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."
If I could go back in time, I would sneak over to a young Catherine Bell's house and whipser subliminal messages in her ear while she's sleeping abour what a catch that Reagan_Fanatic is. *sigh*
"How do we know that killing them as infants would not lead to even worse horrors arising in their place?"
Isn't there an episode of the newer version of "The Outer Limits" that plays around with just this notion? The infant Hitler's nanny is afflicted with visions of the evils that this infant will inflict upon the world, and throws him into a canal? I do remember the show, maybe it was a different series, but somebody's done it.
"If I could go back in time, I would sneak over to a young Catherine Bell's house and whipser subliminal messages in her ear while she's sleeping abour what a catch that Reagan_Fanatic is. *sigh*"
LOL. That you're not with her now proves something, not sure what, but something.
Ah, but you missed the point! Some time travelers already have taken care of evil tyrants who would have been worse that those three, but the Universe will not be denied, and Stalin, Mao, Pol Pot, and Hitler rose to take the place of those who were removed from history. Didn't you see the Outer Limits episode where a time traveler went back to kill Hitler as an infant, but it turned out someone switched babies in the end?
Maybe you could go back and invest in Walmart stock, but put it in a trust that you cannot get to until AFTER you left the present....
Or something like that.
susie
And whose to say that something even worse may not have resulted?
"Didn't you see the Outer Limits episode where a time traveler went back to kill Hitler as an infant, but it turned out someone switched babies in the end?"
Oh, I forgot about the surprise ending. More subliminal predestination to drive ideologocial pseudoscientists batty.
I guess the point is that anything your future self would do do "change" the past would already be reflected in the past as we know it. It's very deterministic.
If you had the ability to travel into the past and make yourself rich?(by buying stocks, betting on horse races, etc.), then you would be rich today. Because the past already happened. That you are not rich today is evidence that you did not do such a thing and that you never will.
SD
"ideologocial"
Good god, I'm going to have to resort to spell check... that would be "ideological."
"That you are not rich today is evidence that you did not do such a thing and that you never will."
But that just so UNFAIR.
I tend to look at time as being like a black hole. When you are born, you start your journey towards the singularity which is death. You cannot escape from the pull of the singularity to return anywhere in the past either in your own lifetime much less before your lifetime. Our own individual existence creates our own personal warp of space time of which there is no possible way to change outside of the control of the will of the creator.
Time travel became impossible on May23,2008 after
the democrat House and Senate supported a bill signed
into law by President H.Clinton that declared time travel
to be discriminatory to women, minorities, and the disabled.
Interestingly enough, Islamics were exempt from the provisions of the bill due to their being totally IN the past.
Well, that seems to throw a wrench in what happen
with the Dr. and Rose in Father's Day.
"The only way this concept holds any water is if you are not visible"
Invisibility is technically possible with nanoscale "LED" like devices, an entire suit of them, reflecting the light from directly behind at every angle. There is some amount of research going on in this direction. So, invisibility alone would be insufficient to prevent some sort of minor change. I think I agree with SoothingDave, that the mere fact that you are, you exist, says that anything that happened in the past, happened. Which opens the door to a fixed future, something that infuriates some, for whatever reason.
Hummmmmmmmmmmmm!
The how did Bones save Edith and allow the nazis to win WW2 before Kirk allowed her to get run over by that beer truck?
Gad! Time travel sure is confusing, ain't it?
She's dead, Jim!!!!!!
Of course the concept is flawed. Time travel is inherently paradoxical. "Bill and Ted's Excellent Adventure" showed that. We need not even bother going back into time to make ourselves rich, we just have to resolve to do it in the future and our present instantly changes. Hence, when Bill and Ted needed Ted's dad's keys, they just appeared. One commented "We have to make sure we remember to go back and steal them" and the other responds "They're here, so we must have."
It's all a pile of illogic and paradox.
SD
"Time travel is inherently paradoxical."
Well, the subject of this thread could very well indicate that, while time travel may appear paradoxical, there is some possibility that quantum mechanics will allow it. But, should this actually be possible, that there is no possibility of altering your present, or "the" present, by doing so.
So it may be technically possible, extremely expensive and utterly useless. Sounds like a gov't program.
SD
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