How do you prove you're from the future?

Question

Let's say a time traveler from the year 2100 comes back to the year 2015. He has a very important message: [horrible thing] is about to happen soon, and he wants to warn us so we can avoid/prevent it. (Yes, this assumes a model in which "paradoxical causality" is not an issue.) The problem is if he goes around saying "I'm a time traveler from the future," no one's gonna believe him. They'd dismiss him as a crackpot.

So, he brings along proof, in the form of...?

This is actually a pretty tricky question, if we place two restrictions on it:

1. He does not have a "time machine". His device sent him back without coming along with him, so he has no way to demonstrate that he's a time traveler by actually demonstrating time travel. (Just as an aside, this is very much on purpose; he doesn't want knowledge of the mechanics of time travel to fall into the hands of people who might use it for nefarious purposes, and part of his plan is to actively sabotage scientific research that led to the development of time travel.) The thing he used--let's just call it a "time catapult"--was able to send a small payload back in time, maybe comparable volume to a phone booth, certainly quite a bit less than the interior of a car.

2. He wants to get the issue of establishing proof of identity over with and out of the way as quickly as possible and move on to more important things, like averting future disasters. This is a real issue; he can't go back arbitrarily far in time; the Temporal Frobulence Theorem shows that it becomes extremely unsafe the further back you go; it's a bit of a stretch even to reach our time!

The two obvious candidates for proof are future technology and knowledge of future events. The first is tricky, because current technological advancement puts us perilously close to the boundaries of Clarke's 3rd Law: any sufficiently advanced technology is likely to not be easily recognizable as such, and anything insufficiently advanced would be likely to just look like someone working in his garage made a breakthrough in some field, and that's pretty cool and all, but obviously it doesn't prove he's from the future.

The second is also kind of tricky. There are two major classes of unpredictable future events: natural and manmade. Bringing official government records of earthquakes, hurricanes, etc. could certainly establish that he is who he says he is, but it would take a lot of valuable time for Mother Nature to furnish the proof. On the other hand, if he predicts unpredictable manmade events, there are all sorts of potential troubles there. Point out the time and place of a major crime? Obviously, he was in on it; let's arrest him! Produce a table of stock market closing values for the next month? Well, he might be right for a day or two (coincidentally, of course!), but as soon as someone starts using the data he provides and attempting to profit by making trades based on it, the Butterfly Effect flutters in and destroys the accuracy of the data.

So, what would be the quickest, most efficient way for our unfortunate herald to establish beyond reasonable doubt that he is a time traveler with accurate knowledge of future events, and at the same time get enough people to listen to him so he can spread his doomsday message?

Answer 1

He should predict Solar Weather and/or Solar Events.

Predicting Earth weather is a complex process, and he's introduced a new variable - himself. And not that he'll have a huge effect, but you never know - the ripples of his arrival could be enough to throw off any predictions, creating doubt that he's authentic.

On the other hand, solar weather - the sun's activity - is also extremely difficult to predict, and is completely isolated from the time traveler's influence. He can pull historical records from various space agencies and publish the results for the next week, in complete confidence that the data can't be effectively hidden or faked.

Answer 2

I'm going to suggest something rather different, given that he's from not far (2100) in the future. All he will need to bring back is the names of his parents/grandparents. With DNA testing of them and of him it would be possible to prove that he is their descendant, something impossible if he wasn't from the future.

Answer 3

There is one more very convincing thing he can bring from the future: actual copies of items from the present. If someone came up with an aged Mona Lisa, the bones of Barrack Obama and the Tiffany Yellow Diamond, I doubt his claims of coming from the future would be ignored.

Now how he can come up with these items in the future is the subject of another story, but I am assuming he isn't just some mad scientist who wants to right some wrongs in the past, but he is an exponent of a troubled species that NEEDS to prevent a catastrophic future, therefore his experiment can be outfitted with some inconsequential items as those described above.

Answer 4

The critics provided the proof themselves

Before he travels back in time, he uses his machine to send along a "parcel of proof" to some point in time after his own arrival. He can then predict that this parcel will arrive out of thin air at a specified moment. By being an extraordinary event, this boosts his credibility.

The clincher however, is that the parcel contains recordings of his stay in the days following the arrival of the parcel. Things which he buried at a secret location and retrieved himself in the future. There could be letters the sceptical inhabitants have sent to themselves, video recordings of people he has met telling how they have finally been convinced that he is a traveller from the future, accounts of the many random things in their lives such as the timing of a sudden onset of rain that ruined their crop, accounts of a kid that fell and broke his leg or of where misplaced items were finally found.

Story-wise this gives you an excuse to introduce the supporting characters in more depth. You can, if you like, arrange for a circle of true believers while keeping the world at large indifferent to his claims. For the reader, the point after which he has buried the parcel marks when the outcome of events starts being uncertain again, possibly building tension in the story. Perhaps we'll also see some dramatic scene where the traveller tries to retrieve the package again, to add a warning to himself about trouble occuring.

Answer 5

The problem with knowledge of the future is that as soon as you make one alteration the future starts to change. Knowledge of one lottery result would be fine, but results after that would rapidly become unpredictable again.

One of the comments is absolutely right though, start by winning the lottery, just send yourself back with a bit of money and a false identity.

Additionally send yourself back in time to shortly before a major disaster and use your lottery winnings to avert it and to invest in a number of companies that you know will grow large. You can also bring back a suitable list of inventions to use your lottery seed money to start working from.

With that level of money and influence you can then not try to convince people, just get them to do what you want without ever mentioning being a time traveler.

If you really want to convince people though then use natural events that will still happen predictably. For example if you know a major earthquake is going to strike new york at 9:13am on Wed 4th August then use your money to place billboards warning people and to place relief shelters and supplies ready.

That will get people listening.

Answer 6

I read a saying somewhere: "If it doesn't have wires sticking out of the case, it's not cutting-edge."

I think carrying 2100-era technology would be a clincher. It's one thing to build a device that holds 500x as much data as any hard drive in existence. It's much harder to package it up in a sleek, friendly interface that's clearly gone through a dozen rounds of feedback and redesign.

Say somebody shows up at the front gates of the White House with a smart-matter robot with smooth, seamless AI, the ability to 3D-print insanely complex objects out of electricity and dirt, and a demonstrated ability to calculate at 3000 petaflops/second (100x faster than the current fastest supercomputer). You can't dismiss that as "something a guy built in his garage." You can't even dismiss it as a "secret government or corporate project." The construction of such an artifact requires too many breakthroughs in too many independent fields.

Heck, I suspect if you took an iPad back to 1995 and handed it over to a team of engineers and asked them, "Future or Nifty?" they'd come back within a few days and say, "definitely future."

So I think it's a more interesting question if you deny the possibility of bringing anything but information back. My solution (riffing off the 'solar weather' answer): use information that has already been generated, but hasn't reached us yet. Random data encoded in electromagnetic waves still flying towards Earth.

For example, the semi-random "hiccups" in the rotation speed of pulsars.

To be thorough, you'd want data of several different phenomena. If all you have is microquake data from pulsars, or the coordinates and times of supernovae... any one thing could be dismissed as "oh, they just made a breakthrough in predicting X." But making breakthroughs in X, Y, Z, and W? Much harder.

Neutron star - Rotation (Wikipedia)

Update: Looks like DanSmolinsk had the same idea.

Answer 7

An easy solution would to have the time traveler use the NIST randomness beacon, or some variant in your story.

The randomness beacon outputs a random number, signed by its key, every minute. By definition, the value of the number is unknown until its time passes, and is immutable after that time.

Before leaving, the time traveler simply looks in the beacon archives, and prints off/memorizes the beacon values near the time he's traveling to.

All the time traveler has to do is publish the results of the beacon for some times after the time he travels to. For example, he could publish the next hour's worth of beacon values right after he arrives. Once that time passes, everyone can see that the time traveler indeed knows the future.

Furthermore, one doesn't have to worry about the butterfly effect with the beacon! Because the NIST beacon/similar beacons use a radioactive source as the random number generator part, previous events have no effect on future events.

From a hackday article explaining it:

More esoterically, one could use the Randomness Beacon to prove that something is newer than a certain date by including a recent Beacon entry. As of this writing, the values for December 31, 2014 are all still up in the air, so I can’t possibly write one of them down yet. But from Jan 1, 2015 and on, it’s trivial to do so. So if I get a bunch of t-shirts made with the midnight value from December 31, it’s absolutely verifiable that I got them made in the new year. In short, you could use the Beacon as a not-older-than dating scheme.

Answer 8

Bring copies of future expensive movies, think Avengers 4. It's not plausible to fake such.

As a bonus, bring additional material, think interviews and making-of documentaries.

Answer 9

Predict astronomical events. If you can supply coordinates and magnitude of supernova explosions, neutron stars oscillations or other similar events, it would be impossible for you NOT to be from the future.

You could be mistaken for an FTL space traveler, but if you bring enough data points from disparate directions, Occam's razor would work in your favor, and between time travel and FTL spaceman, time traveler would be chosen, because it would have less assumptions.

Since the astronomical events came from random points in the sky, it would be impossible to exist one place in the universe where these events could've been seen before being seen on earth (due to lightspeed limitations, it would need to exist one point in space nearer ALL events than Earth - assuming space is quadridimensional like in Einstein's relativity), and that there would be one observer with FTL capability at that point willing to come to earth to lie about being a time traveler.

Just being a bona fide time traveler would have less assumptions.

Answer 10

I feel like a strong approach could be to provide solutions for various problems of that era. Things that the top people in their respective fields have been trying to solve for many years with little to no progress. By convincing them, their feedback should influence others.

• Solving (with proofs) the remaining six Millennium Prize Problems simultaneously would blow the minds of mathematicians.
• Bringing back documentation of cures for various forms of cancer/diseases could convince the medical field.
• As so on with physics, space, etc.

The biggest benefit off of this is that multiple field breakthroughs will cause so much world-wide impact that you'll end up with proof people can experience. It would be hard to say you're just a savant because research by the world's best couldn't do it either and they're specialists.

A few feasible issues are

• The amount of time it would take to provide this documentation and have people take it seriously. (If you could kick-start your first breakthrough, the others could accelerate.)
• Whether or not these solution were indeed solved within the timeframe we're limited to.

Answer 11

A copy of a newspaper. Surely in the future he would have access to historical documents and newspapers among them. A copy of a national newspaper from several days in the future that hadn't even been written yet would surely be some kind of proof. Especially if it remarked on an event that hadn't yet occurred.

Answer 12

I wouldn't actually try to prove I was from the future. I would focus on proving the event would take place. If I couldn't prove it, I would focus on getting the appropriate response in place via a subtle, roundabout way. For example, if the event was an asteroid collision, you forge an email to an astronomer from a trusted colleague telling him where to point his telescope. If the event was a terrorist attack, you send the authorities anonymous tips and maybe even plant some clues yourself.

This might be interesting in contrast to previous more drastic attempts that failed. Maybe previous time travelers assassinated Hitler too early, which caused something even worse to happen, so you agree to be his bodyguard, but send some key piece of information to Alan Turing to help him build his enigma-cracking machine that he never managed to complete in your timeline. Then you fake Hitler's suicide once it's safe to do so.

Or maybe something not so subtle. In your timeline, Saddam Hussein eventually manages to detonate 3 nuclear bombs in America. After several more subtle attempts, you plant some WMD intelligence way before the event, but that's still not enough to get the U.S. government to intervene, so in desperation you perpetrate the 9/11 attacks.

Answer 13

The time traveler should set new video game speed run records using glitches not currently known. For instance, there are currently still large, active communities uncovering new methods in Nintendo 64 games such as Zelda: Ocarina Of Time.

This is a non-violent method which involves no money or physical objects. It minimizes introducing variables mentioned above through lottery/stock manipulation as subsequent events are not based on the outcome of the prior event (i.e., Glitch 2 in Game B will not change upon completing Glitch 1 in Game A).

I am sure this method would garner the time traveler enough media attention and credibility to then springboard to convincing the public on whatever "serious" issue as at hand.

As I'm typing this, it just occurred to me that this was the plot of "The Wizard" when they introduced Super Mario Brothers 3 and the one competitor knew how to get to the early warp zone.

Answer 14

You mention the option of either unpredictable natural or man-made events. If you publish a table of stock prices, then the future will change based on how people use them. What about a table of things people cannot change?

Use daily weather information for a few weeks in the future. You can publish precise highs, lows, conditions for a variety of locations around the globe. Weather is something that is always difficult to predict, and having knowledge of what will happen will not change the outcome. Additionally, you won't have to wait for natural disasters like earthquakes to take place. After a day or two of accurately predicting weather across the globe, people should either believe that you are from the future or are the best meteorologist in all of history!

Answer 15

One of the fairly standard proofs of knowledge of future events is to have the information sealed in an envelope, and hand it to the person you are trying to convince with instructions to open it at the time of, or immediately after, the event. The fact that the other person has it in their possession before an event happens is the proof that you knew it ahead of time. Because they don't see the proof that you held such knowledge until after the event happened, they don't get to meddle with the flow of time, there by avoiding having them take actions that would change the outcomes.

If I were such a time traveler, I would probably pick sports as my proof. Pick whatever major sport was in season for my target region and have a list of the final scores of each matchup. Two weeks or so should give enough evidence to convince people that I knew what the results were going to be before the games were played.

Here is the catch though. By demonstrating that time travel is a possibility, I am pretty much ensuring that someone is going to figure out how to do it. I may try to mislead or derail their research efforts, but knowing that something is possible makes it pretty much inevitable that someone will eventually figure it out. Quite possibly sooner than they did in my original time line now that people are paying attention to it as a real possibility.

If one of my goals is to prevent time travel technology from being developed then I have to work a lot slower and more subtly. I have to use my future knowledge to place myself in a position of influence, without making it obvious that I am from the future.

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Edit in response to comments:

The way the scenario in the beginning of this plays out is that I select the individual I want to convince and come up with a way to approach them after doing a bit of preliminary work. Once I have made contact I say something along the lines of "I have some important information for you, but you won't believe me if I tell you now. Take this envelope, wait until Monday morning to open it, then email me at the address inside after you have verified the information it contains."

When you open the envelope Monday morning you find the scores at the end of each inning for all of the baseball games that occurred in the previous three days. You know the envelope has been in your possession for at least a full day prior to the first game on the list. Now it is conceivable that I could have had a lucky guess on one or two games, or possibly found someone to bribe on a few more, but the probability of me having the outcome of every game across the nation for several days correct down to that level of detail is almost impossible. (The information inside could really be anything, the key is that it is information about events that occurred after I gave it to you; It is inconceivable that I could have accurately predicted the data volume and level of detail without special knowledge; And it is equally inconceivable that I, or any organization supporting me, could have influenced the outcomes of all of those events.)

So obviously something special had to have happened. Could I have tampered with the envelope after I gave it to you? Possibly, but you have not seen me since, and I have made no further attempt to contact you. Could I have been incredibly lucky? Sure, it is possible, but extremely unlikely. And however I pulled it off, wouldn't it make you curious?

If I have a list of such contacts, and I work this same general scheme on each of them independently. One or more of them is going to decide to reach out to me to find out what is going on. Perhaps they do think I managed to pull a fast one on them, so offer to do it again when they can take some informed precautions.

One potential tripping point in this approach is keeping someone from opening their envelope early and trying to exploit the knowledge within. If I am targeting current day, and particularly selecting tech savvy people as my targets, then I can encrypt the data, give them the encrypted file, and then wait to give them the key to decrypt it until after the events occur.

Answer 16

We can already store enormous volumes of information in a pocketable medium. Bring a petabyte of (his current) Wikipedia on his pocket reader.

In so many TV shows and movies, the lone traveller has to do everything from scratch, and his limited resources is the main source of making it interesting.

Why not have a well-researched plan in place? The catapult to the target past might be a one-shot, but going back a week or month is easy and just a couple years is routine.

They can grow their resources and make plans in a small time loop near home: each jump back improves upon the planning and size and effectiveness of the organization.

They can become very wealthy and politically powerful, and recruit talent from the brightest of the population, seemingly (from the outside in normal time) by a combination of luck and omniscience.

Now there may be an inherent issue with the far-past catapult in that any success at changing the timeline will destroy the "present" with its large organized effort in place. Any arrival at all will appear in a different timeline not in their own past, so they cannot send multiple loads. They can send multiple trys though. Each catapult seeds a new timeline and through repetition with variations on the plan the hope at least one of them turns out the way they intended.

For a limited load size and mass (your phone box isn't larger on the inside?) why send a single person w/carry-on baggage? Send nanotechnological robots or seeds for robots and infrastructure. If piloted also, the person is a dwarf (or has the body of a child) to make room for his stuff. That is a detail I've not seen in stories before.

If multiple loads is possible with the thread maintained to the new past only possible if they don't diverge (yet), set up the operation on the far side of the moon. The expedition is in shipping mode to receive as many loads as it can, and only after the thread is broken do they proceed with the mission.

Answer 17

It's actually quite easy. Look at the stock market--this has been rejected by other posters on the basis that making a correct prediction will change the future. The butterfly effect is certainly going to be an issue. To protect against this you must make only one prediction and at a short range.

Have your time machine deliver you to the Oval Office, 10 minutes before the closing bell on Wall Street. I would recommend minimal attire to minimize the nervousness of the Secret Service agents.

Arrive, hand the closest agent printout, tell him to keep it secure. The printout looks like gibberish. You then explain that you are a time traveler, come to warn of a disaster. The printout you just provided is the closing prices for every actively traded stock. There is a simple encoding scheme, even if it goes straight to a cryptographer they'll only have a few minutes to work on it--the crypto guys simply don't have time to bring their heavy guns to bear.

You make thousands of accurate predictions at once--they'll listen. Popping in from thin air will also help.

Answer 18

The answer is Bitcoin.

Block chains are based on a cryptographic proof-of-work protocol: constructing one takes time and effort and processing power, but it's orders of magnitude easier to verify that they are correct.

So either get your hands on 100 years worth of block chain data, or use a 22nd century supercomputer to generate a brand new one, of a length sufficient to impress. Load it up on as many antique terabyte drives as you can carry, get into the time-catapult, and find the nearest influential crypto enthusiast.

This scheme has several advantages: Unlike the 'Almanac', the locals can start verifying right away. There's no risk of butterfly-effect: your block gain doesn't have to match anything from the 21st century, it just has to be internally consistent. You're not bringing any useful technology or information back with you, just proof that you had it before you left.

Once a certain length of block chain is verified, the locals will have mathematically solid proof: Either you are a time-traveller, or you have access to more computing power than all of humanity combined, and have decided to use it to impersonate a time-traveller. Either way, it's probably a good idea to listen to you.

A drawback of this solution is that it's highly technical. Once you've convinced the global mathematics community, the NSA, and Reddit, you're on your own to convince the man-on-the-street.

Answer 19

Bring forth the bugs! - pick a ton of open-source projects, such as linux, and expose all the current security bugs (exposing one won't butterfly-contaminate the others, as the code is already written, saved, deployed on all sorts of machines, and won't auto-update to fix itself) - next, to prevent the ensuing hackfest, distribute the code that would be required to fix this newfound issue - the patches, fixes, etc. - you now have proven yourself as someone with credible world-saving abilities - people can speculate as to where this comes from, if necessary you could blackmail every single government or politician in the world (or just about anyone else) - basically choose things that have already occurred prior to the date that you wish to appear in, but have not yet been revealed to the public (think snowden leaks, only much larger, over more secret organizations, with the juicy stuff selected and chosen)

Answer 20

A reverse-compatible (USB3.0) hard drive full of the most expensive movies, pop songs, selected news media, YouTube, selected Internet, and perhaps selected scientific publications from the year after you arrive for several decades into the future. You're either from the future, or from an alternate Earth future.

However, proving you're from the future is probably a lot easier than gaining the trust of authorities, and avoiding getting abused by people who decide to behave badly when tempted by the potential wealth/power they might think they could hoard to themselves if they captured you.

So, you might want to bring a device that would let you make anonymous undetectable broadcasts, as well. And other things that might help with your personal security and well-being.

Answer 21

By request on the comment thread, I will expand on rmoore's answer and detail how the DNA analysis can prove the time traveler is indeed a descendant of his great-grandparents / grandparents.

This page for a testing website states that their rate of accuracy for grandparent DNA testing is 99,99%. If the grandparents are alive, the odds of the time traveler to NOT be the grandson of these people would be:

0.0001 ^ 4 = 0.000,000,000,000,000,1
1 in 1,000 trillion chances.

Since the amount of people that ever lived is estimated at 108 billions^{source 1 2 3}, the explanation of time travel would be the accepted explanation by Occam's razor. The apple does not fall far from the tree. Also there is the paternal test for the Y chromosome (paternal grandfather) and the maternal test for the X chromosome (maternal grandparents) and the mitochondrial DNA testing (maternal grandmother).

Unless his family has a huge recent history of incest, if the grandparents are already living, there would be no doubt he is a time traveler.

But unfortunately, There is a great chance his grandparents are NOT yet born as of 2015.

Lets assume they sent back a healthy indiviudal, on his prime. Lets also assume that his prime is at 25 years old, and that he was born when his parents were 25 years old, and his parents were born when his grandparents were 25 years old.

This would place the birthyears of our 2100 time traveler in 2075, his parents in 2050 and his grandparents in 2025. His grandparents would be born only ten years-ish from now. This would leave only his great-grandparents alive, in their teens. There is a trend of people having children at a higher age (with all that egg freezing mania and stuff) so I think that this 25 years window is a safe assumption.

Now, great-grandparent dna testing is still mostly unheard of, but looking at genealogy testing, we can get 95% proof that the time traveler belongs to the family line of his father's father's father. With autosomal DNA testing, he can be placed in the family tree of all of his eight great-grandparents (and since your grandparents have not yet been born, they are all alive by 2015). Now, unless they are close relatives (like several of those couples are cousins in love), a simple venn diagram would prove that the very existance of the time traveler would be impossible if he is not a time traveler. Proof by contradiction.

There is no other way our alleged time traveler could be part of eight completely unrelated family lines (and trace your mitochondrial DNA to a few and the Y-DNA to only one). Unless he is really the great-grandchildren of those eight families.

This one has less precision (still beyond reasonable doubt, but would give a hook for the antagonists to descredit our hero) than the grandparents (so the very skeptic may still be unsure, specially if some of the great-grandparents were related), but with some more info about the future, the time traveler would succeed.

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Picture the adventures of a time traveler trying to convince eight teens to do agree to DNA testing, all the while dodging the evil organization and attempting to avoid doomsday.

Also for bonus kicks, he tries to get the matchups of his great-grandparents right, while the teen hormones attempt to negate his family line.

Answer 22

A variant of the lottery numbers ploy: bring some other information which is top secret right now, but part of the historical archives in the future. That should get the immediate attention of government agencies if the time traveler phones them.

Answer 23

Have the person you're trying to convince write a long letter, and post it to you (or your Grandfather). You'll receive it in the future.

Then you produce the envelope out of your pocket, open it and reveal the letter!

Answer 24

It's easier to think about what type of thing you'd bring back 100 years to the past that would convince people you are from the "future" (IE, Now).

Our future man could easily find out what hasn't been invented yet this year and take a product from his time back with him to our time to prove his authenticity. Demonstrating his technical prowess with an unusual device that does not exist anywhere else in the world should be sufficient proof.

If we were to compare it to travelling from now to 100 years ago, all anyone would have to do is take their smartphone out of their pocket and play some music. Not only would the music be strange to the listener, it would be a remarkable technology in itself - even without the ability to connect to a wireless network (a problem with any technology dependent on future infrastructure).

For our man from the future, his handheld matter converter that turns common paper into hot dogs should do nicely.

Answer 25

I'm surprised nobody has stated the obvious: bring back a sports almanac that shows the result of every major sports event until the end of the century.

Answer 26

Send two payloads into the past. First send a probe (or even the time travellers luggage) to March 30. After making sure the probe is sent, then send the traveller to March 1. All the time traveller has to do is tell news agencies that his probe/luggage and maybe artifacts from the future will arrive on March 30 at a specific time and place.

For a real world example of how people react to a time traveller you should also check out the John Titor story. A time traveller revealed himself on internet bulletin boards during the years 2000 and 2001. Caused quite a stir after he posted pictures of his time machine.

http://en.wikipedia.org/wiki/John_Titor

from http://www.abovetopsecret.com/forum/thread62046/pg1

excerpt: This is a picture taken in the fall of 2035 during my training. It shows my instructor beaming a handheld laser outside the vehicle during operation. The beam is being bent by the gravitational field produced outside the vehicle by the distortion unit.

from http://www.strangerdimensions.com/2013/02/04/john-titor-the-man-with-the-machine/

For your time traveller it might also be prudent to remember that doomsday predictions can also attract the wrong kind of audience (ufo and doomsday believers) which could be detrimental when he is trying to prove his authenticity.

Answer 27

What if the time travel resulted in some form of semi-violent catastrophe, or publicly visible entering of our time?

Since we do not know what time travel will do to our reality this might be feasible. If I knew time was of the essence, I'd make sure I'd enter with a big BANG, to get this identification process out of the way ASAP... Of course this might also result in being arrested and potentially tortured to get information.

But lets assume, that the above doesn't happen, and if somehow during this process the Eiffel tower got sucked up in some space time void, or for that matter any other major publicly visible entrance event occurs in a manner that it unknown to us, leaving only our hero as the sole survivor... people will notice.

Answer 28

People seem to be thinking small in terms of "data points required to not just be a charlatan." Rather than a single lottery or a series of sporting games, why not just correctly "predict" the full intraday pricing on a second-by-second basis of, say, 1,000 equity options ?

• Stock option prices are governed by stochasticity, i.e. any given moment a stock option's price is just as likely to go up as down.
• You may be able to rig a lottery or a sporting match or two, but rigging an entire open market is ... unfeasible.

So that's 1,000 stock option volatilities * 28,800 seconds in a trading day = 288,000,000 basically coin flips you accurately predicted.

Answer 29

The "standard" solution to this is to predict the future.

The most straightforward version would be to print out and bring along stock market data for some time following your intended arrival. It is widely believed that the movements of the stock market are impossible to predict precisely, so consistent success at this would be quite convincing. And, if everyone is still incredulous, you could just leverage your information to make a fortune and then simply pay them to do what you want. If you want the time traveler to not have this disproportionate power, you could instead give him a one way hash of the market figures - that way he would not be able to predict what the value will be, but it will be possible to determine whether he had access to the future value at any point.

Alternatives include guessing lottery numbers, weather, sports competition outcomes, and so on. All of these have the drawback of being chaotic, and so if your universe takes a "butterfly effect" approach to time travel, the simple presence of the traveler may disrupt these events and render predictions useless.

To solve this issue, you can try bringing back large scale historical events, which would take more than a flap of a butterfly's wings to alter. For instance, presumably a person traveling to 1913 would have a lot of trouble preventing a world war in early 20th century, even if they did manage to save Archduke Ferdinand. The drawback here is that major historical events may be predicted, and people may ascribe the prediction to extraordinarily sharp deductive powers rather than future knowledge.

Lastly, you could bring back information that was already past at the time of arrival, but would not be widely known until much after. For instance, an important shipwreck was discovered by chance in 1982. If you traveled to 1975 with a map showing the location of the wreck, locating it would be an extraordinary feat. Some could accuse you of stumbling upon the wreck yourself, and trying to spin it into a time travel story, but if you do this for many shipwrecks (or other artifacts) around the globe, that theory will become quite weak. Besides archeological finds, you could go back with information that was a very well kept secret at the time. The nice thing about this strategy is that even if some chaotic process ruins the future you are trying to predict as proof, the past would not be affected (granted this assertion is dubious in a universe where traveling backwards in time is possible) and your proof is safe.

Answer 30

I would say bring news videos from the future, near future, and of the events, needed, make sure that the news anchors shown are very prominent ones that would be hard to miss

Answer 31

Actual "proof" of being from the future is pointless: the goal is to convince people, and few people can be convinced of something in violation with their belief system, regardless of "proof".

How many well established scientific facts are being ignored on a daily basis?

People smoke and eat unhealthy foods, even though it is fairly well established that smoking massively increases risks of disease and death. They drink, take drugs and drive. We still run and build coal fired plants even though the environmental consequences are catastrophic....

Think of the long list of patently insane behaviors people have on this planet. No matter how thoroughly something is proven, you will find people to dismiss it entirely with no evidence.

Using "proof" to convince people to do something is sadly not an effective way to get them to do things.

Suppose someone were to give you abundant proof of an upcoming catastrophe... what do you do next? Who do you contact and how would you go about convincing the people in power and the concerned population to follow your orders?

Proving one is from the future is not just impossible, it's also pointless. If the goal is to convince specific people not to take a specific path, proof of time travel isn't going to do the trick. Better come up with a carrot, a stick or both to get these people moving in the right direction.

Answer 32

I'd just write down the lottery winners for the near future before it's announced, hand them in to the people I want to convince, in an envelope, and ask them to verify after they're announced. After 2 or 3 times, they should believe.

Answer 33

Have someone ask this question, and then post this answer.

Hello all, I am from the future. I come from 2345 AD. We are looking for test subjects for our experiments, and we've been running short. All volunteers will be paid generously, using future cash, or, as we call it, "rubber". I can't say any more or this will cause a ripple effect. Thank you.

Answer 34

It can't be done. If you show me advanced technology, I will assume that you come from a society with advanced technology. If you make predictions of the future, I will assume you have advanced technology that can make those predictions. You might be able to convince specific individual people by targeting a message specifically to them, but any general future predicting or technology marvels are easier to explain without time travel.

Answer 35

We're talking about around 100 years of history and rather than proof, I see credibility as a bigger problem, proof is worthless without it.

Assuming there is no language barrier, even if the protagonist were speaking the same language as the people around him it would be language separated by around 100 years or gradual change. Look at how laughable films from the 1950s look now then invert the context that 1950s language, attitudes and social mores are the norm and the observer is in a minority of 1.

Credibility issues are common to history documentaries. They use the viewer's "modern" perspective to frame events in a way that conforms to biases. A quick glance at 20th century newsreels containing "white man's burden" topics underlines what I'm driving at, all of them from less than 80 years ago. The concept of "modern" is very nebulous and changes from generation to generation.

History is not an absolute - it is simply an interpretation of events and the present is a huge jumble of events with future implications interpreted by the conventional wisdom of that time.

So even with future hindsight, the future time-traveller would have to choose several events that the people of that time and geographic location would care enough about to want to have their preconceptions challenged, and would likely fall foul of any powers that had vested interests in seeing an outcome to fruition. Lets say traveling back in time to stop the birth of Islamic State cells, a little shy of 20 years ago, would pit the protagonist against a hawkish American government policy intent on invading Iraq using a "for us or agin us" approach to anything seen as being critical, and using kidnapping and detainment in Guantanamo Bay against people they deemed to be "enemy combatants".

Answer 36

I'll assume that the time machine can be used multiple times:

Step 1: Get some attention. Go to the pentagon, try to break the security and fail. This way some official people will hear what you have to say.

Step 2: Threaten them: "In 4 hours a bomb is gonna explode at some precise place." This place will be heavily watched after this.

Step 3: Send something from the future at this precise place and time. It can be anything, the important thing is that people see that an object has appeared out of thin air.

From here on out, people should listen to you a lot more.

Answer 37

The iPad one is interesting, but "theoretically" someone could have had a secret processing plant employing one million people, underground, working independently for 50 years, funded by an alien race if necessary. Anyway, the physics of an iPad was known in 1995, if not the mechanics.

So - what about simply predicting a solar flare? Or better still - bring a photo.

Answer 38

If this traveler were time travelling 'within one universe' instead of jumping to other 'local' universes in different states of relative co-existance, you immediate destroy the universe you 'jump from'.

If you are going for the more linear classic approach to time travel, the traveler could bring back something which co-exists in 2100 which is iconic and priceless to boot, but most of all unique - and dare the objector to prove falsehood.

Depending on how many universes you believe in (if any), you could tell them to damage it and then watch the corresponding damage occur. Go further and destroy the item and poof! It disappears. But if so, then so did the traveler's effort obtain it, because it never existed to bring back... but only because he went back with it was it destroyed in the first place. I know causality is not meant to be an issue, but it is! So I think you probably destroy the universe by going back in time at all - at the very least the chances of doing so rise geometrically (towards tangent 90, or something, per unit of observable time, probably). Regardless, he rips wide open the future, which has or has not happened. Perhaps he's beaten the odds? And of course he must, because he exists in the first place!

So I'd wonder whether this time traveler.... is there a future ahead of him with time travel?

My personal feelings are that future events are so intrinsically sensitive to present conditions that one irrevocably determine the outcome of the universe simply by doing nothing. Hell, I am just part of the universe playing itself out as intended, am I not? And if I never learned to tie my shoelaces until I was six, instead of five, for example - stuff like 9/11 wouldn't have happened.

Which is absurd surely? OR IS IT? Time travelling, and a pre-determined future (whilst the chances of one existing are non-zero, is definitely, definitely not our realm.

But yeah OK, causality is not an issue - if he were travelling linearly backwards and wanted proof, an object he could bring back might be something like a radioactive vial with a unique signature of something which has shown measurable decay. Perhaps also the traveler possesses a residual charge of something, or has a little extra amount of 'entangled' particles in all his orbits. A quantum signature.

/BLURT

Answer 39

Bring a future weapon. If I know humans, we continue to grow better at killing each other. Why a weapon? Well, if you are going to the past to change the course of history, that means you are interrupting the plans of powerful people, leaders (upsetting them at least). Once they are on to your motivation, they will try to silence/terminate you even if they are convinced you are from the future. I would even bring a doomsday device as an insurance policy. If the future is so bad that you were sent to the past to alter it, would it really be that bad to destroy the world in the past if your mission failed?

Answer 40

I don't think there is a way to prove that you're from the future without showing off your TARDIS. Yes, you can predict forty trillion data points accurately, but we as a species are far too skeptical. However, this is meant to be more constructive than a simple "No" so here we go.

Given the rate at which science is advancing, it's fairly safe to say that new fields of study will pop up in a hundred years time. Instead of showing off massive advances in robotics, or matter manipulation, show off a new kind of thing, as alien as my cell phone is to Socrates. Most people will still have a little bit of doubt in their heads, so reveal the quadrillion data points ya got. Give stellar maps that show galaxies and planets that are too far away for the light to have reached us yet. Do all the other things these answers say. Before you leave for the past, study all kinds of stuff; biology, robotics, computing, chemistry. Make sure you can answer any question a scientist can throw at you.

Answer 41

If your time traveller wants to prove they came from the future, you don't send a man you send a woman instead. Because she will be wearing clothes of her own future time. But just to be sure, she carries an extra set of her underwear. Why an extra set of her underwear? you chime. The answer's quite simple. No garments change as much as women's underwear.

Think how much difference there is in the styles, construction, and materials of underwear between now and, say, sixty years ago. Any woman in 1950 being shown a set of contemporary undergarments would immediately recognise how much better they were and wouldn't take much convincing they came from the future.

Using underwear as your future person litmus test doesn't lead to any problems with reverse engineering or likely causality violations. Also it's simple and readily portable.

Since a picture is worth a thousand words then picture this and for good measure this too.

Answer 42

Get the largest prime number found from the future.

Now 2^74,207,281 − 1 is the largest prime number. If he is from future it will be larger than this number.

So he can prove he is from future.