Physics from a Rigorous, Experimental Perspective

[Judah_Idris]

I have a physics B.S. It seems like I learned little more than how to solve math problems as an undergrad. I want to know how the physical world works in concrete physical terms as much as is possible, so a big problem I have with physics is that concepts are very often explained in terms of models. I would prefer to know the exact experimental details that led to certain results, or at least understand the reasoning behind the models.

For example, in intro physics we learned that atoms are modeled as electrons orbiting in a huge empty space around a nucleus that contains protons because some guy bombarded a sheet of gold with charged particles and found that most of the charges hit empty space. Even at an introductory level, that description is insufficient for understanding why the atomic model is used.

The problem with models is that they constrain you to think of and interpret phenomena a certain way (in terms of the model instead of in terms of observations or experimental procedures). When you look at things through one specific lens like that, you can miss details or see things in a warped fashion. So I need to know the theoretical details behind the physical models so that I can predict and avoid blindspots caused by thinking in terms of those models.

I'm also interested in how certain oft-used equations (like Schrödinger's) came about.

So what kinds of things could I read to get this information? I'm interested in any of the subjects covered in a typical undergrad physics program as well as astrophysics. I don't trust most stuff that's posted online, but I'd read an authoritative website (like some sort of university website). I have tried a couple philosophy of science books, but they explain only the most general models. I wouldn't know what to read to get, for example, a discussion of the history and implications of viewing electricity/magnetism as a field or viewing atoms as a sort of mini solar system.

Maybe some history of physics books? So far the one I had mainly focused on the social aspect of history rather than describing experiments or tracing how/why certain models were adopted and became popular.

Where could I find, for example, a report of the Michelson-Morley experiment? Not just a description, but the entire experimental setup, observations, results, etc.

Thanks.

 

[FactChecker]

The experiments that lead to and/or support a model are often (usually?) much more complicated than the model is to understand. And they often just verify a small and obscure result that a model predicts. There can be a hodge-podge of confusing experiments that are then cleanly explained by a logical model. The most you can often hope for is to know what aspects of the model were tested experimentally and what the results led to.

 

[PeroK]

Where could I find, for example, a report of the Michelson-Morley experiment? Not just a description, but the entire experimental setup, observations, results, etc.

I tried putting "Michelson-Morely original paper" into Google and, would you believe it, look what turned up:

https://history.aip.org/exhibits/gap/PDF/michelson.pdf

 

[FactChecker]

Consider your example of the Bohr model of the atom. It, and its associated derivatives, are rough representations that allow one to make some sense of the periodic table. If you wanted to know what experiments led to the periodic table, there would probably be tens of thousands. So you can use one model or many thousands of experiments -- your choice. To really understand the periodic table, a much more sophisticated quantum mechanical model is required and the details of that are much more advanced. That theory is probably not accessible in an introductory class.

 

[gmax137]

There is also this, disappointing as it may be: experiments done on atoms (like Rutherford's bombarding gold foil) produce "results" that are not visually enlightening. You don't see the projectiles being deflected or bouncing back; rather, you hear a "click" or not, and then you move your detector over a degree and try again, listening for clicks. Then you plot number of clicks versus angle (or something similar). Ultimately, you come up with a "model" that produces the same "clicks vs angle" plot as the data. That's it. If you go on to say "see, atoms are little solar systems..." well that's just window dressing, "interpretations."

The good news is, the models allow us to do a tremendous number of things we couldn't do before we had the models. Look at the differences between the world today and Rutherford's world, just over one hundred years ago.

 

[Judah_Idris]

The experiments that lead to and/or support a model are often (usually?) much more complicated than the model is to understand. And they often just verify a small and obscure result that a model predicts.

I'm ok with that.

 

[Judah_Idris]

Consider your example of the Bohr model of the atom. It, and its associated derivatives, are rough representations that allow one to make some sense of the periodic table. If you wanted to know what experiments led to the periodic table, there would probably be tens of thousands. So you can use one model or many thousands of experiments -- your choice. To really understand the periodic table, a much more sophisticated quantum mechanical model is required and the details of that are much more advanced. That theory is probably not accessible in an introductory class.

I don't need the equivalent of an introductory class; I've already studied physics at the undergraduate level. I have a B.S. in physics. And I'm not trying to do anything so grand as "make some sense of the periodic table" anyhow. More or less all I want to know is what in those foundational experiments scientists observed and why they interpreted it the way they did to come up with the idea that an atom is a packet of neutrons and protons surrounded by tons of space and orbiting electrons. They didn't have the whole periodic table figured out at that point, so I don't need to have it figured out to understand what they did.

 

[FactChecker]

The experiments motivated the history of theoretical development. If history and motivation are what you want, that is the way to learn it. It is very interesting. It is hard now to realize how little was known at the time of some great discoveries.

 

[Judah_Idris]

There is also this, disappointing as it may be: experiments done on atoms (like Rutherford's bombarding gold foil) produce "results" that are not visually enlightening.

I'm not seeking anything visually enlightening. I know that experimental atomic physics typically doesn't involve visual observations.

 

[hutchphd]

I would prefer to know the exact experimental details that led to certain results, or at least understand the reasoning behind the models.

To do so one would need to crawl into the head of the creator of those results. To know the exact processes that led to the creation of whole truth from an amorphous pile of facts you would need unlearn much that has become common knowledge during the interregnum. I don't know that this is useful or even possible.
The closest I can come is to read a good biography of the individual or an historical treatment of some facet of the edifice. Better still an autobiography.
I like the the work of James Glieck particularly "the Information" and books about Newton and Feynman.
I like https://www.thriftbooks.com/w/the-old-ones-secrets-an-autobiography-through-letters_freeman-dyson/14740025/item/41166161/?mkwid=%7cdc&pcrid=450663950280&pkw=&pmt=&slid=&plc=&pgrid=104669221093&ptaid=pla-929394389010&gclid=Cj0KCQjwtsv7BRCmARIsANu-CQdaIV3ljSAA3XecXElHhRLezES0C3b2ZyK1pXyYLWOqqGF85HhNQa8aAvhYEALw_wcB#isbn=0871403862&idiq=41166161.
Just start reading. If you really want the flavor of something you must carefully bite off a small piece.

 

[Vanadium 50]

To do so one would need to crawl into the head of the creator of those results

This.

You should read the paper by E. Maxwell on the discovery of the isotope effect in superconductivity. It practically starts by saying, "We had some Hg-198 laying around..."

 

[vanhees71]

It's a great advice to study original papers. If they are older, it can be a challenge to understand them, because they are formulated in the language of their time. A good example is the above quoted paper by Michelson and Morley talking about "the luminiferous aether" all the time.

Recently, during working on a manuscript for my QM lecture in the upcoming winter semester, I was in doubt, how the photoelectric effect was really experimentally investigated. I thought that's an easy issue, because it's in all experimental physics books, and it sounds all easy enough, but I was puzzled more and more. So I looked up the original papers by Millikan, who was the inventor of the method with the stopping potential and the first to successfully prove Einstein's formula right and determined Planck's constant with a good accuracy from the measurement (1914). He also investigated the effect for some more years and found the correct formula
$$E_{\text{kin,max}}=\hbar \omega + \Phi_{\text{anode}}$$
in the stopping-potential method. It's usually wrong in elementary experimental textbooks, where it's claimed that it must be $\Phi_{\text{cathode}}$! This is a bit surprising since this was a big issue for Millikan with initially pretty confusing results (which is due to the trouble with "electrochemistry" of the cathode and anode material, oxidation, the vacuum in the tube, and all that) and all this painstaking work finally lead to a Nobel prize for Millikan (together with his even more famous "oildrop work"leading to the determination of the charge of the electron).

One always learns something new when reading the original papers and comparing it to "common textbook knowledge", and be it the details about all the mistakes and lack of understanding in the beginning and gaining new knowledge leading to progress in science.

 

[Vanadium 50]

I looked up the paper. It starts out with "The existence of a small quantity of Hg-198 at the National Bureau of Standards prompted us to investigate its properties as a superconductor."