Take Tyson's tour

kw: book reviews, nonfiction, science, astrophysics, popular treatments

What's not to like about Neil deGrasse Tyson? He has become the public face of science today. I love his updated Cosmos series. I have privately studied astrophysics and cosmology enough that perhaps I could have passed by his new book, but I couldn't pass by the enjoyable way he treats his subject. Astrophysics for People in a Hurry is well worth anyone's time, whether you know anything about the subject or not...particularly if not!

This is a rather small book, on purpose. Dr. Tyson knows that today's young adults want everything fast, they want it now, and they want it without fuss. If anyone can deliver up a basic survey of astrophysics and cosmology that meets these requirements, he can. He does so in 12 chapters.

When I think of astrophysics, I think mostly of stellar interiors, but there is much more to it than that. Clearly, from the flow of the book, astrophysics includes cosmology in its purview; probably 2/3 of the books content is cosmological. But he really does cover all the bases, from the reasons for roundness (gravity wins), to the shapes of galaxies (the tug-of-war between gravity and angular momentum), and to the reasons for modern cosmological theory to include both "dark matter" and "dark energy". Chapters 5 and 6 present these mysteries as well as I have ever seen, and explain why they seem to be required for the universe to work the way we observe it working.

I had the great pleasure to encounter a professional cosmologist on an airplane flight four days ago, and we had the chance to talk a little (he wasn't in my row, so our time was limited by physical endurance of turning heads rather sharply). I asked him a question I'd have asked Tyson if I had the chance, "If a unified quantum theory requires a quantum of gravity, how can a graviton get out of a black hole so as to interact with the rest of the universe? What is the emitting surface for a graviton?" He admitted that he hadn't thought of that before. After we talked a while of other things, then broke off for a while, he nudged me, saying, "Consider this. A black hole has three qualities: gravity, angular momentum, and electric charge, right?" I agreed. He continued, "The electric charge is carried by virtual photons, the bosons of electromagnetic force. Real photons cannot escape a black hole; that is why it is black. But the electric charge remains in effect anyway. Thus, the virtual photons do escape—and return to—the black hole to keep the electric charge in place." I thanked him for providing a marvelous "hole" in my considerations of gravitons and black holes. I suspect this is the same answer Tyson would give. Now, upon further thought, I wonder if the electric charge is held within the black hole, or remains attached somehow to the event horizon. From there (or very slightly above it), even real photons could escape if needed. But if virtual photons can indeed escape a black hole, then virtual gravitons could also.

This matter doesn't enter into the book. What does enter in, is how all the pieces fit together. Tyson gives us plenty of food for thought. One of my favorites is playing a numbers game with molecules and time. Here is my version of "Whose air are we breathing?":

Part 1

• The air above 1 cm² of Earth weighs 1 kg.
• The average molecular weight of air is about 29.
• Thus each kg of air contains about 34.5 gm-moles.
• 1 gm-mole contains 6.02x10²³ molecules (or atoms) of any substance.
• That comes to just over 2x10²⁵ air molecules above each cm².
• The surface area of Earth is 510 million km² or 5.1x10¹⁸ cm².
• Thus the atmosphere contains a bit more than 10⁴⁴ molecules.

Part 2

• Our total lung capacity is around 6 liters (with a rather wide range).
• Our "tidal" capacity, the amount we usually take in with each breath, is about a half liter.
• That is about 0.022 gm-moles, or 1.3x10²² molecules.
• An average person breathes about 23,000 times daily, when not exercising a lot, or about 8.4 million breaths yearly.
• Napoleon Bonaparte lived 64 years.
• In a 60-year span, the number of breaths would come to about 500 million.
• All those breaths add up to 6.6x10³⁰ air molecules.

Part 3

• All the air that Napoleon breathed amounts to 1/15 trillionth of the atmosphere.
• 1/15 trillionth of one tidal breath is 880 million air molecules.

Conclusion: Every breath you breathe contains nearly one billion of the air molecules once breathed by Napoleon…or by anyone else who has lived at least 60 years! Tyson didn't go into all this gory detail. He names a couple of the figures in a two-sentence riff on the subject. I just went through the figures to work it out for myself, and to share it here.

A particular aim of Dr. Tyson in everything he writes, and says in his programs, is to impress us with the power of the scientific method. We don't learn "how the world works" by guessing. We observe, make tentative conclusions based on observations, argue with others about it, eventually turn the conclusions into a hypothesis that we can test, and then repeat as needed. Now, in cosmology, a "test" would take billions of years. This isn't chemistry, for which you can mix a few things in a jar and take a measurement in a matter of seconds or minutes. Neither is it biology; we have no cosmological Gregor Mendel, crossbreeding stars as though they were peas. But we can work out the math and see how it squares with the things we see.

In science, more than in any other endeavor, "No man is an island." No woman either. The popular trope of the loner in a stained lab coat making a major discovery is simply unknown to real science. Even a few centuries ago, when chemistry was emerging from alchemy and astronomy was emerging from astrology, a "lonely genius" was really a highly social being, surrounded by helpers, colleagues, opponents, and many others. The quintessential scientific loner, Isaac Newton, spent much more time discussing his findings and theories with members of the Royal Society, including friends, "frienemies", and enemies, than he did carrying out observations or even thinking out his theories. Without a helpful gadfly-friend to prod him, he'd never have finished writing his Principia. So although Newton was famously anti-social, he still had to interact socially for his science to have usefulness and meaning. But that's the beauty of science. It is our great, collaborative enterprise of looking back at the Universe that birthed us, to see how it was done, and a great many more things of interest also.

This isn't a textbook. It provides not an education in the subject but a vision of what astrophysics is. If you treat it sort of like a textbook, and write down ideas that interest you as you go along, you'll gather fodder for any further studies you might wish to carry out. That's the kind of thing I've done all my life.