"THE ONLY way is up." An earnest student of our physical realities might find room to dispute this jollying phrase. There is also down, and, for that matter, left, right, forwards and backwards. Six ways to go. Then again, the further up you go, the less down you are, and similarly for left and right, forwards and backwards. So that's three independent directions to move in – gravity and local obstacles permitting.
It is a fact so bald that we rarely stop to ask an even balder question: why?
Physicists have wrestled with this perplexing question of space's essential three-ness for a good while now – not, it must be said, with much success. Our best theories of nature supply no clue as to why space might have three dimensions, rather than two, four or 5.2. Even worse, the drive for ever-grander replacements keeps finding hints that the magic ...
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