# Does measuring the age of the universe result in objective observation?

1. Feb 8, 2010

### MattAndMatthe

Let me know if there are any errors or holes in my logic, facts, or assumptions.

I was thinking in regards to time being relative to the observer and the resulting impossibility of an objective measure of time: In determining the age of the universe, our current estimation is about 13.2 billion years. Now, this would be an estimate or measure based on our earthly frame of reference, the universe being 13.2 billion years old as observed by earthlings.

But since any point in the universe can be considered its center, then the 13.2by estimation would result as observed from any other frame of reference in the universe. Therefore, the measure of the age of the earth, as measured in units of time, according to the CMBR is objective and not relative to any frame of reference since every frame of reference is the same.

Also, wouldn't this apply to the estimation of the "diameter" of the universe in light years?

2. Feb 9, 2010

### bcrowell

Staff Emeritus
It's certainly true that certain observers could have had world-lines that started shortly after the big bang and yet have accumulated a lot less than 13 billion years worth of proper time.

The thing you have to realize about cosmological solutions is that they generally have preferred frames of reference. These preferred frames are not provided by the laws of physics (as in aether theories) but by the matter and radiation that are present in the universe. In our universe, the preferred frame is the frame in which the average momentum of the CMB vanishes. The solar system is not at rest relative to this frame, as demonstrated by the dipole component of the CMB.

Any time you have a preferred frame of reference, you also get a preferred time coordinate, which is the proper time measured by observers at rest in the preferred frame. In our universe, this time coordinate is interpreted as the time you can measure by looking out the window and seeing the present conditions of the universe (how hot, how dense, etc.). It's according to this time coordinate that the universe has the 13-billion-year age.

3. Feb 9, 2010

### Naty1

Hi Matt...good questions, not easy conceptsto understand at first.
conventional terminology says there is no center of the universe...so its not good to say "any point is its center" because there is no such point, no even one....no one knows the diameter of the universe...we can only observe as far a light (radiation) has had time to reach us...after the dense ionized gas following the big bang formed atoms and radiation could get thru...how much things expanded before that is unknown...but likely we observe only a tiny fraction of the universe...nobody even knows if its infinite nor bounded nor unbounded.

If I understand bcrowell's explanation, it's a good/valid one based on CMBR radiation...red shift, right?? the remnanent radiation from the big bang. In other words, as the universe expands and ages, the red shift of the CMBR becomes more pronounced....wavelengths appear to get longer and longer due to cosmic expansion. All observers will see the same CMBR because there is no center of the universe....

Is it correct to say that our measures/estimates at 13B years include a correction for our solar system movement? So other observers would have to make suitable corrections for theirs....

Also there are other ways to measure the age of the universe, which you can read about here:
http://www.astro.ucla.edu/~wright/age.html

* The age of the chemical elements.
* The age of the oldest star clusters.
* The age of the oldest white dwarf stars.

Last edited: Feb 9, 2010