When they say that the age of the Universe is about 13.7 billion years, they are giving the age in cosmic time, is that right?. There's this other thing called conformal time which I don't understand. What would be the age of the Universe measured in conformal time?
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2$\begingroup$ Hi Mick. The question I've linked isn't an obvious duplicate, but Pulsar's answer to it explains exactly how conformal time is defined, and he calculates the current conformal age of the universe as 45.93 billion years. $\endgroup$– John RennieJun 10, 2015 at 17:45
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$\begingroup$ It's a bit like the size of the universe measured in light years. Like 45.93 billion light years. That's the size of the observable universe. Now drop the light. Funnily enough, both distance and time are defined using the motion of light. And light has moved 13.8 billion light years through space that has meanwhile expanded by 32.13 billion light years, so in a way, light has moved 45.93 billion light years. $\endgroup$– John DuffieldJun 11, 2015 at 12:52
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$\begingroup$ Is the conformal age of the universe always equal to the proper distance to the particle horizon (minus the word "light")? $\endgroup$– set5Jun 11, 2015 at 13:35
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$\begingroup$ See also Relation between comoving distance and conformal time? $\endgroup$– user10851Jun 12, 2015 at 12:11
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