If you could travel back in time could you change what you have already done?

Question

E.g. A machine which can see into the future rings a bell 20 seconds before you clap yor hands.

Is it possible to hear the bell ring and then not clap your hands (i.e. you were prepared to clap your hands but once you heared the bell you changed your mind) , or will the bell never ring, because it can see into the future that you are not prepared to clap your hands?

Ok would it be possible to clap without the machine ringing the bell?

Surely this proof that time travel is impossible. Because you could just clap even if the machine had not rang the bell and if it did you could just not clap?

Answer 1

You gave the example of a machine that can see into the future and ring a bell but you ended with, 'or will the bell never ring, because it can see into the future...?
Is 'it' referring to the bell or the machine?
Other than the human being, what else made a decision; the machine that rings the bell or did the bell make the decision not to ring; or was it a collaborative effort on the part of machine and bell?
Can you go back into the past and clarify the example for me?:-)
But, to answer your question which was, 'If you could travel back in time could you change what you have already done?'
The theory is that going into the past you would be able to change the outcome of the future that is yet to be since you are now in the past-present.
However, if that theory be true, my question is would it be the right thing to do? Changing just ONE thing in the past affects EVERYTHING in the future.
What I don't like about the concept of time travel is that, albeit the individual may be able to change that which is desirable for him or herself…but what about everyone else?
You will undoubtly change things in other's life that could very well have extremely deleterious effects.
Consider the example of Hitler.
If he were not born, what affect would that have had on the rest of the world?
Everyone talks about the war and the Holocaust; but if Hitler were NOT BORN to set those things in motion, would there be a country called Israel now?
Oh boy...what have I DONE?
Can I go back into the past and fix it so that I never said that?
Doesn't anyone ever stop to think that MAYBE, JUUST MAYBE, EVERYTHING that man does since the beginning of his time, good and bad, is SUPPOSED to happen?
That may, one day, even include travel into the past.
Who knows? There may be some time travelers already traveling through time making changes.
That may be what deja vu actually is. A shift in time caused by time travelers.
It's bad enough that we dig up the past in a feeble and mostly futile attempt to make the present and future better; lets leave actual time travel alone.

Answer 2

Ah, supposition! In my mind a complete waste of time. I will consider it if and when we CAN travel in time. There is no point in waisting brain power on it until then. I think our time would be better put to use on the first challenge. Time Travel.
Cave men probably didn't sit around freezing to death wondering " If I could find a way to control fire, could it in the future be put to use as a way to propel a vehical along a steel track?"

Answer 3

No you won't, you will be only watching yourself doing what you have already done, and I think you will not even know that you are in a previous history of time, every thing electrons photons will take the same track so your thoughts too. An observer can watch you back in time like what do electrons every second around you .... if that were possible ..... and I think not.

Answer 4

Good - looks like I'll be the first with a serious response! I wouldnt say this is pure meaningless supposition because we may one day develop technologies to distort spacetime enough to go back in time. You might ask what would happen if you went back and stopped them from inventing a time machine and this due to a particularly violent version is known as the grandfather paradox. It rests on the assumption that there is only one timeline though.

The many worlds interpretation of quantum mechanics offers a solution. Going back and stopping them from building a time machine would place you in a 'parallel' (actually perpendicular if you want to get technical) timeline where there was no time machine - you'd still exist, and in fact they'd be two of you.

If you went back and murdered your grandfather before he had children (shame on you) you'd still be there - you wouldnt vanish in a puff of paradox because if you did - you couldnt have gone back in time and killed him, but then if you couldnt then you didnt kill him and then you would exist so you could kill him!? Thats the paradox. You'd still be there and you'd get thrown in jail. In the future you came from you'd have vanished at the point you went back in time - if you could somehow escape jail and get back to the future it would be the future of the alternative time line you created and you wouldnt exist in that future. Well one of you would - the one from the other universe! Get it?


Kind regards

**ps. People who say 'no, you could only observe things' need to stop getting all they know about time travel from Harry Potter movies.

Answer 5

No you couldn't change anything because you would only be able to observe. Nice thought though. There was a film on recently about the same thing. Changing what has already happened can have devastating affects on other peoples futures.

Answer 6

In the Star Trek episode "City On The Edge Of Forever" McCoy got pumped full of cordrazine, went nuts, beamed down to the planet, and went through the arch of the Guardian of Forever. When he did this he changed the current time so the Enterprise didn't exist anymore. Kirk and Spock had to go back and fix his mess.

This proves that it is possible to change what you have already done.

http://www.ericweisstein.com/fun/startrek/TheCityOnTheEdgeOfForever.html

Answer 7

If you travelled back in time it would be possible to change what you had done or what others around you had. But remember, changing things in the past is not always the best thing to do. It can dramatically change things in the present and ruin things that would have happened had you not meddled.
BE WARNED!!
lolxxx

Answer 8

The only way to travel through time is to stay in the present moment and go forward through time, one second at a time. You can't go backwards through time, nothing can see the future before it happens, that's all SciFi goofy stories.

Answer 9

It depends on the type of time travel, are you pressing rewind and starting over, or are you merely present, as you are today, observing and interacting with the past? I'd say if you could rewind and retain the knowledge you presently have, you could change your mind.

Answer 10

yes i would....i had a go at my nan once because she kept on talking to me when i was attending a phone call and when i put it down she asked me who it was,when i told her she was like well why didn't you tell me then,i wanted to talk to him(that was apparently what she was saying all along but i heard something else) and i had a stress at her and she ended it by saying that you get angry way too easily,you must calm down in future or it won't lead you anywhere....tht was when i was on holiday and when i came back to england she died a year later on and i never got to see her.To this day i remember those words and i really wish i never had a go at her.iam sorry nan,i really am.