The problem of how stars manage to use helium as a further fuel in the giant E=mc2 pumps, however, hadn't gone much further than where Payne's work and the direct follow-ups had left it in the 1920s. The heat of over 10-million-degrees at the center of our sun was able, barely, to squeeze the positive charges of four hydrogen nuclei together to make helium. To squeeze together those helium nuclei in a burning process to get larger elements, you'd need to get higher temperatures. But the universe was well surveyed.
Where could you find something hotter than the center of a star?
Hoyle's habit of putting things together in his own way now came to the fore. At the start of World War II he was sent to a radar research group, and in December 1944, after an information-sharing mission to the United States, he ended up waiting in Montreal for a rare flight back across the Atlantic.
He wandered around the city and beyond, and also picked up information about the British research group at Chalk River (about 100 miles from Ottawa). Although nobody told him anything official about the Manhattan Project, from the names he heard there—including several whose work he'd known at Cambridge before the war—he gradually deduced the basic stages of the top-secret project still going on at Los Alamos.
The easiest way to accumulate the raw material for a bomb, he already knew from reading accounts published before the war, was by cooking up plutonium in a reactor. He also knew that Britain had not tried building reactors. That meant, he concluded, that the specialists must have found some unsuspected problem with the plutonium route; probably with getting the ignition to operate fast enough. Now, though, seeing the specialists in Canada, including experts in the mathematics of explosions, he realized it must have been overcome.
Oppenheimer and Groves had barbed wire and armed guards and layers of security officers around the plutonium detonation group at Los Alamos. But that was no protection against a man who'd managed to outwit the stern educational establishment of village Yorkshire. By the time he was finally assigned a seat on a flight back, Hoyle had outlined what Oppenheimer's hundreds of specialists had proven. A substance such as plutonium that won't fully explode on its own will certainly crash apart its own atoms if it's squeezed inward abruptly enough. Implosion raises the pressure and temperature enough to do that.
Everyone in the bomb projects had thought of implosion as intensely localized; suitable only for plutonium spheres a few inches across. But why did it have to stay so small? Implosion was a powerful technique on Earth. Hoyle was used to following his thoughts anywhere. Why couldn't it apply in the stars?
If a star ever imploded, it too would get hotter. Instead of being below 20 million degrees, its center could reach—as Hoyle quickly computed—closer to 100 million degrees. That would be enough to squeeze even the larger nuclei of more massive elements together. Helium could be squeezed to create carbon. If the implosion went further, the star would get even hotter, and then heavier nuclei would be created: oxygen, silicon, sulfur, and the rest.
It all depended on a star's actually undergoing this inner collapse, but Hoyle realized there was a plausible reason this should happen. When a star was still at the relatively cool 20 million degrees, and capable only of burning hydrogen, the helium that was produced would build up like ash in a fireplace. When all the hydrogen was used up, that ash wouldn't be able to burn. The upper reaches of the star would no longer be pushed outward by the fires within. They would come crashing inward—just as in the Los Alamos bomb.
When a star implodes inward, that would raise its temperature to the 100 million degrees that is enough to ignite the helium ash. When that helium is used up, a further ash accumulates and the next stage occurs. The carbon can't burn at 100 million degrees, so now a further level of the star crashes down. The temperature gets higher, and the cycles go on. It's as if a multifloor building were slowly collapsing, as the struts holding up one floor after another suddenly buckle and break. E=mc2 is central, for each level of burning—first the hydrogen, then the helium, then the carbon—gets its power from the conversion of mass into energy.
There were more details to come next, many contributed by Hoyle himself, but the idea taken from the atomic bomb had been central in solving the problem. Hoyle had simply switched the implosion process from the few pounds of plutonium laboriously collected on Earth, to a sphere of ultraboiling gas—a star—hundreds of thousands of miles wide, at immense distances away in space. He'd seen how stars can cook up the elements of life. When the larger of these stars used up their last possible fuel, it was also clear they'd have to break apart. Everything they had made would then pour out.
. . .
We tend to think of our planet as old, but when it was newly formed the heavens were already ancient; full of millions of these exploded giants. Their eruptions flung out silicon, and iron and even oxygen, to make the substance of Earth.
A large number of unstable elements such as uranium and thorium were created in the ancient stars' explosions as well, and when these elements floated over, becoming incorporated in the deep body of Earth, their continued explosions shot fragments of their nuclei at high velocity into the surrounding rock.
Along with the initial heat left over from the impacts of Earth's creation, the radioactive blastings from the uranium and similar heavy elements have kept our planet's depths from cooling. Their repeated multitudes of E=mc2 bursts helped produce enough churning heat underneath the surface to make the thin continents on top roll forward, so shaping the surface of Earth.
In some places, sections of the thin crust were pushed crumpling into each other, producing the lifted ripples we call the Alps, Himalayas, or Andes. In other places, the churning heat pulled open gaps that we know by such names as San Francisco Bay, the Red Sea, and the Atlantic. These made excellent collection basins for the hydrogen that had also landed, and as that combined with oxygen, the result was oceans of sloshing water. Iron deep inside the planet sloshed in its own more stately fashion, driven by the daily spinning of the whole globe around its axis. That sent up invisibly streaking magnetic lines, of exactly the sort Michael Faraday described, and reproduced, in the basement of London's Royal Institution 4 billion years later. The result was an invisible network of magnetic force lines, far overhead, helping shield the self-assembling carbon molecules on the surface from some of the worst of the spraying radiation from outer space.
Volcanoes exploded upward—powered by the constant E=mc2 derived heat beneath—and that led to something of a continuous conveyer belt from deep underground. Key trace elements were pushed up into the air, helping produce our fertile soil; great clouds of carbon dioxide were carried upward as well, creating a greenhouse effect in the young planet's atmosphere, and further ensuring the surface warmth needed for life. Where the frictional heat generated by the atoms blasting apart in accord with E=mc2 was especially concentrated, deep-sea volcanoes could billow up even through thousands of feet of cold ocean water—which is how the Hawaiian islands lifted above the Pacific waves.
Fast-forward several billion years, and mobile chunks of carbon atoms emerged (in other words, us!) to wade through low-flying clouds of star-created oxygen, stir caffeine-dense liquids of Big Bang hydrogen atoms, and read about how they came to exist. For we live on a planet where E=mc2 is constantly at work in the technology around us.
Atomic bombs were one of the first direct applications. At the start there were just a handful, laboriously created in the labs of the Manhattan Project, but soon there were many more, as a great infrastructure of factories and scholarships and research institutes became established after Hiroshima. Several hundred atomic or hydrogen bombs were built and ready by the end of the 1950s; today, even well after the Cold War, there are many thousands. To create them there were hundreds of open-air tests over the years, spraying immense gushes of radioactive particles into the stratosphere, there to float to every location on the planet; becoming a part of the bodies of every person alive.
Nuclear submarines were cr
eated, with radioactively exploding elements sequestered inside; pouring out heat that spun the turbines. They were fearsome weapons, yet thereby allowed a curious stability in the most dangerous phases of the Cold War. The previous generations of submarines, from World War II, had been unable to spend much time at battle stations. Cruising on the surface, World War II submarines might just manage to travel at the 12 mph of a person on a bicycle; taking the safer route, underwater, they moved at the 4 mph of a person walking. Once they'd crossed half the North Atlantic or the Pacific, they'd used up so much fuel that they quite soon had to engage in difficult wartime refueling, or turn around and trundle back. With nuclear-powered engines, it was different. Russian and American submarines could get into firing range, and then stay there for weeks or months on end— a dangerous standoff, but one at least making the other side very cautious about any moves that might provoke these hidden vessels to launch their missiles.
On land, huge electricity-generating stations were built, using the high-speed frictional heat of E=mc2 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=mc2 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=mc2 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=mc2 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 c2 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=mc2. 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=mc2. 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.
One of the key insights into what happens next—and within which E=mc2 is once again crucial—was first made by Subrahmanyan Chandrasekhar, a leader in twentieth-century astrophysics, whose career spanned almost sixty years. The discovery came when he was just nineteen, in the hot summer of 1930. The British Empire was in its dying days, but Chandra (the name he usually went by) was still within its dominion, and en route from Bombay to England, where he was taking up graduate studies at Cambridge.
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
Chandra was a cultivated young man, well read in the literature of India and the West, and especially fluent in German. He'd studied Einstein's papers, and met a few of Germany's leading physicists, on their trips to India. He knew that the dense core of a star is under a lot of pressure, and now he began to think about the fact that pressure is a form of energy.
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