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Dave Overton asked the Naked Scientists: Hi Chris,My question is, we think we know the age of the universe because distant galaxies are fading out because of the doppler red shift by running it back to a singularity we calculate the age, but why cant there be objects many more times distant and we just don't know they're there?Fantastic programme,Dave Overton.What do you think?
The comoving distance from Earth to the edge of the visible universe (also called particle horizon) is about 14 billion parsecs (46.5 billion light-years) in any direction. This defines a lower limit on the comoving radius of the observable universe, although as noted in the introduction, it's expected that the visible universe is somewhat smaller than the observable universe since we only see light from the cosmic microwave background radiation that was emitted after the time of recombination, giving us the spherical surface of last scattering (gravitational waves could theoretically allow us to observe events that occurred earlier than the time of recombination, from regions of space outside this sphere). The visible universe is thus a sphere with a diameter of about 28 billion parsecs (about 93 billion light-years). Since space is roughly flat, this size corresponds to a comoving volume of about(4/3)πR3 = 4 *1032 ly3or about 3*1080 cubic meters.The figures quoted above are distances now (in cosmological time), not distances at the time the light was emitted. For example, the cosmic microwave background radiation that we see right now was emitted at the time of recombination, 379,000 years after the Big Bang, which occurred around 13.7 billion years ago. This radiation was emitted by matter that has, in the intervening time, mostly condensed into galaxies, and those galaxies are now calculated to be about 46 billion light-years from us.