Infinite Universe

Posted By: Irish_Farmer

Infinite Universe - 09/19/06 18:58

I don't know too much about this, I just wanted to bring up a point.

Right now, we can view objects that are about 15 billion light years away, and that's why we assume the universe is (roughly) that old?

Well, JCL, you said something about them wanting to discover if the universe was truly infinite in size. But let's say it is infinitely large. Wouldn't the sky always be just completely white? Because there would be infinite celestial bodies to light up the sky.

The only ways I can imagine avoiding this problem are:

1). After a certain point (based on what we can see about 15 billion lightyears), light can't reach earth anymore. Which doesn't seem likely, at least that it would stop so abruptly.

2). Space is infinite, but all of matter is expanding from a 'central point' in the infinite universe. I guess the only question at that point would be, what would cause matter to begin where it did as opposed to anywhere else in a universe of generally infinite size?

Also, if space exists but matter doesn't, is that even physically possible? Wouldn't that mean time also wouldn't exist until the moment that matter originated?

On the other hand I'm not an astronomer, or a physicist, and I haven't studied this too in depth so I could be way off. Just some thoughts, I figured we could discuss.
Posted By: Matt_Aufderheide

Re: Infinite Universe - 09/20/06 04:30

Quote:

Wouldn't the sky always be just completely white? Because there would be infinite celestial bodies to light up the sky.



This is a typical argument agasint an infinte universe. However it is flawed.

For one thing it assumes that all the light from everywhere would have reached us by now; an unlikely proposition when dealing with vast distances.

Another flaw is that it doesnt take into account dark matter; dark matter or even non-light-emitting matter would block the light somewhat, making the "white sky" phenomenon impossible. Even dust can eventually absorb or shadow the light.

Another problem with this argument is that there may be super-large gravity fields, like massive black holes, causing the light to bend away from us.
Posted By: Irish_Farmer

Re: Infinite Universe - 09/20/06 05:33

Yeah, those are good points. I would just think the sky would definately look much...whiter anyway.
Posted By: Matt_Aufderheide

Re: Infinite Universe - 09/20/06 06:13

Yes but think how dim some stars look, and these are very close by; in our own galaxy. Other galaxies themselves are not visible with the naked eye usually.

The term "infinite" is often used when we really mean "indefinite". The universe is certainly indefinite.

Think about this: the Earth is seveal billions of years old, most galaxies are likely more than this many light years away.. so light from the majority of universe has simply not reached yet anyway.

Just assuming that the sky should be brighter if the univere was infinite is a flawed approach for many reasons. In any case, the sky isnt so dim.,. have you looked at the night sky on clear night in country, or the mountains? There are a heck of lot of stars out there...not mentions all the other forms of non-visible radiation. The sky is not very dark at all.
Posted By: jcl

Re: Infinite Universe - 09/20/06 09:11

The argument is not new; it's from the 19th century and called Olber's Paradox.



The solution is not the dark matter, because if it absorbed all the light, it wold heat over time to 6000 F and begin to radiate itself. So the sky would still be bright white, and life on earth were impossible.

The solution is the finite age and the expansion of the universe. The farthest objects we can see are now 46 billion (not 15 billion) light years away. Light from objects outside that area can never reach us because their distance to us is growing faster than the speed of light. Only for that reason it's dark in the night.
Posted By: Irish_Farmer

Re: Infinite Universe - 09/20/06 22:19

Ah! Well that answers it for me then.

One other question, this one might be so obscure that no one has thought to really come up with a generally available answer. However, based on the movement of all the matter in the universe, have they kind of figured out roughly where we are in relation to the 'center'?
Posted By: Inestical

Re: Infinite Universe - 09/21/06 05:24

Hell no. It would've been big news in all science papers and elsewhere. I think people aren't even intrested about that. Our own survival is the priority.

Though, it can be said, if the center would be our sun e.g. we would be somwehere behing Planet X or Pluto. SInce we aren't moving notably circles...
Posted By: William

Re: Infinite Universe - 09/21/06 08:53

Howcome theres no galaxies ect. that by moving farther away from something, are not coming closer to us by a result? Or, is everything strictly moving away from our solar system, and were in the centre(and the point of creation)?
Posted By: Damocles

Re: Infinite Universe - 09/21/06 09:21

An infinite Universe would contain an infinite amount of information.
I personally dont thik that this holds true, that one! process (whatever that is)
created an infinite amount of information in a limited time.


Anyway: Objects cant move faster than light away from us.
even if they "did" they would not exist from our relative point of view.
Posted By: jcl

Re: Infinite Universe - 09/21/06 10:52

I think both questions can be answered.

Where is the "center"? Imagine the hull of a rubber balloon. Every point on that hull moves away from every other point when the balloon inflates. Yet there is no "center point" on the hull - all points are equal. It's the same way in the universe, just in three dimensions. Its a consequence of general relativity theory that the universe doesn't have a center or a border.

As to the information amount: The information amount in the universe is finite, even if the universe is infinite. This is a surprising result from quantum theory. From any point of view the universe is split into Hubble volumes that can not exchange information due to the finite speed of light. Every such Hubble volume has a very high but finite number of quantum states, like 10 ^ 10 ^ 100. The quantum states represent the whole information in the volume. Logically, if you have more than 10 ^ 10 ^ 100 Hubble volumes in the universe, some of them must have exactly the same quantum states - they are exact copies of each other and thus do not add to the information amount of the universe.

As a consequence of this, it's almost certain that the earth, this forum, and yourself exist in infinite many copies in the universe.

If interested, read -> http://www.hep.upenn.edu/~max/multiverse.pdf
Posted By: William

Re: Infinite Universe - 09/21/06 11:35

Quote:


Where is the "center"? Imagine the hull of a rubber balloon. Every point on that hull moves away from every other point when the balloon inflates. Yet there is no "center point" on the hull - all points are equal. It's the same way in the universe, just in three dimensions. Its a consequence of general relativity theory that the universe doesn't have a center or a border.



Thanks for the clear explanation, makes sense. Will have to check out that link you provided.
Posted By: mpdeveloper_B

Re: Infinite Universe - 09/21/06 13:14

nice explanation jcl, i may check the link later, but that is a nice way of explaining the universe.
Posted By: Matt_Aufderheide

Re: Infinite Universe - 09/22/06 08:27

I dislike the notiuons that can be no stable points. What are coordinates unless they are conceptual? The center of the universe can be determined or assumed.
Posted By: Damocles

Re: Infinite Universe - 09/22/06 11:38

I am the certer of the Universe


Even If there is no specific center, there migt be a static "rotation" of the universe.

Ich schreibs mal deutsch weil mir die Fachbegriffe fehlen:

Eine Zentrifuge hat nur bei einer bestimmten Rotation keine Trägheit an den Aussenkanten, und das
ist die Rotation die wir als "Ruhe" bezeichnen.
Es muss also eine Art "Gundrotation" im Universum geben, weicht man von ihr durch beschleunigung ab
(dreht das Karusell) wirkt Trägheit.
Posted By: Alberto

Re: Infinite Universe - 09/22/06 18:50

Irish Farmer

I dont know wether you had already read this topic somewhere
If not , you must be a very smart guy -:)
Actualy the question about the color of the sky is an extremely subtle topic
It was arisen for the first time by T. Young , if I am not wrong.
The solution was found some hundreds years later

To complete JCL's explanation I would like to make the following general consideration
Nowadays you can find a lot of scientific books written for an audience of non specialist
This is good of course
However these kind of books are also somehow deceiving

They try to explain concepts by means of " analogies " without using math, for obvious reasons
For example the "Inflating balloon" which I myself used in an other thread to explain the Einstein's universe

The key point is that when talking about universe or atom , you can not alwayes reason by analogies

Do not try to figure out in your mind the Einstein's universe
Nobody can, even Einstein himself could not

Modern phisics is pure math, up to a certain extent
Posted By: Irish_Farmer

Re: Infinite Universe - 09/23/06 02:02

What I meant was a center from the origin of the big bang, if you will.
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