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How this can be?

  1. Mar 9, 2005 #1
    hi every body

    I read this somewhere:

    in the universe the sum of matter ond energy is constant:


    and E=m.c.c



    but m is not constant so that's mean that c.c is NOT constant and that is conflict with the Relativity :bugeye: :confused:
  2. jcsd
  3. Mar 9, 2005 #2


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    You have math problems. You cannot add two different "species" together.

    When you write "m+E=const", this is already wrong, because m is mass, and E is energy, and with different dimensions, they do not add. The ONLY way to be able to do this (and this is what professional in the field does), is to put mass in the form of energy, so this "m" is really mc^2! What this means is that this "E" has been DEFINED as simply pure energy (EM radiation, gravitational fields, motion, etc...) that has been SEPARATED OUT from the energy of the rest mass of the universe.

    So in essence, what you're doing is not only adding things that have different dimensions, but you are also double counting by re-defining E as the rest mass energy.

    Looks like "Relativity" is still safe again!

  4. Mar 9, 2005 #3
    sorry maybe I didn't understant your point.. WHY its not possible to put energy in the form mass??????

    you mean that E in einstein equation is not the same E that we see in the universe???
  5. Mar 9, 2005 #4


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    I didn't say it isn't possible to make them equivalent, but you cannot do this with algebra. You cannot add things with different dimensions. For example, how do you add i + l, if "i" is current in amperes, and "l" is length in meters? Such a mathematical operation is MEANINGLESS physically. That is what you were trying to do. "m" is mass (usually in kg), and "E" is energy, in Joules, or eV, etc.

    When cosmologists say that the "total energy" of the universe is a constant, what they mean is that "mc^2 + E" is a constant, where "E" is NOT the rest mass energy, but rather energy in forms OTHER than the rest mass. This is because "mc^2" is ALREADY taken care off in the first term of that sum! What you were doing was DOUBLE COUNTING something that has already been taken care of. Furthermore, you were taking "m" literally, meaning you took the mass and then ADDED that to an energy by doing "m + mc^2". This is wrong.

    You need to tell me what you understand as "E" in einstein equation. The relativistic Einstein energy equation has a MORE GENERAL FORM, which is

    [tex]E^2 = (mc^2)^2 + (pc)^2[/tex]

    The first term is what most people know, but this is only the REST MASS energy. One simply cannot use E=mc^2 and let E be anything one likes, because it has been DEFINED in the derivation that this is the rest mass energy. This is exactly the first term in "m + E", where "m" here is implied to be "mc^2".

    Please note that just because the SYMBOL looks the same, it doesn't mean that it carries the SAME meaning everywhere. You cannot learn physics in bits and pieces like this, or else you arrive at rather puzzling conclusion as what we have now. You need to clearly understand the definition of various symbols and equations that were used, or else they make no physical sense.

  6. Mar 9, 2005 #5
    thanx a lot ZapperZ, now its clear.. i really appriciat your help
  7. Mar 11, 2005 #6
    if the amount of matter and energy in the universe = 100% then there is theoretically no possible way that there can be more or less than 100% in the universe at any one time, basically no energy can be created or destroyed, only transfered, and according to you the same goes with matter...

    however, according to a book about conspiracies i got, somebody found a way to create energy using some sort of rotating disc or something, if this is true, then i would expect energy to come from alternate realities, which makes stuff a bit complicated...

    this is my awnser according to GCSE physics, im not too sure about matter, but i'd expect your right
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