Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Time in SR and relativistic mass

  1. Aug 1, 2006 #1
    Is it possible substitutive explanation of SR: "because of larger relativistic mass everything moves more slowly."

    I tried to to get this substitution mathematically, but it not works. I know that lorentz contraction should be included as supposition that things work.

    For instance: a = gamma^3 a1.
    a=acceleration inside of system which moves very fast.
    a1=acceleration seen from not moving observer.
    c=speed of light

    dW = ma dx gamma3, (2)
    when system accelerates and gains additional energy because of acceleration.

    One explanation is that m=m0 gamma^3, but this dissagre with
    W=W0 gamma and W=mc^2

    If Lorentz contraction is included, I get
    m=m0 gamma^2, but I wish m=m0 gamma
  2. jcsd
  3. Aug 1, 2006 #2
    You don't seem to be using the acceleration transformation correctly. Please see


    Also, the speed at which something moves has absolutely nothing to do with mass. Only the amount of momentum and the amount of acceleration are functions of speed.

  4. Aug 1, 2006 #3
    I will check forumulae. Speed has nothing with invariant mass, but it has with relativistic mass. This is concept, which is possibility in relativistic physics. Einstein abandoned it. Some physicist did not abandon it.

    Maybe it is really uselles. But, maybe it is explanation for slower acceleration, seen from v=0 inertial system. In formula above dW = gamma^3 we should give gamma's to some factors. It is the most natural to give it to acceleration. But, we can suppose that time run is not different as in our system and we can give gamma also to mass and lorentz contraction.
    Mathematics do not forbid these alternative possibilities.
    The only problem is, that I do not understand this mathematics enough.
  5. Aug 2, 2006 #4
    Special theory of relativity explains relative nature of inertial systems. But, I think that it can also explain, why time in fast rocket runs slower than in our system. (Or explanation of twins paradox) Explanation is simple: when we accelerated rocket, we gave it energy and mass (relativistic mass). So everything in rocket is heavier and moves slowly, so time runs slower.
    But, condition that calculations work is, that we suppose Lorentz contraction and formula dE = dm c^2.
    It is my intention to find derivation which agree with special relativity. If it is not agree, there is probably one explanation which should say why this time dilatition explanation is not possible.
    For instance: known formula for power P given to rocket is:
    P = dW/dt = gamma^3 m a v.
    m=mass of rocket
    v=velocity of rocket

    It is supposed that relativistic mass equals gamma^3 m. But
    W=gamma W0, so I suppose that
    m=gamma m0.
    So other two gammas can be added to a and v, or to dx in them. (t is regarded as absolute.) I addmit this dx is not clear to me, but, if this is true, it is logical explanation, why longitudinal mass is not equall (the only logically) to gamma m.
    So formula above can be written
    P=gamma^3 m d(dx/dt)/dt dx/dt =
    P=gamma m d(gamma dx/dt)/dt (gamma dx)/dt

    I think that it is contradition in my formula, but
    relativistic energy should be c^2 times relativistic mass.
  6. Aug 2, 2006 #5

    Also no.

    No logical connection.

    Good intention but you are on a (very) wrong path. And it cannot be fixed unless you do some serious studying.
  7. Aug 2, 2006 #6
    Thanks for answers. I read that Einstein abandoned relativistic mass. But I want to understand why, and why some phsicisics do not abandon it.

    But, you will not believe me, I understand ortodox special relativity, their equations and also some general relativity.

    But I think above post is important, but nowhere on google I did not find explanation why above "absolute time" and "mass causes time dilatition" do not works.

    So I understand ortodox special relativity, therefore I will understand, I someone will explain with formulae, why I am wrong.

    If some will write formulae which I do not understand, it is possible to ask for explanation or to find explanation on google.

    Is it somewhere something written about why bigger mass causes slowere time run. Or, it is written, why not.
    Last edited: Aug 2, 2006
  8. Aug 2, 2006 #7


    User Avatar
    Staff Emeritus
    Science Advisor

    We have guidelines against talking about new, personal theories in the main forums here on PF forums. The main reason for these guidelines is that people tend to get too attached to their ideas, and the threads bog down into people "defending" their non-standard ideas.

    I'm going to bend the rules a bit and give you my opinion on why your idea won't work. The main reason I'm bothering is that you don't yet give the appearance of being overly attached to your own ideas. However, I do encourage you to re-read the PF guidelines on personal theories.

    For relativity to work properly, one needs all three of the following elements.

    time dilation, length contraction, and the relativity of simultaneity.

    Your explanation only addresses one of them. Unless you can explain all three, you're not going to get a theory equivalent to SR.

    Note that the 3 elements I listed above are verbal descriptions of the Lorentz transform:

    t' = gamma * (t - v x / c^2)

    This is how time transforms. The time dilation element is the 'gamma' in the formula. Equally importnat is the '-vx/c^2' term, which represents the relativity of simultaneity. The locus of ponts which satisfied "t=0" is a different set of points than that which satisfies "t'=0". Simultaneity is therfore a concept that depends on the frame of reference in relativity.

    x' = gamma ( x - vt)

    This is how sapce transforms. It's the familiar gallileant transform (x - vt) except that it gets multiplied by an additional factor, gamma, which is equal to the time dilation factor.

    Without length contraction and the relativity of simultaneity, your theory is just not going to be able to be equivalent to SR.

    Another way of saying this:

    One of the key elements of relativity is that light travels at the same velocity relative to all observers. Mucking around with the "relativistic mass" of particles which do not travel at the speed of light is not going to achieve this property. To achieve this you need the Lorentz transform.
  9. Aug 2, 2006 #8

    Doc Al

    User Avatar

    Staff: Mentor

    Well said, as always, pervect! With that commentary, I will close this thread.

    exponent137, if you would like to discuss your personal theory, we invite you to submit a post to the Independent Research Forum, subject to the applicable guidelines, found here.
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Time in SR and relativistic mass
  1. Mass in SR (Replies: 2)