One-time pads are uncrackable- mathematical proof exists. That assumes (and it's a rather large assumption) that the rules of using a one time pad are followed.
Messages encrypted with a OTP have been deciphered in the past, but not from any mathematical failing- people simply failed to correctly follow the rules.
1. You need a random process to generate the pad.
This means random, not pseudorandom. Admittedly, modern pseudorandom number generator algorithms are very complex, and trying to reverse engineer (hey!) a PRNG from just a stream of outputs would be a mammoth task. Rules are rules, however complex- if your pad is pseudorandom, your cipher will only be pseudo-uncrackable. The Enigma produced vey complex keys with a convoluted series of rules, but if you know how an Enigma works, as the Brits did, you can use the ciphertext to help find the key, and then dechiper the entire message. This is one area where quantum mechanics fits in- lots of nice random phenomena arise naturally from quantization- I'll get back to that. Also, the key on the pad must be as long as the message you wish to encode- if you try to encode a 2000-character message by using a 1000-character key two times, your security is no longer guaranteed.
2. Only use each key on the pad once.
That's why it's a one-time pad. If you use the same key more than once, you remove the randomness, and create a pattern that can help the cryptanalyst. Deciphering will still be difficult- but if you wanted difficult, you could have just used triple-DES or RSA or elliptic curve crypto- those are all varying degrees of difficult. You want impossible.
OTP is unbreakable, if you follow the rules- but the rules are really hard follow. You need random processes, and once you have these neat pads, you face the Key Exchange Problem- if you have an agent out in the field that you'd like to communicate with, and you must communicate in an absolutely secure fashion, you must get a copy of the one-time pad to the agent- it's the only thing that will decipher your messages. However, you can't just pick up the phone and relay the contents of the pad to your agent- the enemy might be bugging your phones- and hilarious hijinks will no doubt ensue when the enemy uses their new your insecurely transmitted pad to read your secure encrypted messages. Encrypting transmission is a good idea, but you can't use OTP to send the first OTP to the agent- how will the agent decrypt his encrypted pad? The classic analogy is that you're trying to send a key (think physical, lock-opening key) in a locked box that only the key inside the box can open. You could encrypt the key with hardass public key crypto, say 1024-bit RSA, but that isn't unbreakable in the same now-and-forever sense as OTP. It would be vulnerable to quantum computers, and vulnerable to any computer if someone discovered a polynomial time algorithm for prime factorization of really gigantic numbers, or if I win a Clay Mathemtics Prize for proving P=NP. You could of course do what the government does for secure key distribution- send couriers carrying OTPs directly to the agent in the field. This is an expensive, difficult, dangerous method, so better ways were searched for.
This is of course where Quantum Cryptography comes in. Photons all have specific polarizations. You can send a stream of randomly polarized photons through a polarizing filter, and photons with the same polarization angle as the filter will pass, while those with a polarization rotated 90 degrees with respect to the filter are blocked. What then happens to photons that have some intermediate angle? On the macroscale, we can say that the intensity of the light is a function of the angle, and infer that at a 45 degree tilt, 1/2 of the light is blocked, and 1/2 passes through. Enter Quantum Mechanics. It is fairly obvious to see the effect that polarizing filters have on a large scale quantity of light, but what about individual photons? Since the intensity of light at a 45 degree angle is 1/2 its normal value, one can infer that one half of the photons with a 45 degree polarization pass through, while one half are blocked. Simple enough. But if you send just one photon through with a 45 degree polarization, can you determine whether it will pass through? The answer, surprisingly enough, is no. You cannot determine whether a photon will pass through, and you will not know whether it passed through until it hits (or fails to hit) a detector on the other side. Can't determine? That makes it a random process, perfect to set up a OTP. It happens to have some interesting side benefits as well. Since the possibilities are pass and blocked, two possibilities- a string of photons sent at the filter produces a random binary sting of 1's (passed) and 0's (blocked). There is another fascinating benefit- if someone tries to sit in the middle of the photon stream and determine photon polarization, their eavesdropping will be evident- by checking the polarization of a photon in transit, they change the value of the polarization. All two people using quantum crypto need to do is confirm a few values that were sent (this can be done insecurely, since these values will not actually be used in the cipher pad)- if they match up, then send the message, encoded with the OTP, if not, someone is eavesdropping, and so discard the pad. It's a lot more complex than that, of course, but that's the general idea- you can use QC to generate a one-time pad, and then send it in such a way that you know whether or not you're being spied on.
Part of the difference between Xerox and Hoover is that the former is based on a real word - xerography, writing with light (IIRC)
Xerography means "dry writing," referring to the dry powder used instead of wet ink. The name "Xerox" was chosen to make it similar to Kodak, coincidentally also based in Rochester, NY.
Brand recognition can sometimes be more of a curse than a blessing- ask the makers of "Kleenex," which has entered the English language as a general term for facial tissue, regardless of brand.
What's going on in the last picture for the Windows 98 screenshots (Page 4)? Roughly half the text is in Japanese, there's a large window open in the middle that displays the desktop for an Apple Powerbook, and behind it is apparently a web browser with little tags at the bottom of the site with "FreeBSD" and "Powered by Apache" on them. I'm guessing they didn't get this screenshot from official Microsoft press materials....
Re:Only 7 ammendments left in the Bill of Rights
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That Link Is Illegal
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· Score: 1
Nope, if America really wants to get tough on terror, it will have to quarter soldiers in every home. Coming soon in USA PATRIOT Version 2.0!
Well, even the heliocentric model presented by Copernicus contained epicycles. Not quite as many as the Ptolemaic system (which was a mathematical mess by the 16th century as the general model was continually appended rather than torn down and rebuilt), but there were still definitely some. Copernicus created a heliocentric universe that had circular orbits for all of the bodies. Coming from the knowledge that planetary orbits are elliptical, we can see how this leads to problems. For example, if the position of Mars is charted nightly against the background of the stars, there will be instances where it appears to move one direction for a few nights, then stop, turn around, start moving backwards for awhile, then stop, turn around, and then proceed on its usual course!
The way to explain this sort of oddity and yet preserve your blessed circular orbits is to insert epicycles. The planets are traveling in circles while orbiting a central body (the sun, or the earth). With some tinkering, an epicyclic system can be constructed that fits fairly well with observations taken from the vantage point of earth, at least most of the time. Not all the time, mind you, which is why it too had some (in hindsight, again) rather pathetic attempts to patch it up, epicycles on the epicycles and rot like that. Heliocentric theories had been proposed before, as another poster mentioned, by Aristarchus in ancient times, and then Nicholas de Cusa in the 15th century. Both of these models suffered from the same type of complexity that the one put forth in De Revolutionibus Orbium Coelestium.
What made Copernicus different is that he worked out a real mathematical basis for his solar system. Copernicus also correctly realized that the system could be made simpler if the inner planets moved faster than the outer planets, and thus completed their orbits even faster than distance of the circle they covered alone would predict. This seems obvious now- inner orbits must move faster, because gravitational forces varies with the inverse square of distance, but Copernicus lived before Newton, so he wasn't operating with that knowledge. His system was incorrect, yes, but it was at least based on something more concrete than aesthetic value. It then fell to Kepler to divine the true mechanics of the Solar System. His calculations showed that if the orbits of the planets were ellipses, with the Sun at one focus (he introduced the word "focus" in this context, btw), then the whole epicycle thing wouldn't be necessary at all to fit experimental observations. Moving on ellipses meant that the planets did not move with constant velocity- they moved faster when closer to the sun, and slower when farther away. Combined with Copernicus's concept of the inner planets moving faster, bolstered with mathematical properties of ellipses to become Kepler's Third Law, the whole epicycle thing became pretty much unnecessary.
That last sentence should read, If people could eat a balanced diet and get regular exercise, chances are they wouldn't need the product. Three characters can make a world of difference. My powers of proofreading are failing me...
If you don't believe me soak your head in acetone (di-ethyl ketone) for a while.
Maybe you should take the organic chemistry sometime, eh? Acetone is dimethyl ketone, not diethyl ketone. You are correct in asserting that ketones are highly reactive, which is why the kidneys, perhaps the most amazing organs in the body, get called into action. However, the major chemical reactions of ketones and aldehydes are generally very slow without acid or base catalysis. Human blood is buffered at a comfortable pH 7.4, so most of these potential poisons can be trucked to the kidneys without incident.
Unfortunately, I haven't read anything conclusive (certainly not this article) that even casts reasonable speculation on the health effects of long term states of ketosis, and IANA dietician, so I refuse to pass judgement on the diet over the long term. I have decided to avoid the Atkins diet personally, because my family has a rather awful history of kidney problems (kidney stones, polycystic kidney disease, urinary tract infections, cancer, etc), so I don't plan on taking any chances with my pair. However, the evidence I've seen so far suggests that overweight people with normal kidney function can definitely benefit from the diet, and should be able to handle the ketosis, at least in the short term. Also, as many otherposters have pointed out, there are some undesirable side effects to being morbidly obese which might trump those of protein and fat metabolism.
I think that a balanced diet, with fats, protein, and carbs all in moderation, is preferable, in terms of both ease of following, and enjoyment of the food you consume, but I guess most Americans simply cannot eat that way and go about it responsibly. It reminds me of the fine print at the bottom of most diet pill ads, which point out that the miracle weight loss from their product occurs "in conjuction with a balanced diet and regular exercise." If people could eat a balanced diet and get regular exercise, chances are they would need the product.
What makes laser such an interesting word is that the expansion of the acronym is generally totally unhelpful to most people, and really provides little insight on the uses of the object. A laser, as found in a CD player (this is another abbreviation that I dare say would be acceptable in formal writing now, and DVD is another), or a laser printer, or one of those annoying pointer things, can be used without the knowledge that LASER stands for Light Amplified by Emission of Stimulated Radiation. Laser is a convenient word, one that encapsulates the information of a complicated process, but is itself a simple word. I'd wager that many people who use lasers every day have no idea what the expansion of the acronym is, and many probably do not even realize that "laser" is an acronym. This confusion has been helped along, I believe, by words like "phaser," which are not acronyms, but rather inventions of science-fiction, and by idiots who spell the word "lazer." (There is a printer repair shop in my town named "The Lazer's Edge." Ugh.) I imagine that the acronym for laser was expanded much more frequently in the 60s and 70s, when lasers were a new invention, and were not nearly so widespread. Now, the only place I see the acronym expanded is in semi-technical articles that also mention masers- the acronyms are then expanded to provide a helpful explanation of the similarities and differences between the two. This is especially interesting since the maser was developed first, but are far less useful and ubiquitous.
I believe what has happened here is that a split has occurred between "laser," the object, and "LASER," the process of creating a coherent beam of light by which a laser functions. In fact, I have read technical papers that mention things like a "lasing cavity" which imply that laser is no longer an acronym (Light Amplified by Stimulated.....ing...).
I can think of a few other words that are acceptable as acronyms in formal speech, scuba, for example. Names of corporations and entities that traditionally go by initials, like CIA, FBI BASF, MCI, RCA, NBC, and AT&T can be used without explanation, methinks. In some cases, explanation is pointless, like in the case of the Radio Corporation of America (I think they sell other stuff now too), or the American Telephone and Telegraph Company (not so much telegraph traffic, anymore). Also, companies with shortened names in common use: DuPont for the E.I. du Pont de Nemours Company, Nabisco for the National Biscuit Company. Always, always, consider the audience, however. In a Slashdot post, RIAA, MPAA, DDOS, do not have to be expanded, but if I were writing a formal paper for a college English prof, I would expand them upon their first occurrence in the paper, then use the initialisms from then on.
There are a few times when I do not think there is any point to expanding technical acronyms, particularly when writing for a nontechnical audience. That many sound a little backward, but I can recall instances up to a few years ago where newspapers and newsmagazines pointed out that DNA is deoxyribonucleic acid whenever they mentioned it in print. I can only imagine a moment where a person sees "DNA" in print, and is completely baffled, but then sees "deoxyribonucleic acid," and is then totally clued in. Nothing about the name suggests its function as the genetic information molecule for most life on earth, just as nothing about LASER explains how a laser is used to read a CD, or add text to a piece of paper, or put a red dot on the forehead of someone who is about to get shot in the face.
I wholeheartedly agree that Internet slang has no place in formal writing. Slang like b4, ppl, rotflmao, kewl, d00dz, and the dreadful 1337 should be considered no more proper than ain't, cuz, or using double negatives. I use terms like lol, afk, and brb in IM conversations, but I do not in written papers. These are not terms that add anything to a paper- they are not new words, just misspellings of old words. If 1337$p34k produces new words that become commonly accepted (e.g. can be found in a dictionary), then using them in my writing becomes a possibility, but for me, a fairly remote one still- I don't even use contractions in formal writing (which this is not). The Internet has produced a large number of words, some of them not wretched, so I imagine that the exploding chat scene will add more to the language, some of which will not be wretched. All that has really been produced thus far are acronyms that have no logical use in a formal paper (when would you use brb, omg, afk, lol..etc?), emoticons that are completely out of place in a formal paper: Therefore, my opinion of the Supreme Court's decision in Dred Scott v. Sanford: >:-( , and cute misspellings that would make sophisticated prose look like the front page of some rave fan's terrible Geocities website.
As for WTF, LMAO, and RTFM, would you ever use profanity in a paper you wrote for a grade? I realize that the profanity is implied, and these terms lack the connotation of "What the fuck?" "Laughing my ass off," and "Read the fucking manual," but still.... I wouldn't use terms like "fubar" or even "snafu" in a formal paper. I consider polite writing to be free of slang, but at the very least, I expect it to be devoid of profanity, assuming the profanity is not somehow germane to the treatment of the topic.
Well, the above poster is guilty of some oversimplification- experiments like the one described were in fact meant to disprove spontaneous generation on a human timescale, which had been thought to occur. It was once commonly believed that rotting meat spontaneously generated maggots, or that old bread generated mold. Redi showed several hundred years ago that maggots only form on meat if flies are allowed to lay eggs there- he placed meat in two different jars, and put a cheesecloth over one, so they both rotted, but maggots were found only in the open jar. Pasteur used sealed, sterile flasks to show that life does not arise naturally from a growth medium, even on a microscopic scale.
Neither of these scientists, however, understood the timescale of life on earth, nor the conditions of early earth. The Miller-Urey experiment, building off of theory by Oparin, attempted to show that conditions that might have been present in the earth's atmosphere several billion years ago could combine using energy provided by lightning or UV radiation to form a "primordial soup" composed of the building blocks of life- amino acids, carbohydrates, lipids, and nucleic acids. The experiment works as designed- the gases react in the extreme conditions to produce an organic "gunk" that contains many of these building blocks. Controversy still surrounds the issue of the primordial gas composition, particularly whether the early atmosphere was reducing, as Oparin suggested, or oxidizing, which might invalidate the Miller-Urey experiment- a strongly oxidizing atmosphere would not allow even relatively simple organic compounds to form.
Despite the unknowns that are still unresolved, most scientists agree that some sort of process similar to the Miller-Urey type experiments produced the first organic building blocks from inorganic substances present on the earth of 4 billion years ago. The major question is how these simple building blocks arranged themselves into organic macromolecules like proteins, polysaccharides, and DNA and RNA, and from there, into the first forms of what we would describe as life. The transition from boiling brown tar to membranes, replicator molecules, and cellular organization represents a difficult problem (an impossible one, according to those intelligent design folks), and we must make educated guesses with incomplete information about the processes involved. Cyanobacteria microfossils have been found in ancient craton formations dating back 3.5 billion years- some of the oldest rocks on the planet. One billion years before that, the planet was a ball of liquid rock. In the time between, the earth cooled, the oceans formed (well, one really big ocean), organic compounds were formed, and these compounds assembled themselves into self-replicating structures- the beginnings of life.
So yes, spontaneous generation is possible,and in fact responsible for life on earth, but not with today's enviromental conditions- the atmosphere has a different composition (nearly 80% N2, which is almost inert at standard conditions), the weather is less violent (lightning is not nearly as powerful as it was then), and the ozone layer blocks most UV. Howerver, there are a few places left on earth today that could conceivably be cradles of new life- deep-sea vents, for instance. The jump from simple organics to organized macromolecules could easily take over 100 million years, if you're willing to wait. However, even this is an unlikely scenario, it would basically have to occur at a vent with absolutely no other life already present- otherwise any new replicator molecule would find itself in competition with lifeforms that have a 3 billion year head start, and that operate using the brutally efficient DNA/RNA/protein transcription/translation pathway, fine-tuned over billions of years of evolution.
Actually, when I first thought about it, it struck me as rather counterintuitive. If you wanted to pay less in tax, the easiest way to do that would be to underreport income. However, that really isn't that easy, since you send in copies of your W-2s- so assuming you have only legitimate, federally reported sources of income- no under the table cash payouts- your taxable income should be pretty easy to verify.
One area where the wealthy and the poor differ on their tax returns, however, is on deductions. The working poor usually take the standard deduction, since in general they rent rather than own their homes, and thus have no mortgage to deduct interest on. Also, they usually do not have significant investments from which to deduct losses, business expenses are often minimal, and the standard deduction represents a sizable fraction of their taxable income, so taking that is a good idea. For the wealthy, OTOH, itemized deductions usually provide tax relief far in excess of the standard deduction. They are also a gateway to defrauding the IRS, since shady accounting practices can make almost any expense into a deduction. Therefore, the IRS conducts audits to determine the validity of itemized deductions.
Another factor is that if you audit a wealthy person, and it turns out they are in error, the penalties the IRS collects will be much larger than from an audit of a poor person. The IRS lacks the resources to conduct a complete audit on everyone, so they have a strategy that they believe will maximize the amount of revenue collected. Similarly, police cannot patrol every corner of every street 24/7- nor would most Americans want them to, just as most Americans would not want to be audited at tax time each year. Thus, they concentrate their resources on a specific neighborhood, a specific street corner, or perhaps a specific group of people known to have involvement with crime. Is that logical? Yes. Is that fair? Hell no it isn't. Is auditing a certain group more often fair? Ditto. To be accused of a crime because of your race, your religion, your country of origin, the amount of money you make, your politics, the street you live on, or the people you associate with is dehumanizing, and I believe that it violates your rights.
Given that the government seems to equate buying drugs with financing Al-Qaeda (as opposed to some that actually has funded terrorist organizations, like paying federal taxes), I think that the standard party line response would be that the war on drugs is a key part of the war on terror. Ergo, we should treat American citizens like terrorists because they possess narcotics. I can't wait until drug dealers are held as "enemy combatants."
Many of the people whose photos have been taken were stopped briefly for loitering and let go.
Considering that African-Americans have long been been pulled over for Driving While Black, is police persecution for Standing While Black much of a surprise? If you are a young black male in America, you automatically "fit the description" for some fugitive from justice. If you want to suggest that profiling such a large group prevents crime, then I ask, where is the database of white male multimillionaires?
Nice, I was about to recommend that myself. I think it is a well-written, comphrensive text, and it has served me well after gen chem- I still have it on my shelf, and I refer to it from time to time. I'm rather biased toward it, I must admit, since Steven Zumdahl was my general chemistry professor my first year at UIUC. However, it's a very well-known text, in use at many universities, and the majority of reviews I've read are very positive.
I find it interesting that the article suggests towing a wormhole using a "spaceship, presumably of highly advanced technology" to place a created or expanded wormhole in a powerful gravitational field. Maybe I'm just envisioning this wrong, but I don't know if a wormhole is really what I'd consider to be an "object." Rather, as a rift in spacetime, I'd think would be a thing (for lack of a better word) that is defined by both lack of object, and by objects around it, like the hole in a doughnut, and thus the only way to "move" it would be to alter the objects that surround it, like stretching or shrinking areas of the dough to change the location of the hole with respect to locations on the dough . You can't just grab a hole in a doughnut with a pair of pliers and move it around. In the case of wormholes through spacetime, I'd imagine the way to move a wormhole is to warp the space around it with immensely powerful gravitational fields, folding the space around it and causing it to "fall" to its neutron star target. However, this would certainly require a mastery of gravity far beyond what we have presently attained. When the two ends of the wormhole are created/expanded to macroscopic size, they will need to be separated, with one end taken to a neutron star. Building a tow-ship that can warp the space around a wormhole would require far more knowledge about gravity than we presently possess and far more mastery. Despite being perhaps the most obvious of the fundamental forces of physics, it is probably the least well-understood. Gravitions have never been found in particle accelerators, nor Higgs bosons. Gravitational waves have not been conclusively detected. No coherent theory of quantum gravity exists. We will have to be able to manipulate gravity with the ease that we manipulate electromagnetism if an "interstellar tow truck" is to be built. "Highly advanced technology," indeed!
Using the neutron star itself to attract one but not the other would be very difficult, but possibly workable- especially if Podkletnov's spinning superconductor gravitational shield works (which it doesn't, that I am sure of). However, you certainly can't use a natural source to reunite the ends once you've "twin clocked" the exit end- the exit is sitting near the surface of a neutron star- so you really won't be able to pull it away with anything less than another neutron star or a black hole, perfectly positioned to make use of the three body problem to slingshot the wormhole out of the star system. Conceivable, but highly unlikely.
You can't just leave the exit there, either. It would continue to accumulate time difference, so each trip would take you farther from your present time, but actually further and further along in time, since you can never actually travel backwards to before the creation of the exit hole, and since it is in fact still moving forward, albeit slowly, in time. Also, you would leave the exit and find yourself right around the surface of a neutron star, which is a somewhat dangerous location. Worse, you would have to travel at a relativistic velocity to escape the neutron star's monstrous gravity, which means your fast clock would run very slow, so the rest of the universe would be aging faster than you. Also, the nearest neutron star is several light-years away, adding to your return-trip travel time. I'm sure it would be a fantastic adventure, but sort of a waste to fly into a wormhole, travel centuries back in time, and rocket away from a neutron star at nearly the speed of light- only to get back home and find that due to relativistic effects and travel time, you are right back where you started, or even farther along!
I haven't done the math, but I suspect that sort of scenario could be one of several ways the universe is protected from time travel paradoxes- you can go back in time, but due to relativistic time dilation and the effects of gravitational fields, you can never make it back in time to affect events in the past of your light-cone, preventiing you from creating an inconsistent causal loop.
and those bits belong to them till you purchase a copy.
Once I purchase a copy, do the bits belong to me? They do? OK, since I really don't like keeping my bits on a compact disc, I think I'll rip them to high-bitrate mp3. I can't tell the difference anyway. Also, since I like these particular bits, and would like others to experience them, I think I'll share a few with my friends- either the ones across town, or some people I don't know very well that I just met using Limewire. Since they're my bits, I think the decision should rest in my hands.
I'm really surprised that only two Fields Medals were awarded this time around- at least three have been awarded every four years since 1974. Is Preda Mihailescu's proof of Catalan's Conjecture considered too recent for consideration? I'd think that sort of thing, combined with his work on noted hot topic primality would make him an attractive candidate.
Of course, I'm sure they are many others who were also very deserving as well. No, I am not Dr. Mihailescu, and have never met him in fact; it's just when I saw that the Fields Medals were awarded, my first thought was, "I wonder if they gave one to that guy who proved Catalan's Conjecture?" As recent as the proof was (considering the slow, careful peer review that accompanies important purported mathematical proofs), I wasn't shocked to not see his named- I was far more surprised that the committee chose to not award the remaining two prizes to anyone.
Does anyone know why the diagram uses S to represent the base cytosine in the DNA diagram rather than C? Is it simply to avoid confusion with the c they use for carbon in outlining the structure of the bases, or is it part of an outdated labeling convention?
Re:This is the one I use in my e-mail.
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Haiku vs Spam
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· Score: 1
A rude eruption
Composed of natural gas
Farts warm up our globe.
Strictly speaking, even/odd and red/black bets on roulette aren't 50/50 either. They pay 1:1, as you'd expect from a 50/50 bet, but there are 38 spaces on a roulette wheel (37 in Monte Carlo, I'm told though)- 1-36 red/black odd/even, and two (or one) green zeros, which provide another color, and are neither even nor odd (you can debate whether zero is even, but the casino will not be swayed to your POV). This means your odds of hitting red on a red bet on a Vegas wheel are 18/38, or ~47.3%, but the payoff is only 1:1, as if the chance were actually 50%- it would be 1.11:1 if roulette weren't a way for casinos to rip you off. Incidentally, this means you can bet on both red and black, and still lose.
Logan Airport Security
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MIT vs. Las Vegas
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· Score: 2, Interesting
Neat article. However, I was rather perturbedby the opening anecdote about ferrying an enormous amount of cash through Logan Airport- the same one that the hijackers that destroyed the WTC flew out of. Bricks of hundred dollar bills, box cutters, no questions asked... just what the hell does security do there anyway?
Yeah, and that (1985) was also before Challenger exploded. Of course, 1995 would not have been a realistic date for affordable Space Shuttle travel anyway- costs would have been out of control to build that sort of infrastructure, unless NASA considered "affordability" to be in the Dennis Tito sense, and charged passengers 8 figures for a flight.
So what you're saying is, an "omnipotent" Supreme Being does not possess the power to defy a paradox? God does not possess the ability to accomplish things beyond the human scope of reason and logic? How can a being be truly omnipotent if its powers are bounded by logical statements? How powerful is an all-powerful god that can create an entire universe but cannot make a rock both completely white and nonwhite at the same time? Your reasoning simply backs out of a paradox only to step into another paradox.
Having read the paper (forgive me, I'm new here), I'd say the negative time effect is very similar to the FTL transmission results reported earlier. On page 6 of the paper, the caption to Figure 6 reads in part: Note the negative values of tau-sub e (the time spent inside the condensate region) in the region around ka ~/2: Wavepacket simulations show that here the peak of the transmitted wavepacket appears before the peak of the incident packet reaches the condensate. Now, IANA condensed matter physicist, but my best assessment of the effect is that it operates similarly to previously observed, similar phenomena of "FTL" transmission. The incident wave of light contains information for the entire wave embedded in the wavefront- so the peak of the wave is able to be reconstructed on the other side of the BEC, even though the peak itself has not reached the condensate yet. Essentially, since the entire wave of light is defined by a wavefunction, the entire wave can be constructed from the wavefront. Although the process can take zero or even negative time, it is not a violation of general relativity. The light itself propagates at the speed of light, as it must. Since the peak of the wavepacket is recreated before it is actually destroyed, it would seem to be moving faster than the speed of light. However, the information that completely describes this peak is embedded into the wavefront, which travels at the rather pedestrian speed of light (and for a BEC, it is almost pedestrian- the amazing dispersive effects have been shown to reduce c to around 38 miles per hour, an effective refractive index of over 17 million!). While something is technically traveling over a nonzero distance in zero or even subzero time, no unique information can be transmitted in this manner- since the peak is constructed from information in the wavefront, the peak must be composed of information contained in the wavefront. The wavefront is moving at the speed of light, and taking all of the information it has with it at exactly that speed. If we had an ultrafast and ultrasmall computer conceivably, we could dispense with the Bose-Einstein condensate and do this thing ourselves. The wavefront enters a detector, the information is broken down, and the hypothetical supercomputer we have at our disposal uses the information in the wavefront to calculate the wavefunction. It then spits out a wavepacket with characteristics identical to those of the incident packet, and does so before the peak of the incident packet even reaches the detector. The effect is somewhat analogous to the movement of lights on a scrolling theatre marquee. The scrolling itself can actually occur faster than the speed of light, but since the "information" is just a discrete on/off light, no useful FTL message can be encoded. In the same way, the wavefront carries information faster than the speed of light, but the information merely codes for the rest of the wavepacket! Thus, it is not a violation of relativity. If anything, it is an affirmation- the weirdness of quantum mechanics, what with the wave/particle nature of light, is weird in such a way that useful messages cannot be sent faster than the speed of light.
On a completely different note, I was amused to see someone referenced in this paper that/.ers might recognize, if they had actually read the paper. On page 6, the authors propose explanations for this effect, and they suggest a many-body interference mechanism devised by Ray Chiao et al. Raymond Chiao, some of you may remember, is the physicist who had a/. story not long ago about the possibility of a gravitational Meisser effect for superconductors (Can Superconductors Block Gravitational Fields?).
Slashdot Mirror
One-time pads are uncrackable- mathematical proof exists. That assumes (and it's a rather large assumption) that the rules of using a one time pad are followed.
Messages encrypted with a OTP have been deciphered in the past, but not from any mathematical failing- people simply failed to correctly follow the rules.
1. You need a random process to generate the pad. This means random, not pseudorandom. Admittedly, modern pseudorandom number generator algorithms are very complex, and trying to reverse engineer (hey!) a PRNG from just a stream of outputs would be a mammoth task. Rules are rules, however complex- if your pad is pseudorandom, your cipher will only be pseudo-uncrackable. The Enigma produced vey complex keys with a convoluted series of rules, but if you know how an Enigma works, as the Brits did, you can use the ciphertext to help find the key, and then dechiper the entire message. This is one area where quantum mechanics fits in- lots of nice random phenomena arise naturally from quantization- I'll get back to that. Also, the key on the pad must be as long as the message you wish to encode- if you try to encode a 2000-character message by using a 1000-character key two times, your security is no longer guaranteed.
2. Only use each key on the pad once. That's why it's a one-time pad. If you use the same key more than once, you remove the randomness, and create a pattern that can help the cryptanalyst. Deciphering will still be difficult- but if you wanted difficult, you could have just used triple-DES or RSA or elliptic curve crypto- those are all varying degrees of difficult. You want impossible.
OTP is unbreakable, if you follow the rules- but the rules are really hard follow. You need random processes, and once you have these neat pads, you face the Key Exchange Problem- if you have an agent out in the field that you'd like to communicate with, and you must communicate in an absolutely secure fashion, you must get a copy of the one-time pad to the agent- it's the only thing that will decipher your messages. However, you can't just pick up the phone and relay the contents of the pad to your agent- the enemy might be bugging your phones- and hilarious hijinks will no doubt ensue when the enemy uses their new your insecurely transmitted pad to read your secure encrypted messages. Encrypting transmission is a good idea, but you can't use OTP to send the first OTP to the agent- how will the agent decrypt his encrypted pad? The classic analogy is that you're trying to send a key (think physical, lock-opening key) in a locked box that only the key inside the box can open. You could encrypt the key with hardass public key crypto, say 1024-bit RSA, but that isn't unbreakable in the same now-and-forever sense as OTP. It would be vulnerable to quantum computers, and vulnerable to any computer if someone discovered a polynomial time algorithm for prime factorization of really gigantic numbers, or if I win a Clay Mathemtics Prize for proving P=NP. You could of course do what the government does for secure key distribution- send couriers carrying OTPs directly to the agent in the field. This is an expensive, difficult, dangerous method, so better ways were searched for.
This is of course where Quantum Cryptography comes in. Photons all have specific polarizations. You can send a stream of randomly polarized photons through a polarizing filter, and photons with the same polarization angle as the filter will pass, while those with a polarization rotated 90 degrees with respect to the filter are blocked. What then happens to photons that have some intermediate angle? On the macroscale, we can say that the intensity of the light is a function of the angle, and infer that at a 45 degree tilt, 1/2 of the light is blocked, and 1/2 passes through. Enter Quantum Mechanics. It is fairly obvious to see the effect that polarizing filters have on a large scale quantity of light, but what about individual photons? Since the intensity of light at a 45 degree angle is 1/2 its normal value, one can infer that one half of the photons with a 45 degree polarization pass through, while one half are blocked. Simple enough. But if you send just one photon through with a 45 degree polarization, can you determine whether it will pass through? The answer, surprisingly enough, is no. You cannot determine whether a photon will pass through, and you will not know whether it passed through until it hits (or fails to hit) a detector on the other side. Can't determine? That makes it a random process, perfect to set up a OTP. It happens to have some interesting side benefits as well. Since the possibilities are pass and blocked, two possibilities- a string of photons sent at the filter produces a random binary sting of 1's (passed) and 0's (blocked). There is another fascinating benefit- if someone tries to sit in the middle of the photon stream and determine photon polarization, their eavesdropping will be evident- by checking the polarization of a photon in transit, they change the value of the polarization. All two people using quantum crypto need to do is confirm a few values that were sent (this can be done insecurely, since these values will not actually be used in the cipher pad)- if they match up, then send the message, encoded with the OTP, if not, someone is eavesdropping, and so discard the pad. It's a lot more complex than that, of course, but that's the general idea- you can use QC to generate a one-time pad, and then send it in such a way that you know whether or not you're being spied on.
Part of the difference between Xerox and Hoover is that the former is based on a real word - xerography, writing with light (IIRC)
Xerography means "dry writing," referring to the dry powder used instead of wet ink. The name "Xerox" was chosen to make it similar to Kodak, coincidentally also based in Rochester, NY.
Brand recognition can sometimes be more of a curse than a blessing- ask the makers of "Kleenex," which has entered the English language as a general term for facial tissue, regardless of brand.
What's going on in the last picture for the Windows 98 screenshots (Page 4)? Roughly half the text is in Japanese, there's a large window open in the middle that displays the desktop for an Apple Powerbook, and behind it is apparently a web browser with little tags at the bottom of the site with "FreeBSD" and "Powered by Apache" on them. I'm guessing they didn't get this screenshot from official Microsoft press materials....
Nope, if America really wants to get tough on terror, it will have to quarter soldiers in every home. Coming soon in USA PATRIOT Version 2.0!
Well, even the heliocentric model presented by Copernicus contained epicycles. Not quite as many as the Ptolemaic system (which was a mathematical mess by the 16th century as the general model was continually appended rather than torn down and rebuilt), but there were still definitely some. Copernicus created a heliocentric universe that had circular orbits for all of the bodies. Coming from the knowledge that planetary orbits are elliptical, we can see how this leads to problems. For example, if the position of Mars is charted nightly against the background of the stars, there will be instances where it appears to move one direction for a few nights, then stop, turn around, start moving backwards for awhile, then stop, turn around, and then proceed on its usual course!
The way to explain this sort of oddity and yet preserve your blessed circular orbits is to insert epicycles. The planets are traveling in circles while orbiting a central body (the sun, or the earth). With some tinkering, an epicyclic system can be constructed that fits fairly well with observations taken from the vantage point of earth, at least most of the time. Not all the time, mind you, which is why it too had some (in hindsight, again) rather pathetic attempts to patch it up, epicycles on the epicycles and rot like that. Heliocentric theories had been proposed before, as another poster mentioned, by Aristarchus in ancient times, and then Nicholas de Cusa in the 15th century. Both of these models suffered from the same type of complexity that the one put forth in De Revolutionibus Orbium Coelestium.
What made Copernicus different is that he worked out a real mathematical basis for his solar system. Copernicus also correctly realized that the system could be made simpler if the inner planets moved faster than the outer planets, and thus completed their orbits even faster than distance of the circle they covered alone would predict. This seems obvious now- inner orbits must move faster, because gravitational forces varies with the inverse square of distance, but Copernicus lived before Newton, so he wasn't operating with that knowledge. His system was incorrect, yes, but it was at least based on something more concrete than aesthetic value. It then fell to Kepler to divine the true mechanics of the Solar System. His calculations showed that if the orbits of the planets were ellipses, with the Sun at one focus (he introduced the word "focus" in this context, btw), then the whole epicycle thing wouldn't be necessary at all to fit experimental observations. Moving on ellipses meant that the planets did not move with constant velocity- they moved faster when closer to the sun, and slower when farther away. Combined with Copernicus's concept of the inner planets moving faster, bolstered with mathematical properties of ellipses to become Kepler's Third Law, the whole epicycle thing became pretty much unnecessary.
That last sentence should read, If people could eat a balanced diet and get regular exercise, chances are they wouldn't need the product. Three characters can make a world of difference. My powers of proofreading are failing me...
If you don't believe me soak your head in acetone (di-ethyl ketone) for a while.
Maybe you should take the organic chemistry sometime, eh? Acetone is dimethyl ketone, not diethyl ketone. You are correct in asserting that ketones are highly reactive, which is why the kidneys, perhaps the most amazing organs in the body, get called into action. However, the major chemical reactions of ketones and aldehydes are generally very slow without acid or base catalysis. Human blood is buffered at a comfortable pH 7.4, so most of these potential poisons can be trucked to the kidneys without incident.
Unfortunately, I haven't read anything conclusive (certainly not this article) that even casts reasonable speculation on the health effects of long term states of ketosis, and IANA dietician, so I refuse to pass judgement on the diet over the long term. I have decided to avoid the Atkins diet personally, because my family has a rather awful history of kidney problems (kidney stones, polycystic kidney disease, urinary tract infections, cancer, etc), so I don't plan on taking any chances with my pair. However, the evidence I've seen so far suggests that overweight people with normal kidney function can definitely benefit from the diet, and should be able to handle the ketosis, at least in the short term. Also, as many otherposters have pointed out, there are some undesirable side effects to being morbidly obese which might trump those of protein and fat metabolism.
I think that a balanced diet, with fats, protein, and carbs all in moderation, is preferable, in terms of both ease of following, and enjoyment of the food you consume, but I guess most Americans simply cannot eat that way and go about it responsibly. It reminds me of the fine print at the bottom of most diet pill ads, which point out that the miracle weight loss from their product occurs "in conjuction with a balanced diet and regular exercise." If people could eat a balanced diet and get regular exercise, chances are they would need the product.
What makes laser such an interesting word is that the expansion of the acronym is generally totally unhelpful to most people, and really provides little insight on the uses of the object. A laser, as found in a CD player (this is another abbreviation that I dare say would be acceptable in formal writing now, and DVD is another), or a laser printer, or one of those annoying pointer things, can be used without the knowledge that LASER stands for Light Amplified by Emission of Stimulated Radiation. Laser is a convenient word, one that encapsulates the information of a complicated process, but is itself a simple word. I'd wager that many people who use lasers every day have no idea what the expansion of the acronym is, and many probably do not even realize that "laser" is an acronym. This confusion has been helped along, I believe, by words like "phaser," which are not acronyms, but rather inventions of science-fiction, and by idiots who spell the word "lazer." (There is a printer repair shop in my town named "The Lazer's Edge." Ugh.) I imagine that the acronym for laser was expanded much more frequently in the 60s and 70s, when lasers were a new invention, and were not nearly so widespread. Now, the only place I see the acronym expanded is in semi-technical articles that also mention masers- the acronyms are then expanded to provide a helpful explanation of the similarities and differences between the two. This is especially interesting since the maser was developed first, but are far less useful and ubiquitous.
I believe what has happened here is that a split has occurred between "laser," the object, and "LASER," the process of creating a coherent beam of light by which a laser functions. In fact, I have read technical papers that mention things like a "lasing cavity" which imply that laser is no longer an acronym (Light Amplified by Stimulated.....ing...).
I can think of a few other words that are acceptable as acronyms in formal speech, scuba, for example. Names of corporations and entities that traditionally go by initials, like CIA, FBI BASF, MCI, RCA, NBC, and AT&T can be used without explanation, methinks. In some cases, explanation is pointless, like in the case of the Radio Corporation of America (I think they sell other stuff now too), or the American Telephone and Telegraph Company (not so much telegraph traffic, anymore). Also, companies with shortened names in common use: DuPont for the E.I. du Pont de Nemours Company, Nabisco for the National Biscuit Company. Always, always, consider the audience, however. In a Slashdot post, RIAA, MPAA, DDOS, do not have to be expanded, but if I were writing a formal paper for a college English prof, I would expand them upon their first occurrence in the paper, then use the initialisms from then on.
There are a few times when I do not think there is any point to expanding technical acronyms, particularly when writing for a nontechnical audience. That many sound a little backward, but I can recall instances up to a few years ago where newspapers and newsmagazines pointed out that DNA is deoxyribonucleic acid whenever they mentioned it in print. I can only imagine a moment where a person sees "DNA" in print, and is completely baffled, but then sees "deoxyribonucleic acid," and is then totally clued in. Nothing about the name suggests its function as the genetic information molecule for most life on earth, just as nothing about LASER explains how a laser is used to read a CD, or add text to a piece of paper, or put a red dot on the forehead of someone who is about to get shot in the face.
I wholeheartedly agree that Internet slang has no place in formal writing. Slang like b4, ppl, rotflmao, kewl, d00dz, and the dreadful 1337 should be considered no more proper than ain't, cuz, or using double negatives. I use terms like lol, afk, and brb in IM conversations, but I do not in written papers. These are not terms that add anything to a paper- they are not new words, just misspellings of old words. If 1337$p34k produces new words that become commonly accepted (e.g. can be found in a dictionary), then using them in my writing becomes a possibility, but for me, a fairly remote one still- I don't even use contractions in formal writing (which this is not). The Internet has produced a large number of words, some of them not wretched, so I imagine that the exploding chat scene will add more to the language, some of which will not be wretched. All that has really been produced thus far are acronyms that have no logical use in a formal paper (when would you use brb, omg, afk, lol..etc?), emoticons that are completely out of place in a formal paper: Therefore, my opinion of the Supreme Court's decision in Dred Scott v. Sanford: >:-( , and cute misspellings that would make sophisticated prose look like the front page of some rave fan's terrible Geocities website.
As for WTF, LMAO, and RTFM, would you ever use profanity in a paper you wrote for a grade? I realize that the profanity is implied, and these terms lack the connotation of "What the fuck?" "Laughing my ass off," and "Read the fucking manual," but still.... I wouldn't use terms like "fubar" or even "snafu" in a formal paper. I consider polite writing to be free of slang, but at the very least, I expect it to be devoid of profanity, assuming the profanity is not somehow germane to the treatment of the topic.
Well, the above poster is guilty of some oversimplification- experiments like the one described were in fact meant to disprove spontaneous generation on a human timescale, which had been thought to occur. It was once commonly believed that rotting meat spontaneously generated maggots, or that old bread generated mold. Redi showed several hundred years ago that maggots only form on meat if flies are allowed to lay eggs there- he placed meat in two different jars, and put a cheesecloth over one, so they both rotted, but maggots were found only in the open jar. Pasteur used sealed, sterile flasks to show that life does not arise naturally from a growth medium, even on a microscopic scale.
Neither of these scientists, however, understood the timescale of life on earth, nor the conditions of early earth. The Miller-Urey experiment, building off of theory by Oparin, attempted to show that conditions that might have been present in the earth's atmosphere several billion years ago could combine using energy provided by lightning or UV radiation to form a "primordial soup" composed of the building blocks of life- amino acids, carbohydrates, lipids, and nucleic acids. The experiment works as designed- the gases react in the extreme conditions to produce an organic "gunk" that contains many of these building blocks. Controversy still surrounds the issue of the primordial gas composition, particularly whether the early atmosphere was reducing, as Oparin suggested, or oxidizing, which might invalidate the Miller-Urey experiment- a strongly oxidizing atmosphere would not allow even relatively simple organic compounds to form.
Despite the unknowns that are still unresolved, most scientists agree that some sort of process similar to the Miller-Urey type experiments produced the first organic building blocks from inorganic substances present on the earth of 4 billion years ago. The major question is how these simple building blocks arranged themselves into organic macromolecules like proteins, polysaccharides, and DNA and RNA, and from there, into the first forms of what we would describe as life. The transition from boiling brown tar to membranes, replicator molecules, and cellular organization represents a difficult problem (an impossible one, according to those intelligent design folks), and we must make educated guesses with incomplete information about the processes involved. Cyanobacteria microfossils have been found in ancient craton formations dating back 3.5 billion years- some of the oldest rocks on the planet. One billion years before that, the planet was a ball of liquid rock. In the time between, the earth cooled, the oceans formed (well, one really big ocean), organic compounds were formed, and these compounds assembled themselves into self-replicating structures- the beginnings of life.
So yes, spontaneous generation is possible,and in fact responsible for life on earth, but not with today's enviromental conditions- the atmosphere has a different composition (nearly 80% N2, which is almost inert at standard conditions), the weather is less violent (lightning is not nearly as powerful as it was then), and the ozone layer blocks most UV. Howerver, there are a few places left on earth today that could conceivably be cradles of new life- deep-sea vents, for instance. The jump from simple organics to organized macromolecules could easily take over 100 million years, if you're willing to wait. However, even this is an unlikely scenario, it would basically have to occur at a vent with absolutely no other life already present- otherwise any new replicator molecule would find itself in competition with lifeforms that have a 3 billion year head start, and that operate using the brutally efficient DNA/RNA/protein transcription/translation pathway, fine-tuned over billions of years of evolution.
Caffeine-free Jolt? What the heck is that good for?
Actually, when I first thought about it, it struck me as rather counterintuitive. If you wanted to pay less in tax, the easiest way to do that would be to underreport income. However, that really isn't that easy, since you send in copies of your W-2s- so assuming you have only legitimate, federally reported sources of income- no under the table cash payouts- your taxable income should be pretty easy to verify.
One area where the wealthy and the poor differ on their tax returns, however, is on deductions. The working poor usually take the standard deduction, since in general they rent rather than own their homes, and thus have no mortgage to deduct interest on. Also, they usually do not have significant investments from which to deduct losses, business expenses are often minimal, and the standard deduction represents a sizable fraction of their taxable income, so taking that is a good idea. For the wealthy, OTOH, itemized deductions usually provide tax relief far in excess of the standard deduction. They are also a gateway to defrauding the IRS, since shady accounting practices can make almost any expense into a deduction. Therefore, the IRS conducts audits to determine the validity of itemized deductions.
Another factor is that if you audit a wealthy person, and it turns out they are in error, the penalties the IRS collects will be much larger than from an audit of a poor person. The IRS lacks the resources to conduct a complete audit on everyone, so they have a strategy that they believe will maximize the amount of revenue collected. Similarly, police cannot patrol every corner of every street 24/7- nor would most Americans want them to, just as most Americans would not want to be audited at tax time each year. Thus, they concentrate their resources on a specific neighborhood, a specific street corner, or perhaps a specific group of people known to have involvement with crime. Is that logical? Yes. Is that fair? Hell no it isn't. Is auditing a certain group more often fair? Ditto. To be accused of a crime because of your race, your religion, your country of origin, the amount of money you make, your politics, the street you live on, or the people you associate with is dehumanizing, and I believe that it violates your rights.
Given that the government seems to equate buying drugs with financing Al-Qaeda (as opposed to some that actually has funded terrorist organizations, like paying federal taxes), I think that the standard party line response would be that the war on drugs is a key part of the war on terror. Ergo, we should treat American citizens like terrorists because they possess narcotics. I can't wait until drug dealers are held as "enemy combatants."
Many of the people whose photos have been taken were stopped briefly for loitering and let go.
Considering that African-Americans have long been been pulled over for Driving While Black, is police persecution for Standing While Black much of a surprise? If you are a young black male in America, you automatically "fit the description" for some fugitive from justice. If you want to suggest that profiling such a large group prevents crime, then I ask, where is the database of white male multimillionaires?
Nice, I was about to recommend that myself. I think it is a well-written, comphrensive text, and it has served me well after gen chem- I still have it on my shelf, and I refer to it from time to time. I'm rather biased toward it, I must admit, since Steven Zumdahl was my general chemistry professor my first year at UIUC. However, it's a very well-known text, in use at many universities, and the majority of reviews I've read are very positive.
I find it interesting that the article suggests towing a wormhole using a "spaceship, presumably of highly advanced technology" to place a created or expanded wormhole in a powerful gravitational field. Maybe I'm just envisioning this wrong, but I don't know if a wormhole is really what I'd consider to be an "object." Rather, as a rift in spacetime, I'd think would be a thing (for lack of a better word) that is defined by both lack of object, and by objects around it, like the hole in a doughnut, and thus the only way to "move" it would be to alter the objects that surround it, like stretching or shrinking areas of the dough to change the location of the hole with respect to locations on the dough . You can't just grab a hole in a doughnut with a pair of pliers and move it around. In the case of wormholes through spacetime, I'd imagine the way to move a wormhole is to warp the space around it with immensely powerful gravitational fields, folding the space around it and causing it to "fall" to its neutron star target. However, this would certainly require a mastery of gravity far beyond what we have presently attained. When the two ends of the wormhole are created/expanded to macroscopic size, they will need to be separated, with one end taken to a neutron star. Building a tow-ship that can warp the space around a wormhole would require far more knowledge about gravity than we presently possess and far more mastery. Despite being perhaps the most obvious of the fundamental forces of physics, it is probably the least well-understood. Gravitions have never been found in particle accelerators, nor Higgs bosons. Gravitational waves have not been conclusively detected. No coherent theory of quantum gravity exists. We will have to be able to manipulate gravity with the ease that we manipulate electromagnetism if an "interstellar tow truck" is to be built. "Highly advanced technology," indeed!
Using the neutron star itself to attract one but not the other would be very difficult, but possibly workable- especially if Podkletnov's spinning superconductor gravitational shield works (which it doesn't, that I am sure of). However, you certainly can't use a natural source to reunite the ends once you've "twin clocked" the exit end- the exit is sitting near the surface of a neutron star- so you really won't be able to pull it away with anything less than another neutron star or a black hole, perfectly positioned to make use of the three body problem to slingshot the wormhole out of the star system. Conceivable, but highly unlikely.
You can't just leave the exit there, either. It would continue to accumulate time difference, so each trip would take you farther from your present time, but actually further and further along in time, since you can never actually travel backwards to before the creation of the exit hole, and since it is in fact still moving forward, albeit slowly, in time. Also, you would leave the exit and find yourself right around the surface of a neutron star, which is a somewhat dangerous location. Worse, you would have to travel at a relativistic velocity to escape the neutron star's monstrous gravity, which means your fast clock would run very slow, so the rest of the universe would be aging faster than you. Also, the nearest neutron star is several light-years away, adding to your return-trip travel time. I'm sure it would be a fantastic adventure, but sort of a waste to fly into a wormhole, travel centuries back in time, and rocket away from a neutron star at nearly the speed of light- only to get back home and find that due to relativistic effects and travel time, you are right back where you started, or even farther along!
I haven't done the math, but I suspect that sort of scenario could be one of several ways the universe is protected from time travel paradoxes- you can go back in time, but due to relativistic time dilation and the effects of gravitational fields, you can never make it back in time to affect events in the past of your light-cone, preventiing you from creating an inconsistent causal loop.
just hire a hit-man to whack the stupid git.
Hire a hitman? No way. Assassination wants to be free!
and those bits belong to them till you purchase a copy.
Once I purchase a copy, do the bits belong to me? They do? OK, since I really don't like keeping my bits on a compact disc, I think I'll rip them to high-bitrate mp3. I can't tell the difference anyway. Also, since I like these particular bits, and would like others to experience them, I think I'll share a few with my friends- either the ones across town, or some people I don't know very well that I just met using Limewire. Since they're my bits, I think the decision should rest in my hands.
I'm really surprised that only two Fields Medals were awarded this time around- at least three have been awarded every four years since 1974. Is Preda Mihailescu's proof of Catalan's Conjecture considered too recent for consideration? I'd think that sort of thing, combined with his work on noted hot topic primality would make him an attractive candidate.
Of course, I'm sure they are many others who were also very deserving as well. No, I am not Dr. Mihailescu, and have never met him in fact; it's just when I saw that the Fields Medals were awarded, my first thought was, "I wonder if they gave one to that guy who proved Catalan's Conjecture?" As recent as the proof was (considering the slow, careful peer review that accompanies important purported mathematical proofs), I wasn't shocked to not see his named- I was far more surprised that the committee chose to not award the remaining two prizes to anyone.
Does anyone know why the diagram uses S to represent the base cytosine in the DNA diagram rather than C? Is it simply to avoid confusion with the c they use for carbon in outlining the structure of the bases, or is it part of an outdated labeling convention?
A rude eruption
Composed of natural gas
Farts warm up our globe.
Strictly speaking, even/odd and red/black bets on roulette aren't 50/50 either. They pay 1:1, as you'd expect from a 50/50 bet, but there are 38 spaces on a roulette wheel (37 in Monte Carlo, I'm told though)- 1-36 red/black odd/even, and two (or one) green zeros, which provide another color, and are neither even nor odd (you can debate whether zero is even, but the casino will not be swayed to your POV). This means your odds of hitting red on a red bet on a Vegas wheel are 18/38, or ~47.3%, but the payoff is only 1:1, as if the chance were actually 50%- it would be 1.11:1 if roulette weren't a way for casinos to rip you off. Incidentally, this means you can bet on both red and black, and still lose.
Neat article. However, I was rather perturbedby the opening anecdote about ferrying an enormous amount of cash through Logan Airport- the same one that the hijackers that destroyed the WTC flew out of. Bricks of hundred dollar bills, box cutters, no questions asked... just what the hell does security do there anyway?
Yeah, and that (1985) was also before Challenger exploded. Of course, 1995 would not have been a realistic date for affordable Space Shuttle travel anyway- costs would have been out of control to build that sort of infrastructure, unless NASA considered "affordability" to be in the Dennis Tito sense, and charged passengers 8 figures for a flight.
So what you're saying is, an "omnipotent" Supreme Being does not possess the power to defy a paradox? God does not possess the ability to accomplish things beyond the human scope of reason and logic? How can a being be truly omnipotent if its powers are bounded by logical statements? How powerful is an all-powerful god that can create an entire universe but cannot make a rock both completely white and nonwhite at the same time? Your reasoning simply backs out of a paradox only to step into another paradox.
Having read the paper (forgive me, I'm new here), I'd say the negative time effect is very similar to the FTL transmission results reported earlier. On page 6 of the paper, the caption to Figure 6 reads in part: Note the negative values of tau-sub e (the time spent inside the condensate region) in the region around ka ~/2: Wavepacket simulations show that here the peak of the transmitted wavepacket appears before the peak of the incident packet reaches the condensate. Now, IANA condensed matter physicist, but my best assessment of the effect is that it operates similarly to previously observed, similar phenomena of "FTL" transmission. The incident wave of light contains information for the entire wave embedded in the wavefront- so the peak of the wave is able to be reconstructed on the other side of the BEC, even though the peak itself has not reached the condensate yet. Essentially, since the entire wave of light is defined by a wavefunction, the entire wave can be constructed from the wavefront. Although the process can take zero or even negative time, it is not a violation of general relativity. The light itself propagates at the speed of light, as it must. Since the peak of the wavepacket is recreated before it is actually destroyed, it would seem to be moving faster than the speed of light. However, the information that completely describes this peak is embedded into the wavefront, which travels at the rather pedestrian speed of light (and for a BEC, it is almost pedestrian- the amazing dispersive effects have been shown to reduce c to around 38 miles per hour, an effective refractive index of over 17 million!). While something is technically traveling over a nonzero distance in zero or even subzero time, no unique information can be transmitted in this manner- since the peak is constructed from information in the wavefront, the peak must be composed of information contained in the wavefront. The wavefront is moving at the speed of light, and taking all of the information it has with it at exactly that speed. If we had an ultrafast and ultrasmall computer conceivably, we could dispense with the Bose-Einstein condensate and do this thing ourselves. The wavefront enters a detector, the information is broken down, and the hypothetical supercomputer we have at our disposal uses the information in the wavefront to calculate the wavefunction. It then spits out a wavepacket with characteristics identical to those of the incident packet, and does so before the peak of the incident packet even reaches the detector. The effect is somewhat analogous to the movement of lights on a scrolling theatre marquee. The scrolling itself can actually occur faster than the speed of light, but since the "information" is just a discrete on/off light, no useful FTL message can be encoded. In the same way, the wavefront carries information faster than the speed of light, but the information merely codes for the rest of the wavepacket! Thus, it is not a violation of relativity. If anything, it is an affirmation- the weirdness of quantum mechanics, what with the wave/particle nature of light, is weird in such a way that useful messages cannot be sent faster than the speed of light. On a completely different note, I was amused to see someone referenced in this paper that /.ers might recognize, if they had actually read the paper. On page 6, the authors propose explanations for this effect, and they suggest a many-body interference mechanism devised by Ray Chiao et al. Raymond Chiao, some of you may remember, is the physicist who had a /. story not long ago about the possibility of a gravitational Meisser effect for superconductors (Can Superconductors Block Gravitational Fields?).