alright so the universe is infinite. if it is so, how possible it is for it to expand? when something is absolute, the state of it being changed is impossible. you cant increase nor decrease ∞.

so they say its expanding, therefore, if with a new-fangled advance device to measure the size of universe at the speed of light so we wont miss a unit in calculation, we should be able to estimate the size of universe by measuring the perimeter it has covered at a specific time before it expands further.

Not exactly true that the universe is infinite, it is at most near infinite.

That means it is so large that it is like infinity to we earthlings.

The problem is;

Ever since the occurrence of the big bang approximately around fifteen-billion years ago (if my memory serves me well); light rays from distant celestial objects only had that much limited time to travel and reach our perimeter of sight until today... That means, today we are only capable of seeing fifteen billion years back in time (back into the past) through the world's most powerful astronomical telescopes and detectors. We are limited; our "visible universe" from our respective point of sight today is only a radius of fifteen-billion light years, whereabouts light rays from objects further out than that are completely invisible to us since their light rays are still travelling to reach our point of sight!

We can never see the rest of the universe that is outside of our fifteen billion years timeline...

One light year equals the distance that the speed of light has achieved/covered in one year.

The "actual" universe is MUCH larger that we can ever imagine...

The worse is; celestial objects (stars, galaxies, planets etc...) located further away from us are also at the same time moving away from our point of sight faster than the celestial objects located nearer to us...

"Quasars" come to mind... (Being one of the most 'redshift' objects of our visible universe...)

This post has been edited by Benjamin911: Aug 22 2009, 02:30 PM

According to Einstein cosmos, universe is a hypersphere with finite volume without boundary.

Volumes mean matters, spaces and time. Due to the expansion, the matters are moving away from each others and the spaces between them are stretched, hence the volumes of the hypersphere is larger but still finite. Imagine a tennis ball (the hypersphere universe) expands become a basketball.

A finite (finite doesn't mean fix, it means contain) volumes can expand, this is the whole idea.

Just ask another question, can an infinite volumes expand further. This question is meaningless as infinite volumes mark the highest volumes imaginable. Just like what you have quoted.

Ever heard of Doppler Effect? Imagine your are driving a car and an ambulance (with siren on) from the opposite direction. The sound signal from the siren would be weak, stronger, strongest, weaker, weak as the ambulance is moving closer to you and then moving away.

Now replace your car with planet earth and the ambulance with a planet under observation, and sound to be replaced by light.

Distance from two planet could be estimated using the method. Cosmologists encountered that the distances between the planets are getting further, hence by looking backward, these planets were closer and at a point, there were together (singularity) before the explosion.

Don't have answer to your question though, on measuring the perimeter of the universe. However, aren't the extension of the distance between two planets signify the universe expansion already?

Cheers.

nice.rider: Small correction. The Doppler effect refers to the fact that the frequency of the incoming light (which is the case here for astronomical measurements) is increased if the body emitting it and us are moving towards each other [this is called blueshifting], and the frequency drops if the body emitting it and us are moving away from each other [this is called redshifting].

So yeah, your analogy would be to talk about a higher pitch when the ambulance comes towards you, and a lower pitch as it moves away from you

This post has been edited by bgeh: Aug 22 2009, 07:31 PM

Not exactly related, but here is a short video on the Ultra Deep Field
It also give a very brief information on redshift.

http://www.liveleak.com/view?i=00f_1250151235

Wow, that is a very happening video; especially if you really understand what is really going on, or understand what you are really seeing.

BTW, besides Dark Matter and Quasars, also look up Globular Clusters and Seyfert Galaxies...

This post has been edited by Benjamin911: Aug 23 2009, 12:00 PM