Reborn and become a Great Scientist

Chapter 76 24 Bohr vs. Conservation Laws

Bohr, who was far away in Copenhagen, Denmark, naturally could not have foreseen that a paper that might give him a fatal blow was about to be published in the Cavendish Laboratory under the helm of his teacher Rutherford.

At this time, Bohr was in his own office in the building of the Institute of Theoretical Physics at the University of Copenhagen, enthusiastically publishing his high-spirited speeches.

The only difference from before was that the audience sitting on the sofa was not only his assistant Kramers, but also John Slater, who had just graduated from Harvard University and traveled across the ocean to Copenhagen for gilding.

Slater was the first American to come to the Institute of Theoretical Physics. This American who was willing to accept new things also brought a new idea to the Institute, that is, Einstein's photon exists, but at the same time There will be some kind of wave that guides the behavior of the photon so that its motion conforms to Maxwell's wave theory.

This time, before Bohr made a move, Kramers was the first to jump out and teach the rookies.

He justly refuted Slater's idea, copied what Bohr said when he scolded him, and tried to persuade the American to accept the boss's view that the photon could not exist.

However, Bohr listened to some of Slater's ideas, and he thought of the corresponding principle he had proposed before: phenomena in the atomic domain and phenomena in the macroscopic domain can each follow the laws of their respective domains, but when the microcosmic When the laws in the range extend to the classical range, the numerical results obtained by it should be consistent with those obtained by the classical laws.

He felt that the idea of ​​a newcomer, Slater, was not without merit. It was worth spending a lot of effort. Using the principle of correspondence to correct the fallacies in it, he might be able to write a good paper.

As a result, the three people began to stay in the same office day after day, "co-writing" a new paper, just like the communication Bohr wrote to the Journal of Natural Sciences.The specific division of labor is as follows:

Bohr was in charge of pacing back and forth in the room with a pipe in his mouth, occasionally muttering his views to the two of them.

Kramers is still in charge of faithfully recording, never leaving a single word that pops out of his teacher's mouth in his notebook, not missing a spark of thought.

However, Stry, who was the proponent of the point of view, seemed to have nothing to do with what happened in front of him, so he could only sit on the sofa on the other side and stare at the ceiling.

In less than a week, Bohr satisfactorily concluded his new theory, which is surprisingly fast in the history of Bohr's thesis writing.

But the content of the thesis has changed beyond recognition, basically without the shadow of Slater's original thinking.

Correspondingly, the order of authors of this paper is Bohr, Kramers and Slater, so the theory proposed by them is called "BKS theory", This paper is also called "BKS paper".

Of course, Bohr deserved his name as the first author: in this paper, which is as long as dozens of pages, it is densely packed with words, but there is not even a single mathematical equation.

In his first paper on gamma ray scattering, Chen Muwu only used the law of conservation of momentum and law of conservation of energy, which are well known to high school students and even junior high school students.

By means of these two conservation laws, Chen Muwu deduced the conclusion that photons exist.

In order to insist on the bottom line of the non-existence of photons, Bohr proposed a very bold idea: starting from the corresponding principle he proposed before, he denied the two basic physical laws of momentum conservation and energy conservation!
Bohr proposed in the BKS theory that these laws of momentum conservation and energy conservation in classical physics are only established in the statistical average of a large number of collision events, and under microscopic conditions, the momentum and energy of a single electron when it is affected by electromagnetic waves does not Conservation.

His risky move negated the theory put forward by Chen Muwu in his first thesis.

Because whether it is Chen Muwu's first paper, or the physicists who have done a lot of experiments after reading the paper, all they have done is to measure the wavelengths of the incident and scattered gamma rays, which is indeed a statistical average result.

But even so, Bohr needed to spend a lot of space in his thesis to construct an extremely tortuous and complicated new theory in order to provide an alternative analysis for the scattering of gamma rays.

Now, there is only one way to refute Bohr's BKS theory, and that is to find evidence that the wavelength change is not only a statistical average, but also can be intuitively reflected on a single photon and a single electron, that is to say, classical physics The two conservation laws in are also applicable in the particle collision.

Coincidence isn't it?

Chen Muwu asked Kapitza and Blackett to take photos to prove this point!
……

When Einstein first proposed the quantum theory of light, in order to prove its correctness, at the Salzburg Conference in 1909, he proposed a not-so-famous thought experiment, "Einstein Soap Bubble":
He first asked everyone to imagine that the heat of the cathode ray tube could be turned down infinitely low, so that only a single electron could escape from the filament as the cathode every time.

This electron will run straight to the anode and hit a point on the screen there (Figure a).

It was just an unremarkable particle motion that no one bothered to think about, and the scientists present accepted it.

Einstein asked everyone to imagine that the energy of a light source is also adjusted very low, so that this light source can only emit a single quantum of energy each time.

If light is indeed the electromagnetic wave that Planck believed, then the light emitted from this point source should be a spherical wave, like an expanding soap bubble, and "spread" uniformly in all directions at the same time (Figure b).

However, when the spherical wave is absorbed somewhere, all the energy in the soap bubble will suddenly concentrate on that point, because it can only be absorbed as a whole energy quantum (as shown in figure c).

It obviously doesn't make sense that the energy of light spreads out like an expanding soap bubble while being absorbed and then magically concentrates at a single point.

In the end, Einstein concluded that if light is a particle like electrons in the whole process of emission, propagation, and absorption, it is reasonable.

His soap bubble paradox did not attract the attention of the scientists present.

In 1917, when using the Bohr atomic model to deduce the law of quantum radiation, Einstein discovered that atoms can only emit one photon in one direction at a time, and it is absolutely impossible to generate spherical waves like soap bubbles. will never reach thermal equilibrium.

An atom emits a photon in one direction, and the photon travels in a straight line until it reaches its destination and is absorbed by another atom.

Here, the photon exhibits particle properties like electrons, but has no wave properties, which completely violates all the experimental phenomena about light interference and diffraction for more than 100 years.

In order to perfectly resolve the irreconcilable contradiction between the two, Einstein once assumed that there may be a "ghost field" that conforms to Maxwell's equations, so that photons also conform to the wave form.

But the soap bubble paradox he put forward a few years ago once again made him feel trapped.

The "ghost field" of a point light source must spread outward in the form of spherical waves, while photons can only appear in one place.

Einstein could not give a strict mathematical expression to this "ghost field", so he did not officially publish a paper, but only put forward this point of view in the small circle of scientists such as Lorentz and Sommerfeld.

Bohr was also aware of the "ghost field" proposed by Einstein, and he believed that the view of the ghost field was similar to the statistical average proposed by himself in the BKS theory.

So even knowing that Einstein was a firm supporter of light quantum theory, Bohr carefully sent a copy of his BKS paper to Einstein who had returned to Germany, hoping to hear his opinion .

As for the original paper, of course he sent it to the "Proceedings of Natural Science" of the Royal Society of England.

……

When Bohr's thesis was still adrift on the ship and rushed from Copenhagen to London by sea, Kapitsa and Blackett were busy preparing for the end of the term.

Mahjong tiles, the boxy little pieces of bamboo, are so harmful that Kapitsa is determined not to play more than two rounds a day until the spring semester exams and thesis defenses are all over.

And Chen Muwu, who has nothing to do, has already begun to enjoy his leisure time in summer.

(End of this chapter)