Thursday, March 29, 2012

Younger Dryas Impact?

The Younger Dryas was a cold period about 12,000 years ago that lasted about a thousand years. The previous ice age had seemingly ended, but then the Younger Dryas was a return to cold conditions. Many large animals became extinct around that time, possibly because of the rapidly changing climate.
There is a controversial hypothesis that the Younger Dryas was caused by an extraterrestrial impact. See Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling for the original article in PNAS (2007). The controversy peaked with this highly skeptical article Mammoth-Killer Impact Flunks Out in Science (2010).
After a new study failed to find nanodiamonds, impact experts are flatly rejecting outsiders' claims that an impact 12,900 years ago devastated the megafauna.
However the proponents of the impact hypothesis have not surrendered! Evidence from central Mexico supporting the Younger Dryas extraterrestrial impact hypothesis in PNAS (2012) details new evidence from lake sediments in Mexico.

Monday, March 26, 2012

Fiona Apple

Fiona Apple is promoting a new album and her recent performance received a good review at the New York Times: Fiona Apple Returns to the Faithful.
She also has the most charming collection of music videos. Here are my favorites.

That Obscure Object of Confusion

I just watched Luis Buñuel's last film, That Obscure Object of Desire (1977). Even I couldn't help noticing that the character Conchita (the obscure object of desire) was played by two different actresses Carole Bouquet and Ángela Molina. The first time I noticed this, one actress leaves, another one returns, but all the other characters don't seem to notice the difference. What the hell was going on? Strangely enough, I quit noticing the difference too! I can recall the first scene in which I noticed the switch but after that, I didn't notice the further switching at all! In the script, there really was only one character. As an experiment, the filmmakers just chose to use two different actresses for the same part and exchanged them seemingly at random.
Even more weirdly, the two actresses don't really look much alike!

Friday, March 23, 2012

Walter Lewin at ESG

I had the pleasure of lunch today at MIT's Experimental Study Group (ESG). The special guest was Walter Lewin a retired MIT astrophysicist known for his popular online physics courses.
Professor Lewin is 76 but he still has a very sharp wit, however the MIT undergraduates were no slouches either.
He was asked, "What do you tell a student who doesn't like physics?"
"Well, I can tell you that they had a lousy teacher. That's the only possible reason. I can make anyone like physics. I can make a dog like physics."
Laughter from the students.
After being peppered with questions from the students for a half or hour or more, he was asked, "Do you have a favorite area of physics?"
"A least favorite area of physics?"
"Thermodynamics, I hate it"
"Did you have a lousy teacher?"
Everyone laughed including Professor Lewin.

Professor Lewin has a new book out For the Love of Physics.

Tuesday, March 20, 2012

Did Herman Weyl really prefer Beauty to Truth?

There's a famous quotation attributed to the mathematician and physicist Hermann Weyl:
My work always tried to unite the true with the beautiful; but when I had to choose one or the other, I usually chose the beautiful.
Contemporary physicists (in particular String Theorists) have been known to go on about how "beautiful" they find some theory (typically their own haha) especially when hard evidence to support that theory is nowhere in sight. There's usually a kind of tacit implication that the expositor is better in touch with the mysteries of the cosmos than the great unwashed who don't appreciate the "beauty" of their revolutionary new theory. After all the great Weyl valued Beauty over Truth didn't he? Peter Woit points out in a recent blog post Dyson on Fringe Physics, String Cosmology and Hermann Weyl that the context of that quote is quite significant and it's more than a little misleading to take it out of that context. It was published in a paper by Freeman Dyson in Nature on the occasion of Weyl's passing:
Characteristic of Weyl was an aesthetic sense which dominated his thinking on all subjects. He once said to me, half joking, ‘My work always tried to unite the true with the beautiful; but when I had to choose one or the other, I usually chose the beautiful’. This remark sums up his personality perfectly. It shows his profound faith in an ultimate harmony of Nature, in which the laws should inevitably express themselves in a mathematically beautiful form. It shows also his recognition of human frailty, and his humor, which always stopped him short of being pompous.
A particular example of this was Weyl's gauge theory of gravity, which turned out to be fatally flawed, but which he was reluctant to abandon because of its beauty. As it turns out, some of the principles that he used in this unworkable theory of gravity found use later on in other areas of physics. However, just because Weyl liked one of his theories that didn't work out at first, but some of the ideas later proved to be useful, doesn't mean the odds are particularly good at all for contemporary theorists with pet theories they claim to be beautiful. The libraries have aisles and aisles full of journals and dissertations which haven't turned out to be significant and it's extremely likely that the vast majority of them will never turn out to significant, not least because they often contradict each other!
The rest of Woit's blog post is worth reading too, as usual.

Monday, March 12, 2012

Randomness on Your Next Chip?

Generating truly random numbers is actually quite tricky. Intel has announced that its next generation of computer chips, Ivy Bridge will have a new instruction RDRAND which will quickly generate a random number for you right on the processor chip - nice huh. But how random will it be? That may depend on how you want to use the random numbers. One very demanding application is cryptography. Most cryptographic protocols require a very high quality source of random numbers. Is the output generated by Intel's new RDRAND instruction good enough for cryptography purposes? The devil is in the details and the most detailed source of information I could find is this Intel document: Bull Mountain Software Implementation Guide. According to that document the random number is generated in three stages:
1. A Hardware Entropy Source
2. A Conditioner which distills the entropy into high-quality nondeterministic random numbers
3. A deterministic random bit generator which is seeded from the conditioner

The entropy source uses thermal noise within the chip's silicon to output a random stream of 0's and 1's.
The conditioner takes pairs of 256-bit samples from the entropy source and algorithmically combines them into a single 256-bit number which is supposed to be even "more random" than the bits generated by the hardware.
The deterministic random bit generator or DRBG "spreads" that 256-bit conditioned number into as many as 511 128-bit samples.

The DRBG they used is called CTR_DRBG, which defined in section 10.2.1 of the following pdf document from NIST: Recommendation for Random Number Generation Using Deterministic Random Bit Generators. Intel uses the AES block cipher option.

Intel has filed a US patent application, number 20100332574, here's a link to the USPTO page for the application and a link to another patent web site, which I found a bit easier to use.

The Intel Bull Mountain document has a section titled "Guaranteeing DBRG Reseeding"
Some may furthermore feel it necessary, for standards compliance, to demand an absolute guarantee that values returned by RdRand reflect independent entropy samples within the DRNG
which goes on to list a couple of techniques
to guarantee that the random value returned is based on an entropy sample independent from the prior function invocation, and independent from the subsequent function invocation
which may enable one to circumvent the DRBG.

Here's another skeptical discussion of using RdRand in cryptography: RDRAND and Is it possible to protect against malicious hw accelerators?

Too bad, it might have been nice if the raw hardware entropy source was directly available, so that applications could test and manipulate it directly.

The Schneier on Security blog from September 2011 has extensive comments on the new Intel random number generator.

Intel’s Digital Random Number Generator (DRNG) from some members of the Intel team contains some nice slides explaining the architecture.

Conceptual Foundations of the Ivy Bridge Random Number Generator by Jesse Walker of Intel Labs provides slides discussing some of the theory.

I'm working on a web site dedicated to the Intel RdRand facility, currently there's a glossary and bibliography, I'm also working on an article about using RdRand in cryptography which I will post there.

Thursday, March 08, 2012

Manta Trust

Giant Mantas are my favorite creatures of the sea, here's a photo one of my favorite encounters from 2010:
photo by Sten Johansson
I just learned about the web site Manta Trust from Daniel Fernando, who I met in Sri Lanka last year. Daniel is a marine biologist and is very knowledgeable and dedicated to manta conservation. He is based in Sri Lanka - a beautiful country which has abundant and varied marine life but limited resources at this point in its development and history.

The Manta Trust web site is an excellent source of information about manta rays and conservation.
Here's one of my previous blog posts on mantas.

Friday, March 02, 2012

An Opinion about Standing Armies

According to Issacson's biography of Franklin, Old Ben wasn't the only wit at the 1787 Constitutional Convention:
A standing army is like a standing member. It's an excellent assurance of domestic tranquility, but a dangerous temptation to foreign adventure.
--- Elbridge Gerry