>> across **the** **whole** *galaxee* **is** **100,000** light years. so 100,000 times 6 trillio >> and the galaxies you mentioned earlier over 100 billion of those of comparable size? >> yes. >> what about the age of the universe? >> that is a little harder. the best estimate right now is about 13.7 billion years. to do -- we have to calculate things like age. it's not something you can measure. and it depends on knowing e number of other numbers very precisely and we don't know the numbers that precisely yet. so what i say is that if around 40 billion years. quite sure of that. but i don't think that we can be quite sure it's 13.7. it might be give or take a few hundred million years. >> what's the basis for the formulation? >> there are a number of different ways we measure. we can -- we understand that the universe slowed down because of gravity. >> and because it was generating all of the above? >> right. and then it started speeding up again. >> but it didn't preexist all of the above. i mean it didn't fill a container. the universe is not a conta