Astrophysics question

John21 · #1 11-26-2006, 02:49 AM

I'm thinking of a fish inside a bowl, and the fish keeps getting smaller and smaller.

How do we know that our galaxy is not contracting, giving the appearance that the rest of the universe is expanding?

goodsamaritan · #2 11-26-2006, 02:59 AM

Because we'd be able to tell if everything in our galaxy was getting closer together

John21 · #3 11-26-2006, 03:24 AM

[ QUOTE ]
Because we'd be able to tell if everything in our galaxy was getting closer together

[/ QUOTE ]

Relative to what?

Suppose you and all of your component parts shrunk to 1/10 of your current size, how could you determine if the rest of the world expanded or you shrunk?

Lestat · #4 11-26-2006, 04:19 AM

My guess:

We don't just measure distances, but radio active energy, x-rays, gamma-rays, etc. Unless our intruments here on earth (and their sensitivity to data), were shrinking as well, we would be able to detect disparities in the signal images being emitted by stars and other objects within our galaxy as they shrunk.

Now if you want to say that EVERYTHING is shrinking, including everything on earth, etc., then I guess there would be no way to tell. But that would be an illogical conclusion to come to.

wazz · #5 11-26-2006, 05:45 AM

[ QUOTE ]

Suppose you and all of your component parts shrunk to 1/10 of your current size, how could you determine if the rest of the world expanded or you shrunk?

[/ QUOTE ]

It doesn't matter which.... that's like blowing up a triangle to 10x its size then asking what is the new sum of the angles within.

Re your original question.... I'm not quite sure what you meant here. If the universe is expanding and our galaxy is somehow contracting, then it won't be long before we end up in some black hole. I don't see how one specific part of the universe would suddenly deem to contract, though. If the universe were expanding or contracting and our galaxy was doing the same at the same rate, it wouldn't make any difference to anything whatsoever.

wazz · #6 11-26-2006, 05:47 AM

K sorry I misunderstood.

It still doesn't make any difference though. Scales are scales. If Ax = 2Bx, then A5 = 2B5. Someone explain this better than me please.

JayTee · #7 11-26-2006, 06:07 AM

Correct me if I'm wrong John. I think he means that everything is shrinking except for space itself (the fish bowl). Giving the appearance that space is expanding, but in reality it is not.

Borodog · #8 11-26-2006, 01:39 PM

John,

Which do you think is more likely?

JimNashe · #9 11-26-2006, 01:45 PM

If everything was shrinking wouldn't the distances between normal objects expand too? Like the distance between me right now and my tv set is about 2 meters. If both me, the tv set and every meter-measuring rod in the world was shrinking, it would seem to me like the tv was moving away from me.

Borodog · #10 11-26-2006, 02:00 PM

Good point.