Hmm... "birth of the Crab Nebula" or "death of the Great Crab Civilization"?
The progenitor star was (opinions vary) between approximately 9 and 12 solar masses, and of spectral type A, O, or B. Using standard approximations, this gives a lifetime for the star on the main sequence of 20 to 40 million years.
The most-recent 20-to-40 million years of this planet's history has seen mammals evolve into other mammals, bats develop sonar, whales stop paddling around near the shore and move into deep water, and various fructivore monkeys develop bipedalism and expand their brains. But the first 20-to-40 million years of this planet's history included... well, lots of meteorites re-melting the planet's surface, and maybe a little bit of rainfall. Did life evolve? Well, it's not impossible, but most people think that it's pretty improbable - the oceans were still re-forming and being boiled off at irregular but frequent intervals by large impacts. A couple of hundred million years later and you're into a much more benign biogenesis environment, but that's 5 to ten times the time span that's available.
Of course, this analysis assumes that the "Crab Civilisation" were actually in orbit around the Crab progenitor star. They could conceivably have been just "in the area" and got whacked by this upstart star unrelated to their planet's formation. Which would have been pretty upsetting, but could only have been significant during a short interval in the species' history. While they're still trying to understand plumbing and the economies of scale of cities, they're only barely civilised ; a couple of millennia later and they should understand astrophysics well enough to recognise the problem in their skies and develop a mitigation strategy.
No. The council has to consider whether to provide a business with a license to sell "beers, wines and spirits" for consumption either on or off the premises (but not IIRC, both ; but you may be able to get both licenses for one premises). The council can decline to issue such a license for a variety of reasons, including "unfitness" of the license applicant or on advice from the police or on the basis of objections from the public. (My town has a fairly vigorous debate over whether to allow even more pubs in the town centre, but the current depression seems to be knocking that idea on the head.) Failure to award a license can be appealed, and a refusal must then be justified in public. Which some politicians dislike doing. (A friend of mine is on the local council's licensing committee ; I've had too many sound waves on the subject wash over my ears.)
Surely, "the flying" of a modern jet is not the difficult part - it's "the landing".
Relatively old joke concerning piloting : Modern airliners are being designed to do away with most cockpit crew. Engineers and co-pilots will be gone, only leaving room for the autopilot, the pilot and a dog. The pilot's job is to feed the dog ; the dog's job is to bite the pilot if he tries to touch any of the controls.
Of course, being a joke, it ignores certain realities. No-one would seriously design a cockpit like this. They'd dispose of the idea of a cockpit altogether, leaving the trolly dollies with no-one to blow.
If our government has a backdoor, it won't be too long before other governments have access to it too.
What do you mean by "our"?
The only government with any semblance of an intrinsic right to get access to Skype communications before any other government is of course the Luxembourg government.
It's worse than that, they're hostile countries looking to harm our childrens.
Well, there's an obvious and easy way to make that impossible. And since there is such an obvious and easy way of preventing that from happening, that makes you culpable for any harm that does befall your children.
Great minds think alike - I found exactly the same artifact in approximately the same time of searching. I did know before-hand that there has been extensive seismic work in this Porcupine Basin - I read up on it for some work a couple of years ago in the Slyne and Erris basins. So, to pick an area that I don't know... lessee... Great Australian Bight? Oh, how does this look - 5013'5.57"S 114 2'57.42"E ; zoom to about 70km altitude ; two adjoining Atlantises (Atlantii?) ; see your Plato and raise you a DreamTime!
It's pretty uncontroversial (i.e., you have to go out to the extremes where young-earth creationist lunatics cross-breed with gas-guzzlers to find claims of controversy, which is more due to some people's religious delusions than there actually being a controversy) that during the ice-age, global sea levels were relatively low for the good and sufficient reason that the ice which was on land used to be water that was in the ocean basins. BTW, I take it that you're referring to La Grotte Cosquer. As the link image indicates, the paintings themselves are above sea-level (they'd have been pretty unlikely to survive and remain recognisable if they were below sea-level!) ; it's the cave entrance which is below sea-level. As my fellow troglodytes (spelunkers, if you're a transpozzian) say, "the cave imposes it's own entrance restrictions". While the surveying isn't readily available (I bet I could get hold of a survey, through cave-diving contacts, but I'd have to use my influence as a well-established caver, as an ex-cave diver, and as a professional geologist with a long-standing interest in archaeology. But as a responsible geologist, I won't even seek the data ; what I don't have, I can't leak.), I bet that there is an upper entrance. Hydrologically, there's pretty-much got to be an upper entrance - though it could well be presently plugged with debris, or collapsed and hydrologically inactive. While finding such an entrance has obvious interest, I'd be very hard put to justify even looking such an entrance because of the risk of damage to the paintings if a non-diving entrance were discovered.
Oh dear, I found more survey data than I really wanted. That was depressingly easy.
There has been some scientific research done suggesting that the Black Sea at one time was dry,
I don't recall having seen Ryan and Pittman (if I've recalled their names correctly) claiming that the Black Sea went dry. Mostly, they point to considerable shrinkage in area by losing the top couple of hundred metres of the water column. But basinal dessication? Don't recall them ever claiming that.
My guess it that you're conflating the well-established ice-age global fall in sea levels with the equally well-established local dessication of the Mediterranean basin in the Messinian Salinity Crisis (just Google it) at approximately 5 million years ago (before the present cycle of ice ages really got going properly).
For what it's worth - I spent most of last December drilling through a kilometer of Messinian-age salt deposits. It's very definitely non-trivial. If I'd been allowed to keep my notes (or if I'd been interested, to be honest), I'd be able to describe it in nauseating detail.
Logging for 2 years? Who is going to pay for the storage costs, backups, etc.?
Mail the logs daily to the (in-)appropriate police chief. Let them pay the costs of storage and administration. (But make sure to keep your own mail logs, so that the onus falls onto them to explain why they've lost the logs.)
I know - they'll refuse to accept the. But you keep on sending them the data, and hope that a jury of YOUR peers will consider that you've reasonably discharged your obligations. In the event of "something" happening, they're going smash down your front door and take your computers anyway, so you'll need to make sure that the logs are on a suitably short rotation cycle.
Yes and consequences of this action should be either detention or in school suspension.
"Suspension" as in "hang by the neck until dead"? I didn't notice - was the offending person in Texas, where the state murders minors and mental defectives, so neither of those defences are available.
OK, if it's a first offence, I might go for her spending a month in the gibbet cage and just hoping that no-one gets put in the cage above.
Taken as given : speed of light ; wavelength to energy-per-photon relationship ; that simple LEDs emit light of one specific colour (you need to choose your LED with due care and check it's emission wavelength) ; that (electrical) power is the product of voltage and power.
Needs : a darkroom ; ammeters and voltmeters, the better the better ; ripple-tank ; standard kit for demonstrating photo-electric effect.
Days one and two are interchangable.
Day 1 : Photo-electric effect ; show that photons deliver their energy as packets and are thus particles. If you've time, and an appropriate biology lab, you can also show that visual pigments require light of a certain minimum frequency to operate. That you can see red LEDs ties in with this minimum Day 2 : Interference effects ; show how waves interfere with each other, including a demonstration of a double-slit experiment in a water tank. A more mathematical day's work than previously. Day 3 : build your optical double-slit experiment using a red LED as a light source, and measuring the power it draws ; turn the power on the LED down until you can only just make out the interference pattern (record both voltage and current, just for completeness). Repeat for as many you have in your experimental group, and as many times as you can to build up a corpus of results to show the minimum power at which the interference pattern can be observed with a non-integrating detector (i.e. eyeball, Mk-I).
Finally, analysis. You have the power of the LED at which the interference pattern is still visible ; this gives you the number of photons per second forming the interference pattern. Speed of light gives you the spacing between photons while they're in flight (assuming it's not 'bursty'). At some point your students should realise that they are seeing the pattern of one photon interfering with another photon which has not yet left it's source. Wave-particle duality.
If you have time, you could indulge in looking at the experiment's problems. All the electrical power of the LED is assumed to go into the light, but if some goes into heating the LED, then that means that the light flux from the LED is lower, and the photons are spaced further apart. Maybe one photon has left the room before the one it interferes with forms at the LED? Is the LED "bursty"? Well, that's a whole set of other experiments. They're not going to fit into 3 days. Oh, actually, did you mean 3 working days, or 3 full days? And how many hours in your working day?
Ruben Tube.... very interesting. In my day, my self-chosen physics project was trying to measure the velocity of combustion of gas-air mixtures using the passage of the ionisation front in the flame. I never got my equipment design to work, but I had a lot of fun along the way. Various gratuitous explosions and high-voltage generators. GRIN. Actually, I don't think it would have helped much in my project. I don't know. But it sure looks a cool experiment.
the "Ice Bomb" experiment, which is extremely hazardous. [SNIP] it was ripped into pieces.
Sounds pretty cool. Unnecessarily violent - which is it's point. That prompts me to go to the local granite scrap yard (several thousand cubic metres of disused quarry), get some suitably-sized chunks, and repeat the experiment using cylindrical holes, water, epoxy resin and the butt end of a drill bit. Together with a normal freezer, I think that would be sufficient to demonstrate "freeze-thaw action", which is very important in the process of turning highlands into seabeds. Not as exciting, but relevant to my work.
It's worse than this. The Earth has existed for 4.5 billion years and contained a civilization that could reasonable detect radio waves for a little over a 100 years. Thus, the chance of a given Earth-like world having a civilization with roughly 20th century technology is about 45 million to 1.
Broadly true, but unnecessarily pessimistic...
Even if the average civilization lasts a million years, the odds are still 45,000 to 1 that any particular Earth-like world will contain one. The chance of us finding a civilization that inhabits a single nearby Earth-like world is extremely low.
Bear in mind that when I was 20, the number of known extra-solar planetary systems was zero, and that when I was 40, the corresponding number was several dozen, and it's now in the hundreds, then to get to 45,000 examined systems (and therefore an =evens= chance of finding one with a civilisation on it) is going to take between a couple of centuries and a couple of millennia. Still a steep requirement, but since it's only a couple of millennia since our ancestors discovered the benefits of cities...
If civilizations can expand beyond their home planet, then all bets are off, but that brings up the whole "where are they?" question. One presumes that if some sort of empire had spread out among nearby Earth-like words, it'd have gotten to this one as well. Therefore, I think it extremely unlikely that there are any advanced civilizations on a nearby Earth-like world.
Why do you limit yourself to "nearby", and to "earth-like", and to "worlds". Long before we have any conceivable prospect of interstellar travel (or even of significant interplanetary travel), our engineers are going to have to solve the problems of travelling in closed ecologies with high-power, high-radiation, energy sources (barring the discovery of Unobtanium and it's burning to make Unobtanium Impossibilide for fuel the Warp Drive). At which point, living off-planet in centripetal pseudo-gravity fields, digging organic matter out of cometary nuclii and structural materials out of asteroids, all become less of a constraint than finding a "Goldilocks" planet would be.
by the time that you've spent 3 generations sending ships out to the Kuiper Belt to assemble the reaction mass needed for your flight to Alpha Centauri, and another few tens of generations flying to get there, are you really going to give that much of a damn if all that is there to greet you is another cometary system and a bunch of asteroids? Nope, you either settle down amongst them to continue living the way your last 15 generations of ancestors lived (in a ship), or you don't bother to slow down more than necessary to pick up any materials you need, and move right on down the line.
Where are they? I think that they put Pluto in it's weird orbit as a marker, and have put the directions to "Glactic Central" in a 1m-diameter sphere of pure lithium (not chosen at random) in orbit around Pluto. All we have to do is go and find the instructions. Oh, we'll need to develop some technologies along the way, but nothing terribly exotic.
"Complexity" in this context should be understood to say little or nothing about the physical size of the organisms or their multi- or unicellular nature. It is, rather, a comment about the size of the potential gene space for the organisms.
Hmmm, I did mention size ("microbes"), but as I was meaning it as a shorthand for an ill-defined "genetic complexity space" as you're thinking. I would have been more accurate to say that most life on the planet is (probably) still prokaryotic. If you count mitochondria and chloroplasts and the more-recently described methane- and hydrogen- generating organelles of certain organisms, and if you swallow Margulis' assertion that ER/ myosin-actin fibrils, centrioles and intra-cellular transport networks are degraded spirochaetes, then you can probably take out the "(probably)" in the previous sentence.
On SlashDot, you never know the level of the person you're corresponding with. For all I know, you might actually be Margulis!
Humans tend to think of "complexity" in very anthropomorphic terms,
True ; I refer the honourable gentleperson to the comments I made a few moments ago.
If the biochemistry of the life-forms does not allow for very much diversity (remember we're talking about life that presumably does not use DNA or RNA and possibly not even any of our amino acids), there is very little for evolution to work with.
That was implicit in the general discussion, but barely perceivable in the actual article (typical SlashDot ; RTFA is so uncool!). It would take a vastly more confident chemist and/ or biochemist than I am to examine the mechanisms of a novel biochemistry and to deduce it's limits. Bearing in mind that while we're confident of our understanding of basic protein synthetic pathways, we don't really have a clear understanding of how our own genomes control gene activation and/ or suppression...
It took the best part of a quarter-century from Crick and Watson's discovery of the basic structure of our biochemistry before Ohno's concept of "alternative reading frames" was described and demonstrated ; the consequences of this are still being worked out, along with considerably more esoteric ways of using genomes. That should give serious pause for thought before declaring that "X" other biochemistry "does not allow for very much diversity".
It's not hard to imagine a situation where such organisms might relatively quickly reach their maximum potential and evolution - even microbial evolution - effectively stops.
Ummm, actually I do find it quite hard to imagine such a situation. The minimal complexity of an organism is quite substantial - 9000-odd genes is the sort of size Venter et al are looking at? - so if you're going to have a successful organism of ANY biochemistry, then you're going to have to be dealing with quite significant chunks of genetic material (be it DNA, or patterns on the edges of spiral defects in clay minerals [example only, don't take it seriously]. At that point, it gets hard for me to conceive of a system that isn't going to be prone to re-reading the same data block twice, or writing the same block twice. At which point you're in the territory of gene duplication, which is certainly a mechanism for generation of new functions, followed by new diversity.
Nope, you're going to have to work a lot harder to convince me that any genetic system has an inherent upper limit on diversity, where the biochemistry continues to work. As has been pointed out, DNA/ RNA/ amino acid biochemistry can work well enough to survive low pH and high temperature (at least, for some of it's life cycle), and to endure low temperatures for protracted periods of stasis. I don't think that it's going to work at a bright-orange heat though - the RNA would fatally dehydrate. And I wonder what's the upper limit of pH that our co-b
I didn't find it on Google, but about 30 years ago I read an account of a creature like a giant sand dollar that was dislodged from the deep ocean by an undersea earthquake.
Trying to decipher what you're on about...
(and decayed rapidly giving off H2S)
Could you be mis-remembering the occasional oceanic poisonings off the coast of Namibia, due to blooms of a particularly large microbe (up to a mm in diameter) which contains large vesicles that it dumps sulphide wastes into. In the latter stages of a bloom, the sea goes mostly anoxic, and the abundance of sulphide leads to the release of significant hydrogen sulphide.
and that its chemistry required deep ocean temperature and pressure to remain stable. (Note that there are carbon based ocean creatures able to process silicon to create SiO2 structures.)
It's not particularly deep in the areas I'm thinking of. And the blooming involves the organisms moving up and down the water column. Diatoms in particular are perfectly normal organisms that form silica skeletons. They largely control the silica content of the oceans.
They live practically everywhere including in boiling acid, semi liquid rocks, extreme cold, and on black smokers as above... it seems that everytime discounts an environment for carbon/DNA based life someone else finds life there...
What do you mean by "semi-liquid rocks"? As a geologist, I read that to mean rocks with a noticeable degree of plasticity with an implication of this being due to heat. Depending on composition, that's going to be at least a dull red heat for common rock compositions (granite/ andesite/ trachyte), maybe coming down to the sub-red temperatures in the high 300s C where there's a lot of water and possibly a lot of unusual chemistry (carbonatite volcanos, for example ; these are rare). Steel or aluminium might start to soften at 250 C, but only very, very uncommon rocks. In contrast, the highest temperature that I've heard of proteins surviving (note - not necessarily working, but resisting being denatured) has been in the mid-170s C, and the highest temperature for whole organisms working in the high-120s C. Higher temperatures are recorded in "black smoker" environments, but these areas have very very steep (and mobile) temperature gradients so their organisms almost certainly don't get these maximum temperatures consistently.
I'd also query the comment about "extreme cold" ; certainly plenty of organisms *survive* extreme cold, but that's a different thing from being active in extreme cold. For example - the lichens reported from Anarctica no doubt survive temperatures down to -50C and lower ; but do they actually live and grow at these temperatures, or are they in stasis and only start to grow when (for example) sunlight warms their rocks to within a couple of degrees of freezing point? A penguin lives comfortably at 20-odd C while the feathers of its head can be 70C colder.
Why is "increasing complexity" a requirement for life? It's clearly a requirement for evolution,
Where did you get that idea? I see no grounds for requiring increasing complexity for evolution, and indeed, since the overwhelming majority of life on this planet is microbial, as it always has been, there is fair evidence against such a claim.
Consider a range of lifeforms which randomly become more or less complex over time, but have a minimal level of complexity needed to sustain life. Some will become less than minimally complex and die out directly (in the real world, these may be obligate parasites whose host organism then becomes extinct or able to expel their parasites) ; some will randomly become more complex ; some of the more complex organisms will then randomly become less complex while others become randomly more complex.
Over time, you will have an increased range of complexity in your population, but the modal degree of complexity will likely remain where you started - near the degree of minimal complexity.
Just to be clear - I'm not disputing that the complexity of the most complex organisms has increased with time (Adams : "the wheel, New York, wars, and so on") ; I'm disputing that increasing complexity is a necessity for evolution to occur. (It's one of the less common lies that Muslim and Christian fundamentalist proselytes bring out to try to scare people away from thinking about evolution.) (Jewish fundamentalists may falsely deploy the same argument - I've not met such, yet, so can't speak for what lies they tell.)
No, it just means it's a likely candidate, but it's not the only candidate by a long shot.
Carbon isn't the only candidate by a shot of 91 to 1 (well, excluding radioactive elements, which bring their own problems, around 80 to 1) ; and carbon compounds aren't the only compounds by a factor of millions to 1 when you're talking about relatively small compounds.
[SNIP CHEMISTRY] A Carbon + Phosphorous entity has total mass of 12 + 31 = 43 amu ; a similar Silicon + Arsenic comparison weighs in at 28 + 75 = 103amu. So, in liquids at the same temperature, the Si/ As compounds, if all else were equal, would be moving at around 3/4 of the speed of the C/ P compounds. That would translate into the C/ P compounds having considerably higher reaction rates, and being favoured in mixed systems. That doesn't completely preclude Si or As becoming involved in biological systems, but it does weight the dice against them being dominant.
Maybe the disc has a buckle which moves up and down when the elephants step over the irregular back of the turtle.
Religious war coming up - between those who think the "ripple" ("buckle" makes me think of what keeps Angua's armour in place) moves turnwards and those who know that it is moving widdershins.
Sort of like the question of whether the present travelling wave of Himalayan mega-quakes is moving towards Kashmir, or has passed over it. Millions of people's lives (may) depend on the answer. Same question concerning the North Anatolian Transform - have you any plans to holiday there? In comparison, the Californian concerns are quite minor.
Slashdot Mirror
The progenitor star was (opinions vary) between approximately 9 and 12 solar masses, and of spectral type A, O, or B. Using standard approximations, this gives a lifetime for the star on the main sequence of 20 to 40 million years.
The most-recent 20-to-40 million years of this planet's history has seen mammals evolve into other mammals, bats develop sonar, whales stop paddling around near the shore and move into deep water, and various fructivore monkeys develop bipedalism and expand their brains. But the first 20-to-40 million years of this planet's history included ... well, lots of meteorites re-melting the planet's surface, and maybe a little bit of rainfall. Did life evolve? Well, it's not impossible, but most people think that it's pretty improbable - the oceans were still re-forming and being boiled off at irregular but frequent intervals by large impacts. A couple of hundred million years later and you're into a much more benign biogenesis environment, but that's 5 to ten times the time span that's available.
Of course, this analysis assumes that the "Crab Civilisation" were actually in orbit around the Crab progenitor star. They could conceivably have been just "in the area" and got whacked by this upstart star unrelated to their planet's formation. Which would have been pretty upsetting, but could only have been significant during a short interval in the species' history. While they're still trying to understand plumbing and the economies of scale of cities, they're only barely civilised ; a couple of millennia later and they should understand astrophysics well enough to recognise the problem in their skies and develop a mitigation strategy.
"Many deaths" != "species extinction"
No.
The council has to consider whether to provide a business with a license to sell "beers, wines and spirits" for consumption either on or off the premises (but not IIRC, both ; but you may be able to get both licenses for one premises). The council can decline to issue such a license for a variety of reasons, including "unfitness" of the license applicant or on advice from the police or on the basis of objections from the public. (My town has a fairly vigorous debate over whether to allow even more pubs in the town centre, but the current depression seems to be knocking that idea on the head.) Failure to award a license can be appealed, and a refusal must then be justified in public. Which some politicians dislike doing.
(A friend of mine is on the local council's licensing committee ; I've had too many sound waves on the subject wash over my ears.)
Relatively old joke concerning piloting :
Modern airliners are being designed to do away with most cockpit crew. Engineers and co-pilots will be gone, only leaving room for the autopilot, the pilot and a dog. The pilot's job is to feed the dog ; the dog's job is to bite the pilot if he tries to touch any of the controls.
Of course, being a joke, it ignores certain realities. No-one would seriously design a cockpit like this. They'd dispose of the idea of a cockpit altogether, leaving the trolly dollies with no-one to blow.
Wrong.
The greatest threat to your privacy is you yourself.
What do you mean by "our"?
The only government with any semblance of an intrinsic right to get access to Skype communications before any other government is of course the Luxembourg government.
Well, there's an obvious and easy way to make that impossible. And since there is such an obvious and easy way of preventing that from happening, that makes you culpable for any harm that does befall your children.
Great minds think alike - I found exactly the same artifact in approximately the same time of searching. I did know before-hand that there has been extensive seismic work in this Porcupine Basin - I read up on it for some work a couple of years ago in the Slyne and Erris basins. So, to pick an area that I don't know ... lessee ... Great Australian Bight? Oh, how does this look - 5013'5.57"S 114 2'57.42"E ; zoom to about 70km altitude ; two adjoining Atlantises (Atlantii?) ; see your Plato and raise you a DreamTime!
What is the problem with them?
It's pretty uncontroversial (i.e., you have to go out to the extremes where young-earth creationist lunatics cross-breed with gas-guzzlers to find claims of controversy, which is more due to some people's religious delusions than there actually being a controversy) that during the ice-age, global sea levels were relatively low for the good and sufficient reason that the ice which was on land used to be water that was in the ocean basins.
BTW, I take it that you're referring to La Grotte Cosquer. As the link image indicates, the paintings themselves are above sea-level (they'd have been pretty unlikely to survive and remain recognisable if they were below sea-level!) ; it's the cave entrance which is below sea-level. As my fellow troglodytes (spelunkers, if you're a transpozzian) say, "the cave imposes it's own entrance restrictions". While the surveying isn't readily available (I bet I could get hold of a survey, through cave-diving contacts, but I'd have to use my influence as a well-established caver, as an ex-cave diver, and as a professional geologist with a long-standing interest in archaeology. But as a responsible geologist, I won't even seek the data ; what I don't have, I can't leak.), I bet that there is an upper entrance. Hydrologically, there's pretty-much got to be an upper entrance - though it could well be presently plugged with debris, or collapsed and hydrologically inactive. While finding such an entrance has obvious interest, I'd be very hard put to justify even looking such an entrance because of the risk of damage to the paintings if a non-diving entrance were discovered.
Oh dear, I found more survey data than I really wanted. That was depressingly easy.
I don't recall having seen Ryan and Pittman (if I've recalled their names correctly) claiming that the Black Sea went dry. Mostly, they point to considerable shrinkage in area by losing the top couple of hundred metres of the water column. But basinal dessication? Don't recall them ever claiming that.
My guess it that you're conflating the well-established ice-age global fall in sea levels with the equally well-established local dessication of the Mediterranean basin in the Messinian Salinity Crisis (just Google it) at approximately 5 million years ago (before the present cycle of ice ages really got going properly).
For what it's worth - I spent most of last December drilling through a kilometer of Messinian-age salt deposits. It's very definitely non-trivial. If I'd been allowed to keep my notes (or if I'd been interested, to be honest), I'd be able to describe it in nauseating detail.
Mail the logs daily to the (in-)appropriate police chief. Let them pay the costs of storage and administration. (But make sure to keep your own mail logs, so that the onus falls onto them to explain why they've lost the logs.)
I know - they'll refuse to accept the. But you keep on sending them the data, and hope that a jury of YOUR peers will consider that you've reasonably discharged your obligations. In the event of "something" happening, they're going smash down your front door and take your computers anyway, so you'll need to make sure that the logs are on a suitably short rotation cycle.
"Suspension" as in "hang by the neck until dead"? I didn't notice - was the offending person in Texas, where the state murders minors and mental defectives, so neither of those defences are available.
OK, if it's a first offence, I might go for her spending a month in the gibbet cage and just hoping that no-one gets put in the cage above.
Taken as given : speed of light ; wavelength to energy-per-photon relationship ; that simple LEDs emit light of one specific colour (you need to choose your LED with due care and check it's emission wavelength) ; that (electrical) power is the product of voltage and power.
Needs : a darkroom ; ammeters and voltmeters, the better the better ; ripple-tank ; standard kit for demonstrating photo-electric effect.
Days one and two are interchangable.
Day 1 : Photo-electric effect ; show that photons deliver their energy as packets and are thus particles. If you've time, and an appropriate biology lab, you can also show that visual pigments require light of a certain minimum frequency to operate. That you can see red LEDs ties in with this minimum
Day 2 : Interference effects ; show how waves interfere with each other, including a demonstration of a double-slit experiment in a water tank. A more mathematical day's work than previously.
Day 3 : build your optical double-slit experiment using a red LED as a light source, and measuring the power it draws ; turn the power on the LED down until you can only just make out the interference pattern (record both voltage and current, just for completeness). Repeat for as many you have in your experimental group, and as many times as you can to build up a corpus of results to show the minimum power at which the interference pattern can be observed with a non-integrating detector (i.e. eyeball, Mk-I).
Finally, analysis. You have the power of the LED at which the interference pattern is still visible ; this gives you the number of photons per second forming the interference pattern. Speed of light gives you the spacing between photons while they're in flight (assuming it's not 'bursty'). At some point your students should realise that they are seeing the pattern of one photon interfering with another photon which has not yet left it's source. Wave-particle duality.
If you have time, you could indulge in looking at the experiment's problems. All the electrical power of the LED is assumed to go into the light, but if some goes into heating the LED, then that means that the light flux from the LED is lower, and the photons are spaced further apart. Maybe one photon has left the room before the one it interferes with forms at the LED? Is the LED "bursty"? Well, that's a whole set of other experiments. They're not going to fit into 3 days. Oh, actually, did you mean 3 working days, or 3 full days? And how many hours in your working day?
Oh, they do already. Perhaps you mean that they should be officially encouraged to play with fire from time to time.
Ruben Tube .... very interesting. In my day, my self-chosen physics project was trying to measure the velocity of combustion of gas-air mixtures using the passage of the ionisation front in the flame. I never got my equipment design to work, but I had a lot of fun along the way. Various gratuitous explosions and high-voltage generators. GRIN.
Actually, I don't think it would have helped much in my project. I don't know. But it sure looks a cool experiment.
Plainly the XKCD author hasn't heard of Go, or at least doesn't realise that the universe is a subset of Go, not the other way around.
Sounds pretty cool. Unnecessarily violent - which is it's point.
That prompts me to go to the local granite scrap yard (several thousand cubic metres of disused quarry), get some suitably-sized chunks, and repeat the experiment using cylindrical holes, water, epoxy resin and the butt end of a drill bit. Together with a normal freezer, I think that would be sufficient to demonstrate "freeze-thaw action", which is very important in the process of turning highlands into seabeds. Not as exciting, but relevant to my work.
Broadly true, but unnecessarily pessimistic ...
Bear in mind that when I was 20, the number of known extra-solar planetary systems was zero, and that when I was 40, the corresponding number was several dozen, and it's now in the hundreds, then to get to 45,000 examined systems (and therefore an =evens= chance of finding one with a civilisation on it) is going to take between a couple of centuries and a couple of millennia. Still a steep requirement, but since it's only a couple of millennia since our ancestors discovered the benefits of cities ...
Why do you limit yourself to "nearby", and to "earth-like", and to "worlds". Long before we have any conceivable prospect of interstellar travel (or even of significant interplanetary travel), our engineers are going to have to solve the problems of travelling in closed ecologies with high-power, high-radiation, energy sources (barring the discovery of Unobtanium and it's burning to make Unobtanium Impossibilide for fuel the Warp Drive). At which point, living off-planet in centripetal pseudo-gravity fields, digging organic matter out of cometary nuclii and structural materials out of asteroids, all become less of a constraint than finding a "Goldilocks" planet would be.
by the time that you've spent 3 generations sending ships out to the Kuiper Belt to assemble the reaction mass needed for your flight to Alpha Centauri, and another few tens of generations flying to get there, are you really going to give that much of a damn if all that is there to greet you is another cometary system and a bunch of asteroids? Nope, you either settle down amongst them to continue living the way your last 15 generations of ancestors lived (in a ship), or you don't bother to slow down more than necessary to pick up any materials you need, and move right on down the line.
Where are they? I think that they put Pluto in it's weird orbit as a marker, and have put the directions to "Glactic Central" in a 1m-diameter sphere of pure lithium (not chosen at random) in orbit around Pluto. All we have to do is go and find the instructions. Oh, we'll need to develop some technologies along the way, but nothing terribly exotic.
Deserving of including an emoticon that indicates "this author is being funny, not serious"?
Hmmm, I did mention size ("microbes"), but as I was meaning it as a shorthand for an ill-defined "genetic complexity space" as you're thinking. I would have been more accurate to say that most life on the planet is (probably) still prokaryotic. If you count mitochondria and chloroplasts and the more-recently described methane- and hydrogen- generating organelles of certain organisms, and if you swallow Margulis' assertion that ER/ myosin-actin fibrils, centrioles and intra-cellular transport networks are degraded spirochaetes, then you can probably take out the "(probably)" in the previous sentence.
On SlashDot, you never know the level of the person you're corresponding with. For all I know, you might actually be Margulis!
True ; I refer the honourable gentleperson to the comments I made a few moments ago.
That was implicit in the general discussion, but barely perceivable in the actual article (typical SlashDot ; RTFA is so uncool!). It would take a vastly more confident chemist and/ or biochemist than I am to examine the mechanisms of a novel biochemistry and to deduce it's limits. Bearing in mind that while we're confident of our understanding of basic protein synthetic pathways, we don't really have a clear understanding of how our own genomes control gene activation and/ or suppression ...
It took the best part of a quarter-century from Crick and Watson's discovery of the basic structure of our biochemistry before Ohno's concept of "alternative reading frames" was described and demonstrated ; the consequences of this are still being worked out, along with considerably more esoteric ways of using genomes. That should give serious pause for thought before declaring that "X" other biochemistry "does not allow for very much diversity".
Ummm, actually I do find it quite hard to imagine such a situation. The minimal complexity of an organism is quite substantial - 9000-odd genes is the sort of size Venter et al are looking at? - so if you're going to have a successful organism of ANY biochemistry, then you're going to have to be dealing with quite significant chunks of genetic material (be it DNA, or patterns on the edges of spiral defects in clay minerals [example only, don't take it seriously]. At that point, it gets hard for me to conceive of a system that isn't going to be prone to re-reading the same data block twice, or writing the same block twice. At which point you're in the territory of gene duplication, which is certainly a mechanism for generation of new functions, followed by new diversity.
Nope, you're going to have to work a lot harder to convince me that any genetic system has an inherent upper limit on diversity, where the biochemistry continues to work. As has been pointed out, DNA/ RNA/ amino acid biochemistry can work well enough to survive low pH and high temperature (at least, for some of it's life cycle), and to endure low temperatures for protracted periods of stasis. I don't think that it's going to work at a bright-orange heat though - the RNA would fatally dehydrate. And I wonder what's the upper limit of pH that our co-b
Trying to decipher what you're on about ...
Could you be mis-remembering the occasional oceanic poisonings off the coast of Namibia, due to blooms of a particularly large microbe (up to a mm in diameter) which contains large vesicles that it dumps sulphide wastes into. In the latter stages of a bloom, the sea goes mostly anoxic, and the abundance of sulphide leads to the release of significant hydrogen sulphide.
It's not particularly deep in the areas I'm thinking of. And the blooming involves the organisms moving up and down the water column.
Diatoms in particular are perfectly normal organisms that form silica skeletons. They largely control the silica content of the oceans.
What do you mean by "semi-liquid rocks"? As a geologist, I read that to mean rocks with a noticeable degree of plasticity with an implication of this being due to heat. Depending on composition, that's going to be at least a dull red heat for common rock compositions (granite/ andesite/ trachyte), maybe coming down to the sub-red temperatures in the high 300s C where there's a lot of water and possibly a lot of unusual chemistry (carbonatite volcanos, for example ; these are rare). Steel or aluminium might start to soften at 250 C, but only very, very uncommon rocks.
In contrast, the highest temperature that I've heard of proteins surviving (note - not necessarily working, but resisting being denatured) has been in the mid-170s C, and the highest temperature for whole organisms working in the high-120s C. Higher temperatures are recorded in "black smoker" environments, but these areas have very very steep (and mobile) temperature gradients so their organisms almost certainly don't get these maximum temperatures consistently.
I'd also query the comment about "extreme cold" ; certainly plenty of organisms *survive* extreme cold, but that's a different thing from being active in extreme cold. For example - the lichens reported from Anarctica no doubt survive temperatures down to -50C and lower ; but do they actually live and grow at these temperatures, or are they in stasis and only start to grow when (for example) sunlight warms their rocks to within a couple of degrees of freezing point? A penguin lives comfortably at 20-odd C while the feathers of its head can be 70C colder.
Where did you get that idea? I see no grounds for requiring increasing complexity for evolution, and indeed, since the overwhelming majority of life on this planet is microbial, as it always has been, there is fair evidence against such a claim.
Consider a range of lifeforms which randomly become more or less complex over time, but have a minimal level of complexity needed to sustain life. Some will become less than minimally complex and die out directly (in the real world, these may be obligate parasites whose host organism then becomes extinct or able to expel their parasites) ; some will randomly become more complex ; some of the more complex organisms will then randomly become less complex while others become randomly more complex.
Over time, you will have an increased range of complexity in your population, but the modal degree of complexity will likely remain where you started - near the degree of minimal complexity.
Just to be clear - I'm not disputing that the complexity of the most complex organisms has increased with time (Adams : "the wheel, New York, wars, and so on") ; I'm disputing that increasing complexity is a necessity for evolution to occur. (It's one of the less common lies that Muslim and Christian fundamentalist proselytes bring out to try to scare people away from thinking about evolution.)
(Jewish fundamentalists may falsely deploy the same argument - I've not met such, yet, so can't speak for what lies they tell.)
Carbon isn't the only candidate by a shot of 91 to 1 (well, excluding radioactive elements, which bring their own problems, around 80 to 1) ; and carbon compounds aren't the only compounds by a factor of millions to 1 when you're talking about relatively small compounds.
[SNIP CHEMISTRY]
A Carbon + Phosphorous entity has total mass of 12 + 31 = 43 amu ; a similar Silicon + Arsenic comparison weighs in at 28 + 75 = 103amu. So, in liquids at the same temperature, the Si/ As compounds, if all else were equal, would be moving at around 3/4 of the speed of the C/ P compounds. That would translate into the C/ P compounds having considerably higher reaction rates, and being favoured in mixed systems.
That doesn't completely preclude Si or As becoming involved in biological systems, but it does weight the dice against them being dominant.
Religious war coming up - between those who think the "ripple" ("buckle" makes me think of what keeps Angua's armour in place) moves turnwards and those who know that it is moving widdershins.
Sort of like the question of whether the present travelling wave of Himalayan mega-quakes is moving towards Kashmir, or has passed over it. Millions of people's lives (may) depend on the answer. Same question concerning the North Anatolian Transform - have you any plans to holiday there? In comparison, the Californian concerns are quite minor.