# If you could travel to the year 1820, how could you prove you were from the future? **URL:** \ **Category:** In My Humble Opinion\ **Created:** [June 2, 2020, 4:03pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931 "2020-06-02T16:03:34Z")\ **Posts on this page:** 20\ **Page:** 5
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [June 3, 2020, 7:37pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/81 "2020-06-03T19:37:01Z")
> [@Velocity](#): > > If I may semi-hijack the thread a bit: > > If we want to be believed as time travelers in 1820, how would someone from 2220 convince us that he’s a time traveler in our current year? Because he could make predictions like **“Biden will best Trump in 2020 and win reelection in 2024, then Ocasio-Cortez becomes the nation’s first female president, and the first manned Mars landing finally happens in 2037 but it was China, not America, that got there”** …oh, and he is saying all this in some form of futuristic English that sounds horribly mangled to our ears, and we can only barely make out what he is saying. > > How would we believe that he’s actually from 2220 instead of a lunatic who makes educated sounding guesses about the future but still needs to be put in a padded cell? > > Then, how would we convince that 1820 crowd likewise… “And I can tell you about all kinds of great technology that will be invented in the next two hundred years. Well, I can’t tell you the details because I’m not an engineer. But I can tell you they exist. And then you can figure out how to actually build them. Like cold fusion. We have that. I know it has something to do with aluminum. Would I be able to tell you that if I wasn’t from the future?” ---
**Author:** ![XT](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/xt/32/456_2.png) [@XT](https://boards.straightdope.com/u/XT)\ **Post date:** [June 3, 2020, 7:58pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/82 "2020-06-03T19:58:14Z")
> [@Little\_Nemo](#): > > “And I can tell you about all kinds of great technology that will be invented in the next two hundred years. Well, I can’t tell you the details because I’m not an engineer. But I can tell you they exist. And then you can figure out how to actually build them. Like cold fusion. We have that. I know it has something to do with aluminum. Would I be able to tell you that if I wasn’t from the future?” Imagine the sci-fi or futurist books you could write though? You could be a very early Jules Verne, but even more spot on (assuming no butterfly effect that radically changes history in this alternative universe you would be going too)! I recall a movie (don’t remember the name) where a musician goes to an alternative universe where the Beatles never happened and then basically recreates their music and becomes famous (I didn’t watch the whole movie, so no idea how it turned out for him :p). This could be like that, assuming you had the resources and could live long enough to do it. Hell, I can probably recall a few dozen books I could write by plagiarizing future authors works at, oh, maybe 70-80%, just off the top of my head. I don’t know much about music, but musically inclined 'dopers could probably do something there as well, even though 1820 is hardly modern wrt music. Sure, you would only be famous as a futurist long after you are dead, but it could work wrt the OP. Once I strike it rich in various ways I can think of, I could spend my later years (hopefully) writing futurist type stuff, predictive historical stuff and maybe funding some of my own stable of scientists a la Edison to build tech I actually have a fairly solid idea of how it works…I do a lot of this stuff for fun now (like the steam engine part, rocketry, electronics and radio, etc), and I’m pretty confident I could do what I know even with 1820’s materials and tech. If I had lots of money anyway. 😛 I wouldn’t be trying to convince anyone I was from the future though. Just let them be in awe down the road of my mad imagination and predictive skillz. 😉 ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [June 3, 2020, 8:08pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/83 "2020-06-03T20:08:21Z")
> [@Little\_Nemo](#): > > “And I can tell you about all kinds of great technology that will be invented in the next two hundred years. Well, I can’t tell you the details because I’m not an engineer. But I can tell you they exist. And then you can figure out how to actually build them. Like cold fusion. We have that. I know it has something to do with aluminum. Would I be able to tell you that if I wasn’t from the future?” William Tenn had a story much like this called “Flirgleflip” And of course Poul Anderson had “The Man Who Came Early” ---
**Author:** ![iamthewalrus\_3](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@iamthewalrus\_3](https://boards.straightdope.com/u/iamthewalrus_3)\ **Post date:** [June 3, 2020, 9:19pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/84 "2020-06-03T21:19:13Z")
> [@Pantastic](#): > > People say stuff like this, but don’t ever provide details. What improvements on basic machines are you going to propose in 1820? You’re saying you don’t have to remember that much, so it should be something you can quickly point out. I’m not aware of any ‘trick’ improvements you could quickly apply to machinery at the time - most of the big advances weren’t of the ‘here’s an idea’ type, they involved things like improved machining and metallurgy that allowed you to make higher quality materials and better-fitting parts. I gave several examples in my previous post. I’m not saying that you waltz into a machine shop and magically improve it. I’m saying that knowledge of which machines exist and the basic principles they operate on gives you a _massive_ advantage in arriving there. > [@](#): > > This, like most schemes, only seems likely to work if you’ve already convinced people that you are not crazy and have access to special knowledge. I think that if I show up to enough engineers’ and scientists’ offices with a sketchbook of ideas I will eventually find someone to listen to me. And it will only take one, because the ideas are actually good and the science is actually solid. I’m aware that this bears a resemblance to the common misconception that an “idea” for an invention is valuable, compared to actual execution on it. The difference is that if you’re from the future, all your ideas are _actually_ good and you know they’ll work. Edison famously said that he tried 10,000 light bulb prototypes before finding the one that worked. How many would I have to try to get a working one if I start out already knowing the shape of a light bulb, the fact that the chamber has to be evacuated, and that the filament should be a thin strip of metal? It’s the same thing that drives catch-up economic growth in developing countries. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 3, 2020, 9:28pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/85 "2020-06-03T21:28:01Z")
> [@XT](#): > > Imagine the sci-fi or futurist books you could write though? You could be a very early Jules Verne, but even more spot on (assuming no butterfly effect that radically changes history in this alternative universe you would be going too)! I recall a movie (don’t remember the name) where a musician goes to an alternative universe where the Beatles never happened and then basically recreates their music and becomes famous (I didn’t watch the whole movie, so no idea how it turned out for him :p). This could be like that, assuming you had the resources and could live long enough to do it. > > Hell, I can probably recall a few dozen books I could write by plagiarizing future authors works at, oh, maybe 70-80%, just off the top of my head. I don’t know much about music, but musically inclined 'dopers could probably do something there as well, even though 1820 is hardly modern wrt music. The movie you’re thinking of was called Yesterday, directed by Danny Boyle and written by Richard Curtis. But I doubt you’d have success trying to plagiarize Jules Verne novels; most of would only remember the broad outlines of the plots and that’s not enough. ---
**Author:** ![thorny\_locust](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/thorny_locust/32/431_2.png) [@thorny\_locust](https://boards.straightdope.com/u/thorny_locust)\ **Post date:** [June 3, 2020, 9:38pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/86 "2020-06-03T21:38:19Z")
> [@PatrickLondon](#): > > It would depend on there being an outbreak of cholera somewhere, but it doesn’t take a great deal of specialist background knowledge to say to them “Map the cases in an area and check where they get their water from. Then block that supply - take the handle off the pump; and bring in water supplies from somewhere where there is no outbreak. The number of cases in the affected area will drop. If you don’t believe me, wait 30 years or so and see what happens in Soho.” > > Another example would be to look at infection rates in hospitals, and telling surgeons to wash down the operating theatre with carbolic acid and use a clean apron for every operation. Good luck convincing them. Look what happened to [Semmelweis](https://en.wikipedia.org/wiki/Ignaz_Semmelweis); and he was already a doctor, and knew how to function in the time and society. If you happen to be a historian specializing in the period, you might be able to make enough short-term predictions to convince people. If you’ve memorized the sequence of comets in the 19th century, and people are willing to wait around for some years to accumulate evidence, you might convince some people. But most likely you’re not going to convince anybody of anything other than that you are very very weird; which is likely to have some major disadvantages, but which you may not be able to help doing. ---
**Author:** ![Velocity](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/velocity/32/18006_2.png) [@Velocity](https://boards.straightdope.com/u/Velocity)\ **Post date:** [June 3, 2020, 9:49pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/87 "2020-06-03T21:49:04Z")
> [@Little\_Nemo](#): > > “And I can tell you about all kinds of great technology that will be invented in the next two hundred years. Well, I can’t tell you the details because I’m not an engineer. But I can tell you they exist. And then you can figure out how to actually build them. Like cold fusion. We have that. I know it has something to do with aluminum. Would I be able to tell you that if I wasn’t from the future?” Yep, straight to the padded cell you go. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [June 3, 2020, 10:46pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/88 "2020-06-03T22:46:09Z")
I think the hottest thing I would be capable of would be a refrigerator. I would not be able to actually make one myself, but in collaboration with a good tinkerer, I think we could get to the point of constructing a working ammonia absorption prototype that could be improved into a useful production design. If I could establish widespread simple refrigeration in 1820, it would be huge. My partner and I would become gazillionaires. ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [June 4, 2020, 12:07am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/89 "2020-06-04T00:07:58Z")
> [@iamthewalrus\_3](#): > > I’m aware that this bears a resemblance to the common misconception that an “idea” for an invention is valuable, compared to actual execution on it. The difference is that if you’re from the future, all your ideas are _actually_ good and you know they’ll work. Edison famously said that he tried 10,000 light bulb prototypes before finding the one that worked. How many would I have to try to get a working one if I start out already knowing the shape of a light bulb, the fact that the chamber has to be evacuated, and that the filament should be a thin strip of metal? By coincidence, I’m currently reading _Test of Greatness_ by Brian Cathcart. It’s about the British program to build an atom bomb. Obviously, they knew an atom bomb would work. They even had some people working in the British program who had worked in the American program. And they were deliberately duplicating the American implosion design as closely as possible. But the book describes how they would sometimes run into an obstacle where they would spend months duplicating work that they knew had already been done. ---
**Author:** ![DrForrester](https://avatars.discourse-cdn.com/v4/letter/d/8edcca/32.png) [@DrForrester](https://boards.straightdope.com/u/DrForrester)\ **Post date:** [June 4, 2020, 12:50am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/90 "2020-06-04T00:50:53Z")
The quote that popped into my head immediately is by Douglas Adams. In his book, the people from the past were properly prehistoric, not from 1820, but perhaps the sentiment is roughly the same. “The secret is to bang the rocks together, guys!” ---
**Author:** ![Pantastic](https://avatars.discourse-cdn.com/v4/letter/p/3bc359/32.png) [@Pantastic](https://boards.straightdope.com/u/Pantastic)\ **Post date:** [June 4, 2020, 1:04am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/91 "2020-06-04T01:04:43Z")
> [@iamthewalrus\_3](#): > > I gave several examples in my previous post. I’m not saying that you waltz into a machine shop and magically improve it. I’m saying that knowledge of which machines exist and the basic principles they operate on gives you a _massive_ advantage in arriving there. The only example in the previous post are something that you were able to easily describe in enough detail that it might be useful was vulcanization, which is a pretty good trick if you can actually manage to make it work with some sulfur, a stove, and some commercially available rubber. I don’t know that it’s actually that easy to vulcanize rubber just from that description, but that one might work. For the electric light, you’re flat out wrong. You are loosely describing something people already knew - an arc light using a piece of carbon was created in 1802, and the idea of putting it in a vacuum to stop it burning was pretty obvious. But the key detail you bring to the table is wrong - ‘a thin metal strip’ was not, in fact, what Edison used to make his bulb, he used a carbonized piece of bamboo - what you’d need to remember is a ‘a carbon filament’ rather than a ‘thin metal strip’. And making a vacuum good enough for Edison’s design just wasn’t going to happen with 1820s machinery. Other stuff you say you can make is all over the place - refrigerators already existed (they just hadn’t been made practical) so a vague idea for one doesn’t show much, I’m skeptical of your claim of creating a motion picture camera with 1820s photographic technology, and of creating a modern pedaled bike on the fly with only machinery of the 1820s to work with (the bicycle, powered by feet on the ground, was already two years old at this point). > [@](#): > > The difference is that if you’re from the future, all your ideas are _actually_ good and you know they’ll work. Edison famously said that he tried 10,000 light bulb prototypes before finding the one that worked. How many would I have to try to get a working one if I start out already knowing the shape of a light bulb, the fact that the chamber has to be evacuated, and that the filament should be a thin strip of metal? As you demonstrated, your ideas would not all be good, and at least some of them flatly won’t work while others were just repeating things that already existed. You’d have to try a lot more than 10,000 to get a working bulb, since you wouldn’t be able to evacuate the chamber well enough to copy Edison’s design for 40-50 years, and you’d be trying metal instead of the fiber of carbon that actually worked for him. So none of your specifics were actually correct, and the basic idea of running electricity through a lumb of carbon had already been demonstrated 20 years before, meaning that the basic idea of ‘electric light’ would not actually be novel. This isn’t just random nitpickery, the idea that you could just write down a bunch of vague ideas from stuff you sort of remember and impress people to the point that they’re certain you’re from the future and could make billions of dollars with you doesn’t stand up to scrutiny. ---
**Author:** ![kaylasdad99](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kaylasdad99/32/3398_2.png) [@kaylasdad99](https://boards.straightdope.com/u/kaylasdad99)\ **Post date:** [June 4, 2020, 1:52am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/92 "2020-06-04T01:52:32Z")
> [@Kent\_Clark](#): > > Fort me it’s simple. I wear glasses, no line bifocals to be exact. Take me to an 1820 glassmaker. He can tell immediately that my eyeglasses simply can’t be from that time. > > What’s that you say? I can’t wear glasses because I have to be stark naked? Screw it, I ain’t going. Probably best. Without your glasses everybody will know you’re Mansuper. ---
**Author:** ![needscoffee](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/needscoffee/32/1076_2.png) [@needscoffee](https://boards.straightdope.com/u/needscoffee)\ **Post date:** [June 4, 2020, 2:16am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/93 "2020-06-04T02:16:02Z")
> [@kaylasdad99](#): > > Probably best. Without your glasses everybody will know you’re Mansuper. Lol! ---
**Author:** ![susan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/susan/32/17537_2.png) [@susan](https://boards.straightdope.com/u/susan)\ **Post date:** [June 4, 2020, 3:15am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/94 "2020-06-04T03:15:17Z")
The formula for transparent aluminum. ---
**Author:** ![eschereal](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eschereal/32/18939_2.png) [@eschereal](https://boards.straightdope.com/u/eschereal)\ **Post date:** [June 4, 2020, 4:01am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/95 "2020-06-04T04:01:00Z")
> [@susan](#): > > The formula for transparent aluminum. that has [been around a very long time](https://en.wikipedia.org/wiki/Corundum) ---
**Author:** ![Little\_Nemo](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/little_nemo/32/3120_2.png) [@Little\_Nemo](https://boards.straightdope.com/u/Little_Nemo)\ **Post date:** [June 4, 2020, 4:44am UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/96 "2020-06-04T04:44:16Z")
There’s also the factor that your knowledge of the past might stop being accurate as you begin to use it. You arrive in 1820. You know there’s gold in California and you head west. You make sure to arrange things so you’ll collect a good share of the profits (the historic gold strike ended up leaving John Sutter poorer than he had been before). Let’s say you make your “discovery” in 1824. But what happens as a result of the gold strike starting twenty-five years early? One major factor is that California was still part of Mexico. And the United States was not in a position to conquer it in 1824. All that added wealth and the population that would follow might have made Mexico a much stronger power. No Texas independence or Mexican-American War. It might have been Mexico, not the United States, that ended up owning Oregon, Alaska, and Hawaii. And maybe Cuba, Puerto Rico, Panama, and the Philippines. With its western expansion closed off, a smaller United States would have reached its final size much earlier than it did historically. The tensions over slavery might have erupted earlier and the southern states might have succeeded in forming their own country. Your predictions in 1820 about events of the next fifty years would look very wrong. ---
**Author:** ![iamthewalrus\_3](https://avatars.discourse-cdn.com/v4/letter/i/258eb7/32.png) [@iamthewalrus\_3](https://boards.straightdope.com/u/iamthewalrus_3)\ **Post date:** [June 4, 2020, 4:01pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/97 "2020-06-04T16:01:04Z")
> [@Little\_Nemo](#): > > By coincidence, I’m currently reading _Test of Greatness_ by Brian Cathcart. It’s about the British program to build an atom bomb. > > Obviously, they knew an atom bomb would work. They even had some people working in the British program who had worked in the American program. And they were deliberately duplicating the American implosion design as closely as possible. But the book describes how they would sometimes run into an obstacle where they would spend months duplicating work that they knew had already been done. Right. Again, I’m not saying that knowledge of basic principles is sufficient. There’s plenty of engineering to do. But presumably the British program took less time and money than the Manhattan project. > [@Pantastic](#): > > The only example in the previous post are something that you were able to easily describe in enough detail that it might be useful was vulcanization I mean, that was off the top of my head in a few minutes. I don’t actually have hours or days to catalog all the things I know about science, engineering, and technology in the present day and set to work on how to implement it using 200-year-old technology. > [@](#): > > You’d have to try a lot more than 10,000 to get a working bulb, since you wouldn’t be able to evacuate the chamber well enough to copy Edison’s design for 40-50 years, and you’d be trying metal instead of the fiber of carbon that actually worked for him.So none of your specifics were actually correct, and the basic idea of running electricity through a lumb of carbon had already been demonstrated 20 years before, meaning that the basic idea of ‘electric light’ would not actually be novel. I contend that being wrong about some details does not invalidate the value of general knowledge. Edison was brilliant and dogged. All I have to be is dogged and not stupid. If you really think that I’d have to try _more_ designs than Edison you either think that knowledge of the future is an active impediment to progress (I can’t agree with you there) or you think my process would be _very_ bad. > [@](#): > > This isn’t just random nitpickery, the idea that you could just write down a bunch of vague ideas from stuff you sort of remember and impress people to the point that they’re certain you’re from the future and could make billions of dollars with you doesn’t stand up to scrutiny. I’m not saying I convince people with a notebook of vague ideas that I’m from the future. I’m saying I use my vague ideas to “invent” the future and use my success to prove prescience. Of course, I am misremembering that later models of incandescent bulbs used metal filaments. But that doesn’t doom me to failure. I don’t have to build the first light bulb exactly as Edison did for my general knowledge to still be helpful on the path. Perhaps we should turn it around. Imagine that someone from 200 years in our future with whatever the equivalent of a university education and a technical job in a field that doesn’t remotely exist yet comes back with no warning. Do you really think that they couldn’t tell you _anything_ that would be useful to advance engineering or science? Or, as I think you claimed above, holes in their knowledge would not only fail to progress, but would actually make progress _more difficult_? ---
**Author:** ![Pantastic](https://avatars.discourse-cdn.com/v4/letter/p/3bc359/32.png) [@Pantastic](https://boards.straightdope.com/u/Pantastic)\ **Post date:** [June 4, 2020, 4:01pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/98 "2020-06-04T16:01:39Z")
> [@Little\_Nemo](#): > > There’s also the factor that your knowledge of the past might stop being accurate as you begin to use it. Yes, and it doesn’t have to be as dramatic and direct as that - if you are able to ‘invent’ vulcanizing rubber 20 years early, there could be plenty of indirect follow-on effects to disrupt all of your ‘proving I’m from the future’ predictions. The new product on the market could shift what companies become profitable, and their money shifts who gets elected. New tech for tires and joints could greatly affect the pattern of westward expansion, new rubber seals could affect artillery for military purposes. ---
**Author:** ![Dewey\_Finn](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dewey_finn/32/4222_2.png) [@Dewey\_Finn](https://boards.straightdope.com/u/Dewey_Finn)\ **Post date:** [June 4, 2020, 4:09pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/99 "2020-06-04T16:09:35Z")
One thing; even if you were able to reproduce an Edison bulb, what good does that do you in 1820 without the electrical infrastructure to deliver power to it? ---
**Author:** ![Erusiel](https://avatars.discourse-cdn.com/v4/letter/e/6de8d8/32.png) [@Erusiel](https://boards.straightdope.com/u/Erusiel)\ **Post date:** [June 4, 2020, 4:25pm UTC](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931/100 "2020-06-04T16:25:07Z")
I might try predicting the existence of Neptune, which wouldn’t have been discovered until the 1840s. I don’t know off the top of my head where in the sky Neptune would’ve been in 1820, but I might be able to figure it out knowing a) that it was originally predicted as a gravitational influence affecting the motion of the seventh planet (probably still called “Herschel” in 1820), b) that Galileo saw it in the same field of view as Jupiter (but didn’t realize it), and c) that Neptune takes around 165 years to complete a trip around the Sun. Just need to pore over some historical observation data. I could chat up an astronomer or two and make some pre-discovery pronouncements like “the eighth planet is an average distance of 30.06 AU from the Sun, and it’s blue.” [Previous page](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931.md?page=4) [Next page](https://boards.straightdope.com/t/if-you-could-travel-to-the-year-1820-how-could-you-prove-you-were-from-the-future/854931.md?page=6)