Illustration by Tom Bachtell

In 1950, Bruno Pontecorvo, an Italian physicist who had been working on British and Canadian nuclear projects, vanished while vacationing on the Mediterranean. As Frank Close writes in a new book about him, “Half-Life,” Pontecorvo wasn’t heard from again until 1955, when he resurfaced in Russia. There were many wild rumors about what he was working on for the Soviets, among them an “atomic fog.” But Freeman Dyson, reviewing the biography in The New York Review of Books, asks how much rogue physicists like Pontecorvo really mattered: “Perhaps the spies accelerated the production of the first Soviet bombs by two or three years, but those bombs soon became obsolete and were superseded by new designs invented without the help of spies.”

Dyson, as a physicist, must appreciate that the significance of two or three years in the life of a nuclear-weapons program can be relative. Last Tuesday, Benjamin Netanyahu, the Israeli Prime Minister, speaking to a joint meeting* of Congress, at the invitation of John Boehner, the Speaker of the House, dismissed a potential deal that the Obama Administration is pursuing, which would effectively keep Iran from having the means to build a bomb for ten or fifteen years. The time gained would be meaningless if Iran was not first fundamentally incapacitated and transformed, Netanyahu said. “A decade may seem like a long time in political life, but it’s the blink of an eye in the life of a nation.” (The two weeks between Netanyahu’s speech and the Israeli elections may seem like an indecorously short time in political life.) Speaking about Iran’s “tentacles” and its “gobbling up” of other countries, he suggested that President Obama didn’t know what he was doing. Former House Speaker Nancy Pelosi, who shook her head as she watched the speech (more than fifty Democrats stayed away), said that she was “saddened by the insult to the intelligence of the United States.”

And yet, despite Netanyahu’s posturing, there is a serious question about timelines. For several years, Iran has been said to be one, two, or three years away from having the capacity to build a bomb. The Administration’s goal is to prevent it from getting any closer. The rough outline of the deal, judging from leaks and the Administration’s briefings, is that Iran would allow intrusive inspections, limit its nuclear-fuel-production capacity, and give up fuel stockpiles. In return, the United States and its allies would lift sanctions. The deal, reportedly, would have a ten- or fifteen-year sunset clause, although the State Department has indicated that some improvements in inspections would remain. From Netanyahu’s point of view, Iran would then be able to pick up where it left off, and from a position of greater strength, with its economy “unshackled,” as he put it. Iran has cheated before and might try to again (although a deal would make it easier to detect any covert programs), and it could still be sponsoring militias and terror. There are legitimate concerns, but one thing that Netanyahu did not present was any real alternative to the deal.

“Folks, simply demanding that Iran capitulate is not a plan,” Secretary of State John Kerry said, after Netanyahu’s speech. He was in Montreux, Switzerland, where he and other representatives of the P5+1 (the permanent members of the United Nations Security Council and Germany) were engaged in talks with the Iranian Foreign Minister, Mohammad Javad Zarif. Obama spoke of America’s “unbreakable” bond with Israel, but he, too, emphasized that the deal was the best way to stop a bomb—“Nothing else comes close. Sanctions won’t do it. Even military action would not be as successful.”

A problem with the anti-diplomacy position is the one that Dyson confronts: building a bomb has ceased to be a great puzzle; nuclear programs no longer rely on physicists disappearing mysteriously from Italian beaches. When Netanyahu said that the deal, by freeing Iran to be more “aggressive,” would “spark a nuclear arms race” in the region, he was acknowledging that there are any number of countries that, without too much difficulty, could acquire a nuclear bomb if they had the money and the political will. (Saudi Arabia, certainly, has the budget.) At worst, hostile disruptions of the Iranian program could accelerate it by pushing the country’s leaders to abandon the restraints Iran has already accepted. At best, they would do on a small scale something that a deal would do better—create more time.

A key concept in the negotiations is “breakout time”; that is, how quickly Iran could assemble the materials for a bomb if it reneged on a deal. Mostly, this is a question of obtaining enriched uranium, or having the centrifuges to produce it. The more centrifuges a country has spinning, the shorter the breakout time. At the moment, Iran has about nineteen thousand, which it says serve only civilian energy needs; the expectation is that a deal would reduce that number, so that the breakout time would be a year or more.

Breakout time is a concept that might also be applied to politics. What difference can two or three—or ten or fifteen—years make? Between 1949, when the Soviet Union tested its first crude fission bomb, and 1953, when it exploded a hydrogen bomb (perhaps with help from Pontecorvo) the leadership shifted from Stalin to Khrushchev. The years from 1982 to 1991 saw four general secretaries—from Brezhnev to Gorbachev—and the dissolution of the Soviet Union. In Iran, the relationship between Ayatollah Ali Khamenei and President Hassan Rouhani, whose election held some promise for reformers, is opaque, though Rouhani seems to be pushing the talks. The terms are relative here, too; last week, Rouhani called Israel a warmonger. But the world made it through the decades of the Cold War in large measure because of imperfect arms agreements with dubious partners. If we rely only on financial and military threats, nonproliferation will fail.

In an indication of the complexity of the moment, Iran and the United States have a shared goal in Iraq: to take the city of Tikrit back from ISIS. Netanyahu warned Congress not to be “fooled” into thinking that Iran could be a friend in this fight. “One calls itself the Islamic Republic. The other calls itself the Islamic State,” he said. “In this deadly game of thrones, there’s no place for America or for Israel.” On the way back from Montreux, Kerry stopped in Riyadh, in part to reassure the Saudis about the operations in Iraq. (The Saudis oppose isis, but they, like ISIS, are Sunni, and Iran is Shiite.) If a deal were to be struck, all the other challenges related to Iran would remain, Kerry said, “except that we will have taken steps to guarantee that Iran will not have a nuclear weapon.” At least, for a useful period of time. ♦

*An earlier version of this story identified the joint meeting as a “joint session.”