Ο ROGER PENROSE ΛΕΕΙ " Η ΘΕΩΡΙΑ ΤΩΝ ΧΟΡΔΏΝ ΕΙΝΑΙ ΜΟΔΑ, Η ΚΒΑΝΤΙΚΗ ΦΥΣΙΚΗ ΕΙΝΑΙ ΠΙΣΤΗ ΚΑΙ Ο ΚΟΣΜΙΚΟΣ ΥΠΕΡΠΛΗΘΩΡΙΣΜΟΣ ΕΊΝΑΙ ΦΑΝΤΑΣΙΩΣΗ." ΕΣΕΙΣ ΤΙ ΠΙΣΤΕΥΕΤΕ;
EΡΩΤΗΣΗ ΤΟΥ ΒΕΝΝ HARRIS από το πανεπιστημιο της Μελβούρνης.
To call Penrose a mathematician, using a derisory tone, is a gross misrepresentation of Penrose’s areas of expertise. The correct characterisation is that Penrose is one of the few mathematical physicists who really understands General Relativity and has very credible criticisms of mostly US trained particle physicists who moved into unification and cosmology with only an undergraduate knowledge of GR. GR is far more than just a theory of gravitation, its contains deep truths about what we mean by location, and duration, and about the non-existence of coordinate location.
It is false to point at a point in space and give it any meaningful existence. The only thing meaningful is the location of fields and matter in relation to each other and in particular in relation to the gravitational field. Those who think that GR describes a space with a metric which determines distance and duration are very mistaken. The entire diffeomorphic symmetry of GR dictates that under all general coordinate transformations, the underlying structure is invariant. This is what makes location so slippery, because its only real matter (energy-momentum) in relation to the gravitational field (curvature) which specifies a co-location.
The particle physicists neglect the important contribution of the gravitational degrees of freedom, and they way they dominate over matter in the early universe. Inventing inflation to ensure that the matter and temperature are uniform, is wagging the dog. If the gravitational modes were active before inflation, the result would be a non-uniform mess. Penrose, as usual, points out that the fundamental problem is the extremely low entropy of the initial big bang state, which is responsible not only for the homogeneity of the cosmos, but the very arrow of time, generating all the complexity we now see after 13.6 billion years. He points out that for this to be true, right at the Big Bang, a quantity called the Weyl Tensor, (responsible for bending of starlight during an eclipse), must have been exactly zero, meaning the gravitational field was perfectly uniform. Since all matter fields are created out of the vacuum, this condition is necessary for inflation to produce a uniform state, it does not in itself solve the problem. The inflation proponents just look at this and scratch their heads, what do particle physicists understand about General Relativity?
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. This theory is Loop Quantum Gravity. It turns out that the mathematical structure of these quantum states, had been found two decades earlier by Penrose, while looking for possible quantum states of gravity. Like String Theory, LQG is not yet experimentally verifiable either, but it has been used to specify exact states of a black-hole horizon, and in the early universe to avoid an initial singularity. It does what a quantum theory of gravity, which respects GR, would be expected to do. There is much to do, but GR has always been very hard to find and understand its solutions, and any quantum version would be equally difficult. There are proposals for experiments to look at light from distant galaxies, for any sign of the granularity of space, accumulated over billions of years, which may just be detectable in the near future.
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.
αναδημοσίευση από το QUORA 7/6/2017
To call Penrose a mathematician, using a derisory tone, is a gross misrepresentation of Penrose’s areas of expertise. The correct characterisation is that Penrose is one of the few mathematical physicists who really understands General Relativity and has very credible criticisms of mostly US trained particle physicists who moved into unification and cosmology with only an undergraduate knowledge of GR. GR is far more than just a theory of gravitation, its contains deep truths about what we mean by location, and duration, and about the non-existence of coordinate location.
It is false to point at a point in space and give it any meaningful existence. The only thing meaningful is the location of fields and matter in relation to each other and in particular in relation to the gravitational field. Those who think that GR describes a space with a metric which determines distance and duration are very mistaken. The entire diffeomorphic symmetry of GR dictates that under all general coordinate transformations, the underlying structure is invariant. This is what makes location so slippery, because its only real matter (energy-momentum) in relation to the gravitational field (curvature) which specifies a co-location.
The particle physicists neglect the important contribution of the gravitational degrees of freedom, and they way they dominate over matter in the early universe. Inventing inflation to ensure that the matter and temperature are uniform, is wagging the dog. If the gravitational modes were active before inflation, the result would be a non-uniform mess. Penrose, as usual, points out that the fundamental problem is the extremely low entropy of the initial big bang state, which is responsible not only for the homogeneity of the cosmos, but the very arrow of time, generating all the complexity we now see after 13.6 billion years. He points out that for this to be true, right at the Big Bang, a quantity called the Weyl Tensor, (responsible for bending of starlight during an eclipse), must have been exactly zero, meaning the gravitational field was perfectly uniform. Since all matter fields are created out of the vacuum, this condition is necessary for inflation to produce a uniform state, it does not in itself solve the problem. The inflation proponents just look at this and scratch their heads, what do particle physicists understand about General Relativity?
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. This theory is Loop Quantum Gravity. It turns out that the mathematical structure of these quantum states, had been found two decades earlier by Penrose, while looking for possible quantum states of gravity. Like String Theory, LQG is not yet experimentally verifiable either, but it has been used to specify exact states of a black-hole horizon, and in the early universe to avoid an initial singularity. It does what a quantum theory of gravity, which respects GR, would be expected to do. There is much to do, but GR has always been very hard to find and understand its solutions, and any quantum version would be equally difficult. There are proposals for experiments to look at light from distant galaxies, for any sign of the granularity of space, accumulated over billions of years, which may just be detectable in the near future.
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.
αναδημοσίευση από το QUORA 7/6/2017
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