Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100

future, the threshold could be dramatically lowered as the price of uranium enrichment plummets due to the introduction of new technologies. This is the danger we face: newer and cheaper technologies may place the atomic bomb into unstable hands.
    The key to building the atomic bomb is to secure large quantities of uranium ore and then purify it. This means separating uranium 238 (which makes up 99.3 percent of naturally occurring uranium) from uranium 235, which is suitable for an atomic bomb but makes up only .7 percent. These two isotopes are chemically identical, so the only way to reliably separate the two is to exploit the fact that uranium 235 weighs about 1 percent less than its cousin.
    During World War II, the only way of separating the two isotopes of uranium was the laborious process of gaseous diffusion: uranium was made into a gas (uranium hexafluoride) and then forced to travel down hundreds of miles of tubing and membranes. At the end of this long journey, the faster (that is, lighter) uranium 235 won the race, leaving the heavier uranium 238 behind. After the gas containing uranium 235 was extracted, the process was repeated, until the enrichment level of uranium 235 rose from .7 percent to 90 percent, which is bomb-grade uranium. But pushing the gas required vast amounts of electricity. During the war, a significant fraction of the total U.S. electrical supply was diverted to Oak Ridge National Laboratory for this purpose. The enrichment facility was gigantic, occupying 2 million square feet and employing 12,000 workers.
    After the war, only the superpowers, the United States and the SovietUnion, could amass huge stockpiles of nuclear weapons, up to 30,000 apiece, because they had mastered the art of gaseous diffusion. But today, only 33 percent of the world’s enriched uranium comes from gaseous diffusion.
    Second-generation enrichment plants use a more sophisticated, cheaper technology: ultracentrifuges, which have created a dramatic shift in world politics as a result. Ultracentrifuges can spin a capsule containing uranium to speeds of up to 100,000 revolutions per minute. This accentuates the 1 percent difference in mass between uranium 235 and uranium 238. Eventually, the uranium 238 sinks to the bottom. After many revolutions, one can remove the uranium 235 from the top of the tube.
    Ultracentrifuges are fifty times more efficient in energy than gaseous diffusion. About 54 percent of the world’s uranium is purified in this way.
    With ultracentrifuge technology, it takes only 1,000 ultracentrifuges operating continuously for one year to produce one atomic bomb’s worth of enriched uranium. Ultracentrifuge technology can easily be stolen. In one of the worst breeches of nuclear security in history, an obscure atomic engineer, A. Q. Khan, was able to steal blueprints for the ultracentrifuge and components of the atomic bomb and sell them for profit. In 1975, while working in Amsterdam for URENCO, which was established by the British, West Germany, and the Netherlands to supply European reactors with uranium, he gave these secret blueprints to the Pakistani government, which hailed him as a national hero, and he is also suspected of selling this classified information to Saddam Hussein and to the governments of Iran, North Korea, and Libya.
    Using this stolen technology, Pakistan was able to create a small stockpile of nuclear weapons, which it began testing in 1998. The ensuing nuclear rivalry between Pakistan and India, with each exploding a series of atomic bombs, almost led to a nuclear confrontation between these two rival nations.
    Perhaps because of the technology it purchased from A. Q. Khan, Iran reportedly accelerated its nuclear program, building 8,000 ultracentrifuges by 2010, with the intention of building 30,000 more. This put pressure on other Middle East states to create their own atomic bombs, furthering instability.
    The second reason the geopolitics of the twenty-first century might be altered is because another generation of enrichment technology—laserenrichment—is coming online, one potentially even cheaper than ultracentrifuges.
    If you examine the electron shells of these two isotopes of uranium, they are apparently the same, since the nucleus has the same charge. But if you analyze the equations for the electron shells very carefully, you find that there is a tiny separation in energy between the electron shells of uranium 235 and uranium 238. By shining a laser