How to prove you're a time traveller from the (far) past

(Almost like this post but not quite the same - I've seen multiple how to prove you're from the far future but not one how to prove you're from the far past so figured it could be fun to think of a way)

Do I have a story for you. You're not going to believe me but if you play along you will make history (or future or... time travel gives me an headache).

You see I was born in the late 14th century, just another child of just another farmer. I had a normal average life for the time until one day I was out working the field when something just popped up in front of me out of nowhere. I didn't know what it was at the time so when a man came out of the machine I assumed he was god. I was wrong of course, turns out that man is (was?) my future son. He showed me a picture on what he called a "cellphone" of me (maybe a couple of years older then how I am now) holding a baby and said he was that baby and that I was his father in the year 21118.

I learned a lot about future tech (and even brought some of it back like this laptop I'm using to write to you) and how to use it from him. He also taught me how to use his time machine (still no clue how it works, I just know how to use it).

Another thing he said is that I will have to travel to the year 2018 and stay here to do something before traveling to 21118. He said that what I will do in 2018 will be proof in 21118 that I am a time traveler from the 14th century.

Now my question what is that something I have to do in 2018 to prove after I travel to 21118 I'm a time traveler from the past?

Keep in mind that:

• The time machine only has fuel for one more jump.
• I have some things I brought from the past (few coins, knife, clothes and such).
• People won't believe me if I just claim it, I need a proof that can hold up to scientific scrutiny.
• With its fuel empty the time machine will look like a toy. No one will ever believe it to be a real time machine & if I can't use the remaining fuel in 2018 to prove it really is a time machine or I won't have enough to reach 21118
• My son stayed in the past, calling it "stable time loop timey whimey ball".
• No idea who my other descendants are.
• I learned English & Pig Latin from my son (apparently Pig Latin will soon become the most common language spoken).
• (If you can't think of a way without it) I also found this box on the time machine my son left to me, no idea what's in it but it has a note saying it will help.
• Apparently me proving I'm from the past is what leads to the creation of time travel technology in the far future.
• If scientists get really interested, they can run a battery of tests on you, such as isotopic and chemical compounds (like DDT) concentrations, which should yield some normally inexplicable results. The real question can be - how to get those scientists really interested? Few coins may not be enough. – Alexander Feb 13 '18 at 0:59
• Let me be completely frank. No one would fail to believe you're from the past. You would be so ignorant, so awkward, so dependent on a completely obsolete version of your language, that you would be immediately comitted to an asylum where you would be believed by everyone you met (and never released). Your only hope of avoiding this fate would be an I.Q. that makes Einstein and Hawking appear to be stunned holsteins - but then nobody would believe you without letting them take the time machine apart. – JBH Feb 13 '18 at 2:49
• @JBH - well, time travel is a crazy idea; perhaps it gets invented in the asylum? – Tim B II Feb 13 '18 at 3:09
• So proving you're a 14th Century time traveller in 2018 isn't enough - you have to prove it in 21118? That's going to be really hard - their technology can probably fake anything. – Tektotherriggen Feb 13 '18 at 9:24
• The nature of time travel demands that it is created at all times simultaneously – pojo-guy Feb 13 '18 at 12:54

By 21118, I would expect manufacturing technology to be so advanced that they could fake any physical evidence you could provide. Instead, I suggest you first convince us, in 2018, using tree rings and isotope evidence. You will become so famous that you are mentioned in millions of different books and records - so many, that in 21118 they will be actively waiting for you.

Combine Tree Rings, Carbon-Dating and Radioactive Isotopes

In your own time, cut down a tree. If you can get one that's more than about 73 years old, that's ideal (see below). Oak is apparently best (assuming you're in Europe). Cut out a section of trunk (i.e. a complete "wheel"), as thick as you can possibly fit in the time machine. Scientists will analyse the hell out of this, and will probably destroy a lot of material in the process.

When you get to 2018, visit a university with a strong archaeology or mediaeval history department. Ask them, acting all innocent, if they could possibly help you work out how old this tree was. When they compare the rings against their records, they will realise, with high confidence, that the tree must have lived in the 14th Century. But you could just have carefully cleaned an antique stump. The real proof comes by taking samples and analysing the isotopes.

Carbon dating shows how long ago something died - because your tree took a short cut, they will see that it only died recently. But a sufficiently resourced fraudster could have grown the tree in a giant warehouse, with artificial lighting and heating to mimic old weather patterns. This would recreate the historic ring pattern in a recent tree.

Your clincher is the low levels of radioactive elements that were created in nuclear weapons explosions. These have contaminated (at low but detectable levels) the whole world since the 50s and 60s, and they would be extremely expensive to filter out of the hypothetical fake tree nursery. If your tree is old enough, a sceptic would have to explain why you paid for expensive isotopic filtering before you could have known about nuclear weapons.

Now you can tell your real story, and they have a high chance of believing you.

Your own body will feature the same low radioisotope levels as the tree stump. However, as soon as you start breathing, drinking and eating in the modern world, you will start to collect modern contamination levels. If you can immediately find a surgeon willing to sample and analyse your tissues, especially teeth, this will be good evidence. But I doubt many doctors are both ethically flexible and trustworthy enough for this to succeed.

Convincing 21118

Now that 2018 believes you, it's time to become famous. Accept every offer of academic conferences talks, co-authored history books and talk show appearances. Write your memoirs - if you can't write, make a deal with a publisher to hire you a secretary. If your English is too archaic for the mass market, work closely with a ghost writer. Money is no object - a book written by a genuine authenticated time traveller will sell millions.

Have yourself 3D scanned, and get accurate statues made in granite and stainless steel. Spread copies all over the world - in public museums and protected vaults. Have big chunks of your DNA inscribed on vellum, and your fingerprints etched into titanium and launched into geostationary orbit.

When it's time to leave, launch your time machine as a publicised event in front of a huge live audience. Have it recorded in every fashion - HD video, analogue film, monitoring by every scientific instrument available. Remove all doubt.

Most importantly, every single time, state the date and place of your arrival in the future, as precisely as your time machine can manage. The aim is to get yourself mentioned so many times that unless civilisation collapses completely, some record of you reaches 21118 independently of yourself. Ideally, they are waiting to meet you.

This works even if people in the future don't believe the old accounts. People will turn up at the time and place as an excuse for a party, expecting to have a great laugh at the expense of primitive 2018 people who actually believed in time travel! The very fact of materialising in front of their eyes and cameras will be all the proof you need.*

If They Are Not Waiting...

...you will need additional evidence. Back in 2018, you need to have written a long message, and encrypted it. The encryption key must be very long, to prevent brute-force searches (remember, they have ~20000 years to crack it, with much better algorithms and hardware than we have today). The text must be even longer (otherwise a fraudster could choose a fake decryption key to create any plausible message).

Perhaps it's the uncensored version of your memoirs. Perhaps it's an epic poem you write for a loved one you left in the past. When you encrypt it, do so repeatedly, with every algorithm your colleagues can track down, especially those that are thought to be quantum-safe. You don't care about public key, or "proper" digital signatures (you don't care about repudiation). Remember, it doesn't matter if it takes months of processing time to encrypt the message - you can spend as long as you like in the 21st Century before venturing on. Store your message in as many physical libraries, digital archives, vaults and satellites as you can. The people of 21118 must be convinced that you cannot possibly have corrupted so many copies in recent times, even with their technology. Hopefully, when you arrive carrying the decryption key, the idea that you are a time-traveller is more likely than your being a fraudster.

*Maybe you worry that the "welcoming" committee will immediately gun you down and steal the time machine. No need to panic - you know you will survive to have at least one child in the future. Just don't donate to any sperm or egg banks...

Bring an almost-extinct species with you.
you can take an almost-extinct animal with you when you travel to 21118. Since we are currently undergoing another mass extinction, in 19 100 years, the species will probably be already extinct. The extinct species would prove that you are from past.

• Who knows, maybe by kidnapping that near extinct animal you might cause a butterfly effect that results in said species going extinct thus helping to prove your story. However, how is your 14th century farmer going to know what animals are endangered let alone steal one? – Anketam Feb 13 '18 at 2:59
• @Anketam "I learned a lot about future tech (and even brought some of it back like this laptop I'm using to write to you) and how to use it from him. " – IEW Feb 13 '18 at 3:03

Carbon Dating and DNA

DNA mutates, and DNA is in anything from bacteria to viruses. You need to get the DNA of everything tested for age. Chances are, you have flu traces. After you get scientists to agree that this is old, then get everything carbon dated. When your clothes are five days old, but they have traces of the flu on them, chances are you are a time traveler. (This is assuming they don't have the flu in 21118, but any disease would work).

• No traces of nuclear tests in your teeth, bones, etc. – o.m. Feb 13 '18 at 6:12
• Carbon dating won't work because it measures how much time has passed. If you jump forward in time, none of it will pass. Also, it only works with non-living matter. en.wikipedia.org/wiki/Radiocarbon_dating#Principles – Real Subtle Feb 13 '18 at 10:40
• @RealSubtle that’s why. When Carbon-14 says your only 30 years old, but the DNA on your clothes from old things says differently, you can prove yourself to be a time traveler. – gsquaredxc Feb 13 '18 at 13:33
• @GrantGarrison carbon dating a living person would give you an age of 0. The DNA thing is sound, though. Provided the kind of viruses they find in him can be proven to be extinct in the future. – Real Subtle Feb 14 '18 at 7:37
• @RealSubtle oh. I missed the non-living part of your original comment. I will try to think of a workaround for that. – gsquaredxc Feb 14 '18 at 16:35

Nothing at all

When he arrives in 21118, technology would have kept marching on. Personal identity on the Internet in 2018 is becoming increasingly common. It is not hard to extrapolate that by 21118 everyone would have some form of online identity. His lack of existence on any social media platform would be unheard of. His genetic records would not properly match any heritage system that tracks ancestry. He would have no birth certificate and so any attempts to reconcile that would fail.

Also, there are experiments with embedding chips in people, which could serve as a form of unique identification. By 21118 it would not be unreasonable for these to be standard and he would be lacking one. As such his lack of existence in 21118 would quickly make him stand out as an irregularity which law enforcement would likely pick up on and investigate. The investigation along with his testimony would quickly come to only one conclusion that he is not from this time period. Once it got to the news, it likely would go viral.

Stable Time Loop

To further cement this, his son mentioned it is a stable time loop, therefore no matter what he does or does not do that was/will be exactly what he needed/needs to do to keep the time loop stable. So I am taking the simpler and easier option by doing nothing, since that will be/was the correct decision to make.

• This is a GREAT answer, but it does assume that the Second Coming, the zombie apocalypse, WW-III, and First Contact didn't completely upset the system. Indeed, our intrepid traveller might arrive only to find Morlocks. – JBH Feb 13 '18 at 2:58
• @JBH That did occur to me, but the last point in the question states that his arrival will lead to the creation of time travel technology. As such I am assuming that the civilization he arrives in will be capable of inventing time travel technology and not be overrun by Morlocks. – Anketam Feb 13 '18 at 3:03
• While I agree completely with JBH, it also assumes a constant technical and social trajectory. All it would take is a cultural shift like the Butlerian Jihad out of the Dune books and there would be no facebook, implanted chips or other digital integration. Even if this didn't happen, there's still just as likely to be a neo-luddite movement that's probably morphed into a terrorist organisation. Not having any of these integrations could well just get him shot where he stands. – Tim B II Feb 13 '18 at 3:05
• That said, @Anketam, it's still a good answer. :) – Tim B II Feb 13 '18 at 3:07

Hide stuff. A lot of stuff. Preferably things that stand the test of time and are obvious relics of the age that you want to claim to come from. Hide them all over the place. You need to be able to pin point the location of several items that has not been previously found by someone else.

If you want to prove time travel, hide one or more things your son gave you (such as the cellphone or laptop) in a container that is clearly manufactured in your year of origin, along with other artifacts, and hide them in a place your son tells you has not been excavated. Then once you have the interest of scientists or the media. Excavate it publicly together with reliable witnesses.

Edit: I just realized one more thing you might want to do while you're hiding your phone under the foundation stone of a church or something. Take pictures with it. Of you, of the town where you live, of things that definitely will change until modern day, of anything you can imagine that would be hard to fake and may create an interest in your story come our time.

You'll probably still be called a fraud, but at least it's worth a shot.

1) You don't want just one tree slice. Make many. Bring as many as you can with you, hide the others. Bring one/hide one/bring one etc. While you could have grown a tree in an isotopically filtered environment, how did you make the different slices (that will match up when placed together) have different ages?

2) A good hiding place would be Antarctica, somewhere not too far from the south pole. Unless the whole place has melted by then they'll be buried in the ice--and you can date ice layers like you can date tree rings.

Mark all hidden packages "Property of name, traveling through time from 2018 to 21118. Please leave in situ or store until then." Even if a package is found that might get it into a museum somewhere.

And a separate idea:

3) Publish an interesting story. Part of the story deals with an encrypted message--and the message is in the book. The characters never manage to actually decrypt it. You have the decryption key, the message says who you are. Put your book out there on the pirate sites, also, so it ends up in the libraries of those who collect lots of books--hopefully it will persist in such collections over the ages.

• I love the idea of an coded message in a story! I had already thought of encryption (I updated my answer with those ideas), but that's a nice little twist. – Tektotherriggen Feb 13 '18 at 20:10
• The hard part is ensuring that a story gets preserved over that length of time. Most people these days haven't read the original Brother's Grimm fairy tails, let alone Chaucer. You'll have to become at least as famous as Plato or Aristotle to have a chance. – Perkins Jun 4 '18 at 23:28
• @Perkins You miss my strategy. I'm thinking of large collections of e-books on pirate sites. Get it into some of those. It's unlikely anyone is going to filter stories out of such a collection unless they are corrupted, it will only grow with time. Over on The Pirate Bay I find collections > 100gb. – Loren Pechtel Jun 5 '18 at 2:41
• @LorenPechtel that might work if nothing happens to the computer systems. If something does (which over the course of 19,100 years it very well might) then only stories people consider to be worth preserving will survive. The other problem is going to be that anything can be decrypted to anything via proper choice of key and algorithm, so they'll have to be able to recognize the algorithms used and not have broken them or it'll look like a fraud anyway. Public-key cryptography might do it for you though. – Perkins Jun 5 '18 at 18:53
• @Perkins And why do you think there wouldn't be automated format conversions if old file formats grow out of date? Consider the program Calibre, an e-book reader and cataloger. One of it's options is to bulk convert files to another format. – Loren Pechtel Jun 5 '18 at 20:40

Strangely enough, this is actually a perfect use case for biometrics.

Normally, biometrics (when you strip away the hype) have 2 functions that they perform very, very well:

1) Access Management
Most security authentication solutions use a combination of 1 or more of the 3 fundamentals of proving you are who you say you are - Something you have (a key), Something you know (a password), and Something you are (biometrics).

2) Preventing Multiple Registrations
If you're on a system already with a biometric signature, you shouldn't be able to re-register on that system again. That means you can't create 50 aliases and use them for nefarious purposes. They can't stop you registering the first time as Peter Clarke if your real name is Harold Garvey, but they CAN make sure you're not registered again under an identical biometric signature.

There's only one problem; modern biometric signatures work on a DET curve (Detection Error Tradeoff). This means that the computer works out the probability that the recorded signature matches you and then makes a decision. This is why in court cases you hear statements like 'only 1 person in 3 million could have the same fingerprint as the defendant'; it doesn't make you guilty, but the fingerprint AND the fact that you were caught running away with a bloody knife in your hand probably does.

As an aside, iris scanning is the most effective form of biometric signature; lowest DET curve (less false positives), tears in the iris are random meaning identical twins don't even have the same iris scan and the data block required for the signature is so small it could be put on a high res scanning code. But, I digress.

So; your time traveler simply has to apply for a job with an agency that REALLY cares about its security. Get a fingerprint record, DNA, iris scan, voice scan, facial recognition shot; whatever (and as many as) you can. The reason why you want MORE than one is that it allows for triangulation; it's possible in 20k years that you might have identical DNA to someone who lived in 2018, but not identical DNA, fingerprints AND iris scan.

Ensure you pick a company for which the records are going to be kept, and you're all good. Also, get your son to give you the lotto picks for the the next 10 weeks running in 2018. Statistically, the chances of picking 10 lotto number sets IN A ROW borders on the impossible. That way, even if they don't believe you, at least you'll live in comfort in 2018.

• Why would an agency even want to hire a person who only has skills of a 14th century farmer? He also needs to prove to people in 21118 that he is from the past, as such why would any group keep biometric records of people who died over 19,000 years ago? – Anketam Feb 13 '18 at 2:42
• It could be just as easy for him to go to a clearing house for biometric signatures; just tell them that he's been sent for processing by a company he's being employed by. Agreed that keeping records for 19k years is unlikely, but so is time travel. The point was that the thing he can do is store biometric signatures that get preserved, and he can prove he was in 2018. HOW that happens at this stage is hypothetical and I suspect that every answer to this will involve something being preserved for 19k years. – Tim B II Feb 13 '18 at 2:46

Have them test your mtDNA (mitochondrial DNA) and Y-DNA (note that everyone has mtDNA from their mom but only biological men have Y-DNA, from their dad, though in this example, the subject is male). Your halpogroups (named branch) will not exist in the future time period because of occasional mutations in every generation.

One study of Y-DNA found 4 mutations in 13 generations.

Not sure how many alleles they tested but my guess is 450 (the best commercially available test today is called "Big-Y"). But the current Y-DNA matching tests are done with only 37-111 alleles to determine halpogroup, so new halpogroups are slower than that. Though with 25 million (positioned) basepairs on a Y chromosome, the future's ability to test DNA will be vastly superior to ours.
https://isogg.org/wiki/Portal:Y-chromosome_DNA

MtDNA mutates more slowly than Y-DNA does (only 16.5K basepairs to work with). But you will still see new halpogroups every few hundred years.

With 20,000 years in the future, the DNA databases will be enormous (with 20K years worth of data!) and they'll do whole genome testing easily (heck, we can do whole genome today). Plus there's all this extra stuff in our DNA that currently gets dismissed as "junk" but which I'm sure will turn out to be extremely valuable and trackable.

In case anyone is wondering, yes, even with today's technology, you will have no trouble telling which of two samples is the super old and which is the modern day. At least not when testing mtDNA and Y-DNA.

Have children in 2018

Then, in 21118, the combination of genealogy records and DNA testing ought to be good enough to establish you're a distant ancestor, and exactly how distant, and then back it up with genealogy records.

This ought to be good enough to prove you are who you say you are. (Caveat: in the twenty-second century, cloning and genetic engineering might make it possible to fake this evidence.)

Paternity testing

We now have DNA tests that can tell you not just that you're related to an individual, but also determine exactly how. They aren't perfect, but they don't analyze the whole genome. Well, thousands of years into the future, they'll probably be able to analyze the whole genome with relative ease.

See, when a child is conceived, half the genes from you get mixed with half the genes from your partner, along with a small but more or less constant rate of mutations. This process is repeated with each subsequent generation. Scientists today can use this as a molecular clock to guesstimate timeframes for when various species diverged.

In short, a simple blood test (especially by 21118 standards) should be able to establish that a given descendant of yours really is related to you. Which brings me to...

Genealogy

If you hire a genealogist today, they can trace your ancestry back pretty far. It eventually hits a dead end and can't go back farther because records gets spottier and spottier the further you go back.

Eventually, it hits a dead end. That's either 'records before this were stored (say) in a church which burned to the ground in 1747" or you reach the point where the idea of keeping such records hadn't yet reached the region in question.

But going from today into the far future, well, that's different. All those records will be computerized. If you have any living descendants, they should be easy to find for purposes of doing this test.