String theory question

Forgive me if posting a question to a moderated group is not OK.

As I understand string theory of 10 or more space dimensions,
most of those dimensions are tightly wound up so they would
not be visible to us. My question is whether these wound
up dimensions would contribute to an overall curvature of
space time, and if so would that not appear as matter?

Thanks.

On 10/17/2014 8:37 PM, root wrote:
Forgive me if posting a question to a moderated group is not OK.

'root' has an absolute right to do so (but posting
as root can be dangerous!)

As I understand string theory of 10 or more space dimensions,
most of those dimensions are tightly wound up so they would
not be visible to us. My question is whether these wound
up dimensions would contribute to an overall curvature of
space time,

Basically you ask whether those dimensions that are *not*
wound up become nevertheless a little bit curved due to
the other ones being very tightly wound up.

As far as I know that isn't necessarily the case You can
choose those things independently. It is precisely the
problem of string theory that you can choose in many ways
how the dimensions are curled up.

and if so would that not appear as matter?

If indeed you get such an effect, then perhaps you could
single out the way in which the "superfluous" dimensions
must be curled up to match our observations!

--
Jos


Thanks.

Jos Bergervoet wrote:
On 10/17/2014 8:37 PM, root wrote:
Forgive me if posting a question to a moderated group is not OK.

'root' has an absolute right to do so (but posting
as root can be dangerous!)

Is that because my posts somehow pose a danger to the internet?


As I understand string theory of 10 or more space dimensions,
most of those dimensions are tightly wound up so they would
not be visible to us. My question is whether these wound
up dimensions would contribute to an overall curvature of
space time,

Basically you ask whether those dimensions that are *not*
wound up become nevertheless a little bit curved due to
the other ones being very tightly wound up.

As far as I know that isn't necessarily the case You can
choose those things independently. It is precisely the
problem of string theory that you can choose in many ways
how the dimensions are curled up.

and if so would that not appear as matter?

If indeed you get such an effect, then perhaps you could
single out the way in which the "superfluous" dimensions
must be curled up to match our observations!


Thanks. And for a follow up question. If we can consider
coiled up extra dimensions, why not consider that we
haven't always had 3 active dimensions. Suppose we started
out with one dimension, then inflated to two, and thence to
three. Would a theory of inflation still be required to
explain the overall homogeneity of the known universe?

On 10/19/2014 7:30 PM, root wrote:
Jos wrote:
On 10/17/2014 8:37 PM, root wrote:
..
...
Basically you ask whether those dimensions that are *not*
wound up become nevertheless a little bit curved due to
the other ones being very tightly wound up.

As far as I know that isn't necessarily the case You can
choose those things independently. It is precisely the
problem of string theory that you can choose in many ways
how the dimensions are curled up.

and if so would that not appear as matter?

If indeed you get such an effect, then perhaps you could
single out the way in which the "superfluous" dimensions
must be curled up to match our observations!

Thanks. And for a follow up question. If we can consider
coiled up extra dimensions, why not consider that we
haven't always had 3 active dimensions. Suppose we started
out with one dimension, then inflated to two, and thence to
three. Would a theory of inflation still be required to
explain the overall homogeneity of the known universe?

Some people would have it that from three you'd
still need to go to four dimensions to finish it
off..

But after reaching 4 macroscopic space-time
dimensions, would we still need an additional
inflation era? (Is probably what you mean..)

The answer is that the inflation not only has to
explain the homogeneity of the known universe that
you mention. It has to solve:
... The flatness problem,
... the horizon problem,
... the monopole problem, and
... the density fluctuation problem
If your repeated inflation steps do solve these
problems, then no further inflation is needed from
a cosmological prospect. But since you don't give
details of how you propose things to happen, we
cannot judge whether that is the case.

You really need quantitative descriptions of the
inflation processes. (For instance, the latter two
of the problems mentioned are best solved by slow
roll-over type of inflation, AFAIK, and not so
well by the earlier proposed theories of the
inflationary universe.)

--
Jos

In article ,
root wrote:

[...]
Thanks. And for a follow up question. If we can consider
coiled up extra dimensions, why not consider that we
haven't always had 3 active dimensions. Suppose we started
out with one dimension, then inflated to two, and thence to
three. Would a theory of inflation still be required to
explain the overall homogeneity of the known universe?

There's been some recent work on this question (notably
by Stojkovic -- see http://arxiv.org/abs/1304.6444, for
example -- but also Amelino-Camelia and collaborators --
see http://arxiv.org/abs/1305.3153). It's possible that
a mechanism like this could replace inflation, but it's
very highly speculative; there's not yet a really good
model, and it's just starting to attract attention.

Steve Carlip