Science Forums 2

[Tormod]

Michael,

I'll do my very best here (tongue in cheek):

1) If I remember correctly, Rees' suggests that the Big Bang was the beginning of our Universe, but that it was a "local" big bang in what became our part of the Multiverse. There has been and will be an unlimited number of Big Bangs, but for our Universe there will only ever be The One that was the beginning of our time. He does not need to reconcile this with anything, but I think it is obvious to anyone that if you call in a Multiverse to explain the existence of human beings, you kind of push the Causality issue a bit - it's like saying, "okay, there is no God, but there was something before our own Universe. We can never know what it is but it must be there, because we are here."

2) I don't understand your second question, perhaps you need to rephrase it. If you refer to the expansion rate being at the exact level it needs to be to continue expanding forever, well, then I find it rather easy to explain that spacetime is (extremely close to) "flat". If it was not so close to flat, then it would be curved, and the larger the curvation the easier it would be to observe it. In a curved spacetime, time loops should be easier to find, since the distance between two spots in spacetime need not be as far apart as it seems. There is a simple analogy to this - if you take a piece of paper and put one dot on the upper part of the page, and one on the bottom part of the page, then in a flat spacetime the shortest route between the two is a direct line. But in a curved spacetime, the shortest path would actually be to tunnel through the paper from one dot and emerge at the other dot, without moving on the paper at all (because, obviously, the sheet of paper would be curved and not straight).

We do know, of course, that on a local level spacetime is indeed curved, since that is what Einstein proved with his relativity theory. He replaced Newton's idea of attracting bodies with a "gravity well", in which our Sun creates a depression in spacetime, around which our Earth circles. What keeps the Earth from falling into the sun is the speed and momentum of its orbit and (possibly) a repulsive force (the one Einstein called his bigges blunder) which is also the cause of vacuum energy...but on a Universal scale, the local "bumps" in spacetime evens out so in general everything becomes "flat".

But this is written after a long day at work and if it seems totally unreasonable then blame my extreme need for a cup of coffee.

Tormod