Questions tagged [time-travel]

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

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9 answers
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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 ...
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305 votes
42 answers
66k 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....
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50 votes
11 answers
14k 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 ...
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52 votes
21 answers
8k 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 ...
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38 votes
29 answers
8k 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 ...
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55 votes
22 answers
14k 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 ...
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21 votes
3 answers
2k views

Determining your universe's Time Travel Paradigm

How might the occupants of any given universe identify which (if any) of the many proposed Time Travel Paradigms govern their potential use of time travel? By "Time Travel Paradigms" I refer to the ...
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14 votes
6 answers
2k views

How to make the most wealth out of a single "Groundhogday Potion"?

Pennyless Joe, the broke archeologist, finds an old pawn shop selling something curious. A ceramic vial labeled "Groundhog Day Potion". It's a bargain for $1.99. (He buys it, because he is not quite ...
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13 votes
1 answer
2k views

How long can language drift before it becomes indecipherable, and how to minimize drift?

A general question here, relevant to many world-building scenarios. Language drifts, to the point that I likely could never understand old English, but I'm not sure how much. I want to know how long ...
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10 votes
5 answers
498 views

Is three-dimensional time consistent and paradox-free for time/dimension travelers?

This question was edited based on answers already submitted. I am designing a universe with both time travel and alternate realities, but I don't want the whole thing resting on hand-waving and ...
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105 votes
26 answers
19k 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 ...
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50 votes
8 answers
6k 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 ...
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34 votes
20 answers
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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 (...
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17 votes
4 answers
2k views

When could a microscope first be made?

Imagine you have someone sent back in time without warning. He is smart and has a good generalist grasp of science and technology, but is not a master of any particular field. He wants to use a ...
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48 votes
11 answers
19k 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 ...
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5 votes
7 answers
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How hard is it to build a generator if you've jumped to the distant past?

In this question: How far can a time traveller go into the past before his electrical equipment becomes unchargeable? @Mark assures us that "Building a generator can be done at any time:" (just wind ...
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7 votes
3 answers
3k views

Will this approach work for a time traveler to recreate penicillin?

This question is closely related to, but more specific, than the question/comment that inspired it: Could a modern times time traveler produce an antibiotic in medieval times?. Imagine a person is ...
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157 votes
41 answers
53k 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 ...
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94 votes
31 answers
17k 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 ...
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62 votes
14 answers
17k 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 ...
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55 votes
46 answers
20k 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 ...
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44 votes
16 answers
9k 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 ...
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23 votes
6 answers
1k views

30 year groundhogs day: how to increase the world's technology

The premise: Our protagonist was a intelligent, good natured, programmer who just tucked himself in bed at the end of celebrating his 35th birthday, only to wake up as a child on the day of his fifth ...
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25 votes
13 answers
13k views

Could a time traveler prevent the Black Plague?

Meet Todd the time traveler. He's a good boy and has decided to use his powers for good, more specifically he wants to stop the black plague from happening. His powers work in a similar fashion to the ...
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18 votes
5 answers
3k views

How do I manage disease risk while time traveling?

Time travel works...just invented, by you. The tests prove it! Now for the human tests. It works by poking the residual timey-wimey weebley-woobley stuff just enough for you to move yourself and ...
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  • 52.2k
35 votes
7 answers
8k 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 ...
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  • 933
36 votes
7 answers
8k 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 ...
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  • 465
11 votes
12 answers
2k views

Unscrupulous Time-Traveler: How to convince modern people you are a god

You are an dishonest time-traveler from the year 3100. You would like to travel back to our present day, and with your advanced technology, convince us that you are a god. You have unlimited energy, ...
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8 votes
5 answers
690 views

What happens at the interface between two universes with opposite thermodynamic arrows of time?

I saw this old closed question on Physics.SE and thought it would be perfect for here. The original author is long gone, so I thought I'll just have to post it myself. We can consider factors of plot ...
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6 votes
12 answers
1k views

Travel back in time and rise to power

In my story, the protagonist gets sucked almost a millennia into the past (unintentionally) and lands in medieval Europe. How does he take advantage of the situation and rise to power without getting ...
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115 votes
8 answers
51k 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?...
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104 votes
13 answers
25k 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 ...
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45 votes
13 answers
11k views

What does it actually mean to have two time dimensions?

The trivial answer is that it just means "you have two dimensions with inverted sign in your spacetime metric". But the perceptual result of that kind of choice doesn't actually look qualitatively ...
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73 votes
20 answers
17k 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 ...
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74 votes
12 answers
24k 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 ...
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40 votes
14 answers
8k 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 ...
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33 votes
18 answers
8k 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 ...
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32 votes
6 answers
4k views

At what point in European history could a government build a printing press given a basic description?

Say a time traveler ends up back in time and has earned the good graces of one of the nations' kings by sharing some of his future knowledge. Knowing that the printing press was an important ...
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  • 31.1k
16 votes
7 answers
3k views

The Tricky Trouble with Two Time Travelers

tl;dr: What adjustments to a "rewind" power allow multiple equally powerful characters? Background There are many different models of time travel. Personally I find it easiest to tell stories using ...
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30 votes
5 answers
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 ...
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18 votes
10 answers
3k views

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 ...
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  • 6,639
11 votes
3 answers
5k views

Will a modern time traveler survive diseases of the past?

Joe Schmo is your average college graduate who is suddenly transported back to medieval times, without time to prepare. From there the stories, and questions on this site, are all about how he can use ...
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8 votes
4 answers
4k views

Time traveler has identified a unknown epidemic is likely spread by mosquitos. How much can he help combat it?

In the world I'm envisioning, an individual has been accidently sent to a sort of alternate history version of the world, one that is at roughly feudal level of tech/culture, but with the nations ...
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6 votes
7 answers
2k views

Logically consistent time travel

What internally consistent time travel rules would make for an interesting world to model and explore in a game or a book? I exclude the "no free will" setup (where everyone is pre-destined to behave ...
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  • 161
15 votes
10 answers
1k views

How would a time traveller conquer the ancient world?

I have found myself approximately 2000 years in the past, I didn't bring anything with me. But since I am here, I want to conquer the world with my knowledge from the future. Or as much as is possible ...
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11 votes
7 answers
1k views

Defensive strategies against teleporting dragons

I have finally found an edition of the Dragonriders of Pern trilogy - living in Italy, I only had access to it thanks to my father's old books, and he doesn't own the complete series - so I have been ...
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  • 778
3 votes
4 answers
834 views

Would a time traveler to the Bronze Age need to worry about disease? [duplicate]

Inspired by this webcomic. I understand that going back in time has the potential to expose you to a number of diseases that you have no resistance to (e.g.: the Bubonic Plague, Polio, Smallpox, etc.)...
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  • 147
2 votes
2 answers
669 views

How far in the future would a modern human need to go before they were functionally a different species than people of the time?

A staple of fantasy involving time travel is the hero (or heroine) zipping off into the future and then meeting a future lover with whom they go on to have wacky time-based adventures before ...
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  • 45.6k
4 votes
9 answers
1k views

How to convince your past self that you are from the future with limited memories and resources?

Imagine you are a petite, high school girl named Brooklyn. You also happen to be a superhero, and your power is speed. You were on a mission to investigate a suspicious politician with your best ...
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  • 805
1 vote
3 answers
196 views

Using "time travel" to prove past events (e.g moon landings) occurred?

The light (images) from every event in the past are travelling through space at the speed of light as we speak. So.....I am going to build a powerful enough telescope and a spaceship capable of ...
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