Proof that time travel is impossible?

Building on what Tars said, there are some designs for a time machine which would only enable travel back to the time when the machine was constructed. The moment that Thorne wormholes become practical, bookies probably will go out of business, or at least radically change their business model. But Thorne wormholes are not yet practical, so we don’t have to worry about that.

It could be the case that time travel is possible; however, travelling back in time causes the timeline to be changed. As soon as one travels back in time to, say, 1920, the entire world is changed from 1920 on.

The person who travelled back in time instantly vanishes, of course, and all the people who knew about the time machine are in a future that no longer exists.

Then everything’s fine again until the next person invents a time machine…

Or maybe humans die out in the future before anyone has a chance to figure out how to travel in time.

Hmmm. I wonder what’s the most that time travel could cost and still allow you to make money. For instance, if you could travel back in time for a cost of $1,000,000 per year travelled, could you still make loads of money? Of course, travel forward would be free.

A few more speculations, some of them delving into ideas already touched on:

1.) When time travel technology is invented, maybe it will be kept under tightly restricted control and remain so forever. Robert Heinlein dealt with this idea in a classic story called All You Zombies, to name but one instance of a work suggesting this.

Because time travel is used only very sparingly, and by people who carefully limit their activities to approved uses for the public good, no one travelling in time ever places bets–and if they do, another person in on the secret will go back and undo their selfish activities. The upshot: no time traveller ever gets rich from a bet for pretty much the same reason no one has ever used an atomic bomb to get even with all the folks they couldn’t stand back in their home town.

2.) Time travellers are very discreet about being identified as time travellers and so (as suggested by other contributors) they make nominal bets and let the winnings set in a bank for a long, long time. Who could possibly know if all the people who bet on Black Gold in the Kentucky Derby have been accounted for?

I am reminded that Jack Finney wrote an entertain- ing story in which a policeman discovers that time travel is possible after realizing that a fugitive keeps turning up in old news reels of famous sporting events; he traveled back to the twenties and spent years watching Babe Ruth hit home runs, Bobby Jones win golf tournaments, etc.

3.) Building on suggestions in FInney’s story, maybe time travel is a one-way street–you can go wherever you want, but then you stay there. If so, a traveler might only be able to make nominal bets as he can’t explain how he has the millions to bet. Or maybe the bookies caught up with him before he made his departure and “arranged” a refund.

4.) Maybe time travel works like in The Terminator; you can go where you like, but you go there and come back naked and without possessions of any kind.

5.) I’ll admit I don’t much like this last suggestion, but how’s this: maybe the consequences of time travel are very, very mysterious, and so no one who ever tries to make a change in history can succeed. I recall that it was orthodox science in the D.C. Comics when I was a kid (the 60’s), that anyone who attempted to change history would fail, and likely as not would discover that their efforts actually brought about the original course of history in the first place.

Traveling to Superman’s home planet prior to its explosion, Jimmy Olsen falls in love with a Kryptonian woman. One day they are passengers on a huge monorail when Olsen suddenly remembers that there was a horrible disaster on this date, an event comparable to the sinking of The Titanic. At the last possible minute he leaps from the train, pulling his girlfriend along with them. They fall safely into a lake just before the derailment. Then Olsen remembers that history records that there were acutally two survivors of the disaster, a man and woman who inexplicably jumped from the train just before it went off the rail.

There is a much-reprinted story called The Men Who Shot Moses (the author’s name escapes me at the moment). In it a time traveler attempts again and again to alter history, as by giving Madame Currie information about nuclear power with which she accidentally blows up Paris. Each time he returns to the present, however, he finds that nothing whatever has changed. Eventually he meets another traveler (who this is comes as a surprise, but for that you have to read the story). This other time traveler explains to him that they have sort of passed into an alternative reality, and, then again, sort of haven’t; not only can’t they alter the past, they have now developed a sort of ghostlike connection to the present.

There also comes to mind a Max Beerbohm story in which Beerbohm is tapped to take the first trip into the future. When he arrives a hundred years in the future (that is, right about now), he looks up his name in a reference work in a library. He is identified there as the main character in a famous story (author unknown) about a man who traveled into the future and looked up his name in the library only to find that he is regarded as a fictional character.

6.) Maybe the web of cause and effect which forms the world is so intricate and complex that anyone who ever tries to make a change finds that he sets off a million problems in the long run; in a classic short story Ray Bradbury suggested that stepping on a butterfly in the era of the dinosaurs could effect the development of the English language, the outcome of a presidential election, and who knows what else.

As a result, the first person to attempt time travel, whether he places a bet or tries something–anything–else to effect history as it already exists, sets off an infinite series of chain reactions as people try again and again to undo what he has done.

I recall a story where a time traveler goes back to the Nuremberg Rally to assassinate Hitler, thinking he will thereby prevent World War II and the Holocaust. He succeeds in killing Hitler but is shot by his body guards immediately after.

He does not make a better world. Instead, he ends up creating analternative history where the Nazis conquer the world and keep control of it at least until the middle of the 21st Century, the time from which he travelled. To correct this problem, the next bunch of time travellers send an assassin back to stand behind the sniper who shoots Hitler, so that he can be killed before pulling the trigger.

The only thing is, behind that second assassin is a third assassin, sent back from yet another alternative future to shoot the second assassin before he can kill the first assassin, on account of killing the first assassin before he shot Hitler caused even worse problems. Of course, unknown to the third assassin, there is a man standing behind him; a gunman from the alternative world the third assassin created, sent back to kill him before he messes up the world even worse. And behind that fourth assassin? Why there is, of course, a fifth gunman, the one sent back from the world the fourth gunman sent into being, who has gone back in time to kill the fourth gunman before he brings calamity on the world. And behind him? Well… you get the idea.

7.) Maybe plenty of time travellers actually will win fortunes by betting on historic events, but we don’t know about it yet because we are living in the world as it exists before the time travelers go back and change history. In a way, it’s a lovely thought; by the same logic, we could be living in the world before the past gets fixed and the Titanic doesn’t sink, World War II doesn’t happen, and the events of Septemer 11, 2001 are averted. But I don’t think so.

Maybe that’s actually why those market collapses happened. :wink:

The Men Who Murdered Mohammed, Alfred Bester, 1952.

The story is Enoch Soames. In the story Soames is an acquaintance of Beerbohm. Soames travels to the future and finds his only mention is as a character in this story itself (at that future time considered fiction and known to be by Beerbohm).

The Larry Niven, Jerry Pournell version of why time travel is impossible goes something like this.

If time travel exists, then the actions of time travelers alter the nature of the universe from the earliest moment into which they travel. Those changes either decrease the subsequent probability of time travel being discovered, and used, or do not. If a particular traveler does not reduce the probability of time travel after his earliest activity, then more such events will occur. If he does reduce the incidence of time travel, then fewer events will occur. Over the vast reaches of time in the universe, therefore, time travelers themselves must eventually act in such a manner that time travel stops happening at any time.

The ultimate temporal paradox: time travel prevents time travel.


You have to love this brain teaser.

No point tell you folk how time works cos we all know.

Pretty much time travel is possible - look at the stars.

but it is not possible to changed the passed.

1 reasons/theory 2 explainations

  1. If you changed the passed you are not changing anything it already happened so you have no reason to change anything ( enter loop)

  2. The smallest change you make will affected the entire progession of time - i do not believe in fractured time i believe in a constant.

Remember time travel HAS TO HAVE A PURPOSE

Imagion you come accross a constant wahsing machine - on sicne the dawn of time all the colours have mixed together long ago - and you decide that pink is a better colour for them. You travel back in time and place a Micro fiber of a vibrant pink in. You would not see results for a long time but eventually on the smallest level this change affects the colour of every other peice of cloathing.

You future self comes accross this washing machine filled with pink cloathes … no reason to go back an change it is there ? (of course this opens a huge debate and lets not go there)

You can not change the passed you can only observe it without interaction in anyway.

r_k, that was simply brilliant.
I really can’t think of anything to contribute…

(Lou E. Thunder’s first post)

If they set a specific date that no one could travel past… when they went to that date… those ppl would also set a date, because they want to go back in time aswell, and it keeps going like that until we get it today.

Time travel is great! I just had breakfast at the Big Bang Burger Bar. Guess where dinner is gonna be?

back to serious. check these:

If time travel were possible, you could travel to the future, and introduce things into the past. That would mean constantly rewriting history (which would explain the fast pace of invention today). In fact, the enormous progress of Western society (since ca 1700) kinda argues that TIME TRAVEL IS REAL, and we are witnessing the effects of it!
Think of it like the old Soviet Union-the politicians in power would constantly rewrite history-so if you had the GREAT SOVIET ENCYCLOPEDIA, they would mail you new pages, photos, etc., which you would paste over the old ones! That way, sombody like Beria (enemy of kruschev) would literally disappear from the pages of history!

I’m a time traveler.

But you can’t go backwards in time before an apparatus exists. Since no such equipment currently exists, we can only travel forward in time.

This reminds me of a great Orson Scott Card book, Pastwatch, about a group of people in the future who have developed a way to view any point in the past with TiVo-like convience. They set about trying to alter the past to prevent the eminent extinction of the human race due to poor resource planning on their part. They choose one moment, when Christopher Columbus decides to sail West, as the focal point only to discover that this is not the first time that people have tried to change the past. Great read!

OSC’s interpretation of time travel is that once you go back, the future as you knew it is instantly erased and replaced with an alternate reality as a result of your fooling around.

I am Sparticus, I wouldn’t mind the forward only thing if I had some control over the throttle. :slight_smile:

So has any of the time travel books other people have read ever addressed the issue that at different times the Earth is in different positions rotationally/revolvingwise/relative-to-rest-of-universe? None of the ones I have read have. Maybe we haven’t had any trouble with time travelers because they can only jump to times when the earth is in approx. the same position. So they can only move by multiples of Earth’s universal orbit-period. Rather unwieldly, correct me if I’m wrong but wouldn’t that be every ~26 000yrs?

Darn - you beat me to it, CarnalK. But even if you take into account the rotation of the earth and the circling of the sun, and wobbling, there is also the speed at which the entire galaxy is whizzing away from the where we surmise the big bang occurred. If you went back in time, you’d be a long way from home, and would have to get here by fast spaceship. Hmm… perhaps time travel could be a way of space travel, if you could get the intersects right. It would be one-way travel, though, and depending on how far you went in time/relative distance, there might be no way for anyone still here to know whether it worked and you made it alive or not.


I always figure that the movement of the Earth wouldnt have anything to do with time travel. After all, I am currently moving through time at a rate of 1 hour per hour, and yet the Earth’s gravity is holding me in place relative to my position on the globe.

Carnalk, it is a matter of controlling your perceptions to change the speed at which time passes, Einstein even wrote about this. If you need time to speed up, spend it with a pretty girl. If you want time to slow down, sit on a hot griddle.

A possible explanation is the “parallel universe” hypothesis.

What that says if an event occurs that changes the course of history, the universe will split into two. One with the altered history, one without.

So it is entirely possible that the past has been altered a great many times, it’s just that we have no idea where these universes are.

As I understand it, time travel is not only possible, but manditory. And it is one-way.