View Full Version : Expansion Quantification
2004-Jan-31, 11:06 PM
If I have done the arithmetic correctly, a Hubble constant of 72 kilometers per second per kiloparsec converts to 2.3 * 10e-19 meters/sec/meter (a tenth of a billionth of a billionth) for the current rate of expansion. Since there are 4.4e+17 seconds in 14 billion years, the cumulative expansion since the big bang is 10 centimeters/meter assuming that the current measured rate is accurate and valid. Recent measurements lead some observers to believe that the expansion rate is increasing i.e., not constant. It would not be much of a stretch to assume that the Hubble constant has always been a variable and that, due to the much greater density in the early universe and the time dilation attendant thereto, the Hubble coefficient may well have been much less than unity giving the universe a much greater age. Has anyone seen an analysis of how the enormous gravitational field strength present when the universe was 10e-30 seconds old was overcome to not only prevent a black hole type collapse but also to supply the kinetic energy associated with continuing expansion and what the time dilation characteristics of this period were?
There seems to be no evidence for expansion at small scales. At what scale does this expansion characteristic vanish? Local Group, Milky Way, solar system, earth, me, hydrogen, neutron, quark, neutrino, smaller ? :unsure: :unsure:
2004-Feb-02, 07:54 PM
Well, first, you got the units wrong. It's 72 kilometers per second per Megaparsec. One thousand times smaller than your number. If it weren't, the Milky Way would completely be ripped apart and scattered throughout the universe.
I agree with the conclusion that the Hubble constant hasn't really been constant, but it is pretty close, it's not a very fast acceleration.
The enormous gravitational effects at the very beginning were overcome by Inflation. Inflation happened because, since the universe was so small, quantum effects totally dominated the universe and basicall blew it up fantastically faster than light. (Not a paradox because space is not limited by physics, only the stuff inside it is). Similarly, time dilation is only experienced by objects in the universe, not the universe itself. Also, for the first few moments, the forces were almost indistinguishable, so gravity could have been repulsive.
Today, gravitational effects overwhelm the expansion at about the Local Group level. Expansion never goes away, but the four fundamental forces are a whole lot stronger on sizes less that a few million light-years across.
2004-Feb-03, 02:03 AM
Thanks for the units correction and the attendant "microscopic" rate of expansion correction (to 10^-5 centimeters/second/meter or 10^+30 "planck lengths"/second/meter...and growing as well as cumulative expansion since the big bang of 10 kilometers/meter ). (Things don't seem consistent with observations.)
I agree that the effect has not been observed to apply to volumes at or below the Local Group level but I haven't seen explanations (or guesses) for that intensity of gravitational field that exactly balances (or inhibits?), then overwhelms the expansion force. Also, I agree that space is not prohibited from expanding at greater than light speed within the current understanding of the laws of physics provided it contains no matter. It's not clear that the matter in the prior-to-inflation universe can move into the inflated portion of space at greater than light speed. Is magic being invoked selectively? If the inflation were effective at the infinitesmal scale of space dimensions, why were the quarks not ripped apart by inflation? What energy must the preinflationary universe photons have had in order to be detectable in the postinflationary universe?
We do not observe spacetime but the photons which have traveled through matter at various densities as a function of time, so, even though space does not experience time dilation, it seems that time dilation caused by the extreme densities of the early universe should have gravitationally affected both the expansion rate and the photons from that period.
2004-Feb-04, 02:09 AM
Matter can exist in an inflationary universe because relativity only applies to stuff inside the universe. The matter remains below the speed of light within the universe. Since they remain below light speed, and far below, I might add, there isn't much time dilation.
It's hard, if not impossible to explain the fact that quarks remain without using string theory. Basically, the quarks' strings are unwrapped, and they remain pretty much the same no matter how much the universe is inflating. (A great string theory book is The Elegent Universe by Brian Greene). Anyway, quarks didn't even exist during the inflationary period: it was too hot!
As for photons, the Big Bang was so hot that the atoms that existed afterwards were ionized until about 380,000 years after, so that photons couldn't travel without getting reabsorbed.
2004-Feb-04, 01:33 PM
By my understanding of what is being posited:
The universe, immediately after the inflationary period, would have been quite small, probably no larger than the radius of the Oort cloud and much less than one second old. Much more mass than the mass in the currently observable universe was packed into this relatively small volume resulting in extremely high density and near complete opacity (and outside the influence of the magic invoked by inflation and quantum instabilities). If homogeneity were preserved as evidenced by current interpretations of the cosmological background radiation, some mass and/or photons traveled approximately one lightyear in the time interval from
10^-43 to 10^-35 seconds which is a good bit faster than light speed.
All the mass currently in the actual physical universe (much larger than the currently lightspeed limited observable universe) packed into a volume less than that of a sphere of one lightyear radius should have had a large braking effect on expansion as well as have experienced time dilation due to gravitational intensity (all this mass is within the universe).
Using today's set of "epicycles" the mass of the Milky Way would collapse into a black hole if compressed into a volume the size of a sphere of one lightyear radius, and yet much more mass escaped this fate immediately post-inflation.
I have not read/heard much about the initial angular momentum of the universe; is it assumed to have been near zero?
How can I be made to understand???
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