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Comments to this entry
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17.06.2009 12:28
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Comment by Guillaume Belanger
Is there such as thing as a photon or a phonon? Is light, a propagating electromagnetic field, really a wave, and is this wave really quantized into photons? Can a sound wave, a vibration propagating through molecules, be quantized into a phonon? If there is no air, how can there be sound?
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17.06.2009 12:35
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Comment by Guillaume Belanger
If there are no molecules at all, how can there is propagation of sound?
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17.06.2009 14:28
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Comment by Guillaume Belanger
Many cosmologists and astrophysicists alike hold to the Big Bang is a theory as The description of the beginning of it all. It is a useful description with some measurable and/or observable predictions and consequences that seem to correspond, at least partially, to what we see when we turn our eyes and instruments towards the sky. But is it reasonable to believe that everything, starting from space-time arose in a single moment from nothing at all, from a single point, a singularity with quasi-infinite energy density? Even the question where did this single point of energy arise is non-sensical since the notion of space-time cannot yet be invoked to formulate or answer this question. From this shear energy eventually burst out elementary particles: quarks and gluons that gave rise to mesons and hadrons; leptons like electrons and positrons probably in equal numbers; and other bosons, field carriers like photons, Ws and Zs, just as we believe we have detected in particle accelerators when energetic electrons annihilate upon colliding wih positrons. But the density is so high, the mean-free path of particles is so small, that no radiation can come out, no light can escape. As this ball of elementary particle expands and cools, the density drops and eventually photons emerge, and we see these first photons as the cosmic microwave background, well studied and measured. We are still very far from the formation of hydrogen, from which will form the first molecular clouds, from which will form the first stars that will forge helium and the heavier elements, from which will eventually form molecules .
Sound, a pressure gradient, can propagate in gases, liquids or solids. So, in fact, as long as there is something, whether it is air or a dense ball of elementary particles, sound can propagate and is not subject to continual absorption and re-emission as are photons. However, the speed of the propagation depends on the properties of the medium: the ratio of the stiffness to the density, and how can know the stiffness or density of a state of matter that only exists in our imagination, and to complicate matters further, is expanding at prodigious rate whose magnitude we cannot realistically estimate? Well, that's it for me. |