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What process creates mass?

  1. Jan 23, 2007 #1

    I have only taken two semesters of Physics, so please keep that in mind when answering. Thanks!

    OK, I have heard of fission and fusion, and I basically understand them. Smash together some mass, and the result is a little bit of missing mass which creates a ton of energy.

    I have always heard about these processes, but unlike most other topics, I haven't really ever heard about what the opposite process is of each of these. How do you convert energy into mass? I have heard that a person can truly show they understand something by explaining it in simple terms, and I know this sometimes leads to an imperfect explanation, but please don't use terms like Higgs Field or Higgs Boson without a simple explanation of what that means.

    Sorry if I am asking for too much, but I have asked some of my friends, and they can regurgitate the complex words and terms they have learned, but they haven't been able to really make me understand this.

    Thanks very much for any help or information. :smile:
  2. jcsd
  3. Jan 23, 2007 #2
    Heat a potato. It now weighs more. You just can't measure it so easily, unlike nuclear reactions where a significant fraction of the total mass-energy changes form (and escapes).
  4. Jan 23, 2007 #3
    Ok I weighed myself while i was holding a potato, then i heated it and ate it, and then i weighed myself, and the weight was the same.
  5. Jan 23, 2007 #4
    Yes... that was a joke, but I am asking a real question here. I know that energy = mass c^2, so when you add energy to something you are increasing it's mass energy or whatever, but does that mean that mass and energy are the exact same thing? I don't think so, because then a really really cold rock would weigh almost nothing?
  6. Jan 23, 2007 #5
    The theory is that mass and energy are interchangeable in a sense, not that they are the SAME thing. My bit of mass can be changed into energy, but it's not mass and energy at the same time. With heat it's one mass that is containing another (the heat) energy.

    One theory in string theory puts vibrating energy strings as the basis for every particle, but I don't think that's what you're asking. Or if that theory is still being used.
    Last edited: Jan 23, 2007
  7. Jan 23, 2007 #6


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    Re: what process creates mass?

    we simply don't know the answer to such questions very well... not yet...if we do, we could precisely calculate the masses of quarks and leptons.
  8. Jan 23, 2007 #7
    This is something I've wondered for a little while about too...I've only read snippets here and there and haven't studied it because I've just now begun classical E&M in school. I've read that in high energy particle collisions, new mass can be created. I guess it is a humongous quantity of energy that creates a tiny bit of new matter? Why does this happen?

    On a somewhat related note, I got into an argument with one of my chemistry teachers about why you should not weigh hot objects. She tried to reason that since density is dependent on temperature, and d = m / V, that when objects are hot their mass changes...I told her that's obviously wrong, it's the same mass but the volume has changed. I could understand the fact that perhaps a change in volume could affect the weight measurement since there would be slightly more buoyant force (since it is immersed in air) but this effect would be minimal. I proposed that it was probably just a safety precaution and that you shouldn't be fooling around with a beaker of boiling water on a scale anyway, but she didn't concede this. Can you guys shed light on that?
  9. Jan 24, 2007 #8
    the mechanism, as i understand it (which is not much), is that it is a consequence of the fact that both matter and radiation are fundamentally described by waves. it is also for this reason that light and matter interact at all (as in electron excitation, for example). things in the universe are made up of bosons (example: photons) and fermions (example: electrons), both of which can be described as perturbations to an underlying quantized field - this is the achievement of quantum field theory. so what we call matter ("particles") and radiation ("EM wave") are really just collective modes (i.e. stable states) of a vacuum field. these states can interchange in a time-dependent way - which would be what you are talking about, matter to radiation (i assume that is what you mean by 'energy') and vice versa. someone else on the forum, please correct me if i am wrong about any of this.

    when i was an undergraduate, my analytical chem TA told us the same thing. he was a good researcher, so i believe it. i think your 2nd explanation was the reason behind it (that the heat winds up preferentially heating the air around it - except on the bottom where there isn't much air) causing a buoyancy effect that supposedly can be noticed on an ordinary chem lab balance. ive never actually tried this tho - altho i recall many days where i wanted to finish lab quickly so i would just weigh the hot stuff anyways :) if it made a difference, i didnt notice it..then again, an analytical chemist probably would :rolleyes:
  10. Jan 24, 2007 #9


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    No one really knows where mass comes from. Current theory puts it in by a rather involved procedure that has not been verified, and is quite arbitrary. For a book on mass that is fairly elementary, see Max Jammer's classic, available for $5 on amazon:

    Concepts of Mass / In Classical and Modern Physics
  11. Jan 24, 2007 #10
    Thanks to everyone for your answers. Some of them were very interesting. This question sprang about from a discussion on entropy that I was having with one of my friends.
  12. Jan 25, 2007 #11

    Gib Z

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    Well yes basically, To your original question, No one really knows. If anyone says they do, their just going to spit out a fat load of words about The Higgs boson, maybe some amazing TEV particle accelerators, and Quantum Field Theory. Thats another way of them saying, they don't really know, but their trying...
  13. Jan 26, 2007 #12
    can someone here with a PhD in physics and whom is currently doing research in modern physics, confirm that in fact "no one knows" the process of mass->radiation and radiation->mass?

    i am unqualified to evaluate this, but it sounds a bit pessimistic to me.

    more specifically, (a) i find it hard to believe that the standard model works so well (in terms of describing experimental observations) without an understanding of this underlying process and (b) i have noticed that in an area in which i AM qualified to evaluate, that often times people who do not understand or feel comfortable with the mathematical abstractions of something will claim that the current understanding is somehow a sham - sometimes the interpretation for the layman actually brings harm to the promethian samaritan.
  14. Jan 26, 2007 #13


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    In relativity, even a stationary particle has energy because of its mass: [itex]E_0 = m_0 c^2[/itex] where [itex]m_0[/itex] is the particle's invariant mass (which is often called "rest mass"). We call this the particle's intrinsic energy or rest energy.

    This intrinsic energy can be converted into other forms of energy, for example in particle decays such as [itex]\Lambda^0 \rightarrow p + \pi^-[/itex]. The sum of the invariant masses of the [itex]p[/itex] and [itex]\pi^-[/itex] is less than the invariant mass of the [itex]\Lambda^0[/itex]. The difference manifests itself in the kinetic energies of the outgoing [itex]p[/itex] and [itex]\pi^-[/itex].

    Some people describe this by saying that the [itex]p[/itex] and [itex]\pi^-[/itex] have larger "relativistic masses" because of their kinetic energy, so the sum of their relativistic masses equals the relativistic mass of the [itex]\Lambda^0[/itex]. This description is equivalent to the other one using invariant mass, but particle physicists generally prefer to talk about invariant mass rather than relativistic mass. (I worked in particle physics as a graduate student, and I don't remember anyone in the field using relativistic mass.)
    Last edited: Jan 26, 2007
  15. Jan 26, 2007 #14

    Gib Z

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    I assure you quetzalcoatl9, even if most of us here don't fit the description of PhD etc, we know enough to tell you no-one knows for sure. There have been certain theories, and there are people who think they know. But so far, nothing has been confirmed, or generally accepted by the Scientific Community.
  16. Jan 27, 2007 #15
    Thank you again for some of the further explanations. This is a very interesting subject to me... sometimes people say that mass and energy are the same thing, and I don't know that we really know whether that's true or not. Any additional info would be great.
  17. Jan 29, 2007 #16
    I may be talking rubbish here, but am I not correct in saying that mass cannot be created or destroyed, much like energy cannot be created or destroyed? A 'particle' cannot be simply created or destroyed, for example during nuclear fission neutrons are removed from split nuclei, but not 'destroyed', rather the it is simply an exothermic reaction in which the energy does not come from a net loss of mass, but from a smaller amount of energy contained within the particles.
  18. Jan 29, 2007 #17
    No, unless you mean relativistic mass (which is trivially equivalent to energy).

    Incorrect, for example energy can be used to create a particles (say, an electron and positron) in an accelerator lab.

    If you measure the weight before and after you'll see it has changed, but maybe you're onto something. Particle physicists will tell you that some of the rest mass has been converted to energy. Personally, I think it's interesting that we call the chromodynamic potential energy "rest mass", but we call the increased potential energy of a hypothetical box-of-photons (or hot potato) by the name "relativistic mass" (in a frequently disdaining manner despite that in every classical sense the box/root behaves as though it is now more massive than when empty/cold).
    Last edited: Jan 29, 2007
  19. Jan 30, 2007 #18
    Ah, so you can create a 'particle', for example an electron, form only energy and nothing else? It certainly is an interesting idea..
    thanks for the clarification btw ^^
  20. Jan 31, 2007 #19
    Elementric; two photons of high, equal energies and perfectly opposite momentum vectors can collide and produce an electron-positron pair. A photon has no mass but it is most definitely 'something' - so it's not exactly pure energy.
  21. Jan 31, 2007 #20


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    Please note that we still do not have a photon-photon collider. This means that this technique of generating electron-positron pair has not been experimentally demonstrated!

    So of course, the most obvious question following this is, how has e-p pair been generated, especially at SLAC and the now-retired LEP? How would the position be generated at the proposed ILC? I believe this has been mentioned and explained already a few times on here.

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