Is it possible to write about Time Travel without making paradoxes?

[Ruby]

The universe moves causally from one point to the other, and changes states at is goes from one to another. That was the case long before humans were around to invent a concept of time. We may have invented time as a "concept" but we use it to label a real property of the universe.

As for time travel, I don't think physics has rendered travel backwards in time completely impossible (there was an interesting SciAm article on this a number of years ago). Travel forward is certainly possible. The easiest way to resolve paradoxes from traveling backwards is to have the timeline split at the point of any possible paradoxes, so that two separate universes exist (the original and the altered one).

By the way - just going back in time to the same universe you left from is altering the past, and also appears to me to violate some laws of physics, so unless you do something like split the timeline, you've got a big problem.

I read a theory once in a science journal that every time the universe is confronted with a choice (they were talking at a quantum level I think) there is a splitting of the timeline into two separate universes - one in which each choice is made. According to this theory, the timelines merge almost immediately if the choice is minor, take long to do so for more major changes, and if the change is significant enough they never merge. You could work with something like that.

But it seems to me that if you really want to make sure you don't run afoul of paradoxes at the instant the person travels back in time, you completely sever the timelines into two universes.

Even then you've got the problem of adding matter to the universe (remember that the laws of physics, and conservation of mass and energy). I suppose it is open to debate whether or not the universe remains a "closed" system if time travel is feasible. If not, then perhaps those laws don't apply.

Hi Steerpike,

Thanks for explaining this.

But, of course, this just shows how complicated it is. If I split the timeline, I will have multiple versions of the same characters wandering around in space and time, won't I? How on earth would I structure such a book? I already have at least four different time travellers in the plot!

 

[Ruby]

This may be a bit off-topic, but I once came to the conclusion that time doesn't exist at all. We only invented the concept of time to put things in order, looking at the past and to the future. But technically neither the past nor future actually exist. All that exists is the present, this exact moment. All the time the present is becoming the past and in doing so ceases to exist. The past existed for that exact moment that it was the present, and the future of course doesn't exist because it hasn't happened yet, but it will when it's the present. Because of this, I'm convinced that in the real world time travel will never be possible.

Of course in a fantasy story that doesn't matter and you can make time travel possible with matter.

Hi Gryphos,

So you're saying that although time doesn't exist, it should be possible to time travel?

 

[Ruby]

The butterfly effect is that small changes can have large and unforeseen consequences. For example, your MC time travels backwards. A few moments after they arrive, they bump shoulders with some stranger. That bump can cause an ripple effect like a pebble dropped in a pond that touches everything around them. Now that bump causes the stranger to pause for a second to look at your MC. It seems like a nothing interaction, but here are a few things that can happen.

- Because the stranger pauses to look at your MC, they miss meeting eyes with their future wife, and that stops them from ever marrying and having a kid. That kid will never invent the cure for cancer.

-Because the stranger pauses, that makes the person behind them pause too. So everyone behind is a step behind their normal pace. This causes one of them to be one second behind in crossing the street as a runaway dump truck comes roaring by. Before the dump truck missed the person by a second, now the truck hits that person. When this happens, it doesn't just kill that person. It will kill every descendant that person will have, and will affect everyone that person and their descendants will ever interact with in the future. It in effect causes a shockwave through time with unpredictable consequences.

As each of us moves through time and space we affect all those around us in tiny ways, but each of those interactions is part of a cause and effect equation. Add or subtract something from that equation, it won't add up to the same thing.

Remember that pebble in the pond analogy I made above? Now imaging a pond with billions of pebbles being dropped into it. Imagine how the ripples interact, cancelling each other out or reinforcing one another, creating a pattern of ripples. Now try and predict the pattern of change if you stop a single pebble from falling in or drop a new pebble in? It's near impossible to tell what the new pattern will be. All you know is ripples go out, or don't, and how they interact and the end result will be different.

The name Butterfly Effect comes from a short story by Asimov or Bradbury, I think, named The Sound of Thunder. In it somebody travels back in time and accidentally steps on the butterfly and significantly changes the future.

Hi Penpilot, thank you for taking the time to explain all this.

I didn't know it was called 'The Butterfly Effect' but I'd already encountered this problem in chapter two of my WIP when the time traveller, who's a master wizard, has arrived in the wrong year to bring the MC back to the future. His time machine has malfunctioned and he's two years earlier than planned so, although he's met her, she hasn't met him. Now they're going to time travel forward two years but that's going to cause a paradox, isn't it?

I'm probably going to have to rewrite this whole plot or let him use magic instead. Maybe, he'll have to disappear by himself and meet her in the correct year, but even then there would be a paradox!

 

[Steerpike]

Hi Steerpike,

Thanks for explaining this.

But, of course, this just shows how complicated it is. If I split the timeline, I will have multiple versions of the same characters wandering around in space and time, won't I? How on earth would I structure such a book? I already have at least four different time travellers in the plot!

No, there wouldn't be any communication between the timelines, and travel between them wouldn't be possible. I've seen stories that use alternate timelines to get rid of paradoxes, but I don't think I've seen on that addresses the conservation of mass issue, though I can think of how you might do it. But most time travel stories hand wave these issues.

 

[Gryphos]

Hi Gryphos,

So you're saying that although time doesn't exist, it should be possible to time travel?

No, I said that it wouldn't be possible in the real world, but in a fantasy story you could have it and just put it down to magic.

 

[The Dark One]

I think most of this is way too complicated for a story. All you need is a plausible means of time travel (some sort of wonder gizmo) and a satisfying story in which the time travel contributes to the plot without overstretching it. People like time travel stories so will forgive a lot in their pursuit of an enjoyable read.

As for the science of time travel? I can understand (via Einstein) that time travel forward (for humans rather than just subatomic particles) is possible. I don't think it's possible backwards though (in any way we can understand) because if time travel backwards was possible, then someone would have invented it in the future and we'd know about it now. The instant someone in the future invented time travel then everyone else throughout all time would have access to all time. It'd be total chaos. But it's not. So travel to the past is not possible.

I am The Dark One...I have spoken.

 

[Ruby]

No, I said that it wouldn't be possible in the real world, but in a fantasy story you could have it and just put it down to magic.

Hi Gryphos, sorry I didn't understand as on your original post there must have been a typo and you put "matter" instead of "magic".

 

[Ruby]

I think most of this is way too complicated for a story. All you need is a plausible means of time travel (some sort of wonder gizmo) and a satisfying story in which the time travel contributes to the plot without overstretching it. People like time travel stories so will forgive a lot in their pursuit of an enjoyable read.

As for the science of time travel? I can understand (via Einstein) that time travel forward (for humans rather than just subatomic particles) is possible. I don't think it's possible backwards though (in any way we can understand) because if time travel backwards was possible, then someone would have invented it in the future and we'd know about it now. The instant someone in the future invented time travel then everyone else throughout all time would have access to all time. It'd be total chaos. But it's not. So travel to the past is not possible.

I am The Dark One...I have spoken.

Hi The Dark One, and thank you for your advice. I've been told that Time Travel stories always contain plot holes.

I don't want to abandon writing this book, so I'm going to focus on structuring the plot and, as Devor said (above), the characters don't have to time travel much. It's quite a humorous book, probably MG/YA and contains magic, some steam punk and time travel with a couple of would be assassins lurking in the background. Hopefully, the readers will suspend their disbelief as for other genres of Fantasy.

 

[Steerpike]

If ideas about the time line splitting were true, then we wouldn't know about backwards time travel until we reached the date it was invented in our time line and wouldn't always know about it. Another problem solved by that approach.

 

[psychotick]

Hi,

Just to add to the butterfly effect - it's actually far more powerful in terms of change than most people seem to realise. Remember in the real world tiny things can have huge impacts - and that doesn't mean in rare circumstances. It appliesto a great many things. So say you go back in the past a thousand years. You're there only for an hour or so, and you try to remain more or less unnoticed. So you do nothing really. Maybe you walk through a market and nod at a few people.

Now everyone you nodded to is changed by the encounter - in the most minor way. Some of them may wonder who you were and take a moment to think. That moment may make them late home by thirty seconds. They then go and make love to their wives thirty seconds later than they woul have. (Or maybethey have other things to talk about at home because of that nod - something like "Saw a strange guy in the market today!) Regardless fifty million sperm race to fertilise an egg and there is one winner. (Or maybe there is no winner when there shoul have been, or is a winer when there shouldn't have been.) But why would it be the same sperm that succeeds? No reason at all. So in nine months a completely different baby is born. Then that baby lives an entire life changing the lives of everyone he encounters in completely unexpected ways and every baby born after that who has any connection tohim is a different baby. Fairly soon the entire world is filled with completely different people simply by this mechanism alone. Just from a nod.

And there's no actual way to stop this happening.

Cheers, Greg.

 

[Devor]

And there's no actual way to stop this happening.

To bring it back to sci-fi writing, it's a pretty common trope to just say "the universe corrects itself for the little stuff" and handwave it. That kind of statement has the purpose of showing the reader that you know what you're aware of the real world details, even if you're ignoring them, and helps readers to move beyond the disbelief. It creates the illusion that there's an in-book rational explanation, even if it's really just that statement.

 

[The Dark One]

That's right. People always accept the wonder gizmo or the magic crystal, and you have to screw it up pretty badly to reboot their disbelief.

 

[psychotick]

Hi,

The problem is that I can't simply accept a statement like that at face value. Time repairing itself always seems to me like someone is saying that time is some sort of living thing - and that crosses the boundary between sci fi and fantasy.

And there are so many paradoxes to consider. Ignoring the shooting your own grandfather one, one that I like is failure of conservation. To give an example say time travel is invented tomorrow, where does everyone set as their destination or one of them - the crucifiction. But that's everyone until presumably the end of time. Which means that instead of two thousand people there's potentially an infinite number all arriving there at the same moment, and perhaps fracturing the Earth's crust or even starting a singularity. That would have gone down in our history books!

Though to be fair I did actually write a time travel novella in which this same paradox was used as an explanation for the begining of the universe. I.e. everyone turned up in their time machines at the same place and tie, and hey presto - big bang!

Cheers Greg.

 

[Devor]

The problem is that I can't simply accept a statement like that at face value. Time repairing itself always seems to me like someone is saying that time is some sort of living thing - and that crosses the boundary between sci fi and fantasy.

That's not the only conclusion. If time travel were possible, it would imply what we already think we know, that all moments exist simultaneously. That would mean that time is part of a complicated system, and most complicated systems adjust to survive small changes. If the future already exists, then the future would resist that change, sort of like a type of friction. Ripples lose energy as they move away from their source. So could the butterfly effect.

And there are so many paradoxes to consider.

That goes back to a main problem with most science fiction - the science being depicted is often an impossibility. Our technological capabilities are increasing at an exponential rate. But exponential growth ends by crashing into a ceiling. Where? I have no idea. But it's an inevitability that some things will be scientifically impossible. Time travel is almost certainly among them. Any time travel story runs the risk of paradoxes, and bad science, and more, because it's not science. It's fiction.

 

[Penpilot]

Any time travel story runs the risk of paradoxes, and bad science, and more, because it's not science. It's fiction.

This reminds me of a scene I once saw in Dr. Who. One of his companions ask him about the butterfly effect. His response was something to the effect, "Where's the fun in that?"

One of the most highly rated movies in a while, Looper, was a time travel story. It had an awesome story, but a massive plot hole that you could throw all of space and time into. The writers knew this and all they did to address it was have a character say something to the effect, "If you want to talk about time travel we'll be here all day drawing diagrams," effectively hand waving it away.

Time travel stories are fun, regardless of it the science is possible.

If anyone wants to check out a time travel movie check out Primer. It deals with the creation of paradoxes, and it'll make your head spin when you think about it. And if you blink, you'll miss something, and you'll realize what you think you know is wrong. Till this day, I'm not sure if I fully understood everything that happened in the movie. Don't get me wrong it's very watchable, but you have to be paying attention to pick up on the nuances because they don't spoon feed you the info.

 

[Ruby]

Hi,

Just to add to the butterfly effect - it's actually far more powerful in terms of change than most people seem to realise. Remember in the real world tiny things can have huge impacts - and that doesn't mean in rare circumstances. It appliesto a great many things. So say you go back in the past a thousand years. You're there only for an hour or so, and you try to remain more or less unnoticed. So you do nothing really. Maybe you walk through a market and nod at a few people.

Now everyone you nodded to is changed by the encounter - in the most minor way. Some of them may wonder who you were and take a moment to think. That moment may make them late home by thirty seconds. They then go and make love to their wives thirty seconds later than they woul have. (Or maybethey have other things to talk about at home because of that nod - something like "Saw a strange guy in the market today!) Regardless fifty million sperm race to fertilise an egg and there is one winner. (Or maybe there is no winner when there shoul have been, or is a winer when there shouldn't have been.) But why would it be the same sperm that succeeds? No reason at all. So in nine months a completely different baby is born. Then that baby lives an entire life changing the lives of everyone he encounters in completely unexpected ways and every baby born after that who has any connection tohim is a different baby. Fairly soon the entire world is filled with completely different people simply by this mechanism alone. Just from a nod.

And there's no actual way to stop this happening.

Cheers, Greg.

Hi psychotick, thanks for posting this. This would make a very good plot for a time travel book. Maybe YOU should write it. I'd like to read it!
But seriously, isn't "real" life a bit like this anyway? Everything that happens changes you, and if you are late or early you will have a different journey/experience.

 

[Ruby]

Hi,

The problem is that I can't simply accept a statement like that at face value. Time repairing itself always seems to me like someone is saying that time is some sort of living thing - and that crosses the boundary between sci fi and fantasy.

And there are so many paradoxes to consider. Ignoring the shooting your own grandfather one, one that I like is failure of conservation. To give an example say time travel is invented tomorrow, where does everyone set as their destination or one of them - the crucifiction. But that's everyone until presumably the end of time. Which means that instead of two thousand people there's potentially an infinite number all arriving there at the same moment, and perhaps fracturing the Earth's crust or even starting a singularity. That would have gone down in our history books!

Though to be fair I did actually write a time travel novella in which this same paradox was used as an explanation for the begining of the universe. I.e. everyone turned up in their time machines at the same place and tie, and hey presto - big bang!

Cheers Greg.

Hi psychotick, ah, so you have written a book about time travel!

If lots of time machines cause a Big Bang, can you explain how in a recent Doctor Who special, there were three versions of the TARDIS in one scene and there wasn't a paradox or a Big Bang in sight?

In my book, one of the characters takes his grandfather into the future to build the time machine. There must be a paradox there, I guess.

 

[psychotick]

Hi Ruby,

Unfortunately I gave up on Doctor Who after Tom Baker left. He is for me the quintessential doctor. But yes there are endless paradoxes in the show and they are never addressed properly - probably because they can't be.

And yes there are paradoxes in going to the future as well. So let's say your character does as you say and goes to the future to pick up a time machine from his grandson? Let's say he goes a hundred years into the future. Then he goes back and lives out his normal life in the present. At every stage of his life in the present he is changed because of his trip to the future. And that change must affect his behaviour and so in turn affects the world around him. So how does he live a life in the present that is exactly as it should have been had he not gone to the future?

The answers are of a course a philosophical grab bag. The first one is that he doesn't. He lives a different life, and that life is in fact the one that leads to the future where he can find a future in which his past self will arrive (have arrived? Tenses are problematic here.) But that leads us straight into destiny (not the predictions of greatness type.) It means that everything he does from the point at which he left until the point in the future at which he arrived is completely predestined. Not just him but everyone else as well. In short there is no such thing as either free will or chance.

The next choice is the parallel worlds options where, the world split at the point when he travelled to the future. Thus he went to "A" future but not necessarily "THE" future. So that future will not have to exist later. This runs into a different problem, one of energy. If every time I walk down a street and turn right instead of left a new possible universe is created, where did the energy forthat come from? It certainly didn't come from me turning in one direction. And we are talking about the creation of an entire universe here.

And the third option is the one touched on by Devor. The so-called B series of time. In the B series time does not change, but rather we move through it. It's rather like reading a book, where the present is the page your reading, but most importantly every other page in the book - those you've read (the past) and those still to read (the future) exist in exactly the same way that the present does. Now in this scenario time travel is paradox free. The reason is simply that if I take out my little red pen and start rewriting some of the pages from the past or the future, it makes no difference to the page I'm on. They are all already written.

However there are consequences too, and the biggest one is that cause and effect no longer applies to anything. For example if on one page I throw a ball and on the next it is flying, there is no actual reason for it to be flying save that someone wrote that it was. Because every page - every present - is completely indipendant of every other one. So if I change the previous page such that I no longer threw the ball, in the next page it still flies. Which simply means that the reason the ball flies has nothing to do with anything done on a previous page.

Cheers, Greg.

 

[Reaver]

I'm a huge fan of science fiction but I avoid writing anything with time travel for all the reasons mentioned above. That and quantum physics.

 

[Noma Galway]

My personal opinion on time travel is that time is stationary. We can move about in time and nothing will change, because time knew we were going to move about in time. Everything is fixed, to use a Doctor Who term. No moment is in flux.