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Nonspecialist qstns:ie, massless=no space?

  1. Jun 21, 2004 #1
    I have a whole jumble of questions, so I am just going to spit them out (please bear in mind, that I have no background in either physics or mathematics, so in responding, please try to keep formulas to a minimum, unless necessary to do otherwise, or else I will probably just end up lost again)

    1. MOST CONFUSING question : if photons are massless, then they cannot take up space (in order to take up space, you need to have something which fills space. only matter can fill space --> or, to put it another way, if something is to take up space, then it must have matter since only matter can build dimensions, so only that which has matter and thus mass takes up space). if they cannot take up space, then they have no dimensions. if they have no dimensions, then they cannot be in relation to each other or to anything else (ie, if a thing has no dimensions then it cannot be above, below, right, or left of anything else), but obviously they are --> how is this explained. Maybe my confusion is in thinking that energy does not take up space; please explain to me then if and how energy can have dimensions without having matter from which to build those dimensions.

    2. Also, I know that energy and mass can be traded, and I think of it like a race car, going very fast down the track and starting to come apart from the speed, with its various parts blowing off, making it lighter and faster; eventually however, when all the parts blow off, there is no more motion b/c there is nothing to move --> people want to say, I assume, that photons reach the limit of speed and so blow off all their matter but if they have no matter, what moves ? if they don't take up space b/c they have no matter, what moves and how can it, lacking all dimensions and so not in any form of spatial relation to anything, be said to move (ie, if it is not in a relation to anythign to begin with, how can it be said to move in relation to anything at all) ?

    3. Also, even if you can say that they do move, why can they move only as fast as light; with no matter to impede them or allow anything to interfere with them, why can't they move infinitely fast ?

    4. could someone explain how light weighs nothing but can add to the weight of a box in which it is enclosed ? The only way I can wrap my head around this is to say that b/c the frame of reference changed, the properties changed --> the problem with this is that the box is still in the same frame of reference (ie, the universe) as the light when it was weightless/massless, so shouldn't it not change ? isn't the light ultimately changing in the same frame (ie, the universe) ?

    5. And further, if you say that light in a confined space can change weight, but is weightless in the universe, doesn't that mean that the universe is not confined (ie, the universe is infinitely large/unbound) ?

    6. Also, if everything depends on frame of reference, then wouldn't two particles moving near the speed of light but going in opposite directions exceed the speed of light relative to each other ? If that is the case, what about two people moving very fast relative to each other ? Would they age faster than the rest of the planet, even though, relative to everyone except the one other person who is also moving very fast and in a direction opposite to them, they are not moving faster than the speed of light ? I guess I don't understand how it could be the case that the fact that they are moving faster than light relative to each other could cause them to age, but the fact that they are not moving faster than light relative to anyone else could not cause their aging process to remain the same (ie, why does only one of their two relative speeds matter ?)

    thanks for any help anyone can give me,
    -->merc :confused:
  2. jcsd
  3. Jun 21, 2004 #2
    1+2: Mass is supposed to be the result of interactions with a particle called the Higgs boson. If your particle, in this case photons, do not interact with Higgs then they do not have any weight. Think of weight in terms of a key and a keyhole. No match, no weight.

    3: We don't know why light is "slowed" to c, I think. I know that Super String Theory reduce to General Relativity, but whether c is the outcome of some complicated calculations or is "put in" ... Anybody?

    4: It can't. Light has energy and momentum and when it hits a wall the momentum is "transferred". If it's a mirror then the the mirror gains twice the momentum of the photon. That's the workings behind solar sails.

    5: see 4

    6: No. Two particles moving in opposite directions at near c, seen from an observer in the middle, are moving away from each "a little closer" to c, but never faster than c. Einstein showed that the faster you move the slower time is moving. When you stand still time is moving the fastest and when flying at c, time does not advance at all.
    More technical: We are moving through space-time (space AND time) at a constant "speed". This speed allow us to exchange time for space so to say. At normal speeds, non-relativistic, there is no difference to what we are used to, but at high speeds there is: time goes slower and distances become shorter.

    For an introduction to all that, try and google for the twin paradox.

    Hope this helps
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