Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: RayG on 03/09/2015 18:24:46
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Recently, I saw a documentary about the beginning of the Universe. In it, it was mentioned that for the first several hundred thousand years (or something), before any new elements were created through atomic processes, there was no light. If this is the case, then there would be NO limit on speed to corral the expansion of the Universe, correct? No light, no speed limit OF the speed of light to hold it back. Once light is established, then it gets the limits.
Or- unless you smartie pants use the term "speed of light" to refer to the speed of ANY energy, then it's a moot question.
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Recently, I saw a documentary about the beginning of the Universe. In it, it was mentioned that for the first several hundred thousand years (or something), before any new elements were created through atomic processes, there was no light. If this is the case, then there would be NO limit on speed to corral the expansion of the Universe, correct? No light, no speed limit OF the speed of light to hold it back. Once light is established, then it gets the limits.
Or- unless you smartie pants use the term "speed of light" to refer to the speed of ANY energy, then it's a moot question.
That is incorrect. There has always been light, even from the first moments in the Big Bang. But even if there was no light it wouldn't mean that particles couldn't travel faster than c = 2.998x109m/s.
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I think the Universe is expanding faster than light at the moment isn't it? In other words, were you able to travel to the edge of the Universe, you couldn't see or catch up with the expanding margin, even if you could travel at the speed of light.
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for the first several hundred thousand years ... there was no light.
I think that this Documentary may have been referring to the era where the universe consisted of an ionized plasma, which is effectively opaque to light.
In this era, light certainly existed due to the interaction of electrons and protons (https://en.wikipedia.org/wiki/Bremsstrahlung) in the plasma, initially in the form of gamma rays, then primarily X-Rays, and progressing to ultraviolet light, as the universe cooled. But it could not propagate very far before it was absorbed and then re-emitted at a different wavelength, in a different direction.
Today's Cosmic Microwave Background Radiation (CMBR (https://en.wikipedia.org/wiki/Cosmic_microwave_background#Relationship_to_the_Big_Bang)) originated when the universe cooled enough to form neutral atoms, which are transparent to light. This is estimated to have occurred about 400,000 years after the Big Bang, when the temperature dropped below 3000K.
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I think the Universe is expanding faster than light at the moment isn't it? In other words, were you able to travel to the edge of the Universe, you couldn't see or catch up with the expanding margin, even if you could travel at the speed of light.
There are galaxies which are moving away from ours at speeds faster than light (FTL). All those further away are moving FTL too. This has to do with the nature of the geometry of the universe and the expansion. But nothing in the universe travels FTL locally. The only reason galaxies far enough away move FTL is because space is expanding FTL.