How accurate are atomic clocks??

Discussion in 'Physics & Math' started by Prosoothus, May 26, 2002.

  1. Crisp Gone 4ever Registered Senior Member

    Messages:
    1,339
    Hi Tom,

    This is what James tried to explain by placing an alarmbell in the situation (when the observer passes the 270.000 km barrier in the stationary frame of reference). What we are comparing here are the following two events:

    Event 1: For the stationary observer, the light passes at +300.000 km. This is ofcourse after one second for the stationary observer.

    Event 2: For the stationary observer, the light passes at -300.000 km. This is ofcourse after one second for the stationary observer.

    Conclusion: for the stationary observer the two events are simultaneous.

    For the moving observer, our claim is that he sees event 1 happen after 0.229s (which intuitively can be understood because that event "happens closer to him"), while on his clock, event 2 only happens after 4.35s.

    Conclusion: for the moving observer the events are no longer simultaneous.

    This does not mean that for every stationary second, a different amount of time passes for the moving observer, depending on whether the light moves forward or backward. As a matter of fact, regardless of events we are observing, the "classical" time dilatation formula t = <font face="symbol">g</font>t will do just fine in that case (that formula does not apply for all events though). If I remember correctly, that was exactly the 0.435s we used a while back. Conclusion: for one stationary second, only 0.435 seconds pass for the moving observer, or, if we inverse the reasoning: for one second on the moving observer's watch, 2.29s pass on the stationary clock: the moving clock ticks slower.

    Hope this explains why there are two different times.

    Bye!

    Crisp
     
  2. Google AdSense Guest Advertisement



    to hide all adverts.
  3. Prosoothus Registered Senior Member

    Messages:
    1,973
    Crisp,

    Your conversions from one frame of reference to the other are wrong. Let me explain:

    After 1 stationairy second, one beam of light is 30,000 stationairy km away from the observer, while the other beam of light is 570,000 stationairy km away from the observer.

    When you apply time dilation:

    After 0.435 observer seconds, one beam of light is is 30,000 stationairy km away from the observer, while the other beam of light is 570,000 stationairy km away from the observer.

    When you apply length contraction:

    After 0.435 observer second, one beam of light is 68,965 observer km away from the observer, while the other beam of light is 1,310,344 observer km away from the observer.

    Therefore:

    v1=68,965 km/0.435 s = 158,540 km/s

    v2=1,310,344/0.435 s = 3,012,285 km/s


    I don't know why you insist on using two times when we know that one stationairy second equals .435 observer seconds in both cases. It is a fact that both events take .435 seconds for the moving observer because both events took 1 second in the stationairy frame of reference.

    Tom
     
  4. Google AdSense Guest Advertisement



    to hide all adverts.
  5. Crisp Gone 4ever Registered Senior Member

    Messages:
    1,339
    Ehrrrr

    Hi Tom,

    My explanation was perhaps not as clear as I had hoped. Allow me to largely repeat myself, but to indicate where your and my reasoning differ.

    First of all, I hope you agree that the lightbeam arriving at -300.000 km and at +300.000 km (for the stationary observer) are two different events, clearly seperated in space for the stationary observer. They are not seperated in time for this observer, they both occur at time t = 1s (if we take t = 0s the time the lightbeams are emitted, when the two observers coincide).

    Hence: Stationary observer: Event 1 and 2 occur at two different places, at the same time.

    Now we take these two events fixed and calculate how the moving observer thinks of those events. We need to use the Lorentz transformations to do that, and these transformations transform time and space in a coupled way. One direct result is that the concept of simultanity for one observer is no longer preserved. For the moving observer the two events are no longer simultaneous, which means that one event happens before the other, i.e. that the times they occur at are different (in numbers: t = 0.229s for event 1 and t = 4.35s for event 2). The Lorentztransformations break simultanity, that is the key to the apparant paradox.

    The time dilatation formule t = <font face="symbol">g</font>t' is only valid for events that occur at the origin of the moving observer. For example, when he looks at the clock he has on his wrist. For this clock, time will run slower for a stationary observer, who is comparing it to a clock at his origin. The formula is no longer valid for events that do no occur at the origin of the moving observer (i.e. the lightbeam positions).

    "I don't know why you insist on using two times when we know that one stationairy second equals .435 observer seconds in both cases. It is a fact that both events take .435 seconds for the moving observer because both events took 1 second in the stationairy frame of reference."

    Nope, this assumes that simultanity is preserved by the Lorentztransformations. Purely intuitively, you can deduce that the times HAVE to be different for a moving observer. One event happens closer to him (the seperation is 30.000km in the stationary observer's frame of reference). The other event happens quite a bit further away (570.000 km in the stationary observer's FOR). A not entirely correct reasoning would be that it takes longer for the moving observer to "see the light of the furthest event" arrive at the position -300.000 km (for the stationary observer). The moving observer's clock will keep on ticking until he can "know" the light has arrived.

    The above reasoning is not entirely correct (there is more to it than the finite transmission speed of signals) but it might help you understand why there is a difference in times for the lightbeam shining forward or backward.

    Bye!

    Crisp
     
  6. Google AdSense Guest Advertisement



    to hide all adverts.
  7. Prosoothus Registered Senior Member

    Messages:
    1,973
    Crisp,

    Let me put it another way:

    Assume that there are two targets 300,000 km away from the stationairy observer. We both agree that the light hits both targets at the same time in the stationairy frame of reference.

    Question: After 0.435 seconds in the moving observers frame of reference(which is 1 second in the stationary observers frame of reference), did the two beams of light hit their targets??

    Notice, I'm not asking if the observer percieved the beam of lights to hit their targets at the same time, I'm asking did the two beams of light hit there targets after 0.435 seconds in the moving frame of reference.

    You keep on implying that the observer percieves that they hit their targets at different times. You are correct. Even if they did hit the targets at the same time, as I'm suggesting, it would take longer for the light to return to the observer the farthur the target is from the observer. So the observer would not see both beams hit their targets at the same time, even if they actually did.

    It's like two stars exploding at the same time. One star is 100 light years away and the other is 1000 light years away. You will not see them blow up at the same time, but that doesn't mean that they didn't blow up at the same time.

    Therefore, let's take the observers perception out of the example so that it is simpler.

    So I ask again: After 0.435 seconds in the moving observers frame of reference(which is 1 second in the stationary observers frame of reference), did the two beams of light hit their targets??

    Tom
     
  8. Crisp Gone 4ever Registered Senior Member

    Messages:
    1,339
    The discussion is taking the feared course

    Hi Tom,

    "Question: After 0.435 seconds in the moving observers frame of reference(which is 1 second in the stationary observers frame of reference), did the two beams of light hit their targets??" Notice, I'm not asking if the observer percieved the beam of lights to hit their targets at the same time, I'm asking did the two beams of light hit there targets after 0.435 seconds in the moving frame of reference.

    Hrm, we're walking on the edge of physics and metaphysics again

    Please Register or Log in to view the hidden image!

    . What considers the theory of special theory of relativity: no, the beams did not both hit their target, only the beam going along with the observer did (after 0.229s < 0.435s).

    "You keep on implying that the observer percieves that they hit their targets at different times. You are correct. [...] So the observer would not see both beams hit their targets at the same time, even if they actually did."

    I should add that even taking the finite time required for the observer to be informed of this event into account still leaves some "residual time dilatation". I've been thinking about that, and I thought I figured it out but there seemed to be a flaw in my reasoning. I hope James will clarify this a bit.


    I can already feel where this discussion is going to end up (does special relativity describe reality or not). There is no way to experimentally verify this ofcourse, but there is a philosophical counter argument: if the beams DID actually hit their targets, but the observer has not yet perceived it, then the principle of causality breaks down. He might not have perceived the second beam hitting the target, but because he witnessed the first beam hitting the target, he knows deep inside that also the second beam did hit the target, but that he just did not perceive it yet. However, that way, information was transferred faster than the speed of light, and we all know where that leads to (people getting killed by bullets before they were even fired etc). You can question the principle, but I still have to meet someone who observed the effect before the cause had happened.

    Bye!

    Crisp
     
  9. allant Version 1.0 Registered Senior Member

    Messages:
    88
    Oh no done it agin - shifted frames of refernce.

    Lets see if we can undo this. Two clocks staionary 1 meter apart.
    cool and groovy speed of C ok.

    Now speed both of them up. Now to an observer traveling with either clock. (allowed since both are in the same FOR) For this guy the distance apart is still 1 meter and the time taken is the same - cool and groovy.

    Now shift FOR back to the earth, in the first situation we are in the same FOR as the clocks so we see the same thing as the traveler with the clocks.

    Situation two from earth what do we see ? First the distance the clocks are apart "appears" to be shorter ! But then so does the time taken for the light to travel from one clock to the other by the same amount. So let this factor be y ( y will be less than 1) then Distance Travelled as seen from earth = 1 Meter * y ; Time taken as seen from earth = Original time * y ; now devide the two we have (1 * y)/(t *y) or 1/t * y/y or 1/t; Now the original speed in the first event = 1/t so you orginal equation was wrong.

    your equation
    t1-t2 = t3-t4
    is not correct it should be
    t1-t2/d1 = t3-t4/d2

    The first is wrong because it assume d1 = d2. Which is true for an observer with the clocks but not true for the observer on the earth. but distance per time i.e speed of light IS the same.


    Some people cant understand relativity
    Some can do the maths
    Very few understand relativity. - ( Can't remeber who - maybe Feynman ?)
     
  10. James R Just this guy, you know? Staff Member

    Messages:
    30,641
    Tom,

    <i>Why don't the two of you face the fact that there is no solution for the example that I have given, where the light travels at c in both cases.</i>

    I've given you the solution. It's right there in front of you.

    <i>I'm still surprised by your belief that if the observer points his flashlight forward, for every stationairy second the observer experiences .229 seconds, but if the observer points his light behind him, then for every stationairy second, the observer experiences 4.35 seconds.</i>

    That's not true. For every stationary second, the stationary observer sees the moving observer's clock tick off 0.44 seconds. That is a constant.

    Time dilation is not something an object <b>has</b>, as you seem to think, but something an observer <b>sees</b>.

    <i>Obviously, the observer can't experience two time dilations at the same time, can he?? Why don't the two of you think about what you are saying???</i>

    Why don't you think about what we're saying? I'm sick of repeating myself.

    <i>The two of you assumed that Einstein is correct regarding the invariance of light, even though it hasn't been experimentally proven.</i>

    It has been experimentally verified, over and over again in many different ways. Wake up and smell the coffee, Tom.

    <i>Now, it turns out that it can't be mathematically proven either.</i>

    Of course not. That's what the word <b>assumption</b> means.

    <i>I'm sorry I can never accept your explanation.</i>

    That's because of you unwillingness to learn something new.

    <i>The observer's clock can't indicate that 0.229 seconds and 4.35 seconds passed at the same time.</i>

    It doesn't. In fact, it indicates 4.35 seconds 4.121 seconds after it indicates 0.229 seconds. Duh!

    <i>How can you or James possibly prove, using atomic clocks, that 1 stationairy second can equal both 0.229 and 4.35 seconds for the observer??</i>

    That's not what I proved. Please review my previous posts.

    <i>Your conversions from one frame of reference to the other are wrong.</i>

    'fraid not.

    <i>After 1 stationairy second, one beam of light is 30,000 stationairy km away from the observer, while the other beam of light is 570,000 stationairy km away from the observer.</i>

    Yes.

    <i>After 0.435 observer seconds, one beam of light is is 30,000 stationairy km away from the observer, while the other beam of light is 570,000 stationairy km away from the observer.</i>

    Wrong.

    <i>After 0.435 observer second, one beam of light is 68,965 observer km away from the observer, while the other beam of light is 1,310,344 observer km away from the observer.</i>

    Wrong.

    <i>Therefore:....</i>

    Wrong.

    <i>Assume that there are two targets 300,000 km away from the stationairy observer. We both agree that the light hits both targets at the same time in the stationairy frame of reference.</i>

    Ok.

    <i>Question: After 0.435 seconds in the moving observers frame of reference(which is 1 second in the stationary observers frame of reference), did the two beams of light hit their targets??</i>

    One of them did, prior to 0.435 seconds. It hit at 0.229 seconds. The other is still going, from this point of view.

    <i>Notice, I'm not asking if the observer percieved the beam of lights to hit their targets at the same time, I'm asking did the two beams of light hit there targets after 0.435 seconds in the moving frame of reference.</i>

    The questions are indistinguishable.

    You can't ask, in relativity, when an event "really" happened. Each observer has his own reality. The time he measures is the "real" time, as far as he is concerned. Nothing he can do will show things to be otherwise. Time and space are relative. That's the whole point.

    <i>It's like two stars exploding at the same time. One star is 100 light years away and the other is 1000 light years away. You will not see them blow up at the same time, but that doesn't mean that they didn't blow up at the same time.</i>

    That's why you have to take the light travel time into account. Once you've done that, you're left with the Lorentz transformations or the time dilation and length contraction formulae. They deal with events separate from issues of light travel time, as I've already explained.
     
    Last edited: Jun 26, 2002
  11. Prosoothus Registered Senior Member

    Messages:
    1,973
    James R,

    Haven't you been listening to anything that Overdoze of I have been saying on this thread. There has NEVER been an experiment that measured ONLY the one-way speed of light in a moving frame of reference. ALL experiments that have measured the speed of light in a moving frame of reference, have been measuring the AVERAGE of the round-trip speed of light to a mirror, or object, and back. If you believe that there was ever a device made that measures only the one-way speed of light, please share.

    Well then, since it's an assumption let's assume that it isn't correct.

    I noticed that you haven't responded to Overdoze's post. The one where he proves that if you assume that the omnidirectional speed of light is only c in a abslolute frame of reference, you would get the same results as you would from Einstein's relativistic formulas.

    Therefore, thanks to Overdoze, there are now two models:

    1) Relativity model:

    a) There is no absolute frame of reference.
    b) Time dilation occures as an object travels faster.
    c) Length contraction occures as an object travels faster.

    2) Absolute model:

    a) There is an absolute frame of reference.
    b) The omnidirectional speed of light is c only in the absloute frame of reference.

    Pick one. Which one is more logical to you? Overdoze proved that they both give the same results, therefore they are both valid.


    Tom
     
  12. James R Just this guy, you know? Staff Member

    Messages:
    30,641
    Tom.

    <i>Haven't you been listening to anything that Overdoze of I have been saying on this thread. There has NEVER been an experiment that measured ONLY the one-way speed of light in a moving frame of reference. ALL experiments that have measured the speed of light in a moving frame of reference, have been measuring the AVERAGE of the round-trip speed of light to a mirror, or object, and back. If you believe that there was ever a device made that measures only the one-way speed of light, please share.</i>

    Read this, please, and get back to me:

    <a href="http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html" target="_blank">Experimental basis of special relativity</a>

    <i>Well then, since it's an assumption let's assume that it isn't correct.</i>

    That assumption does not accord with experimental evidence. Relativity does.

    <i>I noticed that you haven't responded to Overdoze's post. The one where he proves that if you assume that the omnidirectional speed of light is only c in a abslolute frame of reference, you would get the same results as you would from Einstein's relativistic formulas.</i>

    You didn't look hard enough, then.

    <i>Pick one. Which one is more logical to you? Overdoze proved that they both give the same results, therefore they are both valid.</i>

    'fraid not.
     
  13. overdoze human Registered Senior Member

    Messages:
    310
    HELP!!! LOL

    I'm on this board more or less continuously for a week, and discussion crawls. I leave for two days, and return to find a ton of new posts!

    Please Register or Log in to view the hidden image!

    Arrrgh....

    Ok, I'll just have to go back in space and time to where my last post was addressed by James R and Tom, and pretend none of what followed exists at the moment... First James R:

    First, thank you for stamp of approval.

    Please Register or Log in to view the hidden image!

    However, if you re-read my derivation then you will discover it indeed assumes, even while not requiring, an absolute reference frame. The reasoning used in conceptualizing time dilation relied very heavily indeed on an absolute frame. In fact, you'll notice that under my formulation the absolute frame is the one with the fastest flow of time among all frames of reference. You will also note that the derivation was based lock stock and barrel on bidirectional flows of information. This latter is a concept to which you and Crisp seem to be opposed. Well, I hope I demonstrated the concept is entirely consistent with relativity and all of its experimental confirmations to date.

    Unsupported, true. Unreasonable? If so, then what is the reasonable alternative? Each moving frame exists in its own parallel universe, would be more reasonable? Under what common context do the various FORs co-exist and interact? That unifying context is precisely the "absolute" FOR in my derivation.

    I disagree. The concept is only superfluous if there was a less superfluous alternative. There is none to my knowledge, however.

    Come on JR, I'm sure you've outgrown the typical toddler difficulty of switching perspective. We are, both of us, talking about the same exact effects -- just from two different perches. In your example, the rulers and clocks are stationary with respect to the frame, but it's improbable that in real life they would be stationary in an absolute sense. What your inertial observer would perceive as "no time dilation or length contraction effects" would be precisely the outcome of time dilation and length contraction effects applied to the observer itself. The fact that two distinct FORs observe the same experimental outcome does not imply that there is only one distinct FOR.

    I wasn't going to go into this to such a depth, but since you insist...

    With respect to the first sentence, the GR equivalence of gravitational fields to simple acceleration is in fact flawed at all scales above the differential limit. In real life, gravitational fields are spatially anisotropic, and any gravitational field will induce tidal stresses, however weak, in an otherwise "inertial" observer -- which is physically distinct from straightforward acceleration. So in GR, you cannot contemplate any inertial "objects" directly (because there's no such thing); instead you must subdivide it into an infinity of point-like reference frames, and integrate over the result to derive real-world behavior.

    With respect to the second sentence, even while you are standing on the earth surface, you are still both in freefall as part of a combined you-earth body. If you would recall, this whole thing started with mention of a QM-centric perspective of gravity in terms of gravitons. Well, from this particular perspective the "forces" binding you and the earth together look no different than the forces binding your constituent atoms together.

    With respect to the last sentence, if the ground were providing an upward force with no force to counteract it, you would fly off into space. The fact that you remain on the ground means there is zero net force, or a balance of forces. Either that, or stop using the "force" terminology altogether.

    Well, space-time is also a hypothetical entity at present. I don't believe anyone has detected "space-time" yet. Even detection of hypothetical gravitational waves might amount to nothing more than detection of graviton radiation. Precession of perihelion of Mercury is derivable using light-speed-limited gravitons just as easily as using space-time. Ditto for "frame-dragging", whenever it does actually get measured.

    LOL What causes the plague?
    Nobody knew what caused the plague, but they could describe the symptoms very well. I suppose, with 20-20 hindsight, they were right and it was after all pointless to delve deeper into the problem.
    No requirement, other than the observed facts that remain to be explained (as you said, "nobody knows why...") Are explanations really that superfluous?

    For example, using the conceptual framework I used to re-derive the Lorentz transforms, the concept of time travel suddenly disintegrates. There is only a single, unidirectional, global flow of absolute time, but relatively slower matter-energy reaction rates within travelling reference frames. Time ceases to be a dimension, and returns to its historical role as a mere parameter. So, are conceptual frameworks really so irrelevant when trying to interpret mathematical results? Especially vis a vis what is possible and what is not?

    Ok, now for Tom's reply:

    'fraid not. That is JR's misinterpretation or misrepresentation; choose your favorite terminology. It does imply, via its re-derivation of the Lorentz transforms, that for moving frames it will appear as if speed of light is c omnidirectionally.

    Go over my derivation again; you'll see that you're wrong. That is, time doesn't really slow down in a sense of it being a somehow independent property of the FOR; rather all processes slow down in traveling FORs, in effect leading to their clocks ticking slower. Similar for length contraction.

    That is correct enough. That illusion is precisely the reason behind the consistency of the mathematical formulation of Special Relativity, both internally and with respect to confirmatory experiments.

    No, relativity is quite right. What is wrong, is the popular interpretation (or rather, misinterpretation

    Please Register or Log in to view the hidden image!

    ) of the mathematical and experimental results.
     
  14. overdoze human Registered Senior Member

    Messages:
    310
    BTW JR, Crisp, et al:

    From the website JR posted, at this subsection:

    <a href="http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html#one-way tests">One-Way Tests of Light-Speed Isotropy</a>

    find the following text:

    (emphasis mine.)

    I see I wasn't the first one to think along these lines... But then it's truly rare to be the first, especially in an issue that is a century old.
     
  15. James R Just this guy, you know? Staff Member

    Messages:
    30,641
    overdoze,

    <i>If you re-read my derivation then you will discover it indeed assumes, even while not requiring, an absolute reference frame.</i>

    Your derivation would be no different if I labelled you "absolute" frame as an arbitrary "stationary" frame, as in the usual relativistic derivations.

    You postulate an absolute frame. It is unnecessary. In this situation, Occam's razor says that we should accept the explanation with the fewest number of required entities. Your theory has one more than relativity, so relativity should be provisionally accepted unless your theory makes predictions which differentiate it from relativity (supported by evidence).

    <i>With respect to the first sentence, the GR equivalence of gravitational fields to simple acceleration is in fact flawed at all scales above the differential limit. In real life, gravitational fields are spatially anisotropic, and any gravitational field will induce tidal stresses, however weak, in an otherwise "inertial" observer -- which is physically distinct from straightforward acceleration.</i>

    Yes, I know. How is that relevant here?

    <i>With respect to the second sentence, even while you are standing on the earth surface, you are still both in freefall as part of a combined you-earth body.</i>

    But I'm talking about your interaction with the Earth, not the interaction between the Earth-you system and something else.

    <i>With respect to the last sentence, if the ground were providing an upward force with no force to counteract it, you would fly off into space.</i>

    That would be true in flat spacetime, but this spacetime isn't flat.

    <i>Well, space-time is also a hypothetical entity at present.</i>

    I can walk from here to the other side of the room. There seems to be observable "space" here. I'm sure you have it where you are too. But I don't see any gravitons here.

    <i>Precession of perihelion of Mercury is derivable using light-speed-limited gravitons just as easily as using space-time.</i>

    Link or reference, please.

    <i>Nobody knew what caused the plague, but they could describe the symptoms very well. I suppose, with 20-20 hindsight, they were right and it was after all pointless to delve deeper into the problem.</i>

    The cause of the plague which we now know of is not a "final" cause in the Aristotlean sense.
     
  16. allant Version 1.0 Registered Senior Member

    Messages:
    88
    Overdoze : If understand what you are saying it is the interpretation of SR and GR not the derivation you are arguing.

    This is based on an idea of there being a fastest time rate, minimum mass, this defining the basis FOR. However it is important to note this is a local FOR and not a global one. Two objects both in this state but at two different places can be moving relative to each other and have a different time rate. This is caused by gravity - the curve of space.

    Nor is it possible to choose the slowest since it is possible to find three places call then A , B and C. where A is faster than B, B faster than C and C faster than A. This may sound anti-common sense but then nature never agreed to common sense.
     
  17. overdoze human Registered Senior Member

    Messages:
    310
    Touche

    JR,

    It seems I was wrong. Somehow, I've been under impression that I've seen a lightspeed-limited graviton derivation of perihelion precession. I couldn't find it anywhere after an hour's search, so I don't know what happened exactly. Maybe I saw it in a dream?

    Please Register or Log in to view the hidden image!



    Well, ok, you got me there. Hands down, no contest. However...

    Ok, hold your horses. I don't have a theory (at least not yet), only an interpretation. The interpretation is an answer to the question of "where does relativity come from". In absense of an answer, all you have is an unanswered question, so I'm not sure what Occam's razor has to do with that. As far as I know, Occam also preferred answers to shrugs. (and the answer I'm giving is not just an arbitrarily tacked-on one; it's an integral part of the interpretation.)

    Now, this "entity" I'm "introducing" -- the absolute reference frame -- can we really do without it? Suppose you have two distinct reference frames A and B. One measures time as one thing, another as something else -- and similar for length. Are we to postulate that there really are two distinct time flows in the universe -- one for each frame -- merely by the virtue of their relative movement? If you have a googol FORs, do you have a googol different time axes? And how exactly does the universe support such a wild abundance of distinct coordinate systems at the same time, while simultaneously allowing all of them to interact in a consistent fashion? Or perhaps there is a single time, and a single space, and all the FORs are just measuring them differently? IMHO, it's the latter proposal that has the fewest number of entities.

    And actually, let's count some entities:

    SR:
    <ol>
    <li>All inertial observers are equivalent (Principle of special relativity)</li>
    <li>The velocity of light is the same in all inertial systems</li>
    </ol>

    SR according to me:

    <ol>
    <li>There exists a cosmic medium within which all observable events take place</li>
    <li>Within this cosmic medium, the velocity of light is the same in all directions</li>
    </ol>

    Lessee... Einstein:2, me:2. Seems like a tie, don't it? But IMHO, my premises are more intuitive, simpler, and somehow have a more fundamental flavor.

    Well, there's the rub. Curved spacetime is a mathematical abstraction. Or would you suppose that quantum particles are in reality traveling probability distributions, rather than the latter being merely a mathematical model of the former? Question is, what is behind the model? When you computationally model a fluid, you make do with vector fields. However, they don't exactly correspond to the real-life nature of fluids, do they. Granted, my thought on GR is not nearly as advanced as my SR comprehension, and neither is the requisite math on my side of things. I'm working on it though in my spare time, however slowly... But meanwhile, we should keep in mind that a mathematical model does not necessarily a valid description make. A model, yes. An explanation... it would have to make sense first, won't it?

    Newton had a mathematical model of gravity too, and it held up pretty well in his time. However, he personally despised his own model from the outset (he couldn't grok invisible forces acting over empty distances.) Einstein came up with curved spacetime, but he fudged it to agree with Newtonian gravity; the precise relationship between mass and curvature was never derived from first principles. I don't have a very good understanding of this, but I've seen on multiple occasions people complaining that GR has otherwise inexplicable factors built in that magically compensate for lightspeed-limited propagation of gravitational interaction just so as to conserve energy. As far as I understand, graviton-based models also fail to conserve energy in absense of additional fudge factors (e.g. orbiting bodies react to "retarded" parameters of each other, and spiral out of orbit as a result.) To top it off, Einstein made time into a dimension, which IMHO is a non-starter. Time has no business being a dimension. And so the math works out, but why? Is it because the original premises are correct as stated, or is it because the original premises are in turn a consequence of something that actually makes sense for a change? At least in the case of SR, I've shown the latter to be a distinct (if not an outright obvious) possibility. Apparently, I wasn't the first one either.

    You can make all the claims you want about how spacetime is curved; that doesn't necessarily give you a handle on what is really going on. Computationally, maybe. Exegetically, no. Generally speaking, you've got to be willing to entertain alternatives, as your sig says. Otherwise you end up sounding like a modern-day flat-earther (which in your case would me more like warped-earther

    Please Register or Log in to view the hidden image!

    )

    Ok, I don't see any gravitons either.

    Please Register or Log in to view the hidden image!



    Though I can't help but notice your usage of "space" rather than "spacetime". Fine by me, as I have yet to be startled by the spectacle of anyone strolling along time.
     
    Last edited: Jun 27, 2002
  18. Prosoothus Registered Senior Member

    Messages:
    1,973
    Overdoze,

    I disagree. Relativity states that time slows down. However, both of us agree that time does not slow down, only reactions slow down. There is a huge difference.

    It's like me saying that catalysts speed up time, instead of speeding up chemical reactions.

    Tom
     
  19. Prosoothus Registered Senior Member

    Messages:
    1,973
    James R,

    From the link you provided:

    Since, we can't rule out the fact that the one-way speed of light in a moving frame of reference is not c, we can assume that the principle of invariance of light could be incorrect.

    After all, it's just an assumption anyway.

    As I stated before, and nobody listened to me except overdoze, a light clock proves that the principle of invariance of light is wrong. However, knowing you, you would probably argue that the light clock slows down because time slows down, instead of taking the more rational approach.

    Tom
     
  20. overdoze human Registered Senior Member

    Messages:
    310
    Tom,

    This might be splitting hairs, but relativity as a mathematical framework in fact doesn't say what you claim it says. It's the people interpreting the math that keep "saying" things.

    So while I'm entirely in agreement with you when it comes to interpreting the time dilaiton results (in terms of decreased reaction rate as opposed to stretching some imaginary time metric), the fact remains that the formulas predict all moving mechanisms (including clocks), regardless of specifics, will slow down. That's the unambiguous and indisputable message of the math.

    Well anyway, this is about as far as I'll take this particular debate. So if you want to have the last word, go right ahead.

    Please Register or Log in to view the hidden image!

     
  21. Prosoothus Registered Senior Member

    Messages:
    1,973
    Overdoze,

    I didn't know that. The only people I've ever discussed relativity with are on this board. I've been on this board for months, and everyone has been arguing with me that relativity states that time is slows down.

    If they said in the beginning that clocks slow down, but that doesn't necessarilly mean that time slows down, I would've saved everyone alot of time.

    Please Register or Log in to view the hidden image!



    But then, I wouldn't know what I know now.

    Please Register or Log in to view the hidden image!



    Tom
     
  22. James R Just this guy, you know? Staff Member

    Messages:
    30,641
    overdoze,

    <i>I don't have a theory (at least not yet), only an interpretation. The interpretation is an answer to the question of "where does relativity come from".</i>

    Interpretations abound. You are welcome to yours, of course. If your interpretation has no observably different consequences to mine, it doesn't matter much, does it? Compare, for example, the Copenhagen and Many Worlds interpretations of quantum mechanics (assuming you're familiar with QM). Neither interpretation changes the usefulness of the theory. Both are compatible with it.

    <i>Are we to postulate that there really are two distinct time flows in the universe -- one for each frame -- merely by the virtue of their relative movement? If you have a googol FORs, do you have a googol different time axes?</i>

    Yes.

    <i>And how exactly does the universe support such a wild abundance of distinct coordinate systems at the same time, while simultaneously allowing all of them to interact in a consistent fashion?</i>

    A coordinate system is not a physical thing. It is a mathematical construct. The universe has no trouble support however many you want.

    <i>There exists a cosmic medium within which all observable events take place</i>

    I ask you, then: can we detect this medium? How is having this medium different from not having it?

    <i>Within this cosmic medium, the velocity of light is the same in all directions</i>

    In that case, if you move relative to the medium the velocity of light should change, right? If the medium is "absolutely stationary", it can't also move so as to maintain a constant speed of light.

    <i>Curved spacetime is a mathematical abstraction. Or would you suppose that quantum particles are in reality traveling probability distributions, rather than the latter being merely a mathematical model of the former? Question is, what is behind the model?</i>

    We don't have access to the kind of underlying reality you seem to want. All we have is models for processes. We don't know if an atom really contains quarks, as opposed to the quark model merely being a good description for nuclear processes. We <b>cannot</b> know that. I might postulate that quarks are "really" tiny little jelly beans, or little dragons which fly around in predictable ways. Either theory <b>could</b> be correct. But such a theory cannot be tested, so it isn't much use.

    <i>Einstein came up with curved spacetime, but he fudged it to agree with Newtonian gravity; the precise relationship between mass and curvature was never derived from first principles.</i>

    That's right. Maybe there's a theory out there which does do that. GR isn't necessarily the last word. String theories may have things to say about this, but I can't tell you since string theory isn't my thing.

    <i>I don't have a very good understanding of this, but I've seen on multiple occasions people complaining that GR has otherwise inexplicable factors built in that magically compensate for lightspeed-limited propagation of gravitational interaction just so as to conserve energy.</i>

    Not as I understand it. It's a very neat theory. There's very little in there which is tacked on in an <i>ad hoc</i> fashion. It's much better than QM in that regard, if you ask me - and I think QM is a pretty good theory too.

    <i>To top it off, Einstein made time into a dimension, which IMHO is a non-starter.</i>

    It obviously is a starter. It gives the right answers. Actually, more than that, it generates some amazingly beautiful mathematical symmetries, and leads to new physical insights. And GR just wouldn't work without it. You really have to understand the maths to get the full picture. When you do, it's one of the most elegant in physics.

    <i>You can make all the claims you want about how spacetime is curved; that doesn't necessarily give you a handle on what is really going on.</i>

    Right, but nothing will. We just don't have access to the ultimate reality. Maybe someday we will, but we don't right now, and if we did we couldn't know we did.

    <i>Though I can't help but notice your usage of "space" rather than "spacetime". Fine by me, as I have yet to be startled by the spectacle of anyone strolling along time.</i>

    You're strolling along time whilst you sit there reading this post.

    Please Register or Log in to view the hidden image!

     
  23. James R Just this guy, you know? Staff Member

    Messages:
    30,641
    Tom,

    <i>As I stated before, and nobody listened to me except overdoze, a light clock proves that the principle of invariance of light is wrong.</i>

    If it proved that, you would have been able to show it proved that. I listened to you. I just don't find your arguments compelling.

    <i>I've been on this board for months, and everyone has been arguing with me that relativity states that time is slows down.

    If they said in the beginning that clocks slow down, but that doesn't necessarilly mean that time slows down, I would've saved everyone alot of time.

    Please Register or Log in to view the hidden image!

    </i>

    Relativity is a theory about space and time, not clocks. Nothing about the internal workings of a clock changes when you move past it at high speed. If that happened, it would indeed be a strange universe. What changes is your perception of the clock.
     

Share This Page