Grasping Reality with Both Hands: The Semi-Daily Journal Economist Brad DeLong

Meterror Impacts Once Again

Hoisted from Comments: Frank:

Grasping Reality with Both Hands: The Semi-Daily Journal Economist Brad DeLong: impact rates based on the cratering record are pretty much in line with estimates based on the population of Earth-crossing asteroids. Size distributions roughly fit an inverse square law distribution (i.e., 2 x diameter = 1/4 probability; 1/2 diameter = 4 x probability). Using this one can calculate impact rates based on a probability of a 500 m impactor every 100,000 years. So on average, 50 m projectiles should impact every 10,000 years or so (10 x 10 times more frequent). Once you get down to about 50 m the probability of the projectile exploding in the atmosphere (like Tungusaka) is quite high. Much smaller events might be like nuclear explosions, but they are rare and very unlikely to hit populated areas.

More to the point of the Easterbrook article, I've searched the Web of Science publication database for papers by the chief protagonist in his article. DH Abbot has not published a significant paper in 5 years and has never published anything other than unreviewed abstracts on this subject that I can find. Looks like a squeeky wheel getting Easterbrook's attention, but no follow-up to credible experts in this field.

And then there is the cross-section problem: we have what? 6000 cities each of roughly 100 square miles = 600,000 square miles of devastating impact cross section in a world of 200M square miles. That means only 1 out of 400 50M impacts will be "devastating" if we say that a 50 meter meteorite--2 megatons, Barringer crater-sized--hitting a city is our threshold for "devastating."

So we are down to one devastating every 4,000,000 years--not the one every thousand years of the Atlantic Monthly's lead to Gregg Easterbrook's article.

Reported Deaths and Injuries from Meteorite Impact

From Oberlin College, we read:

Meteorite Impact Structures Student Research:

• 1420 BC  Israel - Fatal meteorite impact.
• 588 AD China - 10 deaths; siege towers destroyed.
• 1321-68 China - People & animals killed; homes ruined.
• 1369  Ho-t'ao China - Soldier injured; fire.
• 02/03/1490 Shansi, China - 10,000 deaths.
• 09/14/1511 Cremona, Italy - Monk, birds, & sheep killed.
• 1633-64 Milono, Italy - Monk killed.
• 1639 China - Tens of deaths; 10 homes destroyed.
• 1647-54 Indian Ocean - 2 sailors killed aboard a ship.
• 07/24/1790 France - Farmer killed; home destroyed; cattle killed.
• 01/16/1825 Oriang, India - Man killed; woman injured.
• 02/27/1827 Mhow, India - Man injured.
• 12/11/1836 Macao, Brazil - Oxen killed; homes damaged.
• 07/14/1847 Braunau, Bohemia - Home struck by 371 lb meteorite.
• 01/23/1870 Nedagolla, India - Man stunned by meteorite.
• 06/30/1874 Ming Tung li, China - Cottage crushed, child killed.
• 01/14/1879 Newtown, Indiana, USA - Man killed in bed.
• 01/31/1879 Dun-Lepoelier, France - Farmer killed by meteorite.
• 11/19/1881 Grossliebenthal, Russia - Man injured.
• 03/11/1897 West Virginia, USA - Walls pierced, horse killed, man injured.
• 09/05/1907 Weng-li, China - Whole family crushed to death.
• 06/30/1908 Tunguska, Siberia - Fire, 2 people killed. (referenced throughout paper)
• 04/28/1927 Aba, Japan - Girl injured by meteorite.
• 12/08/1929 Zvezvan, Yugoslavia - Meteorite hit bridal party, 1 killed.
• 05/16/1946 Santa Ana, Mexico - Houses destroyed, 28 injured.
• 11/30/1946 Colford, UK - Telephones knocked out, boy injured.
• 11/28/1954 Sylacauga, Alabama, USA - 4 kg meteorite struck home, lady injured.
• 08/14/1992 Mbole, Uganda - 48 stones fell, roofs damaged, boy injured.

Meteorite Impact Structures Student Research: The most incredible Chinese report is that of the Chíing-yang Meteorite Shower of 1490.  Supposedly, tens of thousands of people were killed during the shower in the Shansi province.  Yau et al. tell us that "[t]he Chíing-yang incident seems rather implausible in terms of the total number of casualties and the narrow size distribution of the meteorite fragments (Yau et al. 1994)," but they also point out its similarities to the Tunguska event, which would have devastated a populated area.

Yau, K., P. Weissman, and D. Yeomans. "Meteorite Falls in China and Some Related Human Casualty Events." Meteoritics 29, 864-871. [Geobase]

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Impact event - Wikipedia: Near misses and forecasts:

• On 19 May 1996 a 300–500 m asteroid, 1996 JA1, passed within 450,000 km of Earth; it had been detected a few days before.
• On 18 March 2004 a 30 m asteroid, 2004 FH, passed within 40,000 km of Earth only a few days after it had been detected. This asteroid probably would have detonated in the atmosphere and posed negligible hazard to the surface, had it been on impact course.
• On 31 March 2004, a 6 m meteoroid, 2004 FU162 made the second closest near miss pass ever observed (closest so far was The Great Daylight 1972 Fireball) with a separation of only 1.02 Earth radii from the surface (6,500 km). Because this object is certainly too small to pass through the atmosphere, it is classed as a meteoroid rather than an asteroid.
• In 2004, a newly discovered 320 m asteroid, 99942 Apophis (previously called 2004 MN4), achieved the highest impact probability of any potentially dangerous object. The probability of collision on 13 April 2029 is estimated to be as high as 1 in 17 by Steve Chesley of NASA's Jet Propulsion Laboratory, though the previously published figure was the slightly lower odds of 1 in 37, calculated in December 2004. Later observations showed that the asteroid will miss the earth by 25,600 km (within the orbits of communications satellites) in 2029, but its orbit will be altered unpredictably in a way which does not rule out a collision on 13 or 14 April 2036 or later in the century. These possible future dates have a cumulative probability of 1 in 45,000 for an impact in the 21st century.
• Asteroid 2004 VD17, of 580 m, previously was estimated to have a probability of 1 in 63,000 of striking earth on 4 May 2102 (as of July 2006), with risk 1 on the Torino scale, but further observations lowered the estimate. As of the observation on December 17, 2006, JPL assigns 2004 VD17 a Torino value of 0 and an impact probability of 1 in 41.667 million in the next 100 years.
• Asteroid (29075) 1950 DA has a potential to collide with Earth on March 16, 2880. The probability of impact is either 1 in 300 or zero, depending on which one of the two possible directions for the asteroid's spin pole is correct. This asteroid has a mean diameter of about 1.1 km. The energy released by the collision would cause major effects on the climate and biosphere and may be devastating to human civilization. The Atlantic Ocean is predicted to be facing towards the asteroid on the day of the potential collision.
• Asteroid 2007 TU24 with an estimated diameter between 300-500-m came very close to earth orbit by 1.4 ld(lunar distance) on January 29, 2008. The orbit of the asteroid is shown on NASA's website [6].
• Relatively small objects that burn up in the atmosphere can be dangerous beyond their own capabilities. In 2002, U.S. Air Force Brig. Gen. Simon P. Worden told members of a U.S. House of Representatives Science subcommittee that the U.S. has instruments that determine if an atmospheric explosion is natural or man-made, but no other nation with nuclear weapons has that detection technology. He said there is concern that some of those countries could mistake a natural explosion for an attack, and launch nuclear retaliation. In the summer of 2001 U.S. satellites had detected over the Mediterranean an atmospheric flash of energy similar to a nuclear weapon, but determined that it was caused by an asteroid.
• As of March 2008, the Near-Earth Asteroid with the highest probability of impact within the next 100 years is 2007 VK184, with a Torino scale of 1.

The Atlantic Monthly Death Spiral Watch (Gregg Easterbrook Asteroid Devastation Edition)

Why oh why can't we have a better press corps? The Atlantic Monthly features Gregg Easterbook, who writes:

The Sky Is Falling: The odds that a potentially devastating space rock will hit Earth this century may be as high as one in 10. So why isn’t NASA trying harder to prevent catastrophe?

If the odds that a devastating space rock will hit the earth in a century are one in ten, then the chances that we have gone...

• one millennium without a DSR hitting the earth are 0.35...
• two millennia without a DSR hitting the earth are 0.12...
• four millennia without a DSR hitting the earth are 0.014...

It's possible a devastating space rock hit the earth between eight and four millennia ago and we know nothing about it--but it's not terribly likely. It's very hard for me to believe that a devastating space rock has hit the earth since 3000 BC. We have Tunguska--and that's pretty much it[1].

That means that if you started out with a 50-50 prior probability that Gregg Easterbrook knows what he is talking about, your posterior probability that the lead of his Atlantic article is better than birdcage liner given no rock since 2000 BC is 0.0138. But we start with a lower probability than that, don't we? Gregg Easterbrook has a history, doesn't he? I would start with a prior probability that Easterbrook knows what he is talking about of one in a ten, in which case our posterior judgment, given no rock since 3000 BC, is 0.0014. If the Atlantic published an article by Gregg Easterbrook every month, we would have to wait 41 years before there was a 50-50 chance that even one of the Easterbrook articles was right.

"Odds that a potentially devastating space rock will hit Earth this century may be as high as one in 10." Feh!!

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[1] Yes, I know that Easterbrook claims that the abnormally cold weather of 536-537 was caused by a dust cloud raised by a "space object about 300 meters in diameter hit[ting] the Gulf of Carpentaria, north of Australia, in 536 A.D." But I had thought that sulphur left in ice cores in 536-7 was strong evidence that the cause was a volcanic eruption: see http://www.realclimate.org/index.php/archives/2008/03/536-ad-and-all-that/. Easterbrook doesn't mention SO₄ concentrations in ice cores.

Shut Up and Calculate!

Eliezer Yudkowsky wonders aloud just what the Born probabilities in quantum mechanics are. It is, I think, an object lesson that nobody should try to understand quantum mechanics: it simply cannot be done.

We hope he recovers someday:

Overcoming Bias: The Born Probabilities: One serious mystery... is where the Born probabilities come from, or even what they are probabilities of.  What does the integral over the squared modulus of the amplitude density have to do with anything?... A professor teaching undergraduates might say:  "The probability of finding a particle in a particular position is given by the squared modulus of the amplitude at that position."

This is oversimplified in several ways. First, for continuous variables like position, amplitude is a density, not a point mass.  You integrate over it.  The integral over a single point is zero. (Historical note:  If "observing a particle's position" invoked a mysterious event that squeezed the amplitude distribution down to a delta point, or flattened it in one subspace, this would give us a different future amplitude distribution from what decoherence [theory] would predict.  All interpretations of QM that involve quantum systems jumping into a point/flat state, which are both testable and have been tested, have been falsified.  The universe does not have a "classical mode" to jump into; it's all amplitudes, all the time.)

Second, a single observed particle doesn't have an amplitude distribution.  Rather the system containing yourself, plus the particle, plus the rest of the universe, may approximately factor into the multiplicative product of (1) a sub-distribution over the particle position and (2) a sub-distribution over the rest of the universe.  Or rather, the particular blob of amplitude that you happen to be in, can factor that way. So what could it mean, to associate a "subjective probability" with a component of one factor of a combined amplitude distribution that happens to factorize?...

If a whole gigantic human experimenter made up of quintillions of particles interacts with one teensy little atom whose amplitude factor has a big bulge on the left and a small bulge on the right, then the resulting amplitude distribution, in the joint configuration space, has a big amplitude blob for "human sees atom on the left", and a small amplitude blob of "human sees atom on the right.... [T]he Born probabilities seem to be about finding yourself in a particular blob, not the particle being in a particular place. But what does the integral over squared moduli have to do with anything?  On a straight reading of the data, you would always find yourself in both blobs, every time.  How can you find yourself in one blob with greater probability?  What are the Born probabilities probabilities of?  Here's the map - where's the territory?

I don't know.  It's an open problem.  Try not to go funny in the head about it. This problem is even worse than it looks because the squared-modulus business is the only non-linear rule in all of quantum mechanics...

The Great Element Naming Controversy

Abi Sutherland sends us to

Element naming controversy: Finally in 1997, the following names were agreed on the 39th IUPAC General Assembly in Geneva, Switzerland: 104 - rutherfordium; 105 - dubnium; 106 - seaborgium; 107 - bohrium; 108 - hassium; 109 - meitnerium.

In 1999, Glenn T. Seaborg died, still disputing the name change for #105 and adamant about it remaining known as hahnium. His reason concerning Dubna in Russia was that he believed that they had made a false claim about discovering the element for which they had been credited. When the Dubna group finally did release some additional data on the experiment, Seaborg claimed that it was a misreading of the decay pattern of their product. Even then, the Dubna group still refused to remove their claim. Some people in the Berkeley group and some others still refer to it as hahnium.

Huh. I had thought that they had taken Glenn Seaborg's name away from him--that all he was left with was a room in Berkeley's Faculty Club and the Lafayette Library. Now I feel better.

Helium Mines

My problem--actually one of my many problems, but that's a long story--is that I don't understand where our supply of helium comes from. How is there helium trapped in the earth's crust that we can mine? Is it all from the decay of uranium?

Ah. Wikipedia comes through once again:

Helium - Wikipedia, the free encyclopedia: After an oil drilling operation in 1903 in Dexter, Kansas, U.S. produced a gas geyser that would not burn, Kansas state geologist Erasmus Haworth collected samples of the escaping gas and took them back to the University of Kansas at Lawrence where, with the help of chemists Hamilton Cady and David McFarland, he discovered that... 1.84% of the gas sample was helium. Far from being a rare element, helium was present in vast quantities under the American Great Plains, available for extraction from natural gas. This put the United States in an excellent position to become the world's leading supplier of helium.... World War I... 200 thousand cubic feet (5,700 m3) of 92% helium was produced in the program even though only a few cubic feet (less than 100 liters) of the gas had previously been obtained... the world's first helium-filled airship, the U.S. Navy's C-7, which flew its maiden voyage from Hampton Roads, Virginia to Bolling Field in Washington, D.C. on 1 December 1921.... National Helium Reserve in 1925 at Amarillo, Texas with the goal of supplying military airships in time of war and commercial airships in peacetime. Due to a US military embargo against Germany that restricted helium supplies, the Hindenburg was forced to use hydrogen... the reserve was expanded in the 1950s to ensure a supply of liquid helium as a coolant....

By 1995, a billion cubic metres of the gas had been collected... "Helium Privatization Act of 1996."...

For many years the United States produced over 90% of commercially usable helium in the world. Extraction plants created in Canada, Poland, Russia, and other nations produced the remaining helium. In the mid 1990s, A new plant in Arzew, Algeria producing 600 million cubic feet (1.7×107 m3) came on stream, with enough production to cover all of Europe's demand. Subsequently, in 2004–2006 two additional plants, one in Ras Laffen, Qatar and the other in Skikda, Algeria were built, but as of early 2007, Ras Laffen is functioning at 50%, and Skikda has yet to start up. Algeria quickly became the second leading producer of helium....

Nearly all helium on Earth is a result of radioactive decay. The decay product is primarily found in minerals of uranium and thorium, including cleveites, pitchblende, carnotite and monazite, because they emit alpha particles, which consist of helium nuclei (He2+) to which electrons readily combine. In this way an estimated 3.4 litres of helium per year are generated per cubic kilometer of the Earth's crust....

The world's helium supply may be in danger, according to Washington University in St. Louis chemist Lee Sobotka. The largest reserve is in Texas and would run out in eight years if consumed at the current pace.... [H]elium is extracted by fractional distillation from natural gas, which contains up to 7% helium.... 2005, approximately one hundred and sixty million cubic meters of helium were extracted from natural gas or withdrawn from helium reserves, with approximately 83% from the United States, 11% from Algeria, and most of the remainder from Russia and Poland. In the United States, most helium is extracted from natural gas in Kansas and Texas...

Australian Actresses Are Plagiarizing Scott Aaronson's Quantum Mechanics Lecture to Sell Printers

I am not sure that "plagiarizing" is the right word here. But it is a remarkable situation--and there ought to be a way for Robin Hanson's friend Scott Aaronson's to get a printer out of it:

Shtetl-Optimized » Blog Archive » Australian actresses are plagiarizing my quantum mechanics lecture to sell printers: I tried to think of a witty, ironic title for this post, but in the end, I simply couldn’t. The above title is a literal statement of fact...

http://www.youtube.com/watch?v=saWCyZupO4U

Lawrence Hall

Lawrence Hall is the name of a building (the Lawrence Hall of Science) and a professor (Lawrence Hall of Physics). The second came to the Berkeley Monday Faculty Lunch Forum to argue that there is empirical content to the Anthropic Cosmological Principle.

What is this principle? Put it this way. Suppose somebody asks you why the universe is pervaded by an 80-20 nitrogen-oxygen gas mixture, or why it is 300K outside. The answer is that the universe isn't like that but that where you are is like that because if you wet surrounded by chlorine gas or in a place where it is 400K you--and all life like you--would be dead. Our confidence in these "anthropic" explanations is strong because we can point to places we know of that lack the 80-20 atmosphere--the asteroid belt--and places where it is not a shirtsleeve 300K--Cambridge, Massachusetts.

Can this anthropic principle be applied to more fundamental issues? Can we say that the mass of the d quark is what it is because if it were 20% lower than the neutron would be absolutely stable and there would be no stars? We cannot see any places in the multiverse where the mass of the down quark is lower, but our predecessors did not know about the asteroid belt and other places lacking an 80-20 atmosphere, and the anthropic explanation for why there is oxygen around for us to breathe was just as valid then for them as it is for us. Is it doing science to use this anthropic principle--or is it just meaningless and tautological? After all, pretty much everything in the universe has to be the way that it is for there to be a physicist with the same name as a building talking in the Seaborg Room of the Berkeley Faculty Club Monday at lunchtime--start with Lawrence Hall as your premise, and you have "explained" everything, in some sense.

Lawrence Hall thinks that there is empirical content, and his argument goes like this:

• The section of the multiverse that we are in has picked its version of the laws of physics through some process.

• We describe the laws of physics by picking theories and parameter values.

• The way we describe does not match one-to-one to the way this part of the multiverse picks the parameter values.

• Therefore there is a probability pressure gradient out there as we look at possible free parameter values for our theories--either low values are much more probable for this part of the multiverse, or high values.

• So, from our perspective, we would expect to find ourselves in a part of the universe that seems "close" to catastrophe--we should expect, over and over again, to do our calculations and then exclaim: "Wow! We are lucky that parameter X isn't 20% lower (or higher) than it is! If it were, then we couldn't exist!"

• If we find over and over again that our part of the multiverse appears to us, given the way we describe parameter values, to be remarkably close to a knife-edge of fundamental change and disruption is an empirical prediction of the anthropic cosmological principle.

• Thus it is testable, and we are testing it.

Possibilities for Really Cheap Entertainment

From "As You Know, Bob":

As You Know, Bob: "Ahhh! My hand!": Earlier today (well, last evening, now), the eldest kid and I made a nerd road trip up to the new digital-tv transmitter shack up in the hills. All afternoon, I had been brooding about standing at the foot of the broadcast tower while it was radiating a few megawatts of radio energy into space. So, come sunset, I went down to the basement and dug out a couple of 48" fluorescent bulbs, and threw them and the family into the car. We drove over to the nearest high-voltage power line, and we watched the fireflies while we waited for full dark, and then we played light sabers in the gloaming...

"Reduction of the Wave Packet" and Other Mumbo-Jumbo

Effects-that-happen-before-causes department:

Scientific American: Quantum Erasing in the Home.

I am not sure whether this is as disturbing or more disturbing than Bell's inequality.