A few days ago, the Royal Observatory Greenwich announced the winners of its Astronomy Photographer of the Year competition. Click the link to look at these fantastic pictures, or see the coverage in Wired.
The Register is running a great story about Bletchley Park, the architecturally confused site which housed the British code-breaking effort that helped win World War II.
Bletchley was home to Colossus, the world’s first programmable electronic digital computer, and to the machines that broke the Enigma cipher. Proudly restored, much of this equipment is again operating at Bletchley, which is now a museum.
I certainly recommend a visit to this fascinating historic site (a guide, either human or electronic, is probably essential). For those who can’t make it, the next best thing would be to watch the movie Enigma, or of course to read some of the many books that tell parts of this once-secret story.
A recent paper from China studies traffic on Weibo (the Chinese version of Twitter), and finds that “users influence each other emotionally… the correlation of anger among users is significantly higher than that of joy, which indicates that angry emotion could spread more quickly and broadly in the network.”
The image below (from the paper) shows some of the emotional connections (red indicates anger, green joy, blue sadness, and black disgust). It would certainly be interesting to repeat this fascinating study in other countries!
I have mentioned this museum before, but it deserves its own post. The Science Museum in London is a companion to the Natural History Museum, also located in South Kensington.
The Science Museum has seven floors of galleries and exhibits (see this directory). And it’s free! For those who can’t visit this fantastic museum in person, there is a collection of online stuff and a blog.
One of the highlights of my visit was seeing the reconstructed Babbage difference engine – the machine that inspired the steampunk concept. There were also many other interesting objects on display. The Science Museum is well worth a visit!
A favourite exhibit in science museums is the Foucault pendulum, first demonstrated by Léon Foucault in 1851 in Paris, and discussed in my earlier post.
In honour of Foucault’s 194th birthday, Google has put together an interactive “doodle” of his pendulum, with controls to set time and the latitude at which the pendulum is located. See here and here for news coverage. The doodle itself will eventually move from google.com to the doodle archive.
The 2013 Ig Nobel Prize winners have been announced. The biology/astronomy prize went to Marie Dacke and co-authors for their fascinating and not-so-crappy paper “Dung Beetles Use the Milky Way for Orientation.”
The psychology prize went to Laurent Bègue and co-authors for their equally fascinating paper “‘Beauty is in the eye of the beer holder’: People who think they are drunk also think they are attractive.”
There were other prizes too, all for “achievements that first make people LAUGH, then make them THINK.” Take a look!
Brownian motion is the random motion of tiny particle buffeted by molecular collisions. Robert Brown noticed it in 1827 with fragments of pollen grains in water (see his 1828 paper: “A brief account of microscopical observations made in the months of June, July and August, 1827, on the particles contained in the pollen of plants; and on the general existence of active molecules in organic and inorganic bodies”). This YouTube video shows Brownian motion in action:
A theoretical explanation was provided in “On the Motion of Small Particles Suspended in a Stationary Liquid, as Required by the Molecular Kinetic Theory of Heat,” one of Albert Einstein’s Annus Mirabilis papers of 1905. In response, Jean Baptiste Perrin carried out a detailed experimental study, which he reported in his lengthy article “Mouvement brownien et réalité moléculaire” (“Brownian movement and molecular reality”) of 1909. The image below is redrawn from that publication (by “MiraiWarren”), and shows the positions of a particle (of radius 0.53 µm) at 30-second intervals. Perrin won the 1926 Nobel Physics Prize for this work, which helped to finally prove that atoms really existed.
In his 1913 book Atoms, Perrin describes the motion this way: “The trajectories are confused and complicated so often and so rapidly that it is impossible to follow them; the trajectory actually measured is very much simpler and shorter than the real one. Similarly, the apparent mean speed of a grain during a given time varies in the wildest way in magnitude and direction, and does not tend to a limit as the time taken for an observation decreases, as may easily be shown by noting, in the camera lucida, the positions occupied by a grain from minute to minute, and then every five seconds, or, better still, by photographing them every twentieth of a second, as has been done by Victor Henri, Comandon, and de Broglie when kinematographing the movement.”
Before Perrin, some sceptics had doubted the existence of atoms and molecules – which were, after all, invisible. “And who has ever seen a gas molecule or an atom?” asked Marcelin Berthelot in 1877.
The decisive evidence for “molecular reality” was the fact that Avogadro’s number NA could be calculated in several quite different ways, including from Brownian motion. From the diagram above, for example, I calculate that the mean squared horizontal “jump” every 30 seconds is 3 (in grid square units). The first three horizontal “jumps” starting from the top right are 2.1, 0.2, and 2.5 in grid square units, and squaring those numbers gives 4.4, 0.0, and 6.3, for a mean square of 3.6 (but the mean square drops as more “jumps” are considered). According to Perrin, each grid square is 3.125 µm across, so that the mean squared “jump” in metric units is 2.9×10−11. Assuming a temperature of 20°C (293 K), at which water has a viscosity of 0.001002, Einstein’s theoretical work gives:
NA = 8.3144621 × 293 × 30 / (3 π × 0.53×10−6 × 2.9×10−11 × 0.001002) = 5.0×1023
This is a little too low, since 6.022×1023 is the true value, but it’s still remarkably close, and a tribute to the quality of Perrin’s work (although his final value was actually too high: 7.05×1023). Every different experimental approach gave (at least approximately) the same value for NA. Studies of the blue of the sky due to Rayleigh scattering, for example, gave a value between 3×1023 and 15×1023. Studies of radioactivity by Ernest Rutherford gave between 6×1023 and 7×1023. Perrin was able to list several other studies as well. Atoms existed!
In 1908, Wilhelm Ostwald (once a sceptic) wrote in the fourth edition of his textbook on chemistry: “I have satisfied myself that we arrived a short time ago at the possession of experimental proof for the discrete or particulate nature of matter – proof which the atomic hypothesis has vainly sought for a hundred years, even a thousand years. The isolation and measurement of gases on the one hand, which the lengthy and excellent works of J. J. Thomson have crowned with complete success, and the agreement of Brownian movement with the demands of the kinetic hypothesis on the other hand, which have been proved through a series of researches and at last most completely by J. Perrin, entitle even the cautious scientist to speak of an experimental proof for the atomistic constitution of space-filled matter.” (as quoted by Mary Jo Nye)
Perrin concluded his 1913 book Atoms with an acknowledgement both of victory and of further challenges: “The atomic theory has triumphed. Its opponents, which until recently were numerous, have been convinced and have abandoned one after the other the sceptical position that was for a long time legitimate and no doubt useful. Equilibrium between the instincts towards caution and towards boldness is necessary to the slow progress of human science; the conflict between them will henceforth be waged in other realms of thought.
But in achieving this victory we see that all the definiteness and finality of the original theory has vanished. Atoms are no longer eternal indivisible entities, setting a limit to the possible by their irreducible simplicity; inconceivably minute though they be, we are beginning to see in them a vast host of new worlds. In the same way the astronomer is discovering, beyond the familiar skies, dark abysses that the light from, dim star clouds lost in space takes aeons to span. The feeble light from Milky Ways immeasurably distant tells of the fiery life of a million giant stars. Nature reveals the same wide grandeur in the atom and the nebula, and each new aid to knowledge shows her vaster and more diverse, more fruitful and more unexpected, and, above all, unfathomably immense.”
LADEE, the Lunar Atmosphere and Dust Environment Explorer has just been launched, and is off to study the faint wisps of atmosphere around the moon. We look forward to better understanding our neighbour in space.
I’m currently working on a paper about, among other things, random networks. Here is a random network with 120 nodes and 3,600 links. It’s fascinating how much predictable regularity there can be to the process of randomly adding links to a network:
This blog randomly selects from a pool of header images. The images are:
Scientific Gems 
