Wednesday, May 27, 2015

Collision Hazards

The largest ocean going ships are about half a million tons. I would expect that any interstellar ships we or others might build would have to be at least that size in order to survive a journey lasting decades or centuries. Let's estimate a million tonnes - 10^9 kg - roughly twice the mass of the supertanker the Seawise Giant.

I remember the first time I saw a piece of armor plate that had been struck by a hypervelocity projectile. Even though the projectile was only a bit larger than a beebee, it had drilled a hole right through two inches of armor plate. Lower velocity projectiles spread their energy over larger areas. The operative factor is the speed of sound. If the projectile is moving significantly faster than the speed of sound in the target material, there isn't enough time for the forces to be transmitted laterally, and the projectile just keeps boring a hole until it has piled up enough mass in front of it to slow the whole procession, including the shock wave at the front, below the speed of sound.

It's a bit more complicated than that of course.

Suppose you had a large interstellar space craft moving a something like half the speed of light. The kinetic energy would be pretty large:

m*c^2(gamma - 1), where gamma = 1/sqrt(1-v^2/c^2) = 1/sqrt(3/4) = 1.1555, so that available kinetic energy is 1.4 * 10^16 J/kg, or 1.4 * 10^25 J for a million tonne behemoth like that described in the first paragraph. That amounts to the equivalent of 3 billion megatons of TNT - not enough to blow a planet to bits, death star style, but possibly enough to blast a hole right through it. So you might not want to aim your interstellar ship directly at a habitable planet, just in case you had trouble slowing down.

Monday, May 25, 2015

Who Created al Qaeda and ISIS?

Zia-ul-Haq, the Pakistani President, and his Inter Service Intelligence agency, the ISI did, but the money to do it came from Reagan and the Saudis. Reagan and his minions funded the ISI to create the Afghan insurgency against the Russians, but total operational control was vested in Pakistan and the ISI. Charlie Wilson, the Democratic Congressman (and eponymous hero of Charlie Wilson's War) had bought into a propaganda film produced by a glamorous and politically connected socialite who had become a fan of Zia and his insurgents. The film featured a heroic Mujaheddin leader but didn't mention his early career throwing acid into the faces of women in Kabul who went out without their faces covered and provided bipartisan support for giving the ISI everything it wanted.

With full operational control, the ISI had plenty of resources left for building itself into panoptican styled on the KGB, and for fomenting trouble among Indian Sikhs and in Kashmir. But the ISI still had a mission in Afghanistan after the Soviets withdrew - ensuring that Afghanistan was ruled by Islamists friendly to Pakistan or kept in turmoil.

The Taliban and al Qaeda were the result.

ISIS is a simpler story. After Bush Too's war in Iraq, his idiot proconsul Paul Bremer turned the Iraqi army out without jobs or pensions - but with weapons.

How We Got Into Afghanistan

To the extent that we remember at all, Americans have only a dim idea how we got first got involved in Afghanistan. Something about the Soviet invasion, followed by the CIA and "Charlie Wilson's War." Husain Haqqani tells some more of the story in "Magnificent Delusions."

After Army Chief Zia-ul-Hac overthrew the elected government of Pakistan and murdered the elected President, he faced rebellions in some provinces. When the British divied up the subcontinent, they had deliberately divided the Pashtun peoples, placing some of them in Pakistan and the rest in Afghanistan. This resulted in persistent demands for a united "Pashtunistan." Meanwhile, a somewhat leftist government had been elected in Afghanistan and adopted policies (land reform, rights for women) that offended large landowners and Islamic fundamentalists.

Zia responded by training, funding, and supplying Islamist insurgents, creating an Afghan civil war. This war probably played a key role in provoking or enabling the rather small Communist faction into overthrowing the elected Afghan government and taking power. At this point, Zia, pointing to the Communist threat, was able to enlist American President Jimmy Carter into small scale support for Zia-ul-Hac's Afghanistan war - thereby making the US the first great power to become deeply involved. Six months later, the Soviets invaded.

Because Pakistan, against US wishes, was developing a nuclear weapon, the US had stopped all military aid to Pakistan. The Soviet invasion changed all that.

The US policy that emerged immediately after Soviet troops moved into Afghanistan revolved around Pakistan. As Vance wrote in his memoir, Carter was willing to seek congressional approval to waive the legal prohibition on military aid to Pakistan. At the same time the United States would reaffirm its nuclear nonproliferation policy and press Pakistan to provide acceptable guarantees that it would not develop a nuclear weapon. But the first step was to reach agreement with Pakistan on the terms of an assistance package.

The relationship between the United States and Pakistan had flipped. The New York Times headline “Pakistan Is No Longer the Ardent Suitor, but the Prize to Be Courted” captured it exactly. 56 Zia handled the new situation with panache. He was eager to partner with the United States, but he made it seem like a difficult decision. He emphasized Pakistan’s “strategic position” and its being the “backdoor to the Gulf” and praised the United States as the champions of the free world. 57 But he also spoke of the vulnerability of Pakistan to Soviet and Indian pressures.

Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (pp. 247-248). PublicAffairs. Kindle Edition.

In effect, Zia had mouse trapped the US and the Soviets into a confrontation that ultimately would be disastrous to both.

Zia was both a cunning and treacherous fellow, but his plans could not have succeeded without a large dollop of American stupidity.

Here is Reagan, somewhat later:

After meeting Zia, Reagan wrote in his diary for that Tuesday: “The weather turned out fine for the official greeting ceremony for Pres. Zia of Pakistan. We got along fine. He’s a good man (cavalry). Gave me his word they were not building an atomic or nuclear bomb. He’s dedicated to helping the Afghans & stopping the Soviets.”

Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (p. 229). PublicAffairs. Kindle Edition.

Sunday, May 24, 2015

All Physics is Local

In Kerson Huang's book, The Fundamental Forces of Nature: The Story of Gauge Fields he notes that the principle of local gauge invariance "removes the last vestige of action at a distance from physics." The reason for this is that the job of keeping track of the field has been merged with spatial displacement via the replacement of the ordinary derivative in the Hamiltonian by a gauge covariant derivative.

The notion of gauge was introduced into physics by Hermann Weyl, the distinguished mathematician, in an attempt to unify electromagnetism and general relativity. It didn't actually work out in its original version, because, as Einstein pointed out, it implied unphysical effects. As often happens, with a little reinterpretation it was quickly recognized as a key feature of electromagnetism, and with the rise of the standard model and the idea of Yang-Mills fields, the key principle for all the fundamental forces of nature.

I find it mysterious but fascinating.

Class and Inequality

Hunter gatherers are strongly egalitarian. Sedentary agriculturalists tend to develop hierarchical class structures. The lowest classes tend to be profoundly repressed.

Why so? If we dismiss the usual idiotic ideas based on divine ordination or social Darwinism, what are we left with?

One cardinal fact about the sedentary lifestyle is that it permits much higher birth rates. The higher birth rates mean that societies produce a lot more people than they can feed. In effect, to prevent being torn apart by internecine struggles, societies develop what amounts to a designated dying class. Like the development of organized warfare, another agricultural innovation, having an oppressed class increases the death rate.

At least in large societies, two classes doesn't seem to be enough. Perhaps three or more are needed for stability. Because the upper classes are likely to out reproduce and out survive the lower classes, means for class demotion are also needed. That fear of class demotion, for example, forms a central theme in novels like "Pride and Prejudice" and "War and Peace."

The means to escape the Darwinian jaws of brutal class oppression and war were not really available until quite recently in history. Birth control, even mandatory birth control, seems a lot more humane to me that those alternatives.

Friday, May 22, 2015

Going to the Matrices

The expression "going to the mattresses" should be familiar to fans of The Godfather or of Nora Ephron's You've Got Mail. It's what Mafioso, or presumably, book store owners, do when they go to war.

In linear algebra and geometry, the sophisticated prefer to speak of the advantages of coordinate free representations, but, when the rubber meets the road, they often "shut the doors and compute with matrices," as one wag put it.*

I was reminded of that by my current interest in tensor networks, where the action is precisely in matrices (and their higher rank analogs.

* Actual quote, from Irving Kaplansky, speaking of himself and Paul Halmos:

We share a philosophy about linear algebra: we think basis-free, we write basis-free, but when the chips are down we close the office door and compute with matrices like fury.

And a different opinion from Dieudonne:

There is hardly any theory which is more elementary [than linear algebra], in spite of the fact that generations of professors and textbook writers have obscured its simplicity by preposterous calculations with matrices.

Both via Mathoverflow

Locality in Physics

The world looks simpler when we confine ourselves to local interactions. We affect the world mostly by local interactions. If we want to move something, we usually need to push on it. When Newton discovered his law of universal gravitation, with its action at a distance, that conception of locality was profoundly challenged. He didn't like it, but he could discover no satisfactory hypothesis to explain it. Electricity and magnetism turned out to present similar challenges.

The invention of the electromagnetic field by Faraday and Maxwell changed all that. Field strengths, and the forces they generated were now determined by the fields and charges in the local neighborhood, in effect pervading space with an ether that transmitted the forces. Einstein showed that the ether had to be Lorentz invariant and that gravity too could be localized, with the gravitational field now being determined by the matter and fields in the neighborhood.

One reason this is interesting today is the discovery of the fact that the quantum physics of certain many body systems is radically simplified if the Hamiltonians of those systems have the locality property. These ideas are embodied in so-called tensor networks. In particular the quantum entanglement entropy of such systems can be shown to be proportional to the area of the system boundary. Equally fascinating, effective geometry appears to appear naturally from such tensor networks.

For students of General Relativity and String Theory, this should loudly clang several bells with names like Bekenstein entropy, the Holographic Principle, Maldacena duality, quantum information and spacetime, and Wheeler's 'It from Bit'. These ideas are being actively pursued, and Jennifer Ouellette has a popular level article here in Quanta. A semi-technical article on the fundamental tool, the tensor network is:

Wednesday, May 20, 2015

Divorce, Pakistani Style

For various reasons, nearly all of them bad, the US clung to its alliance with the Pakistani generals despite repeated demonstrations that they were unreliable and frequently treacherous allies. This was much more dramatic during the Eisenhower and Nixon years than during the Kennedy administration, mostly because Nixon, like Dulles and Kissinger saw the world thru Manichean glasses. Relatively stable and progressive India, by pursuing socialist ideas and hewing to a neutralist line in the cold war became a "Soviet stooge" for them. Meanwhile, the repressive and incompetent but Sandhurst educated Pakistani generals spoke a language that they could appreciate, even when their double dealings were repeatedly exposed. In their conversations (as revealed by Nixon's tapes) Indira Gandhi was dismissed as a "bitch" and an "old witch".

Nixon did have one relatively good reason for hanging onto the Pakistani generals: Yahya Khan was his pipeline to the Chinese leadership and a key element in his plan to open relations with China.

Meanwhile Pakistan was falling apart. The Bengalis of East Pakistan, a badly treated majority in their own country, were sick of ill-treatment by the Pashtun and Punjabis of West Pakistan who dominated the military and government. After an election dominated by the Bengali party, Pakistan's generals plotted to hold on to power by military force.

The December 1970 election had brought Pakistan’s fissures to the fore. In response, West Pakistanis reacted with shades of ethnic superiority. Soon after the elections a general visiting Dhaka told his military colleagues: “Don’t worry. We will not allow these black bastards to rule over us,” a reference to the darker skin color of Bengalis compared to Pashtuns and Punjabis. 48 “The Punjab is finished, smashed,” an industrialist told the Times. “Our country has gone to the dogs,” he said, because “We will be ruled by Sindh and Bengal,” a reference to the fact that Mujib was Bengali whereas Bhutto was an ethnic Sindhi.

Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (p. 150). PublicAffairs. Kindle Edition.

After feigning negotiations, Yahya Khan unleashed military repression.

US officials knew Ahsan and Yaqub [Pakistani officers who opposed the intervention] well, so Washington should have heard their views. But the United States chose to stand by Yahya. A new military commander, Lieutenant General Tikka Khan, arrived in Dhaka in March 1971 to enforce national unity with US weapons supplied ostensibly to save South Asia from communism. Pakistani soldiers then confined foreign journalists to their hotels before starting “Operation Searchlight,” a ferocious military action aimed at arresting and killing Awami League leaders. During this military operation at least ten thousand civilians were massacred within three days. There was a large Pakistani force already stationed in East Pakistan, but reinforcements and equipment were flown in from West Pakistan to bolster their strength.

Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (p. 151). PublicAffairs. Kindle Edition.

US diplomats, the press, and much of Congress were outraged by Pakistan's atrocities, but Nixon and Kissinger were unwilling to risk their pipeline to China, even while they concluded that Yahya Khan was delusional and not very bright. Kissinger and Nixon may have brighter, but they were also delusional, attributing the slaughter in East Pakistan to Hindu-Muslim conflicts while in fact they were nearly completely irrelevant.

Nixon continued his delusional support of Yahya Khan even after India intervened on behalf of the Bengalis. The Pakistani army quickly collapsed and surrendered, but the generals continued their policy of attempting to deceive their own people.

The headline of Dawn, Pakistan’s major English newspaper, on the day of Pakistan’s surrender read, “Victory on All Fronts.”

Haqqani, Husain (2013-11-05). Magnificent Delusions: Pakistan, the United States, and an Epic History of Misunderstanding (p. 169). PublicAffairs. Kindle Edition.

Readers inclined to think of Kissinger and Nixon as both immoral and not too bright probably won't change their mind on the basis of Haqqani's book. The picture painted of Pakistan's military leadership is more like tragic-comically stupid.

Indian Puzzles

Geological Edition

When an unstoppable force like the Indian subcontinent crashes into an immovable object like the Eurasian plate, the consequences include the tallest mountains in the world and a cadence of earthquakes like the magnitude 7.8 one that struck Nepal last month and a major aftershock in the same region last week.

Many of the geological questions about the collision remain unanswered. How did the Indian subcontinent get so quickly to where it is today? How big was India originally? Even the simplest of questions — when did India meet Eurasia, the tectonic plate that Europe and Asia sit on? — is up for debate, with researchers offering answers that differ by some 30 million years.

From a New York Times article by Kenneth Chang.

It seems that there are many puzzles about the details of the collision, and several inconvenient facts of involving the when, where, and what of the collision. In particular, it's not why the subcontinent is moving so fast, whether there were two or more subduction zones involved, and what has moved under Asia so far.

Tuesday, May 19, 2015

Exploding Superstars

Exploding Superstars: Understanding Supernovae and Gamma Ray Bursts by Alain Mazure and Stephane Basa is a very well-written and interesting book, somewhat marred by flaws which I prefer to attribute to the evil that has come to dominate Springer. If you prefer to avoid the rant and get to the recommendation, skip the next paragraph.

The book is a translation from the French original, and, so far as I can tell, excellently done, but the title is a bit misleading. Although Supernovae and Gamma-Ray Bursts are prominently featured, the real subject is cosmology, as indicated the the original French title, which was something like "the Universe in all its glory". The text makes frequent mention of twenty or so color plates - these do not make an appearance in this English edition - a considerable loss. There are also many dozens of figures and diagrams many of which appear to have originally been done in color but have been reproduced by some idiotic process which destroys detail and contrast, sometimes making them all but unintelligible.

Now to some of the virtues: Clear and enthusiastic text with mostly non-mathematical descriptions of what the modern science of cosmology has learned. The numerous diagrams, despite the flaws detailed above, clarify and explain many key points. There is also a mathematical appendix, which very briefly summarizes many of the key physical points. Another innovation which impressed me was that instead of a bibliography it includes with a webliography, a list of web sites with relevant material keyed to the chapters.

The story that the book tells is that of the interlocking pieces of evidence that give rise to what is now called the "Concordance Model" of our cosmos. It's a story that with a beginning, some possible endings, and wealth of fascinating details. Regular readers of this blog probably know the principal underpinnings: the Hubble expansion, the Cosmological Microwave Background radiation, Einstein's general relativistic theory of gravity, the very large scale uniformity of the cosmos, the apparent flatness of the cosmos at the largest scales, and the multiple lines of evidence indicating that much of the energy and matter in the universe is "dark".

It's a scientific mystery story of the first order, and even though much of the plot has been revealed, many deep mysteries remain: what is the nature of dark matter and dark energy, what physics is responsible for the fact that we live in a matter rather than anti-matter universe, and what led to the Big Bang itself?

Monday, May 18, 2015

FOTD: Once More Into the Breach

The motto on the Hell's Angels home page is a quote from Henry V in Shakespeare's eponymous play. An excerpt from the famous Saint Crispin's Day speech before the Battle of Agincourt.

Saturday, May 16, 2015

Out of Work

Barbara Ehrenreich reviews Rise of the Robots and Shadow Work in the NYT Sunday Book Review. Excerpt:

In the late 20th century, while the blue-collar working class gave way to the forces of globalization and automation, the educated elite looked on with benign condescension. Too bad for those people whose jobs were mindless enough to be taken over by third world teenagers or, more humiliatingly, machines. The solution, pretty much agreed upon across the political spectrum, was education. Americans had to become intellectually nimble enough to keep ahead of the job-destroying trends unleashed by technology, both robotization and the telecommunication systems that make outsourcing possible. Anyone who wanted a spot in the middle class would have to possess a college degree — as well as flexibility, creativity and a continually upgraded skill set.

But, as Martin Ford documents in “Rise of the Robots,” the job-eating maw of technology now threatens even the nimblest and most expensively educated. Lawyers, radiologists and software designers, among others, have seen their work evaporate to India or China. Tasks that would seem to require a distinctively human capacity for nuance are increasingly assigned to algorithms, like the ones currently being introduced to grade essays on college exams. Particularly terrifying to me, computer programs can now write clear, publishable articles, and, as Ford reports, Wired magazine quotes an expert’s prediction that within about a decade 90 percent of news articles will be computer-­generated.

This is not new to many of us, but it is starting to get more public attention. The implications include the greatest shift of power to capital since the invention of slavery.


In my youth I was a big fan of space opera - rollicking tales of interstellar adventure. Of course that requires some unphysical stuff like faster than light drive, etc. I can handle that, but sometimes the details bug me.

The sliver of the Earth that had been decorating the bottom edge of the main view screen suddenly fell away from view as the ship pulled out of orbit and headed for Jupiter.

Nathan wasn’t sure if it was his gentle acceleration curve or the new inertial dampeners, but the sensation was almost unnoticeable.

In fact, it was even a bit disappointing, and he wondered how much the dampeners would help if he really had to punch it. Fifteen minutes later they were traveling at half the speed of light, and Nathan had discontinued his burn.

Brown, Ryk (2012-12-30). The Frontiers Saga: Episodes 1-3 (Kindle Locations 1518-1522). Ryk Brown. Kindle Edition.

I think a well trained pilot ought to be able to figure out that it *was* his inertial dampers. The gentlest possible acceleration curve (constant acceleration) requires that acceleration = velocity/time = 1.5 x 10^8 (m/s)/900 s or 1.7 x 10^5 m/s^2, or about 17,000 times the acceleration of gravity. Either the "inertial dampers" are working really well or the crew would be more than a bit squished.

Not counting relativistic effects, which would make it slightly worse.