# Age of the universe

1. Nov 7, 2009

### land_of_ice

How has it been calculated that the universe really began 13.7 billion years ago with the big bang? Carbon dating or some other method? How exactly did they arrive at this conclusion ?

2. Nov 7, 2009

### nicksauce

If you apply general relativity, you get the Friedmann equations, which govern the expansion of the universe. http://en.wikipedia.org/wiki/Friedmann_equations

Using the equation, you can find an expression for the age of the universe that depends on the current day density of matter, vacuum energy, and rate of expansion (Hubble constant). These quantities can all, in principle, be measured in a number of ways. Plug them into the equation, and it gives you 13.7 billion years.

3. Nov 8, 2009

### qraal

Simply put the Friedmann equations tell us when the size of the Universe goes to zero. Problems arise before then, but not before the Universe is scrunched up into a tiny volume. Observations can't go all the way back to that point in time - the Cosmic Microwave Background is the heat-glow of opaque plasma that we can't see past - so we can't say for sure just how old the Universe really is, just how far back in time it is until the Universe is scrunched up and very hot.

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