Cosmology Question: Expansion Theory

[Áréwn'tháwr]

If the only way we know that the universe is expanding is based on red shift in distant galaxies, this information has been travelling to us for billions of years at the speed of light, therefore this information must be out of date as we are seening the universe in the past. How do we know then, that the universe has not already slowed, stopped, or is now contracting?

 

[Green]

If it were, then there might be some stars that we would be picking up red and blue shifts for. Course, that depends on whether the universe started retracting yesterday or 5 billion years ago

I'm no astrophysicist, but I think there is discussion about the arrow of time having to reverse (reversing entropy) for the universe to go into the Big Crunch. Which doesn't seem to have happened yet

Scientists don't yet know whether it'll be the crunch or the freeze, and personally I don't think we've reached the half-way mark yet anyway.

So, if you're really curious, try some undergraduate physics text books, cos all I can (barely) remember are pop-science books

PS - why is this in the aspiring writers section?

 

[Glyptus]

If the only way we know that the universe is expanding is based on red shift in distant galaxies, this information has been travelling to us for billions of years at the speed of light, therefore this information must be out of date as we are seening the universe in the past. How do we know then, that the universe has not already slowed, stopped, or is now contracting?

Excellent point! How can we know the current, present day conditions of distant regions of space, when we can only see them as they must have existed in the distant past? I'd like to suggest this: If the collapse of the universe had already begun, we’d still be able to see it happening locally. Since there are no "edges", no special place in the universe, once the collapse had begun, it would be happening everywhere, equally in all directions. One day we’d notice that the Andromeda galaxy was a little closer to the Milky Way than we previously thought (relative to the position of distant, “fixed” galaxies). Here’s another, perhaps more obvious clue: Since the light from galaxies moving away from us is red shifted, we’d expect to see blue shifts in the light from a galaxy moving towards us. In fact, our first clue would probably be the detection of any change in the light spectrum of a particular, nearby galaxy.

 

[Aes]

If the only way we know that the universe is expanding is based on red shift in distant galaxies, this information has been travelling to us for billions of years at the speed of light, therefore this information must be out of date as we are seening the universe in the past. How do we know then, that the universe has not already slowed, stopped, or is now contracting?

Ugh...

Apparently, I can't post links to other websites until I have 15 posts and going back butchered everything in my post. Since I really don't feel like rewriting what I said over again, I'll just say this:

It's theorized that the universe is actually expanding at an increasing rate. If you want more info, google "Dark Energy" or look it up at Wikipedia.

 

[wildbill333]

I think that Aes makes a very good point in that we cant exactly know it the universe is expanding, stopped, or contracting because of the fact that what we are seing in space is happening possibly millions of years ago so it is a toss up. know one can possibly know unless it is contracting at a rate higher than that of the expansion, has been contracting for a minimum of 25% longer than it expanded , or has not been moving. and with that i feel must say that all thow i know only what i have been told or concluded on my own about the theorys of expansiasion