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Peter Phillips
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Peter Phillips

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Random reading part 2 - probably the most comprehensible introduction to quantum field theory I've found so far. I got a vague understanding of how a "quantum field' is built up from scratch. This reading was inspired by the statement "Particle physics isn't about particles".

I learned that many of the "quantum" properties of the field fall out of the math/analysis.  e.g. spin, anti-particles (relativity required), fermion/boson, even the resulting 'forces' caused by the field (including when attracting/repulsing). (It does depend on the starter ingredients: e.g. scalar, complex, 4-vector and deciding if you'll include special relativity or not). (And picking the Langrangian, also)

What I didn't learn (thanks to my advanced gloss-over--90%-details reading) is exactly how quantization happens.  Yeah, sure, you can throw together a matter field, couple with "electric" field, and maybe you need to throw in the mass of electron as a parameter (or Higgs-ify it). But why do you end up with only one electron mass?  (Or charge)?

As for it "not being about particles"--the shortest answer, is (duh), QFT is about the field. The next shortest answer is...hard to explain. The "particles" as such are created/destroyed by applying operators to the field. But what is created is kind of like a vibrational mode and might be localized in space, diffuse in momentum or vice-versa.  The operators are analogous to usual operations (addition, multiplication) but operate on an infinite-dimension Hilbert space.  So...a bit more complicated.

This leads to statements like "Well, we can define a particle-counting operator which counts the 'particle' eigenstates and then show it is properly Lorentz (observer) invariant, so, there's your particles."

It's actually exciting.  Although the exploration of field theory requires heavy-duty particle accelerators, the math can can also be used in condensed matter. This could lead to some seriously awesome nanoscale devices, one day.

Disclaimer: my statements are only as accurate as 90% skimming will allow.

http://www.damtp.cam.ac.uk/user/tong/qft.html
A Cambridge University course with lecture notes, covering the canonical quantization of scalar fields, Dirac fields and QED.
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Peter Phillips

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If you don't like my driving, get off the sidewalk!
These young people are trying to shame Russia's assholes by plastering their windshields with massive stickers that say, "I Spit On Everybody, I Drive/Park However I Want."
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Dear Microsoft and Oracle,

Please start work immediately on C#/Java to C++14 translators.
It isn't too late to start undoing the wreckage.

-- Peter
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So, does a beam of electrons (in a vacuum) produce a magnet field just a a wire carrying current?  My guess is, yes, although the electric field will be a lot larger.

If so, what does that mean for Einstein's demonstration that the magnetic field (from a wire) is the result of a difference in electron/proton charge density caused by Lorentz contraction? I imagine I'm missing a detail here.
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As far as I can tell from the Wikipedia my memory is bad.  Einstein didn't show that magnetism results from transformed electric charge densities.  Rather, when transforming between reference frames both the electric and magnet fields are transformed. This means a magnetic field might 'disappear' in a given frame of reference.

However, inertial observers will agree on the resulting forces but disagree on the 'reasons'.  e.g. an electron moving near a wire carrying current.  In the 'lab' frame you reason the electron moves towards the wire because of the wire's magnetic field.  In the electron's frame, there can't be a magnetic force (it isn't moving) but does feel attracted by an apparent electric field (which results from the difference in charge densities).

Or something like that.

http://en.wikipedia.org/wiki/Relativistic_electromagnetism
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Random unusual convertible: A Nissan Figaro, according to the hood ornament.  Never heard of it before. Very round--I should have got an off-angle shot.
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Peter Phillips

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Random reading part 1 -- I found this trying to understand the (paraphrased) statement "Of course, the existence of particles in a system depends on your frame of reference":

(Short answer: The Unruh effect--accelerated reference frames will 'see' thermal particles in the vacuum that inertial frames will not)

https://www.duo.uio.no/bitstream/handle/10852/11139/4350.pdf?sequence=1&isAllowed=y
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Indeed, I went looking for this after watching a talk by Bill Unruh:

http://online.kitp.ucsb.edu/online/fuzzorfire_m13/unruh/

Via Scott Aaronson

http://www.scottaaronson.com/blog/?p=1508
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Two videos from the Tektronix museum in Portland, Oregeon.
The first is shows their popular vector-graphics terminal which I did have occasion to use a few times in school. I didn't realize they also made a personal computer with the same display and a BASIC. (Not pictured).

The second is a demonstration cathode ray tube.  it uses simple electrostatic plates for deflection (instead of magnetic coils.  Note the image is brighter from the rear view than the front.  Apparently real tubes added an foil layer to reflect more of the light to towards the viewer.  The image is coming from someone's custom board.
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I recall using a Tek 4014 at Green Bank to do sanity checks on the data coming off the telescope. They were a bit of a pain to use, but you could check stuff in real time without pulling the paper roll off the chart recorder, so it felt very modern and efficient.

The "xterm" program in Unix/Linux has a 4014 emulation mode -- I was going to say "had", but I just now tried it (on my more -or-less stock Debian Wheezy desktop here), and sure enough, "xterm -t" brings up a 4014 emulator.
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Very exciting, 3 giant telescopes on the drawing board:

http://nautil.us/issue/11/light/the-billion_dollar-telescope-race
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Cartoonist gets to experience weightlessness.  I like the last panel.

http://english.bouletcorp.com/2012/04/15/
You may use these HTML tags and attributes: . 1)Message de Thierry posté le 15 April 2012 à 18:58:38 "Weightlessness" I just learned a word.
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Long before GPS the key problem in navigation was finding your longitude.  Here's a good summary of the competition:

http://www.americanscientist.org/issues/pub/2003/5/the-harrison-maskelyne-affair
MARGINALIA. The Harrison-Maskelyne Affair. J. Donald Fernie. In the early 1700s, European monarchies aspired to power by building world-spanning networks of colonies and commercial ventures. As a result, the merchant fleets and navies that connected and protected these assets were critically ...
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Umberto Eco wrote a very peculiar book sort of related to the quest for measuring longitude, called The Island of the Day Before.
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