ishalon

How do we know the universe isn't far bigger than we think, with stars so far that their light has just not reached us?

Amen-Moses

We don't.

The only thing we can be sure of is that the stars that we can detect are all moving away from us (and each other) at a rate that infers that at some point in the past all the energy/mass was at some single point in space at time = 0. (as measured in this 4 dimensional frame of reference)

If other stars/galaxies existed billions of years before this point in our frame of reference and are also many billions of light years away then we would be completely unaware of them.

Of course an infinte universe is falsified because if the univers were infinite then whichever way you looked you would see the energy from something, i.e the night sky would not be predominently black.

Amen-Moses

Starspun

How does that work? Im curious.

Amen-Moses

Because whichever way you chose to look you would intercept photons from some star or other.

Amen-Moses

Laurentius

AVE


Amen-Moses

Because whichever way you chose to look you would intercept photons from some star or other.

Suppose there is a mansion with an endless number of rooms, each having its own telephone number, and you can become aware of the existence of each room only if you receive a phone call from it. There may be a limited, great but limited, number of peope who can do the job of disclosing you new rooms by moving from one room to another.

Similarly, the universe is infinite, but the number of stars is finite because their lifetime is finite. If the range of our sight were deep enough we could see their dust travel and give birth to a new star to another room only for us to receive the phone call we need.

AVE

David Gould

I do not think this solves the problem.

If there were an infinite depth to the universe then no matter how short the lifespan of stars there would be a continuous light stream to us.

Imagine a star 1 billion light years away from us that came into existence 1 billion years ago, lasted 1 billion years, and then exploded.

There would be a 'chunk' of light 1 billion light years long streaming over us from this star for the next billion years.

Now, imagine an infinite number of stars in the same direction as this star, at ever increasing distances and varying in duration of being.

As time passes, these stars die and new ones are formed. As there are an infinite number of stars, for any duration there must always be a 'chunk' of light from them in our vicinity (infinite number of 'chunks').

And this would be true for any direction you look.

The life cycle of a star does not make any difference, unless I have missed something here.

Of course, this implies a universe of infinite duration as well as of extent.

The unvierse could have come into being 15 billion years ago and be infinite in size, I guess.

Christopher Lord

But that makes little sense (infinate space but not time, or vice versa) because time and space are different demensions of the same thing.

The most likely 'infinate' space configuration is actually a hyperring or hypersphere. String theory hints that this may be the case.

Andromeda123

There's no energy in dark space..... what happened to dark matter, dark energy, cosmic microwave radiation??

beausoleil

For a full explanation of Olbers's Paradox, see...

<a href="http://zebu.uoregon.edu/~imamura/123/lecture-5/olbers.html" target="_blank">http://zebu.uoregon.edu/~imamura/123/lecture-5/olbers.html</a>

Liquidrage

Time out.

I am in direct oppostistion to the view expressed in this thread that the universe isn't infinite.
At least in the "why" expressed here.

It is commonly considered that the universe is so big that the light from some stars have not reached us yet.

And since the universe appears to be expanding. And since it appears that this expansion is accelerating, it is often put forth that there are regions of the universe from which light will never reach us.

It is very possible, or rather probably, that the universe is actually finite.
However, the "why" that was expressed in this thread (we would see light in all directions at all times) does not qualify as showing the size of the universe.

The areas from which light can never reach are called "hidden regions" and would exist whether the universe was infinite or not.

So the sky could be dark at night with or without an infinite universe.

To go back to the original question by ishalon.
I would have to reply, "who thinks that?"
Allmost everything I read seems to agree that the universe is so big that indeed light from all the parts haven't reached us yet.
To bring in what I talk about above here, many think it is so big, and accelerating in such as way, that some light will never reach us.