Is relativity self-contradictory??

Discussion in 'Physics & Math' started by Prosoothus, Aug 30, 2002.

  1. Tom2 Registered Senior Member

    Messages:
    726
    Prosoothus is still stuck in his paper bag.

    I stayed away for as long as I could, but I am astounded that this has not been straightened out yet.

    And Tom2 was previously explaining to you that you are misrepresenting special relativity. Not only that, it seems that you misunderstand the "absolute model", because you presented the following website in support of it:

    http://www.physics.wustl.edu/~visse...ight-clock.html

    which is obviously in accordance with special relativity.

    I'm sure you haven't looked at the relativity document I linked you to, and you probably won't in the future, but I'm going to post a link to it here just in case anyone else is interested in learning something today:

    http://www.fourmilab.ch/etexts/einstein/specrel/www/

    As a side note, I should interject that this is the first of your many non-sequitirs. Aside from the fact that there is no hole in relativity, even if there were, that would not prove your theory, because there are multiple theories competing with relativity. As we shall see shortly, yours is not one of them, because "your theory" is really just special relativity.

    This part is important:
    You have assumed that the speed of the light pulse is the same in both directions, despite the fact that you claim you have not. Your derivation is EXACTLY in accordance with special relativity.

    It should be no surprise, then, that you obtain the relativistic result.

    In an absolute model, the person watching the moving mirrors would observe the exact same time for the round trip as would a person riding alongside the mirrors.

    Stationary observer:

    Upward-moving light pulse has speed v+c. Pulse travels distance l1=d+vt1.
    =>t1=l1/(c+v)=(d+vt1)/(c+v)

    rearranging yields

    t1=d/c (surprise, surprise)

    Downward-moving light pulse has speed v-c. Pulse travels distance l2=d-vt2.
    =>t2=l2/(v-c)=(d-vt2)/(v-c)

    rearranging yields

    t2=d/c.

    This is exactly what would be observed by someone moving along with the mirrors, or anyone else, for that matter in the "absolute" model.

    This is taught in any freshman physics textbook.

    Tom
     
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  3. Prosoothus Registered Senior Member

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    Tom2,


    WRONG. I claimed that the speed of light is only c in the absolute frame of reference. Relative to the moving mirrors, the speed of light is SLOWER or FASTER than c. Relativity dictates that the speed of light is c in ALL frames of reference. (c+v) and (c-v) clearly show that I DON't think that the speed of light is c relative to the mirrors.

    What kind of phony math is that???

    Either the speed is c and the distance is d+vt1, or the speed is c+v and the distance is d. Where the hell did you get the idea to increase the speed AND the distance at the same time. Any moron could see that it would balance out if you did it that way.

    I know you didn't make this mistake accidently. I'm surprised that you would provide faulty math to try to prove your point.

    Tom
     
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  5. Merlijn curious cat Registered Senior Member

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    for all v: t1=d/c

    try (d+vt1)/(c+v) = d/c ?
    you will get
    (1+(vt1/d)) / (1+(v/c)) = 1
    thus
    1+ (vt1)/d = 1+ (v/c)
    vt1/d = v/c
    t1=d/c

    blablablabla
     
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  7. Tom2 Registered Senior Member

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    726
    No, it doesn't. What it does clearly show is that you do not understand physics or mathematics. Furthermore, the bogus conclusion you draw from your "analysis" clearly shows that you don't understand logic, either.

    Relativity
    Assume that the speed of light is as Einstein says and look at it from the frame in which the mirrors are moving along the y-axis.

    Event 1:
    Pulse leaves lower mirror at y1=0, t1=0.

    Event 2:
    Pulse arrives at upper mirror, traveling at speed c. This event occurs at y2=d+vt2, because the upper mirror has moved a distance vt2. It is also the case that y2=ct2. Equating the two expressions for y2 yields:

    d+vt2=ct2==>t2=d/(c-v)

    Event 3:
    Reflected pulse returns to lower mirror. It starts at y2 and travels in the -y direction for a time (t3-t2) at speed c. This yields:

    y3-y2=-c(t3-t2)

    It is also the case that y3-y2=-d+v(t3-t2), because the light traverses the distance d minus the distance that the lower mirror moves. Equating the two yields:

    -d+v(t3-t2)=-c(t3-t2)
    (c+v)(t3-t2)=d==>(t3-t2)=d/(c+v)

    So yes, you did assume Einstein's speed of light postulate--Like it or not.

    Then why don't you get it?

    There's no mistake--that's the correct analysis.

    I'm sorry that you have no understanding of Physics I or of Algebra I, but that's no reason to accuse me of trying to trick anyone.

    Why don't you go get yourself an education? Maybe you can pull yourself out of Krackpot Korner one of these days. Until then, maybe you should think about not posting your "theories" in public. Not only do they damage the credibility of sciforums, but they also pose a risk to impressionable young people who come here to try to learn something.

    Tom
     
  8. Prosoothus Registered Senior Member

    Messages:
    1,973
    Tom2,

    You're an idiot. Relativity dictates that it doesn't matter how fast the mirrors are moving, since the speed of light is c in ALL frames of reference. By incorporating vt2 in your formula, you are applying the absolute model. In the relative model, y2 always equals d regardless of the speed of the mirrors. That's why relativity is called relativity.

    Tom
     
  9. overdoze human Registered Senior Member

    Messages:
    310
    My my, how things have changed

    Just stopped by to see what was up at sciforums. Not much, apparently. Same old debates... LOL

    Ok, with all due respect to all participants in this thread, I think you all have taken this discussion far beyond the elementary level at which it can be easily resolved. You don't need math for it; just some common sense.

    The principal point in question is: why should the speed of light in a vacuum (between the mirrors) depend on the velocity of the mirrors through that vacuum? The two phenomena (light propagating through vacuum; mirrors propagating through vacuum) are completely independent from each other. If there is one and only one vacuum, then the speed of light in that vacuum is an absolute constant. This is the "absolute" reference frame Tom (Prosoothus) is talking about.

    Any other reference frame is defined by dragging the coordinate system along with a matter/energy body propagating through the vacuum. If time and space are defined in absolute terms using the vacuum as the basis, then obviously they do not change no matter how you decide to translate your coordinate system (ignoring gravity for this discussion, since we are focusing on special relativity as opposed to GR.) For moving observers, the only thing that can change is their perceptions of time and distance. IOW, the time dilation and length contraction formulae are mathematical descriptions of the illusions suffered by moving observers.

    These illusions are bred by the facts that
    <ol>
    <li>there is one and only one vacuum in which everything exists, and</li>
    <li>that the speed of light in that vacuum is constant omnidirectionally</li>
    </ol>

    Based on these two assumptions (which are indeed not relativistic philosophically speaking in that they dictate existence of an absolute reference frame -- namely the vacuum) I've already derived the Lorentz transformations in the time dilation/length contraction form before on this forum, and Tom came quite a way to repeating my derivation.

    Note that due to the assumption (2), this absolute-frame theory is not Newtonian. In a Newtonian universe, there would be no limit on speed of light; if a moving locomotive shone a light forward, then that light's velocity would truly, really be v+c in an absolute sense. The second assumption makes the model non-Newtonian and indeed makes it possible for a Relativistic (illusionist) theory to be valid.

    Fact is, however, that there is no known way for us to detect the absolute reference frame of the vacuum, IOW we cannot determine whether an object is absolutely stationary or merely moving inertially. Thus, for all practical purposes SR works. However, from the perspective of interpretation and comprehension, SR's conceptualization of the illusory effects as in fact real is both deceptive and counterproductive as far as comprehensibility goes.
     
  10. Prosoothus Registered Senior Member

    Messages:
    1,973
    James, Crisp, Q, and Overdoze,

    Assuming this experiment is done:

    You have clock A and clock B. They are both next to each other on Earth (they are relatively stationairy). Their times are synchronized. Suddenly, clock B speeds away from clock A, and the Earth, at a speed of .90c. Clock B continues to travel at this speed for one year, and then turns around and travels back to clock A, at .90c, for another year. When clock B returns to clock A, clock B comes to rest (it falls into the same frame of reference as clock A and the Earth).

    When the times of the two clocks are compared, what, according to relativity, will be found:

    1) Clock A is slower than clock B
    2) Clock B is slower than clock A
    3) Clock A is synchronized with clock B

    I don't need to know how much one clock is faster than the other, I just need to know which one is faster. Thanks.

    Tom
     
    Last edited: Sep 4, 2002
  11. zanket Human Valued Senior Member

    Messages:
    3,777
    overdoze:

    Neat explanation. A thought though:

    I see it the other way around, that conceptualizing the relativistic effects as illusory is deceptive and counterproductive. The reason being that the effects are just as real as anything else we label as “real.” For example, in the twin paradox, which is explainable within the realm of SR, the reunited traveling twin (or atomic clock or whatever) is younger in a real, tangible way. When the reality of the effects is accepted, the absolute frame of reference becomes an artifact to explain why it isn’t detectable.

    Having accepted the reality, one can move on to be productive in other areas such as cosmology. For example, at this site about models of the universe…

    http://www.cosmologymodels.com/index2.html

    …is this quote: “There is a problem with this [special relativity universe] model. Consider a galaxy rushing away from us at a constant velocity of very nearly the speed of light. Light that it emitted when the universe was half as old as it is now would just be getting to us now and we could not have a lookback time … greater than half the age of the universe. We find we are able to see much further back in time than this.”

    Because the author ignores or otherwise doesn’t accept the reality of SR effects, he sees a problem where there isn't one. Galaxies rushing away from us at relativistic velocities would really, tangibly be hardly aging relative to us, so, despite the travel time of the light, we could observe them at any age, even prior to the formation of the galaxy, all the way back to the first observable moments after the big bang (the cosmic microwave background radiation).
     
  12. overdoze human Registered Senior Member

    Messages:
    310
    The answer is 2). This is due to the fact that clock B is the one that made the round-trip. If instead A sped up so as to catch up with B, then 1) would be true. It is also possible for B to decelerate and A to accelerate and catch up to it in such a way that 3) would hold. Depends on who is doing the most accelerating.
     
  13. overdoze human Registered Senior Member

    Messages:
    310
    Ok, consider rates of metabolism in a reptilian. You can chill it so that its metabolism goes really slow and its perception of the passage of time slows down accordingly. Or you can warm it up so its metabolism goes faster. Fact is that the reptilian's life span is going to depend on how fast its metabolism goes, so you can control its lifespan by controlling its temperature. You can even freeze it solid and thaw it back a million years later -- so you can expand its lifespan dramatically.

    However, if we took the analogy to relativity toward its typical extreme, we would have to claim that by cooling down the reptilian we are actually slowing down the flow of time in its reference frame. You might find that acceptable, but I find that ludicrous. All we did was slow down the rate of reactions -- and by slowing down this rate, we've slowed down the reptilian's measurements of time. So even though the universe continues to evolve at the same rate as ever, the reptilian's structure is evolving slower than normal due to the "suspension" we introduced through lower temperature.

    It's the same thing with moving objects. In moving objects, quantum interactions limited to light-speed take longer to occur between any two objects separated by a given distance than if these objects were absolutely at rest. This is easy to show just by considering a fixed distance between the objects, and calculating the roundtrip time between them using the speed of light as the speed of force carriers. Thus, in moving objects everything must happen slower -- but more so along direction of motion than orthogonal to it. This assymetry gives rise to "length contraction" in addition to overall "time dilation".

    Nobody disputes the reality of the effects. The point is interpretation. Classical relativity requires us to accept the mind-bending concept of each distinct reference frame having its own time and space manifold. This, despite the fact that all these distinct reference frames must coexist within the same universe. Classical relativity allows for retrograde time travel (at least mathematically) -- but when time is considered as a universal process of change and given that only measurements of it can slow down relative to absolute rest, then it becomes glaringly obvious that time travel is impossible. You might be able to see how this easily eliminates all of the paradoxes with time travel in one fell swoop. Time really ceases to be a dimension or a coordinate; it merely becomes a measurement of reaction rate relative to the absolute.

    That is actually incorrect. The "rushing" is due to expansion of spacetime between galaxies, and not to the galaxies' actual velocities through spacetime relative to each other. For any two galaxies to actually be moving relative to each other at relativistic speeds would be astonishingly unlikely, considering that galaxies tend to form from rarefied matter initially spread evenly through the universe, hence upon collapse averaging all the velocities of individual particles to something close to absolute rest. Only later intergalactic gravitational interactions can set galaxies in motion relative to each other, and such interactions hardly result in relativistic speeds.
     
  14. (Q) Encephaloid Martini Valued Senior Member

    Messages:
    20,530
    When the times of the two clocks are compared, what, according to relativity, will be found

    When clock B arrives back on Earth, both clocks at rest relative to each other will be ticking at the same rate however, clock B will have ticked slower during its journey therefore, clock B will show less time had passed relative to clock A.
     
  15. Crisp Gone 4ever Registered Senior Member

    Messages:
    1,339
    Hi Overdoze,

    I find it strange that as a relativist, you seem to opt for an absolute frame of reference. However, all ingredients for complete relativity (no absolute FOR) are in your post:

    "In moving objects, quantum interactions limited to light-speed take longer to occur between any two objects separated by a given distance than if these objects were absolutely at rest. - ... - . Thus, in moving objects everything must happen slower"

    On the other hand:

    "but when time is considered as a universal process of change and given that only measurements of it can slow down relative to absolute rest."

    On one side, I think you are saying that time dilatation for an observer is an illusion (time goes slower relative to some absolute timescale), while on the other hand you agree that all quantum processes occur slower because of the finite interaction speed.

    Two remarks/questions:

    1) How do you account for additional terms in the Lorentz transformations that are not related to length contraction or time dilatation ? These terms additionally "slow" time, and are unrelated to finite interaction speed.

    2) If all quantum processes occur slower, then wouldn't also the perception of this "absolute time" you propose slow down for the time-dilatated observer ?

    As you probably have guessed, I am not in favour of an absolute frame of reference (or absolute timescale if you like). You seem to have thought things over quite a bit, and I really am interested on what your answers on the above questions will be

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    .


    Tom,

    The question you proposed is basically the twin paradox. There are several possible answers (depending on whether you use special or general relativity). Concerning special relativity, the moving clock (B) would be running behind clock A (left on earth). However, if I remember correctly, if you take General Relativity into account, the answer is different. Unfortunately I haven't been initiated in GR, so I guess we'll have to wait for someone knowing the theory to resolve that issue

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    Bye!

    Crisp
     
  16. zanket Human Valued Senior Member

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    3,777
    overdoze:

    That’s an interesting analogy but too apples-to-oranges. Whereas the chilled reptile’s structure would evolve slower than normal in its reference frame, a fast-moving reptile’s structure would evolve normally in its frame, just slower relative to us. A watch either reptile wears could evidence that.

    The slowdown caused by the time required for light or a force to travel between objects moving apart is a Doppler effect and was well understood when relativity came along. Time distortion is observable regardless of the changing distance between objects. For example, a diagram in one of my books shows one ship circling another. The caption is “The top vessel in this diagram moves in a circle of very large radius around the bottom vessel. Since the two ships are always the same distance from each other, we observe no Doppler effect, but we still see relativistic time distortion.” Also “... while Doppler shifts are the result of changes in spatial separation, the relativistic effect is an actual reduction in the rate of time.” Keep in mind that when objects are moving towards each other, the Doppler effect is a quickening rather than a slowdown.

    So bend your mind already!

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    Perhaps, or you could say that time can actually slow down relative to you, yet it remains glaringly obvious that backwards time travel is impossible.

    Many references say that, but when you examine their reasoning it’s based on speculation.

    I disagree about the odds on both counts. A rough calculation tells me that cosmic expansion in a region of space the size of our galaxy is only 2 km/s. On a galactic or even a supercluster scale, then, gravity far overwhelms the expansion to allow the galaxies to form from rarefied matter initially spread evenly throughout the universe. Nature could have initially set all matter in relatively expanding motion (where every piece of matter is moving relative to the other pieces at velocities ranging from 0 to a limit of c, the faster the remoter) and let gravity coalesce matter as it may, which would be only within pockets of space small enough to allow the gravity to overwhelm the expansion.

    Yep, and it’s always debatable. Regarding cosmological time distortion, I prefer this interpretation from one of my books: “What is the age of the universe now? You can’t really answer that question. ... You can’t assign an age to the whole universe if its parts are in motion relative to each other. Each part has its own proper age. Note that this is not because it takes time for the light to get from the distant parts to you. It is because the ever remoter parts are in ever more rapid motion relative to you.”
     
    Last edited: Sep 5, 2002
  17. Prosoothus Registered Senior Member

    Messages:
    1,973
    Q, Crisp, and Overdoze,

    Quote frome Overdoze:

    Quote from Q:

    Quote from Crisp,

    I don't understand??:bugeye:

    According to clock B's frame of reference, the Earth and clock A sped away at .90c from clock B, while clock B remained stationairy. Why is it that clock B is slower than clock A, and not vice versa?? Doesn't relativity dictate that both of the frames of reference (clock A's and clock B's) are equally valid???

    The reason I brought up this "experiment", was that if it's true what the three of you said, then clock B was ticking slower than clock A because it was travelling faster than clock A in the absolute frame of reference. This would mean that the absolute motion (which overdoze argues can't be determined) of a clock can be derived from the "perceived" time dilation it is experiencing, compared to the time of the stationairy clock.

    Example: If you have two clocks (A and B), and clock B begins to travel at .90c, the difference between the time dilations of the two clocks would be the time dilation factor dictated by relativity ONLY if the clock A was at absolute rest. However, if the time dilation between the two clocks is smaller than the time dilation dictated by relativity, that would mean that clock A is not stationairy in the absolute frame of reference, but that it is moving in the opposite direction of clock B in the absolute frame of reference.

    Tom
     
    Last edited: Sep 5, 2002
  18. overdoze human Registered Senior Member

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    310
    Yes, I see how I might have confused you.

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    Perhaps this might help. I consider two aspects of reality: the actual reality, and measurements of it. This applies to time just as well as to anything else. Thus, there is the actual flow of time, and then there are measurements of it made by observers.

    If an observer's measurement of time is distorted so as to make time flow slower for the observer, then the observer will in fact experience a slower reaction rate. This effect is both illusion and reality, in that it is real for the observer (everything happens slower) but at the same time it is illusory (since time never in fact slowed down; light is still propagating at the same rate even in the observer's frame of reference -- it's only the bidirectional, roundtrip, propagation interval between any two relatively fixed points that increases for the moving observer.)

    If you consider the Lorentz transformations in the time dilation/length contraction form, then there are no additional terms to account for. If you recall, I've already derived these transformations on this forum before. See here:

    http://www.sciforums.com/showthread.php?s=&threadid=7801&perpage=20&pagenumber=8#post124437

    On the other hand, if you're talking about the general form of the transformations that includes the initial separation between events and allows to actually calculate the time of observing a remote event for a given inertial observer, then the additional terms merely have to do with this initial separation between the observer and the event.

    This would be a qualified yes. In fact, not all quantum processes occur slower. Conspicuously, light itself is not affected. Rather, it is all the processes that depend on exchange of information (e.g. through virtual force carriers) that must slow down. This is only due to the extended time interval over which these exchanges can occur, due to the system's motion relative to the medium through which light propagates (the vacuum.) Note that in mentioning "slowing down" and "extended time intervals", I am inherently using the notion of absolute time. Thus no manner of motion could ever affect this absolute, universal time flow; all you can ever accomplish is to slow down reactions in a system by setting it in motion with respect to the absolute reference frame.
     
  19. overdoze human Registered Senior Member

    Messages:
    310
    Apples and oranges are still fruits. And I'm comparing fruits to fruits. The point was that just as frost has a retarding effect on the chemical reaction rates in a lizard, so does motion relative to absolute rest have a retarding effect on the quantum reaction rates of any massive object.

    You misunderstood me. I was not talking about objects moving apart. Rather, I'm talking about objects moving together, maintaining constant distance between each other.

    It's the only reasonable conclusion. The alternative is that we are at the center of the universe, and the rest of the universe is flying away from us. If you take such a primitive, anisotropic, geocentric view, then I can see your point. However, if you assume that our region of space is not special in any way, then the same picture of cosmic expansion away from the observer must be in evidence no matter where in space the observer is located. Given that matter's speed of propagation through space is limited to below c, the only way this could work is if the space itself expanded rather than galaxies flying away from each other through rigid space (otherwise, galaxies farther and farther away from us would eventually have to fly through space at speeds faster than c.)

    I don't pretend to know which calculation you are referring to, but let's just work with your figure. Our galaxy is roughly 100,000 light years across. The distance between two typical galaxies in a cluster is perhaps 1,000,000 light years. At this scale, the expansion would result in 20 km/s. If you take something 15,000,000,000 light years away, it would be traveling away from the observer at 300,000 km/s (lightspeed.) Anything farther than 15 billion light years would actually recede faster than speed of light, which means we will never ever be able to see it. This would be the horizon of the observable universe (for the given expansion rate) -- where "observable" means observable in principle, even in the remotest future. Granted, the figures above are all ballpark estimates, but hopefully you get the idea.

    There is a good point here, but I don't think it's entirely correct. Given an assumption that space expands everywhere uniformly, you can start with the observed local densities of matter and work backwards, considering interactions between the inflationary force, momentum, and gravity, and working with the best estimates of the past history of the inflationary force obtained from averaging observations of distant cosmological objects. You would be able to calculate roughly the point back in time when all currently observable matter was crammed together in densities and temperatures approaching infinity. The time interval between then and now would then be roughly the age of the universe.
     
  20. overdoze human Registered Senior Member

    Messages:
    310
    But they are not equal. Special relativity only discusses inertial reference frames. In your example, clock B is accelerating while clock A is not. This makes all the difference.

    Not exactly. Clock B was traveling faster with respect to the absolute frame of reference on average during its entire trajectory. This means, for example, that it might have been moving slower when it was moving away from A, but moving super-fast when it was returning to A. Or maybe it was moving super-fast when it was moving away from A and slow when it was returning to A. Or any other possibility in between. The reason it works out the same in either case, is due to the symmetry introduced by B's looping trajectory.
     
  21. Prosoothus Registered Senior Member

    Messages:
    1,973
    Overdoze,

    How do you know that B was accelerating from A??? Why are you so sure that A wasn't accelerating from B???How are you determining which clock is stationairy, and which one is accelerating??

    One more thing: For the sake of simplicity, assume that there is no accelleration. Assume that clock B's speed increases from 0 to .90c instantaneously.

    Tom
     
    Last edited: Sep 5, 2002
  22. overdoze human Registered Senior Member

    Messages:
    310
    Because B will feel the artificial gravity, and A will not.

    The time course of acceleration doesn't matter. See the second part of my reply above. That explains the true relevance behind acceleration.
     
  23. (Q) Encephaloid Martini Valued Senior Member

    Messages:
    20,530
    Clock B will experience acceleration on the outbound trip as well as the return trip. According to GR, objects will experience time dilation effects within a gravity well, relative to another observer.

    gLT/c^2

    g = acceleration due to gravity
    L = distance between observers
    T = length of time of gravitational effects
    c = well, you know this one.
     

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