Does anyone can help me with this? It's about Olders paradox which states that if the universe is infinite then the number of stars should also be infinite and we would see our day sky completely filled with stars. In each line of sight we would find a star. Well, we know (according to the most recent theories) that the universe is not infinite and consequentely the number of stars is not infinite. But, supposing that the universe will expand forever will the sky be completely filled with stars?? I mean, is it just a matter of time so we can have a super-bright sky?

Not really a paradox, just incomplete information. The stars/galaxies we see in our night sky are the stars and galaxies whose light has reached us. There may still be infinite stars/galaxies but their light has not reached us yet. Does this mean that light will keep on building up until it all reaches us? - no, because stars die and galaxies die and space is stretching so there will always be galaxies/stars whose light will not reach us, IMO.

you're assuming that the universe is infinite, then?

No, not necessarilly. You can come to the same conclusion using a finite universe that is closed ie. a spherical universe whose light will 'wrap' and reach us regardless but you can use the same explanation I gave to see why all the light will not reach us at the same time. A spherical universe will still have space 'stretching' and only so much light reaching us per time.

The atmosphere and the sun play a role in stars not being visible during the day. If you leave the shutter open on your camera and set it to track with one portion of the sky for an extended period of time eventually your photo plate would be full of stars. You have to remember on the universal level you are talking about enormous distances numbers so large you could not write them without orders of magnitude. That aside if you accept that the Universe had a beginning then it is definately not infinite. Only 50 years ago most astronomers subscribed to the steady state theory where new stars and galaxies were constanly created as the old ones aged and burned out. Physics and cosmology have matured so much in the last ten years that classical newtonian concepts are only viable on a local level. At the quantum level everything we thought we knew about the universe we live in breaks down. Things that are possible on the quantum leve would be considered absurd locally. Imagine that if there was a probability for walking through a wall then if you tried enough times you would eventually find the correct circumstances to actually do it. If you remove the variable of time then it becomes a certainty that you could walk thgrough a solid brick wall. I am looking forward to the next twenty five years as Ed Whitten, David Deutsch, Stephen Hawking, Max Tegmark and a host of others dive deeper into the quantum world. Especially watch out for David Deutsch his research into quantum computing could change everything we accept about the universe and our place in it.

Since we've swayed slightly off topic...

Not necessarilly so either - we may just never know. I've recently had a discussion with a physicist and it seems that some think that space extended to infinity instantaneously at the 'creation' of the universe. If you believe that space is part & parcel of the universe then it may very well be infinite.

And relativity is now used to correct GPS timing.

Careful though, QM is a formalism and an interpretation of reality that is purely housed on concepts and mathematics. Just because we don't understand what is really going on and some mathematical concepts seem to fit that which is 'observed/measured' doesn't mean we are describing reality. I've just gone through a QM 'third-wind' and I've come accross some very good points made about QM. There are 2 papers I just read today - not for the faint hearted...
Transactional Interpretation of Quantum Mechanics
Bohmian Mechanics
...although I do not completely agree with these interpretations, there are some EXCELLENT points raised (and some supposed contradictions) about Quantum Mechanics. It is not as it may seem with QM.

Cheers

ok, i must agree with your explanations! thanks a lot