Posted on 06/17/2005 12:06:22 PM PDT by LibWhacker
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.
Paradox explained
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.
For most of us, the former option might seem most likely, but Einstein's general theory of relativity leads some physicists to suspect the latter.
According to Einstein, space-time can curve back on itself, theoretically allowing travellers to double back and meet younger versions of themselves.
And now a team of physicists from the US and Austria says this situation can only be the case if there are physical constraints acting to protect the present from changes in the past.
Weird laws
The researchers say these constraints exist because of the weird laws of quantum mechanics even though, traditionally, they don't account for a backwards movement in time.
Quantum behaviour is governed by probabilities. Before something has actually been observed, there are a number of possibilities regarding its state. But once its state has been measured those possibilities shrink to one - uncertainty is eliminated.
So, if you know the present, you cannot change it. If, for example, you know your father is alive today, the laws of the quantum universe state that there is no possibility of him being killed in the past.
It is as if, in some strange way, the present takes account of all the possible routes back into the past and, because your father is certainly alive, none of the routes back can possibly lead to his death.
"Quantum mechanics distinguishes between something that might happen and something that did happen," Professor Dan Greenberger, of the City University of New York, US, told the BBC News website.
"If we don't know your father is alive right now - if there is only a 90% chance that he is alive right now, then there is a chance that you can go back and kill him.
"But if you know he is alive, there is no chance you can kill him."
In other words, even if you take a trip back in time with the specific intention of killing your father, so long as you know he is happily sitting in his chair when you leave him in the present, you can be sure that something will prevent you from murdering him in the past. It is as if it has already happened.
"You go back to kill your father, but you'd arrive after he'd left the room, you wouldn't find him, or you'd change your mind," said Professor Greenberger.
"You wouldn't be able to kill him because the very fact that he is alive today is going to conspire against you so that you'll never end up taking that path leads you to killing him."
Tampering with the past leads to disaster! Be warned.
Can the people in the past travel to the future?
I read that story. It was drawn up like a comic book. Wonderful.
I suspect our entire notion of time is an illusion.
Actually, Kurt Godel, a brilliant logician with a philosophical bent, in addition to producing a closed time-loop interpretation of relativity, provided an upgraded and stronger version of the famous Ontological Proof for the existence of God. Kurt Godel's Ontological Proof
That is precisely the argument of Kurt Godel. See A World Without Time.
Everyone's heard of Paul Allen, Bill Gates, and Equality 7-2521... haven't they?
ah.. but once you travel into the future, can you return? :-)
"people don't suddenly fade into the ether "
Unless they're visiting Aruba...
[Inhale...] 'ere.
Thanks for the link.
First define "god."
Then one can attempt to prove whether what you have defined exists or not.
FWIW, wasn't there an episode that dealt with this issue in Star Trek: Next Generation?
"Looks like "some one" has been watching too much science fiction"- Church Lady C;-)~
"In my purely amateurish understanding of how this theory works, you have a nearly limitless set of options to choose from this moment forward - but once you've made that choice, there's no going back."
But, according to the subject of this thread, there just might be the possibility of going back. And, in the act of "going back," you've altered an apparently limitless set of options going forward, effectively limiting these options to only those leading to the outcome of going back. Predestination of a sort. Try to visualise this, not from the perspective of the "now" being left, but from the perspective of the "now" destination, which would not be in the past to those inhabiting that "now."
Not yet enough coffee to enable me to focus entirely on that, but I get the gist of your statement. Fascinating to ponder.
Gibson's doing F451? I remember the old version - it wasn't bad.
"In order for this to be true, there can be no free will."
Careful there, you're going to be called all sorts of derogatory names. In a highly intelligent and scientific manner, of course.
No.
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