# How did the universe get so big so fast? [duplicate]

• The universe started at the big bang around 15 billion years ago.
• The universe is now at least 92 billion light-years in diameter.

Together, don't these mean that the universe, at some time in the past or present, was expanding at a rate of faster than 1 ly/y in every direction? Why is that possible?

## marked as duplicate by Kyle Kanos, John Rennie, ACuriousMind♦, Brandon Enright, David Z♦Aug 1 '14 at 16:20

• Inflation should answer some of your questions. – ACuriousMind Aug 1 '14 at 15:29
• @ACuriousMind: And probably open up many more ;) – Kyle Kanos Aug 1 '14 at 15:37
• Dear @ACuriousMind, most of the Universe's size still grew in the ordinary non-Big-Bang epochs of cosmology, so inflation is in no way necessary to answer this particular question. – Luboš Motl Aug 1 '14 at 15:59
• @Lubos Motl: I didn't really think about that. Thanks for telling me! – ACuriousMind Aug 1 '14 at 16:21

The current rate of expansion is called the Hubble Rate. It is estimated at around 500 km/s/Mpc (Mpc is megaparsec). Or, alternatively, 160km/s per million light years. That means that every second a distance that was $1000000ly$ becomes a distance of $(1000000+1.691\times10^{-11})ly$. Now, you say the observable universe is 92 billion light years across. Then the farthest reaches are 46 billion light years away. This means that every second, somewhere around 7.4 million kilometers are added to that space. Technically, that means that objects at the edge of the visible universe are receding faster than the speed of light, but they are not moving faster than light.
Place a beam of light at that distance travelling away from us. To us, the beam of light would be travelling at $c$ plus the speed due to expansion. So no matter what, the objects out that far are not moving faster than light.