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You're welcome and some more A's Isaac Send a noteboard - 15/10/2012 01:40:01 AM
Another one I have a hard time wrapping my head around deals with the whole accelerating expansion of the universe (space itself getting larger). I have several questions about this:

1) If all the galaxies are moving away from each other, will the Milky Way and the Andromeda galaxies still collide in the distant future?


This is a gross net effect, caused by universal expansion, our Local Group of Galaxies are 'gravitationally bound', which is to say the force between them from gravity overrides expansion. Expansion is roughly linear, double distance, double expansion rate, whereas gravity is inverse square, double distance, reduce force by a quarter. Hence inside a galaxy the expansion is effectively irrelevant. And unlike Stars or planets, galaxies aren't relative tiny dots on an empty ocean, but more like houses in a semi-rural area. We actually define the local group as those galaxies and satellites which will remain together (and eventually merge into one blob) till all creation sputters out.

2) Is the expansion of space effecting the space between star systems within each galaxy? If not, why? Is the Dark Energy effect only occurring to the space between galaxies? Will it at some point effect the space between stars, planets, asteroids, or even the space between my atoms and molecules?


No, again gravity is weak but not that weak. Hubble's Constant is at light year range amounts to about 20 mm/s per light year, or for context, 1 meter per 50 seconds, or 600 km a year, or 1 light year every 15 billion years or so. All the various stars flit around the galaxy under local accelerations and velocities relative to miles per second, not millimeters, at local galactic scale it's like a mule pulling against a team of horses, but inner-galactic it's like a cat pulling against a train. At the Galactic Supercluster scale, between those, the analogy reverses. Hence the universe is falling apart but it's individual sections remain coherent and would merge, minus some bits ejected by the merger.

3) Couldn't the acceleration of the expansion of the universe be explained in another way?


Probably, many have, I generally warn people of developing personal theories about it.


The intuitive mind is a sacred gift and the rational mind is a faithful servant. We have created a society that honors the servant and has forgotten the gift.
- Albert Einstein

King of Cairhien 20-7-2
Chancellor of the Landsraad, Archduke of Is'Mod
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Science Question - 13/10/2012 09:01:08 PM 614 Views
What channel was this on? - 13/10/2012 10:44:29 PM 419 Views
It was an episode of Nova from PBS - 14/10/2012 06:50:24 PM 546 Views
thanks all (and some more Qs) - 14/10/2012 07:30:04 PM 424 Views
You're welcome and some more A's - 15/10/2012 01:40:01 AM 448 Views
Then I have another question - 16/10/2012 05:52:33 PM 417 Views
You can rest easy. - 16/10/2012 08:46:37 PM 454 Views
the part that bothers me actually is - 16/10/2012 11:16:04 PM 381 Views
He's talking about the Andromeda Paradox - 17/10/2012 07:11:01 AM 394 Views
well, I feel a bit better LOL - 17/10/2012 10:58:18 PM 383 Views
Re: well, I feel a bit better LOL - 18/10/2012 04:06:26 AM 390 Views
I saw Brain Greene speak last year. It was pretty cool. - 16/10/2012 04:15:00 AM 587 Views
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