Dimensions 3

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Superstring theory stipulates ten dimensions.
The world around us appears to contain only four (including time).
Something needs to be done about the superfluous six. -
from Lisa Randall's "Warped Passages"

Because you may have 10 Dimensions at subatomic level, does it mean you 'must' have 10 dimensions in the 'physical' world around us
Q [Homepage] 06.29.06 - 3:27 pm #


If they are at the subatomic level they are still in the world around us, but we just can't detect them unequivocally yet with traditional science.
Rae Ann [Homepage] 06.29.06 - 5:14 pm #


These dimensions are very small-- think of a long cylinder(100m) with radius of say 2mm. If you look at it from far away, say 1 km, you will see a long line with no thickness.

But if you get close enough you will see the 2mm thickness.

Similarly to see the very small compactified dimensions you need a really powerful "microscope" (accelerator or something that produces very high energies).
Think of uncertainty principle for a better understanding-- the smaller length resolution you want, higher the momentum (energy) required.

Our everyday world is at an energy scale where these tiny lengths will simply not be "visible". This was a very handwaving analogy-- but this is roughly why we do not "see" these extra dimensions.

There is this completely wrong notion that somehow string theorists simply decided to throw in these extra dimensions-- they are in fact rather tightly controlled by the maths required to implement a physical condition which is necessary for any quantum theory to make sense.
I apologize to the experts who can certainly explain this much better than me, and perhaps manage to be more technically precise.
AR [Homepage] 06.29.06 - 9:14 pm #

"Regarding the Superfluous Six": Since Lubos is on a much-needed long-overdue hiatus, I will officially declare that it is "Amateur Night at The Reference Frame". Moreover, I will boldly volunteer to be the second amateur to take a mediocre stab at Q's thought-provoking question. Let me begin my figurative stabbing...

If one wants to conceptualize "the superfluous six", then one must gain a grasp of brane/bulk cosmology... First imagine dividing the cosmos into a higher dimensional bulk space and a lower dimensional brane space. Next imagine dividing strings into two distinct favors:

(1) open strings and
(2) closed strings.

As a general rule, non-graviton-particles act as open strings and are strictly confined to the lower dimensional brane(s).
By contrast, gravitons act exclusively as closed strings and uniquely behave as cosmic interlopers between the higher dimensional bulk and the lower dimensional brane(s).

Consequently, gravity is the only force in nature which is qualified to travel to-and-fro between the higher and lower dimensions. In addition, it is conjectured that supersymmetry partners exist upon a separate brane which runs parallel to a companion brane.

The closed-loop strings of gravity act as a mediator between these two branes.

Furthermore, gravitons have the potential to display two distinct modes of behavior:
(1) the gravitons - which run perpendicular to the brane - have the capacity to polarize the brane. This polarization leads to gravitational leakage into the bulk.
(2) the gravitons - which run parallel to the brane - lack the capacity to polarize the brane. Non-polarization maintains gravitational sequestration of the brane.

In conclusion: the most reasonable way to make sense of gravity in the universe is to view the universe as containing more than 3+1 dimensions. Best Wishes!
Cynthia [Homepage] 06.30.06 - 12:11 am #

Three dimensions are all we see -- how could there be any more? Einstein's general theory of relativity tells us that space can expand, contract, and bend. If one direction were to contract down to an extremely tiny size, much smaller than an atom, it would be hidden from our view. If we could see on small enough scales, that hidden dimension might become visible.

See Plato for dimensional-referencing
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