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As per title. Supposing time travellers are back in this age from the future, how would they convince the scientific community that they really did travel through time?

Convincing the common person is relatively easy (so easy in fact, that they would most likely start a new religion).

But the scientific community is different. Almost any event "predicted" by the time travellers could be explained away with some sort of conspiracy to make it look like they're the real deal.

I'm thinking predictions of environmental disasters, but that would be evidence more than actual proof.

(Yes, I know that science doesn't really "prove" anything and it builds models based on data, but I'm sure you know what I mean)

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    $\begingroup$ What model of time are we talking about here - will they have created a new branching timeline by coming back? Have they brought the iPhone27 with them? (or any other technology we haven't invented yet) Did they prepare for this contingency before coming back, or are they just an average, unprepared person from the future who was thrown back? $\endgroup$ Commented Nov 11, 2022 at 12:21
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    $\begingroup$ @KerrAvon2055 They brought the iPhone27 with them but it does not provide any evidence because it is identical to the iPhone 11. $\endgroup$
    – Daron
    Commented Nov 11, 2022 at 13:28
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    $\begingroup$ @Daron this comment id gold. $\endgroup$ Commented Nov 11, 2022 at 14:29
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    $\begingroup$ What about DNA? If they claimed to be from, say 500 years in the future, and you were to compare his DNA against current databases, could you identify people alive today as being his great-great etc. grandparents? This person would also be 500 years further from the common patrilineal and matrilineal ancestor of all humans. Would that be enough to make a difference that could be detected? $\endgroup$ Commented Nov 11, 2022 at 20:43
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    $\begingroup$ Bring a nice red, and a white I guess. Caesium-137 "As an almost purely human-made isotope, caesium-137 has been used to date wine and detect counterfeits[12] and as a relative-dating material for assessing the age of sedimentation occurring after 1945." $\endgroup$
    – Mazura
    Commented Nov 11, 2022 at 22:33

15 Answers 15

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A White Paper and a Blue Book

You state that

Convincing the common person is relatively easy (so easy in fact, that they would most likely start a new religion).

But the scientific community is different.

I suspect you’re wrong, and that scientists will be, as a whole, much easier to convince. That’s because the scientific community (unlike the layperson community) has a set process for establishing and proving even the most extraordinary claims.

Works like Newton’s Principia Mathematica, Maxwell's "A Dynamical Theory of the Electromagnetic Field", and Einstein’s Annus mirabilis papers were field-founding, reality-altering publications. Through precise and scientific language, revolutionary ideas were laid out for inspection, and then were examined, analyzed, and, ultimately, accepted by the scientific community.

So stop trying to prove that you’re time travelers: that’s a question of history and biography, not of science. Prove the extraordinary claim that time travel is possible.

Your question includes that as an unspoken, essential aspect that is, to the best of our knowledge, untrue in our own universe. Again, time travel is possible. That means that there are fundamental, incontrovertible physical laws that define that process, that make time travel possible, and which have demonstrable effects.

Your time travelers should publish a comprehensive white paper explaining how time travel works, along with a detailed blue-book-esque compilation of technical documents that lay out how time travel fits into the theory of relativity and the Second Law of Thermodynamics.

Lay out the entire process of how time travel was invented, from the first papers that founded the field, to the building of early prototypes that tested aspects of the theory (negative mass? Negative energy?). Since science is an iterative process, the invention of time travel would have involved thousands of collaborating physicists discovering and establishing a new and revolutionary field through countless reproducible and consistent experiments. Lay out that entire process bare to the scientific community, make it possible for them to fit time travel into their own frameworks of reality and prove to themselves that time travel is possible.

Once you’ve done that, the claim that you are time travelers is trivially believable: after all, you showed up out of nowhere with an entire revolutionary field of science developed, presented, and explored to its peak, a field that makes time travel possible.

Analogy: Trying to prove to Isaac Newton that you flew across the Pacific Ocean in a heavier-than-air plane by showing him a dated newspaper from China is a waste of time. On the other hand, lay out how his laws of motion, combined with Bernoulli’s principle, make lift possible, and then demonstrate the underlying principles and functionality of the internal combustion engine that makes the plane run, and show him the plane operating, and he’ll be much too busy being giddy about the implications of it all to have any reason to doubt your claimed itinerary.

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    $\begingroup$ The only possible problem I see here is that as science evolves, we tend to understand our technology less and less. It may have been a team of 1000s of scientists working with a bunch of algorithms they barely understand themselves who figured out how to make time travel possible, and chances are you need a significant number of them and access to vast libraries of future information that no one remembers off the top of thier head to explain all the incremental discoveries and related mathematics to put it all together. A single forgotten constant could topple the whole deck of cards. $\endgroup$
    – Nosajimiki
    Commented Nov 11, 2022 at 22:32
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    $\begingroup$ The problem I see with this is that you may not want humanity at the current time to know how to build a time machine. Then again, I'm not sure why you would want them to know it's possible at all, much less that you are a time traveller... $\endgroup$
    – Michael
    Commented Nov 11, 2022 at 23:45
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    $\begingroup$ @Nosajimiki This might be true for technology — certainly no one person alive in the world could tell you how every part of a computer, from top to bottom, works— but when it comes to the fundamental underpinnings, there are usually theorists with deep knowledge and understanding of the them. Otherwise, we wouldn't be able to improve/develop our technology. $\endgroup$
    – Daniel B
    Commented Nov 12, 2022 at 0:35
  • $\begingroup$ Someone from our present could also invent time travel and present the idea to the scientific community, without having used time travel. And if people invent time travel before it is invented in the future, it may create a new timeline where no one comes from the future, and time travel is never invented. $\endgroup$ Commented Nov 12, 2022 at 4:39
  • $\begingroup$ Upvoted for "scientists will be easier to convince". The lay public are much less convinced of fundamental principles of relativity (time dilation, relativity of simultaneity) and quantum physics (superposition, uncertainty) than the scientific community is. The key thing is that the thing you want to convince them of is demonstrably true. $\endgroup$
    – kaya3
    Commented Nov 12, 2022 at 10:30
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Go to Stephen Hawking's Party

https://vinepair.com/articles/stephen-hawking-time-travel-party/

Stephen Hawking threw a party where he invited time travelers. He didn't announce his party until after it occurred, theorizing that if time travel was possible, people who were time travelers would be able to attend even if they didn't learn about it until later.

This would at least convince Stephen Hawking. The rest of the scientific community, well maybe he could help you figure that out.

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  • $\begingroup$ Since we already know that nobody came, that would prove the "alternative worlds" theory of time travel. $\endgroup$ Commented Nov 13, 2022 at 1:00
  • $\begingroup$ That's assuming Mr. Hawking didn't kill the guests and cover up everything (or wasn't dishonest in some other way). $\endgroup$ Commented Nov 13, 2022 at 5:38
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High precision timing of as-yet undiscovered pulsars; dates of supernovae -- these are items that should be unaffected by a "new timeline" formed by the act of time travel (because they're centuries or more removed at the speed of causality -- that is, they're actually in the time travelers' past).

World Series results, stock market fluctuations and such are much more susceptible to local timeline changes.

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  • $\begingroup$ "I take it my calculations help explain the perturbations you've been seeing in the rotation pattern of your binary star, but have been unable to explain until… this moment." $\endgroup$
    – Michael
    Commented Nov 11, 2022 at 23:43
  • $\begingroup$ „Dates of supernovae“ - This is likely the best method of all. The exact timing is unknowable before we see the flash, because it is detemined by highly chaotic processes inside the star and the emitted radiation arrives at the speed of light. $\endgroup$
    – w123
    Commented Nov 12, 2022 at 18:22
  • $\begingroup$ This only proves time travel if they are truly future events. If they are actually in the past the travelers could be alien abductees and the aliens have FTL. $\endgroup$ Commented Nov 13, 2022 at 3:59
  • $\begingroup$ @Loren FTL is the same as time travel according to relativity. $\endgroup$
    – sh4dow
    Commented Nov 13, 2022 at 5:01
  • $\begingroup$ @sh4dow No. Unrestricted FTL permits limited time travel scenarios. However, a FTL that is fixed to a reference frame doesn't. $\endgroup$ Commented Nov 13, 2022 at 23:49
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Create enough evidence that they have to believe your time-travelers

Lets take the scientists perspective: When your time travelers arrive and say they traveled through time, there are two possibilities: They actually did or they lie. At this point, lying seems much more likely because people lie all the time and no one has traveled through time so far (as far as we know). A good scientist would now gather more data. Ask them to make predictions would be a good way to distinguish a liar from an actual time-traveler. A single correct answer alone will not convince the scientists:

The time-travelers correctly predict an undiscovered pulsar (@Zeiss Ikons', idea) -> Maybe they're just good at astronomy

They correctly predict supernovae -> maybe they know even more about space

They correctly predict earth quakes -> maybe they're good at geology as well

They correctly predict lottery numbers -> maybe they found a way to manipulate the numbers

But at some point it seems extremely unlikely that they know more about space and geology and lottery and other topics than the entire scientific community combined. Even more unlikely than time-travel, so time-travel is the most likely explanation for the data (correct predictions) collected. At this point, scientist might start to believe them and with even more evidence consider it proven. Wrong predictions would damage the time-travelers credibility severely, so they should stick to things they can predict reliably (@Zeiss Ikon made a few suggestions what to predict and what not).

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    $\begingroup$ The best way to convince the scientific community is to take a scientific approach. Loads of data. $\endgroup$
    – Daron
    Commented Nov 11, 2022 at 13:27
  • $\begingroup$ The only problem with the accurate predictions approach is that their presence in the past might alter events in a butterfly-effect. Something as simple and small as their crossing the road with a bunch of other people, delaying the delivery of a horse meant to win a race by mere milliseconds, would have far-reaching and endlessly fractal consequences that would risk total invalidation of their knowledge of the future. $\endgroup$
    – Lemming
    Commented Nov 11, 2022 at 13:45
  • $\begingroup$ @Lemming this is what I meant with the last sentence. Depending on the type of time-travel this is a risk (Sci-fi takes different approaches here). In this case they should stick to the type of predictions @ Zeiss Ikon suggested. $\endgroup$
    – Matthias
    Commented Nov 11, 2022 at 14:19
  • $\begingroup$ Bringing along future technology would seem to be a way to contribute to this. For example, bring back a cell phone to the 1950's and give an interactive demonstration of something as simple as Candy Crush they can play with themselves, and it becomes highly unlikely anybody from that time would be able to make the breakthroughs needed to create such a demo. Or likewise, somebody from our future bringing along a quantum computer which can efficiently factor large numbers. $\endgroup$ Commented Nov 11, 2022 at 23:12
  • $\begingroup$ (Hmm, I wonder if somebody from the 1950's would even realize how difficult factoring large numbers is...) $\endgroup$ Commented Nov 11, 2022 at 23:13
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The scientist should be the ones to tell the time travelers how they would like it proved.

The way that scientific inquiry works is that it's the scientists, or the ones who need to be convinced that need to be the ones that design the experiments to test the hypothesis. Any system that the travelers employ to "prove" their claims will be met with skepticism and may only serve their purpose by putting more attention to their claims by showing an unexpected result.

The true way that the scientists will be convinced is if they design an experiment, or more likely a series of experiments that would confirm that time travel is the only explanation that fits their observations.

A more pragmatic method is to just pay them

Use your knowledge of future events to gain a substantial amount of tokens of economic exchange (money). Give this money to a team of scientists with excellent reputations, charging them to write rigorous peer reviewed paper titled "On the veracity of specific time travel claims" and give them your full cooperation, along with the mentioned truckload of money.

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I'm thinking predictions of environmental disasters, but that would be evidence more than actual proof.

By this definition, the only proof of a thing is the thing itself. That means no correlation is acceptable, only showing them actual time travel in action. Bring a person back in time to experience something they would recognize as the past. Do this with enough credible witnesses, and others will believe thier testimony.

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Bring back several carbon dated artifacts.

We have collected lots of random junk in museums. Have the time travelers bring back a random selection of that stuff from the future. Chemical testing will show them to be identical to past samples, except that they're notably older.

You can bring back a load of other proof, like several hundred years of movies and music that would be absurd to produce, and scientific devices well beyond human science, but the carbon dated artifacts will be much harder to replicate.

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Have them carbon-date your belongings. This is a method of checking when something is from that doesn't require verbally convincing them. This won't work, however, if you're only from, say, a century from now. In such a case, you'd have to try telling them major political events, etc.

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    $\begingroup$ Carbon dating only dates to the time of death. Perhaps in the far, far, future, there will be such a low concentration of carbon-14 in anything that that alone can be considered proof. $\endgroup$
    – Rafael
    Commented Nov 11, 2022 at 18:56
  • $\begingroup$ "Carbon dating only dates to the time of death." what? $\endgroup$
    – njzk2
    Commented Nov 12, 2022 at 18:46
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  1. Be impressively rich.

Inflation does wonders to our money.

100 years of inflation will move you between the middle class and the multiple 300-feet yacht owner.

  1. Predict well-known random events (lottery numbers, sports results, etc...)

  2. Bring some off-the-mill science - e.g. breaking of some crypto primitives.

  3. Or just be bad and seed time-travel paradoxes here and there and let the Universe deal with them.

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  • $\begingroup$ I think you might mean "compound interest", not "inflation". $\endgroup$ Commented Nov 12, 2022 at 11:40
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    $\begingroup$ I mean exactly inflation. If you are middle class, your monthly income 100 years back would be a fortune. $\endgroup$
    – fraxinus
    Commented Nov 12, 2022 at 12:00
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    $\begingroup$ Could you expand on how someone would demonstrate convincingly that they come from a world where 1USD buys a lot less than it does now? $\endgroup$ Commented Nov 12, 2022 at 16:42
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Imitate Marty McFly. Marty is at a loss to prove toDoc Brown that he really is from the future when he meets him in 1955 (?). When he tries to tell him that the future president is Ronald Reagan, that gets a laugh.

But then he stumbles on the one thing that will convince Doc Brown. He mentions the Flux Capacitor. This is something known only to Doc Brown in that time frame. That does the trick.

So the idea is to find something in the future history of those particular scientists that well be well known down the road, but known only to themselves at the time.

This does mean that you have to anticipate which scientists you are going to meet before you time travel, so you can do the research. Either that, or you have to make multiple trips back to the past.

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Destroy the Doubters

Identify all the most influential doubters who will naysay the time travelling. Record everything that they will say against time travel after your arrival. Encrypt these records (articles, videos, etc.) and distribute them around the world before your arrival. Seed them in warez sites, porn videos, free phone apps, etc. Just make sure they are conspicuous and that people will keep them just to see if they eventually amount to anything interesting (give them clickbaity filenames, etc.).

Then arrive and announce the existence of time travel. Promise to provide proof to anyone who saved one of the suspicious records you seeded around the internet. Wait one week. The talking heads will go crazy and make all their public statements. Then, publish the encryption keys to the sealed records and let people decide for themselves. "Where did you get this?!?" "We just saved the video for 1,000 years, because we knew this day already came. Had to close the loop, you know."

"Scientific Evidence"

For hard-nosed scientists, you can do the same trick, but on a local level: save the raw data produced by the biggest, most expensive scientific instruments (telescopes, particle accelerators, seismographic networks, etc.). Give them the raw data from 1 week in the future, encrypted so they don't know what produces the data until after the time passes. After the data is produced, give them the encryption keys and ask them if this data looks familiar.

Conclusion

Assuming you have enough credible cryptanalysts who can convince the population that there was no way to fabricate this evidence, that should be enough to remove all doubt. The evidence either comes from the most hostile doubters, held in the hands of neutral observers, or from scientists themselves.

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    $\begingroup$ I like this answer. It piques my curiosity on the persistence of quantum sates over time. Something I have never seen expressed in any sci-fi context. If a quantum state was observed in the future would it still be indeterminate in the past prior to the observation? If not, it would indicate entanglement is not bound to time or space... It sure would put the quantum cryptographers out of a job! $\endgroup$
    – Sabre
    Commented Nov 13, 2022 at 17:02
  • $\begingroup$ @Sabre depending on which model of time you subscribe to, current quantum events have already been observed in the future, but we still see them as "indeterminate". $\endgroup$ Commented Nov 13, 2022 at 20:47
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If a time traveler would want to be convincing to scientists they would need to provide information that would take an extreme amount of time to compute or to discover but, if given that information, we could verify it now with less effort. I'm going to provide examples but I'm only going to provide examples of information I think would be interesting but useless to us currently just in case we want to preserve the timeline.

The types of information that would fit this is as follows:

  • Information about undiscovered unstable elements on the periodic table: It takes a huge amount of time to produce this information because scientists need to shoot particles at each other for weeks hoping for probabilistic collisions to occur. This information isn't producible without a large institution and lots of time. If a person was to come with a cheat sheet of useless but accurate atomic data for an undiscovered quick decaying element it would be verifiable with a bit of effort but would ultimately lend credence to the time traveler hypothesis.

  • The locations of interesting stellar phenomena: Its currently possible to detect if stars have planets around them but it takes a huge amount of observational evidence and mathematics to prove their existence. Currently we can only do this one star at a time so that means that most of the stars out there haven't been checked. If someone was to come back in time and start spouting off accurate planet locations that aren't verifiable via amateur telescope but are for bigger telescopes it would lend credence to the time traveler hypothesis.

  • Mathematical proofs for hard but useless problems: There are math problems that, with our current understanding, are hard to solve but easy to verify. This is the class of NP-Complete problems. You could engineer an instance of the "traveling salesmen problem" that takes a couple thousand years(or what ever time you need) to solve via our modern computers (assuming one like that was solved in the future) and bring it back to our time and we could verify quite easily that it wouldn't be solvable in our time given that computers have only existed for less than a hundred years.

There is likely lots more instances of these but these are the only ones that comes to my mind at the moment.

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If the time traveller is not from the too distant future, they could prove it by searching for their younger self among the living population and let scientists do whatever comparison-tests they want between them (fingerprints, DNA, etc.).

However, depending on the modell of causality/ space-time and the influence of time-travel on it, this could bring some high risks with it.

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Show them their watch, it would appear fast, because there is no daylight savings time in the future. ¯\_(ツ)_/¯

ON a real note though, assuming time travel is in fact real...

It would largely depend on which time travel theory you subscribe to.

In some theories, the act of being there created a new timeline in which you would not be able to reasonably assure anything localized but natural would Actually be natural. Many influences on the world could be attributed to many things called "Natural".

Assuming an otherwise parallel timeline, I would go as far outside the sphere of human understanding and influence as you could get. Predict a supernova and its coordinates. One could not witness it in any fashion in advance as its witnessing is it happening long ago. The only way to have known it was to have seen it in the future.

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Make a time travelling car that costs $500

You'll never get published in academia. Don't even bother. Why persuade if you can just render your skeptics foolish beyond doubt?

When 3 million people a year go to the future for holidays and come back having had a great time, time travel will be something that isn't even thought of as a scientific question, but just another uncontroversial feat of engineering.

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