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#245457 - 03/17/08 06:37 AM
Re: John Titor Faxes to art bell
[Re: Darby]
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freshidea
Member
Registered: 03/09/08
Posts: 113
Loc: milky way
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I will see if i can find this physicist, later. Here is an interesting yet old article that reads a bit windedly about the time situation:
Colorado Education
Quantum Time Travel
Victor J. Stenger
Reality Check in Skeptical Briefs June 2000
Since H.G. Wells' Time Machine (1895), time travel has been a recurring theme in fiction. Michael Crichton's Timeline is the latest offering, and given this author's track record, we can expect a blockbuster film to follow in a year or so. All his books read like movie scripts, and this one is no exception.
Time travel has also received considerable attention in serious scientific literature, as in Kip Thorne's 1994 bestseller Black Holes & Time Warps and in several articles in Physical Review and other respectable journals. Since spacetime is curved in general relativity, we can imagine a "wormhole" looping back to join the time axis at an earlier time, just like a walk around the block. However, Thorne did not make it seem very promising that humans, or any information-carrying system, would ever be able to travel though such a wormhole, a quantum fluctuations would likely destroy the system. The best he could do was leave the door open slightly by saying that we still lacked a quantum theory of gravity and so anything is still possible.
None of the laws of fundamental physics, classical or quantum, forbid travel back in time. In fact they do not even distinguish backward from forward. Time irreversibility is implied by the second law of thermodynamics, but as Boltzmann showed over a century ago, this is a statistical effect of the large amount of randomness present in the many body systems that constitute macroscopic objects. Nothing prevents a broken glass from reassembling by chance; it is just very unlikely.
On the quantum scale, however, reverse causality actually seems to be taking place. Experimental results depend on future conditions as well as the past. Indeed, many of the so-called paradoxes of quantum mechanics result when people insist on interpreting quantum events in terms of the one-way time of their common experience. When that restriction is relaxed, most of the paradoxes disappear.
Physicists have known for some time that time symmetry provides a ready solution to a great number of the puzzles of quantum mechanics. John Bell, for example, recognized the possibility but rejected it. He, and many others, resisted the time symmetric solution because of another paradox that then raises its head: Time travel would appear to allow you to go back in time and kill your grandfather when he was a child, thereby eliminating the possibility of your existence. This is the famous grandfather paradox. However, it is not commonly known, even among physicists, that the time-travel paradox does not occur for pure quantum states.
Let me explain this metaphorically. Imagine yourself to be the time traveler and your grandfather to be represented by a pure quantum state vector or wave function. Pure quantum states are characterized by their "entanglement" with each other. Thus your grandfather's state is entangled with the states of all the other men his age. Remember, this is a metaphor for pure quantum states, so all these men are indistinguishable--like electrons or photons.
Now picture yourself going back and trying to find your grandfather and kill him. All the men of his age would be indistinguishable and you would not know who to shoot! The best you can do was shoot one at random. To accomplish this, you do not have to be from the future. Thus no causal paradox occurs. You cannot use information from the future to make the hit.
You might try to identify your grandfather among all these identical men. But this would be equivalent to making a measurement, or observation, which reduces (or "collapses") the entangled state. You could of course do this, but again it would not require any information from the future and so nothing paradoxical takes place.
On the hand, if your grandfather is not a pure (entangled) quantum state, then you could recognize and kill him. This is the situation in familiar, macroscopic life; grandfathers and most other objects are composed of many elementary particles that exist in incoherent, mixed states rather than the coherent superpositions that constitute pure quantum systems. Thus the causal paradox seems to rule out the possibility of human time travel, consistent with Thorne's observation that any information will be destroyed traveling through a worm hole.
In the clever Back to the Future films, the young time traveler Marty (played by Michael J. Fox) had to take certain actions to make sure his father became his father. He had to watch over him, protect him from bullies, and make sure that he dated Marty's future mother (who found Marty strangely attractive). The time travel paradox was solved in these films by having parallel universes. Crichton also utilizes this expedient in Timeline, but Doc in Back to the Future II explains it better.
Unless parallel universes exist, time travel appears to be impossible in the classical world of mixed states while remaining logically possible in the quantum world of pure, entangled states. Furthermore, time travel seems to be taking place deep down in the recesses of our atoms and nuclei. With quantum time travel, we can see how a body can be two or more places at once. It simply starts "here and now," goes back in time and then reappears "there and now." This is fundamentally no more absurd than being at the same place at two or more times, like my sitting in front of the computer terminal, day after day, year after year, decade after decade.
This article is based on the author's latest book: Timeless Reality: Symmetry, Simplicity, and Multiple Universes, to be published this Fall by Prometheus Books.
-----------------------------------
amazing what people will spend thousands of dollars for, there is a force field and it will reach out and grab ya. Is it a singular entity/person or the whole manifesting for the shared unit of us? This is yet to unfold or shall we say has yet to materialize. Being in two places at one time is the simplest form of expression one can grasp when openning up to the possibilities that lay before us without scientific research. That is, there is no hard data for me to share.... Just life experience and what is that worth these days = exactly 0$.
_________________________
When in doubt, accept things as they R
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#245459 - 03/18/08 12:41 AM
Re: John Titor Faxes to art bell
[Re: Darby]
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Darby
Administrator
Senior Investigator
Registered: 05/15/01
Posts: 4594
Loc: Santa Barbara, CA
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freshidea,
Just a follow-up to the Grandfather Paradox:
This is a rather interesting paradox that has far more consequences that simply preventing the birth of the time traveler.
Let's do a thought experiment and have our time traveler first go back in time 50 years - the time just before gramps meets grandma. From there he travels one year at a time into the future for 150 years. At each stop s/he takes a complete census of the entire planet logging the names along with a short family bio every human being (hey - it's a thought experiment involving time travel...he can do this.  )
Our hero now has a complete log of the names, spouses and children of every human on the planet for 150 years starting just before his grandparents got together.
Then he travels back and kills gramps just before he meets gramdma. He then repeats his 150 year journey, one year at a time, taking the census once again. After he's made his first 50 stops - arriving at his "present" - he disovers that there's not a single person on earth that was there when he took the original census. Why is that?
When he killed gramps, grandma married "Fred". But in the original census "Fred" didn't marry grandma - he married "Sue". Sue in turn, because she didn't marry Fred married "someone else". Now, instead of the original three sets of spouses and their original three sets of children out hero no longer detects the original children. Instead he detects three entirely different sets of children. This "one step off-set" of new spouses quickly casacdes across the planet. After 50 years it is unlikely that a single child was born anywhere on Earth that he originally detected in his census. If he carries his census through the entire 150 years what little probability there was at 50 years of finding a common person in both census' all but vanishes.
The kicker here is that he didn't have to kill grandpa for this to occur. Just being there in the area could cause it to occur. Maybe he wanted to see his grandparents meet for the first time. He knows when and where they meet. It's on a street corner - he's walking around the corner, distracted as he reads something in his hand and he bumps into her as she walks the other way around the corner. Bump! Love at first sight. The rest is history. But this go-round, as he stands watching for them, a passer-by has to change course to keep from bumping into him and that change of course results in grandma changing her course. They don't go bump in the night...they never meet. See above for the possible outcome. Same-same.
Take in another step. Grandmother is a time travel BBS fan. Our hero doesn't know this.
When he travels back after taking the census he arrives a few days before the "event", he's a bit bored and decides to post a thread on a TT forum. He believes that this will have little or no effect on history because no one will actually believe him and he neither identifies finself nor does he say anything about why he's there. There are no hints that either grandparent could find useful in discovering that he is their future grandson.
He, unfortunately, has decided to post on grandma's favorite TT forum. It's now the night that his grandparents are supposed to meet. He goes out to his spot to wait for them. Grandma is set for her evening walk. As is her habit, she logs onto the TT site for a quick "look-see" before stepping out. She starts reading our hero's thread and she's hooked. Instead of going for the walk at the "right" time she finds our hero's posts somewhat fascinating and stays home an extra 20 minutes to read his thread. No meeting, no marriage, same cascading result.
In fact this scenario can be generalized. A time traveler can have exactly the same effect on history no matter who changes their plans to read his posts. If in his original census a member was supposed to meet a particular future spouse on a particular date and time but instead decided to read the posts it still comes out the same as above. No meeting, no marriage, same scascading result.
I guess that the only good thing is that no one will know about it or be concerned about it except the orphaned time traveler.
_________________________
E. W. "Darby" Darbyshire
Administrator - Anomalies.net
DarbyII@COX.net
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#245479 - 03/19/08 03:29 PM
Re: John Titor Faxes to art bell
[Re: freshidea]
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Darby
Administrator
Senior Investigator
Registered: 05/15/01
Posts: 4594
Loc: Santa Barbara, CA
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freshidea,
In some regards time travel can be seen as a rather damaging endeavor, as I've referenced above. But, at least based on first principles, there's nothing in special relativity or general relativity that absolutely precludes time travel into the past. If you dig farther into the theories there are some daunting obsticles to overcome - some of which may not be subject to being overcome.
Traveling at superluminal velocity, for instance, doesn't necessarily mean that your clock (from an inertial oberserver's POV) starts running backwards. Yes, as you approach the speed of light your clock does slow down from that POV and it should stop at the speed of light. But it's a bit nieve to conclude that as you pass the speed of light that it starts going in the opposite direction. If you look at the Lorentz Transformation
Gamma = Sqrt (1- v^2/c^2)
it doesn't say that Gamma, the Lorentz Factor, becomes negative. If v > c in the above equation you have to take the squareroot of a negative number because the equation becomes:
Sqrt (1 - (>1)
which is a negative number. The squareroot of that number is imaginery (Sqrt -1 = i). I have no idea, really, how to interpret what it means to travel through imaginery time.
_________________________
E. W. "Darby" Darbyshire
Administrator - Anomalies.net
DarbyII@COX.net
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