Roger Penrose - What Does Quantum Theory Mean?

Roger one of the hot areas is the foundations of quantum theory what does it really mean when you dig down beneath it we know of the conflict between quantum mechanics with a very small and general relativity of the entire universe but from your perspective which has been rather unique in in both mathematical physics and cosmology what do you feel about the fundamentals of quantum theory well I certainly think that quantum mechanics what modern images would work very well at a small level where I mean small mass displacements but it is a sort of average where others as the limit of a more correct theory which applies at all levels when the mass displacement gets small now why I think there will be a deviation all sorts of reasons one is that we don't see a lot of cat superpowers and things like that but more specifically there are conflicts with general relativity now you can phrase this in different ways but the way which I think is most powerful in the sense or not quite the easiest to work out in detail has to do with a conflict between the superposition principle of quantum mechanics which says you know if a happens when the P can happen then superposition of NB happened to where they both concur could coexist now imagine an experiment on a tabletop where you're doing a quantum mechanical experiment and you want to take into consideration the gravitational field of the earth now there two ways you might do this one is simply the ordinary Newtonian where you say well as a force you put that in what's called the Hamiltonian in the quantum in the Schrodinger equation and you just treat it as like any other force that's fine it works but that's not on Stein's view our science view is that the gravitational field of the earth is really equivalent to an acceleration so it goes back to Galileo Einstein made it into a fundamental principle which is the real basis yes the equivalence principle the real basis of general relativity so he says no the acceleration of the earth you by allowing your frame of reference to fall freely there's no gravitational field you do your quantum mechanics all over again transform back to the stationary frame and you get almost the same answer the answer differs by your wavefunction differing by what's called a phase factor now that's a mathematical term but it means normally you say if it's only a phase factor we don't care its equivalent and in fact it would be equivalent if you just had one gravitational field but if you look carefully at that phase factor you see it involves the time cubed now the reason why that's an issue is that it tells you that you're dealing with two different vacuole now that's a funny idea which needs some explanation but it's the thing that people worry about in quantum mechanics quantum field theory primarily where you have to worry about what the vacuum state is and it leads to all sorts of issues which I don't really want to go into here but you do have two different vacuums now it doesn't matter if you're just having one gravitational field you just don't care about the different thank you but if you have a superposition of two gravitational fields it's different because suppose you had as part of your experiment a lump in one location which could be superposed with it being in another location now its gravitational field will have to be taken into consideration but when you look at the gravitational field one love compare it with the other you've got a different vacuum now different vacua are illegal it's illegal to make super positions with different packet that's one of the rules of quantum view theory so you're not allowed to make these super positions so it's telling you know you're stuck but I don't think we're stuck we've got to do something but so you then look and say well when is this different vacuum issues going to make itself felt probably not for a while and you're going to make an estimate how long it would take before this vacuum difference of that cream is going to actually make a difference and I take this to be a measure of the reduction stage so you've got the lump over here and the lump over here to have them coexist in that superposition forever would land you in this vacuum problem so it only lasts well that is certainly at the time and you can work that time out from Heisenberg's time energy uncertainty principle is a good estimate so you say well after a certainly at the time it will become one or the other and then you're out of trouble now that means fiddling with the rules a bit but you've got a fiddle with the rules anyway either you're completely stuck what you do or you say no I'm not completely stuck because I'm only allowing a superposition to last for a length of time which just before it's going to cause me trouble now most people though would privilege quantum mechanics over general relativity and say if we have to make a change which we do we're gonna have to deal with quantity quantized gravity or something we could have to change general relativity yeah because quantum mechanics is more fundamental do you agree with that I agree that most people would say I think that I think it's true that most people says I don't agree with the argument it's true that general relativity only really starts to come into its own for a large system sure but it really does when you take notes black holes and galactic our own galaxy has a black hole which is about four million times the mass of the Sun and it works well general relativity people say there's no known contradiction between quantum mechanics and observed fact there's no non non contradiction between general relativity and observed fact when you take into account what people refer to as dark energy I don't like the term Einsteins cosmological constant land which he introduced were admittedly the wrong reasons in 1917 but it's being there in his equations and in all the cosmology books ever up till now now he's wonderful observations that were made at the end of the last century which do seem to indicate that that term is there ok put it in now we don't have any known conflict between general relativity and observed facts so it's one or the other well I say it's not really one or the other it's a even-handed marriage between one on the other people usually say no quantum mechanics has to be fundamental whatever TR does you've got to fit in with quantum mechanics I think that's unfair and also maybe it's my bias because I've grown up with general affinity but the principles of general relativity are really very powerful and they've produced quite unexpected things most particularly black holes which don't occur in Newtonian not it's only not the kind of things you get out of constants theory so you look for the harmony to be either a marriage between the two a marriage of equals or maybe some fundamental theory sitting below both of them well I would think of that yes it's got to be given both sides which is really a new fundamental theory taking principles from both motive modifying those principles where needed so yeah I expect a change in both theories but in a sense maybe more of a change on the quantum side partly because one of this is a different topic but one of the things I've been working on recently has to do with cosmology and there I have a different view but from what I used to have so it's a different view from the view that here the Big Bang is a place where quantum gravity you know it rules you see so one of the big reasons for studying quantum gravity is to understand the Big Bang the current scheme that I have now is some reason we can get away with classical physics it's not quantum gravity quantum gravity may come in black holes in there singularities yes sure it may come in and very delicate experiments of tiny distances yes sure but when it comes to the Big Bang it seems that we get away with classical physics now that's an outrageous thing to say but but that's what I believe now yes

Channel: Closer To Truth

Views: 167,582

Keywords: Roger Penrose (Academic), Quantum Mechanics (Field Of Study), Closer To Truth (TV Program), Physics (Field Of Study), Time, Cosmology (Field Of Study), Quantum Field Theory (Field Of Study), quantum, science, cosmos, space, education

Id: n9T2DA4k9Dc

Length: 8min 48sec (528 seconds)

Published: Tue Jul 28 2015