How old is the universe believe to be?

Answer 1

We do not know the exact age of the universe, only its age to within some margin of error. As more and better data becomes available, the size of that error range will decrease.

According to the most accurate data available today (January 2009), the age of the universe is 13.73 ± 0.12 billion years old.

This means that we can state with a great level of confidence that the universe is somewhere between 13.61 and 13.85 billion years old.

(That's "billion" with a b, not "million." There are a thousand millions in a billion, so as big a number as a million is, it's only one-thousandth of a billion. There are slightly more than 6 billion people on the Earth.)

The most reliable data comes from WMAP (Wilkinson Microwave Anisotropy Probe), which is an earth-orbiting satellite that studies the cosmic microwave background radiation, a relic of the Big Bang, although this is supplemented by other data from observations of supernova explosions and of the recession speeds of distant galaxies.

We may be able to narrow the range down even more as additional data is collected from WMAP, or once newer, more sensitive, instruments are launched.

There are other experiments and other experiments which, while they do not yield values as precise as this, give us values which are consistent, and thus reinforce the WMAP data as being correct.