Time travel

Discussion in 'Astronomy, Exobiology, & Cosmology' started by Dragonrider, Apr 26, 2006.

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    ... As I believe I may have mentioned previously - the sort of Time Travel events you're describing lead to Terry Pratchett. And that way, hilarity must ensue... I also believe I may have mentioned something about Time Travel being simply murder on the tenses. One never knows where one is with the silly business.

    You are, however, perfectly correct.

    And in no way shape or form, in anything I may have describes do I suggest anything any different.

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    Quite the contrary. Travelling backwards through Time doesn't place anyone in "The Past" - merely just a point in Time & Space which, chronologically speaking, proceeds that one, originally, the Time Traveller leaves and thinks of as being "The Present."

    This is one of the reasons notions concerning Time Travel rapidly become such a pigs ear - one never knows where one actually is. Certainly, if a Time Traveller begins their journey at 12:10 am on August 29th 2006 and arrives ten minutes earlier (as in the diagram above) his pocket-watch (an essential piece of kit for any gentleman Time Traveller of distinction) is ten minutes ahead of everyone else's, his experience tells him that if the purpose of making this journey is to win a wager concerning a coin, the outcome he believes he has already witnessed and knows to be Tails (sorry about the devaluing of currency here by the way, I literally don't appear to have anything on me at the moment with a monetary value exceeding exactly one penny) - Everything as far as the Time traveller is concerned informs him that where he is is ten minutes ago in "The Past."

    The problem is he isn't. Physically speaking, when one Time Travels, one leaves the present and arrives in the present - when and where in Time & Space doesn't matter a damn. Your arrival point, it doesn't matter what it says on either clock or calender, is always the present moment as far as where you arrive is concerned.

    Consequently, events may unfurl exactly parallel to how a Time Travellers knowledge of "History" is concerned - or they may unfold differently. The exact outcome of the wager is absolutely no more certain than it was the first time around, it is only the Time Travellers own perspective of things which makes either him or her believe otherwise.

    Reality both can and may beg to differ.

    To travel through Time is only to travel from one given point in the fabric of Time & Space to arrive at another - chronologically this arrival point may proceed the point in Time & Space one may originally have started out from but all one is ever doing is moving between two separate points in Time & Space.

    One never arrives in "The Past" - what happened is indeed fixed, immutable, unchanging and unchangeable. Nevertheless Time Travel has physically placed the Time Traveller at a point in Time & Space that chronologically conforms exactly to his or her understanding of that point in time they, as a Time Traveller, can only regard as being "The Past".

    To travel forward, either with the flow of or through Time to the point in Time & Space which, chronologically speaking, conforms to the point they originally left - events as they actually transpire as far as reality is concerned are simply what happened. A Time Traveller may view the outcome as being somehow either "wrong" or else "different" - of course in practice this is simply not at all the case, but the Time Traveller, with their unique point of reference as such an individual, will suffer the consequences of such "change" uniquely compared to everyone else.

    The world and reality around them, whatever happens, will carry on just fine - but the Time Traveller, from the moment they first travelled back through Time, remains out of place. Literally, because they are exactly so.

    For a Time Traveller, travelling purely for the sale of travelling back through Time, there is no going back to where they originally started. It's a one way ticket. The very best one could ever hope for, in returning to what corresponds to being the point in Time & Space they originally left, is finding a reality with a history of chronological events so exactly parallelling that which their own particular experience of "History" dictates should be there as to make negligible difference.

    This, once again, is getting to the nub of why Time travel for the sake of travelling back through Time is so supremely and utterly useless.

    If y'can't use it to correctly anticipate the outcome of the simple flip of a coin - what can you actually use it for?

    When viewed and applied in the context of facilitating interstellar travel on a viable basis, Time Travel is the side effect that makes that notion a viable undertaking to strive for in the first place. But Time Travel just for the sake of travelling back through Time...?

    Y'can't even use it to win the Lottery. Being randomly generated a quick jaunt into the future may reveal indeed exactly what each winning number is going to be - but travel back to apply that knowledge and, just as in trying to apply ones knowledge of the future to win a single coin, the actual odds of the numbers Time Travel has revealed to you being the exact same ones that come up when you endeavour to apply the knowledge remain exactly no different than had you never gone to the bother.

    1/14,000 against. The odds of a coin coming up one side over the other - 50/50. Go to Las Vegas all you want, as a Time Traveller one is no more likely to win than any of the other punters there. It never matters quite exactly what ones knowledge of "History" informs them.

    Nothing I've stated in any of these posts either constitutes or is proffered as providing any form of physical prohibitation to the idea of Time Travel whatsoever - quite the contrary. Fix yourself up something that can get you from one star system to the next and back again and still find someone alive enough to give a rip you actually sent out there in the first place and that is essentially everything anyone will ever need to facilitate Time Travel in that specific sense of setting out to displace chronological Time.

    If using worm-holes are your particular bag, it's as good a way as any.

    The point is, affecting Time Travel in this specific "travel back in Time" sense is useless, utterly, and pointless beyond reproach to undertake. Only an idiot, providing they had the means, would actually do it and consider the venture even remotely sane...

    But then again, last time I checked. The world apparently remains full of idiots and we remain the exact sorts to look back at our predecessors and consider ourselves actually smart simply because we can work the appropriate buttons on a computer.

    Quite why that should remain likely to change particularly in any given future I have not the slightest wit to discern.

    Time has always been more than merely replete with more than its fair share of idiots. Who knows, perhaps some of them are actually from it...


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    An eminently appealing notion, and I have the crowfeet around my eyes just to prove it. But nevertheless, factually inaccurate. Time is what happens.
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  3. Pete It's not rocket surgery Registered Senior Member

    A deeply philosophical statement, tied up with questions of parallel universes and "streams of time".

    I agree with you that if that position corresponds to reality, then time travel isn't awfully useful. But... one wonders why such a point of view should be held so dearly?

    A different, and equally unprovable philosophical position (the "eternalist" position) is that events unfold only once, and that the Time Traveller literally can not make anything happen differently. Events must unfold the way they did "the first time around" (Where's my copy of Dr Streetmentioner?)... because that is the way they did unfold. It only happens once, even if the TimeTraveller experiences it twice.

    This is precisely the situation involved with those mathematical beasties known as wormholes. If an item pops through a wormhole to an earlier time, then it was there in the past... going back doesn't add the item to the past... it was already there.
    Last edited: Aug 29, 2006
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    ... Why so dearly, y'ask?

    Pre-determinism. Predestination. The notion that not only does free will not exist, but the basic workings of Cause & Effect actually work the opposite way around: In such a Universe as you describe, Cause no longer simply leads to Effect.

    Specific Causes in The Present have to occur at specific points in time in order for specific Events to occur that, in turn, give rise to specific Consequences - all at the behest of a Future which hasn't happened yet...

    Pete, tell me truthfully. What exactly is there not to want to rail against here with this picture?

    I can easily conceed to the notion that, from the point of view of a Time Travellers own experience of actual Time Travel - they may indeed discern that, apparently what they actually do, no matter how hard they try to alter the outcome of given Historic events, nothing they attempt may appear to make the slightest difference in out come as far as their knowledge of "History" allows them.

    But if we take this to be the actual case, how exactly can the Time Traveller themselves actually know this apparent display of Predeterminism to be the actual fact of the matter?

    If they can be physically present to attempt to "alter" Histories view of events, so too can others unbeknown to them. Equally, if we truly consider History to be a map of the actual Past, the only guide book one can actually reference - History as it stands in the History books merely reflects a consensus of opinion based on whatever evidence happens to be at hand at the time of venturing such opinion.

    The the historical truth regarding any event is continually being changed and updated with the passage of time, discovery of new evidence and greater insight on the parts of Historians concerned.

    Other than what and when, the specific mechanics of History as it stands for one generation alters in the perception of the next. Truths, hitherto sacrosanct, become re-examined, re-interpreted and replaced with others. Does a History book actually provide us with exactly the right facts which may enable a Time Traveller to actually alter the course of events as they have been informed they should be able to in the first place?

    Armed with only such knowledge at the onset, does a Time Travellers failure to change events actually prove Pre-determinism to be the true nature of reality or does it prove only that our actual knowledge of what really happened in the past is simply inaccurate.

    One way or the other, the Time Traveller cannot make a certain determination - quite literally about anything...

    The best and only determination they can make concerning what they may experience can only be based on probability and likelihood.

    Time Travel, quite despite what the notion of such may appear to suggest, kicks the idea of certainty regarding anything pretty much what-so-ever right in the family jewel-case.

    And keeps doing it, Time and Time again...


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  7. Pete It's not rocket surgery Registered Senior Member

    Yes, it certainly present a different picture of time... but our comfortable notion of time was thrown out the window kicking and screaming by Einstein.

    We can rail against it all we like, but railing doesn't make reality.

    I don't know if they can. I don't know if they can't.
    I think it's more productive to consider sending marbles and slips of paper back through time than people...

    Perhaps. I personally don't believe it will ever happen, so I don't think anyone will ever know either way.

    But reasoning that time travel is a Bad Thing is not the same as reasoning that it is impossible, right?
  8. Novacane Registered Senior Member

    Be able to go back physically into time would certainly be an exciting thing. However, changing the past to correct the present is not what I think it's all about. Witnessing history would be the most interesting part of the time travel experience. I think I would take a rain check though on going back past the 65 million year mark. I wouldn't relish the possiblity of becoming a fast food meal for some T-Rex bachelor party.

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  9. eburacum45 Valued Senior Member

    The big problem with time travel is that it messes up causality; the idea that effect always follows cause. There are at least four alternative possibilities associated with the concept of causality in time travel:

    The First conjecture suggests that time travel to the past is possible, but it is impossible to change the past, for instance by killing your grandfather (the so-called Grandfather Paradox).
    If time travel can only lead to events which have already been observed to happen, then the situation is called consistent;
    this is the Novikov self-consistency theory of time travel, and eliminates the Grandfather paradox.
    You can go back in time, but you can't kill your grandfather no matter how hard you try.
    Backwards time travel is deterministic, forward travel (and the normal passage of time) are probabilistic.

    Another solution would be that backwards time travel is impossible;
    That is the second commonly quoted solution to the Grandfather paradox; impossibility (known as the 'boring physics' conjecture).

    The other two main possible solutions are the 'Many Worlds' hypothesis, which seems to be going out of favour with quantum physicists;

    and the 'radical rewrite' conjecture in which you can go back in time, rewrite history, but there is only one timeline which is rewritten by your actions (with a single blind loop representing the original unaltered timeline, which disappears).
    I can't quite see how this would work in practice, but it seems to be the basis for many fictional time travel stories.

    Let's examine what happens if you try to change history, using each of these conjectures in turn;

    If the first conjecture (the Novikov self-consistency conjecture) is correct, you go back in time but nothing you do can change the past. If you try to shoot your grandfather your gun jams, and so on. So when you go home nothing has changed.

    If the second conjecture is correct, (the 'boring physics' conjecture) then your time machine doesnt work, so you can't go back anyway.

    if the third option (the well-known Many Worlds Hypothesis) is correct, you can change history, and create a new timeline; if you go to the future of the new timeline, everything has changed, but your own original timeline exists somewhere in the multiverse, and you might one day be able to find it one day, perhaps by 'sliding' sideways through the many versions of history.

    If the fourth option applies (radical rewrite) you can go back, change the world, but by doing so you destroy the timeline you came from, and create a paradox- your own personal history has been destroyed, and you never got into the time machine in the first place. So where did you come from?
  10. ... Oh, absolutely. Nothing proffered by myself would be constituting even the vaguest whiff of me saying: "Time Travel - Oh, big cosmic no-no." Quite the opposite. In fact, as far as notions go concerning Time Travel goes it actually encompasses all view points regarding the business.

    All I've really being saying throughout is pointing out the observation that, in being successful in such a pursuit and actually travelling back in Time, firm determinations regarding the exact nature of quite whatever they may happen to witness can't be made by the actual Time Traveller.

    A view point concluding pre-determinism, for example, may in practice actually be correct - but simply put the ability to Time Travel wouldn't necessarily in practice make the Time Traveller in question themselves any more privy to the exact nature of the reality they find themselves in than anyone else actually is at any other given point in either Time or Space.

    The actual act of Time Travel itself would indeed be an extraordinary feat to achieve, of that there is no question - but in arriving at ones destination of choice, despite being a Time Traveller, once could be no more certain of the outcome of subsequents, nor the actual reasons behind them, than one would be if on simply stayed at home and never elected to travel back through Time in the first place.

    A Time Traveller may have certain better insights concerning when they are than those he or she may find themselves amongst, but those insights themselves may in practice prove no more either accurate or valid than those of any other individual they might encounter who may never travelled in the same fashion of the Time Traveller in their lives and never will.

    Here, this exact instant, the exact nature of Reality is absolutely no different from that one would experience at any other given point in either Time or Space - barring winding up slap in the middle of a Singularity, naturally. Our experience of the Present is transient, fluid. Looking back in retrospect, the Past from our perspective is fixed, immutable and unchanging.

    What we forget is that, at the actual time, "The Past" as we view it physically speaking was actually no different from that of the present moment now. If we could physically contrive to place ourselves in it, we place ourselves in a reality exactly no different from that we left.

    All Time Travel actually does is allow a Time Traveller to exchange one present moment for another. The means of getting there may indeed be extraordinary in comparison to normal, common experience. But actually being there would essentially be no different from being here in this present moment.

    Up is still up, down is still down and the odds of a flipped coin coming down one side over the other remain 50/50.

    ... I like the wormhole marbles idea by the way, I do - but may I suggest instead of marbles and messages perhaps sending coins instead might prove more practical? I mean, for one thing, no one can possibly slip on a coin and inadvertently break their neck for a start off and, more importantly, when a person espies a coin they immediately move to pick the thing up.

    Anything else may tend to be viewed with suspicion. But, money talks as they say. And it bears a date....

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    I'm not sure which side of the pond you're from Novacane, but over here we have a comic called 2000AD, still going strong today. Back in the mid 70's when it started, before the likes of Judge Dredd and so forth really found its feet, they ran a story called Flesh - You'dve loved it.

    The idea was that 22nd Century mankind, with dwindling natural resources and massive population increase had become no longer capable of feeding people simply through agriculture - so instead they send meat processing stations and cowboys back to the Jurassic Era to harvest the soon to be extinct anyway dinosaurs for meat.

    Ran for about the first 20 editions or so. Needless to say, it ended bloody. Like I say, you would have loved it....

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    ... Y'know, I believe what I adore most about chaps with Big Squishy Brains is their unfailing ability to come up with tripe and find it reasonable....

    Novikov's is a perfect example of this. It sounds perfectly reasonable of the face of it, but consider: History, as it is proffered by scholars, is conjecture. It may be very plausible, given their exists enough evidence and consensus to support it, but still remains conjecture nevertheless.

    Therefore how can a Time Traveller accurately determine exactly what remains consistent with the notion of "History?"

    Say, for example, one travels back to Dallas in 1963, locates James Harvey Oswald in the book repository and distracts at the exact moment he is about pull the trigger - the Presidential motorcade cruises on, a shot from the grassy knoll rings out, Kennedy's brains exit his head.

    Would witnessing should an outcome actually prove the notion of Self Consistency or simple demonstrate that, in practice, it turns out there really was more than one gun man on the job just like Oliver Stone has been maintaining all these long many years?

    The Time Traveller can't tell. Not from what he observes.

    Take the Many Worlds Hypothesis - a Time Traveller may consider themselves to actually be, in successfully travelling back through Time, in one of any number of possible parallels - but how exactly can he prove it?

    Multiple Time Travel excursions to more or less the same point in Time and Space may reveal to them realities which differ both in terms of what happens and specific outcome as a consequence - what would such an observation actually prove regarding what they are witnessing?

    Certainly, on the surface, it may appear to indicate that there exist multiple realities in which both parallel and alternate "Histories" are allowed to play out - but can the Time Traveller conclude that such worlds are simply merely there to be discovered as a consequence of some fundamental disposition the Universe may have of endless replicating itself over and over again simply to facilitate such possible outcomes: or, does the act of Time Travel itself in some fashion actually bring about the existence of such parallel and alternate realities?

    If so, is it the Time Traveller them self in the act of Time Travel that is creating these things or has the Time Traveller simply blundered into one created by some other, more advanced Time Traveller, having travelled further back in Time and so, by their actions, either advertently or else inadvertently created this new reality our hapless friend merely blunders into?

    The Time Traveller, despite being successful in actually travelling back through time, simply can't know, one way or the other, which in practice in fact proves to be the case...

    And basically, it just goes on.

    The best we can possibly provide is the certainty that we, at this moment in time, simply don't have either the means or technology to Time Travel and more significantly than anyone else simply moving with the overall flow of Time.

    However, due to the fundamental nature of what Time Travel as a notion infers, as to all other possible determinations we can conceivably make - all bets remain off.

    Time Travel is basically either doable or it is not. Flip a coin to find the correct answer. You've got a 50/50 chance of being half right whatever happens, but no better than.

    That will always, no matter what transpires, remain the truth of the thing...


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  11. swivel Sci-Fi Author Valued Senior Member

    For that, you don't need time travel. All you need is faster-than-light travel and a very, very, very powerful telescope. Fly away from the Earth at FTL speeds, and aim the telescope at Earth. Watch history unfold.

    The sunlight that bounced off of Napolean getting trounced at Waterloo is still racing across the void, and at many different angles. You just have to catch up to it, and be able to gather it in very, very large amounts.

    I don't think this would work back to the dinosaurs, as that light would probably have degraded to the infrared by now, but most of Human history is still out there.

    Too bad FTL travel is as impossible as Time Travel. Especially since the tool needed for both, wormholes, do not exist.

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  12. Well, that possibly doesn't help. But then again, perhaps it was never the actual solution in the first place...

    Simply just sitting here on our arses chewing the breeze our respective masses are already being constantly compelled to move at velocities significant and not at all inexpensive to achieve via equal means of propulsion alone, all the while at an exact energy cost to ourselves of absolutely bugger all.

    Were we able to fathom some means of freeing ourselves from that ambient motion, slowing down relative to it and then kicking on the close-to-light-speed engines heading towards some portion of our galaxy rushing to meet us head on...

    From the point of view of external observation we would appear to be travelling faster than the speed of light - providing we could, of course, acquire some means of slowing down adequately enough in the first place, naturally.


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  13. Pete It's not rocket surgery Registered Senior Member

    That's what Eddington said about black holes, for equally good reasons.

    The existence or otherwise of wormholes is not known.
  14. Novacane Registered Senior Member

    Actually, we haven't even seen a Black Hole yet. Have we? If we have, then it's 'Show Time'.

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  15. Pete It's not rocket surgery Registered Senior Member

    Depends what you mean by "seen".
    Black holes have been positively identified.
  16. swivel Sci-Fi Author Valued Senior Member

    I can find an expert at any moment in history that didn't believe in something that turned out to be true. Not sure if your comment has any logical weight.

    Unless you are saying that since someone was wrong in the past, it makes it possible for people to be wrong in the future. If that is your point, then I agree. It is still possible for humans to be incorrect.

    Now... to settle which one of us that is, we need to rely on our arguments about the issue at hand. Not list anecdotal evidence that has zero bearing on the subject.
  17. Pete It's not rocket surgery Registered Senior Member

    Since my position is that you could be wrong (ie that your certainty is unfounded and that the possibility of the existence of wormholes is not known), the argument about Time travel is settled, I think.

    We could discuss how the relativity of simultaneity affects presentism if you like.
  18. Novacane Registered Senior Member

    No one is doubting their existance. No one is saying their not there. It's my belief though that 'no' one has of yet, been able to see one or even photograph their physical shape with the exception of photographing a large accretion disk from supermassive Black Holes. Perhaps that's proof enough.

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  19. swivel Sci-Fi Author Valued Senior Member

    It is settled that Time Travel is impossible? I hope that is what you mean.

    If you are saying that Wormholes are real because I can't disprove them, then you are getting into dangerous ontological territory. That's when the Flying Spaghetti Monster and Jesus and Sagan's Purple Dinosaur come swooping into the thread. You are too smart a man to claim something exists because it hasn't been disproven. I know you understand that the burden lies with the wormholers and the string theorists and the dark matter proponents.

    As for the relativity of simultaneity, that is a bad conversation for us. You will source literature that deals with the seemingly bizarre conundrums that human perception creates, while I will be focusing on the reality of a system outside of human perception. That will get us into all sorts of semantic arguments without ever grazing the actual issues. We can try it if you like, but I suggest a new thread for such a topic. We can close this one down if you are now agreeing that Time Travel is impossible and will always remain so.
  20. Pete It's not rocket surgery Registered Senior Member

    No, it's settled that we don't know if it is possible or not.

    No, that would be stupid. I'm saying that neither you nor I know if they're possible or not.
    I'm saying that they are possible within the scope of our current best models of reality - and that's all.

    You presume too much. I'm quite focused on perception-independent reality.
  21. swivel Sci-Fi Author Valued Senior Member

    You might not know if TT is possible or not, but that doesn't extend to myself. I know 100% that TT is impossible.

    Again, wormholes do not exist. The Flying Spaghetti Monster might possibly exist as well, but I doubt both with equal fervor. Your doubt != My doubt.

    I presume just enough. If you think the relativity of simultaneity has anything to say at all about presentism, then you must think that at any moment there is no definable "now". I disagree.

    The reason these issues are so simple for me, but you are mired in doubt, is because I understand time, while you seem to think that the little 't' in equations, and what physicists say about that little 't' has some grander bearing on reality.

    I have all the respect in the world for you, and don't hold this misunderstanding agaisnt you one iota. You are in the company of millions of extremely bright people that also wrestle with these concepts.
  22. Pete It's not rocket surgery Registered Senior Member

    So since it's not possible for you to be incorrect, then I guess you're not human?

    Make up your mind. Do wormholes possibly exist, or do they not?
    Equating wormholes with flying spaghetti monsters is a strawman, since flying spaghetti monsters are not a solution of a well tested physical theory (ie GR).

    I presume just enough. If you think the relativity of simultaneity has anything to say at all about presentism, then you must think that at any moment there is no definable "now". I disagree.

    The reason these issues are so simple for me, but you are mired in doubt, is because I understand time, while you seem to think that the little 't' in equations, and what physicists say about that little 't' has some grander bearing on reality.

    I have all the respect in the world for you, and don't hold this misunderstanding agaisnt you one iota. You are in the company of millions of extremely bright people that also wrestle with these concepts.[/QUOTE]
    Please don't stereotype me. We don't have a chance of a productive conversation if you load me with beliefs and viewpoints wihch I do not necessarily have.

    My position is that the relativity of simultaneity is difficult to reconcile with a universal definable "now", and I'm interested in how you achieve that reconciliation.

    Your distinction between "t" and "real time" is interesting, and I would like to hear more. Do you hold a concept similar to Lorentz's "local time"?
  23. Novacane Registered Senior Member

    When we can go back ten minutes into the past, then I'll really start to worry about the coming weekend.

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