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Dear Final Frontier,
Firstly, may I say how much I enjoy your programme, it covers a wide diversity of topics in 30 mins. I understand your Dec programme has a topic on the Big Bang. I have a couple of questions which have always been a mystery to me and perhaps you could cover in your prog. (unless already recorded).

1. If the Big Bang occured from background radiation where did this come from?
2. If the Big Bang did occur why have there not been subsequent events? Any natural phenonema does not occur just once, we should have had multiple situations but this seems to have been overlooked.

Yours sincerely,
Geoff Booth

Reply
Let's start with the background radiation.
When the universe was very young and compact, radiation and matter continually interacted. The radiation reflected how hot the universe was at any instant. The cosmic microwave background radiation emerged about 300 000 years after the Big Bang, when the universe had cooled down to about 3000 K, cool enough for hydrogen atoms to form. That made the universe transparent, and then the radiation produced at 3000 degrees could travel freely through the universe. That's the radiation we see as the cosmic background, though it has now been redshifted by a factor of 1000, so it looks to us like 3 K instead of 3000.

When the Universe was more compact, more of its energy was tied up in radiation than in matter, but to physics they are both forms of energy. Radiation was certainly dominant just after the Big Bang, but the Big Bang didn't grow out of it. Physics allows us to trace the matter and radiation of the Big Bang back to about 10-43 seconds before time zero, but no further. Before then, the quantum nature of space-time itself must be considered. That time, called the Planck time, marks the earliest time we can investigate. We can't know what the Universe was like in the brief instant before then.

Why wasn't there another Big Bang? There may be one day in the future, if the Universe collapses, though at the moment it doesn't look like that will happen. But even if it does, remember that the Big Bang wasn't a event like an explosion IN space, but rather the expansion of space itself. So, if there was to be another Big Bang, it would be all of space again, not an event within the current universe.

I hope that helps answer your questions, Geoff.