E=mc2 (20 page)

On land, huge electricity-generating stations were built, using the high-speed frictional heat of E=mc
²
to power up generating turbines. It's not the most sensible of energy choices, for even nonnuclear explosions at the generating stations can be pretty terrifying—and nothing deters corporate financial officers as much as the phrase "unlimited liability"; the radioactive walls and radioactive cement base and radioactive residual fuel from every such generator are a lot of liability to be disposed of. In France, however, the government assumes those charges, and doesn't allow court cases against the industry: about 80 percent of the country's electricity is nuclear. When the Eiffel Tower is lit at night, the electricity comes from a slower reenactment of the exploding ancient atoms that took place over Hiroshima.

E=mc
²
continues at work in ordinary houses. In the smoke detectors screwed tight to the kitchen ceiling, there's usually a sample of radioactive americium inside. The detector gets enough power by sucking mass out of that americium and using it as energy—in exact accord with the equation—that it can generate a smoke-sensitive charged beam, and keep on doing so for months or years on end.

The red-glowing exit signs in shopping malls and movie theaters depend directly on E=mc
²
as well. These signs can't rely on ordinary light sources, because they'd fail if the electricity went out in a fire. Instead, radioactive tritium is sealed inside. The signs contain enough fragile tritium nuclei that mass is constantly "lost," and usefully glowing energy sprays out instead.

In hospitals, medical diagnostics constantly harness the equation. In the powerful imaging devices known as PET scans (Positron Emission Tomography), patients breathe radioactive oxygen isotopes. The center of those atoms shatter apart, and streaks of energy coming from the destroyed mass are recorded as they emerge at extremely high speed from the body. The result is pinpointed readouts on tumors, blood flow, or drug take-ups inside the body—the workings of Prozac in the brain, for example, have been studied this way. In radiation treatment for cancer therapy, minuscule quantities of substances such as radioactive cobalt are aimed at tumors. As the unstable cobalt nuclei break apart, mass once again is seemingly torn out of existence, and the resultant energy is aimed with enough power to destroy cancerous DNA.

Yet other unstable varieties of carbon are constantly being formed outside the windows of passenger jets, created by incoming cosmic rays, some of which reach us from distant portions of the galaxy. We've been breathing in the stuff all our life. Hold a sufficiently sensitive Geiger counter over your hand, and it registers the telltale clicks. (What it's actually doing is "listening" to tiny miniatures of Einstein's 1905 equation. Every click of the Geiger counter is a mark that one or more operations of E=mc
²
has taken place, as the unstable nucleus of that new carbon atom plops out the extra neutron it gained high in our atmosphere.) But when we stop breathing—or when a tree dies, or a plant stops growing—no more fresh carbon is coming in. The clicks slowly die away.

This unstable carbon is the famous C-14. It's a clock, and its use has revolutionized archeology. Using carbon dating, labs could prove that the Turin Shroud was a medieval forgery, as some of the carbon in its flax had been running down since the fourteenth century, but not earlier. Carbon fragments could be collected from the Lascaux caverns, and Indian burial mounds, and Mayan pyramids, and early Cro-Magnon sites, and for the first time be used to date them accurately as well.

Soaring even higher, the satellites of the U.S. Defense Department's GPS navigation system create a constantly swirling tessellation beyond the atmosphere. The signals they beam down are constantly shifted out of sync by the time-distorting effects of relativity, as we saw in Chapter 7, and just as steadily have to be fixed, by programmers who adapted Einstein's insights to correct for the drift that would otherwise be created. And finally, perched most distant of all, is the exploding sphere of our sun, using the boomingly magnifying power of c
²
to warm our planet, as it has done for all the billions of years needed for this life-dense vista to evolve.

A Brahmin Lifts His Eyes Unto the Sky
I6

Even though the sun is vast, it can't keep on burning forever. Heating the entire solar system takes immense amounts of fuel, even for a furnace that pumps material directly across the equals sign of E=mc
²
. The sun's mass is now 2,000,000,000,000,000,000,000,000,000 tons, but it consumes about 700 billion tons of its own bulk as hydrogen fuel to keep the multimegaton blasts going each day. In a further 5 billion years, the most easily available portions of that fuel will be gone.

When that happens, and all that remains at the center is helium "ash," the reactions in our sun will start shifting upward a little bit, as fuel closer to the surface starts being pumped through E=mc
²
. The outer layers of the sun will expand, and cool down just slightly enough to glow red. The sun will keep on expanding, and keep on glowing, until it reaches Mercury's orbit. That planet's rock surface will have already melted; fragments that are left will now be absorbed in the flames. Then, a few tens of millions of years later, our red-giant sun will reach the orbit of the planet Venus, and absorb it as well. But what will happen next?

Some say the world will end in fire,

Some say in ice.

Robert Frost published that in 1923, when he was pretending to be an apple farmer in Vermont. But he'd written the first draft when he'd been on the faculty at Amherst, and so had a good deal of time to read. Most science writers of the time had settled on the image, popular from the famous French naturalist Buffon's time through the late Victorian period, of a great cooling down of the universe. But others contrasted that with earlier apocalyptic images from Revelation, where fire and outpourings took over at the end.

What will happen to Earth is actually both. Any beings left alive on the surface of the Earth in the year A.D. 5 billion will see the sun get larger and larger until it fills about half the daytime sky. The oceans will boil away, and surface rocks will melt. Possibly life could migrate to other planets, or survive in deep tunnels, using technology unimagined now; possibly our planet will have long been barren when the emptying sun fills up the sky.

The sun will hold at that great size for about another billion years, as the helium ash left inside takes over the main burning: still seeming to pump mass out of existence; still producing fiery glowing energy in its place. Then it'll shrink, as the supporting struts of that glowing energy become too weak. In time so much fuel will have been emptied out of the sun that the burning will no longer be steady.

This is what will bring in the ice. As fuel pockets inside run low, the sun's surface will sink inward; shortly after, as other dispersed fuel sources get tapped, the energy output will roar higher again, and the surface of the sun will whip upward. Sonic booms are produced each time, but these are nothing like the brief crack of a single plane passing the sound barrier. At this stage, six billion years into our future, it's the final boom of the Titans.

Enough mass is blown away at each bounce upward, that within just a few hundred thousand years, there will be much less of our sun than before. What's left will be too weak to possess the same gravitational field it had before. If the Earth hasn't already been absorbed by the expanding sun, then—after n billion years of steady orbit—the sun's grip will let the planets go. The solar system breaks up, and Earth flies away.

There were storms in the Arabian Sea that August, keeping everyone in their cabins, but when Chandra recovered, he had weeks of quiet cruising before him, several sheaves of paper, and a family habit of always using spare time productively. It was even an occasion when the usual racism of the Empire had its advantages: Chandra was a Brahmin with dark skin, and although the children of some of the white passengers would try to play with him—and he'd oblige—the parents would quickly lead them away.

In the uninterrupted time at his deck chair, he became one of the first to realize something very odd about the objects in the sky above us. It was known that giant stars can explode, with their top portions rebounding away after they've collided with the heavy, collapsing core within. But what happens to that remnant core, after the explosion?

Subrahmanyan Chandrasekhar

AIP EMILIO SEGRE VISUAL ARCHIVES, CHANDRASEKHAR COLLECTION

And energy is just another sort of mass.

Energy might be more diffuse than mass, perhaps, but as E=mc
²
shows, they're both just different versions of the same thing. Once again, the two sides of the equation— the "E" and the "m"—don't actually have to slip across and "turn into" one another. Rather, what the equation's really saying is that a chunk of what we call mass actually is energy: it's just that we're not used to recognizing it in that guise. Similarly, a glowing or compressed amount of energy really
is
mass: it just happens to be in a more diffuse form than we easily recognize as mass.

Chandra was about to glimpse the process leading to black holes. He merely had to trace this logic forward as it spiraled in an escapable catch-22. A compressed star core is under a lot of new pressure, and that pressure can be considered a sort of energy, and wherever there's a concentration of energy, the surrounding space and time will act just as if there's a concentration of mass. Gravity in the remnant star gets more intense, due to all this "mass." But that stronger gravity continues squashing what's left, so the pressure gets greater once more. Since the pressure can yet again be treated as simply more energy, then—as Chandra now saw by the tremendous insight of E=mc
²
—it acts as yet more mass. The gravity ratchets up.

In a small enough star, the buildup of pressure is low enough for the stiff material near the star's center to resist it. But if the star is massive enough, the process keeps on going. It doesn't matter how tough the star's material is; indeed, if it's exceptionally resistant, that will soon just make it worse. For suppose a giant star could hold up under even greater pressure than expected: immense, unthinkable, trillions upon trillions of tons bearing down. Well, that extra pressure would "be" more energy, which would mean it acts just as if it had more mass, and so the gravity would get even stronger, compressing it ever more.

Regardless of how hard the substance is at the core, the inside of the star will be crushed until. . .

Until what?

Chandra had all the openness to fresh thoughts of youth, but even he had to pause now. Could he be predieting that the inside of the star would actually disappear? If he was right, then rips were opening up in the very substance of the universe! He took time off for prayers and meals; he even spent hours politely listening to a Christian evangelist, who explained to this devout Hindu why all religions from India were the work of the devil. "He was a missionary," Chandra remembered later, "but he was also . . . anxious to please. Why be rude to him?"

When Chandra resumed work in his deck chair, he realized that he couldn't actually say what would happen to the remaining substance of the star, as it poured into the hole created by this never-ending collapse. But it was known in accord with other work of Einstein that space and time near the star would be strongly distorted by its presence. No light would ever escape; nearby stars that were pulled into its gravitational presence would get torn apart by what seemed an "empty" location in space.

This, along with other insights, was central to the modern concept of black holes. But once Chandra reached England, his vision was resisted by almost everyone he presented it to; often with less politeness than he'd granted the missionary. Eddington himself, the man who'd been
so
inspiring for Cecilia Payne, was now too old for any more such fancies. It was "stellar buffoonery," he declared. It was "absurd." But by the 1960s there was the first evidence of a star (look in the direction of the constellation Cygnus the Swan, and it's a little to one side) that spins around an area that to our telescopes seems to be entirely empty space. The only thing that would be powerful enough to do this in so small a space would be a black hole. In the center of our own galaxy, there's strong evidence of another black hole, a truly monstrous one, which has accumulated to a great size over the aeons, swallowing, on average, the equivalent of one ordinary star each year. Space-time is actually being "torn" open—as the young Chandrasekhar had been the first to see.

Chandra tried to fight Eddington's hostility in the 1930s, but when he found that even British astrophysicists who believed he was right were scared to back him in public, he ended up leaving England. He received a kinder welcome in America, and in an association with the University of Chicago went on to decades of work-culminating in his Nobel Prize in 1983, over a half century after that Arabian Sea voyage—which proved central in understanding what's in store for us next.

Six billion years from now, if Earth is flung loose from the fuel-emptied sun, any survivors or sensing devices left on our planet's surface will see a horizon darker than today's night sky. For the stars themselves will have used up their fuel and be dying out: the most fiery ones first, then the rest.

Earth's flight won't be stable through this darker expanse. Our Milky Way is already on track to collide with the Andromeda galaxy, and in several billion years, about the time of Earth's escape or immolation in the solar system, the great collision should finally happen. The spaces between stars are so great that most of the dimmed suns will just slowly pass between each other, without direct impact, but the turbulence will be enough to shift an escaped Earth's trajectory once more.

If Earth slingshots inward, then in a few tens of millions of years we will be within range to be absorbed by the giant black hole at the galaxy's center. If we get slingshot outward, however, the end will simply be delayed. By 10
¹⁸
years from now (1 followed by eighteen zeroes, or 1,000,000,000,000,000,000 years from now), all galaxies are liable to have emptied out because of such collisions. The black holes in the centers of the galaxies will slowly travel on their own, sucking mass and energy from the universe wherever they contact other objects. If it's another black hole that they randomly impact, then they simply merge, to become an even larger devourer. A few hours after coming within range of one of these, Earth and any distant descendants on it will be taken out of existence.

By 10
³²
years into the future, protons themselves might have begun to decay, and gradually very little of ordinary matter will be left. The universe will be composed of a greatly reduced category of things. There will be electrons of the sort we're used to, with a negative electric charge, and there will be curious antimatter versions of electrons, with a positive charge, and along with neutrinos and gravitons there will be the swollen black holes, and even a cooled remnant of photons left over from the first seconds of creation, still traveling at their eternal 670 million mph speed after all these ages.

It doesn't end there, for given enough time even black holes can evaporate. Everything they engulfed will be released back—not in any recognizable form, but as an equivalent amount of radiation.

The universe will have ended up in a state curiously transposed from what it was at the start. For in the very first moments of creation, long before the sun was formed, the universe was immensely dense, immensely "concentrated." That great density meant that large amounts of radiation were "pushed" along E=mc
²
, from the "E" side to the "m" side. The ordinary matter we're familiar with took shape out of pure energy, ultimately creating the stars and planets and life-forms we know. But now, near the end of time, over 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 years into the future, it's different. Everything is far more dispersed, far more diffuse.

What will exist then will be spread over distances we cannot imagine. The rush of activity of early epochs will be over. That was just an interlude in the final history of the universe. Now, mass and energy only very rarely transform into each other. There is a great stillness.