13.7 billion years...

[henryc09]

Hi, I've just been wondering about something so if anyone coudl explain it that'd be great. You often come across the statement that we believe the universe to be 13.7 billion years old, but I was wondering how this calculation is made? My main problem is that I'm confused as to whether every reference frame would experience the same amount of time that has passed.

[Masleyko]

Maybe using waves energy and temperatures . :)

[bapowell]

To determine the age of the universe one needs to know:

1) the Hubble constant, H_0, which is the current rate of expansion

2) the current densities of the different matter and energy components of the universe (density of baryons, cold dark matter, radiation, dark energy)

3) a model for evolving back in time

The Hubble Space Telescope provides one of the most accurate determinations of H_0 today; measurements of the cosmic microwave background (CMB) by a variety of instruments, including NASA's WMAP satellite, have furnished reliable determinations of the densities of the various matter and energy components of the universe. Einstein's General Relativity, under the assumption of spatial homogeneity and isotropy gives the Friedmann Equations -- the theoretical model for the evolution of the universe. These are used to determine the universe's age.

The reference frame used in these calculations is the rest frame of the CMB.

[henryc09]

To determine the age of the universe one needs to know:

1) the Hubble constant, H_0, which is the current rate of expansion

2) the current densities of the different matter and energy components of the universe (density of baryons, cold dark matter, radiation, dark energy)

3) a model for evolving back in time

The Hubble Space Telescope provides one of the most accurate determinations of H_0 today; measurements of the cosmic microwave background (CMB) by a variety of instruments, including NASA's WMAP satellite, have furnished reliable determinations of the densities of the various matter and energy components of the universe. Einstein's General Relativity, under the assumption of spatial homogeneity and isotropy gives the Friedmann Equations -- the theoretical model for the evolution of the universe. These are used to determine the universe's age.

The reference frame used in these calculations is the rest frame of the CMB.

Thanks very much. Is there a way you could explain the justification for using the rest frame of the CMB?

[bapowell]

The rest frame of the CMB has some useful properties: it is the rest frame of comoving observers -- those that are at rest with respect to the expansion (think balloon analogy -- comoving observers are points drawn on the surface of the balloon). It is also the frame in which the CMB radiation is isotropic. Time elapsed in this frame can be related to red shift, since clocks can be synchronized by comoving observers in a uniformly expanding universe.

[henryc09]

I see, thanks very much this is a lot clearer now.

[TheTechNoir]

Just something to mention too, not exactly answering the question (it's already been answered anyway) but just something to point out that's sort of related in case you were not aware. Contrary to what some people believe, the average age of the universe in the vast majority of reference frames are extremely close to each other. Likewise the temperature of the universe on a scale of the whole observable universe varies very little from place to place. There are only small exceptions (again on the grander scale, of course in some local regions there will be large differences in relativistic effects or temperatures).

[Chronos]

The background [CMB] temperature of the universe increases with distance [redshift].