Hawking, Whitten, Schwarz & String Theory
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NEXT THING WILL BE THE ROUND TABLE DISCUSSION WHICH WILL BE SYNCH SOUND.
HOW DOES ORDER ARISE IN THE UNIVERSE? IF THE UNIVERSE IS SELF CONSISTENT HOW DOES ORDER GET IN THE UNIVERSE, NOT TALKING ABOUT ENTROPY BUT TALKING ABOUT PHYSICAL LAW. HOW DOES IT GET INTO THE UNIVERSE. AND WHAT ARE YOU GUYS DOING THAT'S GOING TO CHANGE THIS?
(Hawking and interpreter) Well there are two parts to this graph. One is - one is the set of laws that govern the evolution of the universe. And the other is the question of how the universe started out.
(Hawking and interpeter) Wait a minute now reverse ..... Now Green and Whitten have proposed a new set of laws - which would govern the - which are based on the idea - that everything is made up - not of point particles - but of strings. Now Steven would like to ask them - so now Steven would like to ask why they should be - why it should be strings and not something else like membranes, or three dimensional objects. So would you like to comment on why there are strings and not membranes in three dimensional objects.
I'd rather - the first comment why it should be strings rather than points, and then we could try to talk about why it wouldn't be something more complicated yet. The real problem it seems to me is to try to construct a consistent mathematical formulaism that describes gravity in a way that's consistent with the requirements of the quantum theory. And as you're certainly well aware when you try to do this in the framework of point-like particles, you run into the problem of getting infinities in quantum calculations. It's my - it's been shown in many different calculations and it's my impression that it's true in general that it's impossible to make a theory based on point particles in which - in which gravity can be reconciled with the quantum theory. On the other hand when we go to make a theory starting from strings - one dimensional extended objects rather than point particles, we find that in fact gravity is required rather than forbidden in the theory. And furthermore, apparently as far as we've been able to test so far, these infinities which would make the theory inconsistent, do not occur. Now when one tries to do other things more complicated in the strings, we're not sure whether it's possible or not. My guess is that there aren't any consistent quantum theories at all for objects of more than one dimension. That's very difficult to prove because the more complicated the system you consider the harder it is to prove that it doesn't work. But that would be my guess. I'm sure Ed could add to that.
GO AHEAD ED. WE'LL JUST PICK IT UP.
Well actually pragmatically the answer is that string theory works and membrane theory would have the same troubles as quantum gravity. The free membrane is an un-normalizable theory and if you try to do membrane theory you would need string theory to make sense out of membranes. But let me try to address the question briefly on another level. When Kurshee started talking about complex numbers, people must have asked him why he built a complex number out of two real numbers instead of three. And I don't mean the analogy is just tongue in cheek because the string will ..... - is in fact a remon surface and that's becoming increasingly important in the course of time as deeper properties enter. And there is probably a connection.
(Hawking and interpreter)> You're claiming that the universe - is really made up of two dimensional objects. But it is just - but it is just that it looks like that it is four dimensional. - But that space is really a two dimensional object.
Well actually at a deep level I think we don't know what super streams mean. But at the level we know of it perhaps you'd say that space is a ten dimensional object which is apparently four dimensional because of compactification.
(Hawking and interpreter) But why should it compactify to four dimensions? Steven thinks that's probably the weakest point in the string theory. That the dimensional change is - that people have not shown - that people have not shown that the ten dimensional space - will look like four dimensional space.
Allow me to suggest that this is a discussion we should have but maybe not on this camera. I think we should maybe get back to Steven's views about physics and whatever he wants - I mean I'm happy - if you really want (overlapping) > I'M SURE IT'S A VERY INTERESTING DISCUSSION FOR YOU PEOPLE TO HAVE, NOT FOR ME PARTICULARLY TO FILM. IT'S A LITTLE BIT TOO BEYOND ME ......... AND WHAT I WAS GOING TO SUGGEST IS THAT SUPER STRINGS IS GOING TO - AND IT SEEMS FROM EVERYBODY AROUND THAT -
- PHILOSOPHICALLY SPEAKING. THAT MIGHT BE A GOOD ONE TO HANDLE. WHERE DOES GOD COME IN? IF WE HAVE A UNIFIED FIELD THEORY WHERE DOES GOD COME IN? THAT'S ONE OF THE QUESTIONS THAT PEOPLE ARE GOING TO BE ASKING.
It seems to me that strings make a lot of difference to this, because you can ask at any epoch in physics -
HANG ON ONE SEC.
I don't think the advent of strings really changes this question.
........... less hypothetical.
(overlap, laughter) >> I think it's been faced in all its details many times before.
IS THAT RIGHT? LET'S TALK ABOUT THAT.
After 1926 we had a theory which governs all terrestial form and so the questions we like to ask which we think are philosophical about people were essentially answerable, or are answerable in principle than are answerable in practice, because it's too difficult. So I think if you're going to ask is there a big philosophical impact of this particular final step, if it is a final step, it's difficult to see that there are questions which you would raise or would answer which are different from those which have been faced up to before. One can go even further back. I mean once you have the impression that those are a set of physical laws which govern the universe and you exclude other reasoning then you face these problems. And they were faced many years ago by philosophers and scientists. I don't think strings make a big difference in that regard.
LET'S TALK A LITTLE BIT ABOUT STEVEN'S THEORY THEN. STEVEN'S PROPOSAL IS SUCH THAT IF HE'S RIGHT THE UNIVERSE SEEMS TO BE SELF-CONTAINED, THAT THERE CANNOT BE ANYTHING EXTERNAL TO THE UNIVERSE TO HAVE CAUSED IT.
Do you want to comment on that or - (Hawking and interpeter) - I'm sorry ...... - Presumably you would - presumably you can say that the universe? - Presumably you can say that the universe is self-contained - even if - what was right? - Even if string theory was right? - I mean presumably you can say that universe was self-contained even if string theory were right. In fact, if you confine yourself to closed - to closed loops then - then the whole universe is really what? - is really made up of - is really made up of closed two surfaces. Even in string theory - the universe would be - would be self-contained. It would not have any - it would not have any outside cause.
Do you believe that the universe is closed, Steven?
(Hawking and interpreter) Yes I believe it is - compact? - You think it is very - I'm sorry. I think it's very - well I'm still - oh a very attractive idea that it is closed. But Steven is not sure whether it is right. But it would certainly - it would certainly do what if it was? - It would help the situation? - Oh it would answer the question? - But it would answer the question if it were.
It would answer which question?
(Hawking and interpreter) It would answer a lot of questions.
But I mean isn't the - well I'm speaking for myself and not Steven now - but I mean that's sort of the question of whether space is like a sheet with an edge to it or whether it's more like a ball or something - well or take the surface of this eraser which has no edge to it. But that still doesn't answer the question as to whether some outside god - some outside cause or example - a god-created - could create it with an edge or without an edge.
Well since modern cosmology was developed, it's generally been believed that life can't go on forever because the world will end by ice or by fire as it's sometimes expressed - by ice in an open universe or by fire in a closed universe. But Freeman Dison argued a few years ago that in fact if the universe is open it's conceivable that life and civilization can continue to evolve and grow and develop indefinitely adapting in time to the colder and colder and more and more dilute conditions. I think it's at least an intriguing idea.
It's not clear it doesn't work ......
- Freeman at least considers it perfectly conceivable. When Freeman Dyson - when Freeman Dyson originally discussed the question of life in the expanding universe, assuming that the universe is open and will get colder and colder in time, he assumed that the proton was stable. And people have asked what will happen to life if all the protons decay but Dyson at least claims that it's conceivable that you can make living organisms and even civilizations out of an electron positron plasma. Or for all we know maybe a magnetic monopole anti-monopole plasma. Maybe monopoles are the most conspicuous component of the universe in the far future when everything else is diluted away.
(Hawking and interpeter) But if you have monopoles - and anti? - if you have monopoles and anti-monopoles wouldn't they annihilate? And then you would be left with nothing, with just radiation. And it's difficult to build life out of radiation.
The tendency for the monopoles to annihilate were the electron positron pairs isn't as severe as the expansionof the universe. The expansion of the universe is the main thing that makes it get more diluted and colder.
Yes I mean it - I mean some calculations I did indicate that it's true the number of per co moving volume decreases but if you allow yourself to have bigger and bigger volumes there's always - there's always enough left that you have more energy in monopoles than you do in radiation. But whether you can make life out of those things I don't quite know.
THAT'S A VERY SPECULATIVE DISCUSSION. DOESN'T IT APPEAR IN NATURE THAT MOST THINGS CYCLE? IS NOT THE IDEA OF A UNIVERSE THAT EXPANDS AND THEN CONTRACTS INTO A BIG CRUNCH, OR STEVEN'S EQUIVALENT OF THE BIG CRUNCH A FAR MORE SATISFACTORY INTUITIVE EXPLANATION?
(Hawking and interpreter) We don't have any evidence that the universe - we don't have any evidence that the universe would recycle. As far as we know? - As far as we know there's only one big bang. And we do not know whether or not it will expand forever - or whether it will re-collapse. Personally Steven thinks it is -that it's probably just on the -
THIS IS SOUND ROLL 15-16. IT HAS NOT BEEN TRANSMITTED PREVIOUSLY.
That was just because there wasn't a normalizable wave function, right?
Well I basically was ....
But wait a minute, it was a classical system which positively had a positive lam or zero lam?
It was zero lam on the limit when the fields become zero. I mean we - so in other words, right, we assume that empty space didn't gravitate or anti-gravitate. We assumed empty space could be flat.
That was just because there wasn't a normalizable wave function, right?
Well I basically was ....
But wait a minute it was a classical system which had a positive lam or a zero lam?
It was zero lam on the limit when the fields becomes zero. So in other words, right, we assume that empty space didn't gravitate or anti-gravitate. We assume empty space could be flat.
Oh, I see.
But then you're saying that particular regions behaved ...... to fluctuations, is that right?
No not the lam.
(Hawking and interpreter) - regions would behave - some regions would behave like K equals plus 1 universes. And they would re-collapse. But other regions - other regions would have lower density and they would expand forever.
CAN I ASK A QUESTION AND I THINK IT REALLY GOES BACK TO THE BEGINNING THING I ASKED AND IT SHOULD BE THE END OF THE DISCUSSION. WE SHOULD BE ABLE TO SUM EVERYTHING UP HERE. WHY IS THERE ANY PHYSICAL LAW AT ALL? WHY IS NOT THE UNIVERSE TOTALLY CHAOTIC? CAN PHYSICS EVER ANSWER THAT QUESTION? YOU OUGHT TO TALK.
I'm always stunned how successful mathematics has proved to be in the description of physical law.
I don't know why it should be but it's been uncanny really the way mathematics starting with Newton and Maxwell and Goyonda, Einstein and the development of quantum mechanics, the very sophisticated mathematics has proved to be really useful in getting a fundamental understanding of nature. It's a total mystery to me why that should be. But it continues to work and as we try to develop new ideas we seem to continue to have successes at achieving understandings of physical law in mathematical language. It's very remarkable.
(Hawking and interpreter) - I'm sorry ... - but in a sense? - But in a sense - ...... - one basic thing is? - one expected it? - But in a sense - But in a sense the uncertainty principle - is a - he's telling us - he's telling us that the universe does behave in an arbitrary fashion - in a completely unpredictable way. I suppose that we? - to any particular .....? - to intelligent, no ...... - behave in an unpredictable way to something? - to a certain degree? - Yes so in a sense the uncertainty principle is telling us that the universe is behaving in a completely chaotic way to a certain degree. - So one might say - that that was the intervention? - So one might say that that was the intervention of God. But it would be a rather strange kind of God. Because he would be acting in a completely random way.
ONE OF YOU GUYS HAVE TO RESPOND TO THAT.
AUDIO ROLL 15, FILM ROLL 20. AT THIS POINT FILM ROLL 21. THIS IS A RAOUND TABLE DISCUSSION ON JUNE 24th, HAWKING DOC FOR MAN ALIVE.
- Well if the rule is that the rules keep changing every half an hour that is itself a rule. So to really get rules that can't be deciphered you need sort of a sequence of meta rules where each rule is taken from a new dictionary that didn't include the last one.
... go on choosing it .....
.... impossible rules have been excluded experimentally - all these so-called hidden variable theories in which we try to explain the randomness of quantum mechanics in terms of some fully deterministic underlying principle. And there are very definite predictions of that class of theoretical ideas and these have been excluded by careful experiments.
Well, I think that the randomness of quantum mechanics is really a mismatch between quantum mechanics and us. Because we try to -
CAN I GET YOU TO REPEAT THAT WHEN THE CAMERA IS ROLLING?
We think that quantum mechanics isn't deterministic because we tried many positions ...... particles while quantum mechanics tells us about time dependence of wave functions. In its own terms quantum mechanics is deterministic. But there's a mismatch between quantum mechanics and us which makes us think of it as being undeterministic. It's deterministic in its own terms but it doesn't determine deterministically the things that we would like it to determine.
Is that a bit like if you had a die, then quantum mechanics would predict all of the different set of dots but it wouldn't tell you which side has the 1 on it and which side has the 2 on it. I mean it's as if in some sense it determines the whole set of possibilities in a deterministics way but it doesn't tell you which one you yourself are measuring. Is that a fair summary or is that -
It wasn't quite what I meant to say.
(Hawking and interpreter) So Steven is asking Ed, what do you mean?
Well quantum mechanics determines the time dependence of wave functions. Now we would have determined time dependence of positions and velocities. And since it doesn't determine what we think it should have, we complain about that and accuse quantum mechanics as being undeterministic. A quantum mechanical observer would probably just say that it's our mental limitations that we think about positions and velocities rather than wave functions. It's as if we think nature should play dice with cubic dice and nature has chosen in a sense to use an octahedral device, so we interpret it by claiming that quantum mechanics is undeterministics.
In quantum mechanics the questions that you are unable to ask are not reasonable questions. All reasonable questions are answered as well as they can be.
(Hawking and interpreter) - something is .....? - quantum mechanics is deterministic? - If we thought the universe .... - the point is that quantum mechanics? - the point is that quantum mechanics in terms of .... the universe. - Okay the point is that quantum mechanics determines less about the universe than we thought that we could determine. - Sorry, one could? - Is that what you were saying?
No but he's putting quantum mechanics first and us second. And his point is that the question is posed ah in terms which put us first and quantum mechanics second. And that's the wrong way of doing it because quantum mechanics is the reality - the fundamental underlying reality. I think that's what he was saying, isn't it?
(Hawking and interpreter)> Oh yes, it's just that - just that we were under the allusion -oh yes, it's just that we were under the allusion that we should be able to determine more about the universe - than quantum mechanics would allow. - Is that what you were saying?
.... more about different things. A quantum description of a single point particle has an infinite number of degrees of freedom. The wave function, amplitude and phase at every point - so you can determine in a sense more about a quantum particle than a beta classical particle, but they're different things. See, do you think of the observer as part of the quantum mechanical system?
(Hawking and interpeter) Well yes. - If you apply quantum mechanics to the whole universe that would include the observers.
My view is roughly that when you do quantum mechanics of the whole universe, it's deterministic.
(Hawking and interpreter) - Yes, within the framework of quantum mechanics but not within the framework of classical mechanics. Yes, because I mean if I interpret it right and you can correct me that the wave function that Steven Hawking has proposed can be viewed in some sense as a collection of classical universes, a collection of universes in which stars and planets and people have fairly definite positions. But it doesn't just predict one, it predicts a whole ensemble of these - of these universes. And there might be different observers in each one of these - of this set of different universes. And so the whole set would be predicted deterministically, but then if you ask about any individual member you would not be able to predict what that individual member would - what would happen to that individual member if you isolated it from the rest. Is that - I don't know - is that a - would that agree with your view or -
Well it's (inaudible)
SIR, WHAT DID YOU SAY?
I've already expressed my view about the question, so it - (laughter) - we weren't supposed to ...... that.
IT SEEMS TO ME THAT YOU'VE RAISED A FUNDAMENTAL POINT. I THINK WHAT MODERN PHYSICS HAS DONE IS INTRODUCED THE IDEA OF OBSERVER INTO THE BASIC SET OF IDEAS ABOUT THE UNIVERSE WHICH CLASSICAL PHYSICS DIDN'T REALLY DO. AND THIS SEEMS TO ME TO BE AN IMPORTANT QUANTUM LEAP IN CLASSICAL PHYSICS.
When one is taught about quantum mechanics at school, you learn to think about it in terms of discussing some system which is described in quantum mechanical language but you as an observer are treated classically and make classical observations on this quantum system and deduce the rules of how it operates. Now when you want to try to extend this description to the entire universe you're no longer in a position where you can treat the observer as an outside entity since there are, as far as we know, no outside observers to the universe, or at least none that are of any use to us. And so you run into really difficult philosophical questions when you try to deal with the quantum mechanics of the universe. I'm very impressed by Steven's attempts to do this and ah I think they're interesting and may well turn out to be very fruitful in their implications. But I have difficulty really grasping what's involved in the idea of the quantum mechanics of the universe or the quantum wave function of the universe.
In some sense it's very - if you try to put the observer in it's very hard to avoid this picture that somehow the wave function includes a whole set of many different observers and many different classical universes. And of course I suppose most physicists find that very hard to swallow because it seems to be multiplying entities. I mean this view was proposed by John Weelder's student, Everett, and has been known as the 'man worlds' interpretation. And most of us think that it introduces a lot of extra things into physics that you don't really need - in other words other branches of the universe which are completely unobservable. And therefore they think it has a lot of metaphysical baggage. I guess I personally think it's simpler because then you - you can keep the whole equations of quantum mechanics and you have a deterministics theory for the wave function, as Ed Whitton was saying. Or you do not have a deterministic theory that tells exactly what each little piece is going to do but the whole - all the individual pieces fit together in a coherent way so that the whole seems to be simpler than each of the parts.
It's a little like democracy. You might not like the many worlds interpretation but all the alternatives seem to be much worse.
(laughter) YOU WERE GOING TO SAY SOMETHING A LITTLE BEFORE.
Well I also was interested in Steven's opinion on the question of whether the concept of quantum mechanic ineptitudes? as we know it is fundamental or is it just an approximation to the truth?
(Hawking and interpreter) Well, there may be some other theory - which doesn't .... - oh, there may be some other theory which transcends quantum mechanics - but we don't know what it is. - So since we don't know what it is, at the moment Steven is prepared to stick with quantum mechanics.
Tio was suggesting a few days ago an idea which I thought was interesting - that a really good theory shouldn't exist as a classical theory. The separation that first you find a theory and then you quantitize it shouldn't exist if you really found the true theory of the world. And you'd know that theory because the structures would only exist naturally in the quantum framework.
(Hawking and interpreter) Steven says he thinks it is true that the quantum theory comes first. - But then you can obtain a classical theory from it. - Yes, that the quantum theory comes first but you can obtain a classical theory which is an approximation to the quantum theory.
.... classical .... typical as a classical theory? I mean that seems to me a rather admirable theory from the point of view of Tio's comments. It is rather strange classically.
(Hawking and interpreter) - ..... do not make - sorry - do not make sense in the classical theory. - .......... - the basic idea? - They make sense only as point particles. - They make sense only as point particles and not as classical fields.
.... OUT OF FILM .......
So Ed you more or less go along with the ..... many worlds view or -
Ed is not going to say.
Well I don't really know. I do believe that ah like I said, I think that the claim that quantum mechanics isn't deterministic is our own limitation.
BUT DOES THAT TELL US ANYTHING?
Well we already know that quantum mechanics is smarter than we are so that's ........ (laughter)
It's not smarter than we are. It just behaves a little bit more erratically.
Anyone who's looked at the way physical phenomena work in quantum mechanics has observed that quantum mechanics is smarter than any physicist.
That seems to be an inherent lack of quality of the model.
OKAY THANK YOU ALL. I SHALL TRY DESPERATELY NOT TO DESTROY YOUR RESPECTIVE ACADEMIC REPUTATIONS WHEN I EDIT THIS.