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A Random Walk through Oddly Named Physics Things

The views expressed are those of the author and are not necessarily those of Scientific American.


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A few months ago I helped a friend of mine, Rose Eveleth, think of weirdly named things in physics. She could only include five, but there were a few more I thought were worth highlighting. So here they are.

Naming things is difficult. This fact can be attested to by anyone who’s ever had a baby, a hamster, or a punk band. It’s no easier for scientists, who must constantly find names for the things they discover and the theories they come up with to explain those discoveries.

In spite (or perhaps because) of the overwhelming boringness of much technical jargon, scientists are drawn to whimsical or poetic names more than you might suspect. Here are some of my favorites.

Misner’s Mixmaster Universe

The “cosmic microwave background,” or CMB for short, is a kind of radiation: electromagnetic static that fills the entire universe. When you switched on your TV in the pre-digital era and no channel was tuned in, a few percent of that fuzz was the CMB.

Also known as “relic radiation,” the CMB is energy left over from a time shortly after the big bang, when the entire universe was extremely hot and dense.

The thing that puzzled cosmologists was just how uniform the CMB was. They had expected that, because of quantum fluctuations present just after the big bang, the radiation would be patchy: stronger in some places and fainter in others. But this was not at all what was observed: the CMB looks almost exactly the same everywhere in the sky.

In a 1969 paper entitled “Mixmaster Universe,” physicist Charles Misner set out his idea for a solution to the paradox.  Although it sounds like a 1980′s proto-hip-hop group, the theory actually gets its name from a kitchen appliance, the Sunbeam Mixmaster.

The idea was that the early universe went through a phase of so-called chaotic evolution, which did for the cosmos what the Mixmaster does for cake batter, mixing its contents until they were smooth and even.

The Mixmaster Universe is admired for being an ingenious solution to the equations of general relativity. However, it has been superseded by another theory, called “inflation,” which does a better job of explaining the data than Misner’s.

Unlike the physics theory it inspired, the Sunbeam Mixmaster is still going strong, and is probably available at a store near you.

The Luminiferous Aether

Schematic from Michelson and Morely’s report of their experiment, published in the American Journal of Science in 1887.

Anyone who’s ever been forced to take freshman physics knows that light is a wave. (Well, it’s also a particle, but that’s another story.) This fact has been known for a very long time: it was first suggested as far back as the 17th century by the Danish scientist Christian Huygens. For two hundred years afterwards, scientists and natural philosophers struggled with the question: “if light is a wave, then what is it waving?”

Just like sound waves need air to carry them, and ocean waves need water, the idea that light needs to travel through some kind of medium led scientists to propose the rather magical-sounding “luminiferous aether.” The word “luminiferous” refers to light, while the mysterious substance was called “aether” because it was thought to be so rarefied as to be almost impossible to detect. And since we can see light from far-away stars, this aether must fill all of space.

Numerous aether-detection experiments culminated in one of the most famous observations ever made in science: the Michelson-Morely experiment, which attempted to measure the motion of the Earth through the aether. (It’s also probably the only major contribution to physics that took place in Ohio.)

It is a physics truism that not finding what you’re looking for can be more interesting than finding it, and so it was with Michelson and Morely, who failed to turn up any sign whatsoever that the aether was real. The collapse of the aether theory provided strong evidence in favor of Albert Einstein’s Special Theory of Relativity, which was developed in the following decades. Relativity doesn’t need – and in fact can’t have – a light-carrying medium like the aether.

Random Walks

Imagine a very drunk person – a friend of yours – who has just woken up, groggily, in the middle of a football field. He doesn’t remember what made him go to the football field in the first place, and he wants out. Your friend tries walking a little bit, worried that he might need a bit more of a nap first. But no – success! His legs seem to work okay, and he commences his pondersome exit.

Instead of helping out your buddy, you decide to think about science for a while. From your vantage point in the stands, you notice  something interesting. Your friend seems to be so drunk that he can’t take two steps in a row in the same direction. (Hey, it’s happened to the best of us.) In fact, the direction of each step seems to be totally random: he has an equal probability of going north, south, east or west, or any direction in between.

A number of questions come to mind. (At least, they do if you happen to be a physicist.)  How long will it take your friend to get out? What is the probability that he will find himself back at his starting point? If the field is enclosed by a tall fence, with only one exit, how much longer will it take him to escape?

If you were to trace out the path he takes, the shape wouldn’t look like anything you’ve seen in math class. It looks more like the graph of a stock price, or the coastline of Norway, than the smooth parabolas of classical geometry. It is a jagged fractal that meanders around and crosses over itself before hitting the edge of the field.

The drunken voyage that created this shape is an example of a “random walk.” Random walks describe all kinds of phenomena in nature, economics and mathematics. The list of things which can be described or modeled using random walks is too long to include here, but notable entries include the distribution of genes in a population of animals, the path of drug molecules in cancer cells, the process that misaligns the little magnets in MRI machines, and the amount of money you’re likely to lose in a game of roulette.

The Ultraviolet Catastrophe

At the beginning of the 20th century, British scientists Lord Raleigh and James Jeans tried to calculate what you should see when you look at a “black body.” A black body is an idealization: an imaginary object that absorbs and emits light of all wavelengths perfectly. (“Wavelength” is, at least in this context, just a technical word for “color.”) What black bodies look like isn’t just a theoretical question: some astronomical objects, like the sun, are quite close to perfect black bodies.

In particular, Raleigh and Jeans were interested in the “blackbody spectrum”: how much of the emitted energy is stored as red light, how much as blue light, and so on. To solve the problem, they used two of the most venerable theories of 19th-century physics: James Clerk Maxwell’s theory of electromagnetism and Stefan Boltzmann’s theory of statistical mechanics.

The blackbody spectra of objects of different temperatures. The shape of the curves can be calculated using quantum mechanics.

But when they did their calculation, there was a serious problem: the amount of energy stored in the short-wavelength part of the spectrum was…. infinite! This nonsensical result was such a big problem for physics that it was dubbed “the ultraviolet catastrophe” (ultraviolet light being of the of short-wavelength variety.)

The solution to the paradox germinated from the work of Max Planck, a German physicist. Planck introduced the idea that light could not be emitted and absorbed in arbitrarily small amounts; rather it comes in discrete packets that are now called “photons.” It works just like money: you can’t buy less than a penny’s worth of chocolate or dish soap, and an atom can’t absorb less than a photon of light. Armed with this assumption, Planck was able to calculate the blackbody spectrum without any infinities appearing.

At the time, Planck’s idea caused as many problems as it solved, because the assumption that light comes in such discrete packets completely contradicts Maxwell’s theory of electromagnetism. The ultraviolet catastrophe wasn’t resolved until the 1920′s, when a comprehensive theory of quantum mechanics was introduced. Quantum mechanics showed that the older, 19th century theories were incomplete. Amongst many other achievements, quantum mechanics allows for correct calculation of the blackbody spectrum.

Images from Wikimedia Commons.

Colm Kelleher About the Author: Colm Kelleher is a graduate student in physics at NYU, where he investigates the role of geometry in determining order and structure in two-dimensional micro-systems. He mainly does experiments, but likes to dabble in theory and numerical simulations when time allows. He is a graduate of the National University of Ireland, where he received his BSc in 2008. He's also one of the hosts of the weekly science radio show The Doppler Effect, on WNYU 89.1FM.

The views expressed are those of the author and are not necessarily those of Scientific American.






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  1. 1. bjflanagan 10:50 am 03/14/2012

    “Wavelength” is, at least in this context, just a technical word for “color.”

    No, this is incorrect and only a common version of what “everyone knows.” In another version, color is the frequency of light.

    Wavelength and frequency are both scalars, whereas Maxwell, Schrödinger, Weyl and Feynman all tell us quite explicitly, color behaves like a vector.

    Moreover, the technology behind our color TVs and computer monitors employs a vector model, furnishing us will a working proof of principle.

    The true state of affairs can be found in the following quotations, from the leading lights of science and philosophy.

    To paraphrase Dirac, when the path forward seems unclear, follow the math. In order to accurately model color, we require a complex, projective vector space.

    In order to glimpse the utility of this model, the reader is encouraged to google: “complex + projective + vector”

    Should you feel ambitious, please add “gauge” and/or “M-theory” to the mix.

    As is evident from inspection, colors cover areas of the visual field. Curiously, vectors are “dual” to differential forms, which have the dimensions of area.

    This is the same kind of duality which unites the various flavors of string theory into M-theory and which has its provenance in projective geometry.

    ______________________

    Then it turns out that the mixture of the two lights (it is one of the consequences of the laws that we have already mentioned) is obtained by taking the sum of the components of X and Y:

    Z = X + Y = (a + a’)A + (b + b’)B + (c + c’)C.

    It is just like the mathematics of the addition of vectors, where (a, b, c) are the components of one vector, and (a’, b’, c’) are those of another vector, and the new light Z is then the “sum” of the vectors. This subject has always appealed to physicists and mathematicians. In fact, Schrödinger wrote a wonderful paper on color vision in which he developed this theory of vector analysis as applied to the mixing of colors.

    ~Feynman

    Thus the colors with their various qualities and intensities fulfill the axioms of vector geometry if addition is interpreted as mixing; consequently, projective geometry applies to the color qualities.

    ~Weyl

    If you ask a physicist what is his idea of yellow light, he will tell you that it is transversal electromagnetic waves of wavelength in the neighborhood of 590 millimicrons. If you ask him: But where does yellow come in? he will say: In my picture not at all, but these kinds of vibrations, when they hit the retina of a healthy eye, give the person whose eye it is the sensation of yellow.

    ~Schrödinger

    The processes on the retina produce excitations which are conducted to the brain in the optic nerves, maybe in the form of electric currents. Even here we are still in the real sphere. But between the physical processes which are released in the terminal organ of the nervous conductors in the central brain and the image which thereupon appears to the perceiving subject, there gapes a hiatus, an abyss which no realistic conception of the world can span. It is the transition from the world of being to the world of appearing image or of consciousness.

    ~Weyl

    So long as we adhere to the conventional notions of mind and matter, we are condemned to a view of perception which is miraculous. We suppose that a physical process starts from a visible object, travels to the eye, there changes into another physical process, causes yet another physical process in the optic nerve, and finally produces some effect in
    the brain, simultaneously with which we see the object from which the process started, the seeing being something “mental”, totally different from the physical processes which precede and accompany it. This view is so queer that metaphysicians have invented all sorts of theories designed to substitute something less incredible.

    ~Russell

    For instance a star which we perceive. The energy scheme deals with it, describes the passing of radiation thence into the eye, the little light image of it formed at the bottom of the eye, the ensuing
    photochemical action in the retina, the trains of action potentials traveling along the nerve to the brain, the further electrical disturbance in the brain, the action potentials streaming thence to the
    muscles of eyeballs and of the pupil, the contraction of them sharpening the light image and placing the best seeing part of the retina under it. The best ‘seeing’? That is where the energy scheme forsakes it. It tells us nothing of any ‘seeing’. Everything but that.

    ~Sherrington

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  2. 2. bjflanagan 10:54 am 03/14/2012

    PS, Is there an edit function? I see I’ve made a few typos…

    Link to this
  3. 3. benonemusic 8:13 pm 03/14/2012

    Nice concept for a column! I have two requests if there is a sequel: anti de Sitter space and Cabibbo angle.

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