Astrophysics for People in a Hurry (Astrophysics for People in a Hurry Series)

by Neil deGrasse Tyson

The universe is under no obligation to make sense to you. —NDT

The German physicist Max Planck, after whom these unimaginably small quantities are named, introduced the idea of quantized energy in 1900 and is generally credited as the father of quantum mechanics.

transmogrifications

But high-mass stars fortuitously explode, scattering their chemically enriched guts throughout the galaxy. After nine billion years of such enrichment, in an undistinguished part of the universe (the outskirts of the Virgo Supercluster) in an undistinguished galaxy (the Milky Way) in an undistinguished region (the Orion Arm), an undistinguished star (the Sun) was born.

Dominant in this primordial soup were simple anaerobic bacteria—life that thrives in oxygen-empty environments but excretes chemically potent oxygen as one of its by-products. These early, single-celled organisms unwittingly transformed Earth’s carbon dioxide-rich atmosphere into one with sufficient oxygen to allow aerobic organisms to emerge and dominate the oceans and land.

A mere sixty-five million years ago (less than two percent of Earth’s past), a ten-trillion-ton asteroid hit what is now the Yucatan Peninsula and obliterated more than seventy percent of Earth’s flora and fauna—including all the famous outsized dinosaurs.

Nonetheless, they remind us that ignorance is the natural state of mind for a research scientist. People who believe they are ignorant of nothing have neither looked for, nor stumbled upon, the boundary between what is known and unknown in the universe.

We are stardust brought to life, then empowered by the universe to figure itself out—and we have only just begun.

Today, the universe has expanded by a factor of 1,000 from the time photons were set free, and so the cosmic background has, in turn, cooled by a factor of 1,000. All the visible light photons from that epoch have become 1/1,000th as energetic. They’re now microwaves, which is where we derive the modern moniker “cosmic microwave background,” or CMB for short.

The LED revolution in advanced lighting technology creates pure visible light without wasting wattage on invisible parts of the spectrum. That’s how you can get crazy-sounding sentences like: “7 Watts LED replaces 60 Watts Incandescent” on the packaging.

Ordinary matter is what we are all made of. It has gravity and interacts with light. Dark matter is a mysterious substance that has gravity but does not interact with light in any known way. Dark energy is a mysterious pressure in the vacuum of space that acts in the opposite direction of gravity, forcing the universe to expand faster than it otherwise would.

In the grand tally of cosmic constituents, galaxies are what typically get counted. Latest estimates show that the observable universe may contain a hundred billion of them.

The nearest galaxy larger than our own is two million light-years away, beyond the stars that trace the constellation Andromeda.

The most accurate measurements to date reveal dark energy as the most prominent thing in town, currently responsible for 68 percent of all the mass-energy in the universe; dark matter comprises 27 percent, with regular matter comprising a mere 5 percent.

what is the stuff? Nobody knows. The closest anybody has come is to presume dark energy is a quantum effect—where the vacuum of space, instead of being empty, actually seethes with particles and their antimatter counterparts.

Dark energy inhabits one of the safest harbors we can imagine: Einstein’s equations of general relativity. It’s the cosmological constant. It’s lambda. Whatever dark energy turns out to be, we already know how to measure it and how to calculate its effects on the past, present, and future of the cosmos.

Distant galaxies now visible in the night sky will ultimately disappear beyond an unreachable horizon, receding from us faster than the speed of light. A feat allowed, not because they’re moving through space at such speeds, but because the fabric of the universe itself carries them at such speeds. No law of physics prevents this.

In a trillion or so years, anyone alive in our own galaxy may know nothing of other galaxies. Our observable universe will merely comprise a system of nearby, long-lived stars within the Milky Way. And beyond this starry night will lie an endless void—darkness in the face of the deep.

A hundred-ton underground vat of liquid gallium chloride is monitored for any collisions between neutrinos and gallium nuclei. For every successful slam, gallium temporarily becomes germanium. The germanium eventually decays back into gallium, emitting a detectable pulse of X-rays.

The first atomic bomb ever used in warfare had uranium as its active ingredient, and was dropped by the United States, incinerating the Japanese city of Hiroshima on August 6, 1945. With ninety-two protons packed in its nucleus, uranium is widely described as the “largest” naturally occurring element, although trace amounts of larger elements can be found naturally where uranium ore is mined.

Unstable weapons-grade plutonium was the active ingredient in the atomic bomb that the United States exploded over the Japanese city of Nagasaki, just three days after Hiroshima, bringing a swift end to World War II.

One pound of plutonium will generate a half million kilowatt-hours of heat energy, enough to continuously power a household blender for a hundred years, or a human being for five times as long, if we ran on nuclear fuel instead of grocery-store food.

sesquipedalian

Personally, I am quite comfortable with chemicals, anywhere in the universe. My favorite stars, as well as my best friends, are all made of them.

undulate

Earth’s mountains are also puny when compared with some other mountains in the solar system. The largest on Mars, Olympus Mons, is 65,000 feet tall and nearly 300 miles wide at its base.

the Milky Way’s disk is not a sphere, but it probably began as one.

This general flattening of objects that rotate is why Earth’s pole-to-pole diameter is smaller than its diameter at the equator. Not by much: three-tenths of one percent—about twenty-six miles.

twenty-four hours per day, Earth carries anything on its equator at a mere 1,000 miles per hour.

Flattened spheres are more generally called oblate spheroids, while spheres that are elongated pole-to-pole are called prolate.

Consider pulsars. With some rotating at upward of a thousand revolutions per second, we know that they cannot be made of household ingredients, or they would spin themselves apart. In fact, if a pulsar rotated any faster, say 4,500 revolutions per second, its equator would be moving at the speed of light, which tells you that this material is unlike any other.

For all these reasons, we expect pulsars to be the most perfectly shaped spheres in the universe.

were it not for relaxed systems, the ubiquity of dark matter may have remained undiscovered to this day.

At this distance and beyond, light from all luminous objects loses all its energy before reaching us. The universe beyond this spherical “edge” is thus rendered invisible and, as far as we know, unknowable.

There’s a variation of the ever-popular multiverse idea in which the multiple universes that comprise it are not separate universes entirely, but isolated, non-interacting pockets of space within one continuous fabric of space-time—like multiple ships at sea, far enough away from one another so that their circular horizons do not intersect. As far as any one ship is concerned (without further data), it’s the only ship on the ocean, yet they all share the same body of water.

Herschel inadvertently discovered “infra” red light, a brand-new part of the spectrum found just “below” red, reported in the first of his four papers on the subject.

Filling out the entire electromagnetic spectrum, in order of low-energy and low-frequency to high-energy and high-frequency, we have: radio waves, microwaves, infrared, ROYGBIV, ultraviolet, X-rays, and gamma rays.

credit Hertz for recognizing that there is such a thing as an electromagnetic spectrum. In his honor, the unit of frequency—in waves per second—for anything that vibrates, including sound, has duly been named the hertz.

But in all cases, every bit of information a telescope delivers to the astrophysicist comes to Earth on a beam of light.

jury-rigged

The world’s largest radio telescope, completed in 2016, is called the Five-hundred-meter Aperture Spherical radio Telescope, or “FAST” for short. It was built by China in their Guizhou Province, and is larger in area than thirty football fields. If aliens ever give us a call, the Chinese will be the first to know.

Water may be fine for microwave cooking but it’s bad for astrophysicists, because the water vapor in Earth’s atmosphere chews up pristine microwave signals from across the galaxy and beyond. These two phenomena are, of course, related: water is the most common ingredient in food, and microwave ovens primarily heat water. Taken together, you get the best indication that water absorbs microwave frequencies. So if you want clean observations of cosmic objects, you must minimize the amount of water vapor between your telescope and the universe, just as ALMA has done.

Curious how much gas lurks among the stars in galaxies? Radio telescopes do that best. There is no knowledge of the cosmic background, and no real understanding of the big bang, without microwave telescopes. Want to peek at stellar nurseries deep inside galactic gas clouds? Pay attention to what infrared telescopes do. How about emissions from the vicinity of ordinary black holes and supermassive black holes in the center of a galaxy? Ultraviolet and X-ray telescopes do that best. Want to watch the high-energy explosion of a giant star, whose mass is as great as forty suns? Catch the drama via gamma ray telescopes.

The Kuiper belt is a comet-strewn swath of circular real estate that begins just beyond the orbit of Neptune, includes Pluto, and extends perhaps as far again from Neptune as Neptune is from the Sun.

Earth’s Moon is about 1/400th the diameter of the Sun, but it is also 1/400th as far from us, making the Sun and the Moon the same size in the sky

Io is the most volcanically active place in the solar system.

Pluto’s largest moon, Charon, is so big and close to Pluto that Pluto and Charon have each tidally locked the other: their rotation periods and their periods of revolution are identical. We call this a “double tidal lock,” which sounds like a yet-to-be-invented wrestling hold.

The Sun loses material from its surface at a rate of more than a million tons per second. We call this the “solar wind,” which takes the form of high-energy charged particles.

An alternative way to define the edge of our atmosphere is to ask where its density of gas molecules equals the density of gas molecules in interplanetary space. Under that definition, Earth’s atmosphere extends thousands of miles.

Orbiting high above this level, twenty-three thousand miles up (one-tenth of the distance to the Moon) are the communications satellites.