How come Relativity is called a “Theory” when Quantum Mechanics is just “Mechanics”?
They are both theories. Sometimes you will hear Quantum Mechanics referred to as Quantum Theory.
Do a Google search on “quantum theory” (with the quote marks included) and you get tons of hits.
All scientific models are essentially “theories”. There is no fact in science - merely probability based on interpretative observation. Regardless of what tabloids may claim, there is actually no such thing as “scientific fact”.
It may also have something to do with how “ivory tower” GR and SR were. Quantum mechanics immediately applied to light, hydrogen spectrum, fission, solid state physics etc. You’d be hard pressed to find an immediate application for Space-Time curvature.
That’s changed of course over the past 20 years.
not true Grey, without general relativity the gps system wouldnt work at all due to the earths gravity well. time moves slower on the surface relative to the satalites in orbit, if we didnt compensate your gps thingy would be off by several miles constantly.
Well I meant in the early 20th century GR and SR were academic exercises in twisted mathematics. Aside from figuring out Mercury’s orbit and some bending of star light that was it.
QM immediately resolved the black body radiation problem, lead to the discovery of He in the Sun atmosphere, X-rays, fission giving us bombs and reactors. It was immediately applicable.
Your point stands of course. Now we regularly use GR/SR for clocks, satellites and soon observatories. http://www.ligo.caltech.edu/
I’ve never seen such probabilities. Can I ask for a cite on that? What value of probability do we have for QM?
I think he was saying that facts, in other words our everyday little observations, are colored by how we interpret them. QM, on the other hand, is a theory, which is an overarching system of explaining these facts.
I don’t think that’s what he was saying, but I’ll let him clarify. I think the answer to the OP is sheer euphony. “Quantumechanics” has a certain flowing quality that “Quantumtheory” does not. And “Relativisticmechanics” is similarly no good.
Actually, I think that the difference may have arisen because there was no “just” about it. Euphoney and tradition no doubt play a role in why these usages prevail today and interchangable variants are possible, but the names were not originally entirely accidental.
First of all, what do we mean by mechanics. To take the best known book on the subject in the period the names originated, Mach opens Die Mechanik in ihrer Entwickelung (1893; Open Court, 1960, p1) with the definition “That branch of physics which … is concerned with the motions and equilibrium of masses.” It’s also conventional, though Mach doesn’t seem to, to define kinematics as the study of motion. This is a part of mechanics in general - basically the bit that does’t involve the notion of force.
Special relativity is the example par excellance of how kinematics can be a non-trivial subject. After all, most popular presentations of it concentrate on bodies moving at constant velocity. Even without having to worry about forces, the physics is interesting. Indeed, there’s the common argument that the key point of Einstein’s original 1905 paper is that he reduced a problem which people had been think of in terms of electromagnetic forces to one that was purely kinematical. Changing the kinematic underpinnings of classical mechanics changes it, but not completely. For this reason, physicists tend to regard relativity as part of classical physics. The phrase relativistic mechanics is used, but for that part of SR dealing with forces.
As far as I can tell, the first use of the term “Relativtheorie” was by Planck at a conference in September 1906 (Pais, Subtle is the Lord …, Oxford, 1982, p150), Einstein having had no need to name what he was doing in his papers of the previous year. That it’s Planck is unsurprising: he was very much the first person to read the original paper, be convinced and start research based on it. He was also instrumental in convincing other physicists. Since he wrote extensively on the nature of science, it would presumably be possible to clarify what he likely had in mind by a “theory.”
By the time Einstein and relativity become world famous in 1919, the term “theory of relativity” was well established in physics. (Though Einstein himself disliked the use of “relativity”, preferring to emphasise that it was really about invariants.) Both the Times and the New York Times used the word “theory” in the headlines above their oft-quoted articles in November of that year. Neither seems to use the full term however.
In Sources of Quantum Mechanics (North-Holland, 1967; Dover, 1968, p15), van der Waerden identifies the first use of the term “quantum mechanics” as by Born in a 1924 paper “Uber Quantenmechanik.” Prior to then the usage had been strongly “Quantum Theory,” in line with such cases as Atomic Theory, Gas Theory and relativity. Born justifies the new phrase as follows (van der Waerden, p182):
He goes on to suggest that mechanics will now be based on difference equations rather than differential ones.
A year later and Heisenberg calls his 1925 paper “Uber quantentheoretische Umdeutung kinematischer und mechanischer Beziehungen”: Quantum-theoretical re-interpretation of kinematic and mechanical relations. The reference to kinematics is important. From his introduction (p261):
He’s abandoning the notion of a trajectory, which is a kinematical idea. Heisenberg then devotes about a quarter of the paper to kinematics, before explicitly switching to mechanics in general. (Framing the issue this way is an interesting, possibly deliberate, echo of 1905.)
Unsurprisingly, given he proposed the parallel in the first place, when Born writes his followup paper with Jordan - the one that observes that it’s all matrices - they drop any references to kinematics and call it “Zur Quantenmechanik.” Just over a month later and Dirac is submitting “The Fundamental Equations of Quantum Mechanics” to the Royal Society. From then on, it’s my impression that the name prevails in the technical literature, though “Quantum Theory” lingers, especially in popular discussion.
The bottom line is that in 1925, those involved were quite conciously trying to replace classical mechanics with a “quantum mechanics” and their usage is significant. They’re explicit that it’s more than just changing the kinematics, though that comes into it.
Had Einstein and Planck wanted to call it “relativity mechanics” back in 1905-6, I think there’s a fair chance that name might have stuck. But they didn’t.
The question that’s now bugging me is who invented the term “classical mechanics” ?