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DALeffler
2001-Dec-27, 11:46 PM
Why couldn't this acceleration be explained by space itself?

Galaxies are moving away from each other not because of velocity but because space itself is expanding.

If space itself is expanding, why couldn't the acceleration of the universes expansion be attributed to the "new" space expanding?

???

ljbrs
2001-Dec-28, 01:04 AM
Why couldn't this acceleration be explained by space itself?

Galaxies are moving away from each other not because of velocity but because space itself is expanding.

If space itself is expanding, why couldn't the acceleration of the universes expansion be attributed to the "new" space expanding?


DALeffler:

That is exactly what is happening. The galaxies themselves are not expanding (because of the overabundance of the dark matter which is preventing such expansion in galactic groups). On the other hand, the dark energy of space is what is thought to be doing the expanding. It is thought by some that the continuous particle-antiparticle creation and immediate annihilation (that is seen in particle accelerator experiments) may be what is causing this accelerated expansion. However, the Supernova Cosmology Project and the High-Z Supernova Search Team have been studying this for a number of years and the vacuum energy seems to be the cause of this accelerated expansion of the Universe. Whee! Enjoy it. This all came about when the Supernova Cosmology Project and the High-Z Supernova Search Team were attempting to find out the rate of cosmic DECELERATION using Type I-A Supernovas for standard candles. To their surprise, the universe was EXPANDING and ACCELERATING in that expansion! It was selected as the *Discovery of Year* in the 18 December 1998 issue of SCIENCE (written by one of my favorites, James Glanz, who presently writes about science for the New York Times).

O.K. If you are still awake, it is fascinating and ushered in a complete reversal of ideas about the Universe.

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DStahl
2001-Dec-28, 03:31 AM
ljbrs is, as usual, right on the money. I think what you're referring to, though, is the "compound interest" effect: if you have a 'principle' of 1000 parsecs and it is accruing 'interest' at the rate of 0.00006% per year, then if you plot the total distance over a long time you do indeed get a curve describing an accelerating expansion of your spatial 'principle.'

Oddly enough, cosmologists refer to this as a "flat" expansion rate, and to make it appear so they can plot it on logrithmic-scaled paper so that the line is, indeed, flat. Back in the Dark Ages (a few years ago) as ljbrs notes, everyone assumed that the only force changing this expansion would be the decelerating force of gravity. So it was assumed that the the actual expansion rate was just a bit slower than the logrithmic increase. That turned out to be incorrect--the best measurements of the actual expansion rate show an increase over the "flat" logrithmic curve.

But your intuition was right on the mark: the expansion acts just like a bank account with continuously compounding interest--the bigger it gets the faster it grows. Only the cosmologists' tricky ploy of using logrithmic scales can make such an expansion appear flat. There's a nice accessible paper on spacetime expansion by Lineweaver and Davis; I'll see if I can get you a link.

--Don

ljbrs
2001-Dec-29, 01:03 AM
DStahl:

Logarithmic may appear to be *flat* but the actions which they describe are not. Flat is simply a description of the rate of increase which, in the case of the accelerating universe, appears as a flat line, which is deceptive if one is not knowledgeable about logarithms.

Thank you for your input. It is appreciated. It is nice to have so many knowledgeable people posting here on BadAstronomy.

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