Extra dimensions whys and other puzzles.

Why do we live in three spatial dimensions?
Why the Universe is accelerating its expansion?
Why only 4% of the Universe is visible?
Why the gravity force is so weak compared with the other natural forces?
What is the Big Bang? Who created it? Did time begin? Was there anything before?

All of the above puzzles could be solved by the existence of extra spatial dimensions. This is what I learned on Saturday at the Perimeter Institute's Black Hole session "Extra Spatial Dimensions" held by Claudia de Rham.

It is well known that in our real world one extra dimension could make a huge difference. The existence of extra spatial dimensions besides the ones we are familiar is puzzling since there is no experimental evidence of them.

Claudia's explanation is that we could have 2 types of them: small extra dimensions and large. The small one we wouldn't be able to see it while the large ones will keep us confined to a surface making traveling through them impossible since we are unaware of their existence. The particles we are made of are confined to the surface while the gravity spreads along all the dimensions explaining why gravity is so weak (Hierarchy Problem).

There are two explanations for the existence of large extra dimensions: string theory (where the surfaces are known as branes) and topological defect (found in crystals and magnetic domains).

More about these in my next post.

Links:

1. An intuitive representation of 10¹⁶, the order of magnitude of the hierarchy problem.

2. My post on another PI session on spatial dimensions.