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Questions tagged [time-travel]

For questions relating to travel in time. Such travel often involves FTL travel; consider also using the [tag:faster-than-light] tag.

272
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42answers
50k views

How do you prove you're from the future?

Let's say a time traveler from the year 2100 comes back to the year 2015. He has a very important message: [horrible thing] is about to happen soon, and he wants to warn us so we can avoid/prevent it....
207
votes
14answers
29k views

Is there a single historic event which could be changed to cause the USA to use SI units?

I am time traveller with aim to make world better. Last time I went to the past, all I heard was: "Kill Hitler!" So I went to the past and I must tell you, April 1945 was pretty loud in Berlin! ...
140
votes
39answers
45k views

If time travel is possible in the future, no matter how distant, why haven't they come back to tell us?

In a world where time travel is possible, but has not been invented yet, would travelers from the future come back to prove it exists? Surely, they would bring that technology back in time to let the ...
122
votes
33answers
23k views

What cheap modern items can I use to bribe medieval people? [closed]

Inspired by this question about a time traveller. So, I've travelled to the medieval age. Think 12th / 13th century Europe. Unlike the time traveller in the other question, I did bring batteries for ...
108
votes
8answers
28k views

How far back in time would English be understandable to a modern speaker?

As we all know, language in England has changed massively over the centuries. How far back would someone be able to travel in time and still have a basic understanding of what most people are saying?...
98
votes
13answers
21k views

If I went back in time, how could I handle being among the Black Death and survive?

In the near future time I invent time travel. But when perfecting it, something goes wrong and I'm transported back to the time and place of the Black Death. I wasn't prepared for this, and try as I ...
92
votes
26answers
14k views

Would relatively primitive people really confuse technology with magic?

It's common for people to say that if a time traveler or an alien displayed advanced technology to ancient or medieval people, that they'd assume it was magic, and either worship him as a god or burn ...
87
votes
31answers
16k views

My time machine needs to know when it is

I've built a time machine and it works in unmanned testing... sorta. I tell it to go into the past, it disappears, and then comes back to the present. The problem is that it isn't terribly accurate. I ...
73
votes
12answers
21k views

How would people in 17th century Salem react to modern day clothing

So I and two others are working on a time machine, and I accidentally press a wrong button and whoosh, all my friends and I are in 17th century Salem, Massachusetts. Nobody sees us appearing out of ...
64
votes
19answers
15k views

What modern technology would be most revolutionary to ancient Greeks?

In Mark Twain's "A Connecticut Yankee in King Arthur's Court" a nineteenth century character finds himself in medieval England and shortly manages to build all the "modern" inventions: from steam ...
62
votes
13answers
12k views

I travel back in time: how could I know when I landed?

Today a weird guy with a pointy hat offered me and my friends to play a game: We will all travel back in time, to a random date somewhen from the antiquity to modern times. We will have a limited ...
60
votes
14answers
12k views

How to find out a year I'm in?

Let's assume I can travel in a space-time on Earth. Every time I jump I get to almost the same place, but in different past time relative to the first jump: it solves the problem of planet rotation, ...
59
votes
21answers
7k views

Prehistoric messages to the future

I'm one of the test subjects for a new device, capable of sending an individual back to any point in history. I've been told that - due to certain problems with the process - I'll arrive naked, and so ...
57
votes
14answers
15k views

What would be the impact of a modern programmer and laptop being dropped into World War II, possibly breaking Enigma?

I've always found the idea of intelligent every-man sent back in time using his knowledge of the future tech to realistically impact the past. The first time something like this came to my mind was ...
51
votes
46answers
18k views

Plausible reason why my time machine can only go back a certain amount of time?

So, I have built a Time-Traveling machine. It’s a prototype, and I’ve noticed a few kinks in the machine. If the control pad gets jammed in home mode, the universe will repeat the same day for all ...
51
votes
22answers
13k views

How would you bring wealth back to the past?

Edit: A few people have argued that this question is off-topic, and as I write this it looks like it will be closed soon. However, I have written a new (and hopefully better) version of the question ...
49
votes
21answers
7k views

A small group recreating modern technology

Suppose a group of people get transported back in time (say 2500 years). Then, in a manner reminiscent of A Connecticut Yankee in King Arthur's Court, they try to re-design modern technology. Assume ...
49
votes
8answers
5k views

Stopping time, by speeding it up inside a bubble

Imagine I have a device that can stop time for the person who holds it (similar to Bernard's Watch). This device works in a very specific way - it creates a bubble around the user (just large enough ...
48
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9answers
5k views

Are there any ways to allow some form of FTL travel without allowing time travel?

Faster than light travel is a really cool thing to have in sci-fi settings. It allows humans, in relatable time scales, to travel the galaxy and see a variety of worlds. It allows for conflicts ...
48
votes
10answers
14k views

How could we time travel backwards without killing everyone with germs from the future?

Consider a world in which time travel has been made viable possibility. Initially, many are ecstatic at the new technology and the knowledge it will unlock. However, biologists and other scientists ...
46
votes
11answers
10k views

Could medieval people produce automatic firearms if they had access to the schematics?

Assume you traveled back in time to the middle ages, and you brought with you the schematics of a fully automatic firearm. Could a group of experienced smiths and jewelers reproduce it? What would the ...
44
votes
6answers
6k views

How Could A Time Traveller Communicate With Neanderthals?

Context: Your spaceship encountered a Grade III Anomaly (now you really wish you'd have read the darn safety manual to figure out what that would be -- too late now). Structural integrity of the ...
43
votes
27answers
13k views

How could a time traveler have prevented climate change

Let's say a Moon colonist in the future has discovered an alien time machine. A small remnant of humanity still exists on colony worlds in the solar system, but due to runaway climate change, they are ...
43
votes
16answers
8k views

Suitable jobs in Ancient Rome for time travelers

The people of Handwave-land have created time travel technology and are training people to send back to Ancient Rome and become part of the community without disturbing the future too much (to observe ...
43
votes
21answers
12k views

How much could a time traveler earn from selling 2016 tech having traveled back to 2000?

Joe, the average Worldbuilder accidentally slips through time sixteen years back. From September 11, 2016 to September 11, 2000. He gave saving the World Trade Center a thought, but then he decided to ...
42
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15answers
13k views

How does a time traveler prove he or she is from the near past?

Assume a college student from 2018 accidentally traveled to 2023. He is accidentally taken by an alien spaceship that travels close to the speed of light away from earth and then travels back. He is ...
42
votes
12answers
11k views

A person from medieval times comes into our time. What would he notice first?

A medieval person (say from around 1000 AD, and from a rural village) walks through the forest, and through some unspecified mechanism suddenly turns out to be in our time. He is still far away from ...
41
votes
28answers
10k views

Why buy tech from the future?

The Demonstration You're a rich, successful CEO/capitalist working in the electronics business. Your R&D division is exceptional and routinely fabs state of the art processors at bleeding edge ...
41
votes
11answers
10k views

Would time travelling to the present be lethal to a person from the 1200s?

John Smith is a time traveller from the year 2018, he goes back in time to the year 1200 and in the process falls in love with a woman of that era. He doesn't want to abandon her so he decides to ...
38
votes
29answers
7k views

How can I explain that a time travelling apparatus moves itself through time but appears in the same location?

For the purposes of this question, let's ignore the causality issues of time travel itself. Suppose our hero, or an accomplice of our hero, has invented a time travelling apparatus. It works like ...
38
votes
13answers
6k views

Keeping supplies for 1000 years

My main protagonist is going to fast-forward himself in time by 1000 years. He will simply reappear in the same place (marked by a small beacon), the process being instant for him (no hibernation etc)....
37
votes
11answers
6k views

Where could a person from the 14th century appear such that they would not notice modern technology for a week?

In this case, a person from a world similar to ours, at a time and technology roughly equivalent to our 14th century, but with magic. Through some odd spell, this person was teleported far away from ...
36
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9answers
2k views

Time-traveling Combat

Introduction This question is based on the time travel mechanic discussed in my previous question The Tricky Trouble with Two Time Travelers. I'll lay out the rules that I've decided on so far: ...
34
votes
7answers
7k views

How far can a time traveller go into the past before his electrical equipment becomes unchargeable?

My time traveller has a maybe 20-minutes-into-the-future smartphone and laptop. They can store large amounts of data, on the Petabytes level or higher. The time traveller can effectively store the ...
33
votes
18answers
7k views

Can time travel make us rich through trading, and is this a problem?

At different points in history, commodities have been at different levels of supply, and therefore have been at different prices. One good might be valuable in the present while another is nearly ...
32
votes
10answers
5k views

Which jobs could western geniuses, who lived between 1643-1900, have in the modern age related to their talents?

I'm trying to write a comedy where as a plot device I have: Some of the greatest western minds of human history, who lived between 1643 and 1900, are transported into the modern age. I still haven't ...
32
votes
19answers
4k views

Time travel coordinates

My problem is as follows: mr Average Joe has designed a device for time travel in his garage/basement at the moment he has sent the device forward in time (for testing purposes) a couple of times (...
31
votes
6answers
6k views

Could a modern times time traveler produce an antibiotic in medieval times?

Joe Everybody, a modern day man with average knowledge (high school and Wikipedia) in biology, medicine and chemistry, wakes up in an medieval city. He sees a lot of sick people and remembers about ...
30
votes
13answers
6k views

Everything Joe says is true. How can he most help humanity?

Please note: This is not a duplicate of my previous question, and in fact has a quite different premise. Joe is just an average guy, aside from one passive superpower that Joe has had since he was a ...
30
votes
13answers
3k views

With future knowledge, can I prevent the Columbian Exchange epidemics?

I have traveled back to the 15th century with the goal of facilitating the discovery of the Americas by the rest of the world without causing epidemics to wipe out 90% of the American population. How ...
30
votes
10answers
7k views

How do I manage memetic infection while time traveling?

Time travel works...just invented, by you. The tests prove it! After many conversations and significant planning, your epidemiologist significant other has approved your plans for time travel, ...
30
votes
11answers
3k views

How to identify or authorize members of a time travel organisation?

Many organizations today have identity cards, and use passwords and multi-factor authentication to authenticate and authorize people. If there's trouble, things can be done: Identity cards can be ...
29
votes
10answers
10k views

How far back in time would Maths be understandable to a modern mathematician?

Shamelessly inspired by this question (sorry), but I got this question after Michael gave a answer - my mathematician would essentially have to relearn maths, as mathematics in Ancient Greece is ...
29
votes
5answers
4k views

How could the Mafia retain its power in New York into the new century?

A mutant who sees multiple futures has predicted that the world will be invaded by aliens. Every future ends disastrously for the human race with us being wiped out. The only one in which we survive ...
29
votes
7answers
5k views

Is one year a realistic timescale to learn an ancient language if every language you knew didn't exist yet?

Say you've gone back in time Terminator-style (no possessions, no clothes, nothing but you and your cells) to roughly 6,000 BC to the ancient near east. You meet a farmer and his family who take you ...
28
votes
7answers
8k views

How far back in time can I go before people stop accepting my money from the future?

Lets say I go back in time with a wallet full of, say, 150 dollars worth of bills. How far can I be sent back before I reach a point where I'm unlikely to be able to use my money because it looks too ...
28
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5answers
2k views

How to test a time machine?

Eureka! I have a time machine in my garage and it works. I put an apple in it, close the door, set the timer, open the door to an empty machine, wait five minutes and the apple reappears. (Still ...
27
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14answers
5k views

Can a single time travelling person prevent the World Trade Center attacks? [closed]

You are a fellow Worldbuilder and while travelling by train, you fall asleep. Next time you wake up you realize you woke up at Grand Central train station. You quickly realize that you traveled not ...
26
votes
22answers
8k views

A solution for the time-travel paradox - What could go wrong?

Time travel has been invented and it goes like this. You travel backwards in time at the same speed you normally travel forward. Everything is identical - you do all the actions the same but in ...
25
votes
9answers
3k views

Temporal Ethics for bidirectional time-travel with branching time-lines

Before humanity develops actual bidirectional time-travel – assuming it’s possible at all – there will be years, probably decades or even centuries before that during which physics theories prove the ...