What Makes for Empirical Evidence of Time Travel?

[Nikolai]

Assuming that for some reason you were not able to observe the appearance or disappearance of a time machine and were not able to force a meeting with a time traveler, what secondary evidence would convince you that time travel into the past is possible?

[WinkAllKerb'']

read an history book, problem solved you time travelled

Edited May 19, 2016 by WinkAllKerb''

[SargeRho]

Precognition. If the time traveler can reliably predict future events, it would lend credence to him.

That is assuming that the universe is deterministic enough for that to even work.

[PB666]

14 minutes ago, Nikolai said:

Assuming that for some reason you were not able to observe the appearance or disappearance of a time machine and were not able to force a meeting with a time traveler, what secondary evidence would convince you that time travel into the past is possible?

If Hawkings said it was possible. If he could pull three yahoos off the street and get them to drive back and forth in 3 de lorians in an arizona desert and then profess  time travel is possible because even though it triplicates matter energy and violates E = mc2 on the relativistic scale, it somehow explains both dark matter and energy. 

Note: K2 im being sarcastic. 

[p1t1o]

Time travel into the past? Without a machine, or observation of its operation, I'm not sure that empirical evidence even makes sense in this context, as causality will have been violated. I think.

[kerbiloid]

As "and were not able to force a meeting with a time traveler", probably the topic starter means "some publicly known artifact, public event or information".
I.e. a petrified smartphone in dinosaurs' coprolite or a person who had been banned in all bookmakers' offices due to permanent wins.

Edited May 19, 2016 by kerbiloid

[PB666]

9 minutes ago, kerbiloid said:

As "and were not able to force a meeting with a time traveler", probably the topic starter means "some publicly known artifact, public event or information".
I.e. a petrified smartphone in dinosaurs' coprolite or a person who had been banned in all bookmakers' offices due to permanent wins.

It wouldn't be very smart if it was in dinosaur dung, 

Texting while time traveling into the cretaceous. Wouldnt be funny if you opened the sim card showing the T-rexes teeth clamping down on the carrier. Whoops. 

[sevenperforce]

I've thought about this before...I think it is possible to come up with sufficiently extraordinary evidence that we would be safe to accept that SOMETHING out of the ordinary happened. In some cases, time travel might be the best explanation

What would that evidence look like? Well, if you were traveling back in time and wanted to leave irrefutable proof of your presence, what would you write down? You might not be able to leave behind predictions of future events, because you don't necessarily know whether your presence will alter the course of history. Same with language; writing a message in modern English won't do you any good if the English language never develops.

You could, however, leave information that isn't subject to change, but that the ancients would have no way of knowing. For example, you could carve out maps of the surface of the moon and of Mars, along with a large scaled chart of the solar system showing the orbits of the planets, the major moons of each planet, and a variety of comets (particularly ones that could not have been discovered until modern times). You could carve out a large globe showing the exact shape of the continents. You could put skulls next to Vesuvius, Krakatoa, Huaynaputina, Santa Maria, Novarupta, and Mt. St. Helens (since altered history won't keep volcanoes from exploding).

You could also record stuff from science and physics, like the ratios of the masses of all the subatomic particles (that's my avatar, by the way) and/or various physical constants which couldn't be determined until modern times. You could carve out an image of the Milky Way.

Of course, in all those cases, it doesn't PROVE that you time traveled. The same information might conceivably come from an alien visitor. But it's extraordinary enough that time travel would be a reasonable conclusion.

59 minutes ago, p1t1o said:

Time travel into the past? Without a machine, or observation of its operation, I'm not sure that empirical evidence even makes sense in this context, as causality will have been violated. I think.

One can casually construct non-causality-violating time travel systems.

[p1t1o]

1 minute ago, sevenperforce said:

One can casually construct non-causality-violating time travel systems.

"Casually"?

Is that these "closed timelike loop" things?

[sevenperforce]

3 minutes ago, p1t1o said:

"Casually"?

Is that these "closed timelike loop" things?

Yeah.

[p1t1o]

33 minutes ago, sevenperforce said:

<timelike loops>

I was of the impression that it is unknown whether they would have a real-world analogue [being more useful as a mathematical construct for super-brainy stuff], that they can only be possible if certain hypothesis end up panning out. This is about the edge of my pay-grade, I hate time travel, I think it should be outlawed.

[PB666]

30 minutes ago, p1t1o said:

I was of the impression that it is unknown whether they would have a real-world analogue [being more useful as a mathematical construct for super-brainy stuff], that they can only be possible if certain hypothesis end up panning out. This is about the edge of my pay-grade, I hate time travel, I think it should be outlawed.

You cannot have closed timelike loops that can produce interactions that violate causality. At least one paper claims that a quantum computer like set up where they simulate closed timelike loops but that it only works if the out put of an operation does not alter other operations. Check the archives, you can find a link to the paper.

1 hour ago, sevenperforce said:

I've thought about this before...I think it is possible to come up with sufficiently extraordinary evidence that we would be safe to accept that SOMETHING out of the ordinary happened. In some cases, time travel might be the best explanation

What would that evidence look like? Well, if you were traveling back in time and wanted to leave irrefutable proof of your presence, what would you write down? You might not be able to leave behind predictions of future events, because you don't necessarily know whether your presence will alter the course of history. Same with language; writing a message in modern English won't do you any good if the English language never develops.

You could, however, leave information that isn't subject to change, but that the ancients would have no way of knowing. For example, you could carve out maps of the surface of the moon and of Mars, along with a large scaled chart of the solar system showing the orbits of the planets, the major moons of each planet, and a variety of comets (particularly ones that could not have been discovered until modern times). You could carve out a large globe showing the exact shape of the continents. You could put skulls next to Vesuvius, Krakatoa, Huaynaputina, Santa Maria, Novarupta, and Mt. St. Helens (since altered history won't keep volcanoes from exploding).

You could also record stuff from science and physics, like the ratios of the masses of all the subatomic particles (that's my avatar, by the way) and/or various physical constants which couldn't be determined until modern times. You could carve out an image of the Milky Way.

Of course, in all those cases, it doesn't PROVE that you time traveled. The same information might conceivably come from an alien visitor. But it's extraordinary enough that time travel would be a reasonable conclusion.

One can casually construct non-causality-violating time travel systems.

Put "Kilroy was here".

[p1t1o]

1 minute ago, PB666 said:

You cannot have closed timelike loops that can produce interactions that violate causality. At least one paper claims that a quantum computer like set up where they simulate closed timelike loops but that it only works if the out put of an operation does not alter other operations. Check the archives, you can find a link to the paper.

I was hoping there would be some backup for that, thanks, makes me feel much better  I REALLY dont like the idea of causality violations. I'd like to say that stuff that doesn't seem to make sense never pans out, but that is hardly true...

[YNM]

I guess one of the most correct thing, assuming Multiverse doesn't exist, would be Terminator series. Whatever the guardian does the doomsday will happen - the only plot possible to ensure the thing even arrives.

With multiverse though, it's going to be a "hard time". Getting back in time seems to be a good reason to be lost in other universes.

[kerbiloid]

2 hours ago, PB666 said:

It wouldn't be very smart if it was in dinosaur dung, 

Yes, it wasn't very smart for a time traveller to make a selfie with T-Rex.

2 hours ago, sevenperforce said:

Well, if you were traveling back in time and wanted to leave irrefutable proof of your presence, what would you write down?

Spoilers!
For all books, all movies which can remember.

If this works, one would be The One Who Predicted The Future.

If the writers would avoid these spoilers and intentionally change their plots, one would be The One Who Changed The Future.

[PB666]

2 minutes ago, p1t1o said:

I was hoping there would be some backup for that, thanks, makes me feel much better  I REALLY dont like the idea of causality violations. I'd like to say that stuff that doesn't seem to make sense never pans out, but that is hardly true...

I don't think it is allowable accept at the quantum scale, I was creating a thread this morning but cancelled it because of my IPAD was not allowing edits.

Some of the new science coming out that says that the universe is filled with interactions, even possible on the scale of the universe. You can make sense of these things until you go back in time, at which point if there is some preordained interaction from the early universe and go back into time, now that interaction would be split into 2 or 3 ways, this would become non-deterministic if it was initially deterministic. The problem is that we don't know enough about these . . .

In our universe we don't see:
a negative temporal vector
negative mass (which could be seen as a type of space-time energy vector)
negative energy (same as above)

and of course without these you can't have FTL.

This observations makes relativistic observations of FTL, closed timelike loops, wormholes, etc improbable in a scale of spacetime, however there is a black swan.

If we look at the universe as being composed of an infinite number of quantum domains (placeholder domains that then exist for the purpose of populating normal space) that appear and disappear along a space-time timelines governed by comoving space, then we cannot really expect to see any of the three violations, but what if comoving space is very ill-defined, such as boundary between a supermassive blackhole and its very center (which we cannot see). It might get murky and quantum effects in relativistic space could be creepy and unexpected at the observable scale (which we cannot observe). Imagine and electron and positron traveling at each other so close to the speed of light close enough to interact but not close enough to annihilate, and that as they interact clusters of particles might appear to go back and forward in time ever so briefly, as if they were there but not there, because for those particular particles time has all but stopped and very very close to the speed of light quantum time would be something we could clock. Again it would still be limited by the probability that an accumulation of events, but instead of it happening so fast, it would be slow enough to observe, a brief moment before the interactions particles appear and disappear, the interaction occurs and later particles are observed flowing away. 

If I then take this analogy one step further, suppose in the early universe, before space-time exists, when a quantum singularity is giving way to quantum domains, its certainly plausible that you could have negative temporal vectors and negative energy. As energy pours into the Universe negative energy may pour into stable quantum domains (if energy did pour into the universe) and negative energy likewise. You could have a bubble flowing along the negative vector in a dynamic equilibrium with our universe that then collapses on every bit of energy in our universe at some future/past point reconstituting the quantum singularity. But this exception basically proves the point, that we would have to do something really weird to make backward time travel plausible on our time scale. Maybe the potential for time travel exists, but because of determinism in our universe we cannot access it.

You see the basic reason that I have a negative opinion of warp drives, time travel, worm holes and to a lessor degree black hole drives. All of these things require a pattern of behavior that is inconsistent with the relativistic universe. More importantly many of the conservation laws that we have are likely a response to the big bang, and the interactions we observe like G are a part of energy conservation on the universal scale which means we must (should) have some means of conserving long range interactions even if we, to date, cannot observe them other than as scalar field theories.

 

 

 

 

 

 

[p1t1o]

9 minutes ago, PB666 said:

<snippity-snip>

tq:dr

[too quantum:didn't read] 

Jk, I'll try and read it later

[Mr Shifty]

13 minutes ago, PB666 said:

In our universe we don't see:
a negative temporal vector

I don't really know enough about this to comment with any authority, but I thought that our physical laws are all CPT invariant, which means that our "temporal vector" has no special orientation: negative is a label for "toward decreasing local entropy", which is just a convention, since entropy is a macroscopic phenomenon. On a quantum level, there's no way to tell the direction of time by looking at the evolution of a system.

[sevenperforce]

22 minutes ago, kerbiloid said:

Yes, it wasn't very smart for a time traveller to make a selfie with T-Rex.

Spoilers!
For all books, all movies which can remember.

If this works, one would be The One Who Predicted The Future.

If the writers would avoid these spoilers and intentionally change their plots, one would be The One Who Changed The Future.

You cannot even assume that the English language will still exist if you change the future.

Although you can preclude this by traveling back to a more recent time.

There is a nice little pop theory about this. If you were going to time travel without leaving obvious traces, there are some practical considerations. First of all, you definitely need to go to a time prior to widespread photography and videography and photo ids, or you are just running asking for trouble. The last decade of the 19th century is about the latest you could possibly go. At the same time, you don't want to go too far into the past, or you will stick out like a sore thumb due to your accent and language issues, and you will be SOL if you need emergency medical care. You don't much want them to chop off your leg if you stub your toe. So you want to go post-American-Revolution, preferably post-American Civil War just for the medical improvements.

This means the prime time for time travel is 1830-1890, with a particular advantage from 1870-1890.

This also means that if we were looking for evidence of clandestine time travel, we should look between 1830 and 1890.

What evidence might a time traveler unwittingly leave behind? Artifacts are unlikely, and knowledge about the future is impossible to find in the glut of fakers out there. He could leave behind ideas, however. Ideas in philosophy, in literature, in science. Particularly in fiction.

What ideas in fiction would we look for? Well, virtually all tropes in fiction are essentially timeless, going back to Greek myth and earlier. Human flight? Daedalus and Icarus. Teleportation or superluminal speeds? Mercury. Aliens match up with visitors from the stars in Greek and Roman myth. Prophecy, communication over long distances, magical healing...it's all right there in Greek myth.

Except one thing: reverse time travel. Time travel never exists in Greek myth, or in any fiction of antiquity. In fact, time travel into the past never exists in any literature...until the 19th century.

Predki Kalimerosa: Aleksandr Filippovich Makedonskii, 1836. A Russian science fiction story which is the first mention of time travel into the past.
Missing One's Coach, 1838. The first English-language story about time travel.
Paris avant les hommes, 1861. Magical travel to prehistoric times.
Hands Off, 1881. Time traveler changes history, creating an alternate universe.
The Clock that Went Backward, 1881. A machine to transport people short periods into the past.
El Anacronópete, 1887. A vessel which travels through time.
The Time Machine, 1895. Wells's time travel masterpiece.
A Connecticut Yankee in King Arthur's Court, 1889. Twain's time travel masterpiece.

So time travel abruptly enters the world of fiction PRECISELY at the point in history we would expect time travelers to choose as a destination.

[kerbiloid]

Sounds interesting, as indeed XIX century is a vault between savagery and disclosure, and narration is probably the only job for a time traveller (as he cannot do anything more).

Also from time to time I have a feeling that some politicians and philosophers of XIX had met the time travellers from the future, heard their stories about future, but understood them in accordance with a XIX century person conceptions.
But would better avoid politics here.

[PB666]

5 hours ago, Mr Shifty said:

I don't really know enough about this to comment with any authority, but I thought that our physical laws are all CPT invariant

 CPT involves the replacement of matter with antimatter. Even so Lorentz invariance can be broken under certain circumstances, but then that reemphasizes my point, such symmetry breaking is not a likely outcome in our observable universe.

Quote

In standard field theory, there are very strict and severe constraints on marginal and relevant Lorentz violating operators within both QED and the Standard Model. Irrelevant Lorentz violating operators may be suppressed by a high cutoff scale, but they typically induce marginal and relevant Lorentz violating operators via radiative corrections. So, we also have very strict and severe constraints on irrelevant Lorentz violating operators.

Since some approaches to quantum gravity lead to violations of Lorentz invariance,^[2] these studies are part of Phenomenological Quantum Gravity.

And here in lies the problem because gravity is a scalar field, and so what types of scales are we talking about that is tolerant of the violations. I can't prove that the conditions required to break are only suitable at the 'beginning' of our universe, but there is no evidence such conditions exist in our known universe. If you know otherwise I'de be happy to look.

https://en.wikipedia.org/wiki/Modern_searches_for_Lorentz_violation

https://en.wikipedia.org/wiki/Modern_searches_for_Lorentz_violation#Time_dilation

https://en.wikipedia.org/wiki/Modern_searches_for_Lorentz_violation#Gravitation

Edit:

 

Edited May 19, 2016 by PB666
Added dimensional stuff

[G'th]

Everyone knows the story about Ed and how he went back in time to see the dinosaurs and gave them all the chickenpox and thus gave rise to the age of mammals.

[Nikolai]

Okay.  Most of the replies so far, if I'm understanding correctly, have been to posit accurate deliberate foretelling of the future and/or flat statements that "It's not possible".  Let me see if I can shift the gears a little and make this a little more thought-provoking.

The time traveler is trying not to expose the secret that she can travel into the past at will, so she's not going to be dropping artifacts and/or predictions around.  You are not personally acquainted with her in any way.  What kind of evidence would lead you to believe that, in spite of any prejudices you had had or evidences you thought you had properly understood to the contrary, time travel into the past is possible, and that this person in particular is probably doing it?  It's a pretty extraordinary thing, and would require extraordinary evidence; what might that evidence be?

Part of the interesting nature of the question to me is not merely the difficulty of the subject matter itself, but in considering what it is that might cause people to re-think their ideas about how the universe works.

[PB666]

50 minutes ago, Nikolai said:

Okay.  Most of the replies so far, if I'm understanding correctly, have been to posit accurate deliberate foretelling of the future and/or flat statements that "It's not possible".  Let me see if I can shift the gears a little and make this a little more thought-provoking.

The time traveler is trying not to expose the secret that she can travel into the past at will, so she's not going to be dropping artifacts and/or predictions around.  You are not personally acquainted with her in any way.  What kind of evidence would lead you to believe that, in spite of any prejudices you had had or evidences you thought you had properly understood to the contrary, time travel into the past is possible, and that this person in particular is probably doing it?  It's a pretty extraordinary thing, and would require extraordinary evidence; what might that evidence be?

Part of the interesting nature of the question to me is not merely the difficulty of the subject matter itself, but in considering what it is that might cause people to re-think their ideas about how the universe works.

You live in the world and physical laws that exist, if you change the issue of observation, which is intellectual interpretation of a physical process, then you also tamper with the physics.

The critical challenging perspective for you, creating the hypothetical is how does one truly observe the past without changing the past. The better the view you have of the past, the more likely you are to critically interfere. Its quite an energetic adventure to reach the past, and the effort pays off with qualitative information, but the problem is that you may not exist in the future to transmit back the observations if you have interfered with the future timeline. A perfect observation scenario is you are on a meteor that naturally is about to exit our solar system, never to return, you monitor heat from the surface of that asteroid, avoiding observation of entangled photons. Consequently you have low quality data to report. Direct observation means you observed previously entangled photons, in situ observation means you are directly interfering with the massive particles, which means you have altered the timeline. IOW, you cannot use the laws of physics to observe, and then start negating the laws of physics so you won't irreversibly interfere. I'm not saying all observations have a causality effect, but any really informative observations might.

Of course you could observe the Chixulub impact from interstellar space and note the exact date and time. A super powerful telescope might see the crater, and you might then direct future scientist how to study it. . . . .Such supermassive telescopes would still tweeking the orbit of other objects (oort cloud comets, the suns orbit about the galaxy). So you would need to observe, really good observations, but not have mass, not emit EM,

My interpretation is that such a non-interfering time traveler is invisible in the present because they have would have to have no mass or  energy to not interfere in the past. They do not exist. The only alternative I could see is if you traveled at FTL to some point very far away and from that point you observed the past, then you returned to Earth, I think we would know that also, and the quality of your observations would be poor.