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Time travel

  1. May 24, 2009 #1
    I was just watching Ian Morison on Fora.tv about Time, in chapter 14 he talks about wormholes and time travel. You can see the time travel part here:

    http://fora.tv/2009/03/19/Ian_Morison_Its_About_Time#Journeying_Through_Space_and_Time_in_a_Wormhole

    Anyhow, in short he mentions opening a wormhole from his house to his space ship before he starts traveling to Andromeda so his wife can watch him. He flies to Andromeda and back in 8 hours (close to the speed of light) gets back and 5 million years has passed. So he steps through the wormhole to go back home 5 million years earlier.

    But I was wondering, if it would be possible to open such a wormhole wouldn't the wife just see his time slow down to almost a halt when see looks through it at him? And wouldn't he just see his wife's side age 5 million years during his trip?
     
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  3. May 24, 2009 #2

    Dex

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    i think that time travel is impossible. you may ask why?
    1st if we suppose that general relativity is correct, then tahion - particle which is faster then light, should travel in time.
    2nd if we see quntum physics, then light should not be affected by gravitation.

    i think both of these theories need to be developed more.

    and again time travel - determionism vs Heinzenbergs probability .
    If we see ndetermionims then all "time travels" have already been, and the effecte they had made is already "seen"
    IF we see probability then who knows - maybe we`ll se time traveler tomorrow, if it`s possible
     
  4. May 25, 2009 #3

    George Jones

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    These are things that would be seen if Morison made the trip in a standard way without wormholes, and they can be seen also in the wormhole case by looking outside the wormhole.

    The mouth of the wormhole in the house and the mouth wormhole in the ship are identified; they represent the same events in spacetime. If his wife looks through the wormhole, she sees Morrison age at exactly the same rate as she ages. When Morison gets back he has a choice. He can step outside the ship without using the wormhole, or he can use the wormhole to exit directly into his living room. In the first case, his house will have aged by 5 million years; in the case his house will have aged by 8 hours, just as he has.
     
  5. May 29, 2009 #4
    I think you are correct. First of all the Andromeda you see in the sky is not the andromeda of today but andromeda as it was 2.5 Million years ago. If you get there in 4 hrs. It won't be what you expect and when you get back, what you see in the sky is not what you left. I have a fanciful critique of time travel dealing with this issue:

    I look up and I see a “new” supernova light up the night sky. I decide to take a closer look. I determine it is in the Andromeda Galaxy some 2.5M light years away. Of course I have developed a method for superluminal travel. It is based on entanglement. I “ride” a collapsing wave front of two entangled particles one of which is anchored in my galaxy and the other of which is in the Andromeda Galaxy and in a matter of seconds I find myself 2.5M light years from earth in the Andromeda Galaxy in the neighborhood of the Supernova I just saw. Only things look quite normal except for a slightly higher density of non-luminous star debris. I realize of course that the supernova I witnessed on earth happened 2.5 million years ago, so long ago that it precedes all Andromeda’s recorded history which only goes back 1 Million years to the dawn of their civilization. My hopes that superluminal velocities will result in time reversal are immediately dashed. The Andromedans I meet are not even marginally interested in the pictures I took of this spectacular celestial event just yesterday. They are however quite excited when I explain where I am from. As far as they are concerned there are no signs of intelligent life in any of the spiral arms of the Milky Way galaxy, though there are some promising apelike creatures visible in the southern hemisphere of a watery blue-green planet orbiting a rather ordinary magnitude 4 third generation T Tauri Population I yellow dwarf about 26K light years from galactic center. However, by all estimates these creatures won’t be walking upright for another 2M years. And wow, less than five hundred thousand years later, here I am, one of their mostly hairless descendents, star hopping all over the local galactic cluster. That is really something. What about time hopping, I ask? They laugh. Time travel hasn’t even been a fictional topic in Andromeda literature, which is universally acclaimed for its use of harmonic super-positions of 10-dimensional superstring resonance patterns, for more than 1500 Centuries.

    They explain: the confusion about time travel arises when one treats 4-dimensional space time as though time were a 4th perpendicular spatial dimension. It is not. According to Relativity Theory, the time mark associated with each point in space-time is always relative to the observer. From his NOW, space time spreads out around him into the past with the time coordinate dependent on the time it takes light to reach him from that point. We never see the universe as it is now. In fact, the entire universe in the absolute state of NOW is not a meaningful statement, since, post-Relativity, there is no absolute time, i.e. no universal now. But the earth does exist now as it was and always will. To see the earth as it was 200 years ago I have to star hop 200 light years distant. Then my NOW and its 200 year old NOW are the same and I just have to peep through my portable, tunneling quantum telescope to see everything in exquisite detail exactly as it was. In this since the past does exist forever, inviolable, pristine. What remains of the past, which is itself an ambiguous term, is a visual record advancing though space-time at the speed of light and of course the universe of today. (“Yesterday is gone forever; all that remains of it is today. Now, make the most of it!” is in fact the cumbersome name of a well known Andromedan motivational seminar.)

    I receive notice that the next entangled transport back to my home galaxy collapses in a few minutes. I thank the Andromedans but question their certainty on the matter of time travel. It’s more like uncertainty they answer. The closer I wish to examine the then of some long past there-then, the further from its there I have to be. The closer I wish to examine its there, the further from its then I have to be, i.e. now. But I can’t be both in its there and then in my here and now. Put another way: just as you can’t be in two places at the same time, you can’t be in two times at the place. Anyway, my new extra-galactic friends conclude cryptically, as regards what they call my adolescent rebellious and guilt-plagued fantasies of tinkering with the past to get it right, that if I think it through, I’ll quickly realize: plus ca change, plus c’est le meme chose.
     
  6. May 29, 2009 #5

    George Jones

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    In the video, Morrison has presented correctly the wormhole results contained in:

    1) the paper "Wormholes, Time Machines, and the Weak Energy Condition" (Physical Review Letters, Volume 61, Number 13) by Morris, Thorne, and Yurtsever;

    2) the research monograph "Lorentian Wormholes" by Matt Visser.
    I think that professional relativists like Kip Thorne and Matt Visser know the difference between timelike and spacelike dimensions. :biggrin:

    For my own (unreadable) take on this, see

    http://groups.google.ca/group/sci.physics.research/msg/ca7fd4ed9d282afb?hl=en&dmode=source.
     
  7. May 29, 2009 #6
    A wormhole wouldn't actually let you travel back in time; it would just allow you to beat your own image on the way home and avoid the unfortunate time issues in travelling at relativistic speeds. Btw, Andromeda is 15 quadrillion light years away, not 8 hrs.
     
  8. May 30, 2009 #7

    George Jones

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    More precisely, a wormhole time machine will not allow you to travel back in time to time before the wormhole time machine formed.
    :confused::confused:
     
  9. May 30, 2009 #8
    Not unreadable at all, I can read every word! It's just with all the math at first glance it's a bit incomprehensible is all, but perfectly readable. :smile: To go through it will take me more time. For the record, how do I access Physical Review Letters? Is there a separate subscription or do I need to subscribe to Physical Reviews? I am a physician by training (though I got my BS in P. Chem at university of chicago, enrico fermi institute in '67, 42 yrs ago--sigh--) and can access medical data bases like Medlar, but not all science data bases. At this time I would like broaden my horizons a bit and get back to some hard science. It's time, so to speak, to try swimming a few laps in the deep end.

    In any case, for now, let's try it with words. In your andromeda example: I hop into my trusty aafal (almost as fast as light) starship and crank the velocity to the point that the 2.5 M LY trip to andromeda takes 4 hrs on my watch, so I make the 5M LY round trip in 8 hrs. Under "normal" relativistic conditions, the home I return to is 5M years older, in actual fact there may not even be a home to come back to since there is a rumor that less than 10,000 years after I leave, standard earth time, the planet earth is razed to make room for a full service assisted-living condominium for the aging population of Betelgeuse 4 named New Methusela, but I digress. To solve this problem it seems I have opened a "lorentian (?) wormhole" between my ship and the couch in my living room. From your description, it appears that each of the wormhole's 2 portals exist in lock step with the space time coordinates in which it was opened and that the time it takes to enter one portal and exit the other, transit the wormhole, is independent of any ensuing relative motion of the portals during its lifetime but remains a function only of the original physical distance between the two. If not consider the following. I shlep my portal a distance of 5M light years to Andromeda and back, yet I can just hop through on my return and be back in my living room in time for my afternoon tea with my wife. However, when I look outside my star ship on my return 5M yrs later, I see nothing resembling my home which was destroyed ages ago even without the interference of extraterrestrial construction companies. Even if I actually return to the exact coordinates of my garage on earth 5M years later, this point is no longer a short hop to my living room because the earth is not where it was at the start of the trip. Ignoring both the earth's solar and sun's galactic orbits, the galaxy itself has drifted some 10,000 light years towards the constellation Hydra in those 5M yrs. So the worm hole is now stretched at least 10K LY. Can I just step through to my living room where my wife is nervously wringing her hands as she waits for the answer? If, on the other hand I return to the point in space where the earth actually was was when I embarked, assuming I can locate that point since all reference points have also shifted, I find myself either drifting in interstellar space or worse find myself in the vicinity if not inside, some large stellar object, the gravitational effect of which might just "darn" --close-- my wormhole, possibly with me in it thereby making my subsequent appearance on "Discovery TV" difficult. Poor me! :frown: If the wormhole is not destroyed there is a fair chance it might be distorted to the point transit is difficult if not impossible. All of this seems a bit risky. How are these problems resolved?

    I'm sure this objection and others like it are easily answered. If you would be so kind as to take the time, it would help me further understand the phenomenon you are speaking about. Meanwhile I will attempt to work through the math on your website. I didn't see anything that was beyond my pay grade, it's just that the most complicated math I do these days, other than trying to understand the federal deficit is computing half-lives of various medications in the body during conditions of compromised liver function or kidney excretion, which thankfully do not as yet contain lorentian transformations :smile: so I am a bit rusty. All the best, David Katzin.
     
    Last edited: May 30, 2009
  10. May 30, 2009 #9
    Hi again? BTW is travel through the wormhole symmetric? Does his wife have the option of joining professor Morrison 5M years in the future? Is the wormhole good for more than a single transit? In other words if she joins him can they both get back? In the original case, can Professor M take a quick walk around the neighborhood before re-entering his ship and using the wormhole to get home 8 hrs and 15 minutes after he left?
     
  11. Jun 1, 2009 #10

    George Jones

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    Sorry, I haven't taken the time to read your previous post; I hope to soon.

    The wormhole mouths are accessible to anyone who can get to them by normal means:

    Professor M's wife could go 5 million year into future, and then come back to (almost) now;

    Professor M could take a quick walk (or longer and farther) around the neighborhood before re-entering his ship and using the wormhole to get home 8 hrs and 15 minutes or (somewhat later) after he left;

    Joe Smith, who will be born almost 5 million years in the future in what is now Britain, could find the wormhole mouth, travel in time back to now, place a timer-operated nuclear weapon somewhere outside the wormhole, get back in the wormhole, and safely disappear to a time 5 million years in the future;

    etc.

    For possibilities on how to deal with paradoxes, see

    https://www.physicsforums.com/showthread.php?p=1068268#post1068268
     
    Last edited: Jun 1, 2009
  12. Jun 1, 2009 #11
    In post 1068268 you mention 4 methods of dealing with paradoxes. If I am reading the post correctly there are really only 2, since the last 2 methods deal with paradox problems by forbidding time travel altogether. This leaves the first 2 methods. The first is a bit ambitious--rewrite physics from the ground up and may be unnecessary since we actually only have time paradoxes to deal with. The second method of placing constraints has two meanings. 1) Man-made constraints, eg Time-Cops. This of course will not prevent time paradoxes, except in the crime-doesn't-pay sense of prevent, it will just punish perpetrators, for whom being caught in a time paradox loop should be punishment enough--if my time travel prevents my birth, so I am not born and don't exist, so I don't time travel and prevent my birth, so I am born, so I time travel and prevent my birth and so on for eternity. What can the law do to me that's worse? They can only save me!!

    2) If time travel itself is constrained to prevent time paradoxes, then it is effectively blocking any time travel that interacts with the past. This is so if we assume our world's time-line is a continuous fourth time dimension (we would have to investigate to see if this assumption means this 4th dimension is actually "space-like" or not) that can be intersected by time-like curves beginning in the present at t=0, where the intersect points are in the past at times t<0. Postulating the existence of such a definitive time-line seems to imply it has an "is what is" quality. Since if any events can be changed, they must be undetermined, ie there is uncertainty about the outcome. But since all events are at their basis quantum mechanical process the uncertainty includes both space and time--exactly where and when the wave-function collapses is uncertain. If the exact time of any event on the time-line is undetermined then that small but finite length of the time line is fuzzy and there is no exact point to intersect with. Worse that fuzziness--uncertainty-- will spread to all subsequent events that are in some way linked, causally or ortherwise, to that event and ultimately much, if not all, of the time-line will be a bit blurry--forcing us to change movie concepts in mid-stream: Time Fuzz starring Claude van Damme. So the second postulate implies you may go back in time to your past, but you can only witness, you can't affect, what happened there. (Maybe this is actually just a restatement of answer three from the post.) Of course, from a historian's perspective, or treasure hunter's, this would be more than enough payoff to make the trip worthwhile. In fact, where do I sign up?

    In the current case, since the Lorentian worm-hole allows you to move with ease up and back to your immediate and practical future--imagine you make a 1-2 ly round trip in 8 hrs--and transfer information and objects back to your start time, you can easily find yourself caught in a triple free-lunch, grandfather and time-cop paradox. I would submit, using the principle of Occam's razor, that the appearance of such paradoxes implies a failure of current time-travel theory, and until proven otherwise, we should focus there and hold off "rewriting physics from the ground up" until faced with incontrovertible experimental evidence to the contrary.:smile:
     
    Last edited: Jun 1, 2009
  13. Jun 4, 2009 #12

    George Jones

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    Sorry about the typo; should be "Lorentzian."
    No, in the frame of my diagram, the coordinates of both wormhole mouths (portals) change.

    Code (Text):

         t

     8 h  |
          |\
          | \
          |  \
          |   \
          |    \
          |     \
          |      \
          |       \
          |        \
          |         \
          |         /
          |        /
          |       /
          |      /
          |     /
          |    /
          |   /
          |  /
          | /
          |/
         O----------------------------- x
                    |
                 2.5 m ly


     
    In the above diagram, M's wife's spatial coordinate stays fixed at x = 0, while the t coordinate of M's wife starts at t = 0 and ends at t = 8 h, i.e., M's wife continuously progresses up the (vertical) t-axis as she ages 8 hours. One mouth does the same.

    The other mouth moves with M. M starts at x = 0 and t = 0, moves continuously to x = 2.5 million lightyears as (M's wife's) t progresses to 4 hours (bottom slanted line), and then moves continuously back to x = 0 as t progresses to 8 hours (top slanted line).
    The spatial distance from mouth to mouth via the throat remains roughly constant (a few metres) throughout the trip. I know that it seems like the throat should first stretch and then shrink during the trip, but this doesn't happen. Our mind uses our experiences in flat space for visualization, but this situation involves curved spacetime. Our mind introduces distortions, just as distortions are introduced when the curved surface of the Earth is projected onto a flat map.
    If I haven't answered something that you want answered, or if my answers are too terse, just fire away. It might take my a while, but I will always try and get back to this thread.
    You understand the federal deficit?! As Feynman said (more than) a couple of decades ago,

    "There are 10^11 stars in the galaxy. That used to be a huge number. But it's only a hundred billion. It's less than the national deficit! We used to call them astronomical numbers. Now we should call them economical numbers."
     
  14. Jun 4, 2009 #13
     
  15. Jun 4, 2009 #14
    What about "cosmic inflation" or an "expanding universe." These may be difficult concepts for astrophysicists to embrace or demonstrate. For economists and governments they are axiomatic. As for any difficulty in describing the "Big Bang" as creation ex nihilo from a scientific standpoint, again, turn the problem over to the economists. One look at the size of the national debt and we realize he Fed certainly has no problems creating something from nothing. :smile:
     
  16. Jun 5, 2009 #15
    Yes, it seems the "throat" should be stretched out through both space and time--btw what I meant in the question was the portals moved in lock-step with the movement of the inertial frames in which they were opened, not with the initial coordinates of those frames.

    To help understand the unchanging length of the throat does the following analogy work:

    Imagine the universe is a large donut that, because these are recessionary times, is mostly hole. Now imagine all motion from location A to a different location B in this toroidal cosmos normally occurs only along the circumference of the ring. Is it fair to say a Lorenztian worm hole is like a corridor that passes from A through the center of the toroid and back to location B? Now, the length of this corridor is always 2R no matter how far apart locations A and B are and is constant no matter where these 2 locations move to in their donut universe. In the donut case of course the worm hole doesn't offer much of a short cut because the longest trip in this donut universe is only pi x R anyway while the corridor length is always exactly 2R. Similarly in a Lorentzian worm hole, once opened the throat or distance between the two end portals doesn't change, regardless of how far apart the portals may come to be. And isn't this in a way a biproduct of the geometry of our own higher dimensional space which has qualities of an n-dimensional toroid?
     
  17. Jun 11, 2009 #16
    Exactly where is the throat of the wormhole actually located, and when you transit it where are you? What is the energy source and where is it located? In the theory of these wormholes, can one manufacture them at will or are they already present and you simply adapt them to your needs? It seems as if from the point of view of the wormhole, the two portal and throat are stationary and the universe shifts around it asymmetrically since the earth portal follows the movement of the earth and the other portal follows the movement of the ship. If so what is it attached to? To the extent that the wormhole "folds" curves or warps space the energy required must be greater than that required to pilot the ship or why bother with the ship. On the other hand wouldn't this immense energy output mimic a gravity well and act as a drag on the ship?
     
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