# Universe age?, I never really understood that

1. Dec 7, 2011

### leviterande

Universe age!?, I never really understood that

Hi, there is one thing I really never got. they say the universe is 13.7 billion years old. That is because hubble couldnt see any further!!!!? Now this is the part I do not get: "hubble cannot see any further??" WOW! What does it see? Its gotta be something....
The last thing it sees is 13.7 billion old galaxies, right? So what does it see after that? Is it just that hubble cannot zoom anymore?, well thats a different subject.. or is the view only blocked by a shining galaxy? really? What exactly does hubble see at that point or what is limiting it? I mean , there are still infinit galaxies beyond that limit, arent there?

Thanx

Last edited: Dec 7, 2011
2. Dec 7, 2011

### Chronos

Re: Universe age!?, I never really understood that

The age of the universe was not determined by the hubble telescope. And it certainly does not see any galaxies that are 13.7 billion years old [there arent any].

3. Dec 7, 2011

### twofish-quant

Re: Universe age!?, I never really understood that

You see the cosmic microwave background (a.k.a the wall of fire from the big bang). Hubble can't see it, but there are several other microwave satellites that can.

The last thing it seems is 12-13 billion year old galaxies since it takes a billion years (give or take) to form galaxies. Then..... Nothing.....

There may be an infinite number of galaxies in space, but when you are looking at the universe, you are looking back in time, and at 13 billion years ago, you stop seeing galaxies. At 13.7 billion - 300,000 years, you see a wall of fire from the big bang.

It's pretty mind-blowing once you realize that we can see pretty much to the beginning of the universe - 300,000 years. The reason we think that the big bang happened is that we can see it.

4. Dec 8, 2011

### leviterande

Re: Universe age!?, I never really understood that

thanx for the replies. so do you mean that beyond 13.7 billion years back neither hubble or any other telescope see any galaxies at all... only a fire wall? are we really for sure that there arent any galaxies beyond? it sounds awfully strange that we really can see everything to the limit outthere if you know what I mean

5. Dec 8, 2011

### Staff: Mentor

Re: Universe age!?, I never really understood that

The problem is not only did galaxies not form until after the 1st billion year or so after the Big Bang, but before that there was a period in the early universe where everything was so dense and hot that not even light could penetrate this "fog" for any large distances. As the universe expanded it cooled down until finally the fog of electrons and protons cooled down enough to combine and emit the cosmic microwave background that we can see today. There is quite literally nothing to see beyond this point in time. The light simply does not exist.

6. Dec 8, 2011

### phinds

Re: Universe age!?, I never really understood that

I think it's possible that the answers already given, while completely correct, may confuse you because, and I'm somewhat guessing here, you don't quite get the difference between time and distance as regards your question.

As to what we can SEE, that is bounded by the "surface of last scattering" (referred to above as the "wall of fire", and the CMB) which occurred about 400,000 years after the beginning of the universe (which happened 13.7 billion years ago). So in terms of TIME, we can see back to 13.7 - .4 = 13.3 billion years ago.

As to WHERE we see this, that's a bit more complicated. The light that we see from the CMB started towards us 13.3 billion years ago, but it was NOT 13.3 billion light years away when the light was emitted, it was closer. AND, to make it all even more confusing, it is NOW more like 50 billion LY away because since the time that it started towards us, everything has been moving away from us.

The things at the edge of the Observable Universe (that's the non-physical sphere that marks the boundary of what we can see) are now moving away from us at about three times the speed of light.

This does NOT mean that they are MOVING at faster than light speed, it means the distance between us is increasing that fast. This sounds silly at first and is counter-intuitive, but it's due to the expansion of space.

You'll get all this and more in any basic book on cosmology.

EDIT: Oh, and I should add, the fact that we cannot SEE any galaxies beyond the Observable Universe doesn't mean they aren't there. The general consensus is that the non-observable universe (which is just like the OU except that we can't see it) goes on for an enormous distance, perhaps infinity, beyond the OU.

7. Dec 8, 2011

### leviterande

Re: Universe age!?, I never really understood that

This is the closest to an answer I wanted:)

I know its confusing but it is even diffecult to formulate what I am asking. So they say there are like 100 billion galaxies in the OU. it is really wrong then to say thats it . because there could be infinite number of galaxies. why cant we see the non-observable universe? that light hasnt reached us yet? huh.. I just find it pretty unconvincing we found the so called big bang really, we really dont know what that is. maybe the big bang is simply a very usuall occurance in the universe and the so called big bang is simply as significant to the OU as the blackhole center to the galaxy...

8. Dec 8, 2011

### phinds

Re: Universe age!?, I never really understood that

Your doubts are understandable, based on a lack of knowledge of the rather massive amount of evidence that supports the current cosomological model. Keep reading and you'll get more convinced.

By the way, the light from the non-observable universe will NEVER reach us.

9. Dec 8, 2011

### Chronos

Re: Universe age!?, I never really understood that

To be accurate, the surface of last scattering is .0004, not .4 biilion years after the big bang. So we can see back [13.7 -.0004]. . . ~ 13.7 billion years. Theoretically we could see beyond the surface of last scattering - just not in the EM spectrum. A neutrino telescope or gravity wave detector could probe back to nearly the instant of the big bang. We haven't yet figured out how to build a neutrino telescope, but, are working on gravity wave detection [e.g. LIGO]. The unobservable universe is essentially based on the idea that the big bang that produced our observable universe was just a fragment of a larger, possibly infinitely larger, big bang [e.g, eternal inflation].

10. Dec 8, 2011

### phinds

Re: Universe age!?, I never really understood that

blush ... thanks for that correction ... I need to do a better job of connecting my brain to my mouth.

11. Dec 8, 2011

### Staff: Mentor

Re: Universe age!?, I never really understood that

The Big Bang is not something to be "found". It is not hidden or in one specific location. It was EVERYWHERE. The theory simply says that the Universe was at one point in time at a very very high density and expanded from there, resulting in a decreasing density as time went on. Every point in the Universe was part of the big bang.

12. Dec 10, 2011

### Gliese123

Re: Universe age!?, I never really understood that

Telescopes of that kind can't see further than 13.7 billion light years away just because light haven't stretched more than that. I think?

13. Dec 10, 2011

### Chronos

Re: Universe age!?, I never really understood that

We must exercise caution where distance is concerned. A light year is more a unit of time than it is distance. It is pretty much the same thing up to about 2 billion light years, but, deviates rapidly at greater 'distances'. Look up angular diameter distance and comoving distance to appreciate the distinction.

14. Dec 10, 2011

### CosmicEye

Re: Universe age!?, I never really understood that

great explanations. So we cant see passed the wall of fire because we are moving away from it at about 3 times c (as you said), and it will never reach us because we are moving faster than it can travel? I need to read why that doesnt break the speed of light law...

15. Dec 10, 2011

### Chronos

Re: Universe age!?, I never really understood that

Expansion of empty space has no speed limit. That does not prevent us from seeing stuff all the way back to the big bang - except for that annoying surface of last scattering.

16. Dec 11, 2011

### Staff: Mentor

Re: Universe age!?, I never really understood that

No, we can't see past it because if we look back to that point in time there is literally nothing else to see. No light was emitted before this point in time, so you cannot see anything before it.

17. Dec 14, 2011

### twofish-quant

Re: Universe age!?, I never really understood that

No. We can't see past the surface of last scattering for exactly the same reason that we can't see the center of the sun. Once hydrogen-helium gas gets heated to 3000 K, it starts becoming opaque and you can't see through the gas. It's got nothing to do with speed of light or anything like that, and everything to do with the properties of hot gas.

If you take a room full of hydrogen gas and heat it to 3000 K, it stops becoming clear.

18. Jan 2, 2012

### nikkkom

Re: Universe age!?, I never really understood that

I believe we _will_ see farther, we just need to wait a few billion years :)

The place(s) from where we receive CMB radiation today was just filled with hot gas when CMB was emitted. But with passing billion years, that gas (as we look at it) will start forming new galaxies. And of course, we will still receive CMB (with ever-lower energy) - it will be coming from a gas which is (was?) a bit farther out.

19. Jan 2, 2012

### bm0p700f

Re: Universe age!?, I never really understood that

The age of the universe come from measurements of hubble's constant in that;

t$_{age}$= $\frac{1}{H_{o}}$