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Einstein proved right again.

  1. Oct 20, 2003 #1
    An experiment by Italian scientists using data from NASA's Cassini spacecraft, currently en route to Saturn, confirms Einstein's theory of general relativity with a precision that is 50 times greater than previous measurements.

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  2. jcsd
  3. Oct 21, 2003 #2

    Chi Meson

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    "like I always said: that guy is on to something."
    paraphrased from A. Michelson
     
  4. Oct 22, 2003 #3
    This experiment shows that the velocity of light is in fact reduced in a gravitational field. This was originally proven by Shapiro in the 1970ies.

    Why does the reduction of the velocity of light in a gravitational field prove that the spacetime is curved?? This is just a formal way used by Einstein to describe this phenomenon.

    When a light-like particle (like e.g. a photon) passes a massive body it is subject to a lot of interactions with the exchange particles of the fields within the body (e.g. the strong and the electric interaction). These interactions disturb the path of the particle, so that the particle will need more time to pass a specific distance.

    To my knowledge this was not quantitatively evaluated yet as a theory. But as soon as it is done it will us tell what really goes on, in terms of physics.

    What Einstein has done is, from the point of science theory, a so called "geometrized" theory. This method is nomally a mathematically elegant way, but causes us to forget the physics behind.
     
  5. Oct 22, 2003 #4

    Hurkyl

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    So if nobody has been able to quantitatively evaluate this theory in the affirmative, what justification do you have to claim it is what really occurs?


    Well I guess I forgot the physics behind it, because to the best of my knowledge, the only physics that adequately explains gravity is General Relativity.
     
    Last edited: Oct 22, 2003
  6. Oct 23, 2003 #5
    What's the deal with needing to invoke all those extra fields. If spacetime around an object is curved, and light always follows a 'straight-line' path, we know from simple geometry that a curved trajectory is longer than a perfectly straight trajectory. The velocity of light remains c, it just has more distance to traverse. Asides from the mathematics to describe the actual curvature, that is about as simple as physical concepts gets right there.
     
  7. Oct 23, 2003 #6
    light does follow a strait path ok, but if lights path must be strait how can it traverse the curved space time?[?]
     
  8. Oct 23, 2003 #7
    Because light is following a straight path in curved space. The "path of least resistance" so to speak. Remember, the shortest distance in curved space doesn't always look straight.
     
  9. Oct 23, 2003 #8
    Ok so if you were to be riding on the photon then its path would apear to be strait, but if you looked at space and how the light traveled then it would be curved.......sort of like walking only at slower speeds....
     
  10. Oct 23, 2003 #9
    The important thing here is light never slows down. It's always at c. In curved geometry, a curved path can be the shortest. Light takes the "shortest" path thinking it to be a straight shot to where ever it's traveling.
     
  11. Oct 24, 2003 #10
    General Relativity of Einstein does in fact not explain gravity.

    Gravity is one of the big open problems in present physics. Gravity is in conflict with the standard model, it is in conflict with quantum mechanics.

    But a solution is possible. If we take the fact that the velocity of light is reduced in a gravitational field and apply this to the internal oscillations of an elementary particle (as it is stated by the Dirac equation for the electron) then gravity is quantitatively explained and the conflicts to the rest of physics disappear.

    So, the origin of gravity is the reduction of the velocity of light near a massive body. - Why is the velocity of light reduced? This is the open question and to explain gravity means to explain the reduction of the velocity of light.

    Did Einstein explain, why it is? No, he did not! He just stated that the velocity of light is always constant, but the space is contracted/curved in the vicinity of a massive body. This is by his statement the reason why a photon needs more time to pass a specific distance. Why should the space contract?? I found no answer.

    If you sit in your car and push the throttle control, the car will accelerate. That is a normal physical statement. Equivalently you can state that the speed of your car is always constant, but when you push the throttle control, the space in front of the car will contract. This is in fact a possible description of this process, and it can mathematically yield the correct results. But would you do it in this way? And will this explain why this contraction of space happens?

    Einstein has not explained gravity, he only described the facts in a formal ("geometrized") mathematical way. The only quantitative parameter in gravity, the gravitational constant G, was not given by Einstein by a theoretical deduction, but was measured in experiments. And the measurements are, as we know, inconsistent to each other. Why are they? Most probably he theory is wrong!

    If you are interested in the way how gravity follows from the reduction of the velocity of light, I have prepared a site in the web to explain this:
    http://www.ag-physics.org/gravity
     
  12. Oct 24, 2003 #11
    Yeah I guess Einstein was wrong. I mean even with an agreement of 20 parts per million, its still so blatently wrong! The problem with G is that the very limits of our technology will not allow it to be determined precisely. Though one could take a given amount of mass/energy, and how much spacetime curves (again both measured) and derive G, an actual theoretical calculation is not present, I agree. But this cannot come about until we better understand just exactly what spacetime itself is. That does not mean Einstein is wrong. It just means he has a model. But that doesn't mean he is absolutely right either. It just means he's more right than you. But regardless, light does NOT slow down in a gravity well, it merely has to traverse more curved space.
     
  13. Oct 24, 2003 #12
    I think it is a different point.

    "Space" as well as "time" are human abstractions. We cannot measure them, we cannot notice them.

    We can compare the sizes of objects, but we cannot measure "space".
    We can compare the frequencies of periodic processes, but we cannot measure "time".

    So we are very much free to define what "space" or "time" should mean. Our definition of space or time cannot be "right" or "wrong", it can only be practical or less practical.

    By my example of an accelerated car I wanted to show a definition of space, which is not wrong, but which is not very practical.

    In this meaning it is not practical to use space and time in the way as Einstein did it. He is/was not wrong, but he was not very practical.

    I guess that we will find out soon which physical effect delays the motion of e.g. a photon. (I.e. the interaction with the exchange particles of the other forces). After this is made sure, (and I am very confident about it), what will then happen to the model of Einstein of a curved space/time??

    Regarding the measurement of G: The differences of the results are greatly outside the measurement uncertainties (many standard deviations). I guess for the reason: Gravity does not depend on the mass of the gravitational source but on something different, which is however quite strongly related to the mass (e.g. the number of charges of all kinds in the source object).
     
  14. Oct 24, 2003 #13

    Hurkyl

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    How do you figure? Einstein's use of space and time revolutionized physical thinking, correctly predicted many effects that were previously thought absurd, enabled the precise operation of the GPS system, and yields quantitative calculations that agree with reality better than any other known theory of gravitation.


    And one point lost on most people is that modelling space-time with differential geometry (aka "curved space") is less of an assumption than that space-time looks globally Minowski or Newtonian.

    The very definition of a differentiable manifold is that it looks like Rn locally... which is the only thing our experiments have confirmed anyways. It is, pardon the expression, downright silly to insist that space-time must look like Rn globally, and especially because this assumption appears to be inconsistent with the behavior of gravitation.


    You do realize there are twenty-odd parameters in the Standard Model that are not given by theoretical deduction? (not to mention I can't imagine how one can presume that the existance of a ton of fields is any more of an explanation than curved space)
     
  15. Oct 26, 2003 #14
    Let's start from a simple point.

    Some postings ago we had the following discussion which we can relate to the Shapiro experiment:

    We find experimentally that a photon moving from Earth to Venus and back needs more time when the sun has to be passed closely, than at the other time when the sun is far.

    Two explanations:

    1. The velocity of light is reduced in the gravitational field of the sun .... or
    2. The velocity of light is always the same, but the space is curved in the gravitational field.

    The second statement follows Einstein.

    What is the advantage to use the second way (Einstein)? We give up our traditional understanding of space (and of time in the general application). What do we get as a return?

    When we look to the bending of light at the sun, which was observed at the sun eclipse experiment of 1922 (which made Einstein famous), this can be quantitatively explained by a normal refraction process. We know that the velocity of light is reduced in the gravitational field in the following way:

    c(r) = c0*(1-(G*M)/(c0*r^2))

    In every situation where c is dependent on r, we get - very classically - a refraction. This refraction explains quantitatively correct what happened during this sun eclipse. Without any space curvature.

    The same refraction happens within an elementary particle to the internal oscillation going on there. This causes the normal gravitational acceleration.

    I have asked at several occasions whether there are effects of General Relativity which cannot be explained in an analog way. Nobody told me such cases. If you can, please do, I would be really thankful.

    For the details of the cases above I again refer to the web site I made about it:

    http://www.ag-physics.org/gravity
     
  16. Oct 26, 2003 #15

    Hurkyl

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    A more accurate understanding of space-time, gravitational bending of light, gravitational redshift, black holes, gravitational waves, cosmic expansion (hubble redshift), GPS...

    Anyways, before I know how to respond, I must know if you accept special relativity.
     
  17. Oct 26, 2003 #16
    Gravitational light bending cannot be explained by refraction. In refraction, the angle of deflection must be dependent strongly on the wavelength of light. But experiments have shown that gravitational light bending is independent of wavelength.

    Anyway, a "variable speed of light" theory of gravity such as you propose cannot account for the multitude of other experiments concerning gravity that do not involve the deflection of light (Hafele-Keating, Taylor-Hulse, Lense-Thirring, Friedmann cosmology, etc. etc.). Scalar theories of gravity generally do not work (e.g. chapter 7 of Misner et al).

    You haven't even been able to support your claims of what your theory can predict; your web page claims that your theory can account for the perihelion precession of the planets, but you have no derivation of its value (e.g. ~43"/century for Mercury).

    It is up to you to prove that your theory accounts for all known effects, not for other people to check your theory against all known effects. Get Cliff Will's book and calculate what your theory predicts for all of the standard tests of GR. (Some of these tests are summarized in http://www.livingreviews.org/Articles/Volume4/2001-4will/).

    Better yet, calculate the PPN parameters of your theory. If they come out in agreement with experiment, someone might bother paying attention to your theory.

    Until then, it is absurd to believe or even suggest that there are no effects that your theory cannot account for -- you have considered only a tiny fraction of the effects that general relativity can explain, and have not even made truly quantitative predictions for most of them.
     
  18. Oct 27, 2003 #17
    That works also with the approach I gave you. But much easier to understand.

    Sure, I accept special relativity. That means I accept the phenomena of contraction (of objects), dilation (of periodic processes), and the increase of mass at motion.

    However, I do not use as a theory the (geometrized) version of Einstein, but the (physical) version of Lorentz / Poincare which delivers the same results. Special relativity is the consequence of the limited velocity of light by which all fields propagate, and of the inner structure of elementary particles.

    I have described also this in a web site:
    http://www.ag-physics.org/relat

    That is definitely wrong.
    If the velocity of light depends on the wavelength (like in a glass lens), then also the refraction angle depends on the wavelength. The velocity of light in a gravitational field does not depend on the wavelength, so the angle is also independent from the wavelength. That is basic classical physics.


    Hafele-Keating is partially special relativity and is of course in agreement with the model I gave.
    Lense-Thirring can also be explained by the refraction process, similar to the perihelion shift.
    I do not know Taylor-Hulse and Friedmann cosmology, I shall check those two.

    For the perihelion drift you are right, I should give the result in detail. I am going to add it to my web site.

    Formally what I am doing is just a mathematical transformation of the theory of Einstein into something different, which gives us the possibility to understand it as physical phenomena. So the results will not be different.

    You are right that I have to prove my theory myself. But it helps me if you provide me material. So thank you for the reference given. I shall read it and then respond. I have already read something in livingreviews, but did not find conflicts yet.
     
  19. Oct 27, 2003 #18
    My apologies. I was paying attention to the part where you said you were describing light bending by ordinary refraction, not noticing that your theory does not, in fact, describe ordinary refraction.

    All right, prove it: where is your calculation of the magnitude of these effects?

    No, you are not. You are writing down a scalar theory of gravity in a fixed background, which is mathematically inequivalent to general relativity: it doesn't even have the right number of degrees of freedom. (Your field theory has only one independent component of the gravitational field: the speed of light at an event. GR has 10 independent components. It is mathematically possible for the former to be equivalent to the latter.)

    In particular, the gravitational field you obtain for the Sun is mathematically equivalent to the metric,

    ds^2 = -c(r)^2 dt^2 + dx^2 + dy^2 + dz^2

    which certainly is not general relativity's prediction.

    Of course you will never find conflicts if you don't confront your theory with experimental data. For that, you need to make concrete quantitative predictions. You certainly have not calculated even a fraction of the effects that serve as tests of general relativity, so it means nothing that you "have not found conflicts yet".
     
  20. Oct 27, 2003 #19

    russ_watters

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    No. What you are proposing does NOT fit with observations.
    Thats basic classical physics except the part about gravity bending light. In any case, you said before that bending of light from the sun could be explained by the "normal refraction process." So which is it? Gravitational lensing (according to relativity) or atmosphereic refraction (according to classical physics)? Hint: only one can make predictions that fit with observations.
     
  21. Oct 27, 2003 #20

    Integral

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    This is an execellent conversation for the Theory Development forum.
     
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