Time Travel?

Discussion in 'Pseudoscience' started by the legendary shark, Mar 5, 2016.

  1. PhysBang Valued Senior Member

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    I'm not sure that we could, since the GR methods involve closed loops. Well, not counting a wormhole.
     
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  3. The God Valued Senior Member

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    Am I missing something here ? Outside EH things are perfectly normal except possibly twisted curved spacetime, but with finite curvature...Once you get inside EH, the time becomes spatial and breaks down at r= 0 (for Schwarzchild BH). Things are somewhat different for kerr BH as it has couple of horizons.
     
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  5. The God Valued Senior Member

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    Back to popscience Bullshit, after a decent list of some technical papers on aLIGO/GW...
     
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  7. The God Valued Senior Member

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    The popular perception of time travel is being messed up by poposcience publications. For layman the basic
    definition of time travel is going back to past in his frame of reference. Like going back to 2015 or earlier in our frame, while the clock is still ticking for 2016 creatures.......I do not think any one, Paddoboy included, could show that this is allowed (whatever that means) by GR equations. Time dilation is not time travel as far as popular layman understanding is concerned.
     
  8. the legendary shark Registered Member

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    I understand that, and the difference between time travel and time dilation. I don't know if time travel is possible or not.

    I was simply thinking about how, in a universe where time travel is possible, how paradoxes might be avoided.
     
  9. The God Valued Senior Member

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    at this stage of our knowledge , we are able to conclude that any sufficiently advanced civilization, [not withstanding any prohibitive law of physics and biology] could 'impregnate' in the manner ...... by waving the hand.

    Edit : waiving to waving..
     
    Last edited: Mar 8, 2016
  10. the legendary shark Registered Member

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    "Waiving" means "foregoing" or "doing without." Am I missing something, or did you mean "waving"?
     
  11. The God Valued Senior Member

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    I like your humble and honest OP. The fact is there is no any such animal called time travel as defined above. It is an imposibility that someone in March 2016, decides to go back to March 2015, open the sciforum website, create a profile, and post some nice things about time travel....you know all kind of nonsense is possible, go back in 2015 and knock off King John Un, you know what I am saying or go further back and knock of Hitler, or even Einstein. If stupidity or stupid thinking because of improper understanding of science creates paradox, then do you think they require any solution ? Poposcience guys messed up this time travel concept to get business and few gullible believe them.
     
  12. The God Valued Senior Member

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    sorry, I have corrected that, but that post was fun..
     
  13. the legendary shark Registered Member

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    Thank you. As I said, I heard about the time telegraph paradox in a lecture about physics, given by a proper lecturer from a proper university, and therefore thought it was a valid area of discussion. While I do enjoy Star Trek, I don't believe that watching it is any basis for self-education.

    It was my understanding that discussing paradoxes, irrespective of the possibility or otherwise of time travel, is not necessarily pointless. Also, I enjoy thinking about (and trying to learn and understand) these things. It seems I may be alone in this

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  14. The God Valued Senior Member

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    The harsh comment was not on you, you asked a question, you wanted to discuss, fair enough. But there are posters who says that time travel is proved and allowed by GR, this comment is for them. I suggest that you delink time travel with time dilation, things will be different and clearer. There are no paradoxes as time travel as envisaged and as understood by general lay people is not possible. Its like you are going back to same spatial coordinate with reverse arrow of time, but at what rate ?
     
  15. the legendary shark Registered Member

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    I'm sorry, God (and how often have I said that in my life?!), I wasn't getting at you. I was a little frustrated, is all. I live in a place where nobody talks about these subjects, which is why I came here. I am a lay person and freely admit my understanding is very limited - but I do try.

    That was my very idea, that one can't go back to the same spatial coordinates, and was attempting to explain or guess why this might be so. It might be an extra argument against the possibility of time travel. As to the rate of travel, I don't know. I'd guess that if time travel against the arrow of time were possible, then the same speed limit "c" would apply. One cannot travel through space without traveling through time so maybe one cannot travel through time without traveling through space. The rate, I assume, could be anything from 1kph to c and would be relative to the particle traveling.

    Even whilst traveling forward through time, as we all do at a rate of one second per second, we can't go forward to the same point in space - if I walk around in a circle, even when I get back to my start point it's a different point in space as the Earth has revolved, moved in orbit, been dragged after the sun and moved with the galaxy. Even flying around in a circle in space has the same problem, with the possible addition of the extra discrepancy added by the expansion of the universe. So if it's impossible to return to the same coordinates going forward, it makes sense to me that the same impossibility exists if going backwards.
     
  16. The God Valued Senior Member

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    You need to read a bit about reference frames......Once you choose Earth as reference frame, then please do not jump out and say that Earth has also changed its position due to all sort of motions which you indicated in your OP. I am not saying tha earth does not spin, or arouns Sun, or around GC or with Milky way.....but a brief studty of reference frames will get you out of this complexity.
     
  17. the legendary shark Registered Member

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    Cool, thank you.
     
  18. paddoboy Valued Senior Member

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    No, you are wrong again.
    The fact that all frames of references are as valid as each other, and that each frame still sees one second pass as one second, means [as Kip Thorne put it]
    The laws of physics allow members of an exceedingly advanced civilisation to travel forward in time as fast as they might wish. Backward time travel is another matter; we do not know whether it is allowed by the laws of physics, and the answer is likely controlled by a set of physical laws that we do not yet understand at all well: the laws of quantum gravity. In order for humans to travel forward in time very rapidly, or backward (if allowed at all), we would need technology far far beyond anything we are capable of today.
    https://plus.maths.org/content/time-travel-allowed

    But of course it would be nice of you to supply some link supporting your view. That though has never happened as yet, and I don't suppose it will happen now.


    http://arxiv.org/pdf/1401.4933v3.pdf

    Treating Time Travel Quantum Mechanically

    John-Mark A. Allen∗ Department of Computer Science, University of Oxford, Wolfson Building, Parks Road, Oxford, OX1 3QD, UK
    ABSTRACT:
    The fact that closed timelike curves (CTCs) are permitted by general relativity raises the question as to how quantum systems behave when time travel to the past occurs. Research into answering this question by utilising the quantum circuit formalism has given rise to two theories: DeutschianCTCs (D-CTCs) and “postselected” CTCs (P-CTCs). In this paper the quantum circuit approach is thoroughly reviewed, and the strengths and shortcomings of D-CTCs and P-CTCs are presented in view of their non-linearity and time travel paradoxes. In particular, the “equivalent circuit model”— which aims to make equivalent predictions to D-CTCs, while avoiding some of the difficulties of the original theory—is shown to contain errors. The discussion of D-CTCs and P-CTCs is used to motivate an analysis of the features one might require of a theory of quantum time travel, following which two overlapping classes of new theories are identified. One such theory, the theory of “transition probability” CTCs (T-CTCs), is fully developed. The theory of T-CTCs is shown not to have certain undesirable features—such as time travel paradoxes, the ability to distinguish nonorthogonal states with certainty, and the ability to clone or delete arbitrary pure states—that are present with D-CTCs and P-CTCs. The problems with non-linear extensions to quantum mechanics are discussed in relation to the interpretation of these theories, and the physical motivations of all three theories are discussed and compared.
    """"""""""""""""""""""""""""""""""""""""""""""""""""

    So once again, time travel entails difficulties and technologies that as yet we are unable to harness. eg: approaching the speed of light, but the equations of GR certainly allow for such fantastic scenarios.
    It was once common sense as maintained by Newton, that space and time are absolute. We now know that this is totally false and that each has his own personal time.
    The example I always remember is that we have twins: One stays home on Earth, the other sets off in a relativistic space ship at 99.999% "c" for 6 months, turns around and arrives back on Earth another 6 months later. His onboard clocks show that 12 months has passed.....his biological clock shows he has aged 12 months......12 months has passed as 12 months.
    He steps outside the space ship and finds himself on an Earth 230 years in the future...his twin long dead and buried, and a civilisation 230 years advanced from the day he left: 230 years has passed as 230 years.
     
  19. paddoboy Valued Senior Member

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    We do have people that frequent this forum, that totally deny GR and most presently accepted mainstream cosmology.
    As a consequence they need to dispute all aspects of GR, but notice hardly ever supporting their claims with reputable links and such. It has even lead to the ludicrous position of some claiming that the results and confirmations of GP-B and aLIGO are fraudulent. This obviously is as insane as our 9/11 conspiracy pushers and Moon landing deniers.
    The facts are simple: GR allows for time travel. It will be difficult.....it still maybe not achievable, but so to was the aspect of planes and flight.


    We had a great scientist, Lord Kelvin in 1896, only a decade or so before the Wright Brothers famous first flight, write a letter to Major Baden Powell, when asked to join an Aeronautical Society:
    Here was his reply...............
    Dec 8/96

    [Letterhead: “THE UNIVERSITY, GLASGOW.”]

    Dear Baden Powell

    I am afraid I am not in the flight for “aerial navigation”. I was greatly interested in your work with kites; but I have not the smallest molecule of faith in aerial navigation other than ballooning or of expectation of good results from any of the trials we hear of. So you will understand that I would not care to be a member of the aëronautical Society.

    Yours truly Kelvin

    http://zapatopi.net/kelvin/papers/letters.html


    Are you familiar with the Alcubierre drive? Of course highly theoretical and if possible, only attainable by an advanced civilisation with knowledge of a "new physics" as SR/GR was at the turn of the last century.......
    http://www.andersoninstitute.com/alcubierre-warp-drive.html

    Who knows what the future will hold. If we are able rise above our Earthly follies and avoid any astronomical catastrophe, in time, and given enough time, there are many things which we now deem as impossible and unlikely, that will become reality.
     
  20. DaveC426913 Valued Senior Member

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    This is wishful thinking though. It's trivial to suppose there's "something" preventing it. That can be said about anything we have not accomplished yet.
     
  21. DaveC426913 Valued Senior Member

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    That would be for a spherical BH. The solution proposed involves a (albeit highly-contrived) toroidal BH. You can be at the geometric center of a toroidal BH yet still be outside the EH.
     
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  22. PhysBang Valued Senior Member

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    OK, but the complete lack of any backwards causation in any physical phenomena might be enough to grant us a little evidence that there is a legitimate temporal arrow. Add to this that GR is definitely incomplete and we have reasonable grounds for suspecting that there is some physical principle preventing time travel.
     
  23. DaveC426913 Valued Senior Member

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    Probably.

    That argument still makes no sense to me.

    It's starting with the conclusion, and finding a premise to fulfill it. The only reason to suppose it is the a priori assumption that TT is not possible.
     

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