Time Travel

Well there are some theories about time travel back in time. One idea involves wormholes, but then there's the problem of creating a wormhole and keeping it open and stable.

 

Wow I've never met anyone else who's heard of those games. Kain's time machine is a giant chamber though, so not really portable.

 

Primer is a fantastic film if you are wanting something heavily science based to work from - although the mechanism it describes wouldn't work for your scenario. You could however use it to give you an idea of how to handle keeping the concept believeable. It's pretty complicated though - the guy who wrote it is from an engineering/science background and he doesn't babysit the viewer.

 

C'mon, guys. Drive a Delorean at 55 miles per hour. Simple as that.

 

considering all the different theories out there, if you want to go with quantum mechanics, one book i can think of it Timeline by Michael Crichton, which goes over a different theory avoiding the grandfather paradox.

or if you want to try something a little more abstract, i would recommend First Among Sequels in the Thursday Next series by Jasper Fforde. There is a large conflict in this book about the consequences and a very interesting theory about what time really is.

also agree with Elgaisma, Sound of Thunder has a small amount in the end regarding how small things change the future.

 

The Novikov self-consistency principle means, in short, that every time you interfere with past events, you end up making them happen the way they happened all along.

E.g, you go back in time to try to stop the Kennedy assassination, but as you grab the assassin by the arm, you cause him to fire his shot too early. When you get back to your own time, you discover that nothing has changed in the history books - it was you who caused the assassin to fire his gun at precisely that moment and precisely that angle all along.

I don't think this necessarily conflicts with free will - it just requires the universe to conspire against the time-traveller to keep history consistent.

 

That is something I'll definitely consider. Going into my research and such, I knew I couldn't possibly deal with paradoxes. I have too many sub plots that cross hairs, and in the third book of the series travelers from the future enter the scene and attempt to challenge my protagonists, who are still 'stuck' in the past.

 

What about the first time the sequence of events happened, ever? There would be no future from which someone could travel back in time from.

Interesting theory, though

 

There wouldn't really be a different first time. The person traveling back to stop the assassination wouldn't realize that it was always he who actually caused it. Paradoxes become unavoidable.

 

Yes, but the person couldn't travel back when the Kennedy assassination happened at first.

Think of it as a movie. At the start, Kennedy's killed. Halfway through, James (random guy) time travels back and stops the murder. In all future viewings of the movie, James stops the murder.

But what about the first play through?

It's just my theory, sorry that I don't really understand this that much, I'm not too good at it, but stuff like this interests me

 

I agree, and that's where the paradox comes in. I think the idea behind the theory is that is was "always" the time traveler, but as you point out that causes problems.

It's like the story of the guy who goes back in time because he wants to prove Jesus was real, and instead he ends up fulfilling all of the key parts of Jesus' life (for example he cures a blind man; the time traveler is a psychologist and it turns out the man's blindness is psychological and not physical).

In that story, it is clear that it was always the time traveler and never really Jesus. But the paradox persists. No real way to avoid the paradoxes unless you resort to multiple time lines.

 

You could also say that it solves the paradox, if you don't think there's something inherently wrong with circular chains of events.

Think of it this way: The whole film exists at the same time. Someone has directed and edited it in a way that fills all the plot holes and makes it logical. You watch it in a certain order, but it's not created in a certain order. The ending may very well have been filmed first.

 

"You killed Ted, you medieval dickweed!!" Excellent!

Basically I agree with a lot of the other posts. The science will help you up to a point, just make sure you have a good idea where your "jumping off point" is where you go from the science to the fiction. Even the biggest hard science fiction geek will forgive your weird science if you give at least a passing nod/wink when you jump from the science bit to the fiction bit, and most of all as long as you are internally consistent.

In terms of the main science fiction themes I'd say go look at some of the classics. Heinlein wrote some good long/short stories where he really explored the main themes/paradoxes etc, and if you can stomach his sexism and strange Freudian issues he tells a pretty good story along the way.

 

I've read that one, and don't really like the mechanism used for time travel, nor the method used for "disassembly" and "reassembly" of the animals and people who are travelling. It's way too mechanistic (i.e. pretending the world is made out of building blocks that you only have to take apart and re-assemble), and that doesn't fit at all with quantum mechanics. I would say, from a scientific point of view, Timeline is pretty much debunked.

I understand you. What's more, I agree with you, and disagree with Novikov. Time travel can't work within the realms of the Novikov universe.

This is a very good example of the Novikov self-consistency principle, and exactly the reason why I believe it must be wrong (i.e. the whole world view of time travel, in which this principle must be true, is wrong). The first issue is - yes it does conflict with free will. Who says you have to grab the assassin by the arm? Now, I know you can just come up with a different scenario, but that's not the issue. You can easily construct a scenario where the Novikov self-consistency principle leads to the elimination of free will.

The next point is, this ignores the butterfly effect. If you were present - in any form whatsoever - at the Kennedy assassination, this could have an effect that is not immediately apparent. You are there, occupying space that wasn't occupied historically, breathing air that wasn't breathed, consuming food and drink that wasn't consumed. There will be an effect. The butterfly effect says that very small changes, such as the consumption of an extra hamburger long back in the past, can lead to great changes a long time later.

That is why I believe Novikov is wrong, and so is trying to create a universe where there is only one world and time travellers keep popping in and out along the whole timeline. Empirical evidence is with me here, since we have not yet observed any time travellers from the future. Though, admittedly, there might be more explanations for that than one.

In any case, I greatly prefer the multiple-universes theory.

But there is something wrong with circular events. Causality. Exactly what Patrick94 writes - it must have happened for the first time, otherwise it wouldn't have happened.

I guess this is precisely the world view of time travel that Novikov was looking at.

The biggest error with this view is, in my opinion, the assumption that if you travel back 100 years, and do something that wasn't done historically, you get an immediate effect 100 years later in your own time. How is that supposed to work? It doesn't, it can't, it has to be an incremental process (in my opinion).

Consequently, if somebody travels back 100 years, then at this moment, their old world has vanished, gone, and if they want to travel 100 years back to the future, they will land in a completely different world, with completely different people in it.

The whole "grandfather paradox" is in my opinion not a paradox at all, but just the result of a very flawed view of the world. Though, I might perhaps add that I guess many time travel stories try to transport some message/moral rather than accurately depict potential time travel.

 

Double post, sorry.

 

Well, as I interpret the Novikov principle, those scenarios would never occur in the first place - the universe would make sure to never put itself in a situation where people's free will would lead to contradictions.

I don't think the universe is necessarily built starting with the beginning of time working into the future. I imagine that a universe with free will could be constructed by first letting the creatures with free will make all their decisions, and then build the physical universe around those decisions in a way which doesn't lead to contradictions in history.

There are also ways the time traveller could be directly prevented from changing history without violating free will.
For example, they could be stopped by a direct physical force if they were firmly determined to change history. (We're stopped from flying by a physical force (gravity) every day of our lives, but we don't think it takes away our free will.)
The time travellers could also be stopped by little things outside of their control, like cars getting in the way or devices malfunctioning. The more force the time travellers applied towards changing history, the bigger guns the universe would take out to stop them. Like putting your palm against a solid wall - the more force you apply to the wall, the more force the wall applies back on your hand.

I agree that everything, down to the tiniest particle, would need to stay the same when someone travels back to a past event. Moreover, I think people's thoughts would need to stay exactly the same, or there would be a contradiction.
But if we follow the Novikov principle, there isn't a "first" and "second" time the event is rolled up, there's only one time which is viewed from different perspectives. For example, the Kennedy assassination happens exactly one time, and that time it's viewed by the time traveller and a few hundred other participants.

If we draw the universe's time line as a wide band, a person's time line is a thin strip of that band. Travelling backwards in time means cutting loose that strip from some point onwards, and bending it backwards in a loop before letting it rejoin the main band. The time traveller will then have a personal time line in which events occur in a different order, but they'll be the exact same events everyone else witnesses. Even if he goes back to his own childhood and says "hello" to himself, the event only happens one time - there just happens to be two versions of the time traveller that time.

The most likely explanation is probably that time travel is impossible, but where's the fun in that?

The multiple-universes theory is logical, but it's a little sad that you can never get back to your original time line once you travel back in time. At least, I've never heard a good explanation of how that would be possible.
Plus, you end up with two copies of yourself, and the other one's the one who belongs in the time line. You're the stranger without a home.

How do you mean? Novikov says the time line can't change, so there are no changes which need to propagate.

 

There's another problem that is a bit more obscure, I think. A fundamental law of physics says that mass has to be conserved in a closed system (like the universe). You can't have a net creation of mass or a net loss.

All of the atoms that go into making up your body have been around for a long time, right? So an atom that is in my body now might have been in a leaf in 1960. If I go back to 1960, that atom now exists in two places at the same time (as does every other atom in my body), which seems paradoxical in and of itself, and worse yet I've just increased the overall mass of the universe in 1960.

Thoughts?

 

The time-traveler's mass dozen belong in that moment of universe, so therefore it isn't in that moment of universe, making it difficult to interact? (Come up with some mumbo-jumbo for why the eyes catch protons, or how the air can create soundwaves, or how the universe copes with an extra body converting O2 into CO2 and where the carbon is coming from.)

Man, this is giving me a headache. Does energy factor in as well? Maybe if you're running on San Andreas time, the energy you expend in 1960 is taken from wherever you're supposed to be.

 

Well, I didn't invent this. It is really fairly obvious when you consider the Novikov self-consistency principle that you can construct a situation where you eliminate free will. You can have a situation where if a man walks to the left he changes history, and if he walks to the right, he doesn't. According to Novikov, he will walk to the right always regardless of other circumstances. There is no free will.

Compare also the Wikipedia articles on time travel and the Novikov self-consistency principle. There are two very nice animated gifs in the time travel article that illustrate precisely what I mean.

Well, I disagree strongly. Firstly, all the evidence we have shows that time passes continuously. And secondly - how can creatures make a decision if the environment isn't there yet?

Well, I understand principally what you mean, but if such a force existed, it would be so strong that it would prevent time travel altogether. Because your mere existence in a past where you were not before would already be sufficient to change history.

As for gravity, that is a bad example. Gravity defines what it means to fly by its presence, and it didn't stop me from flying yet. It just took some time for us to figure out how to beat it, and we did (balloons, aeroplanes, rockets). I can't see it restraining free will. Although I do understand what you mean (i.e. we still can't just say "I want to spread my arms, flap them, and fly around like a bird - help! help! I'm being oppresssed!" ).

Quite. Not just every particle needs to be in the same position, but also in the same state. In principle that's possible, quantum teleportation has already given us an inkling of how that could work. So I don't see a major problem here for a work of science fiction.

Well, principally, I don't see why you couldn't create a wormhole between two parallel universes and jump in and out between the two of them (assuming it is possible to jump to a parallel universe at all).

Let's say you start on world A at time T. You jump back to the state of the world A at time T-t. However, as you do so, the world is no longer A but A', since your mere presence changes something. You stay in the world for a short time dt. Then you decide to jump back to world A, either at time T when you left it, or at time T+dt. Both should be quite possible, if you can jump around between universes.

Of course, if you are somehow restricted to jumping along only in time, and cannot jump between parallel worlds, there is really no way to get back to world A, once you have started world A'.

Yes, you're right. The world Novikov lives in is completely deterministic, and that alone is a contradiction of free will. Quantum mechanics - at its core - teaches us that the world is not deterministic and that free will very probably exists.

 

Comment: Sorry for two successive posts, but I couldn't add to the other one. Word limit reached? I tried, but couldn't save it.

Strictly speaking, that is not exactly true, but it's good enough to work with unless you consider some exotic effects. A stricter and more fundamental law is the conservation of mass-energy (since the two are correlated, as we know, since Einstein's famous equation). I would say this does indeed pose some problems for some "versions" or "visions" of time travel.

The atoms in our bodies have been around for a very long time indeed. I don't think anybody can say for sure, but I am quite convinced that most of them have been around for longer than five billion years. The hydrogen atoms in your body are the oldest, going back to the creation of the universe itself. All the others were made in stars by nuclear fusion over the course of billions of years, billions of years ago, but I digress...

Yes, you are right, you would be duplicating atoms. Fortunately, though, identical atoms are indistinguishable (apart for their "state", but that is not relevant in this situation), so you might just get away with it. On the other hand, this is again why I believe that there can't be any time travel in a single self-consistent timeline, and believe that if there is time travel, it can only take place involving parallel universes.

Let me just rub those protons out of my eyes, and let some photons back in... ah... much better. (Sorry, couldn't resist!) What you allude to is exactly my point. If you have an additional body that removed photons, creates soundwaves and converts O2 into CO2, then there is no way that the time line is still self-consistent. It can't be. There's no telling what consequences these actions might have later, if you account for the butterfly effect. And of course energy factors into this as well.

 

im actually reading a how to book at the moment called "how to write science fiction and fantasy" by Orson Scott Card. it has a good (brief) section on using space and time travel in it. id recommend it, especially as it only costs £5.

 

But does that mean that time does not happen in chronological order?

@Steerpike, the leaf theory there is a fairly good one, but what would happen if it came about, ie the two atoms coexisting at the same time?

 

That's how I understand it, and I consider that view wrong (which doesn't mean, of course, that you can't write a story about it ).

I sort of answered that above. If you have a question about that, just ask.

 

Assuming the situation is possible to construct in the first place. Perhaps the universe prevents the scenario from occuring before the person needs to make the choice.

Let's make a thought experiment. Let's say you're walking on a garden path, and reach a fork. You decide to take the left path. Normally, you'd say you acted out of free will.

Now let's add an assumption. Someone is watching you from a window, and that person has the ability to foresee the future with 100% accuracy. The person predicts you will take the left fork, which you do.

Does that mean you lost your free will the moment the prediction was made, and suddenly started acting like a robot?

I'd argue that you didn't. The prediction made it possible to know your decision before it occured, but it didn't affect it in any way.

I think time travel with an unchanging time line would work the same way - it would allow you to know of someone's decision in advance, but it would be just as free at the moment they make it.

Well, in quantum physics, particles act as if they know in advance what tests they will be subjected to. Causality doesn't seem to have a clear direction in all cases.

Perhaps the universe tries different configurations and sees what free-will decisions they result in, until it finds one which leads to a consistent time line.

Quantum computers work according to the principle that nature will "test" all possible paths a particle can take, and only the one that "works" will become physical reality. This allows them to try all possible solutions to a problem simultaneously, and only the right solution will be visible at the end.

I imagine the entire universe could work the same way - all possible solutions are tested, and only the consistent ones have a chance of becoming real.

In real life, I think that's likely. But conceivably, the force could block direct attempts to change the time line, while only nudging smaller inconsistencies to keep the time line consistent. It may be good enough for fiction.

Perhaps it is that force which prevents us to travel backwards in time in all normal cases, and we can only travel back by directing our actions so precisely that they will not result in a contradiction.

You're assuming there are two different pasts... one "before" and one "after" someone travels back to it?

What if you jump back in time, then immediately take a wormhole back to your old universe? Wouldn't you end up in the past in your own universe?

 

It means there is more than one chronological order. The time traveller and someone who stays behind experience the same events in different orders. There is no universal time line - there is one time line for each observer in the universe, and they just happen to point in roughly the same direction most of the time.

This is true in conventional physics too, albeit in a more limited sense. Einstein's Special Theory of Relativity implies that events take place in different orders for different observers, when they're moving at high speeds or in strong gravitational fields.

(sorry for making two posts - you can't delete a post once you make a new one by mistake)