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10 months ago in Philosophy of Physics By Rohan

Why three dimensions‑ why not two or four or ten?

We live in exactly three spatial dimensions. Is there a reason, or did we just get lucky?

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By Meera Answered 7 months ago

We don't know, but we have compelling guesses. Classical stability: in 2D, gravity doesn't bind orbits; in 4D+, orbits are unstable. String theory says there are more dimensions, but they're curled up so small we don't see them. Anthropics: complex life might only be possible in 3D. Your observation about 4/3 and 3/4 scaling in biology (metabolism, circulatory networks) is telling. Life optimizes for volume-filling transport in three dimensions. That might not be a coincidence. Maybe the reason we ask the question is also the answer.

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