Is time travel possible based on theory?

Discussion in 'Physics & Math' started by Saint, Jun 9, 2019.

  1. Saint Valued Senior Member

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    Is time travel possible based on theory?
    Something like Back to Future?
    Can we change history so that the present and future will be changed too?

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  3. paddoboy Valued Senior Member

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    Forward time travel is allowed for by GR, but backward travel is not certain and probably is not viable. No one cannot change history.
    https://plus.maths.org/content/time-travel-allowed
     
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  5. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    Not sure if you know my oft post

    Time does not exist

    There is nothing in the future

    Only NOW exist

    And what is commonly referred to as time is really a sort of AGING NOW

    And obvious there is no PAST to travel to

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  7. Asexperia Valued Senior Member

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    Time travel is impossible because there is not a when to go. The past and the future are only mental structures. Time exists in a changeable continuous present (ccp).
     
    Last edited: Jun 9, 2019
  8. paddoboy Valued Senior Member

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    A realistic scenario goes like this......If you and I were twins and I being the more intrepid, headed off into the universe at 99.999% of "c" and travelled constantly for 6 months by my on board ship's clocks and my biological clock, then got lonely and decided to come back, again returning at the same constant speed of 99.999% of "c", returning to Mother Earth another 6 months later, so that according to my ship's clocks and my own biological system, I would have aged 12 months, I would be returning to an Earth around 230 years later, with you, long dead and buried[God bless your cotton picking little soul!!!]
    I won't push the issue re time any further, then to say that within the bounds of GR, spacetime is real.....It can be bent, twisted, warped etc

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  9. Asexperia Valued Senior Member

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    In the paradox of the twins, only one gap would be created in the present of the brother who travels at a speed close to c. That's what happens with GPS clocks traveling on artificial satellites.
    Speed and gravity create a gap in the present of something.
     
  10. billvon Valued Senior Member

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    Going forward - possible.
    Going backwards - there are some mathematically consistent solutions that allow travel backwards through time. However right now we don't know of any way to engineer the required structures (wormholes, ultradense cylinders spinning such that their surface velocity is near the speed of light.)
     
  11. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    OK

    It is well known, for me poorly understood, that stuff AGEs slower (note stuff AGEs slower) the fastest stuff, including us, travels

    Also the stronger the gravity field the slower stuff AGEs

    For me the kicker works like this. Taking the totality of the Universe everything happens NOW

    The visual INFORMATION about what is happening NOW is obviously limited to the speed of light to convey said INFORMATION between one section of NOW and another section of NOW

    Obviously there is lots more but I have to break off for the moment

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  12. paddoboy Valued Senior Member

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    And what that says is that there is actually no universal NOW.
     
  13. Q-reeus Banned Valued Senior Member

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    Nice to see you selectively being so genteel and diplomatic with fundamentally differing opinion of a 'mate'. Anyway - realistic? Your idea of realistic - propulsion of a human being and necessarily much more massive enclosing spacecraft - to 99.999% of c wrt Earth, differs radically to the vast majority of physicists and engineers opinion. Grounded as they are in what is indeed current mainstream opinions of what is actually realistic. Maybe you really meant 'theoretically possible according to SR'. Then learn to write clearly.
    Oh dear. Thanks it seems to that recent mutual James R/paddoboy love embrace over in 'In defense of Space Aliens' thread, all past rancor is pardoned and full ok now evidently given to resume here as full-time SF serial pest. Charmed life for those willing to suck up as a matter of unflinching principle - eh?
    My own opinion on backward time travel has never varied - it's bunkum. Period.
     
  14. Michael 345 New year. PRESENT is 72 years oldl Valued Senior Member

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    Ummm

    So the little green men out there who were well advanced when we had dinosaurs were existing in some sort of future Universe distinct from our NOW?

    Now they have arrive here, curtsey of MR, they are expecting to see dinosaurs???

    And they have traveled back in time???

    No so, of course there is a single NOW

    TRY this imperfect model. The whole Universe is represented by a clockwork artifact. Billion of cogs and stuff

    Lots of the cogs, operating within the artifact, move at different speeds

    In your twin example the almost light speed twin has moved onto a cog which, relative to the cog he left, Earth cog, but but but has a vast vast vastly larger circumference

    While the Earth cog is spinning madly, due to the vastly different circumference the twins cog is almost at a standstill

    When the gear tooth of the earth twin clicks with the gear tooth of the near light speed twin, comparing the AGE, as you mentioned, the light speed twin is young

    However they have both existed in a single NOW

    The different parts of the Universe do vary in speed causing time dilation but like the clock ALL the cogs operate NOW, none are in the future, none are in the past

    So your twin has not traveled in time, merely perched on a different cog moving a a different speed

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  15. paddoboy Valued Senior Member

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    So sad...such paranoia.....followed me over to SFN [where he is permanently banned now] and now here again, so sad...

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    Here's a chart Mick, giving you a better idea and supporting what I said...........the traveler at 99.999 c and returing to Earth 12 months later, finding himself on a planet around 230 years later is valid in SR and mainstream physics..
    http://www.emc2-explained.info/Time-Dilation/#.XP43JmozY2w

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    http://www.emc2-explained.info/Time-Dilation/#.XP43JmozY2w

    Here's an even better one Mick......

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    My example is the last line......
     
    Last edited: Jun 10, 2019
  16. paddoboy Valued Senior Member

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    The finite speed of time assures we have no universal now.....
    But please, let's leave the little green men out of this...we don't want to arouse the gullible brigade with stories of UFOs etc..."nudge, nudge, wink, wink"
    https://www.physicsforums.com/threads/where-galaxies-are-now-or-is-there-a-universal-now.882331/
    And to say we have a universal now, is the same as saying that time is absolute which we know is not the case, and just part of the evidence and reasons why SR is so successful, and as an extension, GR.
     
    Last edited: Jun 10, 2019
  17. Q-reeus Banned Valued Senior Member

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    You flatter yourself. Go check - my first post there was in response to someone else - dealing with - gasp horror- an alternate theory of gravity to GR, I had already raised back here at SF. Which btw afaik has yet to be challenged publicly by anyone in GR mainstream. Please don't train-wreck this thread by pursuing that issue here. I mention it here only to correct your as usual garbled claims.
     
  18. paddoboy Valued Senior Member

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    Whatever floats your boat q-reeus. Delude yourself as much as you like...all contingencies have been examined and reasearched, and guess what? GR still reigns supreme and your Vector 4 will linger and die in cyber space....

    ps: But rest assured, if and when GR is surpassed, like GR surpassed Newtonian mechanics, it simply gave us a more accurate method and of course just as Newtonian is still widely used within its zones of applicability, so to will GR reign supreme and still be correct and used within its zones of applicability, your obvious agenda not with standing.

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    Take it easy!!!

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    and good night my friend...beddy time for me!!!
     
  19. Q-reeus Banned Valued Senior Member

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    If only you possessed superlative knowledge to make such an absolute pronouncement. But you don't, by a long, long way. Quote saved to file for future reference.
    Ah yes. Then follows the 'bob each way - heads I win, tails you lose' caveat. Such courage of convictions. Not.
    Huh? You chose to make yourself my enemy from iirc the very first engagement here at SF. We are not and never were friends.
     
  20. paddoboy Valued Senior Member

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    Gee, you spoil my night!

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    Grow up and stop being so precious!!!

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    Again, its you banned from at least two forums, not me!!
     
  21. Q-reeus Banned Valued Senior Member

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    Go to bed paddoboy/beecee/Maroubrabeach/ASTRO BOY/ or whatever other chameleon aliases you go under. Dreamworld is so much less trouble to justify.
     
  22. Janus58 Valued Senior Member

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    It is not the "strength" of the Gravity field that counts, it is the difference in potential. Even if you had a gravity field that did not vary in strength with height, the higher clock would run faster. Even if you had a gravity field that increased in strength with height, the higher clock would run faster ( an example of this would be comparing a clock at the center of the Earth with one at the surface. At the center g due to gravity is zero, and increases as you move outward. But with zero g at the center, the clock at the center would run slower than the clock at the surface.
    But different observers moving relative to each other will not agree as what set of events are happening "NOW".
    The invariant nature of c ensures that causality in maintained, even when observers might disagree on the order of some events. So for example, If I am looking at a clock one light minute from myself and see that it appears to read 1 minute behind my clock, I will conclude that the clock reads the same as my clock NOW. However, someone else passing me at 0.5c in the direction of that clock, while seeing exactly the same time on the clock as he passes me, will conclude that the clock reads 30 sec later than my clock does NOW. For me, the light left when the clock was at its present 1 light min away and the light took 1 min to reach me. For him, the same light had to have left the clock while he was some distance from passing me, and was much further away from him. Since the light had to travel at c, relative to himself (invariant nature of c), it took much longer than a minute for the light to get to him. And even though the clock was ticking slow due to time dilation, more time passes on the clock between the light leaving and meeting up with him than it does for me.
     
  23. Janus58 Valued Senior Member

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    What in world was that all about? How advanced a civilization is has nothing to do with its conception of NOW. What changes the conception of NOW is relative velocity. Events that all happen NOW for one inertial reference frame will not all happen NOW according to a reference frame with a relative motion with respect to the first. That is what is meant by their not being a universal NOW. Different events are considered as happening NOW for different reference frames.
     
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