Category Archives: Science And Society

I Am Quite Disturbed

…at the thought that commenter “Brian” from this post teaches undergraduates.

Scroll down a ways, and be amazed.

[Update a few minutes later]

I should add, that there’s another howler there:

Regarding Newton’s second law of motion, F=ma is just fine for all physics short of things traveling greater than 0.95 the speed of light, or quantum effects.

He’s apparently confused, thinking that I’m referring to Einstein’s Special Relativity version of Newton’s Second Law, in which rest mass is converted to true mass via the factor gamma, which is a function of velocity, or F = dp/dt where p = m*v, or in the Einsteinian version, p = gamma*m*v.

Gamma is a function of velocity. It’s 1/(1-v^2/c^2)^1/2 (or in words, it’s the inverse of the square root of one minus the ratio of velocity squared over the speed of light squared). For low velocities, it’s one divided by the square root of one minus a tiny number, or simply one, so at low velocities, mass equals mass. But for high velocities, you’re starting to divide one by a very tiny number (as the difference between 1 and velocity squared over c squared becomes infinitesimal), so gamma blows up to be a huge number. That’s why mass approaches infinity as its speed approaches that of light.

As I pointed out in the other thread, in the Newtonian case it is simple to take the derivative:

F = dp/dt = d(mv)/dt = m*dv/dt + v*dm/dt. But dv/dt is acceleration, so we get:

F = ma + v*dm/dt.

The Einsteinian case is a much more complicated derivative, because it’s a much more complicated function of velocity. But it’s not relevant, since we’re not talking about near-light speeds. The fact remains that Newton’s Second Law is F = ma + v*dm/dt. The only reason that we always see it as the more simple (and incorrect) F = ma, is that this is a special case in which the mass is constant (the derivative of a constant is zero, and the second term goes away). This is the case for most physics problems, but it certainly isn’t for rocketry, in which the vehicle is ejecting mass (that’s what makes it go).

Anyway, as I said, it’s very disturbing that this person is teaching anyone, let alone undergrads.

[Update at noon Eastern]

Professor Hall, who does teach undergrads as well as grads (and I’m glad of it), expands on his comment via email:

I think Brian’s a bit of a putz in his comments. However, he’s right about F=ma and F=dp/dt. Derivation of the rocket equation is a little tricky to work out, as you say. However, the chain rule does not lead to the correct equation.

In the 2nd law,

F = dp/dt

F is the sum of all applied forces, and p=mv is the linear momentum of the particle of mass m.

If you apply the chain rule to this equation, you get

F = m dv/dt + v dm/dt

as you noted.

However, in order for the chain rule to make any sense here, the two v’s must be the same v. What v is it?

If it’s the velocity of the particle, then this equation can’t apply to a rocket, since it couldn’t lift off the ground. On the ground, v is zero, and initially dv/dt is zero, so F is zero. If F is zero, the linear momentum cannot change, so v remains zero.

If it’s the velocity of the mass leaving the rocket, then initially F = v*dm/dt, which is essentially correct. However, the v in the dv/dt term is clearly not the velocity of the mass leaving the rocket. It’s supposed to be the velocity of the rocket.

The correct derivation of the rocket thrust equation uses a control volume approach, which is essentially a summation of Newton’s 2nd law over a continuum of particles of different velocities (the rocket and the propellant clearly have different velocities).

This leads to the following vector equation for rocket motion

F + ve dm/dt – vehat A (Pe-Pa) = ma

The terms on the left comprise the sum of all external forces acting on the
rocket.

F includes all the forces such as gravity, drag, ….

The term ve dm/dt is the thrust due to the rocket, where ve is the exhaust velocity and dm/dt is the mass flow rate (negative number, since m is the mass of the rocket, which is decreasing). The vehat A (Pe-Pa) term is the pressure force. Vehat is a unit vector in the direction of ve, Pe is the exhaust pressure, and Pa is the atmospheric pressure.

I’ll just add that a) I’m glad that at least some of my readers and commenters are smarter than me and b) while I didn’t say that the chain rule led to the rocket equation, I did imply it, and that was a mistake, and c) I had known that at one time, but it’s been a long time.

And we are in agreement that Brian is a putz.

Suspending Too Much Disbelief

John Derbyshire, contrarian that he is, didn’t like Spiderman II.

Even comic-book movies must obey certain unities. In the realm of science fiction — and c/b movies are a species, even if a low one, of science fiction — the golden rule is: You can have one highly implausible bit of science. The rest of the science should be sound, or at least should follow logically from the central implausibility. THE TIME MACHINE is a great sci-fi novel because, once you have granted the central, fairly preposterous, premise that time travel is possible, everything else is just basic Darwinism and stellar evolution, as it was understood at the time.

The central notion in SPIDERMAN is that if you get bitten by a spider whose genes have been messed about with in a certain way, you will develop the ability to shoot 100-ft silk threads from your wrists (without, apparently, any loss of body mass). This is preposterous — though not at a sensationally high level, as spider genes can be messed around with in an infinity of ways, and we don’t actually know what would happen if you were bitten by a spider whose genes had been messed around with in way No. 29,485,672.

Having been persuaded to suspend our disbelief with respect to Spidey’s powers, we should not then be asked to swallow any more preposterosities. And we know perfectly well what whould happen if you dumped a fusion reaction into the East River — ka-BOOM.

I haven’t seen the movie yet, but I intend to, and won’t let this curmudgeonly review put me off of it, though I actually agree with the principle. That was one of the things that bothered me about the first movie. Once you tell me he’s been bitten by a radioactive spider, then fine, I’ll buy the superpowers on the part of Spidey. I’ll even accept the notion that, as Derbyshire points out, he doesn’t have to conserve mass.

But Mary Jane has no superpowers, yet she performs a superfeat near the end of the movie, when she falls off the cable that’s being flung around (face it, she wouldn’t have been able to hang on to it that long without her arms being torn off), and then catches the side of the cable car as she falls some distance toward it.

Sorry, just Not.Gonna.Happen. It defies physics and the strength, both muscular and structural, of a normal human body, even one pumped on adrenalin. I enjoyed the movie up to that point, but that bit really bugged me, because there was no good reason for it–it could have been just as exciting while being realistic.

And of course, there’s the other thing that bothered me about the movie–the ending.

Parker was under no obligation to keep Harry in the dark about his father’s end. Just because he was requested to, he didn’t agree to the request, and he did himself and Harry a disservice by allowing Harry to continue to live on in a fantasy world about his father’s true nature, a world that’s likely to cause him to attempt to kill Parker’s alter ego (and hence Parker) in the future.

At a minimum, he should have at least pointed out to Harry that the fact that Spiderman returned his father’s body to his home didn’t mean that Spiderman was the killer. He might not have accepted it, but there would have been no harm in exercising a little logic on him, even if he wanted to spare him the knowledge that his father was a murderer (though again, I think that was no favor).

Also, he’s not protecting MJ by not reciprocating her love. The key is to keep his identity a secret (though not from her). I found it highly unsatisfactory, but apparently it was more important to them to set up some dubious sequel plot than to employ logic, or ethics.

I guess that SF movies will never get made right until they hire me as a script advisor. And listen.

[Update on Tuesday]

For those endlessly or otherwise fascinated by bad movie physics, check out this site (including a review of Spidey I). It says The Core (which I haven’t seen, and probably won’t) takes the prize for the worst movie ever in this regard.

Black Irish?

Archaelogists have discovered evidence that some people in the borderlands of England may be descended from Moors from northern Africa, Roman soldiers brought over to guard Hadrian’s wall. One more interesting ingredient to the mix of Picts, Saxons et al.

Also a little ironic, considering that many of these people are the so-called Scots-Irish who settled much of Appalachia and the American south, with its slavery and anti-miscegany laws.

The Sky Was Falling

It turns out that, for the expedition that lost so many people on Everest eight years ago, Chicken Little was right.

An analysis of weather patterns in May 1996 suggests the mountaineers died when the stratosphere sank to the level of the summit, 29,000ft above sea level.

The freak weather caused pressure and oxygen levels to plunge within the “death zone” – the area above 26,000ft where the oxygen is extremely thin.

The Excluded Middle

As anyone who reads Andrew Sullivan knows, John Derbyshire is probably the most (what Andrew (and other gays) call) “homophobic” writer at National Review.

Apparently, in response to a post yesterday about the genetic origins of homosexuality, he got an email from a (vociferously non-conservative) supposed expert in the field, who wrote:

…if it were a genetic disease defense, it would have a certain very simple and identifiable inheritance pattern, and it certainly does not have that pattern. Identical twins would both have it, but the chance that a homosexual man’s identical twin is also homosexual is only about 20%.

I have a theory about the genetic basis of human sexual orientation, that I never hear anyone discuss, but to me makes perfect sense, and fits the facts (including the one quoted above, assuming that it is indeed a fact). I discuss it here, and in comments to this post.

Simply put, some are born homosexual, some (probably more) are born bisexual, and most are born heterosexual. For the first and third groups, their sexuality is indeed thrust upon them. Errrr…so to speak.

If that’s true, then the twin studies might actually provide some insight into the relative genetic component, assuming they’re separated twins. If two separated twins (the cite above doesn’t indicate whether they were separated or not) turn out to both be homosexual, that to me is a good indicator of homosexuality with either a genetic basis, or uterine environmental basis, or both. Of course, the only way to truly determine the genetic basis may be to allow human cloning…

In any event, it seems to me that my theory would dictate that the cases in which one twin is homosexual, and the other not, are cases in which both were born bisexual, and for various post partum environmental reasons, made different choices as to partners. It also explains why some homosexuals can be “cured,” and others can’t. The ones who can be were never homosexual in the first place–they always had a choice and simply decided to start choosing differently.

Long story short, this “expert’s” provision of this “fact” (and I’m pretty sure I’ve seen different numbers) has little relevance to the debate, unless you really do have the simplistic viewpoint that all people are either purely homosexual, or heterosexual, with nothing in between.

Toppling Dietary Gods

Rear-guard defenders of the food pyramid and conventional nutrition have always claimed that the only thing that matters about diet is the caloric intake, and that protein/carb ratio is irrelevant. Now there’s been a scientific study that proves them wrong.

“A lot of our assumptions about a calorie is a calorie are being challenged,” said Marlene Schwartz of Yale. “As scientists, we need to be open-minded.”

Others, though, found the data hard to swallow.

“It doesn’t make sense, does it?” said Barbara Rolls of Pennsylvania State University. “It violates the laws of thermodynamics. No one has ever found any miraculous metabolic effects.”

Well, sorry, Barbara, apparently someone just did.

It doesn’t violate laws of thermodynamics at all. It only violates the conventional wisdom of folks like you, whose nostrums have been keeping people unhealthy for decades.

The New Totalitarianism

As you may have noticed, I’m back (in San Bruno, not LA, to which I won’t be back until Thursday). In addition to fighting off small procyonidae and wondering at the pacific Pacific, I read a little over half of The Blank Slate, by Pinker. This is a brilliant book, and a very important one, which I can’t recommend highly enough, not just to people interested in evolution, or anthropology, or evolutionary psychology, but most importantly to those interested in sociology and political science. Its scope is broad, and it covers a number of topics of current political strife in the context of the bizarre and mistaken, but common notion (at least on many college campuses) that human beings truly are a “tabula rasa,” a product purely of their environment, and that human nature doesn’t exist.

I’ll probably be referring to it quite a bit in future posts, but I wanted to note this bit from page 157 of the edition that I have (paperback).

The ideological connection between Marxist socialism and National Socialism is not fanciful. Hitler read Marx carefully while living in Munich in 1913, and may have picked up from him the fateful postulate that the two ideologies would share. It is the belief that history is a preordained succession of conflicts between groups of people and that improvement in the human condition can come only from the victory of one group over the others. For the Nazis the groups were races; for the Marxists they were classes. For the Nazis the conflict was Social Darwinism; for the Marxists, it was class struggle.For the Nazis the destined victors were the Aryans; for the Marxists, they were the proletariat. The ideologies, once implemented, led to atrocities in a few steps: struggle (often a euphemism for violence) is inevitable and beneficial; certain groups of people (the non-Aryan races or the bourgeoisie) are morally inferior; improvements in human welfare depend on their subjugation or elimination. Aside from supplying a direct justification for violent conflict, the ideology of intergroup struggles ignites a nasty feature of human social psychology; the tendency to divide people into in-groups and out-groups and to treat the out-groups as less than human. It doesn’t matter whether the groups are defined by their biology or by their history. Psychologists have found that they can create instant intergroup hostility by sorting people on just about any pretext, including the flip of the coin.

The enemy with which we are now confronted easily slips into the same mold (not surprising, since they have long allied themselves with both groups–the Nazis during WW II and the Soviets in the Cold War).

For the Islamacists the groups are religions, the conflict is jihad and a restoration of the Caliphate, the morally inferior people are the kufr and infidels, and the destined victors are, of course, them. Like the Nazis and Soviets, their movement arose from failed states of once-proud people (Weimar Germany for the Nazis, Czarist Russian in the wake of the Great War for the Soviets, and the lost Arab civilization after their defeat in Europe and the establishment of the Ottoman Empire, followed by European colonization).

The only difference (and its significance is primarily that it will make it easier to defeat them) is their almost total lack of any industrial infrastructure, or ability to build one. At least in the case of the Nazis and Soviets, task one was to rebuild the ability to wage war. The Islamists choose instead to use our own weapons, and their own people as cannon (and daisy-cutter, and bullet) fodder. Whether because this is an inability to develop their own capabilities, or a disinterest isn’t clear, but as Pinker later shows, it could be the former–it is, in its current state, truly a failed culture.

As an example, later in the book (again, the application to the Middle East is mine, not Pinker’s) he points out four modes of human transactions (as earlier described by the anthropologist Alan Fiske):

  • Communal Sharing: no one keeps track of who gets what. This mode applies in families, and occasionally in small tribes. It’s also how Marxists and collectivists (in utter defiance of everything known about human nature) imagine the entire world would work, if the theory were only applied “correctly.”
  • Authority Ranking: Dominant people confiscate stuff from the lower ranks. This is how socialism generally works out whenever it’s actually implemented.
  • Equality Matching: People keep track of who gave what, but there is no time value to the transaction (you can repay me in a year or a day, but there is no penalty for delay), and the value of items is fixed in time and space. This works for ritual exchanges, such as trading rings in the Pacific islands, but it’s hard to build a modern economy with it. The giver may often end up with the same item that she gave someone else earlier. As Pinker points out, this may actually happen with Christmas fruitcakes (the theory being that, like the theory that there’s only one electron in the universe that’s simply very busy, there’s only one fruitcake, passed on from person to person every year). Anthropologists will note that this is most common in hunter-gatherer cultures, and being almost literally tit for tat, it’s probably the economic model that’s most natural and comfortable for us, having evolved to it. It appears to be at the core of our intuitive economics notions (which is why it’s important to have good economics education in schools, to overcome this false intuition).
  • Finally, we have the mode called Market Pricing, which is the basis of modern capitalism, and indeed modern life itself.

The latter requires a much more sophisticated knowledge of economics, and complex institutions such as monetary systems, futures markets, written enforceable contracts, credit, and interest (that is, the recognition that not only time is money, but that money held over a period of time is additional money). It also overturns the intuitive notion (to which Marx fell prey) of the labor theory of value, and indeed the very notion of objective, unchanging value (on which the Equality Matching mode is fundamentally dependent).

The Arabs and Muslims have a problem. Their economies are based on a combination of Community Sharing (among clans) and Authority Ranking (of which Saddam Hussein’s regime was an exemplar). Further, their religion, to all extents and purposes, makes market pricing illegal, because the Koran prohibits the collection of interest, thus not recognizing the time value of money. It’s impossible to run a market economy without allowing interest (and, in fact, recognizing this, some Arab states have come up with elaborate schemes to collect it without admitting that they are).

Of course, the Bible has strictures on usury (or interest). In fact, for that reason, only Jews were allowed to be bankers throughout much of history, and the fact that they were perceived to be earning money by using the funds of honest Christians contributed to the historical enmity against them. But few in the post-reformation West take the Bible literally on this particular score (though it survives in the form of some states’ anti-usury laws, which restrict interest rates, recognizing that some interest is essential but still revealing a natural bias against a perceived “unfair” amount).

Thus, while we are indeed dealing with a totalitarian ideology determined to ultimately rule the world, and have all live under its strictures or die, ironically, until Islam is similarly reformed to reflect economic reality, our new totalitarian enemy will never be the threat that the Nazis and Soviets were. And of course, in the wake of such a reform, they would likely stop trying to murder us and take over the world, because it’s all of a piece.

This is not to say, of course, that the threat is not dangerous–what happened two years ago this coming Thursday gives the lie to that. And as we saw on that sunny September morning, they can be very effective even when wielding our weapons (in fact, much more so than when they restrict themselvse to their own). We should be very thankful that they finally got our attention before they got their hands on the really good stuff, and it’s our ongoing responsibility, now that we see them for what they are, that we continue to keep it from them.

One more point, just to preempt any silly notions that the situation is symmetrical, and that we are the new totalitarians, and want to rule the world, and crush it beneath our GI army boots, and tie up the oppressed, force Big Macs down everyone’s throat, prop their eyelids open with toothpicks and make them watch Britney polish Madonna’s tonsils with her tongue.

We don’t oppose them for their beliefs, except to the degree that their beliefs require that they kill us for ours. We don’t want to make everyone Christian, or Jewish. We don’t want to enslave or kill people because they don’t worship the right god, or wear the right clothes, or avoid being raped. If we have an ideology, it’s an anti-ideology–a belief that ideologies have murdered millions in the past century, and that we are going to do whatever we must to prevent more murders of innocents. The “group of people” who we may have to kill are not a group in the sense of race, or class, or even religion, and they place themselves in the group by their beliefs and behavior, not by accidents of birth. We can live with anyone, except people who cannot live with us.

They are in a battle for domination, and rejoice in death–even their own. We are in a battle for own defense, and would prefer that we didn’t need to send our young men and women overseas.

They desire to kill as many innocents as possible–men, women, children, and lack only the means to do so. When they are successful, they ululate in the streets and pass out candy. We desire to kill as few as possible, and only the guilty–those who sit in their caves and palaces and plot mass death. We spend millions of dollars, and risk our own soldiers’ lives to minimize the deaths of innocents, and when, despite out best efforts to prevent it, innocents die, we don’t cheer–we often grieve, and we launch investigations to determine the cause.

Christianity was once a bloodthirsty religion, but it was reformed. So can Islam be.

But Islamism, like its predecessors, is immune to reform. There is no solution, ultimately, except its total defanging, if not eradication.