The Guy Who Fought Einstein... and Won

He battled with Einstein about Quantum Physics, and WON

Niels Bohr was a genius in his own right, contributing hugely to the developing theory of quantum mechanics. In this video, we take a look at what is probably his most famous work - the Bohr Model of the atom.

Before Bohr came along, scientists suspected that atoms contained scattered regions of positive charge, with small negative electrons distributed throughout. This was known as the Plum Pudding model.

Ernest Rutherford, conducting the Gold Foil / Geiger Marsden experiment with his students, realized that this could not be right. When positive alpha particles were fired at a thin gold foil, instead of them all passing right through with minimal deflection, something curious was observed.

Some passed through with minimal deflection, others passed through with large deflections of around 90 degrees, and a very small proportion actually came back almost towards the detector - at nearly 180 degrees of deflection. Rutherford said this was like firing a shell at a piece of tissue paper, and the shell coming back to hit you - very unexpected.

He realized that the positive regions in the atoms must have been distributed over very small regions, with all the positive charge being concentrated there. So when the alpha particles came very close to these regions, they would deflect hugely. A glancing blow resulted in the roughly 90 degree deflections. However because atoms were mainly empty space, the large majority of alpha particles passed right through the gold foil.

Rutherford then developed his Planetary model - with electrons orbiting the positive region known as the nucleus. This was great, but had problems of its own. If electrons were to orbit the nucleus, then they would be accelerating due to their constant change in direction.

The physics of charged objects told us that accelerating charges would radiate, and lose energy. This can be seen from the Larmor formula, which calculates the given power radiated by a charge at a given acceleration.

Therefore, Rutherford's atoms should have been unstable, with the electrons radiating energy away and spiraling inward to the nucleus. This is where Bohr came in.

Bohr realized that there was something holding electrons specific distances away from the nucleus. He called these "allowed" locations "energy levels". His model explained why electrons did not radiate constantly, and also explained the emission spectra observed from atoms. Instead of emitting radiation at all frequencies as electrons spiraled, we would only see specific emissions based on the differences in energies of the allowed levels, whenever electrons transitioned inward.

He also found a wonderfully neat mathematical relationship that explained where the "allowed" energy levels were in relation to the nucleus. He found that an electron's angular momentum in a particular energy level had to be a multiple of the Reduced Planck Constant - a very important constant in quantum mechanics.

The angular momentum of the electron, dependent on the mass and speed of the electron, as well as the radius of the path it was moving on, could be calculated by setting the electric attraction force between the electron and the nucleus to be equal to the centripetal force needed to keep it moving on that orbit. From there, with a bit of math, it was possible to calculate exactly where (i.e. at what radii) the allowed energy levels could be found!

0:00 - Niels Bohr - An Introduction
1:12 - The Plum Pudding and Planetary Models of the Atom
3:16 - The Big Problem with Rutherford's Model
5:14 - The Bohr Model of the Atom
6:17 - What Are the "Allowed" Energy Levels?
8:31 - More About Bohr

[prakshyatsahu]

As a physics student, it was so frustrating to learn each atomic model and then being told " oh its not quite correct " 😢 great video regardless👍

[QuantumPianist]

Beautifully explained. I've never seen a clearer explanation of the Bohr model than this. Thank you.

[aayushashok]

I don't know if I missed something, in the Bohr model, why the electron doesn't just collapse into the nucleus by emitting radiation (even if its in descrete quantities), just like the drawback mentioned for the Rutherford model.

[anisyafs]

wow, the more I learn, the more I realize I do not know. thank you so much for this brilliant video! might have to come back again and take notes to properly understand 💡

[Pavan_Gaonkar]

I need a video about the argument of Einstein against Heisenberg uncertainty principle and bhor's justification to that

[cyclonasaurusrex]

Should also mention his wife Margrethe. Beautiful relationship.

[umeshchandramakwana]

Hey Parth where are you now days... waiting for your more videos!

[dominicestebanrice]

Superb presentation! Thank you. The content is so concise that it highlights how Bohr's model (a) fails to explain the lack of EM radiation from a charged electron that changes direction - he deliberately just ignored that inconvenient truth, and (b) fails to justify the specific energy levels - the balancing of orbital radius and angular velocity that you explained so well, that allows for an electron's stable "orbit" does not need to be quantized, it is perfectly amenable to an analogue treatment. Like al the other models, Bohr's is useful but ultimately not truthful.

[TerryBollinger]

Parth G, thanks! You have a knack for getting me to look at an old idea from a different angle. In this case, the traditional question has the problem backward: It’s not why the electron fails to emit radiation while constantly accelerating around the nucleus, but why the electrons cannot “feel” any acceleration while in an orbital.

Another way of saying that is an electron in a stable orbital perceives itself as being in freefall, just like an astronaut in orbit under gravitational acceleration.

Interesting! The question then becomes one of why, and how, an oddly gravity-like freefall form of acceleration emerges if, and only if, the acceleration behavior of the electron drops into the quantum realm.

Must think on this one a bit!…

[BibblowsClassics]

Anyone knows how those videos are made

[The_Green_Man_OAP]

4:24 Is there an actual experiment
demonstrating that❔ 🤔

If I had a charged sphere 🔵 💫
in microgravity orbiting another,
then would it do the same❔🧐

[JegaSingam]

A question if you are kind enough to answer, is the radius referred to in the video, the mean radius?

[Clavdivs]

One extra piece of information you might add is the theory of neutron decay, because beta emission (electrons) is too high energy to come from orbits so people though the nucleus must contain electrons (plum pudding model). Fermi's theory of neutron decay explained the phenomenon and so completed the model. Though very advanced the theory was initially rejected.

[LuisAldamiz]

He has the very same face as an old school mate of mine: Antuñano. Incidentally today in the subway a girl with also the exact same face (maybe a relative of my old friend?) sat in front of me, I didn't dare to ask if she was relative of Bohr... nor of Antuñano either.

Respectfully I don't think he won, he just was onto something but never really understood it well enough. Nobody has to this very day.

[thejanhasaranga]

Thank you for all the content you have posted so far. I was wondering that you could possibly post a video explaining how magnetism arises in materials from a quantum mechanical perspective?

[AdrianStoica-eb]

Bohr was a true scientist...
Einstein more Sci-fi writer...😂😂

[KaliFissure]

We need to extend Bohmian mechanics to its logical extreme...
We take fields and reinterpret them as the flow vectors of a gluon like fluid substrate.
Allow true outflow but to maintain system closure this must local have a reciprocal inflow.
A hydrodynamic model treats spin as a true rotational component of the fluid flows.
Treating the fluid as gluons, orientable, is like having a prefect dielectric where convergence creates a positive charge and divergence negative.

[billschwandt]

It's unbelievable how little science knows about static electricity.

[pauljohnson]

That's the guy he said bury your head in the sand and just do the maths. Einstein said that you need to understand what's actually going on and he'll be ultimately proved right. So it'll be Einstein who''ll be telling him to bog off.

[PrinceSarraf]

Brother, make Einstein wear glasses too 😎😅