Wikipedia:Reference desk/Archives/Science/2008 October 11

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October 11

gas constant?

why should we use a constant for gas equations?where does the universal gas constant come from?i couldn't find any information about history of gas constant(R)? —Preceding unsigned comment added by 88.242.106.180 (talk) 00:57, 11 October 2008 (UTC)

You may want to have a look at gas constant and Boltzmann constant for a more detailed treatment of the topic. Briefly, the gas constant (R) is a proportionality constant which describes how much energy is stored in a mole of (ideal) gas molecules per degree of temperature. (The related Boltzmann constant, k_B, describes the quantity of energy per molecule.) TenOfAllTrades(talk) 01:40, 11 October 2008 (UTC)

A pity nothing is said in the articles about experiments like in de:Universelle_Gaskonstante#Ein Experiment zur Ermittlung einer Näherung der Gaskonstante, or how the constant was measured to this accuracy. --Ayacop (talk) 09:26, 11 October 2008 (UTC)

If you can translate from the german, the English Wikipedia articles could probably benefit from your help. --Jayron32.talk.contribs 12:46, 11 October 2008 (UTC)

Back to the gas constant. The SI system was carefully constructed to in general, avoid these sort of proportionality constants. Many calculations would require them, except that the units are defined to be compatable in ways that generate proprotionality constants of "1". The situation with "R" is because the SI unit for temperature, kelvin, is created not to be compatable with other SI units, but be compatable with the Celsius scale. Since the size of a Celsius unit is arbitary (there's nothing inherently useful about being 1/100th the difference between the sea-level freezing and boiling points of water), the size of the kelvin is arbitrary as well. One could define a temperature scale where 1 degree was equal to the the amount of energy contained by 1 mole of molecules, and under THAT scale, R would be equal to 1. However, for other reasons of convenience and history, we use the Kelvin scale, so we are stuck with a non-unitary R values. --Jayron32.talk.contribs 13:00, 11 October 2008 (UTC)

I'm not entirely sure I'd agree with that. While interconversion among SI units is very straightforward and generally avoids weird proportionality constants, such constants are almost always necessary in calculations which describe physical processes in the real world. (The energy of a photon is equal to its frequency multiplied by 6.626x10^-34: the Planck constant; the gravitational attraction between two bodies is the product of their masses divided by the square of their separation distance, multipied by 6.674x10^-11: the gravitational constant. And so forth.)

The seven base SI units trace their roots to essentially arbitrary roots which don't have any universal scientific or physical significance. (The meter was originally based on a rough measure of the Earth's circumference; the second on arbitrary divisions in the length of Earth's day; the kilgram tied to the density of water.)

To get rid of arbitrary constants of proportionality, physicists will resort to systems of so-called natural units which peg most physical constants to be exactly 1. Under (for example) Planck units, the speed of light, the gravitational constant, the reduced Planck's constant, Boltzmann's constant, and the Coulomb force constant are all set to be 1, and other units defined from there. Such systems can make calculations dramatically 'neater' and eliminate the risk of 'losing' a constant in a complicated expression. The downside of such systems is that they generate base units which aren't convenient for 'everyday' usage. (The base unit of temperature in Planck units is about 10³² kelvin, and the base unit of time is about 10^-44 seconds.) TenOfAllTrades(talk) 14:51, 11 October 2008 (UTC)

Use of Oil

Generally what percentage of a barrel of oil is used strictly for fuels such as gasoline and diesel? How much is used for plastics and other products? I had heard that oil used for fuels was low - around 20% - and the bulk of every oil pumped out of the ground was for other products like plastic. Is this true142.68.216.154 (talk) 02:35, 11 October 2008 (UTC)

You might want to look at this link [1]. Which deals with oils use for energy. Only 20-30% of the energy we use goes to transportation but almost all of that energy comes from oil. I know that doesn't answer you question but it is probably the origin of you mangled statistic. What comes out of a barrel of oil depends on what the oil is like (where it was found) and how you crack it but this link gives you and idea of how an average barrel gets fractioned [2]. The key chunks of plastics are mostly derived from natural gas. The other components are derived from side products in process of refining oil for gasoline/diesel. Transportation fuel is the largest and most powerful market for oil, plastic just removes 4.7% of the barrel of what would other wise be a waste stream to burn for heat/electcity or maybe converted into hydrogen. In addition consumers can afford to pay more for natural gas to heat their homes and produce electricity than chemical producers can afford to pay for natural gas as a feed stock. The price of natural gas in North America has forced many chemical producers to close up shop and move to places with cheaper natural gas like the Middle East and Africa. I think BASF cited this when they closed plants around 2005 among other companies. I hope that helps.--OMCV (talk) 03:28, 11 October 2008 (UTC)

yeah, the demand for gasoline/fuel oil basically requires economically to "crack" as much of the petroleum that can possibly be used into the proper weights. In addition, the advent of fuel injection and the associated in-tank fuel pumps have made it possible to add the lighter petroleum fractions into gasoline which would have created a lot of vapor lock in the carbureted engines with the fuel pump on the engine, and used to be disposed of. In fact, (according to what i read) the vapor pressure on gasoline has risen enough even just in a decade or two to saturate the vapor capture systems on cars from the 80s. basically, any oil that goes into plastics is leftovers that would otherwise be waste. Gzuckier (talk) 05:22, 11 October 2008 (UTC)

Plants with edible stems

Are there plants other than Rhubarb with edible stems?74.50.200.72 (talk) 06:41, 11 October 2008 (UTC)

Cattails Ζρς ι'β' ^¡hábleme! 07:18, 11 October 2008 (UTC)

Leeks and spring onions are commonly eaten in the UK. Axl ¤ [Talk] 07:20, 11 October 2008 (UTC)

The pedia does it again -- try Edible plant stems for a nice list of munchies. (It doesn't mention mushroom stems/stalks which are not notable but edible.) Julia Rossi (talk) 07:25, 11 October 2008 (UTC)

Mushrooms are also not plants. —Ilmari Karonen (talk) 07:33, 11 October 2008 (UTC)

(ec) A lot of herbs are edible in the whole (or at least their above-ground parts are), so I guess they count. At the other end of the scale, pine phloem is edible (if not very nutritious), though the whole trunk isn't. —Ilmari Karonen (talk) 07:31, 11 October 2008 (UTC)

Rhubarb's culinary cousin Celery certainly qualifies, doesn't it?--Jayron32.talk.contribs 12:44, 11 October 2008 (UTC)

Noisy faucet

My kitchen faucet, which works well otherwise, makes a high pitched whine when running hot water through it. Why? Dismas|^(talk) 15:19, 11 October 2008 (UTC)

There is some air in the pipes. As the air flows through the the narrow opening, it makes a sound. Axl ¤ [Talk] 18:50, 11 October 2008 (UTC)

As water flows through your faucet, there may be regions of turbulent flow; there may also be areas of lower pressure created by the flowing water. (See Bernoulli's principle for more details on how that might arise.)

Turbulence and low pressure can generate noise in at least a couple of ways that would be more dramatic with hot water than cold. First, the solubility of air (mostly oxygen and nitrogen) drops with increasing temperatures. In other words, cold water that left the treatment plant or well saturated with air will be supersaturated after being heated in your water heater. The reduction in pressure and increase in turbulence as the water approaches your faucet will encourage that air to come out of solution and form bubbles; turbulent movement of bubbles generates noise.

Even in the absence of dissolved air, you might still see effects due to cavitation. Hot water has a higher vapor pressure than cold, and hot water may actually boil in regions of low pressure within the plumbing. The formation and subsequent collapse of bubbles of water vapor can generate noise as well. TenOfAllTrades(talk) 19:06, 11 October 2008 (UTC)

Quote identification

With regard to the Fermi paradox: "If there are so many alien civilizations, why haven't they visited us? I decided to do an experiment. I wanted lobsters for dinner. I put a plate on my table, sat down, opened the front door, and waited for a lobster to crawl onto my plate. Three hours later, no lobster came. I ended the experiment, concluding there are no lobsters in the world."

This "quote", which is obviously not word-for-word, is from a show that aired on Discovery Channel a few years ago. --99.237.96.81 (talk) 16:34, 11 October 2008 (UTC)

Lobsters are not a highly intelligent species in an advanced technological civilization with a desire to explore the universe. Axl ¤ [Talk] 18:56, 11 October 2008 (UTC)

If they were, is it a given that we would even notice? ;) --Kurt Shaped Box (talk) 02:01, 12 October 2008 (UTC)

A bad analogy is like a pickle playing chess. TenOfAllTrades(talk) 19:12, 11 October 2008 (UTC)

A quick web search indicates that the story is variously attributed to "a SETI offical", and Timothy Ferris (who is not a SETI official). Ferris is a science popularizer, though, so he may be quoting someone else (or he could be the originator - it's hard to tell). I can't find anything that looks like an "original" source. (Most web hits for "lobster Fermi Paradox" are for Accelerando (book).) -- 128.104.112.147 (talk) 19:42, 11 October 2008 (UTC)

Thanks, but I was actually looking for the name of the show I saw the quote on. --99.237.96.81 (talk) 22:42, 12 October 2008 (UTC)

Well, the other issue is that we may be the only advanced civilization in our galaxy, but our galaxy is such an isignificant fraction of the whole universe its hard to say definately we are the only ones. Back to the lobster analogy, imagine putting out your plate and waiting for a lobster to crawl on it from the moon. There universe may be teeming with advanced civilization, but we lack the ability to detect evidence of it because its too far away. --Jayron32.talk.contribs 20:17, 11 October 2008 (UTC)

The Fermi paradox is really a pretty shakey proposition. We are a civilisation - have we visited any alien species? Could we even if we knew which star system thay lived at? Even if they lived on Proxima Centauri (the closest star to the Sun) - we currently have no clue whatever how we could get to them. Why would we expect that other civilisations would have any better ideas than we do?

Even if they are smarter than we are - or have simply been around a lot longer...if travel between the stars is impossible for us right now - maybe it's impossible, period. Worse still - how do they know we're here? Our SETI detectors are unable to detect a signal unless it's either beamed on a narrow-beam directly at us - or a broadcast signal that's VASTLY more powerful than the most powerful signal we've ever sent into space. We don't routinely beam narrow-beam signals at stars - so they would need much more powerful radio receivers than we currently have in order to hear us...and again - if we don't know how to do that, why should we assume that the aliens do?

Also, we've only been transmitting radio signal with any strength out into space for less than a hundred years - so only aliens within 100 light years could possibly know we're here - and only those within 50 light years could possibly have gotten here after hearing us...if it took them a while to plan the mission and get it funded and launched - they might have to be much closer to have gotten here yet. There are only 1000 stars within 50 light years - and only 50 or so within 20 light years. It's perfectly possible that none of those 50 stars have planets suitable for life.

From what we know - even if aliens are REALLY common around our galaxy - and even if they have close to light-speed travel and radio receivers that are vastly more sensitive than ours, it would STILL be quite surprising if they were able to get here to visit us. Far from being a paradox, Fermi's claim is just wrong.

SteveBaker (talk) 01:28, 12 October 2008 (UTC)

That's assuming that they'd even be interested in contacting us. What's to say that they wouldn't view us as savage, warlike, power-hungry carnivorous beasts with just enough brainpower to be a potential threat to *their* peace-loving civilization should an encounter occur - and decide to steer well clear? Either that, or they see that we're just lumps of meat restricted to 3-dimensional space with no subspace hivemind capability and think 'bleh - who cares about that?'. ;) --Kurt Shaped Box (talk) 02:14, 12 October 2008 (UTC)

Perhaps they're preparing an application for a hyperspatial express route? Axl ¤ [Talk] 09:49, 12 October 2008 (UTC)

Or they've seen what we do to the lobsters whenever they venture forth from the ocean in an attempt to engage in peaceful communication with us... --Kurt Shaped Box (talk) 19:13, 12 October 2008 (UTC)

We are very young on an astronomical scale, and we are advancing at a significant rate. For the purposes of the Fermi paradox, we are not advanced. We have never left this solar system, but we currently emit very large amounts of radio waves, and have even done so with the intent of contacting aliens. We are currently quite capable of interstellar travel, as can be seen by Project Daedalus. Unless advanced civilizations stop sending stop sending out signals, there would logically be roughly spherical areas around where each one began where all, or at least many, of the stars are emitting suspiciously large amounts of a small band of electromagnetic waves. — DanielLC 16:07, 12 October 2008 (UTC)

I've got to disagree.

Project Daedalus is a joke - it requires Helium-3 as a fuel. Which they propose to mine from Jupiter over a 20 year period using robotic probes...we are SO far from even being able to start making the robots that would autonomously mine the fuel for the darned thing - we're nowhere CLOSE to being able to do that. The craft itself weighs 50,000 tons...getting that into orbit would require 2,000 shuttle launches! And all of that to get a small number of teeny-tiny robotic probes to one of the nearest stars. Worse still - those probes would shoot past the star at 12% of the speed of light - leaving only a very short period for observation and science! It's also true that this is not just a matter of science. There is also the matter of politics. There is no conceivable way of getting a government to fund a massive 20 program to mine fuel for a 50 year program which would take another 6 years to report back results. Worse still - nobody who was alive at the start of the program would be alive at the end. The cost of launching the components into orbit alone would be 160 times the cost of the ISS! With present funding levels, NASA would be doing nothing else for a thousand years! Politicians will never allocate that amount of funding to achieve a goal that not one of their voters will live to see through to completion. All of this for at most a couple of hours of science data captured at such a high speed that detailed photography would be impossible! A thousand years of funding for a probe that might just fail when it gets there? I don't think so.

No - we REALLY don't know how to do interstellar travel...not in any kind of practical manner. If aliens managed to build a Daedalus - it would pass us by so quickly that we'd never notice it passing.

You say that we're pushing out a lot of radio waves - but not on an interstellar scale. Recall that the very best radio telescopes we have would be unable to detect broadcast signals of the strength we're putting out from a distance of the nearest star.

You say that we're young on an astronomical scale - perhaps we are - but perhaps we're already pushing the outer limits of what's possible? Because we can't know that there are vast improvements in space technology out there - it's perfectly possible that we're already close to hitting the limits. You can't claim that it's paradoxical that we haven't seen any alien visitors - it's perfectly reasonable given what we know. More to the point - I could claim that because we haven't seen any aliens (and the math makes it seem like there must be lots of them out there) then it must be that we're close to the limits of the technologically possible.

SteveBaker (talk) 20:56, 12 October 2008 (UTC)

Isn't there a theory doing the rounds that radio waves of the strength we tend to emit will peter out into the background radiation after a couple of light years? I seem to remember reading about that a while back. --Kurt Shaped Box (talk) 19:09, 12 October 2008 (UTC)

You're assuming that aliens would have to be specifically contacting us. I've always understood the paradox to be that the aliens should have reproduced, or created replicating machines all over the galaxy. Star systems are extremely valuable resources, any intelligent civilization that's billions of years old would probably be using a lot of them. Such a civilization could leave artifacts everywhere, and why haven't we found them?

It would only take one run-away planet-eating Von Neumann probe a long enough time ago to give a long dead civilization a long-lasting legacy.

This, of course, assumes that an intelligent civilization can survive for billions of years, and it assumes a whole bunch of scientific advances are possible but that we simply haven't made yet.

I would like to think that by the time humanity is a billion years old that we've at least sent probes out to a significant segment of the Milky Way, Even if we need to dismantle some planetoids to do so. (Sorry, Pluto.) I think it's that kind of hope that drives the Fermi Paradox. APL (talk) 19:02, 14 October 2008 (UTC)

A point that nobody else raised is that there are many kinds of civilizations that are much more stable than our own. The society in Nineteen Eighty-four is an example--without overpopulation, environmental damage, or global warming, it's much more likely to survive for millions of years than a civilization that's developing quickly.

I also don't believe an advanced species would prefer to use radio waves that spread out spherically. If I had the choice, I would send energy to only the intended destination, not to the boundary of the star system. Laser, or at least directional antennas, are much more energy efficient than ominidirectional radio transmitters. --99.237.96.81 (talk) 22:42, 12 October 2008 (UTC)

That's true - directional transmission makes a heck of a lot more sense. But we aren't talking about aliens talking to us...we're talking about aliens LISTENING to us and then coming to visit. We aren't transmitting to them on nice tight, efficient beams - mostly because we don't know where they are so we don't know where to point the radio beams. So they have to find us based on omnidirectional spherical waves that drop in energy as the square of the distance - and are therefore almost completely indetectable after a lightyear or so of travel.

It would be a different story if we had a powerful ultra-tight-beam transmitter tuned at the "water hole" and undertook a program of transmitting the prime numbers as a series of pulses that were sent at regular intervals to each of the 1,000 nearest stars. That would hopefully catch the attention of any civilisation within ~50 lightyears - and you could start looking for responses from them about 100 years from now.

SteveBaker (talk) 20:15, 13 October 2008 (UTC)

would you freeze in space with nothing on

if i went into outer space without a suit would i freeze instantly? why? is there no oxygen or something?--Majorcolors1 (talk) 17:59, 11 October 2008 (UTC)

You wouldn't freeze very quickly, if at all. In a vacuum (ie. when there's no air) the only way to lose heat it by radiation, which is very slow. You would suffocate long before you froze. We have an article on it: Human adaptation to space#Unprotected effects. --Tango (talk) 19:00, 11 October 2008 (UTC)

Well, it also depends on how you were exposed to the vacuum. If your space suit just suddenly disappeared and all the gas surrounding your body expanded rapidly, the gas would cool so rapidly that the outer layers of your body would be chilled to below freezing. If on the other hand, there was only a slow leak in your space suit until there was no air left, you probably would not freeze, unless your spacesuit was conductive. --M1ss1ontomars2k4 (talk) 20:59, 11 October 2008 (UTC)

Yeah, the gas would cool, but it would be nowhere near your body after a fraction of a second, so how would if affect you? And your spacesuit being conductive won't make any difference since there is nowhere for the heat to go, it still has to be radiated. --Tango (talk) 22:46, 11 October 2008 (UTC)

Well, it depends on the temperature of your spacesuit, I suppose. If it were colder than you (it wouldn't be unless you were in the shadow of something, right?), then you might have a problem. But I'd assume that spacesuits are very insulating, or they'd be conducting heat to/from you all the time. --M1ss1ontomars2k4 (talk) 23:14, 11 October 2008 (UTC)

Your spacesuit is in contact with you and nothing else, so it's almost certainly the same temperature as you. --Tango (talk) 23:25, 11 October 2008 (UTC)

I think the most horrifying thing is that without external pressure your bodily fluids begin to boil, starting with the water on your tongue. Plasticup ^T/C 03:28, 12 October 2008 (UTC)

Your skin is able to provide enough pressure to prevent most bodily fluids from boiling - but your eyes, the interior of your nose, lungs and mouth would certainly have problems with that. For water to boil at body temperature, the pressure has to be down below 100mm of mercury - that's about one eighth of an atmosphere. That's about the pressure at 40,000' - but people have successfully flown unpressurized aircraft at higher altitudes than that. Supermarine_Spitfire#Speed_and_altitude_records - for example, shows a flight up to 51,000' at which air pressure is down to about 76mm of mercury - where the boiling point of water would have dropped to 32 degC - 90 degF. SteveBaker (talk) 03:51, 12 October 2008 (UTC)

Perhaps in those instances the gradual pressure change allowed the liquids to boil off more subtly, but there is no doubt that suddenly being thrust into a near-zero pressure environment makes your tongue boil. It actually happened to one unfortunate gentleman. Plasticup ^T/C 05:48, 12 October 2008 (UTC)

While the plane may not have been pressurised they would almost certainly have been wearing an oxygen mask so the pressure on their mouth and nose would be much greater, and wearing a full face mask wouldn't surprise me. They would probably also have had a pressure suit to apply pressure to the rest of their body (although that wouldn't be vital, since skin can do the job in a pinch, as you say). --Tango (talk) 11:43, 12 October 2008 (UTC)

You would certainly freeze, Tango, although not before you suffocated. Heat loss by radiation is given by the Stefan-Boltzmann law: $P=\sigma (T^{4}-T_{0}^{4})A$

where

σ is the Stefan-Boltzmann constant, about 5.7e-8 W/m2K4

T is the body temperature, normally about 310 K

$T_{0}$ is the cosmic background temperature, about 3 K

A is the body surface area, about 1.7 m2

(I'm ignoring the emissivity of skin which is, to my surprise, close to unity. [3])

The result is about P = 879 watts, dropping to about 528 watts at freezing point. That is a significant rate of heat loss. Let's see how quickly you would freeze.

Energy to cool a 75 kg body from 310 K to 273 K: 75 kg x (310 K - 273 K) x 4000 J/kg.K = 11.1 MJ

Energy to freeze a 75 kg body at 273 K: 75 kg x 333 kJ/kg = 25.0 MJ

At an average 700 watts rate of cooling, it would take (11.1 MJ + 25.0 MJ) / 700 W = 14 hours to freeze you solid. But I imagine that, if you were losing heat at 879 W, you would start getting frostbite quite soon after exposure.

--Heron (talk) 15:47, 12 October 2008 (UTC)

That 3K figure is for deep space away from any heat source. If you are in Earth orbit and not in the shadow of the Earth you are more likely to burn than freeze (the average daytime temperature on the moon is 107°C according to our article and that's pretty much the same as being in space at the same distance from the sun). Space suits have sophisticated refrigeration units in them. You would get very cold in the shadow of the Earth, though, so in LEO you would be going from over 100 degrees above to over 100 degrees below every hour and a half or so. Of course, you lose conciousness in about 15 seconds from hypoxia, so it doesn't really matter. --Tango (talk) 17:09, 12 October 2008 (UTC)

Damn Interesting has a great article on exposure in space here

In the absence of atmospheric pressure water will spontaneously convert into vapor, which would cause the moisture in a victim's mouth and eyes to quickly boil away. The same effect would cause water in the muscles and soft tissues of the body to evaporate, prompting some parts of the body to swell to twice their usual size after a few moments. This bloating may result in some superficial bruising due to broken capillaries, but it would not be sufficient to break the skin. -- Within seconds the reduced pressure would cause the nitrogen which is dissolved in the blood to form gaseous bubbles, a painful condition known to divers as "the bends." Direct exposure to the sun's ultraviolet radiation would also cause a severe sunburn to any unprotected skin. Heat does not transfer out of the body very rapidly in the absence of a medium such as air or water, so freezing to death is not an immediate risk in outer space despite the extreme cold. -- For about ten full seconds– a long time to be loitering in space without protection– an average human would be rather uncomfortable, but they would still have their wits about them. Depending on the nature of the decompression, this may give a victim sufficient time to take measures to save their own life. But this period of "useful consciousness" would wane as the effects of brain asphyxiation begin to set in. In the absence of air pressure the gas exchange of the lungs works in reverse, dumping oxygen out of the blood and accelerating the oxygen-starved state known as hypoxia. After about ten seconds a victim will experience loss of vision and impaired judgement, and the cooling effect of evaporation will lower the temperature in the victim's mouth and nose to near-freezing. Unconsciousness and convulsions would follow several seconds later, and a blue discoloration of the skin called cyanosis would become evident.

-- MacAddct1984 ^{(talk • contribs)} 16:08, 12 October 2008 (UTC)

I don't believe you'll get the bends - and I don't believe that your blood would boil. You are making the mistake of assuming that the pressure inside your body drops to zero. It doesn't because your skin is able to exert a force to keep your innards under pressure (to some degree at least). So pressure inside your body will remain at some fraction of an atmosphere. As I explained before - for water at body temperature to boil, you need the pressure to be below one eighth of an atmosphere - and I'd certainly expect your skin to be able to do that...at least for short periods...in the longer term, you're dead anyway. The liquid on the surface of your eyes, inside your mouth and near other orifices will boil because they WILL fall to zero pressure - but not your blood.

As for getting the bends - I'm not sure what the threshold for getting the bends is - but remember that your body is pressurised to one atmosphere when you are just 32 feet underwater - you can happily snorkel to that depth and come up quickly without getting the bends - and that's the same pressure differential as going from normal air pressure into a vacuum. Note also that astronauts have their space suits pressurised at only half an atmosphere anyway (to keep them flexible apparently) - so the drop is more like coming up from 16 feet to the surface...which I can do in any decent swimming pool with a diving board. How many people get the bends in a swimming pool?

SteveBaker (talk) 20:11, 12 October 2008 (UTC)

The above sounds kind of like what was posited in one sci-fi book I read once (set in 2017, astronauts thought they were in space, trapped underground, to get out had to get through this place w/no pressure & properly fitting suit caused some nasty bulging/bruising; someone might know what I mean). But, I always thought that the lack of pressure in space was so huge that one would literally "pop" instantly. I'll have to read that article on exposure to space when i have more time. I guess it wouldn't be as instnat as I thought.Somebody or his brother (talk) 17:00, 12 October 2008 (UTC)

The classic scene is the one in 2001 (movie) when Bowman is forced to cross from the 'pod' into the main spacecraft without a helmet. SteveBaker (talk) 20:11, 12 October 2008 (UTC)

There's also that scene in Event Horizon where Baby Bear gets locked outside of the airlock. IIRC, he bled from his eyes and his veins began to bulge. Mind you, the ship went to hell and back, so anything's possible... -- MacAddct1984 ^{(talk • contribs)} 22:54, 12 October 2008 (UTC)

That's more or less what happened in Total Recall too...it didn't seem very convincing. SteveBaker (talk) 23:46, 12 October 2008 (UTC)

Robotics - what is static stability?

I find definition of "static stability" as it relates to missiles and whatnot, but not as it relates to robotics. It sounds like it means just the concept that when a robot is at rest it should be stable, but I don't know for sure so I decided to query the WP community. Smaug 18:01, 11 October 2008 (UTC)

Ack nevermind. Just found the answer: "A statically stable robot can stand still without falling over." So I was right. Smaug 18:02, 11 October 2008 (UTC)

Stability is a slightly more subtle thing. With very great care, you can balance a coin on it's edge - but it's not stable - the slightest knock or jolt and it'll fall over. When you leave the coin lying on it's side - then it's very stable - it takes a HUGE jolt to make it flip over. That's "static stability". A statically stable robot would not only be able to stand still - but it would be able to do that with the power turned off - and it wouldn't fall over if you knocked it hard. SteveBaker (talk) 01:05, 12 October 2008 (UTC)

There is also a strange condition between stable and unstable called astable, where the system is in an unstable state, but if disturbed merely goes to another similarly unstable state. Our article redirects to multivibrator which is certainly an example of a device in an astable condition, but not the most informative one. A ball lying on a flat surface is in astable equilibrium, the slightest force on it will change its state, but only to another one exactly the same. A cone has all three types of stabilty: stable if on its base, unstable if on its apex, and astable if lying on its side. In terms of robotics, walking is a challenge to the designer because it requires astable equilibrium. A walker is continually falling, but never does so as he/she immediately moves to another falling state on the other leg. The mechanical equilibrium article appears only to cover static equilibrium. SpinningSpark 12:01, 12 October 2008 (UTC)

Jobs in the private spaceflight industry

It seems that private-sector spaceflight is really taking off (pun not intended) these days. I'm really excited about what's happening with it lately, and I really want to be a part of it all. I'm preparing to go into college starting next semester and I still haven't made up my mind on what I want to specialize in. My question is, what sort of degrees would be useful to the private spaceflight industry? My goal is to collect skills that would make me indispensable to a company in this field. I'm not particularly good at anything as it is. I have some very basic computer programming skills (I could get better, though) and I'm extremely bad at math (I'm aware that this is a huge drawback for what I seek). Does anyone have any suggestions for the career I should choose and what I should learn about in school? Thanks. 63.245.144.77 (talk) 20:11, 11 October 2008 (UTC)

My goal is to collect skills shows you are very wise, that is exactly what will make you indispensable in any field. I'm literally doing the same thing right now. I'm already "competing" against future neurologists(m.d.) who are still in their undergrad. Just think of the bell curve. You have to compete to be in the top 5, in whatever you genuinely want to excel at. The problem is you don't know who the other top four are. You have to be extremely motivated, and (possibly even more importantly) you have to know where to direct your efforts. Its just that (if you live in U.S.A.) most teachers who are great at teaching math, all conspire to make sure that they aren't your math teacher. Math is a dealbreaker, and you need to be an expert at quantitative reasoning. Specific advice: study rigorously and take the LSAT (its a puzzles test mainly), make yourself better at math (ask questions on the math ref desk anytime--always glad to help aspiring rocket scientists), and become a master of metacognition as that's the only way to change your brain's wiring about motivation. Sentriclecub (talk) 21:05, 11 October 2008 (UTC)

There are certain jobs that exist in any industry - personnel (aka human resources), accounts, etc., which you could go for. Jobs specifically related to space flight would be physics and engineering related, most likely, with some mathematicians as well. All of those involve quite a lot of maths, unfortunately... They will certainly need programmers to do simulations and things, but you would need the maths and physics knowledge in order to know what to program. I think, in short, you can't be a rocket scientist without maths! If you're interested in the space tourism side of the industry, you could try studying hospitality and tourism. While you would be learning about land based hotels rather than space hotels, there would be transferable skills. There will be lots of new legal issues with the new sector opening up, so I'm sure they'll need lots of lawyers - working out what jurisdiction a space hotel or moon base falls under could be quite interesting, as would extraterrestrial real estate. Really, they're going to need people from all disciplines, so just pick something that sounds interesting as a degree and then apply for whatever jobs you're suitable for (a lot of jobs just require a degree and it doesn't matter what it's in). --Tango (talk) 20:52, 11 October 2008 (UTC)

Learn Mandarin and business. If by "private spaceflight" you mean space tourism, it's likely many of the punters will be the Chinese nouveau riche showing off their wealth. If you mean it to include privately launched spacecraft in general (including satellites) then a lot of that business will be Chinese entrepreneurs blanketing the middle kingdom with cheap video messaging services and such. -- Finlay McWalter | Talk 21:21, 11 October 2008 (UTC)

There are really a vast range of skills that are going to be needed when private spaceflight really takes off - I would start with a solid grounding in math and science - probably physics, electronics and computer science would be good places to concentrate your efforts. But if you can learn as much breadth of science as possible - and enjoy doing it - then I think your speciality can be almost any science-related subject and you'll find jobs are available. But that wide knowledge base is critical. No small rocketry company can afford to have an extreme specialist in a very narrow field on their staff - they need generalists. SteveBaker (talk) 00:57, 12 October 2008 (UTC)

Obviously you'll want to master all of the intellectual disciplines enumerated by my venerable RefDesk colleagues, but you shouldn't neglect your physical health. Competition for the jobs of first generation space pilots will be nothing short of astronomical, and you will need to be in peak physical condition to remain in contention. Plasticup ^T/C 05:42, 12 October 2008 (UTC)

You're assuming "job in private space travel" means being a pilot - the vast majority of the jobs will be ground based. I didn't even discuss becoming a pilot because the competition is so great it's barely worth considering - you would need to already be an experienced aeroplane pilot, it's not a job you can get straight out of college. --Tango (talk) 11:46, 12 October 2008 (UTC)

Oh - sure. Forget being a pilot. They won't need many pilots and EVERYONE who ever dreamed of being Buck Rogers is going to be after that job. Supply and demand means that that's going to become an increasingly low-grade job. These space-planes are going to be automated to death and you won't need any more skills than (say) an airline pilot needs to fly one. I'm assuming that the interesting, high-dollar jobs are on the ground. Design, test, construction, launch. SteveBaker (talk) 15:10, 12 October 2008 (UTC)

I'd expect the spaceship pilots themselves to be recruited exclusively from the pool of experienced military test pilots anyway... --Kurt Shaped Box (talk) 19:07, 12 October 2008 (UTC)

I think Virgin Galactic are recruiting experienced commercial pilots, not just military. You need a lot of experience, though. While SteveBaker is right about the automation, that only applies to routine flights - if something goes wrong you need to be able to take manual control and know what to do. While lots of people will want the job, there won't be many people qualified, so the supply is actually very low and I would expect them to be extremely well paid (there will be equally well paid jobs on the ground and probably a few better paid jobs, though). --Tango (talk) 20:20, 12 October 2008 (UTC)

Commercial spaceflight is going to be all about weight. For the early passenger flights, they'll be able to charge a small fortune for each seat - filling one of those seats with a non-paying pilot is a costly thing to do. There is really no practical reason why you couldn't fly the spaceplane from the ground and use automation for the majority of the flight. The "when something goes wrong" argument is really untrue. In modern commercial aviation, pilot-induced errors by far exceed pilot-corrected mechanical faults. (Don't consider situations where the pilot lands the plane with one engine out - that could have been done from the ground - I'm talking about situations where the plane would have crashed had the pilot not been physically aboard the plane to fix something.) We could drop the pilot anytime if it were not for the legal ramifications and the fact that people might be a tad nervous about flying in a plane with no pilot. But in a 500 seat 747, adding a handful of crew makes almost no difference to your revenues and keeping passengers happy is more important. But in a 5 seat space-plane, losing 20% of your revenue is a tough business decision. NASA puts human pilots on board the space shuttle - but those people would need to be there to carry out the mission anyway - so the cost of having them there to fly the shuttle is $0. Remember the Russian Buran space shuttle did it's one and only flight entirely under automation. So whether there will be many space-plane pilots in the future ends up being more a matter of how secure the passengers can be made to feel than any actual NEED for a pilot to be physically present in the cockpit.

SteveBaker (talk) 23:02, 12 October 2008 (UTC)

As someone who works in the airplane business (specifically, avionics) I don't think the situation is quite as clear-cut as that; our avionics are not yet good enough (and, importantly, robust enough) to permit pilotless teleoperation on a large scale. In a few years, maybe. Although I will agree that the decision to have a pilot on the first suborbital ships will be partially a technical one and partially a financial one (the non-paying-passenger argument you made).

Oh no, I have contradicted Steve!! :) — QuantumEleven 14:11, 13 October 2008 (UTC)

And what do you do when the radio antenna falls off during re-entry? Even if the radio control works perfectly, I would imagine (I'm not a pilot) it's far easier to fly a plane when you can feel what it's doing that when you can just see lots of numbers on a computer screen. You get genuine feedback from the controls as opposed to simulated feedback that will be inevitably delayed, you can feel the turbulence as it affects the plane rather than just seeing the results on the screen a split second later. Having an actual pilot is very important. Unfortunately, getting accurate statistics on the matter is rather difficult - the failure rate of unmanned spacecraft is much higher, I believe, than manned (there are certainly far more accidents, although there are far more launches so the ratio may not be so different), but they are much more careful with manned craft so that's to be expected. --Tango (talk) 14:31, 13 October 2008 (UTC)

(unindent) I don't agree with ANY of the things you just said!

• What you do if an antenna falls off is what you do if the tailplane falls off. The trick is to design it so that doesn't happen. This is really very easy with stuff like electronics. You can easily have three or four of everything.
• Flight simulators (which I used to design) have hydraulically actuated haptic feedback devices on the controls that have real "feel" to simulate the effects you'd feel in a real plane. They work very well. It would be entirely trivial to measure the forces on the flight surfaces and provide feedback to a pilot on the ground. However, most modern planes don't provide that feedback anyway. An F16 fighter (for example) has a rock-solid steel bar for a joystick that provides no feedback whatever - it doesn't even move! It operates by measuring the force you apply to it. Several modern airliners have little joysticks like on videogames with no feedback whatever. So this is neither necessary - nor difficult to provide if it were necessary.
• The delay in getting feedback isn't going to be critical for space planes. Things just don't happen that quickly until you are about to touchdown on the runway - and at that point you are so close to the transmitter that the speed-of-light delays are irrelevent. Things that need human-response-time rates but not human intelligence can be handled by computers. Things that don't need that response rate but which do need human intelligence can be done from the ground. The only problematic things are things where human response rates AND human intelligence are required - and if you have a system that's designed that way then you have a disaster just waiting to happen because humans are highly fallible when pushed to perform quickly.
• The US military fly planes (called UAV's - Unmanned Aerial Vehicles) by telepresence and computer control all the time. Their pilots mostly sit in the Pentagon building - flying the planes from halfway around the planet via satellite links. This gives them speed-of-light response rates that are about the same as the worst case for an unmanned spaceplane. The technology is extremely well established and there are WAY more UAV's over the skies of Iraq than there will ever be spaceplanes in orbit at any given time. This is a solved problem. The Soviet Buran space shuttle flew an entire mission including launch and landing under remote control...and that was with soviet era hardware from 20 years ago.
• The failure rate of unmanned spacecraft is high because they can save money by cutting back on the safety systems. They don't have anything like the amount of redundant systems when launching a cheap telecomms satellite as they do on the shuttle (for example). But note that shuttle launches are not exactly reliable - having the pilots on board hasn't helped them at all - I don't think there has been a single case where the crew were able to do something to save the spacecraft that couldn't have been done without them.

SteveBaker (talk) 20:03, 13 October 2008 (UTC)

• • I'm not going to comment on the spaceflight angle so this is slightly OT but while I agree one of the reasons why airplanes have pilots is because not having pilots make the people nervous I would disagree that if it can be done by remote control then you don't need the pilot. I find it hard to believe, especially in the current security environment, that there will be much support for having commercial planes being operatable by remote control due to security concerns. Even though if you develop it right, the risk of an unapproved person being able to take control of the plane by hacking or breaking the system is probably lower then a hijacker, this won't necessarily allay the concerns of a lot of people including I suspect many politicians. Plus there is still the physical aspect/risk of having many planes controllable from a single point. So in other words, for commercial flight, if you need it to be done by remote control then you need a pilot since remote control is not likely to be acceptable. Also I should point out that while I have no doubt UAVs are resonably successful, it's unlikely we will have complete statistics on how many of these have crashed in the near future given this is likely to be consider sensitive information to the US military Nil Einne (talk) 10:07, 15 October 2008 (UTC)

Organisms living inside crude oil

Just out of curiosity, are there any organisms that live in oil deposits in the ground? Surely there's at least some kind of bacteria that have taken advantage of the energy in the oil. 63.245.144.77 (talk) 20:14, 11 October 2008 (UTC)

Check out entropy, oil has less usable energy than the stuff it started out as. Then again, evolution is more a model to fit past data, and it really doesn't hold any prediction ability. (The evolution sentence was a joke. -sorry) If that dream organism existed, it sure would have a monopoly and would propogate very quickly. I'm guessing that biology doesn't work that deep below ground, its sequestered by too much rock. Any organism fit for glycolysis surely would have a field day down there! All those C-H bonds, maybe cockroaches could live down there? Good question, I am very curious myself and hope someone can explain this better. Sentriclecub (talk) 20:46, 11 October 2008 (UTC)

You are incorrect. Evolution is a testable theory that has significant prediction ability. Organisms that are fit for glycolysis are essentially all organisms (yes, including humans). Oil is not sugar. It doesn't matter how good we are at glycolysis; we will in no way be able to digest oil. Cockroaches can't live down there because there's no oxygen. Evolution theory essentially tells us that if there were a way for life forms to get down there and adapt, they would (organisms will adapt to fill open niches). However, they'd have to pass through the intermediate layers of rock, which do not support any life whatsoever. Obviously things cannot live in an area that supports no life, so it's pretty much impossible for any organisms to end up down there. Entropy is also not related to any of this, because entropy has little to do with how much chemical potential energy something has. The amount of useful work that can be done with a given amount of enthalpy is decreased by the temperature times the change in entropy (see Gibbs free energy). Oil has less usable energy (per unit mass, probably) than the organic matter it started out as due to inefficiencies in converting organic material to oil. --M1ss1ontomars2k4 (talk) 20:57, 11 October 2008 (UTC)

Endoliths have been found 3 km down in rock (ref). It seems the only limit on how deep these guys can go is increasing temperature, so it's possible they go down a lot deeper (this article claims maybe 7 km). -- Finlay McWalter | Talk 21:11, 11 October 2008 (UTC)

And there are places where oil literally oozes from the surface of the earth at sea level. No - the remoteness of oil from bacteria isn't a reason they might not have evolved to use oil as an energy source. SteveBaker (talk) 00:52, 12 October 2008 (UTC)

It's hard to find a niche on Earth that doesn't have some kind of life living in it, so I wouldn't be at all surprised if there is something living in oil deposits underground. I know nothing about it, though. --Tango (talk) 20:54, 11 October 2008 (UTC)

Note there are (a rather small minority of) oil geologists who subscribe to the abiogenic petroleum origin theory, wherein oil deposits are not only inhabited by microorganisms (particularly thermophiles, both bacteria and archaea), but are actually made by them. -- Finlay McWalter | Talk 21:03, 11 October 2008 (UTC)

Read Ananda Mohan Chakrabarty to learn about one scientist who created and patented organisms which eat oil. Not sure about the "in the ground" part. It might be undesirable to release bacteria which consumed all the oil under the ground. Edison (talk) 00:03, 12 October 2008 (UTC)

In order to extract usable energy from oil (which is essentially hydrocarbons), one would need be able to create compounds with lower internal energy (enthalpy, or H) than the hydrocarbons. This is generally accomplished via oxidation. However, in order to oxidize these compounds, a source of some usable oxidizing agent needs be present. The most likely source of this is oxygen itself, and underground oil has no access to this. From a purely chemical point of view, that oil underground is safe from nearly any biological organism that might be able to "eat it". There may be some that exist that can consume oil at the surface, but that is because of the availibility of free oxygen. --Jayron32.talk.contribs 11:48, 12 October 2008 (UTC)

The fact that oil has "bugs" is well known although I can't find a good that talks about it in specifics. There is more chemistry that life than preform than photosynthesis and standard respiration, take a look at extremophiles. Even without oxygen life goes on. One of methods that eventually get used on every oil field is water injection (oil production). Its a standard part of enhanced oil recovery. According to Matthew Simmons book this process has been in effect for sometime within the Ghawar Field. But that is important for other reasons. Our concern here is that if oil producers flood wells with water containing dissolved oxygen life flourishes in the oil field eventually complicating or preventing oil recovery. It standard practice to use aquifers of sterile brine from strata above the oil fields for the purposes of water injection. This brine is for all intensive purposes free of oxygen and life. In leu of a brine aquifers, water form the surface needs to have the oxygen removed and life killed prior to injection. Regardless check out the water injection (oil production) I think its the only place on wikipedia that covers life in oil. As far as the science goes I don't know how much is well known publically besides methods to kill the "bugs" described in Society of Petroleum Engineers publications. Oil companies would rather people not know that they are exterminating rare forms of life in the process of bringing them their gasoline.--OMCV (talk) 03:39, 13 October 2008 (UTC)

Part of what inspired me to write this question was the memory of a ninth grade biology experiment we did on the first day of school where we put some water and some vegetable oil in an empty water bottle and then shook it up creating little shperical globs of oil, which are essentially the same structures in cellular membranes. Anyway, I explained this experiment to a friend of mine who wasn't in that class and I just said "oil" not being specific, so he made his own version...with motor oil. Nevertheless, it still worked the same even though it wasn't transparent. Anyway, a few weeks later, I noticed long strings of bacteria or mold or something growing in my experiment, which I stupidly set in a window sill in my room (source of energy). Coincidentally, My friend had set his in a window too and...lo and behold, there were strings of bacteria in the motor oil too. I know from personal experience that life can survive in oil if there's a source of energy, but can it survive under the ground? I'd be extremely surprised it it couldn't, actually. I recently found out that there's huge slimy colonies of bacteria in the cracks between rocks in gold mines in South Africa three miles below the surface. Scientists think that cells living at such extreme depths were the cells that repopulated the surface after huge meteorite impacts destroyed all surface life billions of years ago. So bacteria can definitely get that deep. If bacteria can live off of rocks using chemosynthesis as a source of energy, they can live off of oil in a similar way.

I guess I just answered my own question, but I'm still curious as to the nature of things living in oil. I'm surprised I can't find any info on it on google.63.245.144.77 (talk) 05:29, 14 October 2008 (UTC)

From a quick search of Nature (journal):

• Biodegradation of oil in uplifted basins prevented by deep-burial sterilization - "Biodegradation of crude oil by bacterial activity - which has occurred in the majority of the Earth's oil reserves..." (28Jun01)
• Biological activity in the deep subsurface and the origin of heavy oil - "At temperatures up to about 80 °C, petroleum in subsurface reservoirs is often biologically degraded, over geological timescales, by microorganisms that destroy hydrocarbons" (20Nov03)
• Crude-oil biodegradation via methanogenesis in subsurface petroleum reservoirs - "has been attributed to aerobic bacterial hydrocarbon degradation..." (10Jan08)

Bacteria in crude oil? Early and often. And as you note, bacteria in deep rocks unrelated to petroleum are known and may be the progenesis of current life on earth. Sign up for an account and I can email you copies of those papers and many more. Franamax (talk) 09:15, 15 October 2008 (UTC)

Oh yes, here in Canada we're talking about harnessing those bacteria - though I'm not too enthused about injecting little lifeforms into the second-largest store of petroleum on the planet, seems to me one or two things could go wrong in that process and we could, umm, come to regret the decision. Franamax (talk) 09:26, 15 October 2008 (UTC)

Strange thermodynamics question

Say we have some ideal gas. It undergoes an adiabatic expansion from 1 Liter to 2 Liters and does no work. What are ΔU and ΔH for this process? I already know ΔU (ΔU = ΔQ + ΔW, all of which are zero), but I don't quite get ΔH. So far, we have that dH = dU + PdV + VdP. dU is zero, PdV is zero (no work done). But what's VdP? Since no work is done, can we say that the external pressure is zero and constant, and thus VdP is zero? --M1ss1ontomars2k4 (talk) 20:30, 11 October 2008 (UTC)

Your question is self-contradictory, I'm afraid. If you let the ideal (or any) gas expand adiabatically from V₁ = 1 L to V₂ = 2 L, it will perform work equal to integral of PdV from V₁ to V₂. On the other hand, if you put external pressure to zero, the gas will not do any work, but the expansion will not be adiabatic. The only way to stay adiabatic AND to have zero pressure is to have initial pressure = 0. That implies either an ideal gas at initial T=0, or ideal gas with zero particles in the volume considered. Hope this helps. --Dr Dima (talk) 03:58, 12 October 2008 (UTC)

Why would it not be adiabatic, if external pressure were zero? Reversible adiabatic processes are isentropic but this is not really reversible, if the external pressure were zero. --M1ss1ontomars2k4 (talk) 04:04, 12 October 2008 (UTC)

Sorry, I misunderstood your question. I thought you are referring to reversible (isentropic) adiabatic expansion process. If you are referring to non-isentropic adiabatic expansion with zero work performed, the enthalpy H should stay constant. indeed, H = U + PV. In your process (non-isentropic adiabatic expansion with zero work performed) U does not change, and PV is zero all the time so it cannot change (both PdV and VdP are zero). Thus, ΔH = 0. For an ideal gas that means that you stay on an isotherm. Indeed, U = DNT/2 where D is number of degrees of freedom per particle, N is total number of particles, and T is temperature. As long as U stays constant, so does T. Hope this answers your question. For clarity, it is important to realize that the initial state for your process is out of the equilibrium: pressure is zero but NT/V is not zero. That happens when you suddenly remove a wall separating gas in volume V₁ from the void in the rest of the volume V₂, where V₂ > V₁. And a final note: many physicists, including myself, normally use the words "adiabatic process" only when they are talking about reversible adiabatic ( = isentropic ) process. A process in which ΔQ = 0 and ΔN = 0 but entropy increases is simply referred to as "irreversible process". Keep that in mind and you'll be fine ;) --Dr Dima (talk) 01:17, 13 October 2008 (UTC)

Intelligent Life in the Universe/Voyager Golden Record

I have been interested in the Golden Record that is on Voyager 1 and 2. I learned about how it is there in case Voyager encounters intelligent extraterrestrial life on its journey. If other intelligent extraterrestrial life created something similar and it went through our solar system, would we have any way of knowing? —Preceding unsigned comment added by 75.169.21.144 (talk) 21:28, 11 October 2008 (UTC)

It would probably be difficult to spot unless it passed very close to Earth. I expect any radio transmissions would be pointed back towards where it's come from, if there even are any (the Voyager craft will stop transmitting millennia before they reach other stars). Because they operate so far from the sun, they use nuclear power rather than solar panels, which means they don't have a particularly large reflective area so would be very bright. You would probably only see one if it passed close to Earth and you happened to point a large telescope in the right direction at the right time. --Tango (talk) 22:39, 11 October 2008 (UTC)

if such a device entered the solar system, it might have a circuit to trigger a beacon which would send radio sugnals to get our attention. When Voyager was launched, we did not know how to build a device which would "wake up" and send out signals after tens of thousands of years. Edison (talk) 23:56, 11 October 2008 (UTC)

It's probably safe to say that we still don't know how to build such a device. We have no idea what happens to our spacecraft after tens of thousands of years, since we've only had most of the supporting technology and advanced materials for less than a century. We could design a system to be "very reliable" and develop some system (software?) to wake it up in a few millenia, but there is no way we could test the reliability of it over thousands of years. HALT testing only goes so far in estimating certain types of failure. Nimur (talk) 00:37, 12 October 2008 (UTC)

Most of it doesn't need to be operational for 10,000 years, it just needs to sit there, so there isn't a whole lot that can go wrong (you would want some good shielding from radiation, etc, but that's about it). I think the real problem isn't the time, it's the cold, electronics break pretty quickly if they get too cold and the power requirements of keeping the probe warm for 10,000 years are most likely beyond us at the moment. --Tango (talk) 11:51, 12 October 2008 (UTC)

The point is that once Voyager gets away from the Oort cloud, there is no reason why it shouldn't keep moving off into the galaxy for millions or even billions of years. Over all that time - it is perhaps possible that some alien species would find it. It seems unlikely that they'd be able to decypher it though. The plaque and record are really poorly designed IMHO. SteveBaker (talk) 03:30, 12 October 2008 (UTC)

I think the likelihood of anything finding it is probably less than the likelihood of making any sense of it. Assuming something beyond dumb and impossible luck, any species that had the technology to locate that particular need in the interstellar haystack should be able to figure out the technology without too much difficulty, I'd imagine. --98.217.8.46 (talk) 03:33, 12 October 2008 (UTC)

That doesn't diminish how undeniably cool it is. We recorded the fundamentals of our species in a (hopefully) universal format and sent it careening into the depths of space. That has an intrinsic value to our species, even if it never facilitates communication with another. Plasticup ^T/C 05:23, 12 October 2008 (UTC)

I agree that it's an interesting statement, one that says more about the act of creating it than it does about its potential discovery. But it's worth noting that the selection of content says more about the people who created it than it does about the human species. Not all members of our species would agree on what the fundamentals were. For example, from what I can tell via Voyager Golden Record, there were no religious texts included whatsoever. No doubt Sagan may have thought that "Johnnie B. Goode" was more fundamental to understanding US culture than the Bible, but I'm sure there would be those who would vehemently disagree. ;-) --98.217.8.46 (talk) 13:33, 12 October 2008 (UTC)

It's about putting our best foot forward, I suppose. Plasticup ^T/C 16:14, 12 October 2008 (UTC)

There don't seem to have been any texts included at all, religious or otherwise. It looks like among the vocal music there was none with a religious text, but it's not as though an extraterrestrial could tell what the words meant anyway. -- BenRG (talk) 19:15, 12 October 2008 (UTC)

Well if we were really a space-faring society, i.e. one with personal and commercial inter-planetary travel, then I suspect that Space Traffic Control would monitor every rock much bigger than a ping-pong ball and fairly quickly notice a new metallic object entering the solar system. Obviously that makes assumptions about what the distant future of space travel might be like, but there is no reason to assume that ET will be as primitive as us. Dragons flight (talk) 06:03, 12 October 2008 (UTC)

If Voyager I ever travels through a planetary system similar to our solar system then it will be moving very fast indeed by the time it reaches the vicinity of an Earth-like planet's orbit. At the moment it is about 100 AU from the Sun and is travelling at about 17 km/s. If it fell into the gravity well of a star similar in mass to the Sun then at 1 AU from that star it would be travelling 10 times as fast, so 170 km/s. At this speed it covers a distance equal to the diameter of the Earth's orbit in about 20 days. So not much time to detect it, and quite difficult to catch it if it is detected. Gandalf61 (talk) 10:31, 12 October 2008 (UTC)

Ummm, your numbers are off. Falling into the sun's gravity well would only give you ~42 km/s at Earth's orbit. Dragons flight (talk) 16:51, 12 October 2008 (UTC)

42 km/s is escape velocity from the solar system starting from the Earth's orbit. But Voyager I is going much faster than escape velocity, mainly due to gravity assists from Jupiter and Saturn on its way out of the solar system. In the absence of interactions with planets, velocity of a free-falling spacecraft is inversely proportional to the square root of distance from the Sun (by conservation of energy), so 17 km/s at a distance of 100 AU becomes 170 km/s at a distance of 1 AU. Gandalf61 (talk) 20:19, 12 October 2008 (UTC)

I don't follow your calculation. Falling adds to the velocity, it doesn't multiply it by something (what it adds is dependant on initial velocity, but I can't see how you end up that result). --Tango (talk) 20:38, 12 October 2008 (UTC)

No, 17 km/s approximately goes to ${\sqrt {17^{2}+42^{2}}}\approx 45$. The energies, which are proportional to velocity squared, will add not multiply. You seem to just multiplying by 10 since that is the sqrt of 100, which is wildly wrong. Dragons flight (talk) 21:15, 12 October 2008 (UTC)

Yes, you are right. Escape velocity is inversely proportional to the square root of distance from the Sun, not velocity of spacecraft. Total cock-up on my part. Gandalf61 (talk) 10:11, 13 October 2008 (UTC)

Even if we spotted an Alien Voyager probe, we'd have no way of retrieving it to read the alien golden record. We'd have to just hope that it settles into a stable orbit until we were ready to go after it.

Of course, who knows? Maybe one day our own space travel will advance to the point where Voyager 1&2 will wind up in the Smithsonian one day. (Or at least the CD-Roms on Mars.) APL (talk) 12:54, 14 October 2008 (UTC)

What does Radioactive Waste look like?

I read the article on radioactive waste, but I'm still not sure what the final "stuff" looks like. In popular culture, it's usually depicted as this glowing green stuff, but I have a feeling that's not really what it looks like. I guess in other words, what does the radioactive waste inside of those containers look like? ScienceApe (talk) 22:37, 11 October 2008 (UTC)

Radioactive waste can be unprocessed, in which case it's just raw fuel rods (containing fuel pellets). So that's just thin shiny cylinders filled with little metal cylinders the size of short stacks of coins. For reprocessed waste, high-level waste can be encapsulated in a number of ways; one is in glass blocks (or disks). -- Finlay McWalter | Talk 22:48, 11 October 2008 (UTC)

Radioactive waste (low level) can be clothing, rags, mops, cardboard, bottles, and many other materials which could become contaminated with radioactive materisl, as when there is a fluid leak in a power plant which releases radioactive materials that must be cleaned up. It goes in drums and gets stored. Edison (talk) 23:54, 11 October 2008 (UTC)

What's the fluid usually? ScienceApe (talk) 01:13, 12 October 2008 (UTC)

My understanding is that most high-level radioactive waste is produced in reprocessing plants—acids and washes used to separate out plutonium from other fission products and things like that. Probably just looks like sludge. If you google "hanford waste tanks" you can find images of a lot of liquid waste—nothing very interesting. Certainly not glowing green goo. --98.217.8.46 (talk) 03:16, 12 October 2008 (UTC)

So it would look like just some thick brown fluid? ScienceApe (talk) 14:42, 12 October 2008 (UTC)

For the record, the Cerenkov radiation in nuclear reactors causes them to glow blue, not green. Radioactive waste stored in water could also glow blue if there was enough of it, but more likely it would be broken up into small enough portions that there would not be a human perceptible glow. Dragons flight (talk) 04:13, 12 October 2008 (UTC)

Another form of nuclear waste is the power plant after decommissioning. Especially the material that contained the reactor core. So that would look like construction material, I suppose. Metal plates and such? Amrad (talk) 07:01, 13 October 2008 (UTC)

And concrete.

Note that when it comes to disposal, sludge is not favoured, because if the container were damaged it could leak into groundwater. I believe, the British Nuclear Decommissioning Authority favours "microencapsulation", where liquid wastes are immobilised inside containers with a grout. AlmostReadytoFly (talk) 10:06, 13 October 2008 (UTC)