Age of the Universe

[Jdaniel343]

If the age of the visable universe is 13.8 billion years, according to the latests I could find on line, why is the universe not 27.6 billion years old, since what we are seeing is 13.8 billion years in the past?

[Strange]

The basic figure for the age comes from looking at the Hubble value (how rapidly space is expanding). This is roughly constant and you can trace the expansion back to an early hot dense state about 13.8 billion years ago. This is supported by various other observations such as measurements of the cosmic microwave background radiation (CMBR).

 

This means that the earliest structures (galaxies) that we can see are less than 13.8 billion years old; I think the oldest galaxy seen so far is about 13 billion years old. The CMBR dates from about 360,000 years after the initial hot dense state when the universe had cooled enough to become transparent to photons.

 

Not sure where your 27.6 billion comes from ...

Edited January 17, 2014 by Strange

[Spyman]

If the age of the visable universe is 13.8 billion years, according to the latests I could find on line, why is the universe not 27.6 billion years old, since what we are seeing is 13.8 billion years in the past?

You can't count that we are 13.8 billion years old and then add the age of the light on top of that, this place where we are and the stuff that we are made of, are of equal age as the photons in the light we see from the edge of our view.

 

The age of the Universe is assumed to be equal everywhere inside the Universe, there is no location that is older than anyone else. The entire Universe is thought to come from the same moment, making all places and original energy to be of equal age.

 

However since light has a finite speed, photons emitted from distant places need more time to reach us and will therefore show us things that happened a long time ago when the Universe was younger.

 

If it takes light 13.8 billion years to reach us from the edge of our visible universe then our visible universe needs to be around 13.8 billion years old, if the universe was younger then the distant light would not have enough time to reach us and if the universe was older then we should be able to see light from more distant parts further away.

 

(Note: Not included in this simple explanation is the expansion of space, the cosmic microwave background radiation and other things complicating our view.)

Edited January 17, 2014 by Spyman

[michel123456]

If the age of the visable universe is 13.8 billion years, according to the latests I could find on line, why is the universe not 27.6 billion years old, since what we are seeing is 13.8 billion years in the past?

I guess your 27.6 billion figure comes from the fact that the farthest object observable at the East is 13,8 BLY away and the farthest object observable in the opposite direction at West is also 13,8 BLY away. So you added the 2 figures.

 

Well, it is nothing like that following the standard explanation.

 

I'll try to explain something I have many difficulties to accept*:

_first of all no object traveled through space a distance of 13,8 billion Light Years, or 27,6 BLY in order to come from a singular point to the place it is today. It is assumed that the Big Bang (the singularity) happened everywhere. It means that all objects observable in the sky were roughly created at the place where there are.

_secondly, the object you are observing today in your telescope is the object as it was 13.8 billion years ago (roughly). So you are observing a very young object, meaning its a baby: you are observing it as it was a few instant after its birth. The Theory that allows this object to be 27,6 BLY away from another object is called Inflation.

 

-------------

*it is an euphemism, in fact I do not accept any of the 2 statements.

Edited January 17, 2014 by michel123456

[Strange]

Actually, inflation isn't needed to explain the fact that farthest things we can see are 13.8 billion light years away (*); that is simply due to the age of the universe. It true whether inflation turns out to be required or not.

 

Inflation was proposed to solve other problems to do with homogeneity, etc. (as explained on the page you link to).

 

(*) Or, more accurately, the light from them has been travelling for 13.8 billion years. They were about 5 (?) billion light years away when the light was emitted and are now something like 46 billion light years away.

 

(But well done for spotting that 27.6 is 2x13.8 - that went right over my head for some reason!)

Edited January 17, 2014 by Strange

[Jdaniel343]

I guess I just don't understand. It seems if I look at something that happened 13.8 billion years ago that was 13.8 billion years ago.

I'll try this again.

Say I am sitting on another planet today that is 2 million light years away. I have a very power full telescope and look back at the earth and I see dinosaurs roaming earth.

What I am missing on while sitting on this other planet is that 2 million years of time has passed and there are humans now inhabiting earth and are actually looking back at them and what they see is what happened on that planet 2 million years ago.

[Strange]

So when you look at a galaxy that is 13 billion light years away, you are seeing it as it was 13 billion years ago (when the universe was still young). It may not even exist any more.

 

I don't really see what the problem is.

Edited January 17, 2014 by Strange

[Jdaniel343]

That is my point. What I am looking at is 13 billion years ago. If it was 13 billion years ago wouldn't the age of the universe be twice that to get to a state of how it is today.

[Strange]

No. It is 13 billion years ago. What you are sing is the universe when it was just 0.8 billion years old.

 

If you were looking at something 13.8 billion light years away and that thing was itself 13.8 billion years old then you would be right. But the thing you are looking at is very young (equivalent to the Earth being populated with dinosaurs in your example).

[MigL]

Not to be picky Jdaniel343, but if you were on a planet 2 million years away you wouldn't see dinosaurs. You'd have to be at least 65 million years away to see them.

[Jdaniel343]

My Bad. Your right about the 65 million years.