Dorky Poll: Usage Question

I was waffling between A and B, but the correct answer for me was C. I notice that as of right now, the votes are evenly split between A and B, so I think I chose correctly.

I am curious about the correct answer.

K

I dunno, since one of the options is "not quantum" would not all three other options together count as "quantum"?

I generally use "classical" in the sense of non-quantum, but that is because I am usually writing papers on quantum theory and need a catchy word to encapsulate classical probability, information and the like. This is extremely common practice in quantum information theory. However, even in this restricted sense of "non-quantum, it is not clear exactly what "classical" is supposed to mean. For example, I have read papers and books in which each of the following definitions of "classical" is adopted, often implicitly:

- Obeying the laws of classical probability, information, etc. (the sense I normally use).
- An experiment describable by a local hidden variable theory, hence not able to violate a Bell inequality.
- Anything that is efficiently simulatable on a classical computer.
- An experiment describable by a noncontextual hidden variable theory.
- An experiment in quantum optics that obeys the classical Maxwell's equations for mean values, but may be remarkably nonclassical in other respects, e.g. experiments involving coherent states and linear optics devices.
- An experiment involving a large number of particles in the thermodynamic limit at temperatures too high to observe quantum effects.
- The classical limit of QM where systems obey approximately classical equations, e.g. the Wigner function is positive and obeys Liouville's equation, due to decoherence or similar effects.
- The previous definition with the addition of a well defined ontology for quantum theory so that you can say there really are particles following the classical trajectories, e.g. Bohmian mechanics supplemented with decoherence.

Obviously, this can be very confusing. Because of this, I think the non-quantum definition of classical should never be used without qualification, e.g. I am always careful to say things like "classical probability distribution" rather than just "classical state". It would be better if we had a more fine-grained terminology for these things so that the word "classical" could be banished from the literature, but it is so popular that we are probably stuck with it.

Of course, even the "pre-modern" definition of classical is problematic because "classical physics" should really refer to ancient Greek and Roman physics rather than anything from the Newtonian era (anyone for Enlightenment Physics?). Of course, the "classical music" is already an extreme violation of this meaning of the word and is too established to dispense with. IMHO, the music people can be blamed for this whole confusion.

As far as I can tell, relativity is "classical" in the idiolect of all physicists I know, but not in most popularizations.

What the up to date physicist would call their best model of any phenomena as of 1890.

I'd say "classical mechanics" if pre-quantum and pre-GR, but "classical physics" is pre-quantum but not necessarily pre-GR.

I voted "A" because with no other context I think that's the best option. As Matt does, I often use "classical" to mean "non-quantum," but only within the context of a discussion of quantum mechanics. Without that context, I generally assume that relativity is also excluded. (Conversely, if I encounter the term "classical" while reading about relativity I presume that "non-relativistic" is the important point.)

There are days when I think it means "not quantum" but I went with "A" because it also jibes with the move beyond Newtonian/Galilean physics, when we had to acknowledge that the physics of both the fast and the small deviate from that. And Einstein sent us on those paths with his 1905 papers, even if he didn't like the way that quantum one turned out. If we can lump relativity and quantum theory into something called "modern physics," then what preceded it should be classical physics.

For want of a none-of-the-above option, I voted for "being of pure intellect."

Classical physics excludes both quantum and GR, but it includes large portions of certain fields (e.g., statistical mechanics and plasma physics) which did not exist or were not fully developed by 1900. Arguably, special relativity should also be excluded, but since you can derive SR from classical electrodynamics, I'm willing to let that slide.

I went with b, as my gut feeling before I saw the answer-options was "not quantum". Of course, my last physics course was A-level, more than a decade ago now.

Since my degree was in Classics, my very first thought was **** platonists!

It's odd that so many people think "classical" excludes GR, since pretty much the entire community of people who work on gravitational physics use the phrase "classical GR" to mean that they aren't considering quantum effects. (Google it. Or notice that Landau & Lifshitz treat GR in their book The Classical Theory of Fields.)

It's context sensitive.

It's odd that so many people think "classical" excludes GR, since pretty much the entire community of people who work on gravitational physics use the phrase "classical GR" to mean that they aren't considering quantum effects.

That's actually what prompted this, because prior to reading a bunch of stuff about relativity fairly recently, I had never heard "Classical" used in anything other than the "Pre-Modern" sense. So "Classical GR" sounds very odd to me.

I've always heard "classical" as synonymous with "Newtonian" - which is to say, Deadliest Son Of A Bitch In Space but he hasn't noticed the way his rules stop working so well once you get closer to the speed of light.

As a music major in college, I would never confuse "classical" with orchestral music in general. If I were going to be cute, I'd say that classical physics is anything post-Renaissance and pre-Romantic -- e.g., between Newton and Faraday, exclusive.

Further to what Stripey Cat said, a real, honest-to-God humanities major would probably associate classical in the context of physics with atomists like Democritus and Epicurus, the mechanics of Archimedes, etc, etc.

In mathematics, it happens quite frequently (especially in a rapidly developing subfield) that the phrase "the classical result of X and Y" refers to something only 15 or 20 years old.

My background is more chemistry than physics. The definition I wanted was "not quantum and not relativistic", which is not quite the same as "pre-1900". This particularly goes if "classical" modifies "mechanics".

Classical mechanics is only a subset of classical physics, but it still includes special relativity. I have a book to prove it: Classical Mechanics by Herbert Goldstein. Originally published in 1950, but still in use a quarter of a century later, when I was a student. I later heard that Goldstein had published the second edition 1980 (must be a record of some sort), and the third in 2001 (another record).

In my mind, the classical notion is best summed by Einstein's mentality that locality be a principle part of physical reality. That means what happens locally should be affected by local effects. That would include GR in my book and make quantum very 'non-classical'. It's unfortunate, to me at least, that so much of our physical thinking on these types of matters is determined by class titles and not the content of those classes.

Mechanics with the Lorentz transforms existed before 1900. What changed in 1905 was the "relativistic" interpretation of why those relationships are needed.

I include SR, but not GR, in "classical" mechanics mainly because you can't legitimately do anything with Maxwell's equations without acknowledging that they are valid in any inertial coordinate system if and only if special relativity describes the relationship between inertial coordinate systems. General Relativity is not confirmed, nor needed, at that same level.

I went with A, but I wish I'd read the comments first.

I'd definitely go for B as I've only ever seen "semi-classical" refer to a first approximation to a quantum mechanical effect whether that occurs on top of Newtonian (typical in atomic physics) or a relativistic "classical" system (in Hawking-style work).

My course on Classical Mechanics included a chapter on SR.

I'm waffling between A and B as well, and I think that avoiding "classical" altogether might be best. Just because the term is grandfathered, doesn't mean we have to stick to it.

In a book about relativity, I'd say A, in a book about QM, I'd say B. Words meaning pre-QM, pre-SR and pre-GR would likely be preferable.

In my community, and I think also in the GR community, classical is used exclusively as non-quantum. I guess the difference is whether you want to distinguish subjects chronologically or logically. For the latter choice, there is no logical way to distinguish Einstein equations from Maxwell equations, they both describe relativistic phenomena. If you are making a historical statement though, the order in which they were discovered makes one classical and one "modern", I suppose.