Charlie Stross:
Charlie's Diary: LOGIN 2009 keynote: gaming in the world of 2030: I don't think we're likely to get much more than a terabit per second of bandwidth out of any channel, be it wireless or a fibre-optic cable, because once you get into soft X-rays your network card becomes indistinguishable from a death ray...
Sean Carroll presents the ultimate "who are you going to believe--me or your lying eyes? argument:
Boltzmann’s Universe | Cosmic Variance | Discover Magazine: Take for granted that we are exactly who we are — in other words, that the macrostate of the universe is exactly what it appears to be, with all the stars and galaxies etc. By the “macrostate of the universe,” we mean everything we can observe about it, but not the precise position and momentum of every atom and photon. Now, you might be tempted to think that you reliably know something about the past history of our local universe — your first kiss, the French Revolution, the formation of the cosmic microwave background, etc. But you don’t really know those things — you reconstruct them from your records and memories right here and now, using some basic rules of thumb and your belief in certain laws of physics.
The point is that, within this hypothetical thermal equilibrium universe from which we are purportedly a fluctuation, there are many fluctuations that reach exactly this macrostate — one with a hundred billion galaxies, a Solar System just like ours, and a person just like you with exactly the memories you have. And in the hugely overwhelming majority of them, all of your memories and reconstructions of the past are false. In almost every fluctuation that creates universes like the ones we see, both the past and the future have a higher entropy than the present — downward fluctuations in entropy are unlikely, and the larger the fluctuation the more unlikely it is, so the vast majority of fluctuations to any particular low-entropy configuration never go lower than that.
Therefore, this hypothesis — that our universe, complete with all of our records and memories, is a thermal fluctuation around a thermal equilibrium state — makes a very strong prediction: that our past is nothing like what we reconstruct it to be, but rather that all of our memories and records are simply statistical flukes created by an unlikely conspiracy of random motions. In this view, the photograph you see before you used to be yellow and wrinkled, and before that was just a dispersed collection of dust, before miraculously forming itself out of the chaos.
Note that this scenario makes no assumptions about our typicality — it assumes, to the contrary, that we are exactly who we (presently) perceive ourselves to be, no more and no less. But in this scenario, we have absolutely no right to trust any of our memories or reconstructions of the past; they are all just a mirage. And the assumptions that we make to derive that conclusion are exactly the assumptions we really do make to do conventional statistical mechanics!
Boltzmann taught us long ago that it’s possible for heat to flow from cold objects to hot ones, or for cream to spontaneously segregate itself away from a surrounding cup of coffee — it’s just very unlikely. But when we say “unlikely” we have in mind some measure on the space of possibilities. And it’s exactly that assumed measure that would lead us to conclude, in this crazy fluctuation-world, that all of our notions of the past are chimeric...
A colleague in another building emails me, inquiring why the Brookings Institution is holding Gregg Easterbrook out as an "expert" on "environmental policy; global warming; science; space policy; 'well-being' research; Christian theology..." and pointing me to Andrew Northrup:
The Poor Man: Dear God make it stop:
[Gregg Easterbrook's] Creepy Cosmic Thought: A running mystery of cosmology is gamma-ray bursts.... Astronomers assume gamma-ray bursts must be natural in origin.... [But] what if they are the muzzle flashes of horrific planet-killer weapons? Recently Louisiana State researchers... detected very strong gamma bursts coming not from deep space, but from about 3,000 light years distant.... [My] reaction: Great, maybe there is an interstellar war going on just 3,000 light years away....
[E]ven if there is never any way to exceed or circumvent the light-speed barrier, relatively nearby planets might still fight by hurling nuclear bombs at each other at 99 percent of light speed.... John Duezabou of Helena, Mont., adds this creepy postscript: “A bellicose or paranoid extra-solar civilization that could accelerate an object to 99 percent of light speed wouldn’t need to launch bombs at us. They could shoot anything with devastating results, because the kinetic energy of a moving object is half its mass multiplied by the square of its velocity, or KE = 1/2 mv2. Thus, one pound of anything — a pint of vanilla ice cream, for instance — accelerated to 99 percent of light speed has an energy of about 4.8 megatons, roughly the blast yield of the largest hydrogen bombs.”...
Andrew comments:
Now, that a man who writes a sports column likes to fantasize about space wars and disaster movie plots is not news. That a widely-published man who is employed by the influential Brookings Institution... doesn’t have any sense of what that Einstein fellow was on about might be news...
My colleague comments:
UPDATE: Brad Johson of the Center for American Progress is on the case
Sean Carroll writes:
Quantum Hyperion | Cosmic Variance: The orbit of Hyperion around Saturn is fairly predictable; happily, even for lumpy moons, the center of mass follows a smooth path. But the orientation of Hyperion, it turns out, is chaotic — the moon tumbles unpredictably as it orbits, as measured by Voyager 2 as well as Earth-based telescopes. Its orbit is highly elliptical, and resonates with the orbit of Titan, which exerts a torque on its axis. If you knew Hyperion’s orientation fairly precisely at some time, it would be completely unpredictable within a month or so (the Lyapunov exponent is about 40 days). More poetically, if you lived there, you wouldn’t be able to predict when the Sun would next rise.
So — is Hyperion oriented when nobody looks? Zurek and Paz calculate (not recently — this is fun, not breaking news) that if Hyperion were isolated from the rest of the universe [except for the gravitational pull on it by Titan and Saturn], it would evolve into a non-localized quantum state over a period of about 20 years. It’s an impressive example of quantum uncertainty on a macroscopic scale.
Except that Hyperion is not isolated from the rest of the universe. If nothing else, it’s constantly bombarded by photons from the Sun, as well as from the rest of the universe. And those photons have their own quantum states, and when they bounce off Hyperion the states become entangled. But there’s no way to keep track of the states of all those photons after they interact and go their merry way. So when you speak about “the quantum state of Hyperion,” you really mean the state we would get by averaging over all the possible states of the photons we didn’t keep track of. And that averaging process — considering the state of a certain quantum system when we haven’t kept track of the states of the many other systems with which it is entangled — leads to decoherence. Roughly speaking, the photons bouncing off of Hyperion act like a series of many little “observations of the wavefunction,” collapsing it into a state of definite orientation.
So, in the real world, not only does this particular moon (of Saturn) exist when we’re not looking, it’s also in a pretty well-defined orientation — even if, in a simple model that excludes the rest of the universe, its wave function would be all spread out after only 20 years of evolution. As Zurek and Paz conclude, “Decoherence caused by the environment … is not a subterfuge of a theorist, but a fact of life.” (As if one could sensibly distinguish between the two.)
But gravity works--presumably, at some level--by massive objects constantly bombarding each other with gravitons, so we are also averaging over all the possible states of gravitons that we are not keeping track of, aren't we? That should cause decoherence too, shouldn't it?
I am confused. Not as confused as I am about the powers of the Vice President of the United States as President of the Senate, but confused.
From Matt Springer:
Built on Facts : Physics from All Around: Via Swans on Tea, we have Assume a Spherical Physicist from the excellent blog The First Excited State. There's an exploration of several approximations, including how N + 1 = N is for all purposes true in percentage terms for very large N. But how about this one, mentioned in my undergrad thermodynamics textbook (Schroeder, if you're curious)?
(10^23)N = N
You don't believe me, but it's in some respects true for very large N.... Yeah, the approximation is inaccurate by a factor of Avogadro's number. But in lots of thermodynamics calculations that's a trivial error...
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.
From Oberlin College, we read:
Meteorite Impact Structures Student Research:
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]
Impact event - Wikipedia: Near misses and forecasts:
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...
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!!
[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.
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...
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.
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...
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...
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.
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...
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.
"I now know it is a rising, not a setting, sun" --Benjamin Franklin, 1787
J. Bradford DeLong, Professor of Economics at U.C Berkeley, a Research Associate of the NBER, a Visiting Scholar at the Federal Reserve Bank of San Francisco, and Chair of Berkeley's Political Economy major.
Among his best works are: "Is Increased Price Flexibility Stabilizing?" "Productivity Growth, Convergence, and Welfare," "Noise Trader Risk in Financial Markets," "Equipment Investment and Economic Growth," "Princes and Merchants: European City Growth Before the Industrial Revolution," "Why Does the Stock Market Fluctuate?" "Keynesianism, Pennsylvania-Avenue Style," "America's Peacetime Inflation: The 1970s," "American Fiscal Policy in the Shadow of the Great Depression," "Review of Robert Skidelsky (2000), John Maynard Keynes, volume 3, Fighting for Britain," "Between Meltdown and Moral Hazard: Clinton Administration International Monetary and Financial Policy," "Productivity Growth in the 2000s," "Asset Returns and Economic Growth."
The Eighteen-Year-Old is going to college next year, which means that I need to think about making more money. (The idea that one might write checks to rather than receive checks from universities is now strange to me.) So I have signed up with the Leigh Speakers' Bureau which also handles, among many others: Chris Anderson; Suzanne Berger; Michael Boskin; Kenneth Courtis; Clive Crook; Bill Emmott; Robert H. Frank; William Goetzmann; Douglas J. Holtz-Eakin; Paul Krugman; Bill McKibben; Paul Romer; Jeffrey Sachs; Robert Shiller;James Surowiecki; Martin Wolf; Adrian Wooldridge.
