"Joseph Lazio" wrote in message
...

For the record, dark matter is not a theory. Dark matter is a
hypothesis to account for various discrepancies between theory and
observation.

If one assumes that general relativity is the correct theory to
describe gravity[1], then various observations indicate that there is
far more matter around than we detect via emission of photons. So one
has two options:

1. There is dark matter, matter that is either too faint for us to
detect or in some cases that is hypothesized not to emit photons at
all.

2. General relativity is not an accurate description of gravity.

There has just been a short series of programmes on UK
TV on string theory, based on Brian Greene's "Elegant
Universe", and discussing the hypothesis that gravity
is weaker than other forces because it 'leaks' between
branes. Is there consideration given to the apparent
discrepancy being due to the converse, a leakage of a
gravitational effect into our brane from others?

George