While I was chatting with Rob last night, we discovered numerous words that carry a commonly understood denotation and/or connotation for most of us mortals, while in the world of the physicists, they mean the exact opposite. Some of these supposed double meanings are admittedly due to a layman's limited understanding of the sciences, while others legitimately boggle our intuitive sense of vocabulary and would lead readers down opposing paths of understanding based on their backgrounds.
While poking around on wikipedia today I discovered that words like this have a title: autoantonym. And, as could be expected from the famously confusing English language, there is a surprisingly long list of words that fit this description. Here are the ones specifically relating to physics that Rob and I talked about last night:
Background...as in: the cosmic microwave background (CMB).
When I hear this term, I intuitively imagine that the object (or form of electromagnetic radiation) in question would be occupying a space far off in the distance and have no presence locally. I've seen the photos of the CMB and have always pictured it in my head as depicting an unimaginably distant wall enclosing the ever-expanding bubble of our known universe.
In reality these cosmic microwaves are all around us. When an old analog TV flips to a channel it's not able to pick up clearly, a portion of that black and white fuzz is a remnant of the big bang. No matter where a radio telescope is pointed...even towards the blackest visual void...the CMB is almost uniform in every direction. When Rob hears the word "background", he understands it as something that's everywhere...all around us, while for me, I think of something more akin to a painted panel of scenery at the back of a stage.
General vs. Special Relativity.
Now, maybe this is only a mistake that I made for years. Undoubtedly, the rest of you are far more enlightened and never assumed, as I did, that something labeled "special" must be more privileged, intense, and perhaps, difficult than something labeled "general". And I still think that most often this is the case. "General" boarding only begins when the first classers and those needing "special" assistance are taken care of. As an undergrad one takes a mass of "general" classes while perhaps only later deciding what he or she might pursue as a "specialty". When you come down with an illness, in most cases you first have to see a "general" practitioner before later being referred to a "specialist". So special relativity must be waaaaay more involved and interesting than general relativity right? Wrong!
Special relativity basically says that "all laws of science shall be the same to all observers no matter their location or how they are moving in the absence of gravitational fields" (from answers.com) and that "the speed of light in free space is the same for all observers regardless of their motion relative to the light source" (from wikipedia). SR deals with a flat spacetime and most of us first encountered the idea through Einstein's famous thought experiment involving a speeding train car and flashes of light as observed by an occupant of the train as well as a casual Joe on the platform. Rob told me last night that the equations of special relativity don't employ devices more complex than a number with an exponent. You don't have to know calculus to understand special relativity.
On the other hand, you definitely need lots of highly complex mathematics to even scratch the surface of general relativity. GR is a theory of gravitation...or wait...here's how wiki puts it (now, remember how easy it was to explain the basics of SR above?): "general relativity is a metric theory of gravitation whose defining feature is its use of the Einstein field equations. The solutions of the field equations are metric tensors which define the topology of the spacetime and how objects move inertially". Got that?
One thing that stands out to me as an important difference between the two is that while SR deals with a flat spacetime, the spacetime of GR is warped and curved...and it's definitely a lot more challenging to explore. I'll leave the rest to the real physicists.
A related autoantonym is the word Generic.
I encountered the double meaning of this word while reading the first paragraph of Rob's most recently published paper: "Degeneracy measures for the algebraic classification of numerical spacetimes"...you can probably see why I wasn't able to read the whole paper.
Evidently, in the past we could only understood a classical gravitational field by looking at "extremely symmetric" solutions, but now, (drumroll please) because of fancy new technology, we have an unprecedented opportunity to dive into "truly generic simulations"!
Wow...um...generic...is that good?
Well, it certainly doesn't mean that we're all going to Canada to pick up the latest cheap-cheap-cheap black hole simulations. I believe that generic in this context refers to something complex and nuanced...something that more closely mirrors the intricate beauty of nature. Who knew? "Generic" is the new SPECTACULAR!
The last word that came up during our conversation is Theory.
Now, this has certainly been a controversial word lately. When many people hear the word "theory" (as in the "theory" of evolution) they imagine that it refers only to an "educated guess", or even just a random "hmm...I wonder". When I looked up online definitions for theory I found that they run the gamut from "an unproven conjecture", to "a set of sentences in a formal structure" (this one is math related), to "a well-substantiated explanation of some aspect of the natural world". This ambiguity can have unfortunate or even dangerous consequences.
What is important to realize about this word that appears frequently in both popular and scientific circles is how rigorously it is employed when referring to a bit of scientific knowledge. The scientific method begins by asking a question and then attempting to answer that question by formulating a hypothesis. A hypothesis is the real "educated guess" and should be presented in such a way so that it is testable and falsifiable. Once a hypothesis has endured the rigors of intense scientific scrutiny, it then can be labeled a "theory" and is "constructed of a set of sentences which consist entirely of true statements about the subject matter under consideration." (from Wikipedia). Even at this point (and contrary to some popular belief), scientists are always willing to accept the possibility that their ideas may be disproved or revised in the future...as long as the new proof also remains open to the same process of falsifiability as its predecessor, and is equally supported by facts and/or observations.
The "theory" of evolution has endured and blossomed under the watch of thousands of persistently skeptical scientific minds over many years. The mechanisms by which organisms change over time have been observed in nature and employed by plant and animal breeders the world over for centuries. There is no question that the selection of genetic traits, natural and artificial, can significantly mold a living thing to fit its environment or better serve the needs of a human caretaker. Evolution is a fact. It has not been intelligently refuted. So despite all this minor semantic confusion, evolution should be universally accepted as a law of nature.