Current Events > physicist: paradox-free time travel plausible

(+) Yeah! (+)

https://www.sciencealert.com/a-physicist-has-come-up-with-the-maths-to-make-time-travel-plausible

No one has yet managed to travel through time at least to our knowledge but the question of whether or not such a feat would be theoretically possible continues to fascinate scientists.

As movies such as The Terminator, Donnie Darko, Back to the Future and many others show, moving around in time creates a lot of problems for the fundamental rules of the Universe: if you go back in time and stop your parents from meeting, for instance, how can you possibly exist in order to go back in time in the first place?It's a monumental head-scratcher known as the 'grandfather paradox', but now a physics student Germain Tobar, from the University of Queensland in Australia, says he has worked out how to "square the numbers" to make time travel viable without the paradoxes."Classical dynamics says if you know the state of a system at a particular time, this can tell us the entire history of the system," says Tobar."However, Einstein's theory of general relativity predicts the existence of time loops or time travel where an event can be both in the past and future of itself theoretically turning the study of dynamics on its head."What the calculations show is that space-time can potentially adapt itself to avoid paradoxes.

To use a topical example, imagine a time traveller journeying into the past to stop a disease from spreading if the mission was successful, the time traveller would have no disease to go back in time to defeat.Tobar's work suggests that the disease would still escape some other way, through a different route or by a different method, removing the paradox. Whatever the time traveller did, the disease wouldn't be stopped.Tobar's work isn't easy for non-mathematicians to dig into, but it looks at the influence of deterministic processes (without any randomness) on an arbitrary number of regions in the space-time continuum, and demonstrates how both closed timelike curves (as predicted by Einstein) can fit in with the rules of free will and classical physics."The maths checks out and the results are the stuff of science fiction," says physicist Fabio Costa from the University of Queensland, who supervised the research.

The new research smooths out the problem with another hypothesis, that time travel is possible but that time travellers would be restricted in what they did, to stop them creating a paradox. In this model, time travellers have the freedom to do whatever they want, but paradoxes are not possible.While the numbers might work out, actually bending space and time to get into the past remains elusive the time machines that scientists have devised so far are so high-concept that for they currently only exist as calculations on a page.We might get there one day Stephen Hawking certainly thought it was possible and if we do then this new research suggests we would be free to do whatever we wanted to the world in the past: it would readjust itself accordingly."Try as you might to create a paradox, the events will always adjust themselves, to avoid any inconsistency," says Costa. "The range of mathematical processes we discovered show that time travel with free will is logically possible in our universe without any paradox."The research has been published in Classical and Quantum Gravity.

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Sounds like clickbait science.

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I dunno, seems like a lot of work went into it

here's a link to where you can download it:

https://iopscience.iop.org/article/10.1088/1361-6382/aba4bc

Abstract
The theory of general relativity predicts the existence of closed time-like curves (CTCs), which theoretically would allow an observer to travel back in time and interact with their past self. This raises the question of whether this could create a grandfather paradox, in which the observer interacts in such a way to prevent their own time travel. Previous research has proposed a framework for deterministic, reversible, dynamics compatible with non-trivial time travel, where observers in distinct regions of spacetime can perform arbitrary local operations with no contradiction arising. However, only scenarios with up to three regions have been fully characterised, revealing only one type of process where the observers can verify to both be in the past and future of each other. Here we extend this characterisation to an arbitrary number of regions and find that there exist several inequivalent processes that can only arise due to non-trivial time travel. This supports the view that complex dynamics is possible in the presence of CTCs, compatible with free choice of local operations and free of inconsistencies.

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Physics students are not physicists

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tbf, in the article, it said that a physicist said the math checks out

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I'd rather see these people with this kind of intelligence focus on something more important.

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Basically sounds like Novikov's self-consistency principle.

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So Back to the Future is bullshit?

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So, if I go back in time and kill Hitler before he committed his atrocities, all of his victims would magically kill themselves? Or would someone else step in for him to avoid the paradox?

This is still nonsense. Nice try, Mr. Physicist.

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Silver Bearings posted...

So, if I go back in time and kill Hitler before he committed his atrocities, all of his victims would magically kill themselves? Or would someone else step in for him to avoid the paradox?

This is still nonsense. Nice try, Mr. Physicist.

Stalin.
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g0ldie posted...

As movies such as The Terminator, Donnie Darko, Back to the Future and many others show

do they, though?

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I want to go back in time and see Katy Perry's naked boobs in their prime

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I think that I remember a Twilight Zone episode where a woman went back to the past and killed a baby Hitler, and Hitler's nanny was like, "oh, no", and bought some lady's kid to replace the baby

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I saw this news earlier... And thought it was funny because a UofT philosophy undergrad recently got into MIT for writing a paper on whether time travel is possible.

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NeonOctopus posted...

I want to go back in time and see Katy Perry's naked boobs in their prime

The only thing that will fix 2020 is nudes of 2010-2012 Katy Perry being released

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This demonstrates that when multiple local regions communicate with each other in the presence of CTCs, there is a broad range of communication scenarios which still allow freedom of choice for observers in each region without the development of a logical inconsistency such as a grandfather paradox.

[...]

Our results are derived in an abstract framework, that does not depend on the details of the dynamics or of the space-time geometry. Further studies will be necessary to find genuine physical scenarios realising the acausal processes we have discovered.

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So, it turns out Bill & Ted were right all along.

Silver Bearings posted...

So, if I go back in time and kill Hitler before he committed his atrocities, all of his victims would magically kill themselves? Or would someone else step in for him to avoid the paradox?

Someone already went back in time and killed Rudolph Hitler.

This has been discussed before. There is a theory that time is immutable. Meaning that even if you change something in the past that history will try to correct itself. This guy just has math to prove that.

Also it would probably make a branch in the time flow making it a parallel universe.

There is also the theory that time travel is possible but the farthest back you can go is when the time machine was turned on. Thus breaking a lot of rules we hold dear as at that point time would technically be predetermined.


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Just to note, this is just a mathematical construct. Perhaps all of reality can be represented by mathematics, but not all mathematics represents reality. This study notes that the theory has no physical equivalent and there is no physical phenomena that is represented by this mathematical framework.

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Pogo_Marimo posted...

Just to note, this is just a mathematical construct. Perhaps all of reality can be represented by mathematics, but not all mathematics represents reality. This study notes that the theory has no physical equivalent and there is no physical phenomena that is represented by this mathematical framework.

So it is...useless?

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Silver Bearings posted...

So it is...useless?

utilitarianism is a bad way to view science (and most things in general)

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Time, uh, finds a way.

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ThyCorndog posted...

utilitarianism is a bad way to view science (and most things in general)

As an engineer, I disagree, but your opinion has been noted.

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Silver Bearings posted...

As an engineer

same here. my opinion stands

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Silver Bearings posted...

So it is...useless?

Unless we can use this as a starting point to discover actual physical phenomena, its use is limited pretty much to the instructive or intellectually stimulating.

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If time traveling created new universes (forks in time), where does that energy come from?

Going back in time doesn't even make sense to me, as if there was a recording in the universe that recorded the previous state of the universe.

It's a fun dream, but unlikely.
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Didn't they basically just describe Stein's;Gate

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Notti posted...

If time traveling created new universes (forks in time), where does that energy come from?

Going back in time doesn't even make sense to me, as if there was a recording in the universe that recorded the previous state of the universe.

It's a fun dream, but unlikely.

That is because you are only seeing time going in one direction, just like how a 2D being is not seeing the third plane.

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What if going back in time and killing Hitler is part of a larger, meta timeline?

If, in 2025, you use a time machine to go back in time and kill Hitler, you dont create a paradox because Hitler still existed and history wasnt changed until 2025, and your decisions to act only occurred while the original history was still intact?

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You see, we live in the timeline where a time traveler went back in time and killed the Fhrer, trying to prevent WWII.
Time itself fixed it by replacing the Fhrer with a painter.

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Foppe posted...

That is because you are only seeing time going in one direction, just like how a 2D being is not seeing the third plane.

I see it like this:

https://futurama.fandom.com/wiki/Dark_matter_engine
" I understand how the engines work now. It came to me in a dream. The engines don't move the ship at all. The ship stays where it is and the engines move the universe around it."
Cubert Farnsworth"

Just as that explanation is ridiculous, it's the same way I see actual time travel.
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