caltech.

The entrance into a wormhole would be spherical—a three-dimensional entrance into a four-dimensional tunnel in spacetime. As is the case with all closed timelike curves, a trip through a wormhole would be “like any other journey,” Carroll says. “It's not that you disappear and are reassembled at some other moment of time. There is no respectable theory where that kind of science-fiction time travel is possible.” For all travelers, he adds, “no matter what they do, time flows forward at one second per second. It's just that your local version of ‘forward’ might be globally out of sync with the rest of the universe.”

Although physicists can write equations that describe wormholes and other closed timelike curves, all the models have serious problems. “Just to get a wormhole in the first place, you need negative energy,” Carroll says. Negative energy is when the energy in a volume of space spontaneously fluctuates to less than zero. Without negative energy, a wormhole's spherical entrance and four-dimensional tunnel would instantaneously implode. But a wormhole held open by negative energy “seems to be hard, probably impossible,” Carroll says. “Negative energies seem to be a bad thing in physics.”

Even if negative energy kept a wormhole open, just when you would be on the verge of turning that into a time machine, “particles would be moving through the wormhole, and every particle would loop back around an infinite number of times,” Carroll says. “That leads to an infinite amount of energy.” Because energy deforms spacetime, the entire thing would collapse into a black hole—an infinitely dense point in spacetime. “We're not 100 percent sure that that happens,” Carroll says. “But it seems to be a reasonable possibility that the universe is actually preventing you from making a time machine by making a black hole instead.”

Unlike black holes, which are a natural consequence of general relativity, wormholes and closed timelike curves in general are completely artificial constructs—a way of testing the bounds of the theory. “Black holes are hard to avoid,” Carroll says. “Closed timelike curves are very hard to make.”

Even if wormholes are physically implausible, it is significant that they fit in with the general theory of relativity. “It's very curious that we can come so close to ruling out the possibility of time travel, yet we just can't do it. I also think that it's annoying,” Carroll says, exasperated that Einstein's beautiful theory might allow for something so seemingly implausible. But by contemplating that annoying possibility, physicists may gain a better understanding of the kind of universe we live in. And it may be that if the universe did not permit backward time travel, it never would have come into existence.

Did the universe create itself? General relativity describes the universe on the largest scales. But quantum mechanics provides the operating manual for the atomic scale, and it offers another possible venue for closed timelike curves—one that gets at the origin of the universe.

“On a very small scale (10−30 centimeter) you might expect the topology of spacetime to fluctuate, and random fluctuations might give you closed timelike curves if nothing fundamental prevents them,” says John Friedman, a physicist at the University of Wisconsin–Milwaukee. Could those quantum fluctuations somehow be magnified and harnessed as time machines? “There's certainly no formal proof that you can't have macroscopic closed timelike curves,” Friedman says. “But the community of people who have looked at these general questions would bet pretty heavily against it.”

There is no doubt that the creation of a loop in spacetime on either a quantum scale or a cosmic one would require some very extreme physics. And the most likely place to expect extreme physics, Gott says, is at the very beginning of the universe.

In 1998 Gott and Li-Xin Li, an astrophysicist now at Peking University in China, published a paper in which they argued that closed timelike curves were not merely possible but essential to explain the origin of the universe. “We investigated the possibility of whether the universe could be its own mother—whether a time loop at the beginning of the universe would allow the universe to create itself,” Gott says.

Just as in standard big bang cosmology, Gott and Li's universe “starts” with a bout of inflation, where an all-pervasive energy field drove the universe's initial expansion. Many cosmologists now believe that inflation gave rise to countless other universes besides our own. “Inflation is very hard to stop once it gets started,” Gott says. “It makes an infinitely branching tree. We're one of the branches. But you have to ask yourself, Where did the trunk come from? Li-Xin Li and I said it could be that one of the branches just loops around and grows up to be the trunk.”

A simple two-dimensional sketch of Gott and Li's self-starting universe looks like the number “6,” with the spacetime loop at the bottom and our present-era universe as the top stem. A burst of inflation, Gott and Li theorized, allowed the universe to escape from the time loop and expand into the cosmos we inhabit today.

It is difficult to contemplate the model, but its main appeal, Gott says, is that it eliminates the need for creating a universe out of nothing. Yet Alexander Vilenkin of Tufts University, Stephen Hawking of the University of Cambridge and James Hartle of the University of California, Santa Barbara, have proposed models in which the universe does indeed arise out of nothing. According to the laws of quantum mechanics, empty space is not really empty but is filled with “virtual” particles that spontaneously pop into and out of existence. Hawking and his colleagues theorized that the universe burst into being from the same quantum-vacuum stew. But in Gott's view, the universe is not made out of nothing; it is made out of something—itself.

A cosmic chess game For now, there is no way to test whether any of those theories might actually explain the origin of the universe. The famed physicist Richard Feynman compared the universe to a great chess game being played by the gods. Scientists, he said, are trying to understand the game without knowing the rules. We watch as the gods move a pawn one space forward, and we learn a rule: pawns always move one space forward. But what if we never saw the opening of a game, when a pawn can move two spaces forward? We might also assume, mistakenly, that pawns always remain pawns—that they never change their identity—until we see a pawn transformed into a queen.

“You would say that's against the rules,” Gott says. “You can't change your pawn into a queen. Well, yes, you can! You just never saw a game that extreme before. Time-travel research is like that. We're testing the laws of physics by looking at extreme conditions. There's nothing logically impossible about time travel to the past; it's just not the universe we're used to.” Turning a pawn into a queen could be part of the rules of relativity.

Such wildly speculative ideas may be closer to philosophy than to physics. But for now, quantum mechanics and general relativity—powerful, counterintuitive theories—are all we have to figure out the universe. “As soon as people start trying to bring quantum theory and general relativity into this, the first thing to say is that they really have no idea what they're doing,” says Tim Maudlin, a philosopher of science at New York University. “It's not really rigorous mathematics. It's one piece of mathematics that sort of looks like general relativity and another little piece of mathematics that sort of looks like quantum theory, mixed together in some not entirely coherent way. But this is what people have to do because they honestly don't know how to go forward in a way that makes sense.”

Will some future theory eliminate the possibility of time travel into the past? Or will the universe again turn out to be far stranger than we imagine? Physics has advanced tremendously since Einstein redefined our understanding of time. Time travel, which existed only in the realm of fiction for Wells, is now a proved reality, at least in one direction. Is it too hard to believe that some kind of symmetry exists in the universe, allowing us to travel backward in time? When I put the question to Gott, he replies with an anecdote:

“There's a story where Einstein was talking to a guy. The guy pulled a notebook out and scribbled something down. Einstein says, ‘What's that?’ The guy says, ‘A notebook. Whenever I have a good idea, I write it down.’ Einstein says, ‘I've never had any need for a notebook; I've only had three good ideas.’”

Gott concludes: “I think we're waiting for a new good idea.”

Tim Folger is a freelance journalist who writes for National Geographic , Discover , and other national publications.

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Here's How Black Holes Cause Time Travel

Scientists Finds Better Way to See Blackholes

A researcher explained how time would be distorted inside a black hole. According to the researcher, entering a black hole would be like traveling through time.

When it comes to space and time travel, many believe that this idea can be achieved through dilation. The concept of time dilation refers to the different times measured by two clocks if one of these devices is on Earth and the other one is on a spaceship.

As the spaceship carrying one of the clocks moves at light speed, time here would appear to be much slower compared to the time measured by the clock on Earth. Theoretically, the same phenomenon would occur if the same spaceship enters a black hole.

In a post on Quora , researchers Atharva Palshetkar of the CTES College in India explained that for the spaceship in the black hole, time would appear to be moving at a normal pace. However, looking outside the black hole from within would reveal that time is actually moving at a much faster rate.

“Now if someone was supposed to see you falling down a black hole, he would see you going slower and slower, taking weeks, years and even decades, until you reach a point where light can’t escape the black hole’s event horizon,” Palshetkar explained.

“Meanwhile, while you enter the black hole everything you see outside will begin to speed up outside,” he continued. “Your family, kids, grandkids, hundreds of generations will rise and fall in just matters of minutes or hours.”

According to Palshetkar, those inside the black hole will eventually get to witness billions of years pass by on the outside without getting affected since, in their current state, time is still moving at a regular pace.

Of course, Palshetkar’s explanation of how black holes cause time travel is just a theory. Due to several factors, not much is known about the nature of black holes. For one, it is also impossible to visit a black hole to study it since the nearest one over 6,500 light-years from Earth. In addition, scientists have already stated that humans will most likely not survive if they get sucked into a black hole.

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Scientists clear up how supermassive black holes came to be (hint: big seeds)

Emily Kwong

The origin of supermassive black holes has stumped scientist for a long time. They now have the answer to this question: very massive seeds.

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Could humans use black holes to time travel?
Black holes form natural time machines that allow travel to both the past and the future. But don't expect to be heading back to visit the dinosaurs any time soon. At present, we don't have ...
Physicists observationally confirm Hawking's black hole theorem for the
The signal was a product of two inspiraling black holes that generated a new black hole, along with a huge amount of energy that rippled across space-time as gravitational waves. If Hawking's area theorem holds, then the horizon area of the new black hole should not be smaller than the total horizon area of its parent black holes.
Are black holes time machines? Yes, but there's a catch
Black holes form natural time machines that allow travel to both the past and the future. But don't expect to be heading back to visit the dinosaurs any time soon. At present, we don't have ...
Trap Doors in Time and Space: Teleportation, Time Travel, and ...
Time travel To escape from a black hole, you must effectively travel faster than the speed of light. ... For a detailed account of the quantum theory of time travel and the results of our ...
Black Holes, Relativity And Time Travel
Yes, in theory at least, as general relativity does allow for a tunnel through space-time linking two distant points in time, which then form a circular time loop called a wormhole or Einstein-Rosen bridge. Similar to a black hole, a wormhole would have a massive gravitational field capable of bending space-time, but in contrast to a black hole ...
Physicists Just Figured Out How Wormholes Could Enable Time Travel
Physicists Just Figured Out How Wormholes Could Enable Time Travel. Physics 16 July 2023. By Mike McRae. (gremlin/Getty Images) Theoretical physicists have a lot in common with lawyers. Both spend a lot of time looking for loopholes and inconsistencies in the rules that might be exploited somehow. Valeri P. Frolov and Andrei Zelnikov from the ...
Famous Stephen Hawking theory about black holes confirmed
The black hole area theorem, which Hawking derived in 1971 from Einstein's theory of general relativity, states that it is impossible for the surface area of a black hole to decrease over time.
Do black holes explode? The 50-year-old puzzle that challenges ...
The first, Albert Einstein's general theory of relativity — in which black holes manifest themselves — links gravity to the shape of space and time, and is typically relevant only at large ...
Are black holes time machines? Yes, but there's a catch
Black holes form natural time machines that allow travel to both the past and the future — but watch out for "spaghettification". ... Albert Einstein's general theory of relativity tells us ...
Black Holes Could Work as Time Machines
Black holes form natural time machines that allow travel to both the past and the future. ... Albert Einstein's general theory of relativity tells us matter and energy have a curious effect on ...
Stephen Hawking's final book suggests time travel may one day be
Light speed. Einstein told us that space and time are parts of one thing - spacetime - and that we should be as willing to think about distances in time as we are distances in space.
Is time travel really possible? Here's what physics says
Relativity means it is possible to travel into the future. We don't even need a time machine, exactly. We need to either travel at speeds close to the speed of light, or spend time in an intense ...
Stephen Hawking
Stephen Hawking explains how we could use the extreme gravity of a black hole to travel to the future.Into The Universe With Stephen Hawking - Time TravelThi...
Time travel is possible
Since the travel time on the green path could be very small compared to the red, a wormhole can allow for the possibility of time travel. Panzi, CC BY-SA. Over the past few decades well-known ...
Physicists observationally confirm Hawking's black hole theorem for the
The signal was a product of two inspiraling black holes that generated a new black hole, along with a huge amount of energy that rippled across space-time as gravitational waves. If Hawking's area theorem holds, then the horizon area of the new black hole should not be smaller than the total horizon area of its parent black holes.
Can we time travel? A theoretical physicist provides some answers
The simplest answer is that time travel cannot be possible because if it was, we would already be doing it. One can argue that it is forbidden by the laws of physics, like the second law of ...
Astrophysicist says he has cracked the code for time travel
Decades of research into black holes and Einstein's theories of relativity led to the time travel equation. While hospitalized for a heart condition, Mallett had a revelation. "It turns out that black holes can create a gravitational field that could lead to the creation of time loops that could allow us to go back in time," he explained.
Time travel: Is it possible?
There are other scientific theories about time travel, including some weird physics that arise around wormholes, black holes and string theory. For the most part, though, time travel remains the ...
Black holes may make time travel possible
Teleportation and travelling forwards through time may be possible through wormholes, the bipolar black holes that link different regions of the universe. This is the conclusion drawn from a model created by Kyriakos Papadodimas of CERN and Rik van Breukelen of the University of Geneva. Instantaneous travel and travel into the future would ...
Is Time Travel Possible?
Time traveling to the near future is easy: you're doing it right now at a rate of one second per second, and physicists say that rate can change. According to Einstein's special theory of ...
Can you time travel through a black hole?
A month near a black hole might be equal to several years back on Earth. This is step one for black hole time travel: Just fly near one for a bit and then come back. You'll find that a lot of time ...
Can Time Travelers Reach the Past via Wormholes?
Unlike black holes, which are a natural consequence of general relativity, wormholes and closed timelike curves in general are completely artificial constructs—a way of testing the bounds of the ...
Why you age slower on a plane (and other incredibly strange ...
Einstein correctly predicted that time slows when you're flying fast, but to experience "time dilation" most spectacularly, you'd have to travel into a black hole, says astrophysicist Chris Lintott.
Here's How Black Holes Cause Time Travel
According to the researcher, entering a black hole would be like traveling through time. When it comes to space and time travel, many believe that this idea can be achieved through dilation. The ...
Scientists clear up how supermassive black holes came to be (hint: big
KWONG: This theory was eventually confirmed in 1964, but it set up another mystery - how do black holes even begin? For a long time, scientists were only sure about one origin - that black holes were created through the collapse of a very massive dying star. That is true, but it didn't fully explain how supermassive black holes came to be.

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