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Reference this thread for more on the putative time machine.

So my intrepid time travelers set out in their DC-3 in late September 1962, not really knowing where they are going or how to get back. Their first jump, where they badly overshoot their mark (this was supposed to be just a test), lands them in 1519. Using astronomical observations they recognize and compensate for their error, next emerging in 1885 (all of these jumps are within ~100 mile radius of Perth, Australia) where they land well clear of civilization, flag down a train headed into town, and find a current newspaper which lets them calibrate their position in time more precisely. They next land in 1929, again covertly...the lead scientist wants to tell his twelve-year-old self how to travel through time and hopefully save some trouble for the next go-round. But, as they are headed home, their jury-rigged stabilizing field generator burns out and they are dropped into the night sky above Perth in July of 1944...and [spoiler] in this timeline, Japan did invade Australia and is pushing south trying to split the country. The front lines are well away from Perth but the RAAF is extremely paranoid about strange aircraft.

Fortunately, the protagonists (who both served in the RAAF during the War) recognize this. One remembers a base a short flight away where he was stationed briefly which might be a bit lower-key. He doesn't know the current recognition codes but lands at the base using "radio failure" procedures. The welcoming committee, fortunately for them, is led by an old chum who recognizes him. Upon being told that they're using the DC-3 to deliver a secret research device the chum obliges them with petrol, paraffin (kerosene, for their APU...they don't explain why they need it, just that they need it), and a surplus 25 Hz synchronous motor which can be adapted to replace their burned-out alternator and give them more fine control of their travel through the time continuum. They return successfully to late September 1962, arriving four hours after they disappeared.

With that as the setup, here is the question: Given those stops and the location in the vicinity of Perth, what object or objects could the protagonists bring back with them to demonstrate successful time travel into the past to all but the most hardened skeptics?

[spoiler] For those skeptics, traveler #1's next move will be a solo jump to November 1st to bring back next month's racing form...only to find upon his arrival there that the USA and USSR have nuked themselves into oblivion....

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    $\begingroup$ Looks like your world is built and you're asking about the actions of characters within your world. Such questions are not about worldbuilding and aren't permitted on this site. $\endgroup$
    – sphennings
    Sep 11, 2022 at 4:20
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    $\begingroup$ I like the frame and setup of your question, however I would recommend rephrasing your question to be less plot-specific and more world-specific to fit this SE. Eg. what could Earth's time travelers that go back to the past between the 1900s- and 1950s be able to bring back to verify the existence of time-travel? $\endgroup$
    – Enthu5ed
    Sep 11, 2022 at 23:23
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    $\begingroup$ I know this is nitpicking, but in 1885 it would be difficult to find anywhere within 100km of Perth to land a DC3, let alone enough space to get back off the ground. I believe around that time the only train line running into Perth itself was the Eastern line out of Guilford, so you'd want to have your characters aim somewhere around there, but it's hilly and densely forested at this time. Can you factor in a smaller aircraft like a Fokker Universal etc that's more of a "bush plane"? $\endgroup$ Sep 12, 2022 at 2:26
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    $\begingroup$ @AaronLavers, I don't consider it nitpicking. One of my objectives is to find possible prototype locations. I was looking at an area about 3-4 miles east of Gwambygine. It's fields now, but I don't know how much the land was resculpted by settlement. For an airliner the DC-3 had good 'bush' capability; my Dad flew one in Korea. As far as settler memories, one of my assumptions is that minor and singular disruptions in the timeline are quickly forgotten by those not directly and personally involved. BTW, for my purposes they don't have to make it to Perth...just to a newsstand. $\endgroup$
    – ehbowen
    Sep 12, 2022 at 3:47
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    $\begingroup$ There's very little that they could bring back which couldn't be dismissed as fakery at some level. Even an extinct animal like the Tazmanian Tiger could be dismissed as them merely having discovered a living specimen. Short of bringing back a trilobite or a T-rex there aren't a lot of options. To really prove it, go back and leave something anachronistic. $\endgroup$
    – Perkins
    Sep 12, 2022 at 18:21

14 Answers 14

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  1. What about taking a telescope and movie and still cameras?

Photographs of the night sky should show what latitude they are in. Photographs of the positions of various prominent constellations, the southern cross, the Magellanic clouds, and the Milky Way would establish roughly what time of day and/or season of year it is.

If the Moon is visible photographs of its phase and what stars appear near it will be helpful.

Photographs showing the positions in the sky of all visible planets will be useful. Photographs of the more visible moons of Jupiter and Saturn would be very useful compared to other astronomical images. It is possible to find the universal time by the positions of the moons of Jupiter. I believe that the Cassini compared the time from the positions of the Jovian moons with the local time to find the longitudes of many places in France for their great 18th Century map.

So film of the positions of as many solar system planets and moons as possible will be very helpful in establishing their date. I think that the positions of as few as ten solar system objects will be unique, never to be repeated in the entire history of the solar system.

  1. Getting a sample of air would be a good idea, since the air in 1519 would be free of radioactive fallout from atomic tests. The nuclear test ban treaty banned atmospheric tests was signed only 11 months after September 1962, and it was discussed a lot in the previous years.

Biochemist and science fiction writer Isaac Asimov pointed out the dangers of radioactive fallout in milk. Nobel prize winning Chemist Dr. Linus Pauling became one of the main advocates of ending atmospheric nuclear testing.

Pauling also supported the work of the St. Louis Citizen's Committee for Nuclear Information (CNI).[98] This group, headed by Barry Commoner, Eric Reiss, M. W. Friedlander and John Fowler, organized a longitudinal study to measure radioactive strontium-90 in the baby teeth of children across North America. The "Baby Tooth Survey," published by Louise Reiss, demonstrated conclusively in 1961 that above-ground nuclear testing posed significant public health risks in the form of radioactive fallout spread primarily via milk from cows that had ingested contaminated grass.[102][103][104] The Committee for Nuclear Information is frequently credited for its significant contribution to supporting the test ban,[105] as is the ground-breaking research conducted by Reiss and the "Baby Tooth Survey".[106]

[https://en.wikipedia.org/wiki/Linus_Pauling#Nuclear_activism][1]

It seems to me that it would have been impossible for scientists in September 1962 to be unaware that 1962 air had more radioactive fallout than pre 1945 air, and so taking air samples would be very obvious to them.

And of course the farther back in time they went, the less air pollution would be in their air samples.

  1. Water samples taken from a specific place in the past could be compared with water samples taken in the same place in 1962, which should show differences in pollution.
  2. If there is a specific famous tree at a specific place in Perth that might be old enough to be alive and recognizable in the past, they could bury a message with a small piece of modern technology like a watch in a time capsule in a specific location relative to the tree, planning to have scientists unearth it after they return to 1962.
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    $\begingroup$ The telescope and camera is an excellent suggestion. I was leaning towards having him take observations of Uranus to determine his chronological location (as he's at a known physical location), and it would be only natural to snap shots of the observations to take back. I think I'll outfit him with a 10" Cassegranian Astrola (philharrington.net/cave3.jpg) as well as a Navy Mark V aircraft sextant and a Contax 35mm camera with the proper telescope adapters. Thanks! $\endgroup$
    – ehbowen
    Sep 11, 2022 at 18:40
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    $\begingroup$ So you got some clean air and clean water did you? I think we could make some of that now, with a filter! Haw haw! We're time travelers too! And that watch you had us dug up from the old tree - buried it last week, did you? Haw! <snort> Your pictures from the planetarium are also very nice. $\endgroup$
    – Willk
    Sep 11, 2022 at 22:58
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    $\begingroup$ @Willk I believe a qualified astronomer could readily distinguish an astrophotograph taken through a 10" reflector at high magnification from a fake crafted in the best planetarium in the world 60 years ago, especially if he had access to the original negative. $\endgroup$
    – ehbowen
    Sep 11, 2022 at 23:50
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    $\begingroup$ Charles Stross has a variant on the radioactive fallout idea in one of his Merchant Princes novels, in the form of a plant; while filtering out pollution is easy, the ratio of isotopes would be much more expensive to fake $\endgroup$ Sep 12, 2022 at 6:40
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    $\begingroup$ For flavour: write a note saying "this air sample was taken by time travellers in 1885", put it inside a glass bottle and seal it up. That way you can prove it isn't merely an old sample. $\endgroup$
    – N. Virgo
    Sep 12, 2022 at 8:00
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Bring back An Extinct Animal With You

Just bring back an extinct animal back with you, animal species go extinct all the time, so just bring back some animal that is extinct in the present. Australia has confirmed at least 13 animal species that have gone extinct since European Colonization of the continent, and Europeans discovered Australia in 1606, your time travelers will at one point be almost a hundred years earlier than that when the only people present on Australia were the aboriginals. But most of the 13 animals went extinct between the 1850s and 1950s, which is where the time-travelers spend the majority of their time, so they don't have to collect the animal in the 1519 jump.

An Example of An Animal:

I looked at Wikipedia's list of extinct Australian animals, and one animal stuck out from the rest: The Paradise Parrot! some say it was the most beautiful bird in the world. It was fairly common in its area, and extraordinarily colorful, even by parrot standards, it was around 30 cm tall(so it could probably fit in time machine.) Its nests were in hallowed-out termite mounds, commonly at ground level, and was fairly easy to catch. It started to decline in population after the 1880s(so it should still be fairly common in 1885, and especially 1519), the last live specimen was sighted in 1927, so it would be known to be extinct in 1962. It seems to fit the bill! However, The Paradise Parrot has a big fatal flaw, it is native to eastern Australia. Which is on the other side of Australia from Perth, which is in Western Australia. Maybe you could handwave that it somehow was brought over to Perth from people. It could also be a problem keeping it alive, as its diet is limited(According to Google it ate grass seeds)

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    $\begingroup$ Heh. I've just got this mental picture of two guys trying to herd a moa into the time machine. And they wind up with a female, followed by an aggressive and protective male. That could be an entire chapter of a book. $\endgroup$
    – BillOnne
    Sep 11, 2022 at 19:39
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    $\begingroup$ @ehbowen The animal doesn't have to be collected in the 1519 jump, most of the 13 animals went extinct between the 1850s and 1950s, which is the time period the time travelers spend most of their time in. Being in 1519 just gives them the greatest chance of finding those extinct animals since there are no Europeans rapidly lowering their numbers. $\endgroup$
    – KaffeeByte
    Sep 11, 2022 at 19:41
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    $\begingroup$ perhaps there is even a twist - the animals they bring back are the last of their kind, and thus they are the cause for the "temporary" extinction. $\endgroup$
    – IronEagle
    Sep 11, 2022 at 21:58
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    $\begingroup$ @KaffeeByte won't work in the main body of my story, but I can write it in as, upon their return from 1962 after that first trip, they say between themselves, "What might convince them? I know! Let's jump back two hundred years and bring back a Paradise Parrot!" But that trip never actually happens; they have higher priorities after they find that the secret has leaked out to malevolent forces. $\endgroup$
    – ehbowen
    Sep 12, 2022 at 20:06
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    $\begingroup$ Another possibility that will require less "handwavium" that the Paradise Parrot is the Long Tailed Hopping Mouse. Their territory included Western Australia, although whether that include 100 miles radius of Perth is not clear, They could be captured, since a number were taken into captivity, and they were plenty small enough to fit within the space constraints of the enhanced DC-3 in use. And it went extinct sometime in the very early 20th Century, so they for sure around in 1519, and also 1885. $\endgroup$
    – dgnuff
    Sep 12, 2022 at 22:34
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Missing child rescued.

The child went missing in 1929 and was presumed to have been murdered. In fact the child was abducted and would have died where she was abandoned in the bush but the time travelers intervene and rescue her. They bring her to a hospital in 1944 where her injuries are treated and she lives.

It has only been 15 years since she disappeared. Her family is all still alive. The public remembers because it was in all the papers. And the girl remembers her family. She tells her story.

They believe it is time travel because she has not aged at all. She is still 10.

For a fiction this is as dramatic and heroic a time travel exploit as one could hope to have. Also, in 1962 the rescued girl will be 28, done with her studies, and a fine addition to the time travel team as depicted in the movie.

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    $\begingroup$ Oh, this might allow for a fine Bootstrap paradox! A 28 year old time traveler saving her younger self in 1929... $\endgroup$
    – Nzall
    Sep 12, 2022 at 12:24
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    $\begingroup$ For a fiction this is as dramatic and heroic a time travel exploit as one could hope to have. - In reality, the time traveler will be tossed in jail. $\endgroup$ Sep 12, 2022 at 18:44
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    $\begingroup$ @Mindwin Perhaps in today's hyper-litigious world, but I would expect that to be much less likely 60 years ago. I would also think they'd only go to jail if someone pressed charges, and I assume the rescued girl would testify on behalf of the people who rescued her and gave her an extinct animal as a pet. (This is Australia, so the animal will invariably be some kind of awful lizard, but kids love weird pets that have been dead for hundreds of years.) $\endgroup$
    – Tom
    Sep 12, 2022 at 19:24
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    $\begingroup$ Interesting idea. But this would have to be a whole plot line in itself. How do the time travellers find the kidnapped child? How do they rescue her? Presumably the police tried and failed. Do the time travellers have some knowledge from the future that enables them to succeed? $\endgroup$
    – Jay
    Sep 14, 2022 at 3:31
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    $\begingroup$ @Jay - she is not part of the plan. They need to totally stumble into her as they are charged up and on their way - no turning back. If they could collect her at their leisure they should bring her back to her parents in her own time. They scoop her up as they are leaving because they are good people. Her proving the time travel was totally unintentional - they were counting on their air and water collection and photographs of the night sky. $\endgroup$
    – Willk
    Sep 14, 2022 at 13:27
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Evidence of the Present, Left in the Past:

This can be a bit specific to whom they are trying to prove things to. So the actual details are up to you.

Write a letter while in the past and leave it with someone who will pass it on, OR in a place that is unimpeachable. Without a chain of custody on the message, it can be challenged or questioned. But if it is a hand-written note in a first edition original of a book in a library (where the book is secured and not available to the public), then even the existence of the note will likely be historically documented (and possibly documented everyone who ever looked at the work as well).

Similarly, leave a message that can be authenticated today in the past. For example, if a coded message is published in a newspaper before the code existed (like a message in a military code that can only be decoded with a machine or a computer) then the very existence of the message is a matter of public record.

How anyone would make the message, or know to bring it with them, is another matter.

You can leave something modern and organic in the past. What is up to you. Radio carbon dating was invented in 1946. A Tommy gun buried in 1519 might be faked, but how did the handle and powder get to be 400 years old?

And if the old chum is the one who they are trying to convince, then perhaps he has a burned out alternator in his basement that is stamped “made in the USA 1956.”

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    $\begingroup$ I didn't think of that last. That's an excellent suggestion! $\endgroup$
    – ehbowen
    Sep 11, 2022 at 18:50
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    $\begingroup$ Radio carbon dating does not work properly on things that were alive after the fossil fuel industry started. This is because the C14 content of fossil fuels is effectively zero. So the ratio of C12 to C14 in modern organisms is drastically different to what it was in pre-industrial eras. It is even worse for organisms that lived in a location close to some large source of fossil fuel produced CO2 such as a coal-fired factory, a roadway, a city that burns a lot of nat-gas, etc. The indicated date will be more than 20 thousand years before present. $\endgroup$
    – BillOnne
    Sep 11, 2022 at 19:29
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    $\begingroup$ @BillOnne Agreed. Depending on the example, uranium–thorium or ionium–thorium dating may be more useful. $\endgroup$
    – J.G.
    Sep 11, 2022 at 21:48
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    $\begingroup$ @BillOnne It's not even perfect in the pre-industrial eras since the level of volcanic activity in the world also throws off the ratio in unpredictable ways. It works best when you have samples of a precisely-known age to compare to. $\endgroup$
    – Perkins
    Sep 12, 2022 at 18:29
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    $\begingroup$ A coded message that can only be decoded with a computer and which is distinctive enough to survive and be discussed by historians... You mean, something like, say, the Voynich Manuscript? :-D $\endgroup$
    – Perkins
    Sep 12, 2022 at 18:30
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This was the theme of a Black Adder episode: Black Adder Back and Forth

Black Adder bet his friends that he could go to the past and return with a variety of items as specified by his friends. He had a large variety of things prepared in a closet, chosen on the basis of knowing his friends. He had a fake time machine set up in his basement and planned to sneak into the closet and return with the various items and win the bet.

Oddly, Baldrick had produced an actual time machine from Davinci's drawings. And they then had many adventures retrieving the specified items. Returning to the basement they find that his interference with the past had affected the present in a disagreeable fashion. So the return to the past and arrange that Black Adder was the King and married to an absolute smashing lady.

Now, being King may not be the goal of every young school boy. But there is a lesson here. If you can make minor changes to the past then you can tweak things so that the outcomme is as you would wish. Money, fame, power, all are available to the person who can make minor changes in the past.

So, the thing one would bring back from the past would be enormous wealth and power.

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    $\begingroup$ There is a very good empirical argument against time travel: you would think some tourist would be unable to resist taking selfies during the crucifixion, or the assassination of Caesar, and this seemingly odd behaviour would have made its way into the Gospels, or historical accounts. $\endgroup$ Sep 11, 2022 at 21:51
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    $\begingroup$ @SimonCrase, in my model each new "timeline" overlays the original. So there could be one billion separate timelines, each with one or two travelers, at the Bethlehem stable with each traveler ignorant of the others. They all meet Mary and Joseph, but to M&J they're all just a blur and quickly forgotten. Unless, that is, something 'special' happens to reinforce the new thread and make it the main track. $\endgroup$
    – ehbowen
    Sep 11, 2022 at 23:43
  • $\begingroup$ Or trading on the stock market... where behaviour is monitored very closely indeed these days. Which doesn't rule out Dr Who or a couple of other scenarios, but it does rule out a lot $\endgroup$ Sep 12, 2022 at 6:46
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    $\begingroup$ I don't see how being rich and powerful proves you time-travelled. If Elon Musk declared he was from the future most people would think he went off the rails. $\endgroup$
    – Aubreal
    Sep 12, 2022 at 17:07
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    $\begingroup$ @SimonCrase or caused the crucifixion itself: Story where every attendant of the passion of Jesus Christ turns out to be a time traveller? $\endgroup$
    – Ángel
    Sep 12, 2022 at 22:14
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Nothing

You have the time machine. Time-travel with the skeptics. It is the smoking gun that proves time travel.

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Edited

A fresh slice of a tree, for dendrochronology.

The sample should be obviously fresh. It should demonstrate it has been cut down recently from a growing tree. A small branch with not-yet-dried leafs would be a good proof.

Of course the sample should contain the final year ring, to reference the cut year. A sample from the trunk center will not satisfy, because we wouldn't know how much year rings have been left outside. Also the sample should contain enough year rings (20 would be enough?).

The tree should be endemic for the region (in this case - Northern Australia). Tree species that are ubiquitous for many regions can be useless. Year ring signatures can differ for different regions for the same epoch, because of climate differences etc. But for endemic tree the region can be determined without doubt.

The only my concern here - was dendrocronology developed enough in 1962? At least for modern time it would be good sample to proof you have traveled to the past.

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    $\begingroup$ Comparing the bark with its origin tree is the only way of proving time-travel, the bark alone can't do much, this is what I understand. But how do you prove the bark comes from this tree and not another between hundreds, if not thousands? $\endgroup$ Sep 12, 2022 at 14:18
  • $\begingroup$ @Tortliena - ok maybe bark is not necessary. I've edited yhe answer $\endgroup$
    – Heopps
    Sep 13, 2022 at 7:28
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What if, instead of bringing something back, they mailed a letter to a trusted friend that reads "Do not open until instructed." The letter, which is sealed and has a postmark of 1944 (or whatever), reads "Atomic bombs dropped on Hiroshima and Nagasaki, 1945. Russians launch Sputnik, 1957. Yankees defeat Reds in 1961 World Series," etc.

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    $\begingroup$ Won't work for my purposes. I'm postulating that the structure of time is formed by repetition, as events cycle through billions upon billions of times until they achieve stability. A time jump is a one-off which upsets that stability until a new one coalesces. Which might have the Yankees defeating Pittsburgh in Game 7 of 1960... $\endgroup$
    – ehbowen
    Sep 12, 2022 at 22:46
  • $\begingroup$ @ehbowen Big, big problem: You have a time machine that can alter the past before it's creation. The only stable state is one in which time travel is never invented. If time travel is easy (as it appears to be in your world) that state is only reached when there are no inventors--no intelligences to have a story about. $\endgroup$ Sep 14, 2022 at 1:47
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Any high profile, handwriten document or piece of art.

For example, if you went to the year 1600, bring back the Mona Lisa. We know it was painted circa 1506, and radiocarbon dating would easily prove your version is 100 year old when it should be 500.

A meticulous comparison of your Mona Lisa and the one in the Louvre would show they do match perfectly, which is technically impossible.

Just replace the Mona Lisa with whatever high profile piece of art your character can bring back from 1885 Perth.

Of course, actual time travel is so improbable that it will always be more rational to believe in some sort of forgery, up to somehow altering the results of carbon dating. But you will have to somewhat handwave this objection, whatever your character brings back from his trip.

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    $\begingroup$ If the Mona Lisa disappeared in 1600, would anyone know about it today? $\endgroup$ Sep 13, 2022 at 15:25
  • $\begingroup$ @user253751 just return it when you're done $\endgroup$ Sep 13, 2022 at 19:36
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    $\begingroup$ @RotemShalev i mean, that's only basic civility (^_^) $\endgroup$
    – armand
    Sep 13, 2022 at 22:36
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People. Ask your friend for volunteers. He probably can't spare able-bodied soldiers nor would most people be willing to go, but maybe someone who has no family and recently acquired severe disability through a war injury is hanging out in camp waiting for extraction.

People identical to some well-recorded person but 18 years younger would be hard to explain away, even if the 1962 version vanishes as the younger one leaves.

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Time travel is a very implausible claim. Whatever evidence for it you present, it will only be "proof" if all other more plausible explanations can be eliminated; and time travel is so implausible, that there will be many alternative explanations for whatever evidence you present which are more plausible than time travel. "More plausible than time travel" is a very low bar to clear.

You have a photograph, or video, of the night sky with all the stars where they should be 100 years ago? Unconvincing, it must be a fake, even if it is very accurate and there is no evidence the film has been manipulated in any way; at best you have proved that photography was invented much earlier than previously thought. A missing item that was stolen 200 years ago? Well, it had to be somewhere, perhaps one of your ancestors was the thief and your family kept it hidden until now. An extinct animal? Evidently, that species is not really extinct. A letter postmarked 1944 predicting major world events? Even if the postmark can be established as unimpeachably genuine, you might have sent 20,000 such letters to yourself and thrown out all of the ones whose predictions didn't come to pass.

Of course any of the above will get you some believers, to a greater or lesser extent, because many people are credulous and want to believe. But these things will not convince skeptics; they are not proof beyond reasonable doubt. You could bring back a human being and do a DNA test to show that this exact person died before I was born, and I would sooner believe the DNA test is inaccurate or the people who performed the test are stooges. To be honest, even if you took me on a trip in your time machine, I would only be convinced that you have the resources to put on a very elaborate and immersive historical reenactment with a huge set and a large cast of actors. Implausible, but not as implausible as time travel.

Personally, if you wanted to bring something from the past to convince me that time travel is real, you would have to bring me from the past. An hour or two of conversation should be sufficient to establish that the person I'm talking to really is (was?) me; but I don't think there is any other artefact which I could identify with enough confidence to really be convinced.

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Heopps has half an answer. Likewise, M.A. Goldring has half an answer.

Bring back a fresh chunk of tree from both of your earlier hops, as big as you can handle.

However, it's not just the ring sizes that you're interested in, but the detailed composition. The C-14 ratio for the two samples will be substantially different. The 1885 chunk will also show shifting ratios, neither will show the same ratio as 1962 and neither will show nuclear weapons isotopes.

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  • $\begingroup$ I was going to suggest some air, based on the nuclear testing impacts. $\endgroup$ Sep 14, 2022 at 4:13
  • $\begingroup$ @RossMillikan That would be an awful lot easier to fake than the tree. $\endgroup$ Sep 14, 2022 at 18:24
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That depends a lot on how skeptical the people are that you are trying to convince.

You claim you took these pictures of the night sky in 1885? I think you just created some fake pictures. The best photographic experts say they can't see any evidence that they're fake? That just proves that you did a very good job of making the fakes.

You show us an animal that went extinct decades or centuries ago? Huh, I guess it didn't really go extinct after all. There must have been some small colony of survivors somewhere. The theory that a few examples of this creature survived in some isolated place is a lot more plausible than your time machine story.

You produce this person who claims to be from 1885? Obviously they're just acting out a role. They are an accomplice who is in on the scam in one way or another. Anyone can SAY "I am from 1885." Again, which theory is more plausible: That you paid someone to claim to be from 1885? Or that you invented a time machine?

Etc.

Of course other people might be easily convinced. Showing a newspaper with an 1885 date on it might convince some, and the idea that you had a fake newspaper printed would never occur to them.

I saw a "documentary" once about ghost hunters. They introduced various members of the team. They described one as "the skeptic", and he says how it will take solid evidence to convince him that ghosts are real. Then at the end he hears a strange noise in the haunted house that he can't explain and he announces that he is convinced. I laughed and laughed. Either he was a fake from day one, the script said he was supposed to call himself a skeptic and then end up being convinced by the lamest evidence, or if this program was at all real, he was extremely gullible.

On the other hand, I've had plenty of conversations where I present someone with what I consider a pile of evidence on some controversial subject, they have no rebuttal to any of it, but at the end they declare they are unconvinced.

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You could probably just take an ice sample from antarctica from the past, then compare with one from the present. Its uhh... not close to perth, but ill let you figure out how the characters get down there.

When a layer of ice forms in antarctica, it traps some air in it. As layers continue to build, it continues trapping air. What you end up with is layers of ice with air from different time periods trapped in there. You can dig up a rod of this ice, and then measure the different layers and what the air trapped in different layers is like to gain info on the climate of the time this air got trapped in.

Think of it like newspapers. If you put down an old newspaper, and then continue putting newer newspapers on top of it, eventually you could drill out a section of newspaper, and see the change in the newspapers over time from this sample.

So if you get an ice sample from... lets say 100 years ago, and its a sample that measures lets say 100 years of climate, bring it back to the present, you could get a second ice sample that measures the past 200 years, and we would see that the bottom half of that sample is identical to the ice sample you brought back. We have to get a larger sample in the present because more ice has formed, we have put more newspapers on the stack, so the stack is thicker, but it would be really hard to fake something like trapping air in ice.

Of course, someone can say "Well they just took two ice samples and broke off the present half of one". It would likely be obvious that one of the samples has been broken somewhere though. And if you preserve the top layer of ice on the past sample, we could probably see that that top layer is fresh, something that would be impossible if the sample was found in the present.

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