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Differences matter and radiation

  1. Sep 8, 2004 #1
    Let me start by saying that I'm just a layman afficionado to physics.

    As I understand, most physicists believe that fundamentally, all what fills up the universe (all kinds of matter particles and all forces) must be different configurations of some unique "fundamental energy", and that at sufficiently high energies everything would merge into some single "entity". The different configurations we observe happened when symetries got broken by the cooling of the universe.

    It seems to me that among what we observe in the universe, there is a quite radical separation between matter and radiation. The most obvious difference being that radiation stayed massless and thefore fills the universe "at the speed of light", which in turn determines a completely different interaction with space and time as compared to matter.

    What is it that actually differentiates radiation from matter? just the fact of not having acquired rest mass?
    Was there a definite symmetry breaking which defined the fate of the fundamental energy to become either matter or radiation?
    If so, why did some energy turn into matter and some other into radiation, and not all energy into one or the other?
    Sorry if I'm too naive ....
  2. jcsd
  3. Sep 8, 2004 #2
    Part of your question inquires about the formation of the universe, which is mostly unknown and not well understood. Radiation is a form of energy transfer (like light), whereas matter, like you said, has mass.
  4. Sep 8, 2004 #3


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    As far as I undersand it, symmetry breaking and the fact that some forms of matter acquire mass is supposed to all be the result of the Higgs boson / Higgs mechanism. Since nobody as actually seen a Higg's boson yet, the answers to these questions are all rather speculative.
  5. Sep 15, 2004 #4
    Our current physics describe quite well both matter and radiation in a unified way, I believe this alone is a great achievement.

    But it still seems to me that we describe the universe very much involving the elements "space" and "time" (spacetime) e.g. we use physical theories to predict how a certain system configuration will have evolved through space after a certain period of time has elapsed.
    I feel this might be a bit biased towards the "physics of matter". Because we are made of matter we tend to be more interested in understanding how matter will behave through space and time, or how the complete universe (matter + radiation) will appear to a material body such as us.

    I wonder if our science descriptions take enough account that a big portion of our universe (radiation) interacts with spacetime in a very different way.

    For radiation not having a rest frame of reference, it seems spacetime has a different meaning (if it has any at all). It seems that the "physics of radiation" might not necessarily involve spacetime coordinates in the same way as the "physics of matter" do.

    It's not so clear to me if our "physics of radiation" (although they seem to accurately describe the events) do really take account of the way radiation interacts with spacetime (how radiation "really" behaves) or they just take care of describing "how radiation will appear to behave to a material entity")

    In summary I wonder if we really reflect in our physics the fact that our familiar references to interactions with spacetime may only be applicable for (or required by) the matter portion of the universe.

    If a sentient being could exist made of radiation alone, would she introduce spacetime in her physics theories in the same way we do?
  6. Sep 15, 2004 #5


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    In these forums we must stick to physical theories backed by physical evidence. What physical evidence do you know of which supports your opinions?

    If there is none then this topic is pure speculation, which can turn into crackpottery in a hurry. If you can relate your ideas to physical evidence please continue, otherwise do not.
  7. Sep 16, 2004 #6


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    It's certainly fun to speculate about this, isn't it?!

    Let's set the context a bit though ... we currently have two very good theories in physics - quantum mechanics (this is a shorthand) and general relativity. Both theories are 'good' in the sense that they are internally consistent, and consistent with experimental and obervational results, within their respective domains of applicability. However, we recognise that the two are mutually inconsistent in certain domains, e.g. short time, high mass density. Indeed, how to extend/modify/replace one or both these theories is currently consuming vast amounts of time and effort of some of the brightest physicists who have ever lived - you can read about some of their efforts in the Strings (etc) section of PF.

    In some ways it's intensely frustrating - it'd be so cool to examine what's happening at energies where all four forces are equally strong, or on timescales as short at the Planck time, etc ... but we can't because there's no way we could create those conditions in any earthly lab and we are unlikely to be able to for at least several centuries. We may be able to observe, indirectly, what happens in these regimes, because some natural phenomena may get close to them, e.g. near the heart of a quasar, or around the time of the core collapse of a supernova, or when two neutron stars collide, ... or by examining the ~300,000 year old imprints of the early history of the universe in the CMBR.

    :cry: this means, AFAICS, that interesting speculations such as that which you posted will not be part of physics unless they can be reformulated in equations, and those equations shown to produce results fully consistent with all the observational and experimental results to date.
  8. Sep 17, 2004 #7
    thanks Integral, I get your point.
    I know questions such as "what does time mean for a photon?" have been posted so many times only to get answers such as "the question is meaningless so forget about it". And I accept that, really!
    Believe me it was not my purpose to speculate about any crazy ideas at all, but rather to:

    - Learn about what physics says about the processes by which the primeval energy turned into either matter particles or massless particles ( is it correct that some symmetry breaking defined that ? if so, do we have any guess why some of the energy acquired mass and became matter and some other did not and became force carrier ? )

    - Understand if it's correct to say that "before" that happened, spacetime did not exist as an extended entity (the 4 dimensions only started to unfold as from the moment any matter came to be formed)

    - Understand how physics treats massless particles, in particular if references to spacetime must also be included in the equations for them

    I'm only interested in learning, not in speculating
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