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Author Topic: How do we know that the universe is expanding?  (Read 5422 times)

Offline thebrain13

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How do we know that the universe is expanding?
« on: 13/12/2006 04:30:58 »
I know Ive asked the question before. But I can not find the answer myself, I guess I'm not a very good researcher. The question is, what is the evidence for an accelerating universe, besides the redshift?

Can someone just point me in the right direction.
« Last Edit: 17/12/2006 10:12:06 by chris »


 

Offline Soul Surfer

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Re: How do we know that the universe is expanding?
« Reply #1 on: 14/12/2006 00:04:28 »
The redshift shows an expanding universe. 

The evidence for the acceleration of the expansion  (as opposed to an even expansion or a slowly decelerating expansion like a ball thrown upwards decelerates unfe rthe influence of gravity)  comes from observations of type 1a surpernovae in distant galaxies.

A type 1a supernova is the result of a white dwarf star having extra mass dumped onto it from a companion star that has turned into a red giant.  This causes the mass of the white dwarf to exceed a critical limit and explode violently in what is essentially a large nuclear explosion.  This process should produce very precisely similar explosions and so the maximum brightness should be similar and allow the distance of the galaxies to be estimated quite accurately
 

Offline thebrain13

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Re: How do we know that the universe is expanding?
« Reply #2 on: 14/12/2006 04:21:09 »
I meant expanding universe, although I said accelerating. So essentially, your answer is very simple. They measure the galaxies as moving faster and faster away, hence acceleration.

Now I have a different question. You cant measure an accelerating universe before you can measure an expanding one. So your saying scientists have the ability to measure the galaxies relative distance over time all along, yet they needed to find the redshift to find out that the whole universe is expanding?

Why when I watch carl sagen, does he say, edwin hubbles discovery of the redshift dramatically changed our view of the universe? Why do people today still propose alternative redshift theories, with the intent of proving the universe is static? If astronomers are capable of measuring the effect directly, why isn't this argument closed? Why doesn't carl sagen say, scientists measure the galaxies as getting wider and wider, case closed?
« Last Edit: 14/12/2006 06:25:42 by thebrain13 »
 

Offline Soul Surfer

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Re: How do we know that the universe is expanding?
« Reply #3 on: 14/12/2006 19:57:03 »
Some people will always insist on not accepting the simplest and most obvious reasons for things it is in the nature of human cusseness  :-)
 

Dr. Praetoria

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Re: How do we know that the universe is expanding?
« Reply #4 on: 14/12/2006 20:56:14 »
One of the better "proofs"  that the universe is accelerating, is that the absolute luminosity of some supernovae are dimmer than they should be, therefore indicating this expansion is accelerating.  There has been some conjectural ideas that "dark energy" or a fifth force is acting--a type of accelerating factor causing a kind of expansion pressure that increases with distance (anti-gravity effect).  This concept was first proposed by Einstein in order to keep the universe in a steady state form, which was later proven not to match astronomical observational data.  Now, it appears that Einstein was correct, all along.  Does it mean that the universe is "open" and the end will be freeze and not burn? [:I]
DocN
 

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Re: How do we know that the universe is expanding?
« Reply #4 on: 14/12/2006 20:56:14 »

 

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