## Wednesday, July 23, 2014 ... //

### An interesting interview with Dirac

A few days ago, we talked about Wigner's friend. But who was he?

Edwin Steiner told us about a remarkable interview with Paul Dirac that was done by one of Dirac's few friends (and brothers-in-law), Eugene Wigner, and by Thomas "paradigm shift" Kuhn:

Interview with P. A. M. Dirac By Thomas S. Kuhn and Eugene Paul Wigner At Wigner’s home, Princeton, New Jersey April 1, l962
Spoilers

Dirac talks about the absence of any social life during his childhood. He lived with his parents in an isolated house. The parents didn't sleep with each other and didn't even eat with each other. He could only talk to his father in French. He had one younger and one older sibling. One of them committed suicide at age of 24.

Concerning mathematics and physics, we learn that Dirac has had almost no exposure to algebra – although his greatest contributions to physics seem to be all about algebra. He would notice the quaternions but he was an autodidact in all these matters.

When it comes to calculus and differential equations, among other things, he would be affected by his training in engineering. You know, books on engineering want to get the right results and ignore rigor as long as one may reliably learn to do the important things correctly.

Dirac would soon adopt this pragmatic attitude – and he also began to appreciate all approximate theories – although his natural inclination would be very rigorous ("only exact, rigorous insights matter"), of course. I must say that my built-in attitudes as well as experiences had been virtually identical. My natural desire would be to care about rigorous exact insights only but due to the random features of the environment, I would actually be influenced by lots of practical and pragmatic books (maybe my father's manual/practical orientation helped as well). For example, I first learned about Taylor expansions, Fourier expansions, as well as the matrix multiplication from a book dedicated to engineers.

(It was a bit surprising that even non-smooth functions admitted Fourier expansions which are composed of smooth sines and cosines; it was strange to hear that the inner and matrix products based on simple products of entries in table were "fundamental" in any sense, and so on. But of course that I would understand the validity and depth of all these things rather soon afterwards.)

The interview covers lots of the social circumstances, the effect of the First World War, Dirac's move from Bristol to Cambridge etc. At some point, he starts to study the Bohr theory of the atom. Heisenberg visits Cambridge, too.

He also says that in the Continental Europe, Heisenberg's paper would be viewed as a minor improvement of the Bohr-Sommerfeld quantization conditions etc. The fact that it was a revolution wasn't appreciated. It's doubly remarkable given the fact that even now, 90 years later, many people – including professionals (in the sense of being paid for physics, not in the sense of being truly competent experts) – still have a trouble with the new picture of the world that Heisenberg, Dirac, and others would discover in the 1920s.

BTW quarks are celebrating 50th birthday these days. Congratulations to Murray Gell-Mann, too.

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Quarks were necessary when Otto Stern received his 1944 Nobel Prize for observing the Dirac equation failed - big time - for calculating proton magnetic moment. The proton was thus a composite particle. 70th birthday.

Was Dirac's equation the first step on the way to quantum field theory?

Don't forget there are 5(!) sessions of the interview, linked at the bottom of each transcript

As you probably know the historic roots of quantum theory are Planck's derivation of the black body spectrum and Einstein's analysis of the photo effect. So the need to quantize the electromagnetic field must have been clear already when quantum mechanics was first established. But Dirac's equation and the theoretical and experimental establishment of positrons was clearly a very important step.

The very first step was his 1927 work on the quantization of the electromagnetic field.

You may want to download a copy of "The Strangest Man: The Hidden Life of Paul Dirac, Mystic of the Atom" , 2009. It's a good read and seems to include much of the information from the transcript.

Somewhat OT, Cynthia, but I think I am preaching to the choir--
https://firstlook.org/theintercept/article/2014/07/23/blacklisted/

Slightly off subject: Some years before he died, Dirac gave
one of his rare interviews. In it, at some point he rather casually
reflected that lately he'd begun to suspect that Einstein may
have been right all along. He did not elaborate, at least as
far as that interviewer was concerned. I've wondered since
then, was Dirac referring to the famous Einstein-Bohr debate
about the completeness of QM? Does anyone know?

A great book definitely. A good summary (54 min) is made by the author, Graham Farmelo, at this conference, also very recommendable:

-- very interesting indeed and makes perfect sense. Thanks!

Which left-wing interventionists are you referring to?

Cockpit shows clear evidence od Su-25 machine gun fire entering and leaving from two sides. It was taken down by fighter jets coming upfrom below it and aiming directly at the pilots so they would have no time to radio anything in. Where is the autopsy report of the Pilots? Where is the official ATC transcripts?

Is this claim about "clear evidence" yours, and are you an expert in these guns? Or what are your sources?

What you write sounds pretty important although I've seen similar claims before.

Wiki says the SU-25 has a "service ceiling" of 23,000 ft. Maybe it can get a lot higher and be effective at 33,000 ft. I wouldn't know.

But anyone could have plugged the debris with extra bullet holes on the ground.

I doubt any of the evidence can be guaranteed clean now.

That's quite a performance given that the SU-25 has a service ceiling of 23000 feet and a top speed of Mach 0.82. And the cockpit isn't pressurized.

A few weeks ago there was a similar rubbish claim that MH17 was shot down by an Aphid air to air missile fired from an SU-25. On the same day a Wikipedia editor with a Russian address was found trying to insert a 33,000 foot ceiling on the SU-25 page. Check the page history on 21 July.

Haha! Nothing surprises me. :)

All sides involved have been caught with their pants down. Agendas and misinformation abound. I don't believe ANY source outright, and especially not our government or media.

However, I still think the odds-on favourite is that the pro-Russians did it with a captured BUK but that it was also either an outright cock-up or there may have been some deliberate misdirection/gaming by Kiev intended to induce such a cock-up for propaganda purposes.

I very much doubt the Russian military themselves were directly involved but, again, it wouldn't surprise me if they, or some 'freelance' Russian enthusiast, tried to 'twist the wrist' and get the finger to point at Kiev, as your Wiki story would tend to indicate.

Who knows? I don't.

Even our WWII Spitfire had a "service ceiling" of 36,500 ft (spurious 3-digit precision?) apparently but (wild guess coming) I doubt that it had a pressurised cockpit, rather only an oxygen mask for the pilot.

So perhaps the much lower ceiling of the SU-25 has more to do with the capabilities of it's engine at various altitudes and the role the aircraft was designed for (ground attack mostly, I think)?

But without some expertise (and I don't have any) it's hard to know whether the SU-25, or some variant, could climb to 33,000 ft for a quick-burst intercept. Maybe it's speed at that height though wouldn't be enough to intercept the airliner, even with a favourably placed intercept path. Again, I don't know. It seems unlikely though. Also angle of attack for taking out the cockpit? Approaching and firing from underneath might risk failure since bulkheads and stuff might protect the crew. A head on attack at a closing speed of, say, ~1,000 mph? The pilot would have to be a bloody good shot. Doesn't feel plausible to me. Even an attack at roughly 90 degrees would have a closing speed of ~700 mph in a last-second turn. Again, it feels implausible. So to some extent it would have to be from either sideways-behind and/or above-behind. But then there's that bulkhead-etc problem again. So, FWIW and what I've read, like you I doubt an SU-25 shot up the cockpit.

There are a lot of armchair experts offering their opinions on blogs but I haven't come across any killer points.

First Investigators on the scene : https://t.co/8L93CoIiFE

The Su-25's didn't have to climb to the same level to shoot from below. Also eyewitnesses saw two Su-25's trailing MH17

Show me the black box and the ATC transcripts