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Is Mass an absolute frame?

  1. Jan 14, 2012 #1
    As stated in SR, mass of the object increases with its velocity right?

    Lets assume that all the objects in the universe have consciousness and they all know what their rest mass is...(Leave photons out of the argument)..
    And also assume they all can measure their own mass at any instant...

    Since they all have mass, they surely can find whether they are moving, accelerating or at rest at any instant of time.. So this means that mass is the absolute frame of reference of the universe, dont u think?

    If the above statement is true then there is no need for relativity as the objects always know when they are moving and when they are at rest...
    From the mass variance formula you can even calculate your own velocity... :confused:

    Any thoughts about where i went wrong?

    Thanks in advance..
  2. jcsd
  3. Jan 14, 2012 #2
    Not exactly... I suggest you read this:


    From an object's rest frame it cannot detect any relativistic effects. It's only when you look at an object moving in your rest frame that you see effects like time dilation, length contraction, etc. (I'm using the word "look" pretty loosely here.)
    Last edited: Jan 14, 2012
  4. Jan 14, 2012 #3


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    If you have an observer that knows his rest mass, there isn't any way for him to tell how fast he's moving, and I really don't quite understand why you think there should be.

    So this is probably where you're going wrong, but it's unclear why you're going wrong there.
  5. Jan 14, 2012 #4
    Imagine a flat surface with two men on it..The rest mass of both of them is same...
    Man A is moving with a velocity v relative to the Man B who is standing still(v =0)..

    Since motion is relative, we can either say Man A is moving while Man B is at rest Or
    Man B is moving while Man A is at rest...

    So from A's view, B's mass increases.. And from B's view, A's mass increases..
    Now consider a 3rd FoR (say God's frame) , from there the god sees that Man A is moving while Man B is at rest...
    So According to the God, Man A's mass increases while Man B's mass remains constant...

    Now as i stated in the original question, All three people has a device which would tell all other's mass as well as his own mass at any instant...
    So if A uses the device, he would read his rest mass coz he thinks B is moving... But at the same instant if god uses his device, then he would read A's mass to be greater than what A measured in his own frame...

    How can they read different masses for the same person at the same instant?
    An object cannot possess two different masses at the same instant...

    Only possible way to eliminate this ambiguity is to declare mass as the Absolute frame...
    So Man A's rest frame is just an illusion... In reality, He is moving relative to the B and he would read his mass to be greater than his own rest mass...
    And as for the B, he would read his own mass to be equal to his rest mass, since he is not moving...

    We cannot say B is moving relative to A since B's mass remains same throughout the event.. And hence with mass, we can say what is moving and what is not......

    Note: The Above conclusion is just my assumption....
  6. Jan 14, 2012 #5
    for the original post: This may be the easiest way to think about it:

    I would clarify the statement this way:

  7. Jan 14, 2012 #6
    [That's not all they read differently!!!!]

    [A really crude analogy: It's raining. No it's not. Resolution: two observers at different places or maybe different times or both! Whose right?? Bring them together... at the same x,y,z,t coordinate (worldline point) and they will agree.]

    Different observers in general make different observations. Einstein showed the equal validity of all inertial frames of reference..... and the nonexistence of one frame representing absolute rest. That's a version of 'the principle of relativity'.

    Einstein found that space and time CAN vary in different inertial frames...so different observers make different measurements. .......But they are NOT inconsistent.

    Lorentz transforms are the correct ones to use with all physical laws: when you make such 'adjustments' to bring observers together their apparently different measurements will agree. In other words, different observers are in fact separated not by fixed time and fixed distance but by the lorentz transforms.

    Check out the Wikipedia article where it makes these points:


    [This means different observers are NOT separated by fixed distance and fixed times but rather they are separated via the Lorentz transform.]
    Last edited: Jan 14, 2012
  8. Jan 14, 2012 #7


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    Not any more. Did you do what I asked you to do in your previous thread when you brought up this subject?
    If you haven't done this search and read up on this subject, please do it now.
  9. Jan 14, 2012 #8


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    You seem to be under the impression that a moving object will detect its own increasing mass. That is incorrect. An object always is motionless relative to itself and whatever method it uses to determine its mass, it will get its rest mass. It is only observers moving relative to the object that will measure a higher mass for it.
  10. Jan 14, 2012 #9


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    Then you aren't considering a "third" frame, At most, you have add an additional observer to the rest frame of Man B.
    Again, god's frame is just B's frame. It seems like you are trying to equate "god's frame to being an absolute frame. In other words, you are assuming the existence of an absolute frame to prove the existence of an absolute frame.
  11. Jan 14, 2012 #10
    Careful! It looks like you're assuming your conclusion by already defining an absolute rest frame for B.

    That's better!

    The "God" point of view is no different from B's point of view. You don't make this frame special by calling it "God's frame".

    The error here is to consider that mass is an intrinsic, unchangeable property that a body "possesses". It isn't: mass (as defined in relativity) is different depending on what frame is used to measure it. Your statement above is absolutely correct: in the frame where A is stationary, B's relativistic mass is more than his rest mass, and in the frame where B is stationary, A's relativistic mass is more than his rest mass.
  12. Jan 14, 2012 #11


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    You seem to be conflating (i.e. combining and confusing) rest mass and relativistic mass.

    The rest mass of an observer does not increase when they move.

    So if A is stationary, his rest mass is some number M_a. If A is moving, his rest mass is the same number, M_a.
  13. Jan 15, 2012 #12
    So the rest mass remains constant no matter how fast you move, it is only the inertia that increases not the mass???

    Imagine the two same men A and B.. this time B is riding a bike while A is standing still... So B burns some energy(fuel of bike) to move while A is at rest... The other way around, B burns some energy to stay in his rest frame while A is moving without spending energy...
    How is this possible?

    Different topic:

    If relativity is true, then geocentric theory of the universe is just as true as the heliocentric theory... So that makes galileo's observations wrong... why do they have to discover that the Sun is at the center of the solar system and all other planest revolve around it?
    So the frame from which galileo, copernicus and many others imagined our solar system is from the god's frame(i.e. a frame out of the solar system)... I can say boldly that from earth's rest frame, the whole universe revolves around it.. But it just doesnt seem right..

    I m not sure which post you are referring to.. So can you please post the link here?
  14. Jan 15, 2012 #13
    Yes, the rest mass remains constant. The "relativistic mass" increases. The distinction between rest mass and relativistic mass can be confusing, which is why many writers prefer not to use the concept of relativistic mass. Instead, they use only the concepts of momentum and energy. See for example:


    You don't need to burn energy just to keep moving at a constant speed in a straight line (see Newton's first law). The bike rider is burning more energy than the person standing still because he is working against friction and air resistance.

    It's easy to get stuck on the idea that one of the men is "moving" while the other is "at rest". To simply state "B is moving" has no meaning, since all motion is relative! What is really happening is that B is moving relative to the ground and air, whereas A is at rest relative to the ground and air.
  15. Jan 15, 2012 #14


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    Click on the little arrow to the right of a user name and it will take you to the original quote. So if you click on the arrow next to my name in this post, it will take you up to post #7 where I quote you and my response where you can do some more clicking to get the previous thread.
  16. Jan 15, 2012 #15
    Sorry I forgot about that the newton's first law...
    But there are no inertial frames in the universe, so can we avoid the SR altogether ?, since SR is valid only in inertial frames....
  17. Jan 15, 2012 #16
    I did the search but im getting many threads, which one you are referring to?
  18. Jan 15, 2012 #17


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  19. Jan 15, 2012 #18
    What do you mean by that?
  20. Jan 15, 2012 #19
    Any frame of reference which is not undergoing acceleration is an inertial frame.
  21. Jan 15, 2012 #20
    Every possible FoR in the universe has some kind of acceleration cause every mass attracts everyother mass, so there are no inertial FoR in the universe...
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