Naked Science Forum
Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: thedoc on 18/07/2013 12:30:01

Will asked the Naked Scientists:
This is another dark matter related questions, but first to the point there
theoretical physics and fiction met.
Edwin Abbott Abbott wrote Flatland, a story where a two dimensional square in a two dimensional universe meets a sphere and is introduced to the third dimensional.
How could we tell if there was another set of three dimensions perpendicular to our own?
And given that the likes of string theory requires about 17 dimensions, could dark matter be the result of a gravitational effect of bodies in dimensions currently undetected?
And how improbable is it?
Take care,
Will
What do you think?

You better define a dimension first. And then prove singular dimensions to exist, to make it a reality. We have three we see, we postulate, not prove, other 'singular' dimensions to exist. but before a experimental proof of one isolated dimension I will still consider myself free to have my own thoughts about it. A much better expression is 'degrees of freedom' and it's better because it does not state what is is, other than something, as a spin, can do things, and find 'directions' of a sort, that makes no sense from the degrees of freedom we find us to have, which are four, one temporal and three spatial.

There are some versions of string theories with 10 or more dimensions which might receive some confirmation from the LHC.
If these "hidden" dimensions exist, they may be rolledup to a very small size. But if they are not too small, the LHC (or some more powerful collider) may be able to produce the particles predicted by these theories.
Gravitational lensing may provide some additional evidence.
See: http://en.wikipedia.org/wiki/Why_10_dimensions#Testability_and_experimental_predictions

Time is not a 'dimension' in the same way I would describe a spatial 'dimension though.
In a spatial dimension you are presumably free to to choose any direction, think of it as a flat paper to see how I mean. But 'time', or its 'arrow' to express it clearer, has only one direction. so it's not really the same. As degrees of freedom though it becomes slightly more unclear, as I think. Because thinking that way I don't think it matters what 'directions' you give a degree of freedom. A length is just a length, it's a degree of freedom, as a width can be seen as another. This is from looking at a combination of degrees of freedom, as the way we once started from, defining those 'singular dimensions', we might expect
Alternatively, I think you can use the same argument, that the three spatial degrees allow for any direction, going out from some defined origin, in that 'plane'. But the temporal degree of freedom has only one direction, as far as we can measure experimentally.
What one should consider is that length, width, and height, has its original definition from the world we exist in. Any piece of matter will present us with those definitions, looking and measuring. Imaginatively though, you should be able to interchange any of those spatial descriptions, as a length for a width, finding it to express the exact same.
So what makes sense from defining dimensions from a piece of matter becomes trickier if you look for how to define each spatial dimensions 'uniqueness'. They should be interchangeable as I see it, as they will imaginatively, each one treated as a isolated degree of freedom, become the exact same in form of the description you then can make.
But the arrow will still be unique.

Thinking of it that way, also considering a Planck length to become a 'original unit', you then might assume a universe of two 'dimensions' :) if you like, a unique arrow and Planck 'length'. Although you definitely need more, properties enabling it to mirror, or twist, into the way we observe the two other spatial degrees of freedom existing. But to prove something you need to find the right experiments, pointing toward what you think is right.