Are There Infinitely Many Stars?

If the Universe is expanding how do we know that it does not have infinite stars?The only explanation I know of, is that if there were infinite stars, the sky would be full of light of those stars. �But now that we now that there is indeed an horizon, is there any other method?
- Tomas Gavi?o (age 32)
Mexico

 Your great question about how the sky seems like it should be lit up if there were an infinite number of stars is called "Olber's paradox" (). It goes back to at least Kepler in 1610. 

We actually don't know if the universe is finite or infinite. We do know that distance stars are receding from us, That makes the light from them Doppler shifted, and for fast enough speeds it's Doppler shifted out of the visible range. So even if the universe is infinite, we only see visible light from a finite part. 

Here's an old discussion of the same question: /

Mike W>

(published on 07/12/2015)