The MYSTERIOUS NUMBER that Shaped our Universe! Fine Structure Constant

References:

Chapters:
0:00 - Historical context of Fine Structure Constant
2:54 - What is the interpretation of Fine Structure Constant?
4:25 - How is alpha useful?
6:44 - How Arnold Sommerfeld found it
10:04 - How is alpha measured?
10:36 - Why is 1/137 significant?
12:40 - Where did fine structure constant come from?
13:50 - Fine Structure constant is NOT constant!

Summary:
This constant represented by the Greek letter alpha is just a dimensionless number, so no matter what units you use, it will always have the same value, about 1/137. If it was different by just 4%, life may not exist. What is the Fine Structure Constant? What does it mean? And why is it important?

At one time it was believed to be exactly 1/137, but today we have measured it more precisely, and it is not exactly that. it is now one of the most precisely measured constants. There is more than one way to interpret it. It is the ratio of the energy needed to overcome the electrostatic repulsion of two electrons, and the energy of a photon with the wavelength lambda λ.

The simplest way to think of it is the ration of the speed of an electron in a classical orbit to the speed of light. In other words, the speed of an electron orbiting an atom is about 1/137th the speed of light.

The number is directly related to the strength of the electromagnetic force. The higher the value, the greater the strength of attraction between an electron and a proton, and, the greater the repulsion between two of the same charges. One way to think of the fine structure constant is like coulomb’s constant expressed in dimensionless units.

This constant is found everywhere because in our macro world, the two fundamental forces we directly experience most are gravity and electromagnetism. Since electromagnetism determines chemistry, alpha is critical for life.

In Feynman diagrams, Alpha is related to the probability that an electron will emit or absorb a photon. It was German theoretical physicist, Arnold Sommerfeld who introduced it in 1916 when he was expanding the Bohr model of the atom. Prior to his work, Niels Born's model of the atom failed to explain the observed light emission of atoms. The energy levels appeared to split into two, whereas Bohr's model only predicted one. Those additional levels were very close to each other. But they indicated that Bohr’s model was incomplete. Sommerfeld was able to show that there is finer structure to the atom, that it has sub-orbitals.

Alpha can be measured experimentally at cyclotron accelerators by accelerating an electron in a magnetic field, and measuring its magnetic moment. The electron acts like a spinning bar magnet. The magnetic moment is related to the strength and direction of the magnetic field created by this electron. The alpha value can then be figured out from this measurement.

Why is this number 1/137 so significant? First, it’s a small number. This means that electromagnetism is relatively weak at least compared to the strong nuclear force. Consequently, electrons orbit on average, at a substantial distance away from the proton, which allows electrons to be available for exchange with other atoms, so that chemistry can take place. And thus life is possible. However, this number is not too large, because otherwise atoms would not form in the first place.

In 1957, English astronomer Fred Hoyle and others found that the abundance of carbon in the universe could be explained only if the fine structure constant had a value that made the nuclei of helium atoms more likely to fuse to produce carbon nuclei than otherwise. They calculated that if this constant was different by 4%, Carbon and Oxygen may not have existed.

What determines the value of α? Some believe it was set at the moment of the big bang due to the initial conditions from quantum fluctuations. Others think that there are tiny hidden dimensions that fix the value.

Is alpha really a constant? No. Alpha changes as a function of the energy, according to QED. It is very close 1/137 at zero Kelvin which is roughly the temperature of the universe, and at room temperature. But at 10^15 Kelvin near the big bang, it would would have been around 1/127, but after a few minutes it would have reached 1/137 as today.
#finestructureconstant
So why do we then call it a constant, if it actually isn’t? The answer is for most practical purposes in our current universe, it is constant.

[--alex--]

The craziest thing about fine structure constant is that Pauli (who was absolutely posessed by this number), when he was sick and dying, was taken (without neither him, nor doctors realizing it) to the hospital's room no. 137.

[huwphillips]

I've watched quite a few videos on this subject and Arvin has by far done the best job in explaining it. Well done Arvin, first class channel

[litltoosee]

For those interested, there is a very well done, and also not well known movie that involves the FSC, available on Youtube Movies. It's entitled "UFO", starring Alex Sharp, David Strathairn, and Gillian Anderson. Now before you roll your eyes and giggle, the film takes a very plausible look at the possibility of the FSC being employed as a measure for intelligence, and the basis of a universally common mathmatical tool for communication. It's a good watch and it's well written and produced.

[colinfew]

Fantastically easy to follow. This man is an absolute legend.

[vishnus.p.]

“If you can’t explain something to a first-year student, then you haven’t really understood.” — Richard Feynman
Now that's what you are doing !!! The way you explain each of your video makes any average person understand it !!! You are a good teacher and content creator !!!

[thestragequack]

This is one of the criminally underrated channel on YouTube. You're an amazing educator, sir.❤️

[Petrov]

The graphics and especially the meticulous accuracy in key details is astonishing. I can’t imagine the amount of time and effort invested in these masterpieces.

[petermarksteiner]

You didn't mention Arthur Eddington who came up with a theory why the denominator of the fine structure constant must be 136. When better experiments showed it to be 137, he came up with another theory. This earned him the nickname of Arthur Adding-one. Recently, Sir Michael Atiyah revived Eddington's work from its well-deserved oblivion, embellished by yet another theory to explain the decimal places. I tried to read Sir Michael's paper: it's very well written, but I'm afraid it doesn't make much sense. He was nearly 90 and would die a few months later.

[jedgrahek]

I watch a number of physics and astrophysics channels, and I have to say, you really do what you claim. Your explanation of concepts is always a perfect balance between full proper explanation and a little random fun... and your videos have that same vibe, like you clearly know what you're talking about, but I don't feel like there's a test coming up, which is the vibe of some other popular physics channels. This is really good stuff, glad I found you.

[dray]

Of all my years of watching physics lectures and books, this is the first i heard of this. Alvin keep up the good work on illuminating these missing subjects. Thanks

[ChannelSRL]

I've been waiting for a more comprehensive coverage of this topic -- and you delivered as usual.

[Chon]

For real, i want this channel to be more popular! It is incredible how you explain everything about physics!!!
Thank you very much!!

[nuefar]

My new favorite physics YouTube channel. No one else is talking about any of these obscure yet super interesting topics. Thank you sir!

[GururajBN]

I had never heard or read about the fine structure constant. Many thanks for the illuminating talk. Learnt something new today.

[PareshDesai]

Learnt something new for today. Now I will never forget 1/137 as magical number.

[zerk]

The highlight of my Sunday! Thanks for being good at what you do, Arvin Ash team! 👍🏼

[The_NASA_GUY]

Thanks for the explanation. I applaud the fact that you I said “I don’t know.” One of the problems in physics today is that not enough scientists say that phrase. I think it opens the path for others to look in that direction.

[mmotsenbocker]

this is an amazing video. I have watched 5 times and will look for the QED video next. I cant believe such high quality, insightful videos are found here

[solomonlalani]

Never to miss Arvin's explanation. Always a lot to learn! Keep going Arvin - you're helping the humanity! Besti wishes!

[bentationfunkiloglio]

Best physics discussions online! Thank you for putting these videos out.