Wikipedia:Reference desk/Archives/Science/2011 November 27

= November 27 =

Radio distance
I apologize in advance. I think I've read the answer to this question before but when I searched it I found nothing. Now to the question.

Say that humans wanted to communicate with extraterrestrials, how close would they have to be to receive the message before the radio signal weakens to the point it can't be heard? Thanks, and sorry again. 64.229.180.189 (talk) 04:42, 27 November 2011 (UTC)


 * No simple answer to that. It depends a lot on the bandwidth, power transmitted and sensitivity of the receiving equipment. Shannon–Hartley theorem demonstrates that the narrower bandwidth, the further the signal can be picked up for any given signal strength. That’s why  such  puny transmitters on say the Voyager deep-space probes can still be picked up. --Aspro (talk) 09:47, 27 November 2011 (UTC)


 * Is it reasonable to ask how far out an Arecibo like observatory could observe the Arecibo message? Its target was 25,000 light years away; were they counting on a much more sensitive receiver then they themselves possessed? -- 203.82.66.204 (talk) 10:16, 27 November 2011 (UTC)
 * That's a very reasonable question; the formula to calculate it is a standard formula. I would use the RADAR equation, because I consider two-way communication a requirement ( ...but this hides a lot of important details of the alien technology in the $$\sigma$$ - I figure, it's just as well to assume it's a constant, because the total available information about $\sigma$ is zero bits ); but if you only care about the outbound signal, you can use half of the RADAR equation.  (Equivalently, you can use the calculations for apparent magnitude, by calculating the signal flux on the receiver's end, using values from the effective radiated power on the transmitter's end).  The exact numbers to "plug and chug" in this case are not trivial - you have to dig through detailed specification sheets to find the exact numbers you want: power per band, and antenna gain.  You can try to estimate these values from the general specifications of the dish and the supporting electronics; or you can try to derive them from first-principles of optics and antenna thermodynamics.  Ultimately, the antenna gain is limited by the angular resolution of the dish; modern technical tricks like synthetic aperture won't work on the Arecibo message (because it did not coherently repeat its transmission for a long time).
 * You might also want to characterize the noisy channel the signal propagates through - in other words, instead of naively assuming that Interstellar Space is a perfect vacuum, you can account for the signal degradation due to weird effects (high energy particle interactions, occasional collisions with a stray hydrogen atom, and so on).
 * After characterizing the signal's size and shape and power for the receiving end, it's a fairly trivial calculation to estimate the receiver required to discern the signal from the background noise.
 * It is my opinion that the creators of the message did not sincerely believe that this instance of the message would ever be received; the idea was to encourage the effort. If the signal were intended to be received, I think its creators would have sent a much simpler message that was coherently repeated much more often.  I am not alone in this opinion: even Carl Sagan, who helped craft the message, wrote: "The Arecibo message was clearly not intended as a serious attempt at interstellar communication, but rather as an indication of the remarkable advances in terrestrial radio technology."  Nimur (talk) 15:46, 27 November 2011 (UTC)

Our SETI article and accompanying graph might help. It states that the Phoenix search "was sensitive enough to pick up transmitters with 1 GW EIRP to a distance of about 200 light years." Detection range should be considerably improved for a directed transmission. (E="Equivalent") Confusingly, the graph's 1 GW EIRP signal line appears to intersect the TS line ("typical sensitivity achieved by a targeted search such as Phoenix") at closer to 20 ly than 200 ly. -- 203.82.66.204 (talk) 01:00, 28 November 2011 (UTC)

With its 70 dBi gain at 2.38 GHz, Arecibo has an EIRP of 10 TW (1013W). Extrapolating its power line and the TS reception line, they should intersect at about 1800 ly, which is probably a reasonable guesstimate of the effective transmission distance using our current equipment. On the other hand, a 10 TW signal will have 100 times the range of a 1 GW signal, so from the Project Phoenix figures, the range would be 20,000 ly (which is nearly the range of the the Arecibo message targets). -- 203.82.66.204 (talk) 01:43, 28 November 2011 (UTC)


 * I believe that the discrepancy is due to the dated "SS" and "TS" signal flux values in the graph which comes from chapter 5 of NASA's 1981 publication Life in the Universe.  If, in the 15 years leading to Project Pheonix, targeted search receiver sensitivity increased by a factor of 100, then the range would have increased by a factor of 10.  Now, another 10 to 15 years later, we should be able to do even better if we wanted to, so communication (and not just detection) over a range of 20,000 ly should be possible.  At such a range, latency may be a problem. -- 203.82.66.204 (talk) 11:25, 28 November 2011 (UTC)

Can "Ice Giants" become comets just as Kuiper-belt objects can?
Hello, again! I have a question about Uranus and Neptune—the former "gas giants," now reclassified as "ice giants."

As far as I'm aware, trans-Neptunian bodies such as Pluto, Eris, and Sedna (if they somehow found themselves closer to the Sun) would probably grow tails and become comets. I also heard, back in the 1980s, that Chiron, the first-discovered, trans-Jovian asteroid (not to be confused with Charon, Pluto's largest-known satellite) is sometimes seen with a coma as well.

Since most—if not all—of these objects are mostly ice by volume, I cannot help but wonder how the similar (albeit much larger) planets Uranus and Neptune would react if they were closer to the Sun. Since both those worlds are largely ice by volume, would they become gigantic comets as well?

Pine (talk) 06:38, 27 November 2011 (UTC)


 * I don't think so, because their gravity field is so huge that it will utterly overcome the miniscule effect of solar radiation pressure and thus prevent the gas from forming a tail behind the planet. 67.169.177.176 (talk) 06:58, 27 November 2011 (UTC)
 * Wouldn't their magnetic fields protect them. Gravitational hold of upper atmosphere would reduce if they became less dense due to heating by increased stellar radiation. SkyMachine (talk) 07:12, 27 November 2011 (UTC)
 * Does Earth have a tail? Does Venus?  And their gravity is a lot less than that of Uranus or Neptune.  So if neither Earth nor Venus have any kind of appreciable tail, then ain't it logical to conclude that Uranus and Neptune, with their much bigger gravity, won't have a tail even if placed in the same orbit as Venus? 67.169.177.176 (talk) 08:17, 27 November 2011 (UTC)
 * Surface gravity of Uranus is only 0.886 g (less than Earth's), Neptune's is 1.14 g. Earth has plasma tail resulting from its magnetosphere. SkyMachine (talk) 08:32, 27 November 2011 (UTC)
 * Wikipedia says "some astronomers are starting to refer to Uranus and Neptune as "ice giants"..." (Gas giant), not as definitive about it as the OP is. Rmhermen (talk) 15:24, 27 November 2011 (UTC)


 * The article Gas giant explains that "ice", "rock", and "gas" have nothing to do with the actual phase of matter and more to do with composition: "methane/water/ammonia", "silica", and "hydrogen/helium", respectively. Every planet gains and loses mass by particles colliding and solar wind ripping off bits of atmosphere, so one might say that there is a "tail" to every planet. But that's wrong: as comets don't have an atmosphere or gravity to hold one in, all the melting crud gets blown away by the sun as it comes near making a spectacular tail. For a planet-sized object, gravity would keep any such effects to a minuscule level, even more so for the Ice Giants given their mass. SamuelRiv (talk) 20:31, 27 November 2011 (UTC)

Capacity of brain
If the human brain was somehow reduced to a computer, what would its configurations be? in terms of total size (in bytes or Megabytes), and processor speed, RAM etc? — Preceding unsigned comment added by 117.192.205.86 (talk) 07:03, 27 November 2011 (UTC)


 * One thing for sure, it would have much more RAM and processor speed than any supercomputer ever built. (Especially if you're talking about the brain of a genius like Einstein.)  :-)  67.169.177.176 (talk) 08:20, 27 November 2011 (UTC)


 * Actually, I think we might lose on speed. Computers can certainly do math calcs far faster than our brains.  Of course, our brains are also doing many other things at once, like visual processing and running our body, but this is also true of most computers, especially time-share mainframes.  As for total capacity, computers are catching up quickly there, and may soon surpass us.  Where computers can't compete at all is in creativity. StuRat (talk) 16:46, 27 November 2011 (UTC)


 * See Mind uploading. The simple answer is we don't know enough to come up with anything close to a useful estimate, except perhaps for human brain memory in bytes although even those generally seem very variable. Nil Einne (talk) 12:35, 27 November 2011 (UTC)

This is a question I've spent quite a bit of time thinking about. I believe the usable memory storage capacity of a human brain is somewhere in the vicinity of one terabyte -- i.e., 1000 GB. Most figures that you see in the literature are much larger, though. It is really impossible to give a meaningful value for processing speed -- even for digital computers giving a value requires identifying a "unitary operation", and the unitary operations in digital computers have hardly any relationship with those in brains. The really impressive thing about brains, from a computational point of view, is their memory bandwidth, defined as the speed of information transfer from long-term memory to dynamic memory -- I estimate this as somewhere on the order of several GBytes per second for the human brain as a whole. Looie496 (talk) 18:11, 27 November 2011 (UTC)


 * There are decent upper bounds that have been established with some confidence. A 1994 (old) physics paper gives an upper limit of about 0.29 bits-per-synapse for a somewhat-realistic neural network. A synapse is a link between two neurons -- the electrical wiring, analogously. A bit is a storage unit used in computers: 8 bits in a byte, and one billion (10^9) bytes in a gigabyte (Gb). A modern computer hard drive has around 500Gb, which can snugly hold a large music, movie, photo, and video game collection.
 * From the wiki articles, there are some hundred trillion (10^14) synapses in the brain (~1 billion per mm3). Most human memory is believed to be stored in the hippocampus, which at up to 3.5 cm3 in size, would have maybe 3.5 trillion (3.5x1012) synapses, or 1 trillion bits, or about 128 Gb. You can give a comfortable margin of error but still have a 1.5-terabyte hard drive, which sells for less than $100 these days.
 * Surprisingly small, no? But biology uses information in a very different way. 128Gb is enough storage for a pretty-exact video of your entire sensory experience for a month, but this is not how we remember the past. Instead, we record distinct experiences in "photographic" significant events and ordinary experiences in terms of a "practice-makes-perfect" adjusting memory. By remixing it all together when we make decisions, we (and all animals with a central nervous system, most of which can't even store 10Mb) are able to see and react to the world around us.
 * And for reference, the human genome has only 25000 genes, most of which are shared with all other animals on Earth. How much raw code does it really take to distinguish you and I, and why? We're working on it... SamuelRiv (talk) 20:12, 27 November 2011 (UTC)


 * This page suggests it would take 20000 TB to fully model all the connections between neurons in the brain. The range of the above estimates from 130 GB to 20000 TB, is illustrative of the uncertainties surrounding the question of how information is actually stored in the brain.  Until we have a better sense of how the brain really operates, it is unlikely that we will be able to come up with a very precise answer for how much data it could store.  Dragons flight (talk) 23:25, 27 November 2011 (UTC)

Thanks for the brilliant answers guys. another thing: how are "feelings" processed? is it possible to convert feelings like love, grief, joy, etc into computer code? i.e. can it be replicated by computers (robots)?

117.192.212.166 (talk) 17:23, 28 November 2011 (UTC)


 * The 20000 Tb figure you linked, Dragons flight, is to fully map the entire brain. That is all of who and what you are and includes memories, sensorimotor functions, ability to concentrate, etc. As a map, it also stores the synaptic weights directly. My calculation was of the amount of information that is stored as memories, which is significantly less than the complexity of the network (a neural network is an inefficient structure for most tasks, but it's a great jack-of-all-trades).
 * Therefore, since scientists are 100% confident about everything having to do with the brain, 130 Gb is the absolute scientific factual truthful storage capacity of human memory. (But seriously, though, that 10-10000 Gb range I offer should mean something.) SamuelRiv (talk) 19:47, 29 November 2011 (UTC)


 * I am very skeptical of the modelling of synapses containing a bit or less of information. The paper says "it seems unlikely that a real synapse is able to maintain a large number of distinct stable states".  But i don't believe it.  Consider the complex behavior of the common Paramecium, which as described in that article is even believed to be capable of learning to distinguish between light levels.  Consider the eye of Erythropsidium, capable of distinguishing the direction from which light comes.  The neuron is an organism much more complex than these simple microbes, which may indeed have some awareness of the activity in which it is involved. Wnt (talk) 21:50, 29 November 2011 (UTC)


 * One way to think of it, Wnt, is that a synapse is more of a mathematical function than a chunk of raw data. Functions can still be reduced to a finite set of information, but the notion of a "12-bit function" (which is a minimal size to find the direction of light, as in your example (3-2-3) ) implies significantly more power than 12 bits of storage (which can barely encode the extended Roman alphabet). This is the counterintuitive nature of networks - they are robust structures that instantly process complex inputs into something abstract and simple. Essentially, the relevant and rich environment that is processed is never stored - it just goes in one end and out the other. The desktop-computer-hard-drive analogy is a fun way to quote sensational facts, but it also obscures (or rather, illustrates) the fact that biology does not work in that paradigm. SamuelRiv (talk) 23:32, 29 November 2011 (UTC)


 * Considering that brains' neural connections can change themselves (though not under conscious control - neuroplasticity) largely depending on use, there may be some covariance in the brain-memory system, and the source for an external user is different for human brains vs. computers vs. robots and artificial intelligence. Brains contain more than data storage, as knowledge is different from information. ~ AH1 (discuss!) 02:24, 1 December 2011 (UTC)

why does boiling point of water decreases at higher altitudes?
Dear friends,i have following queries: 1.why does boiling point of water decreases at higher altitude?

2.boiling point of water is 100 degrees..is it a constant value or variable?on what parameters does it vary?

3.i read in some website that "in pressure cooker,pressure increases and so boiling point of water increases.... this helps in quick cooking...".. i am not clear with this issue..pls can anybody explain me in simple words?

Regards, -Navneeth — Preceding unsigned comment added by Navneeth tn (talk • contribs) 08:34, 27 November 2011 (UTC)


 * Air pressure decreases at increasing altitude, it is entropically favourable to boil at a lower temperature.
 * Boiling points are dependent variables, it depends on the pressure of the system. Under extreme conditions, an extremely strong electromagnetic field may increase the boiling point of a substance, because of molecular deformation.
 * The increased pressure in the pressure cooker, increases the boiling point of water. As a result, water can convey more energy at a higher temperature into cooking the meal, so that it takes less time. Imagine this situation, you want to dig a hole of one cubic metre. Which would kind of spade would complete the task in the least amount of time, a small spade or a large spade? A large spade. Water that can carry more thermal energy, can transfer a larger amount of energy per unit of time than water that can carry less thermal energy. This is accomplished by increasing the boiling point of water, by applying pressure. Plasmic Physics (talk) 08:57, 27 November 2011 (UTC)

Thanks a lot for all those who gave their views. Regards, -Navneeth — Preceding unsigned comment added by Navneeth tn (talk • contribs) 14:37, 28 November 2011 (UTC)
 * Plasma Physics, with my deepest respect for your knowledge, Navneeth did ask for simple words. I am a native English speaker but cannot understand what "entropically favourable" means. Richard Avery (talk) 15:13, 27 November 2011 (UTC)


 * Think he simply means that disorder in the vapour stage is greater than that in the liquid.--Aspro (talk) 15:26, 27 November 2011 (UTC)


 * An aside: As an analogy: You know how a good Featured Article that has take a few knowledgeable editors hours to craft and find good references for (entropically dis-favourable), can (under the present policy of any-one-can-edit-regardless-of-their-motivation) in just a few dozen quick edits, reduce the article  to gobbledygook.   Well. Featured Articles are orderly sets of  information which are "entropically favourable" to “article rot” do to a lack of a WP protocol that can provide hierarchical oversight.  Thus ensuring our work here is never ending. Oh Sisyphus, how I  empathise with you!--Aspro (talk) 15:56, 27 November 2011 (UTC)


 * Y...e..s, thank you Humphrey.  Richard Avery (talk) 08:27, 28 November 2011 (UTC)


 * First you must understand the difference between water and steam. In water, the atoms behave like balls in a ball pit. When you increase the temperature, the walls of the ball pit start vibrating and some of the balls start flying around.
 * In reality, the atoms are a bit sticky, so they like to stick together. But when they stick together they can't fly so well, and when they collide in flight, they will bounce off each other instead of sticking. The balls at the bottom (sticking together) are like water, and the balls that are flying are like steam.
 * If you have a very deep ball pit (say 2 metres deep), then the pressure at the bottom is so strong that it's much harder for the balls to fly. If only the bottom of the ball pit is heated (vibrates), then you must vibrate stronger to turn this water into steam. The same happens if you put a heavy lid on the ball pit. Steam needs more space than water, therefore the pressure increases and you need more vibrations to make the same number of balls jump around.
 * Under normal conditions, you cannot cook food with more than 100 °C. When you heat more, the energy is used to turn more and more water into steam, and the temperature just stays the same. If you want higher temperatures, you must fry your food, because oil has a higher boiling point. And when you try to fry without any oil, the temperature can get higher and higher and your food gets black.
 * At high altitudes, it is as if we are at a point less deep in the ball pit, so the pressure is less and the boiling point is less than 100 °C. And in a pressure cooker we have a higher pressure, so that the boiling point is more than 100 °C. Hans Adler 16:00, 27 November 2011 (UTC)

Thanks a lot for all those who gave their views. Regards, -Navneeth — Preceding unsigned comment added by Navneeth tn (talk • contribs) 14:38, 28 November 2011 (UTC)

why do people start bleeding when they climb hill stations of higher altitudes?
dear friends,pls explain my doubt.
 * Regards,
 * -Navneeth — Preceding unsigned comment added by Navneeth tn (talk • contribs) 08:38, 27 November 2011 (UTC)


 * Possibly because of the reduced atmospheric pressure; Maybe some of the vessels may give way because the blood pressure remains same, but atmospheric pressure decreases. 'm not sure, better let one of the regulars reply here.  Lynch 7  09:01, 27 November 2011 (UTC)


 * Agreed. Areas where capillaries come close to the surface are the most susceptible, such as the inside of the nose and the lungs. StuRat (talk) 16:41, 27 November 2011 (UTC)


 * Oh, that is so wrong. Hypoxia causes a shift of blood volume from the veins to the arterial system. This causes (or is) pulmonary hypertension (the heart is trying to get more blood though the lungs), (of coarse, there is also less oxygen uptake at altitude so it don't help much; thus it becomes chronic) (note: sea level with 21% oxygen, pulmonary hypertension is normally due to vascular constriction). The nose appears to act (through evolution or chance) as  a sort of safety valve. Its better to bleed from there (I suppose) than from the retinas in  the eyes . The external air pressure does not have the same proportional  effect as a low oxygen atmosphere created in an  environmental  chamber at sea level. The  pulmonary arterial pressure still goes up. Astronauts can get by with absolute pressures of 5 psi and sometimes less on pure O2. Can your hear me Major Tom ?  ….. 'ang on  'uston; iv got 'er noze bleeed...!!!  --Aspro (talk) 22:31, 27 November 2011 (UTC)
 * Goes without saying:  at altitude, a  nose bleed is a worrying symptom that needs a medical evaluation  by someone who is is familiar with altitude sickness – time is of the essence.--Aspro (talk) 22:44, 27 November 2011 (UTC)


 * What is "so wrong", Mike Lynch's comment ? ? StuRat (talk) 05:07, 28 November 2011 (UTC)


 * Now have you noticed, why I phrased  that the WP article (mentioned below) "has a little about this”--Aspro (talk) 22:54, 27 November 2011 (UTC)


 * The article on altitude sickness has a little about this. --Aspro (talk) 09:35, 27 November 2011 (UTC)

Thanks a lot for all those who gave their views. Regards, -Navneeth — Preceding unsigned comment added by Navneeth tn (talk • contribs) 14:38, 28 November 2011 (UTC)

I suspect at least part of the responsibility can be placed on the extremely dry, cold conditions typically found at high altitudes. I know at least one person who suffers nose bleeds when the air gets very dry. - Running On Brains (talk) 18:27, 29 November 2011 (UTC)
 * Aspro's answer is kinda better I guess. My major is in aerodynamics, not human physiology, so that must explain the affinity towards pressures and the limited knowledge of the human body  Lynch 7  18:08, 30 November 2011 (UTC)

Blue butterflies of Japan
what small blue butterflies are often found in Japanese cities? Simply south...... "time, department skies" for 5 years 23:30, 27 November 2011 (UTC)


 * This looks kinda blue? [[image:Euploea mulciber1.jpg|thumb|Euploea mulciber 日本語: ツマムラサキマダラPlace:Itami City Museum of Insects,Hyogo,Japan]] --Aspro (talk) 23:48, 27 November 2011 (UTC)


 * Wikipedia doesn't seem to have a List of butterflies of Japan, even though there are many other locations in Category:Lists of butterflies by location. However, I found one here: . The Polyommatinae subfamily of the Lycaenidae are the butterflies called the "blues", so jumping to the Lycaenidae section of that list might help a bit - except that some blues may in fact be brown, and many Lycaenidae aren't blues. Hope that helps some small amount. Arhopala japonica is another pretty blue Japanese butterfly, but I have no idea how common it is or whether it's found it cities. Card Zero  (talk) 01:51, 28 November 2011 (UTC)


 * Well, there's Sasakia charonda, the national butterfly of Japan, but they're nymphalids, so quite large (and our article on it is a bit shabby). As Card Zero said, a lot of lycaenids are blue. There are also some blue hesperiids (skippers). Members of the latter two families are usually small, very common, and easily recognizable.--  Obsidi ♠ n   Soul   20:35, 28 November 2011 (UTC)