B Proof of the existence of atoms

[bhobba]

Then Einstein worked out the maths of the fluctuations in atom fluxes and showed that by chance billions more atoms could collide with one side of a smoke particle than the other for short periods, and it became a lot less defensible.

Interestingly this led to the theory of random walks that has many applications in many areas of applied mathematics, not just physics. Mostly these days, mathematicians lead the math used in applied math and physics in general, but this is a case where physicists lead the way. Even today, it sometimes happens.

Thanks
Bill

 

[Son Goku]

No no, Democritus was right. It's not his fault that our atoms are misnamed. Using his terminology, neutrinos and quarks and electrons and so forth are atoms.

I think modern particles are so far from anything he imagined, e.g. in typical states their properties and even their number are undefined, that one can't really say he was right.

 

[PeroK]

I think modern particles are so far from anything he imagined, e.g. in typical states their properties and even their number are undefined, that one can't really say he was right.

I suspect that even if Democritus had come up with the basics of QFT, you'd give him no credit!

 

[Son Goku]

I suspect that even if Democritus had come up with the basics of QFT, you'd give him no credit!

Hardly, he's my favourite 5th Century Thracian.

 

[bhobba]

I think modern particles are so far from anything he imagined, e.g. in typical states their properties and even their number are undefined, that one can't really say he was right.

Yes, QM has changed our view of the world a lot. In hindsight, we only have experience with 'clumps' of quantum stuff and can only probe the quantum world by interacting with those clumps. That this led to a theory predicting the probabilities of those interactions (aka observations) is only expected. We are lucky, though, in that mathematical analysis shows it is just an example of a broader class of probabilistic theories than ordinary probability theory and led to the creation of a new area of mathematical investigation called Generalised Probability Theories:
https://arxiv.org/pdf/2103.07469.pdf

Some arguments suggest it is just the most straightforward generalised probability theory after ordinary probability theory:
https://arxiv.org/abs/0911.0695

Note this in no way explains what is 'really' going on at the quantum level. Quantum foundations are still an active area of research. It just elucidates why we ended up with the theory we have. The bottom line is none of us has direct experience with the quantum world, and QM reflects this.

Thanks
Bill

 

[Son Goku]

Some arguments suggest it is just the most straightforward generalised probability theory after ordinary probability theory:

There's a lovely undergrad level derivation of this in Jochen Rau's new textbook "Quantum Theory: An Information Processing Approach".
He shows only quantum and classical prob are compatible with basic statistical principles like "operationalism", i.e. the ability of another party to confirm the claimed prepared state.

 

[bhobba]

There's a lovely undergrad level derivation of this in Jochen Rau's new textbook "Quantum Theory: An Information Processing Approach".
He shows only quantum and classical prob are compatible with basic statistical principles like "operationalism", i.e. the ability of another party to confirm the claimed prepared state.

Thanks for the heads up. Just purchased the book and can report my 'reaction'. Could be 'the' undergrad book on the why of QM. Not what it means - that is much much harder - but why it is the theory we have.

Thanks
Bill

 

[Hornbein]

Lavoisier more or less introduced the idea of atoms before he had his head removed by those nasty French Revolutionaries in 1794.

Lavoisier was the head tax collector of Paris. He had the city surrounded by a wall in order to facilitate tax collection at the gates. Imagine having to go through customs in order to reenter your own city. Parisians had made short trips to the country to get out of the oudure and mud, now these took long detours and waits for inspection. What a pain in the @@$@$! In my opinion Lavoisier's wall was a significant motive for the revolution. The proportion of the upper class who were executed is smaller than generally supposed but Lavoisier might have been number one on the blacklist.

 

[bob012345]

He shows only quantum and classical prob are compatible with basic statistical principles like "operationalism", i.e. the ability of another party to confirm the claimed prepared state.

This sounds more like philosophy than physics.

 

[sophiecentaur]

This sounds more like philosophy than physics.

The distinction is very blurred when you get down to it. It’s like love and marriage “…………”.

 

[bhobba]

The distinction is very blurred when you get down to it. It’s like love and marriage “…………”.

As Feynman said philosophy (or what some consider philosophy anyway) was once used to make progress eg positivism and relativity. These days symmetry arguments are more in favour. They too may fail to work just as many marriages do. But that does stop people from trying.

Thanks
Bill

 

[bob012345]

As Feynman said philosophy (or what some consider philosophy anyway) was once used to make progress eg positivism and relativity. There days symmetry arguments are more in favour. They too may fail to work just as many marriages do. But that does stop people from trying.

Thanks
Bill

Nature does not seem to always obey every symmetry physicists conceive of.

https://www.nobelprize.org/prizes/physics/1957/summary/

https://www.nist.gov/pml/fall-parity

 

[sophiecentaur]

Nature does not seem to always obey every symmetry physicists conceive of.

https://www.nobelprize.org/prizes/physics/1957/summary/

https://www.nist.gov/pml/fall-parity

We will only ever see a sub set. That rankles in some minds.

 

[vanhees71]

The distinction is very blurred when you get down to it. It’s like love and marriage “…………”.

That's a good metaphor: Love=Physics; Marriage=Philosophy. As soon as you get into philosophy it's becoming more likely the physics is gone soon...

 

[bob012345]

That's a good metaphor: Love=Physics; Marriage=Philosophy. As soon as you get into philosophy it's becoming more likely the physics is gone soon...

I would think physics is more like marriage because there is always someone telling you what you cannot do.

 

[hagopbul]

rutherford experiment on scattering of alpha particles?

 

[KipIngram]

I remember being told the same thing in a physics class, late 1970s. I was surprised to hear this, especially that Planck was among the sceptics. How could the father of quantum theory not believe atoms exist??This is a very interesting addition to the "story." Especially when combined with
Thanks too to @anorlunda for "promoting" this thread.

My understanding was that Planck quite hated his own "quantum hypothesis" that got him across the black body radiation finish line. He was convinced it was some form of trickery, but was just more or less desperate for the win.

 

[berkeman]

My understanding was that Planck quite hated his own "quantum hypothesis" that got him across the black body radiation finish line. He was convinced it was some form of trickery, but was just more or less desperate for the win.

Reference links please.

 

[vanhees71]

It's well known that Planck didn't like his own discovery, and during the long rest of his long life he was looking for an explanation within classical physics. You can read this in almost all books on the history of quantum theory or biography about Planck.

 

[weirdoguy]

You can read this in almost all books on the history of quantum theory

E.g. in "Constructing quantum mechanics, volume I" by Duncan and Jenssen. Great book.

 

[epenguin]

rutherford experiment on scattering of alpha particles?

that was the unforeseeable finding that the positively charged matter of the atom is concentrated in a tiny volume of it.

The atoms themselves (and electron) accepted before that.

 

[KipIngram]

Reference links please.

I'll try - it's been a long long time since I encountered that.

Edit:
Ok, I found this - it's not the same thing I read years ago, but it gets at it:

https://physicsworld.com/a/max-planck-the-reluctant-revolutionary/

A quote from there:

As to the quantum discontinuity – the crucial feature that the energy does not vary continuously, but in “jumps” – he believed for a long time that it was a kind of mathematical hypothesis, an artefact that did not refer to real energy exchanges between matter and radiation.

There is also another thread here:

https://www.physicsforums.com/threads/plancks-radiation-law-act-of-desperation.686243/

 

[bob012345]

It's well known that Planck didn't like his own discovery, and during the long rest of his long life he was looking for an explanation within classical physics. You can read this in almost all books on the history of quantum theory or biography about Planck.

We might say then that Planck wasn't very discreet about nature being discrete...

 

[sophiecentaur]

We might say then that Planck wasn't very discreet about nature being discrete...

We have all been 'helped' into that paradigm and it's easy too take it for granted. It must have been a real struggle at the time and with a lot of great brains opposing the idea very competently.