1121
Question of the Week / Re: QotW - 16.04.05 - Can two planets share the same orbit?
« on: 07/03/2016 13:31:00 »
Yes
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1122
Physics, Astronomy & Cosmology / Re: What is spin.
« on: 21/02/2016 00:37:23 »
Alas, spin is itself an analogy. Subatomic particles behave as if they are spinning tops, so protons neutrons and electrons have a magnetic moment aligned with the spin vector and the Pauli exclusion principle, that no two electrons can occupy the same quantum state, is obeyed if electrons have spin quantum numbers of ±½.
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1123
Physics, Astronomy & Cosmology / Re: What radius to a human observer does light fail to give an observation?
« on: 15/02/2016 19:11:14 »Can you or anybody please describe in your own words what (A) observes of (B) as (B) moves way?
B subtends a smaller angle at A as he moves away. At some distance the angle will be less than the angular resolution of A's equipment so A will not be able to determine the size or shape of B (by direct observation, but there are indirect methods of estimating the mass of B at any distance) but if he is emitting or reflecting light he will always appear at least as a point source of photons.
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1124
Physics, Astronomy & Cosmology / Re: What radius to a human observer does light fail to give an observation?
« on: 12/02/2016 16:19:44 »
"Vanishing point" is an invention of artists, architects and cartographers. It is also a classic road trip film - to my mind the best ever. It has no meaning in physics.
The human eye can probably detect a single photon, though in practice we could not distinguish it from the background "noise" in our brains, so in principle there is no limit to the distance at which you could detect a single source in an otherwise empty universe, provided you can wait long enough.
As for your second point, it's nothing to do with quantum weirdness. On a really clear, dry night you can shine a laser into the sky and not see the beam if it's pointing away from you.
The human eye can probably detect a single photon, though in practice we could not distinguish it from the background "noise" in our brains, so in principle there is no limit to the distance at which you could detect a single source in an otherwise empty universe, provided you can wait long enough.
As for your second point, it's nothing to do with quantum weirdness. On a really clear, dry night you can shine a laser into the sky and not see the beam if it's pointing away from you.
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1125
Physics, Astronomy & Cosmology / Re: Does pi stand for "perfectly incomplete" ?
« on: 09/02/2016 22:55:06 »
π is much more important than its feature in euclidean geometry. It turns up in spherical geometry, whcih is the basis for terrestrial navigation, and the equation eiπ = -1 is fundamental to a whole swathe of calculus including the reconstruction of 3D images from magnetic resonance signals, and bandwidth compression algorithms.
You can indeed calculate π from an infininte series but, as with the one quoted by lightarrow, since the series is multiplied by a constant, that doesn't define π, which is a fundamental constant. The series derives from the properties of π, not the other way round. unlike e, which is indeed defined by a series and derives its properties from that series.
You can indeed calculate π from an infininte series but, as with the one quoted by lightarrow, since the series is multiplied by a constant, that doesn't define π, which is a fundamental constant. The series derives from the properties of π, not the other way round. unlike e, which is indeed defined by a series and derives its properties from that series.
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1126
Radio Show & Podcast Feedback / Re: Is Zika virus a public health emergency?
« on: 08/02/2016 22:40:59 »
Seems like a scam and an outrageous coverup to me.
The recent incidence of microcephaly in Brazil is about 100 times greater than the reported number of cases associated with Zika infection. The real problem seems to stem from the government-mandated vaccination of pregnant women, an off-label use of a vaccine designed and licensed elsewere for 10 - 12 year-old kids only. Why 10 to 12? Presumably because it could harm younger kids and in the opinion of the manufacturers and the FDA, should not be administered where there is a likelihood of the recipient being pregnant.
Zika infection is generally considered fairly insignificant and is by no means new.
So the question is who was bribed into mandating it, and whether any official heads will roll (of course not!). Not a medical problem, just another job for the accountants and police to investigate and the politicians to sweep under the carpet.
The recent incidence of microcephaly in Brazil is about 100 times greater than the reported number of cases associated with Zika infection. The real problem seems to stem from the government-mandated vaccination of pregnant women, an off-label use of a vaccine designed and licensed elsewere for 10 - 12 year-old kids only. Why 10 to 12? Presumably because it could harm younger kids and in the opinion of the manufacturers and the FDA, should not be administered where there is a likelihood of the recipient being pregnant.
Zika infection is generally considered fairly insignificant and is by no means new.
So the question is who was bribed into mandating it, and whether any official heads will roll (of course not!). Not a medical problem, just another job for the accountants and police to investigate and the politicians to sweep under the carpet.
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1127
New Theories / Re: Is distance an absolute invariant?
« on: 07/02/2016 00:36:25 »Is distance an invariant, is a length of a distance invariant?
This was answered way back on 29 January, Reply #1.
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1128
Physics, Astronomy & Cosmology / Re: Why did everything look green?
« on: 21/01/2016 11:19:18 »
Probably "colour fatigue" from travelling in a predominantly red environment.
The brain has a subtle colour balance mechanism that eventually makes skin look the same in either natural or artificial light, despite the ambient color temperature being very different. Colour transparency film used to be made (possibly still is) in different varieties for indoor and outdoor use because "true" rendition showed swans to be blue if you photographed them on a sunny day and looked at the slide indoors.
I think the brain looks for the nearest it can find to white in any scene, then adjusts its overall colour mapping to make it white. If the ambient light contains a lot of red and blue (as it does in the Grand Canyon and the Australian outback, especially on a cloudy day) the brain "adds green" to make the whitest thing look white. Now if you introduce a genuine white, and snow is the best there is, that will appear green until the brain readjusts.
The phenomenon applies to all colours and is important when designing instrument and control panels. I think the readjustment is particularly slow where the ambient is green-deficient. Our eyes are most sensitive to green light and don't perform as well when it is absent. I find driving in Australia very tiring because the outback rocks are red and deep blue with little or no green, so my eyes are continually changing focus to correct for the chromatic aberration and the scenery always looks fuzzy.
After you have been in the snow field, or even seen recognisable patches of snow for a while, your brain will have recalibrated to true white and your skin would appear normal again.
The brain has a subtle colour balance mechanism that eventually makes skin look the same in either natural or artificial light, despite the ambient color temperature being very different. Colour transparency film used to be made (possibly still is) in different varieties for indoor and outdoor use because "true" rendition showed swans to be blue if you photographed them on a sunny day and looked at the slide indoors.
I think the brain looks for the nearest it can find to white in any scene, then adjusts its overall colour mapping to make it white. If the ambient light contains a lot of red and blue (as it does in the Grand Canyon and the Australian outback, especially on a cloudy day) the brain "adds green" to make the whitest thing look white. Now if you introduce a genuine white, and snow is the best there is, that will appear green until the brain readjusts.
The phenomenon applies to all colours and is important when designing instrument and control panels. I think the readjustment is particularly slow where the ambient is green-deficient. Our eyes are most sensitive to green light and don't perform as well when it is absent. I find driving in Australia very tiring because the outback rocks are red and deep blue with little or no green, so my eyes are continually changing focus to correct for the chromatic aberration and the scenery always looks fuzzy.
After you have been in the snow field, or even seen recognisable patches of snow for a while, your brain will have recalibrated to true white and your skin would appear normal again.
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1129
Physiology & Medicine / Re: Why does my daughter weigh more when she's asleep?
« on: 20/01/2016 21:11:52 »
The term "dead weight" originated from observation. Most adults can carry another conscious adult of the same build, but it takes four people to lift a patient off an operating table, and a dead dog is a lot more difficult to move than a live one.
I think conscious animals tense their muscles and move their limbs when lifted, so as to keep the center of mass above the lifting point(s) and distribute the torque moments evenly between them, making it easier for the lifter to control the load.
I think conscious animals tense their muscles and move their limbs when lifted, so as to keep the center of mass above the lifting point(s) and distribute the torque moments evenly between them, making it easier for the lifter to control the load.
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1130
Cells, Microbes & Viruses / Re: Do GMO's have inbuilt resistance?
« on: 20/01/2016 20:58:39 »
Here's the bad side of the good side!
Suppose I market a GM wheat that consistently produces say 20% more yield than any natural variety at no extra cost to the farmer. Now suppose you are a farmer. You have to sell your wheat in a market where your next-door neighbor is using my seed, so he can undercut your price by 20% every year. 20% is a big deal in this business, and the absolute consistency of my product means that he can afford to increase his acreage of wheat, knowing that he will get a good, cheap crop every year.
So eventually you will either go out of business, or have to use my cheaper, more reliable material. And the same will apply to every farmer in the area, and eventually in the world. The Good Thing is that there will always be enough wheat, at a consistent price, and everyone is happy.
Except that my GM wheat is sterile (because the anti-GM lobby insists that it must be!) so you can't re-seed from your own crop. Every farmer has to buy my seed or end up with an unreliable crop that he can't sell at a profit.
So within about 20 years, I have complete control of the world market for wheat. I can charge what I like for the seed, or even refuse to supply it altogether to countries that don't espouse Sharia law, or farmers whose name begins with R.
If you think this can't happen, look at the political influence of Saudi Arabian oil, or the world's economic dependence on Chinese manufacturing: a small but consistent price advantage can turn into a monopoly within a generation, and that is a Bad Thing, especially where food is concerned.
Suppose I market a GM wheat that consistently produces say 20% more yield than any natural variety at no extra cost to the farmer. Now suppose you are a farmer. You have to sell your wheat in a market where your next-door neighbor is using my seed, so he can undercut your price by 20% every year. 20% is a big deal in this business, and the absolute consistency of my product means that he can afford to increase his acreage of wheat, knowing that he will get a good, cheap crop every year.
So eventually you will either go out of business, or have to use my cheaper, more reliable material. And the same will apply to every farmer in the area, and eventually in the world. The Good Thing is that there will always be enough wheat, at a consistent price, and everyone is happy.
Except that my GM wheat is sterile (because the anti-GM lobby insists that it must be!) so you can't re-seed from your own crop. Every farmer has to buy my seed or end up with an unreliable crop that he can't sell at a profit.
So within about 20 years, I have complete control of the world market for wheat. I can charge what I like for the seed, or even refuse to supply it altogether to countries that don't espouse Sharia law, or farmers whose name begins with R.
If you think this can't happen, look at the political influence of Saudi Arabian oil, or the world's economic dependence on Chinese manufacturing: a small but consistent price advantage can turn into a monopoly within a generation, and that is a Bad Thing, especially where food is concerned.
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1131
The Environment / Re: Anti-desertification: can we regenerate deserts?
« on: 22/12/2015 23:45:52 »
Pretty soon, half of the world will realise the religion of any sort is a Bad Thing, and the perverts who influence the young by threats of bogeymen or promises of infinte sexual pleasure in the afterlife will be discredited for ever, in favour of rational thought. Until then, I guess things will continue to get worse, with good christians murdering doctors or buggering choirboys, and good muslims murdering everyone else. But one day, Joe Public will stop and say "why do we tolerate this fairytale bullshit?" and take arms against superstition and juju. Either that, or we will all die a horrible death from overcrowding or failure to submit to whatever bizarre rituals the last bent mullah demands of us.
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1132
Physiology & Medicine / Re: Is synthetic biology a eugenic philosophy?
« on: 16/12/2015 23:44:26 »
We spend a lot of time and effort trying to produce "better" crops and animals, and a fair bit of time seeking out a mate who will give us the sort of offspring we would like to have. Being able to do these things precisely, first time, and without havng to kill off lots of sentient beings that don't meet our specification, would clearly be a Good Thing. Problem is that, not having previously had access to molecular biology, human eugenics has always been seen as forcing people to breed or not to breed according to some third party specification, which is a Bad Thing.
Euthanasia: good. The hallmark of civilisation is that you can choose how and when you die. Humans should be accorded the same respect and dignity as the law requires us to give to other suffering animals.
Abortion: good. Or at least not bad. Every baby a wanted baby. About 30% of human fetuses abort spontaneously anyway. It would be preferable not to create an unwanted fetus in the first place, and there really seems to be no excuse for doing so, but mistakes happen and the best contraception isn't 100% effective yet. Any rational person can see the difference between a born baby and a fetus: aborting a potentially handicapped fetus does not equate to denigrating handicapped children and adults.
Cloning: pointless as far as humans are concerned - we aren't short of people, the occasional twin or triplet is fun, but unlimited copies of me, whilst clearly desirable for world peace, the advance of science and music, and the ultimate sexual satisfaction of all women, would leave all other men redundant and unable to find mates, which would be a Bad Thing. It's a Good Thing for potatoes and bananas, however.
The law is fairly clear on the responsibility for the behaviour of your dog and your child, and for the spreading of weeds, cattle and vermin from your land. I don't see any difference if you made the offending article in a test tube, but anything considered human would be held increasingly liable for its own actions as it grew up.
Euthanasia: good. The hallmark of civilisation is that you can choose how and when you die. Humans should be accorded the same respect and dignity as the law requires us to give to other suffering animals.
Abortion: good. Or at least not bad. Every baby a wanted baby. About 30% of human fetuses abort spontaneously anyway. It would be preferable not to create an unwanted fetus in the first place, and there really seems to be no excuse for doing so, but mistakes happen and the best contraception isn't 100% effective yet. Any rational person can see the difference between a born baby and a fetus: aborting a potentially handicapped fetus does not equate to denigrating handicapped children and adults.
Cloning: pointless as far as humans are concerned - we aren't short of people, the occasional twin or triplet is fun, but unlimited copies of me, whilst clearly desirable for world peace, the advance of science and music, and the ultimate sexual satisfaction of all women, would leave all other men redundant and unable to find mates, which would be a Bad Thing. It's a Good Thing for potatoes and bananas, however.
The law is fairly clear on the responsibility for the behaviour of your dog and your child, and for the spreading of weeds, cattle and vermin from your land. I don't see any difference if you made the offending article in a test tube, but anything considered human would be held increasingly liable for its own actions as it grew up.
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1133
Physiology & Medicine / Re: why don't hearing aids work better
« on: 12/12/2015 23:58:19 »
Many mechanisms at work here.
We know that animals locate the source of a sound from the phase difference between the pressure waves reaching the ears. This is going to be larger for medium frequencies (500 Hz - 5 kHz) than for bass notes but above 5 kHz the wavelength is much less than the width of the head so you can get "aliasing", with multiple solutions to the phase-position equation. However it happens that the key elements of speech are in the 500 - 5000 Hz range, so we can train ourselves to discriminate the speech of the person we are looking at, from ambient noise. The intelligent binaural hearing aids Evan mentioned, presumably use a similar processing algorithm to improve directionality.
The ear itself also has a directional "dispersal" characteristic that modifies the perceived spectrum so that even a single ear provides some directional clues. A single hearing aid with a fairly nondirectional microphone can't inject all the information needed to locate sound sources as accurately as two functional ears, and a single cochlear implant probably won't generate useful phase information at all.
There is also a strong predictive and trigger element in speech recognition. I often fly with a very experienced pilot who depends on lipreading on the ground, but even in heavy radio traffic he picks out every call for our plane because he is acutely sensitive to the callsign that precedes each message, and, being aware of our situation in time, space and proximity to other aircraft, also has a high degree of anticipation. This can help in a formal situation, in an office or conference room, but clearly isn't much use on the classic "cocktail party" environment, unless you have latched on to one or two key words.
The inconspicuity question is a good one, and I think fashions may change. Kids used to listen to bulky Walkman tape players with tiny insert earpieces, but current fashion seems to be to match a postage-stamp sized ipod with aviator-style headphones that announce "I am cool". Binaural hearing aids could surely be built into spectacles so even those with perfect eyesight could wear plain lenses in a frame that comfprtably carries a bigger battery (hence more signal processing power) and a better microphone.
We know that animals locate the source of a sound from the phase difference between the pressure waves reaching the ears. This is going to be larger for medium frequencies (500 Hz - 5 kHz) than for bass notes but above 5 kHz the wavelength is much less than the width of the head so you can get "aliasing", with multiple solutions to the phase-position equation. However it happens that the key elements of speech are in the 500 - 5000 Hz range, so we can train ourselves to discriminate the speech of the person we are looking at, from ambient noise. The intelligent binaural hearing aids Evan mentioned, presumably use a similar processing algorithm to improve directionality.
The ear itself also has a directional "dispersal" characteristic that modifies the perceived spectrum so that even a single ear provides some directional clues. A single hearing aid with a fairly nondirectional microphone can't inject all the information needed to locate sound sources as accurately as two functional ears, and a single cochlear implant probably won't generate useful phase information at all.
There is also a strong predictive and trigger element in speech recognition. I often fly with a very experienced pilot who depends on lipreading on the ground, but even in heavy radio traffic he picks out every call for our plane because he is acutely sensitive to the callsign that precedes each message, and, being aware of our situation in time, space and proximity to other aircraft, also has a high degree of anticipation. This can help in a formal situation, in an office or conference room, but clearly isn't much use on the classic "cocktail party" environment, unless you have latched on to one or two key words.
The inconspicuity question is a good one, and I think fashions may change. Kids used to listen to bulky Walkman tape players with tiny insert earpieces, but current fashion seems to be to match a postage-stamp sized ipod with aviator-style headphones that announce "I am cool". Binaural hearing aids could surely be built into spectacles so even those with perfect eyesight could wear plain lenses in a frame that comfprtably carries a bigger battery (hence more signal processing power) and a better microphone.
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1134
Plant Sciences, Zoology & Evolution / Re: Are white eggs no longer readily available in UK supermarkets?
« on: 11/12/2015 21:20:47 »
Very much a matter of fashion. It's almost impossible to buy brown eggs in the USA, or white eggs in the UK, from a supermarket. On the other hand, people who are determined to differentiate themselves by their food purchases can find brown eggs in the USA and vice versa by asking those thin, pallid people who tend to work in "health food" shops, who usually know a rogue smallholder with "minority" chickens. And I can't imagine any francophone giving a tuppeny damn about the color of the shell, as long as the albumen is fresh enough to make a decent meringue or ile flottante. All of which probably says something about Canadian nutritional sociology!
My guess is that any unfashionable eggs end up as feedstock for bakeries, but selective breeding has pretty much eliminated chance from factory farming.
My guess is that any unfashionable eggs end up as feedstock for bakeries, but selective breeding has pretty much eliminated chance from factory farming.
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1135
Physics, Astronomy & Cosmology / Re: What would happen if you switched on a laser pointer in space?
« on: 08/12/2015 14:40:09 »
Light has momentum, and momentum is conserved, so the pointer would move backwards. You can indeed measure "radiation pressure" when a light beam strikes an object.
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1136
The Environment / Re: What should India do about its methane-excreting cows to stop global warming?
« on: 07/12/2015 10:39:30 »
One for the dinner party: who caused more harm, Dr John Snow or Sir Joseph Bazalgette?
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1137
General Science / Re: How radioactive are people?
« on: 06/12/2015 16:54:40 »
For what it's worth, a fetus receives about 1 millisievert of radiation dose from maternal potassium. This is equal to the annual dose limit for a member of the public from radiation arising from "work practices", and the dose limit to a fetus from its mother's work.
Just for fun, I use a package of "Lo-Salt" (other brands are available) salt substitute to demonstrate radioactivity to my lecture classes. It sends my contamination monitor into "alarm" condition every time. So much for government health warnings.
Just for fun, I use a package of "Lo-Salt" (other brands are available) salt substitute to demonstrate radioactivity to my lecture classes. It sends my contamination monitor into "alarm" condition every time. So much for government health warnings.
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1138
Physics, Astronomy & Cosmology / Re: What would happen if I connected a pipe from the atmosphere into space?
« on: 05/12/2015 23:34:45 »
Absolutely nothing will happen. The atmosphere already extends from the ground to the edge of space, by defintion of "edge of space".
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1139
General Science / Re: Big Bang
« on: 02/12/2015 16:13:48 »
Either nothing, or the Big Implosion. But since either concept contradicts our understanding of "happen", you have opened up quite a can of worms.
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1140
Radio Show & Podcast Feedback / Re: Do fish really have a 3 second memory?
« on: 01/12/2015 19:10:32 »
Considering that eels and salmon can return to their birthplace after spending years in the sea, it would be remarkable indeed if their cousins had no memory. And anyone who has fished for big carp with a rod and line will know that they can display as much cunning and sensitivity as a dog.
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