At Prospect Magazine, he narrates the string theory showdown:
One of the key predictions specific to string theory is that the three dimensions of space (up-down, left-right and front-back, say) and the one dimension of space (past-future) are not all there is to the fabric of reality. String theory insisted that there are in fact not four but ten dimensions of spacetime—and Witten’s M-theory added one more. We don’t see these dimensions because they are “compactified:” in effect rolled up and hidden away, much as the three-dimensional form of a hosepipe looks like a one-dimensional strand from far enough away.
Proposing something as dramatic as seven extra dimensions, without offering the slightest prospect of testing to see if they are there, is a step too far for some physicists. String theory develops its arguments carefully and systematically, extrapolating from the physics we already know using sound mathematical reasoning. But it cannot avoid making many assumptions on the way, which we have no means of validating, and so it can seem to be nothing but a tissue of speculation. That’s why nailing your flag to the mast of string theory has come to be seen as an expression of faith rather than reason, and physics has become polarised into believers and sceptics. Those tensions have been ramped up by the fact that, during the past several decades, string theory looked a little like a monopoly that you had to buy into if you wanted to make an impression in fundamental physics. (It’s important to remember, though, that this was only one highly specialized enclave of the entire discipline.)
As in, you can buy it, but you can’t sell it?
See also: Multiverse cosmology: Assuming that evidence still matters, what does it say?
In search of a road to reality
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