Quora: “Roger Penrose says, “String theory is fashion, quantum physics is faith, and cosmic inflation is fantasy.” Is he right?” From Brett Harris on the road to reality guy, Roger Penrose:

I am getting tired of pointing out that String Theory arose out of particle physicists attempting to quantise the linearised version of GR, normally used in make perturbations to Newton’s laws in the solar system. This produces a free spin-2 graviton at 0th-level, and then they attempt to use first order interactions to construct a full interacting quantum field theory of gravitons – in FLAT space – which has none of the full symmetries of GR, and it fails miserably by throwing up infinities at all orders. Not to be daunted, they added supersymmetry to cancel the infinities, but that did not work as expected, so they invented Strings instead of points, to remove the short distance interactions. Why would this ad-hoc procedure produce anything like Quantum GR? It gets worse, they quantise this strings in FLAT spacetime, but find that they need 10 dimensions instead of 4, so they then ‘compactify’ 6 to get something like our world. Problem is, there is about 10^500 different ways to do this – hence the multiverse. Never before has such a failed theory taken on such a life of its own, at least the Aristotelian epicycles produced decent predictions.

As it turns out, when a group of physicists including Lee Smolin and Carlo Rovelli, who understood GR, actually found a way to quantise the arbitrary curved spacetime of GR directly, respecting its symmetries, what dropped out was a real theory of quantum gravity, with no extra dimensions, no supersymmetry, no 10^500 different universes, just a set of quantum states of space, based on simple geometrical solids connected like Lego, each with unique quantum numbers, which at the large scale looks like the space-time of General Relativity.

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Penrose’s views on Quantum Theory are speculative, but there are many different interpretations, and at least he makes proposals which can be experimentally falsified. He speculates on dimensional grounds, that the Planck Mass, usually associated with a quantum black hole, when turned into everyday units, is about 2 x 10–5 grams, which is tantalisingly close to the scale above which quantum properties are not observed. He conjectures that the gravitational disturbance caused by the movement of this mass, is responsible for the “collapse of the wavefunction” which occurs during quantum measurement on a macroscopic system. Perhaps more controversial, he suggests that there may be processes in the human brain at this scale, which may allow quantum mechanical effects to be related to consciousness. He enlisted a medical researcher Stuart Hameroff to assist his development of these ideas. But none of this is anything other than scientific enquiry, ultimately decidable by experimental data. More.

That’s more or less how we think of string theory too. It exists to avoid questions rather than to answer them. We are glad Harris still has a job.

*See also:* The multiverse: The long march of progressive politics through science institutions: Basically, the multiversers rounded up push poll signatures and the other poor questioning sots put up a website discussing the science issues. The latter will probably lose, regardless of evidence. In the age of marchin’, marchin’ and shoutin’ shoutin’, the science doesn’t actually matter much. The marchers and shouters won’t admit that, but they will act like it. That is how we will know.

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In search of a road to reality