Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Is Matter Made Up of Photons?

  1. Jul 5, 2008 #1
    Hi,

    When I studied the special theory of relativity, I encountered a description of mass-energy conversion that both enlightened and troubled me. According to this description, the "conversion" (not really a physical conversion) of mass to energy is merely based on changes in our perspective. Take a ball at rest. The relativistic energy of the moving subatomic particles that make up the ball seem to the observer to be the rest mass of the ball itself. In other words, the energy of the moving particles is seen to be mass. However, should the observer "shrink" himself to subatomic proportions, he would see the subatomic particles darting wildly about (perhaps not a wholly accurate description...but it doesn't matter here). What happens now is that the kinetic energy of these subatomic particles that he took to be mass previously, he now views as energy. The process remains the same should he keep shrinking down in size.

    I was enlightened because I thought this to be an elegant and illuminating description of the "conversion" of mass to energy and vice versa. I was also troubled, however, because of a certain implication that this, in conjunction with the fact that light has no rest mass, had. To me, the above description suggests that ultimately, as the observer becomes smaller and smaller (perhaps even infinitely small - just theoretically), there has to come a point where he no longer sees a particle with rest mass, but just one with relativistic mass.

    The reason is simply that any particle with rest mass should be made up of smaller moving particles, which means the observer can keep shrinking down to these smaller particles. So the end of the observer's journey naturally comes when he encounters a particle with no rest mass. Since such a particle necessarily travels at the speed of light, it implies that this particle is a photon.

    Doesn't this mean that all matter is actually made up of photons?


    Thanks in advance for your replies/insights. (By the way, I'm no expert in relativity, so if you see any mistakes, corrections are most welcome)
     
  2. jcsd
  3. Jul 5, 2008 #2
    I don't quite like that way of phrasing things as it suggests that "mass" and "energy" mean different things depending on your size. I'd prefer to say they are exactly the same stuff regardless of your point of view. No shrinkage necessary. Certainly, a moving object has more "weight" than the same object standing still. Whether you're big or small. A particle has mass/energy when it's tiny and you can see it moving, and it also has the same mass/energy when you're so big that it looks stationary. I mean literally, if you throw a book it does actually weigh a little more while it's in flight.

    The standard model says you are wrong, and many fundamental (meaning not composed of anything else) particles do have rest mass. Sorry.

    Of course, the standard model could be wrong, but I have no idea what kinds of crazy rules you'll have to satisfy if you want to make quarks composed of other particles and still make all the particle collider experiments make sense.

    No it doesn't. There are at least three massless particles that travel at the speed of light (photons, gluons, and gravitons, if you believe in them).

    Heck no. Photons have no charge or color, and therefore cannot easily account for most properties of matter. Similarly for the others (though gluons have color). Also, what would keep them spinning around in one place? Photons don't interact with each other (except gravitationally). Also, photons have some properties that don't make any sense for most particles, since they are little pieces of an electromagnetic field.

    EDIT: In the above, when I say "color" I mean as in the strong force, not as in colors of light.
     
    Last edited: Jul 5, 2008
  4. Jul 5, 2008 #3

    Mentz114

    User Avatar
    Gold Member

    Hi worwhite,

    having read your first paragraph, I too am struck by the elegance and simplicity of the argument. There is certain logic in saying that 'rest' mass arises because some energy is confined, which makes it 'at rest' wrt to the observer. As the observer shrinks his region of perception, what was at rest is now seen to be moving.

    There is a hint of this in the quantum mechanical description of a particle as a wave-packet. The group velocity of the WP is always < c, but there seems to something there moving at c. This phenomenon is called 'zitterbewegung' ( which roughly translates as 'zig-zag motion').

    http://en.wikipedia.org/wiki/Zitterbewegung

    Interesting post.

    M
     
  5. Jul 6, 2008 #4

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    There have been previous postings in here that have suggested the same thing, and there are problems with this scenario if taken at face value.

    The main problem here is that you are considering only ONE aspect of the conservation law, i.e. the conversion of mass into energy, while ignoring other conservation laws. Let's take, for example, something that we know as of now that has no internal structure - an electron. By your argument, we can say that an electron is made up of photons, because we can covert an electron into photons, and vice versa. So conservation of mass-energy is preserved.

    But that would be shortsighted, because you are ignoring a whole other conservation laws, such as spin and charge. Photons cannot make up spin of 1/2 (the spin angular momentum of an electron), and they also carry no charge. So clumping photons together to produce an electrons just doesn't work.

    One can see that there's a lot of things involved beyond just the mass-energy conservation in generating particles out of photons. A pair-production of electron-positron pair simply doesn't just make use of the mass-energy conservation. It must also make use of charge, spin, and momentum conservation laws. That is why pair production are always, always done in the vicinity of a massive object, such as beryllium nucleus, to take up some of the momentum.

    There are many conservation laws that needs to be taken care of, not just mass-energy.

    Zz.
     
    Last edited: Jul 6, 2008
  6. Jul 6, 2008 #5
    Good point but alternatively one could argue that an electron's speed is the speed of light while its velocity is obviously sub-light speed.
     
  7. Jul 6, 2008 #6

    jtbell

    User Avatar

    Staff: Mentor

    :confused:
     
  8. Jul 6, 2008 #7
    Electrons don't travel at a velocity equal to the speed of light.
     
  9. Jul 6, 2008 #8
    I think she means looking at things in terms of 4-velocity. Every object's "speed" is c in that sense, right?
     
  10. Jul 6, 2008 #9
    Thank you for all your replies so far.

    Xezlec: For your first point, I actually meant "mass" as rest mass. Certainly a moving object has greater mass than a stationary one (with no scaling-down involved, as you said), but the rest mass remains the same. It's a good point though, I had also thought about this before. My fault for not making it clearer.

    As to your point that not only photons travel at the speed of light, I think that's absolutely right (actually I was hesitant when typing out the word "photons"). I seek a certain amount of understanding in this case, as I must confess to an ignorance in other theories such as the standard model and quantum mechanics (which, of course, I will strive to remedy in the future).

    Nonetheless, the point I'm trying to make is that if the description of what rest mass actually is (in the first paragraph of my post) is accurate, then it follows that something that has rest mass is necessarily made up of something that has no rest mass (be it light, gravitons etc). In other words, rest mass cannot exist per se, implying a permanent substance of matter. As such, it would suggest that fundamental particles with rest mass cannot exist. This point is quite separate from the various conservation laws, which, I understand, must be satisfied as well.

    At this point, I would like to bring in something that Mentz114 observed - "There is a hint of this in the quantum mechanical description of a particle as a wave-packet". This mirrors my own thoughts exactly. When you get right down to it, what is matter? As mentioned, there are issues with assuming the existence of a permanent substance of matter (i.e. fundamental particles with rest mass). I'm not sure if these issues are resolved with the quantum mechanical description of a particle, which doesn't insist on a definite "form" and location for the particle (this statement is probably a little inaccurate, but I hope the idea gets across).

    Again, I must say that I'm no expert, and I understand that much of what I have said may be incorrect, especially considering my lack of knowledge. Insights, observations and corrections are, as always, most welcome.
     
  11. Jul 7, 2008 #10

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    I'm not sure how you can get away with saying that. If the properties of the individual constituents of the object doesn't add up to that object (plus any external factors), then your claim isn't valid. We have seen nothing so far that is consistent to your claim, i.e. show me something where the components what make up a system go by a "quite separate" rule from various conservation laws. Your use of E=mc^2 IS an application of an conservation law! So you cannot claim that it is "separate" while you pick and choose whichever conservation laws to suit your needs.

    Look at something as large as a buckyball, or a supercurrent consisting of 10^11 particles. The whole conglomerate is consistent with the sum of all the properties of the individual constituent of the system.

    But the "wave-packet" is NOT your "photons". You can't mix those two together and assume that just because both are 'waves', then they are the same thing.

    You seem to consistently pick on just one property of a system and using the similarity (eg. "waves" and "mass-energy") to claim that these are the same thing, but ignoring other inconsistencies (i.e. photon has no charge but an electron does). That is like saying an orange and the sun are the same thing because they are both roughly spheres, while ignoring other properties that make them different.

    Zz.
     
  12. Jul 7, 2008 #11
    ZapperZ: Thank you for your reply. I think I should take more time to phrase my posts, it seems that I've failed to be clear on what I meant.


    "So you cannot claim that it is "separate" while you pick and choose whichever conservation laws to suit your needs."

    What I meant by "separate" was that while the idea of a fundamental particle with rest mass may satisfy conservation laws, it didn't seem to agree with the idea of how rest mass is "converted" to energy and vice versa. When I said "...the various conservation laws, which, I understand, must be satisfied as well.", I meant that for any theory, all the conservation laws should be satisfied.

    "But the "wave-packet" is NOT your "photons". You can't mix those two together and assume that just because both are 'waves', then they are the same thing."

    I did not mean to imply that the wave-packet is a photon. Nor do I think that they are the same simply because they are both waves (in fact, I don't believe I said anything at all to suggest that). I'm merely speculating that while the description (in the first paragraph of my post) seems to rule out the existence of fundamental particles with rest mass, the quantum mechanical description of such particles (not photons) may actually show that they can exist, because they provide a very different explanation of the nature of such particles. That's what I meant when I said, "As mentioned, there are issues with assuming the existence of a permanent substance of matter (i.e. fundamental particles with rest mass). I'm not sure if these issues are resolved with the quantum mechanical description of a particle".

    Perhaps I should rephrase my question: "How can there be fundamental particles with rest mass, if the description (given in the first paragraph of my post) is accurate?"
     
  13. Jul 7, 2008 #12

    Dale

    Staff: Mentor

    I don't think this is correct at all, even just for mass-energy conservation. If I understand what you are saying by "particles darting wildly about" you are talking about the thermal energy of the particles which is, at the microscopic scale, fundamentally kinetic energy. While thermal energy does contribute to the proper energy (or invariant mass) of an object, the thermal energy is an insignificant fraction of the total energy. In other words, if you look at the thermal energy of an electron in a ball you will find that it is much less than the 511 keV that is released when it is anhilated. The "darting around" energy of the electron is nowhere near sufficient to account for that.
     
  14. Jul 7, 2008 #13
    Dale: That's a good observation. But if you noticed, I said that "The relativistic energy of the moving subatomic particles that make up the ball seem to the observer to be the rest mass of the ball itself". So I meant that the total energy (both K.E and the "rest energy") of the subatomic particles contributes to the rest mass of the ball, not merely the K.E.
     
  15. Jul 7, 2008 #14
    It is worth noting that the conservation of charge does not discount the possibility of matter being made up of photons.

    For example when a positron and an electron anihilate, two photons are produced. Total charge is conserved in the anihilation. Conversely a photon can be "made" into an electron as long as a positron is produced at the same time to conserve charge, momentum, etc.

    It is also worth noting that while a single photon has no rest mass, a system of two photons going in opposite directions has a total rest mass as a system. Rest mass is not a property that is exclusive to things we normally think of as being "solid". Photons have the all the properties we normally associate with mass such as having momentum or inertia and as being a source of active gravitation.

    Some theories (although not necessarily accepted mainstream ideas) think of particles like electrons as composed of self gravitationally orbiting photons. A nice appeal of this idea is that photons are not created or destroyed or accelerating from rest to c and vice versa but always moving at c but sometimes it is linear and measurable or tightly circular in the way that appears stationary on the macro scale.

    This post in another thread states that "Much of the work needed, to show that a self-confined, single wavelength photon, has the fundamental properties of an electron was done by J. G. Williamson and M. B. van der Mark." See https://www.physicsforums.com/showpost.php?p=1778031&postcount=19
     
  16. Jul 7, 2008 #15

    Dale

    Staff: Mentor

    That's fine, but then you never get to the "massless" point that you were talking about. You still have a particle whose total relativistic energy consists of some KE and some rest energy (aka mass).
     
  17. Jul 7, 2008 #16

    Dale

    Staff: Mentor

    Actually, this is incomplete. A photon requires some matter to interact with in order to create an electron-positron pair.
     
  18. Jul 7, 2008 #17

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    But this is quite different than saying matter is made up of photons. A bunch of photons simply cannot be squeezed together to produce a photon. The very fact that we need (i) a "mirror" particle, which is its antiparticle and (ii) a massive particle to conserve momentum, both implies that the creation of mass out of photons are not simply a trivial conversion of mass into energy or energy into mass. Pair production is not the evidence one can use to say that matter is made up of photons.

    In pair production, where masses are formed, there are no "photons going in opposite directions". All pair production that we currently have are gamma photons going through dense material such as beryllium, and not via photon-photon collision. So your example of the possibility of a system having a "rest mass" via 2 photons going in opposite direction cannot account for the creation of pair production, because that is now how we currently create those particles.

    Zz.
     
  19. Jul 7, 2008 #18
    Dale: "That's fine, but then you never get to the "massless" point that you were talking about. You still have a particle whose total relativistic energy consists of some KE and some rest energy (aka mass)."

    When I said that the "rest energy" of the subatomic particles contribute to the rest mass of the ball as well, I don't mean to imply that as we go deeper down the rabbit hole (so as to speak), all constituent particles will always have this rest energy. Take your example of the electron - as you said, it obviously has more than just K.E, it also has "rest energy". Therefore, I'm arguing (ok I'm not really arguing, just saying that maybe...just maybe) that an electron is made up of constituent particles whose energy make up its rest mass. As we go smaller and smaller, we may eventually come to a point where the particles have no rest mass (doesn't have to be photons, it can be other kinds of massless particles - I mentioned this mistake just now). Note that these particles have relativistic mass though, because they do have kinetic energy.
     
  20. Jul 7, 2008 #19

    ZapperZ

    User Avatar
    Staff Emeritus
    Science Advisor
    Education Advisor

    The problem here is that at some point, you have to base your scenario on something other than just speculative, i.e. on solid, verified physics. You'll notice that a lot of the responses that you've been getting have been based on physics that we know of and have been verified. If all you care about is speculation, then all bets are off. I will tell you right off the bat that I have a very vivid imagination and can come up with things that you might not even have thought of. I don't think this is something you are looking for, i.e. some pie-in-the-sky that could easily be a waste of time.

    I believe that my initial outline of the problems with photons or other "massless particles" (what are these? gravitons, which is another speculative, unverified particle?) making up particles such as electrons (we haven't talked about other hadrons yet) have not been sufficiently answered. That, in itself, should cause you to go back to square one and solve that first before proceeding another stage.

    Zz.
     
  21. Jul 7, 2008 #20

    Dale

    Staff: Mentor

    Your conclusion is completely illogical, it does not follow in any way from your initial observation. You start with the correct initial observation that thermal energy, which contributes to proper energy (aka invariant mass), is actually kinetic energy, and then go from there to suggest that therefore all fundamental particles are massless. I'm sorry, but this is a huge non-sequiter.

    Other than your personal preference for massless fundamental particles, do you have any reason to believe that the electron is not a fundamental particle?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Is Matter Made Up of Photons?
Loading...