Can mass be created or destroyed?

  1. Sorry, I'm just a physics newbie.
     
  2. jcsd
  3. Well, the simple answer is matter cannot be created or destroyed.

    The more complicated answer is that in some nuclear reactions particles can be converted into energy ( like in a hydrogen bomb). If that happened to your atoms you would said they were destroyed. If you consider the familiar equation E=mc2 it means there is an equivalence between matter and energy.

    I'm sure someone else will give us a more complicated answer.:smile:
     
    kena likes this.
  4. mmwave: You mean yes, matter can be created or destroyed, right?

    Other examples: matter-antimatter annihilation, pair production by energetic photon...

    Correction: mass in the conventional sense can be destroyed, but mass/energy is conserved.
     
    Last edited: Aug 17, 2003
  5. LURCH

    LURCH 2,514
    Science Advisor

    As far as we know, mass cannot be created or destroyed, it can only change form. Matter can become energy, and energy can become matter, but always according to e=m2. So, when a matter-antimatter reaction occurs, the mass of the matter (and antimatter) is converted to energy of equal mass, which propogates outward in verious forms (heat, light, a kinetic shockwave, sound waves, etc), and gets spread out thinner and thinner throughout the cosmos, but never looses anything in quantity. If you ever found a way to capture all the energy that was released in the reaction, and condense it back together into matter, you would have the same amount of mass as the original amount of material used.
     
  6. jcsd

    jcsd 2,226
    Science Advisor
    Gold Member

    Mass means invariant mass and it can be destroyed and created that can be seen in the anihilation of a low energy and high energy electron-poistron pair (equation 1 is an anihilation of a low-energy pair whereas 2 and 3 are high energy pairs).

    1) e+e- → γγ

    2) e+e- → uû (π°) *

    3) e+e- → μ+μ-


    *I couldn't find the correct ascii symbols for antiquarks

    In these equation the mass on left hand side of the equation totals 1.022 Mev/c2, but on the right hand-side the mass is 1)0 2)1.057 3)2.114, so obviously the mass has changed during these anhilations.

    As long as you understand though that invariant mass is essientially 'mass-energy' and can be converted back and forth between other sorts of energy (e.g. K.E.).
     
  7. No. In our everyday lives it is sufficient to say that matter is not destroyed. Your examples are for physics labs and stars and are really the conversion of energy to matter or matter to energy covered in my second paragraph. I believe the better way to look at it from a physics stand point is that matter is just a form of energy.
     
  8. jcsd

    jcsd 2,226
    Science Advisor
    Gold Member

    btw can everyone see the character set I've used for the equations in my last post?

    Just in case you can't, here's the equations in written form:

    1) electron + positron -> two photons

    2) electron + positron -> an up quark and an up antiquark (a neutral pion)

    3) electron + positron -> a muon and an anti-muon
     
  9. Hi Jcsd,

    I could read your first character set so thanks for doing the ascii thing too. EDIT: could NOT read them

    Why would they call it invariant mass if it can be converted to energy and disappear? That seems like variation to me. :smile:
     
    Last edited: Aug 17, 2003
  10. Hurkyl

    Hurkyl 16,090
    Staff Emeritus
    Science Advisor
    Gold Member

    It's invariant under Lorentz transformations; any two (inertial) observers will record the same invariant mass for an object, in contrast with things like speed, kinetic energy, or distance which generally vary between different observers.
     
  11. Ivan Seeking

    Ivan Seeking 12,529
    Staff Emeritus
    Science Advisor
    Gold Member

    It seems that this issue of "invariant mass" and "mass" is really just a matter of definition.

    What term can we use to address the "source" of inertia and gravity?

    ...if the term "mass" is now treated as meaning rest mass.

    Does the concept of mass beyond this notion fail for some reason, or is this this merely a convention?

    Perhaps the concept of mass, beyond rest mass, is thought to be simply unnecessary?
     
    Last edited: Aug 19, 2003
  12. Can mass be created or destroyed?



    If it couldn't the bigbang would have never occured. People fail to realize that. They say that nothing existed before the big bang. Well if that's true then WHAT BLEW UP? :-) So either we deny physics its rules or throw bigbang out the window, the communities choice.
     
  13. jcsd

    jcsd 2,226
    Science Advisor
    Gold Member

    No all the matter aound today was there at the time of the bigbang contained within the singularity.
     
  14. russ_watters

    Staff: Mentor

    Option A. It is a fundamental part of the Big Bang theory that the rules of science break down at a point just after the Big Bang. So the normal rules don't apply. The truth is we don't know where the matter came from. But it did come from the Big Bang.
     
  15. How would you go about creating/destroying mass? What exactly would you do?
     
  16. jcsd

    jcsd 2,226
    Science Advisor
    Gold Member

    see my previous post. In 1) (invariant) mass is destroyed in 3) it is created
     
  17. But that was not what I was asking, obviously. I'd like to know just how one can create or destroy matter.
     
  18. jcsd

    jcsd 2,226
    Science Advisor
    Gold Member

    Well, no it's not obvious that that wasn't what you were asking as those are a few of the ways of creating and destroying mass (matter).
     
  19. Mass and energy are not things they're properties of a system. If you define your system to include all the products of the interacting particles then the mass and energy remain the same.

    If a nuclear weapon is detonated in a vault the vault weighs the same before and after the detonation.
     
  20. I don't think so. In order for an act of creation to occur there must be a creator. I'd like to hear about such an act, with emphasis on what the creator would do to create mass.
     
  21. pmb

    pmb 0

    The anwswer to this question depends on what you mean by "mass." There are two senses in which the term "mass" is used in physics. One is what some people call "relativistic mass" and the other ios what some people call "rest mass." And then it will depend on what you mean by the mass of a system of particles since this is often the case people speak of when they speak of the mass of a system.

    In the following I'm assuming that energy is conserved which is almost always the case.


    If you mean "relativistic mass" then the answer is that mass is always conserved - i.e. it's a constant. No matter how you count it the mass is conserved.

    If you mean "rest mass" and then that too is conserved - *if* you defined the mass of a system of particles as the energy in the rest frame divided by c^2. If you simply add rest masses then no - mass is not conserved. Same with "invariant mass" since they're the same thing. But the system mass will depend on how you define it. Some people call the mass of a system the sum of the rest masses and some do it the other way

    With regards to the mass = rest mass definition = Taylor and Wheeler explain all this in their text "Spacetime Physics - 2nd Ed" - the relavent part is online in my web site

    See
    http://www.geocities.com/physics_world/stp/stp.htm

    I have permission to post that from the author.

    jeff said that mass means invariant mass and if one defines invariant mass as the magnitude of the total 4-momentum then what jeff claims is not true. And mass is not always defined to mean invariant mass (counter examples from relativity texts are Rindler (2002), Mould (1994), D'Inverno(1992), French (1968), etc). Not even for a large majority of the time. And jeff also implied that invariant mass is not conserved and that's not true either. Since invariant mass is defined as the mass in the rest frame and then in the rest frame its defined as "energy in rest frame"/c^2 so since energy is conserved then so too is mass.

    For a worked out example of mass to energy conversion (mass changes form but not value) see

    http://www.geocities.com/physics_world/sr/nuclear_energy.htm

    For an explantion of what invariant mass is and why it's conserved see

    http://www.geocities.com/physics_world/sr/invariant_mass.htm

    In the case jeff gave its rather easy to see why invariant mass "of the system" is conserved Since both


    Pete
     
Know someone interested in this topic? Share a link to this question via email, Google+, Twitter, or Facebook

Have something to add?