New model 'permits time travel'
If you went back in time and met your teenage parents, you could not split them up and prevent your birth - even if you wanted to, a new quantum model has stated. Researchers speculate that time travel can occur within a kind of feedback loop where backwards movement is possible, but only in a way that is "complementary" to the present. In other words, you can pop back in time and have a look around, but you cannot do anything that will alter the present you left behind. The new model, which uses the laws of quantum mechanics, gets rid of the famous paradox surrounding time travel. Although the laws of physics seem to permit temporal gymnastics, the concept is laden with uncomfortable contradictions. The main headache stems from the idea that if you went back in time you could, theoretically, do something to change the present; and that possibility messes up the whole theory of time travel. Clearly, the present never is changed by mischievous time-travellers: people don't suddenly fade into the ether because a rerun of events has prevented their births - that much is obvious. So either time travel is not possible, or something is actually acting to prevent any backward movement from changing the present.
posted by Unknown @ 9:33 PM
4 Comments:
Surely merely by travelling back in time you would be changing history- doesn't quantum theory argue that merely observing has an effect? By standing somewhere in the past you would be having a tiny effect- even something like the air currents flowing around your body- doesn't chaos theory state that a minute difference like this can grow to cause immense changes elsewhere? If time travel is possible then surely a more coherent argument would be that there are many possible "futures"- each action you took in the past would have an effect on the future, but one separate from your own- as if reality was splitting off into different "time streams".
Any thoughts?
Hmmm...
Time travel without major consequences on future events doesn’t look very probable...
Carl Sagan was a very nice guy but this "cosmic censorship" thing is dangerously close to superstition...
"Carl Sagan was a very nice guy but this "cosmic censorship" thing is dangerously close to superstition"
I'm not sure. If time travel is possible and you can change the past, why isn't our present unstable and our history books made wrong by visitors from the future? It's not a stupid question. But jay.mac has a point: According to quantum theory, you will affect a system even by measuring it.
The many universes theory seems to be the only one which would allow time travel to occur. The theory can best be summed up by imagining you wake up in the morning and go to the kitchen- you can either have a coffee or not have one. According to the many universe theory/multiple realities/time streams (pick whichever name you like best) in one reality you have the coffee and in one you don't. The universe has, for all intents and purposes, split into two separate ones- in one time stream you have the coffee and in the other you don't. Now the outcome of not having a coffee might be exceedingly minor- but say for example that later that day you felt a bit more tired than usual and lost your temper, yelling at a co-worker. He in turn gets annoyed and maybe loses his temper driving home. And so on and so on. A tiny choice initially but, as in chaos theory, a small input difference into a complex system can have a vast effect later down the line. So if we consider a time traveller coming back in time and the effect it would have we can use this model- in one "stream" he comes back and prevents his parents getting together to conceive him. It seems to be a paradox as his parents did get together and he does exist- but we can use the different streams model to explain this- in one stream he came back and altered the past while in another he didn't- that would be the past he knows, his own personal history. Big problem with time travel if such a theory were correct would be in travelling through the streams- it might seem like a good idea to go back and tamper with time but it would be reassuring to know that you could return to your "own" present at the end of the day.
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