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Time Travel

  1. Apr 27, 2005 #1
    I'm interested in knowing anything about time travel into the past. If anyone has any insight about this it would be helpful.
     
  2. jcsd
  3. Apr 27, 2005 #2
    I did some research on it a while back because i got interested in John Titor's rhetoric. From what my memory has now, you would have 2 Kerr black holes which would interact with eachother in such a way as to form a singularity.

    Although, they are doing some research in Rhode island and at cern with super miniature black holes created from smashing gold together in particle accelerators. they said the resulting plasma displayed black hole type properties consuming more energy than it released or something to that effect.

    But i dont see how a black hole could get you to another time, i do not see a relationship.
     
  4. Apr 27, 2005 #3
    Kip Thorne's book Black Holes and Time Warps is an excellent layman's resource on this topic.
     
  5. Apr 27, 2005 #4

    JesseM

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    Kerr black holes already are singularities. Anyway, Titor's explanation was basically just technobabble that doesn't make any sense in terms of physics, despite the inclusion of a few buzzwords like "Kerr black hole" that actually are used in physics.
     
  6. Apr 27, 2005 #5

    DrChinese

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    One of the most practical issues with respect to "sci-fi" time travel...

    Where would you travel to?

    Not a simple question at all. Earth rotates, as does the solar system and the Milky Way. So we do not move even close to a straight line. Since we have no idea how fast we are moving through space, even in a relative fashion, it is impossible to estimate where we where an hour ago. So if you went back in time and expected to be on Earth, you better make provision to instead end up in outer space somewhere.
     
  7. Apr 27, 2005 #6
    Do you understand what "relative" means?

    But I agree that this is an oft-unaddressed problem with time travel to arbitrary times. It could be argued that the time machine follows an inertial path through space-time, but I think that this would mean that Earth-based time machines would end up in the centre of the planet!

    I think it is more practical (it's funny to talk about practicality and time travel in the same sentence!) to imagine a time machine which requires a device at both ends of the journey. However, this would disallow travel to times before the device was built, which would upset the plot devices of a few SF authors.

    Wormhole time travel as described in theory by Kip Thorne involves travelling between two ends of a spacetime "wormhole". It doesn't allow travel to an arbitrary time or place - the other end of the wormhole must be moved to the location you wish to go, and the time difference is fixed unless altered by time dilation.
     
  8. Apr 27, 2005 #7

    JesseM

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    To even say that there is a point in space now that uniquely coincides with "the position of the earth an hour ago", regardless of whether we can know where that point is or not, is to assume the existence of absolute space, in contradiction with relativity. And as PeteSF says, you seem to be misunderstanding what "a relative fashion" would mean, it is certainly possible to say how far the earth has moved relative to some inertial observer.
     
    Last edited: Apr 27, 2005
  9. Apr 27, 2005 #8
    Does anyone know of any websites with information on the possibilities of time travel in to the past?
     
  10. Apr 27, 2005 #9

    JesseM

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  11. Apr 27, 2005 #10

    DrChinese

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    Just the opposite, I don't mean to imply there is or is not an absolute reference frame. What I said (or meant) was there is no relative position for the Earth to use as an anchor. Presumably, the place I would want to go back to - were I going back in time - would be the "same" place I am now. I certainly dispute the idea there are observers out there who could assist in this process as they will be just as confused. None of them would be sitting in a preferred position to assist us. Because of the various orbits we are a part of, I doubt we could ever obtain enough information to determine our effective velocity. It is very dynamic.
     
  12. Apr 28, 2005 #11

    JesseM

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    The "same" place relative to some physical landmark like the earth, or the "same" place in some absolute sense?
    Assist in what process? Other observers couldn't find a point that was objectively the same place in a frame-invariant way, but they could certainly find the point that was the same place relative to their own frame--normally when people talk about measuring positions or speeds "in a relative fashion", they mean measuring them relative to a particular observer's rest frame. For example, if you are driving at 50 mph down the road in my rest frame, then in my frame the point you were an hour ago is 50 miles behind your current position, while in your frame the point you were an hour ago is exactly the same as your current position.
    What does "effective velocity" mean? If you think there is some absolute, frame-invariant concept of our "effective velocity", then you are saying the theory of relativity is wrong. It's not just a concept of us not being able to obtain enough information to determine it, it's that relativity says that in principle their can be no notion of a velocity that does not depend on an arbitrary choice of reference frame (except for the velocity of light, which is the same in all reference frames).
     
    Last edited: Apr 28, 2005
  13. Apr 28, 2005 #12
    Forgive the lacadasical usage of singularity, but it was a "relationship" of some sort between two kerr black holes. I found the paper i wrote about it last semester.

    Also looking into CERN and the institute at rhode island (forget the name) would yield some interesting studies that may take to your liking.
     

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  14. Apr 28, 2005 #13

    JesseM

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    In your paper you write:
    Who are these "some" who believe that the merging of black holes would be the basis for time travel? I have never heard any physicists suggesting such a thing, only John Titor's technobabble.
    What studies? Is the institute in Rhode Island Brown University (where I went to college, coincidentally)? Note that physicists had suggested the possibility of micro-black holes being created in supercollider collisions well before John Titor posted his story, he was no doubt cribbing the idea from something he had read.
     
  15. Apr 28, 2005 #14

    DrChinese

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    I am not arguing the validity of relativity, and I think you are reversing my meaning. If someone went back in time 10 years, without traversing space, they would end up far away from Earth. If they went back 1000 years, they would be even farther away.

    If you COULD measure the begin position and the end position of Earth, you MIGHT think you had determined the Earth's "effective" velocity - in other words the direction and rate the Earth is moving. You might use that to extrapolate to points even further in the past. But that would be false, because that value will change with each begin point and end point. And no observer can tell you any information that will change this. Because there is no absolute reference frame, there is no way to determine anything other than movement relative to some observer who is of course also moving. (And no one is moving in anything close to a "straight" line anyway, due to various orbits.)

    So as I said, if you traveled to the past, where would you go back to? Empty space probably. :smile: And even if you did pop out near Earth, what direction would you be heading in? And how fast? If you were to go back in time, and didn't match velocity with the Earth, it might be a bit of a problem for you. :smile:

    So I am not saying there is an absolute space coordinate system. But presumably practical time travel would need to adjust for a few extra critical factors that I don't believe you could ever learn.
     
  16. Apr 28, 2005 #15

    JesseM

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    Your phrasing is still implicitly assuming absolute space--what does "without traversing space" mean? Do you agree that in the example where you are driving down the road at 50 mph in my frame, then in my frame the "same point in space" that you are now is 50 miles ahead of the position your car was an hour ago? Do you agree that in your own rest frame, the "same point in space" that you are now was still inside the car an hour ago? So if you're in the car and you send your body back in time an hour "without traversing space", will you end up still inside the car, or will you end up 50 miles in front of the car? If you think there is a single true answer to the question of where you would end up if you travelled in time "without traversing space", then you are assuming there is a preferred reference frame. After all, in some inertial frame, the position coordinates of the earth 10 years ago are exactly the same as the position coordinates of the earth today--why is that frame any less valid than any other?
    Why "probably"? The question is just undefined, since there is no "natural" place that the laws of physics say you should expect to end up. The whole idea of instantaneously disappearing from one point in spacetime and reappearing in another has no basis in any known theory of physics--instead, physicists who speculate about the real possibility of time travel are thinking of something more like a wormhole, where you travel continuously through a weirdly-curved region of spacetime and end up inside your past light cone.
     
    Last edited: Apr 28, 2005
  17. Apr 28, 2005 #16
    If it wasnt a referenced link, i dont remember where it came from. I mentioned a computer graphic representation of the merging of two, it was these people who speculated on the possibility.
     
  18. May 3, 2005 #17

    loz

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    regarding time travel into the past

    Just read your post asking about time travel into the past so I thought I'd give you some info you may find useful. Time travel itself is relatively easy with the use of a tardis but since these are in short supply there is a more difficult way to accomplish backward travel in time.
    Imagine the universe exploding and spiralling about itself, each particle or conglomeration of matter travelling at slightly different velocities. After countless eons this difference means that certain areas are much "older" than others. In effect these "older" particles exist in a universe which was created relatively longer ago than the "younger" particles.
    Now instead of particles lets say stars and planets .Imagine a star system with a considerably greater velocity than our own comes around in a massive orbit allowing you to hitch a ride as it passes if you zoom into space in a straight line directly upwards. As you are caught in its gravitational field you manage to land on a planet orbiting one of its outermost stars. You would then be in a much younger universe (relatively speaking) than the one you had just left due to the time dilation effect of the velocity. Hitch a ride on a fast enough particle and you theoretically go to a very young universe(relatively). Of course the converse is true and you could hitch a ride on a slower planet and end up in a relatively older universe.
    I think maybe you want travel in spacetime but since the timewars between the daleks and the timelords that technology seems to have been lost forever. Since I dont know your level of expertise or age i will give a very easy way to work out time dilation which really emphasises it's simplicity.
    Take 2 pieces of square card and for the purpose of this example mark one with a 5X5 grid. If you were to travel at 60% the speed of light that would be 3/5 of the cards length (3/5 = 60%/100%) so cut out a square 3X3 from the cards corner. Now cut up the remaining 16 squares (5X5 - 3X3) and form a new square with them. The resulting square would be 4X4 so at 60% the speed of light one second to you would actually last 5/4 (oldside/newside) seconds or 1.25 seconds to the control(given that the observer is travelling at negligible speed). Multiple cards and velocities can be used and the sides measured against each other for relative time. The actual equation is as follows

    (squareroot(Csquared - Vsquared))/C

    hope you find this of help and if so drop me next weeks winning lottery numbers.
     
  19. May 3, 2005 #18

    chroot

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    loz,

    You have absolutely no idea what you're talking about. Let me welcome you by pointing out that personal theories are not welcome here. Virtually everything you've said is either gibberish, or simply wrong. Warning issued.

    - Warren
     
  20. May 3, 2005 #19
    Not to put what loz said on par with Einstein's work, or to say i agree with it :rolleyes: , but much of physics was once someone's personal theory.

    "curved space...such nonsense...how could space possibly be curved...the man belongs in a nuthouse."

    Quote of a naysayer from Einstein's Dream
     
  21. May 3, 2005 #20

    loz

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    hello this is not a personal theory it is derived from michelson morley or einsteins time dilation equation


    the explanation as to relative age is infact true as countless experiments show so that chronological age can differ from actual age . I did use artistic license with regard to the explanation and used the star system as an example to demonstrate the idea but overall the argument is sound. A photon emitted in the bigbang would if it continued till now would not have aged and so could be said to be zero hours from creation. Or did I explain it in such a way as to make you believe that i was suggesting you could actually travel back in time rather than visiting an object with a different chronological perspective?
     
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