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Thursday, June 30, 2005
Happy Birthday Special Relativity
One hundred years ago today, June 30th, 1905, Albert Einstein's Special Relativity paper, Zur Elektrodynamik bewegter Körper (On the Electrodynamics of Moving Bodies) was received for publication by Annalen der Physik, and hence this is the date it bore when published on September 26th, 1905. His paper on photoelectricity, Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristishen Gesichtspunktfor, for which he was awarded the Nobel Prize in Physics for 1921 "for his services to theoretical physics and in particular for his discovery of the law of the photo-electric effect", had been published in the June 9th issue of the same journal. These papers, along with his explanation of Brownian motion (published July 18th), his doctoral dissertation on the size of molecules and determination of Avogadro's number (received August 19th, 1905, published February 8th, 1906), and his paper on the equivalence of mass and energy (published November 21st, 1905), Ist die Trägheit eines Körpers von seinem Energieeinhalt abhängig? (Does the Inertia of a Body Depend upon its Energy-Content?) which contains the concept, but not the actual equation "E=mc²", were the highlights of Einstein's miraculous year of 1905. All of these papers are collected in new English translations in the eponymous book, which is now available in paperback. A detailed chronology of events in Einstein's life in 1905 has been published as part of the Einstein exhibit by the American Institute of Physics, along with a chronology of his entire life.Posted at
14:30
Grey List Experiment: Spam Grand Slam
For the last day and a half I've been experimenting with Jef Poskanzer's Graymilter mail filter. This filter, using a technique called "greylisting" originally described by Evan Harris in 2003, exploits the fact that most spam-sending robots do not fully implement SMTP--in particular, they fail to handle a transient failure status (450) and re-send the mail later as required by the protocol. Grey listing exploits this failure to comply with the standard by issuing 450 failures to the first attempt by any IP address to send mail (unless it has been explicitly named in a white list). When a rejection is sent, the IP address is placed onto a list which, some time later (25 minutes by default), is added to a temporary white list and permitted to send mail. Any legitimate mail client will, then, after the initial rejection, eventually deliver the mail. Once on the provisional white list, connections from the client will be accepted for two days, so mail from regular correspondents will not be delayed. I installed the grey list filter about 36 hours ago, and its impact has been dramatic. In the first full 24 hours it has been in production, the total number of spam messages received and discarded by Annoyance Filter has fallen from a mean of about 170 per day to fewer than 30. (Note that this total is the cumulative effect of both grey listing and the greeting and hello delays I implemented previously. A naïve calculation suggests that each accounts for about half of the reduction in spam, but to be sure the filters should be tested independently in isolation from one another.) Reducing the raw volume of incoming spam, before filters, to about 30 messages a day represents a roll-back of the current state of the Internet slum to the situation about five years ago--here's a situation where regress is progress! The only downside of grey listing is the delay in receiving mail from new correspondents while their IP addresses percolate the the dynamic white list pending the next re-delivery attempt. I approach this philosophically--"It's only E-mail; who cares?" Looked at through these glasses ("If it mattered, they'd have sent a FAX"), filtering E-mail becomes a more tractable undertaking.Posted at
00:08