456

Stop one ship from either sailing into a storm or (later) being taken over by pirates. In 1793, Thomas Jefferson ordered a set of instruments from France that would let the US calibrate to SI units, but the ship hit a storm at sea, blowing his ship into the Caribbean. There it was attacked by pirates (British privateers). The materials never arrived. By the ...


421

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.


250

In all probability, we, 21st century barbarians, will not be very well loved by our 23rd century descendants. Non-historians of that age will probably group us together with the generations of the late 20th century, and refer to us collectively in their high-school level history courses. We are the generations who baked the earth and poisoned the seas. ...


205

Rubber No seriously a cheap waterproof rain slicker or pair of rubber boots will bribe the average person very easily, waterproof materials were nonexistent. It is also really easy to demonstrate and you can buy them at a dollar store. The best they had at the time were merely water resistant materials which tended to stain since they were soaked in oil. ...


179

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'...


167

In the film Primer, there was a time travel machine that could only jump as far back as when it was first turned on. This puts a practical limit to how far back you can jump to the point where time travel was invented in the first place.


166

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 ...


130

Go back to the cold war era and start a "Russians are trying to warm the planet" scare. You will need a lot of money to fund some big advertising campaigns. You also want to seed a few specific technologies like nuclear and solar power to try and push them along. Let ignorance and paranoia work towards the betterment of mankind for a change. It's ...


129

There's an old fashioned option You can't travel back in time to a point before the invention of the first time machine. That means of course that the first person to invent a time machine couldn't travel back in time to point before his own invention, and possibly initially thought it didn't work, which is true for a given value of true.


122

Because the earth orbits the sun at 30km a second, the solar system is moving at 20km a second and the galaxy is moving at 230km a second! Any time travel will result in the people being dumped out into the void of space... Maybe we need to set up some beacons to guide people to the earth through time and we can only set these up now...


117

If they are just bringing the drives, and not the attached computer, this is pretty much impossible. The infrastructure simple isn't there in 1300 to refine anything to the necessary purities to even begin manufacturing microprocessors. See this answer to get an idea of how hard this is to do: How long would it take to create a Windows 1.0 capable machine ...


116

There are a few options: Aluminum. Until modern times, it was essentially impossible to produce in any significant quantity, making it far, far, far more valuable than gold. It is also a useful metal in its own right, being strong and light. And it should break down within 500 years, so it won't leave any archeological evidence in the modern day. Price: ...


112

It's a lot more complicated than it sounds. Not just for the fact that the language changed considerably over time, but because it is highly dependent on in which circles you commune. The higher the educational background, the less trouble someone from 'modern day educated London' would have understanding early modern English (what we know as 'Shakespearean ...


108

A previous time machine crashed and exploded on August 12th 1941 during a test flight. Maybe sabotage or a design fault. The explosion and shockwave will exist forever at that point in time. The explosion acts like a reverse black hole. The closer you get to the point of time of the explosion, the more power you need to bypass the shockwave emanating from ...


104

Zippers! Zippers have not yet been invented. Do keep that in mind. If there are any obvious zippers, this will be a source of wonderment. People were a lot more sharp eyed than you think back then, so they aren't going to miss that. Hoodies come in many different styles--some have zippers in the front, some are pullovers. The ones on pants might not be ...


104

Knowledge. Bringing wealth to the past requires simply knowledge. You have the outcome of horse races, lotteries, inventions, share prices, stock market falls etc etc etc. Your head could easily hold enough information to make you rich beyond your wildest dreams if you can go back in time........


103

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 ...


102

If you can deploy a good quality, wide-angle telescope and take photos of the night sky over a period of more than a few days, you can determine the time down to seconds over a wide range of history. It would probably be good in the range of a million years pastward or futureward. The technique would be, first, to get a basic orientation by finding ...


98

Yes, 100% Yes Just because the stranger doesn't know how to build it or how it was manufactured doesn't mean that you can't reverse engineer it. With 10 devices, you even have some spares so you can perform destructive testing on all 10 of them if it gets you enough data to make a replica. This is even more important since it performs the actions of your ...


89

As far as I can determine, the closest we have to hard data on this (which is not that close) would be first contact with people who have been isolated for a long time and have not developed or used technology themselves. This page lists six relatively recent incidents: 6 Isolated Groups Who Had No Idea That Civilization Existed (cracked.com, 17 aug 2012) ...


85

The biggest advantage I see being given here is simply processing power. You have a machine that can run calculations at a speed that would beggar imagination for someone living in that era. In relation to the Artillery mentioned in another answer. Generally, an artillerist would consult his range tables to determine how to aim his cannon...rather than ...


85

If you have European blood in you, are aged between 19 and 45 and are physically fit, the chances of you being brought down by the plague would be very little. Read this Scientific American article for details. Also this livescience article states that the pandemic altered the genes of European people. The Europeans who survived the plague developed ...


83

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 ...


83

If you travel in the recent past (say, not before 1930): a shortwave radio. Listen for news bulletins. Works everywhere. Time to determine what year you are in: one or two hours, depending on what broadcasts you receive. If you travel the just a little bit less recent past: a longwave radio. May or may not work; for example, it may not work in the middle of ...


82

Spice Trader First they pick up lots of spices at their local Mall-Wart. Then they carry them back in time to when they were fantastically valuable. Profit! Traders come from faraway countries and don't speak Latin very well. They have exotic looks and don't even know how to tie a proper toga! And they have some weird religion that means they do odd ...


79

No automatic weapons, without industrialization You need machines to make modern firearms. You can't hand-rifle a barrel. And while a hand-operated barrel-rifling machine can be made, this is not the best. Et al. for every other thing. Something like 90 machines were needed for the Enfield (iirc). Plus you need good materials. Springs? You don't ...


79

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 ...


79

Radioactive isotope dating. Each of us born in the late 20th (second half) or early 21st Century have in us a small portion of the calcium in our bones replaced by an Isotope of Strontium 90 that is a by-product of above-ground Nuclear testing, common in the early 1960s. See reference here. As with all radioisotopes, there is a very predictable rate of ...


77

I don't think the premise of the question holds water. It seems to assume that pathogens have a single scalar "deadliness" score (like hit points in a game) which is higher for modern germs, such that we only survive because our drugs are correspondingly more potent. But that's not how it works. Suppose a time traveler brings a population of penicillin-...


77

Here's another option that is often forgotten: Time travel might need an exit system available at the destination. Since we don't have an exit system in our time, time travellers cannot visit us. For example, time travel might be done through a wormhole whose two ends are shifted in time relative to each other, so if you enter one opening, you come back ...


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