← Quantum Man: Richard Feynman's Life in Science (Great Discoveries)

# Quantum Man: Richard Feynman's Life in Science (Great Discoveries) - Comments

Scientific biography is an excellent way to learn science, and in that regard is a purely selfish endeavor. However, anyone who undertakes to write about *Feynman* should realize that their work will be put under the microscope.

I agreed to write a scientific biography in part because it gave me the opportunity to read all of his papers, but I had no idea of how significantly writing about Feynman's life would affect my own. -- Krauss

I have most of Feynman’s work in my own library, including out of print material, but I do not make the large claim to have read all of it. Even if one does not have the time to read *everything*, it is useful to have it on your shelf for future reference. Anyway, I found the following statement remarkable:

“Instead it is the square of the wave function that gives the probabilities. This one fact is responsible for all of the strangeness of the quantum mechanical world because it explains why particles can behave precisely as waves, as I will describe now. First, note that the probabilities for things we measure are generally positive (we would never say that there is a probability of minus 1 percent of finding something) and the square of a quantity is also always positive, so quantum mechanics predicts positive probabilities -- which is a good thing. " -- Krauss, page 53

I will not quibble that the wave function is a complex number and complex numbers when squared are not usually positive. I assume Krauss did not want to have to talk about complex numbers, and so made a simplification. But I do not take kindly to any biographer of Feynman who claims to have read all his papers and who states that probabilities cannot be negative. The fact is Feynman showed both in classical physics (the diffusion equation was the example he discussed) and quantum mechanically that probabilities can be negative.

Neither Mehra in “The Beat of a Different Drum” or Gleick in “Genius” mention Feynman's work on negative probability. In fact, Gleick quotes the mighty Dirac: “Negative probabilities are quite absurd”. So this work of Feynman is even more interesting, because we see another example of where Feynman’s understanding surpassed that of his personal hero, Dirac. The first time that happened is when Feynman figured out what the formula for quantum mechanical action was, and it was that insight, that Dirac came very close to but missed, that allowed him to discover his path integral formulation of quantum mechanics.

Permalink Sat, 12 Feb 2011 04:07:38 UTC | #591145

sorry.. but your note rubbed me the wrong way... so I am going to respond more aggressively than I might otherwise... my goal was not to show off or be pedantic.. you note I used the word 'generally' when talking about probabilities, and you also note that there was no need to mention complex numbers in the paragraph I wrote.. talking about negative probabilities would have not helped any explanation of what I wanted to convey.. so I am glad you know about negative probabilities.. As for reading all of his papers, it is fairly easy, as he didn't write that many of them..

LMK

Permalink Sat, 12 Feb 2011 05:07:35 UTC | #591156

@Comment 4 by lmkrauss ...my goal was not to show off or be pedantic...

I had assumed the goal of a biography was to capture the spirit of the man and his science, and explain his remarkable achievements. Feynman was famous for working everything out for himself, and trusting nobody. And in the negative probability paper, he even says as much -- he says he wants to look at the ‘tacit assumptions’ and see if they can be altered. And he does it! We assume probabilities cannot be negative, but he shows us we are wrong. And he does it classically and quantum mechanically. And for me at least, that is quite remarkable. So that is why I am not happy when in a book on Feynman, his achievement is not only omitted, but kind of the opposite result is implied. Yes, I fully understand that it did not have to be stated in *that* section, but I also understand it was not stated *anywhere* in the book, even in the section on Bell’s work where it could have been inserted as a side remark when negative probabilities are, once again, touched upon.

OK? You had a *whole book* to mention Feynman's very interesting work. And you didn't.

Reading Feynman's papers is easy? What is that? A joke? Just the *Selected Papers of Richard Feynman* is 992 pages. But it does not come close containing everything that he did.. If by reading, you just mean reading in a very superficial sense, and not working out and reproducing for yourself his calculations, then perhaps.

Permalink Sat, 12 Feb 2011 06:15:14 UTC | #591169

the scientific papers... that is what is important.

I do not know what section on Bell's work you are referring to.

And last, because I don't plan on getting into a protracting conversation here, the purpose of the book was to describe his significant contributions that have had a major impact upon our current understanding of nature. I chose the topics with this in mind, and the discussion you find fascinating was not one of them. It is a matter of subjective opinion I suppose, and we disagree about its significance. I hope you enjoy the rest of the book.

Permalink Sat, 12 Feb 2011 06:40:50 UTC | #591174

I am delighted to see this. Several of my friends and I had picked this book for a discussion group topic some time ago, and have been waiting for it to become available.

Lawrence, I expect you have continued the clear and flowing writing of your earlier books, so I am looking forward with keen anticipation to reading this one and adding it to my library re the great Richard Feynman.

-Q

Permalink Sat, 12 Feb 2011 06:45:16 UTC | #591176

I will definitely order this. I find Feynman a fascinating character, and I would love to know more about his ideas. I have promised myself that someday I shall actually understand what a Feynman diagram truly means, but at the very least I think they are great artistically!

I'm so glad you are writing this, Lawrence, I enjoy your clarity and enthusiasm.

Permalink Sat, 12 Feb 2011 07:38:34 UTC | #591184

Lawrence, please forgive me, but when I read this book and I will, mainly because I am such a big Feynman fan, I will probably read it with Feynman's voice in my head. I hope you won't mind? But I will not be able to help myself.

Permalink Sat, 12 Feb 2011 07:54:35 UTC | #591187

Comment 7 by lmkrauss

the scientific papers... that is what is important.

I do not know what section on Bell's work you are referring to.

Fair enough...here it is:

Feynman derived a beautiful physical example of Bell's work by showing that if one tried to mock up a classical computer that could produce the exact same probabilities that a quantum system would produce for some observable quantities as the system evolved, then the probability of some other observable quantity would need to be negative. Such negative probabilities make no physical sense. -- Quantum Man, page 281

Regarding

And last, because I don't plan on getting into a protracting conversation here, the purpose of the book was to describe his significant contributions that have had a major impact upon our current understanding of nature. I chose the topics with this in mind, and the discussion you find fascinating was not one of them.

Well, yes, it is a matter of opinion. I think extending the definition of probability to include negative numbers is mathematically interesting. Not just because he succeeded in generalizing a set of mathematical axioms, but because he did it in a way that was scientifically fruitful, and that is pretty tough to do. Also, he was able to achieve a simpler understanding of the Coulomb interaction in quantum electrodynamics by allowing virtual photons to have negative probabilities, and *that* appeals to my taste.

But, yes, I agree, the assessment of what is scientifically interesting and worth mentioning is subjective and will depend upon who you talk to and what they know, and a protracting conversation is not my intent either.

Permalink Sat, 12 Feb 2011 08:32:45 UTC | #591193

Permalink Sat, 12 Feb 2011 11:47:01 UTC | #591229

Dr. Krauss,

I haven't read your biography of Feynman yet - it's hard to get new books where I live, in rural Costa Rica, but I have read Gleick's and Mehra's. (I have also read Feynman's published papers, and most of his unpublished papers, notes, correspondence, etc, as I kept a copy of the contents of his filing cabinets in my house for 2 years, on loan from his heirs.)

I find Mehra's scientific biography, which was authorized by Feynman, and for which Feynman granted interviews, shortly before his death, to be quite good. It does not "dumb down" the science, which is, I think, what Feynman would have preferred. You write,

yet while many anecdotal biographies exist, no one had yet conveyed to the public why he is a hero to most living physicists today. I agreed to write a scientific biography...

In my opinion, Mehra did quite a good job of conveying why Feynman is a hero to most living physicists today. On the other hand, I question whether it is really possible to convey Feynman's contributions in any meaningful way to the general public, particularly in light of Feynman's response to a reporter from People magazine, who, in 1985, asked him to explain what he had shared the 1965 Nobel prize in physics for. Feynman replied, "If I could explain it to the average person, it wouldn't have been worth the Nobel Prize."

Can you compare your scientific biography to Mehra's? Would you recommend that I read your biography in light of what I have written above? More generally, is your biography written for people who can actually understand and appreciate Feynman's contributions to theoretical physics, or for people who actually can not? And if the latter, how have you "conveyed to the public why he is a hero to most living physicists today?"

Mike Gottlieb

Editor, *The Feynman Lectures on Physics*

Coauthor, *Feynman's Tips on Physics*

Permalink Sat, 12 Feb 2011 13:24:24 UTC | #591243

To bethe123 and lmkrauss, I fervently wish you *would* make this into a protracted discussion because it would be a good one! My potential career in physics and astronomy got derailed by computer programming, and while I'm no longer conversant with the details my interest in this topic has never diminished. Please continue; I am starved for these things.

Permalink Sat, 12 Feb 2011 15:56:36 UTC | #591264

THanks to all.. I have found this discussion illuminating and useful.

First, to Bethe31.. I have softened overnight.. I realized after I wrote you that I had a brief sentence or two related to Bell's work when discussing quantum computers.. (I had initially been thinking of a whole section, which I knew I hadn't written) But had I put an aside about negative probabilities as a mathematically useful formal tool in certain instances, it would have required me to make an aside of at least several pages and maybe more to adequately explain what I was talking about, and I expect this would have confused more than enlightened, but I agree that was a judgment call that is by no means indisputable.. and I do appreciate your point of view, and your taking the time to relate it.

To Mike Gottlieb: The book is certainly not written at the mathematical level of Mehra (or in fact of Schweber's book, QED..., which I found even more illuminating.. On the other hand, I believe I succeeded in conveying what I intended, and you can be the judge.. I do know that I put what I think are insights in there that professional physicists may find useful, even though it was written in the context of a popular book.. I can also say that several of my colleagues who have read it, including Bjorken, Wilczek and Rees have found it interesting and useful, which gives me confidence..

hope this helps..

Permalink Sat, 12 Feb 2011 16:41:18 UTC | #591277

Permalink Sat, 12 Feb 2011 17:15:39 UTC | #591280

I am a major Feynman fan, as much as anyone can be a 'fan' of a scientist, and so no doubt this book will be added to my reading list as soon as it is released in Ireland. I have watched and read all of Richard Feynman's various books, lectures and documentaries several times, and I credit them for inspiring me enough to leave my career in business and return to school to learn physics and enjoy the 'pleasure of finding things out'.

Permalink Sat, 12 Feb 2011 18:33:14 UTC | #591297

Comment 19 by Sample

The index is available in the preview and it looks like a lot of fun. I am looking forward to reading the book (even the four pages given to string theory).

Mike

Permalink Sat, 12 Feb 2011 19:37:54 UTC | #591308

I really like reading Feynman. I was so surprised when I heard his voice, I thought it was a Goodfellas outtake. Not in a bad way though.

Probably what we need. Science Gangsters.

Permalink Sat, 12 Feb 2011 21:35:54 UTC | #591339

Permalink Sat, 12 Feb 2011 22:15:00 UTC | #591347

I've just pre-ordered this on Amazon and I can't wait to get it! In the UK we have to wait till May though :(

Like most here - I love Feynman. I don't even remember how I got hooked on everything Feynman! It just happened.

It's funny though - as much as I admire Feynman, I can certainly see why some people found him annoying. I do share a sympathy with Gell-Man there. I believe Gell-Man can be equally obtuse too however!

Lawrence, if you enjoyed doing this biography - would you ever consider doing one on Steven Weinberg? Of course with his blessing. He's another man I find infinitely interesting and it would be great for you to interview him all you can before the inevitable.

J R

Permalink Sun, 13 Feb 2011 00:12:52 UTC | #591375

I believe I succeeded in conveying what I intended, and you can be the judge.. I do know that I put what I think are insights in there that professional physicists may find useful, even though it was written in the context of a popular book. I can also say that several of my colleagues who have read it, including Bjorken, Wilczek and Rees have found it interesting and useful, which gives me confidence.

Fair enough. I will pick up a copy at the Caltech bookstore when I make my annual visit in May.

Permalink Sun, 13 Feb 2011 01:17:11 UTC | #591393

bethe123: We assume probabilities cannot be negative, but he shows us we are wrong.

No; we are right, but with a negative probability.

Permalink Sun, 13 Feb 2011 01:52:50 UTC | #591398

I look forward to reading this . I did read his book long time ago "Who the hell do you think you are ,or something like that " the title being inspired by something his wife said ( The book is now missing from my shelf) Evidently I've loaned it to someone and not gotten it back
surprisingly so I thought ,those who loaned the book were mostly artist and not scientist .His appeal extended beyond the hard core physics .With statements like "If you think you understand Quantum Mechanics ,You don't understand Quantum Mechanics" maybe a slap in the face to a purest but a humbling expression to our humanity

It's man , we're all in it togeather

Permalink Sun, 13 Feb 2011 12:47:22 UTC | #591475

Comment 26 by Laurw

Comment 12 by bethe123 :

Feynman derived a beautiful physical example of Bell's work by showing that if one tried to mock up a classical computer that could produce the exact same probabilities that a quantum system would produce for some observable quantities as the system evolved, then the probability of some other observable quantity would need to be negative. Such negative probabilities make no physical sense. -- Quantum Man, page 281

This is *not* an example of assigning negative probability to something. It just means that he showed that the quantum computer is working in an essentially different way. It's a reductio ad absurdum, and the "absurdum" part is deriving a negative probability.

he was able to achieve a simpler understanding of the Coulomb interaction in quantum electrodynamics by allowing virtual photons to have negative probabilities, and

thatappeals to my taste.

Do physicists now routinely think of virtual photons as having negative probabilities? Whatever would this mean in terms of their quantum state?

It's not uncommon to come up with some unusual way of interpreting reality, like this. That doesn't mean it somehow IS reality.

It's like Stephen Hawking's concept of imaginary time, making spacetime locally Euclidean by multiplying time by i. Does that mean that "time is imaginary"? Or, like the idea that "there's just one electron, it zips back and forth in time and becomes a positron sometimes" (which I think came from Feynman).

If those things work as a model of reality, that's interesting. But when there are other models of reality that also work - which is true in these cases I think - the model is just a model.

I wonder, if probabilities can be negative, why can't they be >1 ? Is the probability supposed to be limited to a range between -1 and 1? That sounds strange. Or are they supposed to be somewhere inside the complex unit circle?

Permalink Sun, 13 Feb 2011 15:37:15 UTC | #591501

Two books everyone should read are "Surely You're Joking, Mr Feynman!" and "What Do You Care What Other People Think?" Both are simultaneously hilarious and serious, a wonderful combination.

Feynman's friend Ralph Leighton helped with these, and also made the trip to Tuva they were planning (because Richard wanted to visit Kyzyl, the city with no vowels), unfortunately after Feynman had died. The trip became a movie called "Genghis Blues," wherein an American throat singer entered and won some of their contests featuring that indigenous art form. If you've never heard throat singing, by all means check it out!

The Feynman Lectures on Physics were some of my textbooks in the 60s, by the way, when he was still going strong at Caltech. I was in San Diego but never went to attend any of his lectures, a regrettable lapse if there ever was one.

Permalink Sun, 13 Feb 2011 15:40:10 UTC | #591502

Comment 28 by God fearing Atheist

If a variable has a range [-1, +1] it is not a probability. A probability has a range [0,1]. If any physicist thinks it is, s/he can fuck off and find another name. :-)

Permalink Sun, 13 Feb 2011 16:20:27 UTC | #591506

Comment 29 by cepmk

For those who would like to see him at his best:

http://www.vega.org.uk/video/subseries/8

It's a total classic

Permalink Sun, 13 Feb 2011 17:34:30 UTC | #591526

@Huzonfurst My potential career in physics and astronomy got derailed by computer programming, and while I'm no longer conversant with the details my interest in this topic has never diminished.

That could be an advantage. Max Born states:

Einstein expressed over and over and again the thought that one should not couple the quest for knowledge with a bread-and-butter profession, but that research should be done as a private spare-time occupation. He himself wrote the first of his great treatises while earning his living as an employee of the Swiss Patent Office in Berne. He believed that only in this way could one preserve one’s independence. -- Max Born, The Born-Einstein Letters

I often seen remarks on this forum (usually when string theory is mentioned) that academics have the freedom to research what they want. In practice, that is not always the case.

Back to the negative probabilities…The negative probabilities seems to be generating a large number of posts so appologies to the admins and LMK if that represents a partial thread derailment. The paper can be found in the book “Quantum Implications, essays in Honor of David Bohm”…but it is possible by leveraging both Google Books and Amazon preview, to read the entirety of Feynman’s paper online. It was I believe out of print for a while, but happily is now available once again.

But had I put an aside about negative probabilities as a mathematically useful formal tool in certain instances,... -- LMK

@LMK’s categorization of the technique as ‘formal’..... I am not sure Feynman ever did anything formally as he seemed to have acquired a dislike of ceremony from his father, but the word has a few different meanings.

In algebra, one can talk about formal power series…and in that situation, you study expressions like a0x + a1x*x + … without any regard to what the x’s actually mean. You just manipulate the expressions with the “formal” rules of algebra. But the x’s are understood to be indeterminate symbols.

I’ve also seen the word “formal” used to describe the situation where a proof or derivation in mathematics was “formally” correct meaning the proof had the correct form, but it remained to actually mathematically justify each step of the derivation.

So, it is an interesting question, are negative probabilities just a formal tool in the sense that we are only formally manipulating the expressions and not caring what the symbols actually physically mean (and perhaps suspecting that the concept of negative probability is meaningless all along) because ultimately we get the correct answer? It is not a trivial question.

Einstein rejected quantum mechanics precisely because of this type of question. Perhaps the best answer to the question of the meaning of negative probabilities is to just read the paper of Feynman and let his work speak for him. *It is pretty clear he is thinking physically the whole time, not just playing mathematical games*. However, there is one remark in Feynman’s paper that should be emphasized. He states it is the simplest way of looking at the problem of the Coulomb interaction in quantum electrodynamics. And there is a long tradition in science in giving preference to simplicity. I will quote Max Born and Einstein once again:

With regard to simplicity, opinions will differ in many cases. Is Einstein’s law of gravitation simpler than Newton’s? Trained mathematicians will answer yes, meaning the logical simplicity of the foundations, while others will say emphatically no, because of the horrible complications of the formalism.

Einstein’s comment on this is simply: "The only thing which matters is the logical simplicity of the

foundations” -- Max Born, ibid, page 161

But even if you don’t agree with Feynman that in QED the simplest understanding of the Coulomb interaction is given by the method of negative probabilites, Feynman gave a reason in his Nobel lecture for why it is still useful for the idea to be understood:

Theories of the known, which are described by different physical ideas may be equivalent in all their predictions and are hence scientifically indistinguishable. However, they are not psychologically identical when trying to move from that base into the unknown. For different views suggest different kinds of modifications which might be made and hence are not equivalent in the hypotheses one generates from them in ones attempt to understand what is not yet understood. I, therefore, think that a good theoretical physicist today might find it useful to have a wide range of physical viewpoints and mathematical expressions of the same theory (for example, of quantum electrodynamics) available to him. This may be asking too much of one man. Then new students should as a class have this. If every individual student follows the same current fashion in expressing and thinking about electrodynamics or field theory, then the variety of hypotheses being generated to understand strong interactions, say, is limited. Perhaps rightly so, for possibly the chance is high that the truth lies in the fashionable direction. But, on the off-chance that it is in another direction - a direction obvious from an unfashionable view of field theory - who will find it? Only someone who has sacrificed himself by teaching himself quantum electrodynamics from a peculiar and unusual point of view; one that he may have to invent for himself. I say sacrificed himself because he most likely will get nothing from it, because the truth may lie in another direction, perhaps even the fashionable one.

But, if my own experience is any guide, the sacrifice is really not great because if the peculiar viewpoint taken is truly experimentally equivalent to the usual in the realm of the known there is always a range of applications and problems in this realm for which the special viewpoint gives one a special power and clarity of thought, which is valuable in itself. Furthermore, in the search for new laws, you always have the psychological excitement of feeling that possible nobody has yet thought of the crazy possibility you are looking at right now. -- Feynman, Nobel Lecture

Permalink Sun, 13 Feb 2011 18:14:20 UTC | #591527

Comment 1 by Zelig

Feynman's directness, clarity and honesty always impressed me greatly, as did his apparent affirmative spirit. I look forward to reading the book.

Permalink Sat, 12 Feb 2011 00:33:42 UTC | #591112