Klaus Fuchs makes a full confession and is put in prison.
The good news, for him at least, is that when he was betraying his country he was giving information to an ally, not an enemy. That makes the penalty (under British law) fourteen years in jail, as opposed to a death sentence.
He ends up serving less than fourteen years, due to good behavior, and is released in 1959. He goes on to live a pretty normal life, filled with marriage and more atomic research, until he dies at the age of seventy-six.
Harry Gold ends up cracking under pressure as well.
This led to one of the most famous espionage trials of the century, the exposure of a ton of Soviet spies, the beginning of the Red Scare of the 1950s, and the death sentence for both of the Rosenbergs.
Gold, because he confessed everything, had his death sentence commuted to thirty years in jail.
Gold serves his time and is released in 1965; he dies seven years later.
Ted Hall, on the other hand, gets away scot-free.
Hall goes back to school to study physics, meets a girl named Joan, falls in love, and unlike what Gold did with his love, he confesses everything to her. They get married.
The decrypted telegram incriminating Hall surfaces, but he's ready for the feds when they arrive.
Despite intense questioning, Hall remains calm and doesn't give anything away. He knows that the feds are really reluctant to use the telegram in court, and so unless he confesses they can't nail him for anything. So he just…doesn't.
Eventually the FBI gives up.
The Hall family (they have three children) moves to Britain where Hall begins work at Cambridge University.
In 1995 the KGB's decoded messages are made public, and Hall is once again questioned—but this time by reporters. He declines to discuss details, but he does say that if he could do it all again he would've done things differently.
Ted Hall dies four years later at the age of seventy-four.
Robert Oppenheimer takes over as director of the Institute for Advanced Study in New Jersey and continues to work in Washington, D.C. as a scientific adviser to the government on atomic energy policy.
Oppenheimer and other scientific advisers are pondering the possibility of a hydrogen bomb, which would use fusion instead of fission.
The difference is that the power of such a bomb would be limitless: The more hydrogen you add, the bigger the blast. This would be terrifying.
They're debating whether building such a bomb would escalate the Cold War, or if it would cause the Soviets to back off in recognition of the U.S.'s obvious superiority.
The scientists all agree that building a hydrogen bomb would only further endanger the human race and escalate the Cold War—outcomes that nobody wants.
Except for Truman. He wants—no, needs—them to build a hydrogen bomb in order to beat the Soviets in the arms race.
Because he's the president, Truman wins the argument, and the scientists build a hydrogen bomb.
When it's tested in 1952, the hydrogen bomb is five hundred times more powerful than the bomb that took out Hiroshima.
The Soviets test out their own hydrogen bomb less than a year later.
Oppenheimer continues to argue for a de-escalation of the arms race, and this gets some attention from Lewis Strauss, chairman of the Atomic Energy Commission (AEC).
Strauss is annoyed at Oppie's opposition, so he accuses Oppenheimer of being disloyal to America. He digs up the FBI investigation from way back when and asserts that Oppenheimer has been a Soviet spy from the beginning.
Strauss strips Oppenheimer of his security clearance, therefore impeding his ability to advise the government.
Oppie has two options: walk away from the whole situation, because he knows he's fighting a losing battle, or demand a hearing for unfair treatment.
Oppenheimer gets a hearing but Strauss, who uses illegally obtained information against him in court, rigs it from the start.
Strauss accuses Oppenheimer of being a secret communist and not being honest about the whole Chevalier incident.
The judges—all handpicked by Strauss—buy Strauss's argument and rule against Oppenheimer.
Oppie is broken. His devastation over being betrayed by his own country that he worked tirelessly for is unbearable.
The FBI continues to monitor all of his movements and phone calls for suspicious activity.
Oppenheimer continues working in Princeton until his retirement in 1966. He dies a year later at the age of sixty-two from cancer of the throat.
Meanwhile, the arms race continues.
A massive hydrogen bomb tested on Bikini Atoll renders the island uninhabitable up to present day.
The Soviets test a bomb three times the size of the one from Bikini Atoll, which is just ridiculous.
Great Britain, France, China, and India all develop their own atomic bombs, too.
By the mid-1980s, the U.S. and Russia have sixty-five thousand nuclear bombs. Whoa. It's enough to destroy both countries within minutes—heck, it's enough to wipe out humankind.
Towards the end of the 1980s the United States and U.S.S.R. begin to negotiate treaties to reduce their number of atomic weapons.
However, since then Pakistan, North Korea, Israel, and probably Iran have developed their own nuclear weapons.
This is a frightening scenario: Say Pakistan and India go to war and drop fifty atomic bombs on each other (this is considered a "small" nuclear war). The firestorms as a result of the explosions would release so much dust and smoke into the atmosphere that it would make the planet colder and darker for ten years. Basically, everyone would eventually starve to death because no one could grow any food.
Long story short: we are capable of wiping our species off the planet in a matter of minutes. Sleep well tonight.