Shulou(Shulou.com)11/24 Report--

On July 16, 1945, before the United States tested the world's first atomic bomb, physicists Enrico Fermi and Oppenheimer were betting on whether the atmosphere would be burned by a nuclear bomb. He may have been joking at the time, but many of the world's top scientists have thought about it to ensure that the world is not accidentally destroyed by the first atomic explosion.

The story begins a few years before the first nuclear bomb exploded, and Edward Taylor, a physicist involved in the Manhattan Project, said, what happens to the air if a nuclear bomb explodes in the air? Their concern is that the intensity of a nuclear explosion may be so strong that it fuses atoms in the air. And this fusion will release energy, so that other atoms around them will also be fused. The resulting chain reaction will spread to all the air on the earth and eventually destroy the earth.

Physicists envision two possibilities, but some calculations are needed to solve the problem. The first possibility is that when a nuclear bomb explodes, its energy expands outward in a sphere, and if that energy leads to additional fusion, the sphere will become larger and larger until it consumes everything. Another possibility is that when a nuclear explosion occurs, even if it fuses in the surrounding air, it actually loses more energy to the environment than it gains, so eventually the sphere will dissipate harmlessly.

Physicists have found that most of the fusion energy gain will come from a single reaction. 78% of the air we breathe now is nitrogen, which is relatively less stable than other atmospheric gases. The fusion reaction between two nitrogen nuclei produces magnesium, alpha particles and 17.7 trillion electron volts. The energy sounds small, but the danger here is that the air is so rich in nitrogen that if all these nuclei undergo the same fusion reaction, the energy released will be huge.

In addition, when a nuclear bomb explodes, a huge kinetic energy hits the air violently. Impacted protons and neutrons are relatively good at grabbing the energy they give to maintain the temperature of the plasma. On the other hand, the electrons flying around are not, they radiate energy quickly. When you provide energy to an electron and then slow down in the presence of an electric field (such as a field from charged particles in a nuclear plasma), it will trade some of its kinetic energy for electromagnetic energy and slow down. This so-called Bremsstrahlung is the main energy loss that physicists consider during a nuclear explosion.

Now that we know the main energy gain and energy loss in a nuclear explosion, in theory, if the energy gained during the event is greater than the energy lost in the environment, our atmosphere may be ignited. So if we divide these two values, we can see how close the atmosphere is to that very important point of ignition. We define the energy loss divided by the energy gain as the safety factor, and hope that this number is much larger than one.

Physicists have concluded from complex calculations that the safety factor could be as low as 1.6. An intuitive comparison is that the safety factor of the engine in the car is higher than this. This value is so low that if any of the calculations deviate by a few percentage points, we are at risk of human extinction. The safety factor is so low that a rational person would not take such a big risk, so why do nuclear tests continue?

In fact, the most important temperature is missing in these mathematical calculations. In these calculations, if the safety factor is close to 1, the temperature of the nuclear explosion needs to be as high as 1000 billion Kelvin. At that time, even the highest temperature produced by the theoretical fusion bomb was only about 100 million Kelvin, a thousand times lower. As a result, they increased the safety factor from one to more than 1,000, and taking into account this enhanced safety factor, the original report concluded that current calculations show that there is no ignition point in the atmosphere.

The huge safety factor is not enough to quell concerns, and scientists have calculated that to maintain the fusion temperature and produce a chain reaction, the explosion needs to produce a huge fireball more than 100 meters in diameter. In other words, all of a sudden, in a spherical region with a diameter of more than 100 meters, it is several orders of magnitude brighter than the sun, which is very impossible. In addition, they found that the energy needed to create this apocalyptic atmosphere is 20 times that contained in the entire world's nuclear arsenal. We don't have the nuclear technology to ignite the atmosphere.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

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