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Is the law of conservation of energy 'wrong' ?

  1. Jul 2, 2004 #1
    According to an audiobook i've been listening to about 'E=MC^2', at C (the speed of light) energy will not speed up an object and the energy will become 'mass'. Can anyone confirm this?
    Surely this also means that the amount of energy in the universe will be ever changing and that using the law of conservation of energy when working with energy in mechanics is incorrect?
    Perhaps the law of conservation of energy should be ammended to 'the total sum of mass and energy is a constant' ?
    Thanks for clearing this up.
  2. jcsd
  3. Jul 2, 2004 #2
    yes, this is true, when the object hits the c barrier, any extra energy, or force is used to increase its mass. This has been confirmed at various locations. Stanfords linnear accelerator can make an electrons mass 3000X its rest mass by speeding up the motion of the electron. And about your second claim, remember, mass is energy.
  4. Jul 2, 2004 #3
    The laws of conservation of mass and the laws of conservation of energy are (in the classroom) usually separated like so because the speeds you are dealing with are significantly smaller than c.

    In it's truest form, the law is written 'the law of conservation of mass-energy', to include both, although they are basically one in the same.
  5. Jul 2, 2004 #4
    Thanks for the prompt responses, i find this sort of thing pretty interesting.

    I don't really see how mass is energy, can you expand on that a little or provide me with an internet link? Thanks.

    How would one go about transferring the mass back into energy?

    Could this theory support that of the 'big bang' - ie, when matter expanded outwards it could not move at the speed of light and so become mass?

    What mass is created? Protons? electrons? How is it determined which type is created?

    Wouldn't light energy going at the speed of light heat up when passing starts, and gain mass?

    Thanks for any answers.
  6. Jul 2, 2004 #5
    For the most part the law of the conservation of mass is the same as the law of the conservation of energy. Mass is always conserved, always! So long as by "mass" you understand that its relativistic mass. When a particle's speed is increased its mass increases. That mass came at the expense of the mass of something else.

    To see what all this mass-energy thing means see the topics on mass and energy at -- http://www.geocities.com/physics_world/sr/sr.htm

    Last edited: Jul 2, 2004
  7. Jul 2, 2004 #6
    It really easier to think of mass and energy as basicly the same thing. Or atleast mass as just another state of energy.
  8. Jul 3, 2004 #7
    Thanks for the explanations and the link people. Very interesting stuff.
    You should see about downloading it for yourselves, obviously most of you understand it well already but it does provide some insight into the life of various scientists and you may pick up something you missed before.
  9. Jul 3, 2004 #8


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    Er... Knowledgeispower, you might want to be wary about pmb's link. I am aware of at least one argument, where several members (and these members are not crackpots) disagreed strongly with his physics - specifically, his treatment of the concept of mass.

    Many ways. Nuclear reactions can result in a decrease in mass, as it is converted to energy. Matter-antimatter annihilation involves full conversion of mass. For relativistic mass, simply slowing down would convert the mass back into energy.

    Whaa...? The mass increase only applies to particles which have rest mass. They would have gained mass, if they were gaining energy, but we consider the Big Bang usually to be a single event, so the initial matter would have had the same energy, and so mass as they did at the beginning, barring reactions between each other - which is what we think happened.

    Mass increase (and I know this would annoy pmb, but still...) occurs at all velocities, not just c. It is just very insignificant at low velocities. The formula is M = M0 / ( 1 - (v/c)^2)^0.5, where M0 is rest mass. This mass isn't extra particles, or anything, but just a measured increase in mass, from a frame of reference travelling at that relative velocity. If you were the object, you wouldn't notice anything at all.

    I don't quite understand what you mean here.
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