Deep conclusions from simple questions

kw: book reviews, nonfiction, science, physics

Little toys like this were popular when I was a youngster, and similar toys still are. Suppose you opened a matchbox toy box and a full-size truck popped out? This is analogous to what happens every time a photon is emitted from any light source, such as an incandescent bulb or LED. Light we can see has a wavelength around half a micron (or about a 2-millionth of a meter). The atoms that release photons of this light are much smaller, by a factor of several thousand. The photons are actually emitted by the electrons in these atoms, and an electron itself is a great deal smaller than that, but we don't know quite how small. The classical radius of an electron is about 3x10-¹⁵m, or 20,000 to 30,000 times smaller than the atom in which it (usually) resides, but quantum mechanically, it has a radius of exactly zero!

All this underlies the title of Marcus Chown's fascinating book The Matchbox that Ate a Forty-ton Truck: What Everyday Things Tell Us About the Universe. Thinking about it, I found it curious that the same principle operates on a scale we can see, except we aren't able to visibly see the actor: The little radio antenna in your bedroom or kitchen has an antenna not much bigger than your hand, but when you are receiving an AM station (in the US at least), the radio-frequency photons it absorbs by the trillions to convey the program have a wavelength between 1/6 and 1/2 km. The station at 1210 that I often listen to has a wavelength of 248m, which is 2,500 times the size of the antenna in my kitchen clock-radio. This is similar to the ratio between the size of a photon of blue light to that of an atom of tungsten.

The book is in three sections, one on atoms, one on stars, and one on the universe, in a total of eleven chapters. A number of the points the author makes relate to randomness, specifically the "uncaused action" of random choice in quantum events. For example, when you look out a window and also see your face being partly reflected, it means that about a twentieth of the photons that leave your face are being reflected back to you, while the rest pass through the window. Of course, someone standing outside and seeing you, also sees the landscape behind them, by the one-twentieth of "landscape" photons moving toward your window that are reflected outward. How does a photon choose whether to bounce or pass through? Nobody knows. We have math to describe what happens, but how? Ha!

In a later chapter, the richness and complexity of the material universe is shown to have its source in such random choices. Just the fact of a window pane doubles the possible places a photon can choose to go. But there is a subtler effect. Consider a photon zipping along, that passes "near" something ("near" meaning at a distance that is not too large compared to its own wavelength). It is likely to be deflected, or diffracted, but by an amount that cannot be predicted. You can predict that some percentage of the photons taking that path will be deflected through an angle greater than one degree, but which photon takes which angle? No can figure.

Now let us suppose that photon is not scheduled to pass "near" anything for the next five seconds (it can go a long way in that time). There is still some finite probability that it will deflect by a degree or more. Maybe that probability is a few trillionths of a percent, but it is not zero. That photon could be miles (it just doesn't feel right to say "kilometers") from the nearest atom of matter, and still "feel" the tendency to diffract.

Now, consider that every photon in the universe is subject to such diffraction effects arising from every object in the universe. The fact that our telescopes show us objects millions and billions of light years away tells us that these effects are unimaginably small, but we have the math to predict exactly how small!

How does this affect the richness of everyday objects? Louis de Broglie found that one out. Quantum choices affect all particles, not just photons. Electrons have a wave nature, but so do photons and even baseballs and trucks in motion on the highway. It is just that things big enough for us to see have very, very small wavelengths, because wavelength is inversely related to kinetic energy. The proportionality constant is 1,240 eV-nm; a wavelength of 1nm is borne by, not just a particle, but any object with a kinetic energy of 1,240 eV, such as an X-ray photon, or a baseball moving so slowly that it would take it six hours to move a millimeter. How about a nearly-visible wavelength, like 1mm, or a million nm? Energy goes down by one million, velocity goes down by a factor of 1,000, and 6,000 hours to go one millimeter? That's almost a year.

Thus, while matter particles can also make quantum choices, it happens on a scale to subtle for us to see in everyday life. But the fact is, huge numbers of quantum choices have been made, because the universe is more complex now than it was a long time ago. The chapter in question goes into quite a discussion of this, which I can't hope to summarize in a blog post.

Every point in the first ten chapters is backed up by solid science. Things may not suit our intuition, but then, our intuition is based on problems bigger than whether one-twentieth of the light bounces off a sheet of glass. Our ancestors had to learn to avoid being eaten by predators or trampled by large herbivores, and to catch a few of them in the process, to stay living. But in the last chapter, there is no science to go on, and we are as free to speculate as the author is, or indeed anyone.

You can buy this bumper sticker from Uncle Shlomo if you like. It is the title of Chapter 11, which discurses on Fermi's most famous question: when his colleagues were talking about whether there were Martians or other aliens anywhere, Enrico Fermi considered a while, then blurted out, "Where is everybody?"

Maybe there's a big "Earth is full" sign (or a bunch of them) at the boundary of the Solar System. Maybe there's no sign, and nobody to read it. Maybe the nearest aliens live too far away for detectable radio signals to reach us, or they aren't trying anyway. Could we detect old episodes of I Love Lucy from a distance of even a parsec or two? (That's 3.25-6.5 l-y.) Will a technology every be developed, by anybody, that would allow some kind of space probe to travel between the stars, even at 1% of the speed of light? (A mere 3,000 km/s, or 100 times Earth's orbital velocity.) That's a kinetic energy of half a million kWh per baseball, or 2.5 million kWh/kg. The daily energy budget of a small city would be needed to boost a 1kg object to 0.01c. Then it needs to use similar amounts of energy to stop when it gets somewhere interesting. Making a replica of itself is easy compared with making the energy source for its replica to go on its way.

I take it as a given that not many civilizations (probably none) would consider such space probes as worth the trouble. That leaves us with no visitors. So how about those old radio and TV programs? Will we ever detect an alien All in the Family? I have supported SETI through SETI@home on and off for years. They face great odds, because they aren't looking for inadvertent broadcasts; they are looking for purposeful signals, attempts to communicate. While that narrows the search to some "magic" regions that would be likely targets of such attempts, it also narrows the field of possible communicators to those who are willing to support gigawatt transmitters pointed everywhere. Will alien environmentalists try to block operation of giant transmitters in their courts? That's a lot of "wasted" energy!

The great thing about a book like this is the myriad of spinoff ideas. My posts over the past few days were triggered either by things I read in the book or by articles I read to find backup for some of the author's points. Just consider the triple-alpha process (which I didn't post on yet). It is the reason you and I exist, for it is absolutely required for carbon to be created in stars.

This nuclear process depends on three things: the isotope ⁸Be having a half life near 10^-16s (rather than 10^-24s), ¹²C having a metastable resonance at 7.65MeV, and ¹⁶O having such a resonance at a higher energy (it is in fact 9.64 MeV). The 7.65MeV resonance was predicted by Fred Hoyle based on the fact of his own existence, and such was his stature that a team of scientists spent ten days to find out if that resonance existed. It does. It remains the only successful prediction of the Weak Anthropic Principle. If its energy were much lower or much higher, there would be lots less carbon in the universe. If the oxygen resonance were at a lower energy, there'd be less carbon also, but if it were much greater, there'd be too little oxygen to form silicate-based planets such as Earth.

I do believe I'll simply close before another digression occurs to me. Great book!