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Relativity VS Absolutism?

  1. Oct 10, 2006 #1
    How does relativity accounts for rotaional motion, which is a non inertial reference frame?

    How does relativity responds to Newton's thought experiment to prove the existence of absolute space? He argued that the curvature of the water inside a rotating bucket, demonstrates the true motion of the water in reference of what must be absolute space. (he used a similar thought experiment using two spheres conected by an ideal rope in an empty universe. If these spheres rotate, a tension force is created on the rope, which indicates the "real movement" in reference to absolute space).
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  3. Oct 10, 2006 #2
    If I understand the argument properly, it is stating that we must consider space absolute because there is a difference between the bucket of water rotating in a stationary Universe (the water in the bucket is concave) and a stationary bucket in a rotating Universe (the water in the bucket is level). Therefore, the argument states that the bucket's rotation is absolute, and not just relative to the rest of the Universe (and absolute motion implies absolute space).

    To me, it seems like the fallacy is to believe that we can treat a rotating bucket of water as a unified frame of reference (relative to the rest of the Universe). Treating the bucket as a single, unified frame of reference is required for the illustration to work. However, as soon as the bucket is rotating, we introduce kenetic energy, and therefore, the bucket of water has many parts with many different momentums. In order for us to regard the bucket of water as a unified frame of reference compared to the rest of the Universe, the bucket of water would have to be at rest with no internal motion.

    For example, if we have two soccer balls next to each other at rest, we can regard them as the same relative frame of reference. However, as soon as we kick one and introduce that kenetic energy, then they no longer share the same frame of reference. It is the same thing with the bucket.

    The concave surface of the water has only to do with the injection of kenetic energy in that specific system, and absolutely nothing to do with the rest of the Universe (rotating or not).

    At least that is my novice opinion. :-)
    Last edited: Oct 10, 2006
  4. Oct 10, 2006 #3
    I am not sure what you mean by account for.
    Rotational motion is indeed a non inertial motion.

    Nope, objects prefer to follow a geodesic which in flat space is simply a straight line. The bucket, or more accurately the EM forces inside the bucket, is stopping the water from following a geodesic.
    Last edited: Oct 11, 2006
  5. Oct 11, 2006 #4
    By looking at the water in a bucket, yes, you can tell absolutely whether the bucket is spinning (or otherwise accelerating). This is true both in real life, and also according to relativity.
  6. Oct 11, 2006 #5
    Well, SR, does not account for rotational motion, in fact it is based on two principles:

    -the principle of relativity applied to two systems of coordinates in uniform translatory motion and

    -the constancy of the velocity of light.

    On the other hand it is known that Einstein applied the principle of relativity to Mawwell's equations making then the magnetic field relative, which is not true in the reality out there, it's just a theoretical supposition, not in agreetment with real experiments. Additionally if that application of the principle of relativity were true, then SR had to do with the electromagnetic field, and GR with the gravitational field and we know those two forces are not unified.

    My best regards


  7. Oct 11, 2006 #6


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    Say what???!!!

    The WHOLE impetus for Einstein to come up with SR WAS due to the non-covariant nature of Maxwell Eqns under galilean transformation. The old Maxwell eqns were the one that had no "agreement with real experiments", because it simply didn't follow the covariant aspect of Newton's Laws. We now know that the relativistic form of Maxwell eqns. become covariant under the more generalized Lorentz transformation.

    The fact that c is a constant in all inertial frames that we have measured so far IS an "agreement with real experiments" regarding SR!

  8. Oct 11, 2006 #7
    Thank you for your reply!!!

    You wrote:
    Yes, Maxwell's equations was not covariant with the old principle of relativity expressed by the galilean transformations either. I don't get what you mean when you say that Maxwell's equations were not in agreetment with real experiments, so what about the works of Faraday, Ampere, Oersted? What about the whole applications with permanent magnets on which our civilization rest? Those applications are not based on the principle of relativity when applied to Maxwell's equations, that makes the magnetic field relative.

    Yes, light is a constant when dealing with Maxwell's equations, so I don't find any problem with taking it as a principle, the problem is with the principle of relativity when applied to Maxwell's equations, sorry but I can't follow Einstein anymore because of this, you should show me a real experiment where the magnetic field is cancelled because of a relative movement, something Einstein did not mean in the intro of his On the Electrodynamic of Moving Bodies either.

    My best regards


  9. Oct 11, 2006 #8


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    You lost me here. There's an "old principle of relativity"?

    Look at the relativistic maxwell equations. Can you tell me how it is non-covariant?

    Look at the non-relativistic maxwell equations. Can you tell me how that is covariant?

    I meant as in the most general form. It would be as silly to announce that maxwell equations have no "agreement with real experiment" the same way you are claiming that relativistic Maxwell equations have no "agreement with real experiments". I mean, ALL the experiments on light ARE "real experiments", unless you don't think light has anything to do with Maxwell equations. Every single relativistic corrections to the band structure calculations in solids ARE the relativistic form of the electromagnetic interactions, i.e. the Maxwell equations! So what more "real experiments" do you want?

  10. Oct 11, 2006 #9
    Hello ZZ,

    You asked:
    Of course, the principle of relativity, is not new, Galileo in his Dialogues, established it clearly in his discussions against those that argued about the ptolemaic system, and it was called the principle of relativity in classical mechanics.

    By covariant I've always understood that those equations are always valid, independently of the frame of reference, and this is what happens with Maxwell's equations, and specially with the magnetic field, it is always there, in the reality out there, we do not need a theoretical supposition for its existence, and let alone the principle of relativity.

    relativistic Maxwell equations have no "agreement with real experiments"? This is precisely, what I don't buy anymore: they are not relative, if they were, then would the magnetic field be cancelled by a relative movement; this is the real experiment that I want.

    Another thing is the Lorentz transformation group and its association with Maxwell's equations, the time dilation problem and so on, that does not need to be framed within the principle of relativity to be valid. Here is a real challenge for physicists, but then we must be very critics not to include eather to justify that group, of course, and in this endeavor, we must reconcile uniform translatory motion and circular motion, the electromagnetic field and the gravitational field just as they are reconciled in the reality out there.

    My best regards

  11. Oct 11, 2006 #10


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    So, in other words, you really do not CARE nor pay attention to a whole zoo of other experimental evidence. You just want ONE particular one as a necessary and sufficient experimental evidence?

    And what's with the "magnetic field be cancelled" stuff? If you have a problem with this, then you have a problem with Maxwell Equation in the first place, NOT SR. Shoot some electrons at some velocity, and then transform to a frame having the same velocity. Without invoking SR, do you have a problem with not observing a B field in that frame?

    I don't get it!

  12. Oct 11, 2006 #11
    No. Covariant equation means it is valid in any ref. frame as it is made of covariant quantities. Covariant quantity means it transforms in a particular way with respect to some set of transformations.

    e.g. the magnetic field (in some direction) is not always there, but instead can be transformed away by choosing a suitable reference frame.
  13. Oct 11, 2006 #12
    Hello ZZ,

    Yes, it is what is called a critical experiment, just one and that theory will fall.

    No, please, not thought experiments, but real experiments, we know how all QM depends of the behavior of the electron and its intrinsic magnetic field... to say transform to a frame having the same velocity, is a thought experiment that will take you to cancel or deny the existence of the magnetic field, please note that this is not real, but just a theoretical supposition that came in that moment Einstein wrote:

    Now, the principle of relativity requires that if the Maxwell-Hertz equations for empty space hold good in system K, they also hold good in system k...

    But let us quote a real evidence very akin to the subject, as violation of parity, bilateral symmetry and SR are so:

    As Yang C.N. commented in his Nobel lecture, "The fact that parity conservation in the weak interactions was believed for so long without experimental support was very startling. But what was more startling was the prospect that a space-time symmetry law which the physicists have learned so well maybe violated. This prospect did not appeal to use".

    Please note that in this violation of parity, the electron and its assymetric behavior in a strong magnetic field played the central role.

    My best regards

  14. Oct 11, 2006 #13


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    What "thought experiment"? You've never measured static fields from static charges before? And you've never measured fields from uniformly moving charges before? I have!

    So unless you are claiming that having a charge static in your frame is DIFFERENT than transforming to a uniformly-moving static charge frame, then we have REAL experimental evidence for both! If you claim that there IS a differences, then you have a bigger fish to fry than your displeasure with relativity - you have all of physics to deal with.

    And would you like to point out to me under WHAT condition is there such parity violation? Does it occur ALL the time, such as under strong interaction and EM interaction? Or is it only specific to weak interaction?

    If all you can do is to quote people as your 'evidence', then you haven't understood the physics. You have taken things out of context and use it in places where it doesn't belong. Unless you can show me why having static charges isn't the same as transforming to an inertial frame where that charge is moving, then this whole point is moot. There are many particle accelerator physicists such as me who would invite you to go visit one and see how we transform from lab frame to the particle's frame so often in many of the dynamical description of particle beam physics. If such a thing isn't valid, we would have noticed inconsistencies in both descriptions by now.... unless you think we are dumb enough to not notice such a thing.

    Ironically, those CP violations that you quoted are obtained out of particle accelerators/collider experiments. So take that!

  15. Oct 11, 2006 #14
    Hello ZZ,

    All my life, as electrical engineer, I worked for more than 30 years, not properly speaking with fields, but with energy, electromagnetic energy, based on Maxwell's equations, and I never saw such a thing as a magnetic field cancelled by a relative movement, my point. We can cancel the effects of inductive(magnetic) power by capacitive power, but not by a relative movement. On the other hand if the magnetic field were relative it would be impossible for two space-ships moving in relative movement to each other, not to detect the effects of the relativity of the magnetic field, without distortion in the information interchanged and stored in the magnetic field of their hard disks: it would be a real chaos, would it not?

    Yes, I know it is just in weak interaction, but is it not enough to have one experiment, to have the whole thing down?

    The next serious thing we have to do is to consider the relation among SR, bilateral symmetry as described by Hermann Wey, the philosopher of relativity and the philosophy behind the breaking of parity, but do we really want to consider this seriously when we have to preserve as a dogma the principle of relativity?

    My best regards


    PS: My apologies if I've offended you with my criticism of SR.

  16. Oct 11, 2006 #15


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    But just because YOU haven't seen it, doesn't mean it doesn't exist. Again, when was the last time you were at a particle accelerator? You also haven't seen a neutrino "all your life". Does that mean it doesn't exist? Have you worked with superconductors before? No? Then it doesn't exist?

    The logic on why you claim something to be faulty is itself faulty. The FACT that a charge at rest in your frame of reference produces NO magnetic field is ample prove to me of what you're asking for. If you disagree, then you also have to throw out ALL of physics, because you are questioning the covariant principles of the laws of physics that depends entirely on "gauge invariance" concept. So this is no longer a problem with just SR. You might as well object to all of physics.

    Not if the same thing doesn't occur in strong, EM, and gravitational interaction!

    Besides, why would you pay attention to the results from such an experiment in the first place, when it is implicitly assumed that SR is valid in those experiments? It appears that you accepted the result of such an experiment while denying the fundamental principle that the experiment USED in producing its result! If you don't think high energy experiments such as those DEPENDS on special relativity, then you REALLY need to get your head out of the clouds and start reading something beyond just the superficial understanding that you seem to have here.

    Then may I point out to you the philosophy forum, because this is no longer physics. And like I said, you have more of a problem in understanding physics in general, not just SR. You have more of a problem of accepting the covariant nature of the laws of physics in different inertial frame. This has nothing to do with SR. You have a problem with classical E&M, newton's laws, thermodynamics, etc... etc. So stop picking on just SR.

  17. Oct 11, 2006 #16
    Edgar “EP”
    I too have no clue how you can deny SR with Maxwell.
    It is really not nearly as complex as working with EM equations.
    Galileo’s Relativity and Special Relativity both agree on the same local affects. – you splash water on your face while flying at hundreds of miles an hour in a plane and the water moves as if you were on land because in moves relative to you. Of course Galileo used high speed sailing boats for his example.
    Where they disagree is in how to add speeds together and that SR principle seems solid to me, (you haven’t found something like tacyons have you?)
    SR even works in a classical view, with 3D and absolute time (which requires picking a preferred frame), just as well as in 4D “space-time” where a preferred frame is not possible.

    Haven’t you read (try Einstein’s Heroes) what impressed Einstein so much about Maxwell’s equations? They are mathematically self contained and accurately give correct results regardless of what physical theory they are applied to. Classical Galileo’s Relativity, SR Classical, SR 4D, even GR or QM no matter how you apply Maxwell the same speed for light, matching experimental results is predicted. So whatever “dogma of SR” you’re not comfortable with it cannot be due to Maxwell.

    If you have some example where applying Maxwell with SR gives an inaccurate answer the first think you need to find in the error in how you applied it.

    As to the OP issue on Rotational Motion , it may not be linear inertial motion but Rotational Motion or SPIN is certainly inertial.
    The spin nor the energy stored in that spin is going to change unless and until some force is applied to it as any change to spin will be resisted.
    And it will take a force and energy being added to an object to establish any spin or rotational motion if it has no spin.
    What more can be required of inertia?
    As to absolute space – maybe it is.
  18. Oct 11, 2006 #17
    But doesn't there need to be a constant force/acceleration to maintain the spin? At any instance of time, the momentum vector of any particle is linear, not angular. If the bucket wall fractures, the water will not continue spinning; instead it will spill out according to its prefered linear direction.

    It does not seem like we can base reference frames on angular momentum as we can with linear momentum; in fact they seem completely incompatible.

    For example, we ought to consider a rock resting in California, and another rock resting in India to have different reference frames based on the spin of the Earth.
  19. Oct 11, 2006 #18
    Ok, I think we are loosing track here....
    Anyway, If I move fast, very fast, around the bucket I will see no curvature of the water (would I?). But if I spin the bucket, then the curvature is produce, indicating its true motion relative to absolute space. Mach argued that if we rotate the universe around the bucket we will observe a curvature of the water, but unfortunately this experiment can't be done. Any ideas how Special relativity responds to this???
  20. Oct 11, 2006 #19
    SR does not use angular momentum as the basis for reference frames -- it uses linear momentum. The two possibilities are incompatible.

    As I said before, I believe the fallacy with the thought experiment is that it has to treat the spinning bucket as a unified reference frame. An observer outside of the bucket would observe different relativistic effects between the near side of the bucket and the far side of the bucket. In order to treat the bucket of water as a single reference frame, it must be at rest (not spinning).

    If the Universe instead rotated around the bucket as you suggest, then you would see the disruptions/tensions/distortions in the Universe due to the monsterous force required to keep it spinning (what ever that force is), and you would not see distortions in the bucket. If there is no kenetic energy in the bucket of water, then the concave surface will not form regardless of what is happening in the Universe around it.
    Last edited: Oct 11, 2006
  21. Oct 12, 2006 #20
    Not exactly, but gravity probe B has been measuring something quite similar.
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