Also, iirc naïve aerodynamic calculations extrapolated to infinite drag at the speed of sound, which they were sure wasn’t correct but didn’t know what the correct math was. They did know that in WW2 fast fighter planes in power dives suddenly got into trouble as they reached Mach 0.8 or 0.9
I had no idea! This just blew my mind.
Not a proper aviation buff, but I’ve played my share of sims and such and always thought the boom was just an instant, like a whip.
Famous pictures like this don’t help with the confusion:
Maybe a sonic cone or sonic spray would’ve been better…
The “Theory of Everything” (TOE). Really? Every damn thing??
Can it explain why my socks disappear in the dryer? Can it explain my taxes? Can it explain where I left my car keys?
Too cocky. Too ambitious. Too hypothetical. Too “hold my beer, I’ve got physics to solve.”
Lets dial it back and rebrand as: “The Theory of a Pretty Impressive Amount of Things That May or May Not Explain the Universe If You Take it with a Grain of Salt”
I can imagine walking up to a snooty theorist with a stick up his ass at a physics conference and asking:
“What are you working on?”
“A theory.”
“A theory about what?”
“Everything.”
[smack!]
I’ve heard singularity. Although I believe that picky folks say that the singularity is inside a black hole.
I like the “Backbone of Night.” I don’t remember which language/culture that’s in. Carl Sagan spoke of it in Cosmos.
Subsequent discussions of ‘singularity’ did not help me.
The basic idea is that when a star runs out of fusable material and starts to cool down, it begins to contract and various things happen depending on the initial mass of the star. But very briefly, smaller stars only shrink to the point where they remain stable due to the repulsive force of electrons, called electron degeneracy pressure. These remain as white dwarf stars for a long time. Larger stars may erupt in supernova explosions but if there’s enough mass remaining, even electron degeneracy pressure can’t keep them from collapsing further.
In stars with larger masses, electrons are ripped away and combine with protons and there’s nothing left but neutrons. Such stars, if below a certain mass, will stop shrinking due to neutron degeneracy pressure, the next stage of super-compression of matter. These become neutron stars, the densest material in the universe, where a cubic inch is more massive than a big mountain on Earth.
But if a star is sufficiently massive, not even neutron degeneracy pressure can prevent further collapse. This is the mind-blowing part. It just keeps collapsing without limit, to an end state that theoretically is a dimensionless point of infinite density. That’s one version of the singularity. It’s always surrounded by an inescapable event horizon whose size depends on the amount of mass in the singularity. The event horizon is one-way – you can enter it, but, just like Hotel California, you can never leave. So it’s impossible to know what the singularity actually is except by conjecture and mathematical modeling, because (with maybe some esoteric arguable exceptions) no information can ever get out of a black hole.
Others can probably explain this better than I could. In any case, I think terms like “black hole”, “event horizon”, and “singularity” are quite meaningful and reasonable.
You make good points, and this needs to be highlighted for the purposes of this thread. Mathematicians cringe when physicists say something like that. A singularity cannot have a finite extent, by definition. Doesn’t stop physicists from misusing the term.
I’ve also noticed that with Falcon 9 launches, Max-Q (the maximum extent of aerodynamic pressure on the vehicle) is closely coupled with it going transonic (i.e. breaking the ‘sound barrier’).
The important thing is that “singularity” is really a mathematical term, not a physics one. “There is a singularity at the centre of a black hole” is really “the solution to the equations of general relativity is singular at the centre of a black hole” not “there is a physical object called a singularity that is predicted to exist at the centre of a black hole”.
Some approximations of fluid mechanics have solutions with singularities when the flow reaches the speed of sound. It just means that those approximations stop being good approximations of reality in those situations.
I was going to post that. You do not need to introduce black holes to worry about singularities; they already come up in the study of the Newtonian n-body problem.
I understand. But I still think it fits reasonably into this thread, even if is is not worst named. In the literature, it is denoted O(n), which is so far so good, but in the literature (see also physics, chemistry…) they absolutely talk about the “orthogonal group” and orthogonal matrices.
PS I mean “matrices whose rows are orthogonal” do not form a group under matrix multiplication
Perhaps I should add, if A is a matrix like \bigl(\begin{smallmatrix}2 & -2\\1 & 1\end{smallmatrix}\bigr), then AA^{\mathrm{T}} and A^{\mathrm{T}}A are not both diagonal. So we have a situation where the rows are perpendicular but not the columns.
Related to this thread, but doesn 't apply to English: I dislike the ‘Student’s T-distribution’, which in Dutch is named Studentverdeling or Student distribution.
I know it is named after the originating author (or his pseudonym), but as the name has a non-mathematical meaning as wel, this brings up irrelevant associations. The student distribution of Harvard is not a Student distribution. But as Wikipedia taught me, this is apparently less an issue in English where it is more clearly called ‘Student’s T-distribution’.
I have a similar issue with Eigen value. In Dutch it is called Eigenwaarde which is also the word for ‘self esteem’. Very confusing.
Non-English rant over.
I have only heard of his t-distribution. Is that not what people think of when they hear “Student distribution”? [also NB “student” ≠ “Student” in English.] A man is allowed more than one distribution, though. Conversely, the Cauchy distribution is apparently the same thing as the Lorentz distribution, as well as whatever else it is known as.
I meant ‘the distribution of students of Harvard is not a Student distribution’, which shows the kind of confusion this name can cause.
It might be. I am sure you can get a t-distribution out of it; depends what you measure 
(Also note that you can get the standard normal distribution as a limiting case.)
Or just the “t-distribution.” As you say, not an issue in English.
And the only place I’ve seen "eigen-"anything in English is in connection with eigenvectors and eigenvalues.
Thank you for this! I sheepishly admit I wasn’t sure about this until now. (I’m in my mid-50s).
Breaking the sound barrier.
Not really a bad term.
In the 1940s, it meant figuring out how to fly faster than sound, because all their aero equations went wacky at that speed (sorta like how nowadays the equations of GR & QM go wacky at black holes) and airplanes that approached those speeds encountered all kinds of frequently fatal problems. Which, in the days before telemetry and ejection seats, left little evidence of what had gone wrong.
Eventually they figured out how supersonic flow worked. Kinda like water and ice, supersonic flight is quite different from subsonic, even though it’s made of the same stuff: air & speed & dynamic pressure.
Then the problem became designing a machine which could fly controllably in both regimes. A very tall order at first. Nowadays it’s no big deal. But you are still designing a machine that needs to live in two very different environments, and successfully negotiate the complex transition between them.
And the process of accelerating or decelerating across the transition speed has a lot of transient challenges. It is still a barrier, but more in the sense of say a rivermouth is a barrier between a ship transiting downriver in calm freshwater then entering the saltwater ocean full of large waves. Conditions differ on the two sides, and are especially confused at the interface. Woe betide the boat that crosses the barrier while ill-equipped for the conditions on the other side.
Booms:
Yeah, booms are continuous. A coast to coast SST would drag a cone of explosive noise across 3000 miles of cities and countryside.
@Reply’s pic is good, but any still pic of a continuous phenomenon is going to mislead. A still image, frozen in time, of flames, or of an explosion in progress, or of a car cornering aggressively makes it look like those things aren’t dynamic and continuous. We know they are, but that’s because most of us have experienced those things in real life.
Thanks to regulations and how aviation has evolved, sonic booms are not everyday experiences for anyone. A few times per lifetime is probably typical.
This YouTube short does a better job of showing that the shockwave is continuous. We still see the cone coming and going, but that’s a matter of slightly differing humidity along the path of the jet.
The fact the shock being dragged by the jet is going by at 800 or 1200 mph means any given observer only experiences it briefly, even one traveling at ordinary car or train speeds. Unlike watching a flame, there’s just no way to keep pace with the boom / shockwave and experience it in its continuous glory.
Mathematics, especially abstract algebra, is full of ordinary words that have been used in ways that they are not suggestive. Examples: group, ring, field, category. Field is especially troublesome as its definition changes somewhat as you cross the Atlantic. In its French (corps) and German (Körper) translations, it comes across as body. Does this suggest in any way, an algebraic system that has operations of addition, subtraction, multiplication, and division (but never by 0)?