All science is either physics or stamp collecting. ~ Ernest Rutherford
When I was in college, I wanted to be a physicist. There were two reasons for this. First, physics is the crown jewel of the sciences. If you don't think that's true, just ask a physicist. Second, physics is the science of everything. If you don't believe that, just think about how may disciplines have "physics" in their title, like geophysics, astrophysics, and biophysics. Modern chemistry is dependent on quantum theory, as is electronics, and who came up with quantum theory? Why, physicists, of course.
Regrettably, the physics thing didn't work out. As someone once said (or should have said), "Those who can, do. Those who can't do, teach. Those who can't teach, kibbitz."
Since physics is the study of nearly everything, it is might seem natural that physicists would be obsessed with a theory that encompasses everything. In fact, until the early twentieth century, that didn't seem to be much of a concern. But, early in the century, Einstein came out of the woodwork with a flock of papers that culminated in his Special and General Theories of Relativity. In an incredible burst of genius, Einstein tied together electromagnetism, gravity, time, and mass-energy equivalence (among other things) into one unified whole. It was beautiful.
Then, along came the Copenhagen Gang, with guys like Wolfgang Pauli, Werner Heisenberg, and Paul Dirac, led by that Einsteinian arch-nemesis, Niels Bohr, dragging their quantum theory in with them. Okay, they weren't really a gang (nor did they all come from Copenhagen), but given Einstein's antipathy to quantum theory, one can imagine his having a view of them in black leather jackets. What upset Einstein was that while Relativity portrays a deterministic, predictable view of the universe, quantum theory depicted a world of uncertainties in which only probabilities could be assigned to any event.
(Ironically, the theory Einstein despised derived its name from a term Einstein invented, the quantum, to describe the photon's discrete packets.)
Now, no one disputed that Relativity worked extremely well on large scales, but even Einstein was forced to admit that it failed in the realm of the very small, at atomic levels. Quantum theory, on the other hand, while describing the atomic world well, collapses into ordinary Newtonian and Einsteinian behavior at large scales. Einstein spent much of his life searching for a theory to unify the nuclear and the relativistic forces into one theory, the Grand Unified Theory (GUT), or, as it has become colloquially known, the Theory of Everything.
Einstein failed, but it hasn't stopped everyone in physics from trying ever since. There is a dream physicists have that there is a formula that somehow brings together Einstein's Field Equation (the famous one with the cosmological constant) and quantum theory. It would be short, succinct, and fit on a physicist's business card.
The dream is still unfulfilled. String theory has been touted until we're all tired of it as the road to GUT. The one or two of you who have read this blog before know how I feel about that. Briefly, string theory is an outrageously complicated way to explain things that have already been explained while not really predicting anything on its own. Despite periodic pronouncements over the last few years by string theory advocates, string theory hasn't succeeded in doing any better job of explaining what's going on than standard quantum theory does. And, despite our ability to use quantum mechanics to describe what goes on and make predictions of what will happen in the subatomic universe, there are too many uncertainties (not of the quantum type) for scientists to reconcile that universe with the big one all around us.
It turns out that we don't understand the big universe all that well, either. For example, over the years, we've come to realize that the observable universe doesn't have enough mass. At one time, it was thought that 75% of the universe was unaccounted for; the number is now around 95%. To try to explain this anomalous situation, physicists and astronomers came up with "dark matter", a sort of ... something...that we can't see, can't describe, but can observer...sort of ...indirectly.
When dark matter failed to account for all the observations, a new element, dark energy was invoked. Now it's felt that most of what we can't find is actually dark energy. Except that we don't know what that is, either. It also turns out that what little we thought we knew about dark matter may be wrong now, too.
Which brings me to Phlogiston.
Back in the days of alchemy, one of the many things that puzzled those practitioners was the business of combustion. Take a piece of would and set it on fire. After a while, you've got a pile of ashes that don't look anything like the wood we started out with. Obviously, something interesting was going on here. So, back in the 18th century or thereabouts, the alchemists decided that everything had something called Phlogiston in it. When you burned ("dephlogistonized") a thing, the Phlogiston was given off and what was left, the ashes, were the real substance of the burned object. As to Phlogiston itself, it was colorless, odorless, tasteless, and weightless. Note that if you left off "weightless", you'd have a pretty good definition of dark matter.
Matters stood this way until Lavoisier demonstrated the actual nature of combustion, demonstrating that it was, in fact, rapid oxidation. Yet, prominent thinkers like Priestly resisted the oxygen hypothesis in favor of Phlogiston. It took some years (and the passing of some of the more prominent doubters) for Lavoisier's work to become fully accepted.
Phlogiston was an attempt to explain something we didn't understand, but it was an improvement over invoking superstition and myth. It was an attempt to bring scientific methodology to bear, albeit in an early, halting way, in studying a phenomenon. Today we're much more knowledgeable and sophisticated. We've got geniuses like Hawking, Thorne, Guth, following in the paths of Einstein, Feynman and others. But, for all their brilliance, we're still peeking out into a vast universe (and into a vast quantum world) and trying to figure out what the Phlogiston is. That's not a bad thing. Knowing what you don't know is a big step toward knowing it.
You'll have to excuse me now. I think my dinner is beginning to dephlogistonize.
Postscript: After I thought about the cute Phlogiston angle, I did a little web searching and found someone else had this clever idea. I wasn't surprised; with a bazillion people blogging out there, it was inevitable that someone else would have heard of Phlogiston and linked it to dark matter. At least I was wordier about it. Whether that's a good thing is open to debate.