We already have tools to jump forward in time, but to go back we'll need something completely different: a wormhole / Tim Folger
The article was published with the approval of Scientific American Israel and the Ort Israel network
Very fast flight allows for forward travel in time. Traveling back in time is much more difficult, but according to mathematics it is possible, using geometric structures called closed time-like curves.
A wormhole is one such curve. You enter it through a spherical opening. Inside, everything will look completely normal, and so will the passage of time.
Closed time-like curves are useful for testing theories about the universe. For example, if there was such a curve at the beginning of the universe, it would have allowed the universe to create itself.
Quantum mechanics - and perhaps the nature of the universe itself - may prohibit the existence of wormholes and thus prevent travel back in time. Physicists simply don't know yet if this is indeed the case.
H. G. Wells published his first novel, "The Time Machine", in 1895, a few years before the end of Queen Victoria's six-decade reign over England. An even longer lineage then drew to a close: the two-hundred-year era of Newtonian physics. In 1905, Albert Einstein published his special theory of relativity, a theory that completely changed Newton's concepts of time and space, and to Wells's joy, one can assume, opened a window to something that was impossible under Newton's laws: time travel to the future. In the universe according to Newton, time was stable everywhere and at all times. He didn't speed up or slow down. For Einstein, however, time was relative.
Time travel is not only theoretically possible, it has already happened in practice, although not in the way that Wells envisioned. According to G. Richard Gott, an astrophysicist at Princeton University, the record holder for time travel so far is Russian cosmonaut Sergei K. Krikalev. During his long career, which began in 1985, Krikalev spent more than 803 days in space. Einstein showed that time passes more slowly for bodies in motion compared to bodies at rest. So when Krykalev flew at a speed of 27,000 kilometers per hour on the Mir space station, his time did not flow at the same rate as on Earth. During his time in orbit, he aged 1/48 of a second less than humans on the ground. From his perspective, therefore, he traveled 1/48 of a second into the future of the Earth's inhabitants.
It is much easier to see the effect of time travel at greater distances and speeds. If Krikalev were to leave Earth in 2015 for a round-trip journey to the planet Betelgeuse, which is about 520 light-years away from us, at a speed of 99.995% of the speed of light, the duration of the journey for him would be ten years. However, after he lands and leaves the spaceship, he will discover to his astonishment that everyone he knew has long since died, since a thousand years have passed on Earth: he will arrive in 3015. "We can travel in time to the future," says Gott, "It's just a question of money and engineering!"
Beyond the practical challenge, a leap of a few billionths of a second into the future, or even a leap of hundreds of years, is a fairly simple matter. But going back in time is much more difficult. Einstein's special theory of relativity forbade such movement. After ten more years of work, Einstein presented his general theory of relativity which removed this limitation. However, no one yet knows how to do this in practice because the equations of general relativity have many solutions. The different solutions have meanings with different characteristics of the universe, and only some of the solutions create conditions that allow travel back in time.
The question of what solution, if any, describes our universe remains open, and this requires even deeper research: how many changes would be required in the basic physics to allow time travel? Does the universe itself somehow prevent such journeys, even though Einstein's equations do not rule them out? Physicists continue to speculate, not because they think time travel will ever be practical, but because just thinking about this possibility has led to some surprising insights into the nature of the universe we live in, including a hypothesis about how it was created in the first place.
A new look at time
In his special theory of relativity, Einstein made time flexible, which would surely have pleased Wells, whose foresight he believed that in our universe three-dimensional space and time are woven together into a four-dimensional whole. Einstein reached his revolutionary results by investigating the implications of two fundamental ideas. The first idea was that even if all motion is relative, the laws of physics must look the same for everyone, everywhere. The second idea was that the speed of light must be the same for all observers, regardless of their state of motion. If everyone sees the same laws of physics in action, everyone must also reach the same result when they measure the speed of light.
To make the speed of light a universal limit, Einstein had to abandon two common sense notions: that all observers would agree on the measurement of a given length, and that they would also agree on the duration of a given event. He showed that a moving clock passing quickly past a stationary observer will tick more slowly than a stationary clock next to the same observer. Also, a fast moving bar will shorten. However, for a person moving along with the clock and the ruler at the same speed, the ticking rate of the clock and the length of the ruler will appear completely normal.
At normal speeds, the distortions of space and time described by special relativity are negligible, but they become significant for any body moving at a speed approaching the speed of light. For example, many experiments have shown that the decay rate of unstable particles, called ions, slows by an order of magnitude when they travel at speeds close to the speed of light. These accelerated muons are, in fact, tiny time travelers, subatomic cricalebs, that skip a few billionths of a second into the future.
Gedel's strange universe
The clocks, rulers, and muons we've talked about so far run forward in time. Is it possible to send them in the opposite direction? The first person to use general relativity to describe a universe where travel into the past is possible was Kurt Gödel, the famous creator of the incompleteness theorems that limit what mathematics can and cannot prove. Gedel was one of the most prominent mathematicians of the 20th century, and one of the strangest of them: among other things, he adopted a diet of baby food and laxatives.
Gödel gave this model of the universe to Einstein, his skeptical friend, as a gift for his 70th birthday. The model had two unique features: First, it described a rotating universe, which created a centrifugal force that prevented gravity from sucking in all the existing matter. This provided the stability Einstein required from any model of the universe. Second, it enabled time travel, which made Einstein deeply uncomfortable. In Geddel's universe, space pilots can go on a journey and reach a point in their own past, as if they had completed a revolution on the surface of a giant cylinder. Physicists call such trajectories in space-time "closed time-like curves".
A closed time-like curve is any path in space-time that returns to its starting point. In Gaedel's rotating universe, such a path encircles the entire universe, similar to the latitude of the Earth. Physicists have invented various types of closed time-like curves, which allow, at least in theory, to go back into the past. But perhaps surprisingly, the journey along these curves will be quite ordinary: disappointingly, through the windows of the spacecraft, only stars and planets will be visible, the usual sights in deep space. Even time, as measured by the spacecraft's clocks, will move forward as usual. The hands will not start moving backwards, even though eventually the spaceship passengers will reach a place in space-time that existed in their past.
"Einstein was aware of the possibility of closed time-like curves as early as 1914," says Julian Barbour, an independent theoretical physicist who lives near Oxford in England. According to him, Einstein said: "My intuition is fighting it with all its might." The existence of these curves will create all kinds of problems in causality: how can you change the past if it has already happened? And there is, of course, the old paradox of the grandfather: what will happen to the time traveler if he kills his grandfather before it has time to meet the grandmother. Will this crazy traveler ever be born?
Fortunately for causality enthusiasts, astronomers have not discovered any evidence that the universe is rotating. Gedel himself, it seems, rummaged through galaxy catalogs looking for clues that his theory might be correct. The model of the universe he created may not have been realistic, but he proved that closed time-like curves do not contradict the equations of general relativity. The laws of physics do not rule out the possibility of a journey into the past.
An annoying possibility
In recent decades, cosmologists have used Einstein's equations to create a variety of closed time-like curves. Unlike the giant who invented an entire universe to allow their existence, the modern practitioners in the field distort the space-time only in parts of the universe.
In general relativity, the planets, stars, galaxies and all other bodies in the universe that have mass distort space-time. The distorted space-time, in turn, affects the movement of these bodies. As the late physicist John Wheeler put it: "Space-time tells matter how to move; Matter tells space-time how to curve.” In extreme cases, space-time may be distorted to such an extent that it creates a path from the present to the past.
Physicists have proposed some exotic mechanisms for the creation of such orbits. In a 1991 paper, Gott showed how cosmic strings, infinitely long and thinner-than-atom structures that may have formed in the early days of the universe, allow closed time-like curves to exist where they intersect. In 1983, Kip S. Thorne, a physicist from the California Institute of Technology (Caltech), began to investigate the possibility of traveling back in time through a closed time-like curve of the "wormhole" type: a kind of tunnel connecting two different places in space- time. "According to the general theory of relativity, if you connect two different locations in space, you also connect two different locations in time," says Sean M. Carroll, Thorne's colleague at the California Institute of Technology.
The entrance to a wormhole is spherical: a three-dimensional entrance to a four-dimensional tunnel in space-time. As with all closed time-like curves, the journey through a wormhole will be "like any other journey," Carroll says. "The traveler will not disappear and be re-created at another time. There is no theory worthy of its name in which time travel in the style of science fiction is possible." According to him, for all passengers, "and no matter what they do, time flows forward at the rate of one second every second. The thing is, your version of 'forward' is out of sync with the rest of the universe."
Physicists can write equations that describe wormholes and other time-like curves, but all models have serious problems. "For a black worm to form in the first place," says Carroll, "you need negative energy." Negative energy appears when the amount of energy in a certain volume in space spontaneously drops below zero. Without negative energy, both the spherical entrance to the wormhole and the four-dimensional channel itself would immediately collapse in on themselves. A wormhole held open by negative energy "seems very difficult to achieve, probably impossible," says Carroll. "In physics, negative energies are a bad thing."
Even if negative energy keeps the wormhole open, once we get ready to turn it into a time machine, "particles will move through the wormhole, and each particle will loop back countless times," Carroll says. "This means an infinite amount of energy." Because energy warps space-time, the whole thing will collapse into a black hole: a point of infinite compression in space-time. "We're not XNUMX percent sure that's what will happen," says Carroll, "but it seems very likely that the universe is preventing us from building a time machine by creating a black hole instead."
Unlike black holes, which are a natural consequence of general relativity, wormholes or any other type of closed time-like curves are completely artificial structures: a means of testing the limits of the theory. "Black holes are hard to avoid," says Carroll. "And it is very difficult to create closed time-like curves."
Even if wormholes are physically improbable, the fact that they are consistent with general relativity is important. "There is something interesting in that we are so close to ruling out the possibility of time travel, but we still can't do it. It's also quite upsetting," says Carroll, frustrated that Einstein's beautiful theory allows something that seems so implausible. However, by studying this unsettling possibility, physicists may better understand the kind of universe we live in. It's also possible that if the universe didn't allow for time travel, it wouldn't have been created in the first place.
Did the universe create itself?
General relativity describes the universe on the largest scales. Quantum theory, on the other hand, provides the operating instructions for the atomic scale, and it offers another operating platform for closed time-like curves, one related to the origin of the universe.
"On a very small scale, of ten to the power of minus 30 centimeters, fluctuations in the topology of space-time are expected. Random fluctuations may form closed time-like curves. This is on the assumption that there is no fundamental law of nature that prevents this," says John Friedman, a physicist from the University of Wisconsin-Milwaukee. Is it possible to somehow increase these quantum fluctuations and turn them into time machines? "There is no unequivocal proof that macroscopically closed time-like curves cannot exist," Friedman says, "but the people who have studied these general questions tend to think they don't exist."
There is no doubt that creating a loop in space-time, whether on a quantum scale or on a cosmic scale, will require particularly extreme physics. According to Gott, the most likely place for the appearance of such physics is the beginning of the universe.
In 1998, Gott and Li-Shin Li, an astrophysicist now at Peking University in China, published a paper arguing that closed time-like curves are not only possible, but necessary for explaining the origin of the universe. "We investigated the possibility that the universe is its own parent: could a time loop at the beginning of the universe have allowed it to create itself," Gut says.
Gut and Lee's universe "begins" with a burst of inflation, just like in the familiar Big Bang cosmology, where an omnipresent energy field drove the initial expansion. Many cosmologists now believe that this accelerated initial inflation also led to the creation of many other universes in addition to our own. "It is very difficult to stop this kind of swelling once it has started," says Gott. "She creates a tree with infinite branches. We are one of these industries. But the question arises: 'Where did the race come from?' Li-Xin Li and I said that maybe one of the branches just goes back and becomes the race."
space-time loop.
Illustration: The universe today, cosmic inflation, space-time loop. Credit: Nigel Holmes
Credit: Nigel Holmes
A simple 6D sketch of the universe-starting-itself looks like the number XNUMX, with the space-time loop at the bottom and the present-day universe at the top. According to Gott and Lee's theory, the inflationary burst allowed the universe to escape the time loop and evolve into the universe we now inhabit.
This model of the universe is hard to imagine, but according to Gott, its important advantage is that it does not involve creation from nothing. However, Tufts University's Alexander Vilenkin, Cambridge University's Stephen Hawking, and James Hartl of the University of California, Santa Barbara have all proposed models in which the universe did come from nothing. According to the laws of quantum mechanics, empty space is not really empty but full of "virtual" particles that are created and disappear spontaneously. Hawking and his colleagues hypothesize that the universe emerged from this bubbling quantum vacuum. In Gott's view, on the other hand, the universe was not created out of nothing but out of something: itself.
A cosmic chess game
As of today, there is no way to check if any theory among all these theories can indeed explain the origin of the universe. The famous physicist Richard Feynman compared the universe to a mighty chess game of the gods. The scientists, he said, are trying to understand the game without knowing the rules. We watch the gods move their feet one step forward, and conclude a rule: feet always move one step forward. But what if we've never seen the beginning of a game, where my habit is allowed to move two steps? We may also mistakenly assume that legs always remain legs and never change their identity, until we see a leg become a queen. "You will say that it is against the rules," says Gut, "that my habit should not be turned into a queen. Well, it turns out that it is allowed! You've simply never seen a game reach this extreme. This is what the study of time travel looks like. We test the laws of physics by examining extreme conditions. There is nothing logically impossible about traveling back in time, it's just not the universe we're used to.” It is possible that the laws of relativity include turning my legs into queens.
Such wild speculative ideas may be closer to the realm of philosophy than physics, but in the meantime quantum mechanics and general relativity, both theories with solid experimental support yet counterintuitive, are all we have to understand the universe. "Once people start trying to bring both quantum theory and general relativity into this, the first thing to say is that they have no idea what they're doing," says Tim Modlin, a philosopher of science at New York University. "This is not about well-founded mathematics, but a piece of mathematics that reminds of general relativity together with another small piece of mathematics that reminds of quantum mechanics, and the two pieces are mixed in a not entirely consistent way. But that's what people have to do because they really don't know how to move forward in a logical way."
Will any future theory raise the possibility of time travel to the past? Or will it be revealed once again that our universe is stranger than any imagination? Physics has come a long way since the days when Einstein redefined the way we understand time. Time travel, which was only an imaginary possibility in the eyes of H. G. Wells, has been proven to be realistic, at least in one direction. Is it completely absurd to believe that there is a certain symmetry in the universe that allows us to go back in time? When I present this question to Gott, he answers me with an anecdote:
"They say that Einstein once talked to a guy who suddenly pulled out a pad and scribbled something down. Einstein asked 'What is this?' And the guy answered: 'It's a notebook. Whenever I have a good idea, I write it down. 'I never needed a notebook,' Einstein said, 'I only had three good ideas.'"
"I think," says Gott, "that we are waiting for a new good idea."
About the writers
Photo by Tim Folger
Tim Folger
Writer for Discover, National Geographic and other magazines. He is also the series editor of The Best American Science and Nature Writing, an annual anthology published by Houghton Mifflin Harcourt.
22 תגובות
Curious, and if someone from the future told us about it - would a rival believe him?
It may sound silly, but I really wonder: if traveling back in time was possible, isn't it likely that someone from the future would have already told us about it?
rival
You're a Jew?
Out of the box,
What I would give to go back in time with you in a time machine to any period of your choice, to see with your own eyes that there was never Mount Sinai and that there was never an exodus from Egypt, and to see how these funny folk tales evolved over the generations and how the animals and humans evolved as well, although In a slightly different way than the stories... 🙂
I wonder what excuse you would come up with when you saw it with your own eyes. In fact there is no need for a time machine at all, there is plenty of evidence that all shows us that what happened is exactly what I have written here.
Waiting, vaccinations.
We are miracles
Pay attention to the point:
"So what happens if we place two clocks side by side, one of them a normal clock and the other a clock that measures the age of the universe by measuring the radiation temperature?"
We put two clocks side by side, one a cesium clock and the other a radiation clock, or temperature clock in the language of the crowd. We reset them to the same time and put them in the Batiz Al Nabi space in a non-accelerated system and filmed both of them on video.
At moment 0 the photo shows 0 on both clocks.
When the photo shows 10 hours on the cesium clock - what will the radiation clock next to it show?
Israel
In my understanding, the background radiation constitutes its own reference system. If you accelerate in a certain direction, you will see a blue shift in the background radiation in front of you, and a red shift behind you - the shifts are relative to the measurements you made before the acceleration.
This is an answer to what the clocks will show. I think that anywhere and anytime, you will be able to fly to a "point" that will be so-called static, meaning that the background radiation will be uniform in every direction.
Israel, time is relative. One's perception of time in reality is different from the other's. There is no "correct" clock. There is agreement on an hour according to Greenwich. There is an agreement on when Jesus the Kofif was born and there is an agreement on the age of the universe according to the calculations of the researchers.
There is no absolute time. Time is individual.
Even insects and plants have their own times…
It is true that everyone ultimately relies on the clock of the universe,
But the universe also has its own times and the one who determines them is omnipotent. ?
The direction of the arrow of time to the future and not to the past is determined by my understanding of the big bang theory: due to the expansion of the universe, its density decreases and does not increase, hence the unidirectionality of the arrow of time.
This was not obvious at the end of the 19th century when the universe was considered static and infinite, and Poincaré, a mega-mathematician, proved that entropy ends up reversing.
However, in my opinion, a conflict arises between the big bang theory and special relativity: according to the big bang theory, the universe has a definite age - about 13.7 billion years - which can be measured by measuring the temperature of the cosmic background radiation and converting it to time using the relevant Friedman formula. Time is the same at every point in the universe at a given moment.
According to relativity, time is relative and moves slower in a relativistic system than in a temporally synchronized system.
So what happens if we place two clocks side by side, one of them a normal clock and the other a clock that measures the age of the universe by measuring the radiation temperature? What is the "correct" time, especially if both clocks move relative to a system of synchronized clocks?
The arrow of time is the central organizing idea in the perception of human reality - without it, life probably would not have succeeded in creating a system that manages to maintain itself in a consistent and productive manner (those who are familiar with cyclical structures and the problems they create in computer science know what this is about).
The nature of reality itself will not be known to humans for "a long time", and in any case the key to understanding it is first of all what time really is...no one really knows what it is, and its splitting into subjective time and physical time does not help either, the essence is painfully missing.
Happy Holidays and kosher with Israel.
Out of the box,
I'm glad you agreed to put in the effort and read the book even though it clearly goes against your worldview and the things you believe in. I can't say that I'm particularly optimistic about the possibility that it changed your attitude to the subject in any way (and this is in light of quite a few disappointing conversations I've had with devout believers like you) but we'll wait to hear your impressions after reading.
May you also have a kosher and happy Passover 🙂
rival
Definitely nearing completion
Comments in Gaza after Passover
Happy and kosher Passover
interesting
Out of the box,
The answer is that we don't know, just as we used to not know why there are earthquakes and why there is lightning in the sky. This is no reason to assume that an old grandfather in the sky (who is not clear how he himself was created) said a magic spell and suddenly the universe was created.
PS - How are the preparations for Passover progressing? Is there any chance that you will finish reading the book in the next few weeks? ("Why evolution is true")
So how did the universe begin?
Do you know anything?
By itself.. in a constant cycle.. the amount of power (energy) for this cycle. If it is from itself and in a regular cycle then it is unlimited. and not even in number.. and if it is not so where does the initial motivation come from.. is there logic.. or not.. is the reality of the beginning of time found to be above time.. so it can also be suddenly?.. when did this suddenness really begin.?
These are questions that arise as I understood from the article.. Maybe someone has a completely clear answer to these questions?
To be precise, there is no high-speed propulsion today, but we are getting closer to it faster than most of us think, and it will happen in another 200 years or more.
Already in satellite movement we see a relative time effect between an atomic clock in a satellite and an atomic clock on Earth and GPS satellites take into account this non-synchronization. Moving at a speed of 0.1C, relativistic effects will be clearly felt - albeit at a weak intensity such as the twin paradox. Already by raising an atomic clock to a high mountain, leaving it for a week and taking it down, a difference of 20 nanoseconds was measured. The practical news is that rocket propulsion is not suitable for space travel and it is a possible alternative. I have previously described the possibility that a nuclear core would fuel a spaceship for 13 years. Leaders of countries are not pushing for a trip to Mars, while entrepreneurs such as Elon Musk at least claim that they believe in colonizing space.
Recently there was an experiment with laser propulsion. I understood that the experiment was successful and they are planning a probe that will reach 0.125C the speed of light to demonstrate the concept of a technological ability to move at such a speed. We are not there yet but there is movement there and a summary article about it can be found https://en.wikipedia.org/wiki/Photonic_laser_thruster
For those who do not believe that Wikipedia is an unreliable source. You can always check the reference at the bottom of the article or search on Google.
We are still very far from a years' time travel into the future:
At the moment the maximum speed we have reached in space is about 70 km per second.
To reach the situation described in the article, where a person spends 10 years on a spaceship at a speed of 99.995% of the speed of light and returns here in the year 3000, we would have to reach a speed of almost 300,000 km per second.
It's a bit of a jump from 70 to 300,000, even the newest ideas of nuclear propulsion provide maybe 3% of the speed of light, no more.
I don't think it will be possible to easily reverse the direction of time progress from high entropy (disorder) to low entropy (order, information) - since the probability = the number of possible combinations for disorder compared to the probability for order - is infinitely high. Much much more than 6.022E23 or its assembly. Violation of the entropy principle is a violation of the second law of thermodynamics. Even if there is an entropy transition from parallel locations, I still believe that these are different universes from ours in one universe. I don't pretend to understand the following: I read somewhere that in a black hole past, present and future exist together, and about the holographic principle - and there was an article about the law of equal areas discovered in black holes and I saw the concept of a black hole according to Kip Thorne in an interstellar book where the movement inside the hole is In a spread time space - where you can move past, present and future.
I don't think there is a single opinion on this. I recommend to those who have the patience to read from the beginning to the present.
An interesting question about time reversal is the reversibility of entropy.
Because a Newtonian system by its very nature is time-reversible. There is no problem in terms of Newtonian physics to reverse the order of events so that early comes after late, a projectile will return to the barrel and a phantom will land in reverse.
Entropy, on the other hand, increases in both directions: past and future.
Poincare drove poor Boltzmann crazy with this question until the latter gave up and returned equipment.
A question in your opinion regarding the future unified complete theory:
Right now both relativity and quantum theory present us with ideas that are against our intuition. Could this be the case because we are not seeing the whole picture? Is it possible that when we see the whole picture all the strange phenomena will fall into place like puzzle pieces that form one logical picture? Or is the texture and nature of the universe such that it doesn't fit logically with our day-to-day experiences?