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Mass can turn into Energy, or is it Matter which can turn into energy?

  1. Oct 26, 2013 #1
    What's the difference between Mass and Matter? Which of them is equivalent to energy?
    Can mass exist without matter?
    What does the universe mainly contain? :
    Mass and Energy
    Matter and Energy
  2. jcsd
  3. Oct 26, 2013 #2
    mass is just a property of matter.They are kinda one and the same.There is no abstract mass somewhere out there that has no matter attached to it.

    Not all matter has mass , some of it is massless like photons , but that another story.
    Everything that has mass also has energy, potential, kinetic or otherwise.

    The explored universe mainly contains just matter , but there is a huge portion which we don't know yet , we have a fancy word for it " dark matter" not because it's dark but rather because we have a rather " dark picture" of it as of yet.
    Anyways whatever is out there must be something physical of that you can be sure.
  4. Oct 26, 2013 #3


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    Matter is composed of fundamental particles. Mass is a measurable quantity associated with both matter and energy.

    Absolutely. A box with light inside has more mass than a box without light. Or, if you want to get rid of the box idea, we can say that a volume of space with lots of light in it has more mass within it than a volume of space with no light inside, everything else being identical.

    Ignoring dark energy, as that gets confusing when talking about what the universe is composed of, the majority of the universe is mass in the form of dark matter.
  5. Oct 26, 2013 #4
    Ok. So when we say 'mass turns into energy' then actually we are saying 'a measurable quantity associated with both matter and energy turns into energy'. Sounds confusing to me.
    Also if only 'a measurable quantity associated with matter turns into energy' then where is the left out (matter without mass) ? And what is that?
  6. Oct 26, 2013 #5


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    Yes, it's a bit confusing.
    To quote wiki:
    In physics, mass (from Greek μᾶζα "barley cake, lump [of dough]") is a property of a physical system or body, giving rise to the phenomena of the body's resistance to being accelerated by a force and the strength of its mutual gravitational attraction with other bodies.

    To make it even more confusing, certain units of measurement, like the electron volt, can refer to BOTH mass and energy.

    Mass is typically used to refer to the invariant quantity of energy a system has in its own rest frame. For example, a rocket traveling at 99% c will have zero kinetic energy in its own frame of reference, whereas in the frame we are measuring its velocity against it will have a great amount of kinetic energy. However the mass of the rocket will remain the same no matter what frame we measure from, as will the energy associated with this mass. Having a term like "mass" makes it much easier to do physics.

    There is no matter without mass. All fundamental particles have mass, as do the composite objects they build into.

    Edit: Photons are not usually considered to be matter.
  7. Oct 26, 2013 #6


    Staff: Mentor

    Mass doesn't "turn into" energy. Mass has energy, and energy has mass.
  8. Oct 26, 2013 #7
    If so, then Matter has mass and mass has energy and again energy has mass...
    Who 'has' the property and who 'is' the property?
  9. Oct 26, 2013 #8


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    Perhaps another way of looking at it will help.

    Instead of saying energy has mass, we could say that X amount of mass is equal to Y amount of energy. For example, a kg of mass is equal to approximately 9x1016 joules and vice versa. It doesn't matter which unit you use, the overall effects are the same.
  10. Oct 26, 2013 #9


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    I don't think that question has any scientific meaning.

    How could you experimentally test that question?
  11. Oct 26, 2013 #10
    Ok let me restate my original question:

    If we can say X amount of mass is equal to Y amount of energy,
    Can we say J amount of matter is equal to K amount of energy?
  12. Oct 26, 2013 #11
    Yes we can.
    Last edited: Oct 26, 2013
  13. Oct 26, 2013 #12


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    Mass converts to energy per E=mc^2.

    All matter has mass.

    But matter is a non-technical term. Matter = stuff. Most people would say that matter is made up of atoms, atoms are made up of fundamental particles.
  14. Oct 26, 2013 #13


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    Provided that J is measured in units of mass, then yes, where K = J c².
  15. Oct 26, 2013 #14
    Conclusions: (are they all correct?)

    1. Mass and energy are two ways of measuring the same thing.
    1. Every system has mass or energy or both (as mass and energy are equivalent)
    2. Thus, Matter has mass or energy or both.
    3. Mass of a matter can not be 'converted' into energy in the sense that they are actually same thing.
  16. Oct 26, 2013 #15


    Staff: Mentor

    The first 1. and 3. are fine, but I would restate the second 1. and 2. as follows:

    1. Every system that has mass has energy (as mass and energy are equivalent)
    2. Thus, Matter has both mass and energy.

    By the way, I thought that I should clarify, the mass I am discussing here is "relativistic mass". There is another definition of mass called "invariant mass" which has a slightly more complicated relationship to energy. Specifically: ##m^2 c^2 = E^2/c^2 - p^2##
    Last edited: Oct 26, 2013
  17. Oct 26, 2013 #16
    Also note that most of the time (>90%) when physicists use the word mass they mean rest mass not relativistic mass. Rest mass is not equivalent to energy since their relationship also includes the momentum p. If you ask my opinion, I would abolish the concept of relativistic mass all together since it is more trouble than it is worth.
  18. Oct 27, 2013 #17
    Mass is a measurement of matter, which is any physical substance. Matter and energy are not necessarily the same thing, although all matter contains some degree of potential energy. Einstein's theory E=MC^2 states that the amount of energy in matter (E) equals its mass (M) times the speed of light (C) squared.
  19. Oct 27, 2013 #18
    This is the best answer I think. You dont really need the word "matter" in physics at all, it adds nothing new to any theory.
  20. Oct 31, 2013 #19
    I hope now I am correct:

    Relativistic mass is a measure of systems Energy.
    Energy is a measure of system's Relativistic mass.

    Matter or it's mass, doesnt 'turn into' energy.
    Relativistic mass and Energy are two ways to represent a same thing.
  21. Oct 31, 2013 #20


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    Er.. no, I think you've made it worse.

    We usually do not deal with "relativistic mass". In fact, in many circles, this term is seldom used.

    Mass can be converted into energy, and energy can be converted into mass. These are "invariant mass", and that is the only mass that matters (no pun intended).

    I am not sure why you have a problem with each one being converted into the other, or why you need to make a distinction between "relativistic" mass etc.

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