kw: book reviews, nonfiction, science, physics, magical thinking
If people think about it at all, they might imagine that an astronomer's work bears some resemblance to this beguiling image. Dr. Felix Flicker takes advantage of this impression in his new book The Magick of Physics: Uncovering the Fantastical Phenomena in Everyday Life. His focus is on quantum physics and quantum mechanics, which still seem magical to me and nearly everyone. (The image came from a Pinterest pin, which pointed to Kai Fine Art, a digital art aggregating site.)
Just for fun, consider this picture, an architect's rendering of the Extremely Large Telescope being built at the site of the Paranal Observatory in Chile. The center of the Milky Way is in the southern sky, so a lot of big telescopes are in use or in the works to study that part of the sky. The high plains of Chile are high and dry, with very clear sky, so they are a great place for astronomy.A real astronomer works nowhere near the telescope, unless a new detector is being added to its arsenal. Usually, the work is done from an office at lower altitude, directing the actions of the instrument over an Internet connection. Ah, science! These days far too much of it is done in an office, at the keyboard. The primary mirror of the ELT has an area of 0.3 acres, and its focal length is about 120 feet. Most suburban houses, and the lot they sit on, could comfortably fit inside, stacked two or three deep! Note: That's inside the telescope, not just inside the (much larger) dome, which is the size of a small stadium, rolling roof and all.
Reading through, I realized how disconnected I am from contemporary culture. It isn't just that I'm old; I've never been well integrated into the culture around me. I took notes. The author mentions at least 30 books, TV shows and movies, clearly expecting them to be familiar. Several more classic works such as Tao Te Ching (Daodejing) are given the same treatment, while other subjects, classic or modern, are at least given a bit of introduction. Of the 30, I had never heard of 14, I had seen or read at most three, and the rest were just names I'd heard before. The author is really, really trying to be "with it" (does anyone say that any more?).
Dr. Flicker is particularly interested in the ways quantum physics gets into various areas of everyday life, "the middle realm" (not microscopic, not cosmic). For example, polarization is a quantum phenomenon—and so is reflection off a pane of glass: which photon bounces, and which one passes through, is a "quantum choice". The interaction of light with most surfaces causes the reflected light to be at least partly polarized. These pictures illustrate it:
The picture at the right was taken through a polarizer, the lens of my sunglasses. The purpose of the glasses is to reduce glare; the company logo near the top of both pictures shows the effect. If you look closely in the right picture, it reads "Craftsman", upside down. The blue effect on the body of the mower is because the polarizer is less effective for blue light, so some gets through. Metal objects, such as the throttle lever at center left, don't polarize scattered light, only insulating materials such as plastic, rubber (the tires) and asphalt.
Our eyes can detect polarized light, just a little. The author describes how to activate the Haidinger Effect, or Haidinger's Brush, which allows us to see whether light is polarized, and determine its direction. So far, the method hasn't worked for me, but I'll look into it more. Seeing polarization is useful in a sunlit environment, because the light scattered from the sky is polarized. The effect is strongest 90° from the Sun. If you are wearing polarizing sunglasses, look at the sky with the Sun off you your right or left, and tilt your head (or remove the glasses and turn them). The sky will be darkest when the top of the glasses points toward or away from the Sun. There is no explanation in classical mechanics for polarization, but we use it frequently. The screen on your phone or computer or TV uses polarization to regulate the colors on the screen. Photographers use a rotating polarized lens to adjust the darkness of the sky in landscape photography.
This may puzzle us because we don't realize the energy needed for us to see the house across the street. Light from the Sun bounces off the house and to our eyes. Millions of photons pass through the pupils of our eyes every second, to be detected in our retinas. Houses and eyes and retinas are big and heavy compared to photons of light. The molecules the demon is watching are very small and light. At least two or three photons must bounce off a molecule and into the demon's eyes, in the span of a few billionths of a second, for the demon to determine its path in time to open or close the gate.
A little math fun: The kinetic energy of an atom of argon or a molecule of oxygen or other gas at the freezing point of water, 0°C, is about 0.035 eV (1 eV is an electron-volt). The energy of a visible photon—let's pick a reddish one at a wavelength of 620 nm—has an energy of about 2 eV. If it bounces off an oxygen molecule, the molecule will receive a kick about 50 times greater than the energy it already has. It would pop off in a new direction with a velocity commensurate with a temperature of 10,000°C or more. The chance of such a photon-molecule collision is very low. It would take such a bright light shining into the chamber for the demon to "see" the molecules that he would enjoy a truly toasty environment! However, his seeing would be useless, because the molecules would scatter about such that he couldn't gather any useful information about sorting them by velocity.
Photons that wouldn't affect the molecules very much would need to have a very low energy, as low as 0.01 eV. That corresponds to a wavelength of 124 microns. The demon's eyesight would then be rather blurry; these far-infrared photons are almost microwaves. It couldn't see sharply enough to know whether the molecule would go through the hole if the gate were pulled back.
I was happy to see something on page 236, that the environment "measures" what quanta are doing. A tenet of quantum theory is that a quantum has no fixed location or velocity until a measurement is taken, whereupon its position and velocity become known, within the bounds of accuracy imposed by Heisenberg uncertainty. The Copenhagen Interpretation of quantum mechanics insists that the measurement must be by an intelligent agent, such as an experimenter in a laboratory. I consider that point of view to be nonsense. Fortunately, our author never mentions the CI, so while he may "believe" it, at least he doesn't press it upon us.
Consider what happens in your eye. Back to the millions of photons per second that enable us to see. As a single photon with a wavelength of 620 nm travels from the red roof on the house across the street to your eye, it doesn't matter if it is a wave or a particle. It makes the trip in a ten-millionth of a second (from the photon's point of view, were it to have one, no time at all would pass). Upon arriving at the cornea, the photon behaves as a quantum particle, with a 5% probability of bouncing off. Let us assume it enters, at a slightly deflected angle because of refraction (also quantum effect). A few mm further on, passing through aqueous humor behind the cornea, it encounters the lens, which is denser. There, assuming it doesn't reflect, it is refracted again, and yet again when it passes from the lens to the vitreous humor that fills most of the eye. In bright light the pupil of your eye is about 2 mm in diameter. This causes a slight deflection of the photon's path because of diffraction, but in the eye, the difference is smaller than the size of a detector cell, so we can neglect it. About 20mm behind the lens, the photon encounters a rod or cone cell in the retina, where it is absorbed, and its energy is deposited in the cell, with a probability depending on the color sensitivity of that cell. If the cell is R type this red photon is probably absorbed; a little lower probability if it is G type, and much lower if it is B type or if it is a rod cell, which is also blue sensitive, and can't see 620 nm photons at all. In the space of less than 25 mm this photon "acts like" a wave at some points, and like a particle at others. There are at least five interactions, and all are described by different quantum mechanical computations. Which is the "measurement"?
Let's look further at diffraction. As an amateur astronomer I am deeply familiar with it. Diffraction limited optics are the goal of telescope makers, and the greater the width of the primary lens or mirror, the less diffraction is experienced. For example, the little telescope my father and I made 65 years ago has a three-inch mirror. I usually use it with a magnification of 30x or 60x. At 60x, the planet Jupiter appears to be about 2/3 of a degree across, or a little bigger than the Moon appears without magnification. The maximum useful magnification is 120x, because of diffraction. Here is why. Three inches is 76 mm. The wavelength of light usually used to determine visual acuity is 550 nm, or 0.00055 mm. Their ratio is 1:138,000 or 0.00000724, which is the tangent of 0.000414 degrees, or 0.0249 arc minutes or 1.49 arc seconds. About 1.5 arc seconds is the resolving power of a 3 inch diameter telescope. Human vision varies, such that the smallest separation between two points that someone can see is between one and three arc minutes, or between 60 and 180 arc seconds. Divide these two numbers by 1.5 and we find 40 and 120. For someone with very sharp vision, even using my telescope at 60x, they'll see the image as slightly blurry, while other people need 60x, or 90x, or 120x to see everything the instrument can show.
If a telescope has a larger mirror, the details it can show will be smaller, in exact proportion. Thus, a 30-inch diameter telescope could see (or "resolve") details as small as 0.15 arc seconds...BUT! The atmosphere messes things up. Except in very rare cases, a telescope on Earth cannot resolve better than 1/3 of an arc second. So an amateur astronomer will rarely buy or make a telescope larger than 14 inches. This is why professional astronomers either use telescopes outside the atmosphere (Hubble and Webb, for example), or they use costly "adaptive optics" that can mostly compensate for the vagaries of atmospheric distortion.
With that windy explanation behind us, I can get to the point. A photon is typically millions of times smaller than the largest telescope mirrors, yet it can "detect" the size of the mirror, and its path after entering the instrument is modified a little as a consequence. This is also true of a hole of any size is placed in the path of light going from anywhere to anywhere else. If you have a searchlight on the Moon (where there is no atmosphere) with a beam 36 inches wide, and half a mile away you place a board with a 24-inch circular hole in it, and then a further half mile away you put a screen, the bright area on the screen will not have a sharp edge. It will be a little blurry because the "diffraction limit" of a 24 inch hole is 0.186 arc seconds, or a ratio of 1.1 million to 1. Divide a half mile by 1.1 million: 0.0024 feet or 0.029 inch, about 3/4 of a millimeter. It isn't much but it's visible. If you put a lens with a diameter of 24 inches and a focal length of half a mile in the hole, it would focus the light to a point about 3/4 mm across. Back to the question above: where was the measurement made? The 2-foot hole participated in the measurement, as did the eye that observed the screen.
A consequence of such reasoning is this: Every quantum interaction is affected by the whole Universe. No matter how big a "hole" a photon passes through, or how far it is from the "edge", its path is affected. No matter what kind of quantum weirdness we want to measure, we can't perfectly isolate the interaction from the "environment" (everything else). In all our experiments, we just reduce "outside influences" to an acceptable minimum that allows the phenomenon we want to examine to occur.
Dr. Flicker writes in terms of wizards and spells, taking advantage of a humorous milieu to help us understand how things like "holes" can move through a semiconductor as though they were electrons with a positive charge, but are not positrons, which would energetically annihilate nearby electrons; things like fractional charges exhibited in some instruments, that have nothing to do with the 1/3 and 2/3 of an elementary charge that our Standard Model theory posits for quarks; things like MRI machines (that used to have the word "nuclear" in their name but that scared the public), which work because of superconductivity, a quantum effect we don't understand well but have learned to employ.
I hope you enjoy the humor and the allegories (each chapter begins with an allegorical story). I sure did. Physics is a long-held love of mine, and I like this fresh take on it.
I must make a few corrections (sorry, Doc!). On page 186, we read that a diode, a rectifier, "detects" an AM radio signal, converting the oscillating radio-frequency voltage to direct current. A key word is missing: the radio signal is converted to fluctuating direct current. In AM radio the audio frequencies cause the carrier wave's strength (amplitude) to fluctuate. When the rectified signal goes into earphones, the steady direct current is ignored, and the audio frequencies activate the earphone speakers, so we can hear the audio that has now been separated from the radio-frequency carrier wave.
On pages 190 and 191, explaining transistors: the example mentions adding arsenic (a Group V element) to silicon to make it n-type (negative, because it has added electrons), and adding germanium to make it p-type. Germanium is Group IV, the same as silicon. One must instead use a Group III element such as gallium (I am sure that is what the author meant!). Gallium "robs" the silicon of electrons, making it p-type (positive).
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