suliman on 15/2/2009 at 01:11
My uncle presented me with this question a few weeks ago, and I can't think of any explanation to it. He doesn't know the answer and is genuinely curious, so you're not helping me cheat here or something:)
Okay. We all know about that graph Hubble made 80 years ago. The universe is expanding, and the further we are from a certain galaxy, the faster it moves away from us. Redshift and all that. Now, say there's a galaxy two billion light years from us. It will move away from us faster than a galaxy that is one billion light years away from us. What we see of the first galaxy is how it was two billion years ago, and what we see of the second one is how it was one billion years later. The more recent we see of a galaxy, the slower it moves. How does that fit in with all the 'the universe's expansion is accelerating' stuff?
The 'silly' in the title is in case this whole thing turns out to be a frame of reference blunder or something. 8 months without school waiting for university turned my brain into mush:p
RocketMan on 15/2/2009 at 01:20
I'm not sure I understand that last question... The acceleration of distant bodies from each other due to expansion isn't directly linked to what part of it's history we're able to view although there is an indirect connection. The expansion thing has to do with the residual energy from the inflationary period of the big bang causing space itself to stretch and therefore the distance between bodies itself is expanding. As the space expands, locations in that space, while maintaining the same coordinates, SEEM to accelerate away from each other as the metrics used to measure space (like square cells on a piece of graph paper) get ever larger. Because the faster receeding objects tend to be further away, they also happen to have more distance to cover for their light to reach us, which is why we see them further in their local past.
Sulphur on 15/2/2009 at 06:39
Yeah, it has to do with frame of reference. Remember, we're not stationary observers either - our galaxy is moving at the same time, too. So we have a velocity relative to both of your galaxies that has to be taken into account as well.
dvrabel on 15/2/2009 at 16:01
All the galaxies (including ours) are moving away from a central point, as they move further away the distances between each one also grows (imagine the galaxies as points on the outside of a balloon being inflated).
The expansion of the universe isn't accelerating -- it's decelerating due to gravitational forces. There is debate on whether it will continue to expand or whether it will eventually start to contract.
Koki on 15/2/2009 at 16:13
I still say the whole acceleration thing is bullshit.
Fringe on 15/2/2009 at 16:59
If there's one person I'd trust more than years of accumulated evidence and solid theories that have made numerous accurate predictions, it's Koki.
suliman on 15/2/2009 at 17:45
Yeah, my high school level physics tell me that it makes sense for the universe to deccelerate and eventually shrink, since gravity is the only force at work here. However, this does not take into account dark energy and probably a whole lot of other things I don't know anything about. My uncle insists that the universe's expansion is accelerating, and (
http://en.wikipedia.org/wiki/Accelerating_universe) wikipedia agrees(AND WIKIPEDIA IS NEVER WRONG), which is the whole point of the question. He claims that because the universe is accelerating and because the most updated image we have of it are the galaxies nearest to us, they should logically be the ones that move the fastest.
Say there are three galaxies moving in the same direction.
1--2--3 ->
Now, say you're on galaxy #1. Hubble's law tells us that #3 should move away from you faster than #2. You see #3 further back in time than you see #2. The more recent the image of a galaxy you get, the slower it moves.
Koki on 15/2/2009 at 19:48
Quote Posted by suliman
Yeah, my high school level physics tell me that it makes sense for the universe to deccelerate and eventually shrink, since gravity is the only force at work here. However, this does not take into account dark energy
And dark matter - both of which are the things which irk me about the whole thing the most.
Professor A: Oh my god, the entire universe is expanding and accelerating at that! How could that be?
Professor B: Well... if there was a shitload of matter we can't interact with in any way, it would make sense!
Professor A: More like two shitloads!
Professor B: Hyuk hyuk
I know it provides the answer - but so does saying "God did it". This is not science.
