This basically happened in Stephen Baxter’s The Time Ships, which is a sequel to H.G. Wells’ The Time Machine.
Basically, a group of soldiers from the Time Traveler’s era get stranded millions of years back in time. By the time the Traveler gets back to his time of origin, the world has changed so much that it’s completely unrecognizable.
Right. But altering the past isn’t an automatic paradox is all I’m saying. There are some actions that, if there is a single time-line, could cause paradoxes, and then there are actions that never would. I think the paradox causing changes would be very rare. I don’t have anything to base this on since this is all speculation and time travel probably isn’t possible anyway*.
*Of course there is a theory that if a time machine could be built one day, then you could only go back to the time it was built. So if a time machine ever is built in the future, then no-one could come back to our time anyway.
Looping in a single timeline like this causes problems - obviously there are all the usual paradoxes, but there’s the fact that all of the loops will already have taken place.
Take for example, the common scenario where the time traveller hands some object to his past self, which he keeps in his possession until it’s his time to go back and pass it to his past self.
Aside from the fact that this scenario can create objects out of thin air, there is the question: how many times around the loop has the object gone? once? - no, because it’s an unbroken loop, it’s infinitely many times - and any physical object is going to wear away to nothing after an infinite amount of handling, therefore there is no object to be handed over and the scenario breaks, as soon as it exists.
Same thing if the commodity is information - if time travel exists, and loops are created, they will eventually do something that will either destroy the universe, or prevent their own occurrence.
I never saw things like this as a paradox. So looking at the object, let’s say it’s a stapler. It’s manufactured and then sold to Tom. Tom goes back 10 years and hands it to his younger self. Now in 10 years there are two staplers until Tom goes back 10 years with the stapler he just bought and gives it to his younger self.
Here is an illustration I made.
Yeah but Mangetout was talking about if older Tom never bought it, just got it when he was young from the older Tom, etc.
Just because you don’t see it that way doesn’t mean that it isn’t a paradox. That’s pretty much the definition of a paradox/time loop. And there is only one stapler. Sometimes it appears twice in the same timeline, but it’s still the same stapler.
If time travel is linear: whatever the traveler brings back will somehow be destroyed (or even makes a contribution) so that the events happen in the exact same order that they did leading up to the creation of the time machine. In the time traveler’s world, he already went back.
Much more likely though is the idea of parallel time streams, and the effect you describe would create branches in the time continuum.
It has to be this. Either your travelling back in time created a new timeline, so that means any paradox you cause also creates alternative timelines; or you cannot create new timelines at all, there is only one, we’re in it, and everything you do has already happened because you were always there from the beginning, making paradoxes impossible.
What is the paradox in the chart that I made?
ETA: And the same stapler twice vs two staplers is a difference without distinction.
Forget paradox, I don’t think that’s possible in the first place. In order to give the stapler to younger Tom older Tom would have to get the stapler from somewhere outside of the loop. The only other scenario I could see would be this.
Tom buys a stapler.
Tom goes back 10 years and gives himself the stapler.
In 10 years, instead of buying another stapler Tom goes back 10 years and gives younger Tom the stapler that he has.
In my opinion, the same thing would happen that would happen if you shot your grandpa (assuming one time-line)
You shoot your grandpa.
You’re not born, so you don’t go back and shoot him.
He’s not shot, you’re born, so you go back and shoot him.
Repeat infinity.
So I don’t think you’d cause a paradox, I think you would get caught in an infinite loop. Unless infinite loops are paradoxes.
They could come back to now but someone (me) would steal the time machine to go back and murder the inventor of Farmville when he was child.
Then I’d go see the Doors in concert and probably loose the time machine.
Psst…it’s, “probably lose the time machine.”
Paradoxes create time loops. Or they create alternate time lines, depending on which theory of time travel you’re using.
In a linear theory, they wouldn’t. They would just be sabotaged, destroyed, eliminated, or otherwise incorporated into the same timeline the traveler is from, like the number of times hitler avoided assassination and still started the holocaust.
Tom doesn’t need to buy a stapler. He got one ten years ago from himself.
I don’t see how that is possible. And yes, paradoxes aren’t possible, but I don’t even see it as a paradox. As stated in my previous post, he had to get the stapler first. In other words, I don’t see how you can start with a closed loop.
Now once he gives the stapler to his younger self, then in 10 years time he’ll still have the stapler (assuming he kept it), but he can’t give THAT stapler (or version of the stapler if you prefer) to his younger self. Doing that would cause a paradox or a loop.
In a linear theory, the stapler would be destroyed and/or lost, and his future self would still be on the same path in giving it to himself. He would be unable to avoid giving himself the stapler AND sending the stapler back in time. The only paradox here is that in the original example, his future self doesn’t have the memory of receiving the stapler, which he should.
A good example of this can be found in The Time Machine (2002). The hero is unable to alter a past event no matter how many times he tries. His fiancee still dies but in different ways. His future self still has the same motivation to create the time machine, while his time traveling self will remember all the ways she died.
In my examples Tom remembers buying the stapler. In the first he buys it, and gives it to himself 10 years earlier. Now in 10 years he buys the stapler (just like he always has) and now has two staplers, or if you prefer, the same stapler twice. He goes and gives the stapler he just bought to his younger self, just like he did before. And all is right with the world.
My recent point was, if, instead of going to the store he just returned the 10 year old stapler to the past, then that would cause a problem.
If time travel was possible, I don’t know that I would buy the theory that you can’t alter the past, because going back and doing anything is altering the past. Even if it’s not written down in a history book. Now there may be laws against creating paradoxes, but unless and until time travel can be proven as possible, I guess we’ll never know.
That’s the problem with this example. Tom never buys the stapler. The stapler he gives is the only stapler. The stapler he gets, remembers, and gives is the same stapler. There is no paradox if we are using a linear theory.
Here’s how the example should be stated:
Tom buys a stapler and somehow loses it or is destroyed and he can’t find a replacement. 20 years later, he finds that model of stapler is now made and wants to sending it back to his past self. He invents a time machine with the purpose of send it to himself back in time. However, during the trip, he somehow loses the stapler or drops it. He tries again with the same result. The lost stapler(s) is(are) found and sold. Past Tom buys one, and the example starts again from the beginning. In this timeline, before the stapler is invented, the same number of staplers always existed.
To continue this example: Future Tom tries 100 times and is unsuccessful 100 times. In the past, there are now 100 of those staplers, but Past Tom was unaware that all of them came from himself. When Future Tom decides to give up, it was already predetermined that he would give up at 100 tries.
Linear timelines are so boring. 
missed window: Also, let’s say Future Tom goes back in time and then breaks his machine. However, he doesn’t have enough funds to get replacement parts. He is then forced to sell the stapler to get the part. He may have been the original seller of the stapler to himself.
Conversely, let’s say he forgets to bring the stapler. Rather than waste a trip back, he sees the exact same stapler on the bench and picks it up. This may be how Past Tom lost the stapler to begin with.
All events have already happened and don’t affect anything.
