Re: E=mc2 ( 27 Sep 1905- 27 Sep. 2007) is 102 years old.

Willem wrote:
Thomas wrote:
) <snip> .... Why the universe is four dimensional
) (or where the additional dimensions went that should exist according to
) string theory) is another question. Some people believe it is a
) topological constraint.

You know how they say that the universe is closed in on itself ? Like a
4-D sphere ? As in, when you go on for long enough in one direction, you
end up where you started. (Disregarding speed and time limits, etc.)

It's an open question whether it is open. Current observations seem to indicate that the universe is exactly on the edge between closed and open (namely Euclidean).

Well, they also say that those other dimensions are such that you only
have to go a very very small distance to end up where you started.
In the order of angstroms perhaps.

I know - though it is IMHO backwards - a theory should at least get the number of observable dimensions right. (-: Otherwise, I think that there should be at least a method to measure those dimensions somehow, but...
that's all high-energy physics, highly speculative.

Also, the best reason I heard for there being 3+1 (large) dimensions is
that if there were more or fewer, then the world/universe as we know it
could never have existed. So, in all the universes out there with all
kinds of different dimensions, the 3+1 universe is the one that spawned
the creatures that could pose the question 'why are there 3+1 dimensions?'.
I forgot the name for this line of reasoning...

Strong antroposophic principle? It's a pretty weak argument because it is again speculative how live would or might look like otherwise. We know too little to answer that. It has also been argued that the value of the fine structure constant (1/137) is "just that to make life (the way we know) possible". The bracket is often omitted.

Greetings,
Thomas
.

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