Night Sky

[Karnuvap]

If the universe contains an effectively infinite number of stars then everywhere you look in the night sky you should see a star. If this is the case then why is the night sky not brilliant white - ablaze with this infinity of stars?

[Tormod]

I am sensing a trick question. :) Should we debate this or provide answers?

[modest]

I also suspect Karnuvap knows the answer, but this is the Q & A forum, so...

 

This is known as Olbers' paradox. Proposed by... German astronomer Heinrich Wilhelm Olbers.

 

If the universe is infinitely old and infinitely large then a person might expect every line of sight (everywhere they look in the sky) to end at a star. This would make the sky (day or night) about as bright as the sun in every direction.

 

Of course, big bang theory has a finite age placed on our universe and has it expanding (which puts a finite size on the visible universe) thus the paradox is resolved :)

 

~modest

[Karnuvap]

OK - I confess I did know the answer.

 

Don't forget that the stars themselves don't last forever either.

 

Thanks for indulging me - I promise that the next question (that I am about to ask) I do not know the answer to.

 

The Vap.

[litespeed]

Flat or Curved - The Long Answer

 

Recent experiments seem to show the universe is flat and hence infinite, even if it DID begin in a big bang. The experiment apparently sent lazer beams out in such a way as to create a triangle with some third 'constructed' side out in space. The goal was to measure the total angles and see if they added to 180 degrees, indicating flat, or some other sum that would indicate the universe is curved, hence finite.

 

An analogy would be triangles drawn on an uninflated baloon with 180 degrees total angle, then the baloon blown up and a different total is observed, changing as the baloon gets larger and larger, always approaching 180 degrees, but never reaching that number. The recent experiment is not considered definitive, however, because the universe might be curved so little that we do not have instruments sensitive enough to measure it.

 

Anyway, I am skeptical infinities exit in our universe, including the universe itself, as well as singularities in black holes. The apparent absence of infinite cosmic rays and/or microwave background radiation seem to support this. Another possibility I have not seen discussed is this: infinite universe with finite mass.

 

Finally, even if the universe is infinite with infinite mass [postulating some mechanism to keep infinite cosmic rays from killing us], our visible part of the universe DOES seem to have a finite mass. Accordingly, if our part of the universe continues to expand at an increasing rate the entire issue is moot.

 

This is because all the fussible matter will eventually get used up in dieing stars, and the entire, currently visible place will go dark. The remaining heavy elements in planets, neutron stars etc will simply continue to speed away from each other in the dark.

[litespeed]

Inindental PS:

 

If the universe had a beginning it will never become infinitely old. It will always have an age. I mention this because it helps me to put the term 'infinite' into a more understandible context.

[theblackalchemist]

Can we also add that the sky *could* have been white? and when the universe was created, it started

m o v i n g a w a y ?

Does this also mean that before the big crunch, the universe's sky will be again white??

TBA

[litespeed]

Dear Alchemist

 

According to the big bang theory the universe was, for a few hundred thousand years, too dense for light to exist. Then electomagnetic radiation suddenly sprung into existence. At that time there would have been lots of light, as you mention. Background microwave radiation is the residue of this event.

 

Further, all of astonomy recently suffered one of those once in a lifetime "ooops" moments. Specifically, experimental evidence is overwhellming the universe is expanding at an INCREASING rate. Accordingly, the generations old arguement of whether universe expansion is slowing down enough to reverse course to create a 'crunch' is now moot.

 

At least until some other 'big ooops' moment trips everyone up once again. Well. Fool me once, shame on you. Fool me twice, shame on me. It is important to realize ALL THESE THINGS are and have been theories based upon data accumulated up until that time. And we have several billion more years till OUR star gets cranky.

 

 

Can we also add that the sky *could* have been white? and when the universe was created, it started

m o v i n g a w a y ?

Does this also mean that before the big crunch, the universe's sky will be again white??

TBA

[ossium70]

i actually recently read a book with this quote in it. now before i answer with an idea as to why this quote may be wrong. i would like to touch on the idea of a universe that is not infinite.

 

Does it wrap in on itself? if so wouldn't the light from a single star itself eventually eluminte the universe...

for example no matter which direction you look you would see the star coming from every position since every direction eventually returns to the same location.

you have to take into account that the universe is big and we are not the center of it so the light takes off and we see it now, but as it travels in other directions it takes much longer for it to reach us but it eventually will. Do this millions upon millions upon millions of times more and the combining light of every star should eventually light up the sky's. NO?

 

This idea can go much more indepth but i am simple stating the basics..

[enorbet2]

Hello

I hope this isn't OT since it's probably at least a tangent but I don;t know where else to post it and google hasn't helped. I never took Riemannian Geometry or Spherical Trig but it seems to me I recall in basic Calculus that it is possible to solve equations by slicing a figure up into smaller and smaller segments until one side approaches a point. Since a point cannot have curvature one is left with a simpler figure. If three points describe an angle it becomes a simple angle, no longer compound. So my question is, in trying to understand the larger question in this thread, is the sum of angles in a triangle actually changed when it is on a curved surface? Or put another way, even in a local environment, has it been decided that space is flat or curved? The implications here are kinda blowing my mind right now. Can someone point me to somewhere, preferably with some math, that I might better understand this? or even a more appropriate thread?

[Karnuvap]

Ahh yes - the eternal question of whether space is curved and, if so, what shape is it?

 

I think that the current thinking is (based on the amount of matter that there is distorting space) that space IS curved and it is curved in what is geometrically called a "Saddle". This is otherwise known as the pringle shape which is to say that the angles of your triangle will add up to LESS than 180 degrees.