Age of Universe

[ravisastry]

Hi All,

how is the age of universe calculated ? i read a few articles/wiki etc and its estimated to be roughly 13.7 billion yrs old. Have we considered the time dilation effect here ? cause we are measuring the electro magnetic radiation travelling in an expanding universe and in an accelarating environment, time runs slow. Hence the actual age of universe should be greater than 13.7 ??

Thanks,
Ravi

[Fredrik]

13.7 billion years is the value of the FLRW (http://en.wikipedia.org/wiki/FLRW) time coordinate here and now. It's also the time experienced by an object that's been at constant spatial coordinates for the entire age of the universe. Any object that's been moving relative to such a "stationary" object will have experienced a shorter time.

So what objects are "stationary" in FLRW coordinates? The answer may surprise you. All the galaxies are approximately stationary in these coordinates.

[ravisastry]

thanks for the explanation and it seems logical that all the galaxies are "stationary" as the whole of universe is expanding uniformly. but, a ray of light(or any EMR) which originated during the big bang, is travelling in the accelarating universe. It is subjected to various gravitational pull (from different astronomical bodies) and hence wont the time for this ray of light be different when compared to all the stationary galaxies ?

[Fredrik]

"The time for this ray of light" suggests that there's a meaningful way to define the time "experienced" by a massless particle. There isn't. And the most meaningful definition would be to define it as 0. See e.g. my posts in this (http://www.physicsforums.com/showthread.php?t=315122) thread about the "photon's point of view". In particular, #8 and #14. You can also check out the currently active thread on the same topic.

[Chronos]

The 13.7 billion years number has been derived from a number of independent sources, so it seems pretty solid. Do you have a particular objection?