# Isn't the date of the Big Bang a bit bogus?

If I understand correctly, the date of the Big Bang is an extrapolation of acceleration of the universe's expansion through time based on the erroneous assumption that the universe is approximately 13 billion years old. The age of the universe, as far as I can tell is based on the speed of light and the fact that the furthest we could possibly see into the depths of the universe is approximately 13 billion light-years. Isn't that sort of a cat chasing his tail? It seems that there is no valid reason for believing that the universe is really of a radius of ~13 billion years. That is just as far as we can see. If this is wrong and there is a valid reason for believing that the universe is ~ 13 billion years old, then that fact makes for a very interesting possibility. That the expansion rate of the universe is equal to the speed of light, which leads to a very interesting suggestion that I pursued for quite awhile (until it became apparent that the suggested size of the universe is not what it seems), that the expansion rate of the universe is equal to the speed of light. Or, put another way, is it possible that the speed of light is based on the expansion rate of the universe?

• The spacetime at the edge of the observable universe is already expanding away from us at well beyond the speed of light. Jun 10 '15 at 12:20
• You need to find out how the age of the universe is determined. Jun 10 '15 at 13:52
• I think I know my date of birth better than +/-37 million years. Jun 11 '15 at 15:15

I'd like to correct a couple misonceptions that might be confusing you.

1. If I understand correctly, the date of the Big Bang is an extrapolation of acceleration of the universe's expansion through time based on the erroneous assumption that the universe is approximately 13 billion years old.

This is a false assumption. The observable universe is much, much larger than a sphere with a radius of 13 billion light-years. The radius is actually ~46 billion light-years (see, for example, Gott et al. (2005)).

2. The age of the universe, as far as I can tell is based on the speed of light and the fact that the furthest we could possibly see into the depths of the universe is approximately 13 billion light-years.

Look at pela's answer here, if you don't want to go off Stack Exchange (or see Wikipedia for another starting point). See how the age of the universe is calculated. As an approximation,$$t_\mathrm{Uni} \sim \frac{1}{H_0} = 14\,\mathrm{billion\,years}.$$This only relies upon observations of the movements of stars.

3. That the expansion rate of the universe is equal to the speed of light.

The universe is not expanding at the same rate at all distances from us. Objects further from us recede at greater speeds.

• Just to note, I realize that not everything is moving away from us at the speed of light. Maybe a better way to describe it would be that any two most distant points in the universe would be accelerating away from each other at the speed of light. Of course, if the universe is 46 billion lightyears radius, this suggestion doesn't work. Thanks for the deep insights. Jun 11 '15 at 15:23
• @MikeFowler Thanks for that clarification; I misunderstood you. My fault on that one. Jun 11 '15 at 20:18
• @HDE226868: +1 if you cite the 46 billion ly radius statement or point to a link for more info.... Aug 16 '15 at 1:47
• @jvriesem Done. Aug 16 '15 at 14:13
• @HDE226868: The observable radius is actually larger than the Hubble sphere, if that's what you were referring to.... Aug 17 '15 at 13:16