Bayes' theorem

I was hoping maybe KAZZA could explain this to me. People are talking about a flat universe using this theorem. It does not make any sense to me.

HELP!

Hey. Bayes theorem is just a basic theorem in probability that can be used to analyse the likelihood of certain events being true given certain results. There is a nice example on Wikipedia.

http://en.wikipedia.org/wiki/Bayes%27_theorem

The notation P(A|B) means the probability that A is true, given that B is true.

To illustrate, let A be the probability that you are alive at the end of the week, and B be the probability of you being hit by a car (touch wood).

P(A), or the probability of A, is quite high (I hope) say 0.99 which means 99%.

P(B), or the probability of B, is quite low, say 0.05 (5%).

However, if you are hit by a car then the probability of you being alive at the end of the week drops significantly. So to represent that we use P(A|B) which means the probability of you being alive at the end of the week, given that you've been hit by a car. P(A|B) might be something like 0.5

Moral of the story: Look both ways before crossing the road....



As for the flatness of the universe, basically they've just taken some existing data and done a new statistical analysis on it using Bayes theorem. Bayes theorem itself has nothing to do with cosmology. I don't know if their results are valid or not, and I would have to look at the papers in detail to work it out. However, since lots of people that are much smarter than me are going to be doing that anyway and then publishing papers, it's probably easier just to wait a few months and see what the consensus is.

The existing data showed that the universe was more or less flat, and there are other lines of evidence that suggest it is pretty flat as well, so I'm betting that there is a mistake in their work.

Well, they haven't actually said that it's not flat, just that the likelihood is only 65% or something based on that particular data set.