Wikipedia:Reference desk/Archives/Science/2008 September 12

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September 12

If the LHC created a black hole...

Or more generally, if a black hole were to appear on or near Earth's surface(presumably a small one, but let's say it's just big enough to avoid collapsing into Hawking radiation), how long would it take to swallow up the entire planet? And what would happen to the rest of the solar system? 68.123.238.140 (talk) 02:10, 12 September 2008 (UTC)

Longer than the expected life of the solar system, and no effect. Even if it swallowed the Earth in a day, the solar system would be fine -- you'd still have an Earth-ish mass orbiting the sun. — Lomn 02:25, 12 September 2008 (UTC)

Another related question: how big would a black hole need to be in order for there to be exactly 24 hours before the earth was gone? Nadando (talk) 04:07, 12 September 2008 (UTC)

Cannot be computed exactly. In fact, a silly question (do you need a 24h message in advance?). Next black hole question, please. --Ayacop (talk) 08:00, 12 September 2008 (UTC)

So you could use a vacation day, of course... --- OtherDave (talk) 10:40, 12 September 2008 (UTC)

It's amazing how ill-informed scientific reports, scare stories and other paper selling drivell is generating an unprecedented interest into an amazing scientific work that might have gone unnoticed outside of the ususal aficionados. 190.244.186.234 (talk) 11:47, 12 September 2008 (UTC)

I think the scientific community has underestimated how well a little irrational fear can benefit them if they spin it right. --98.217.8.46 (talk) 12:42, 12 September 2008 (UTC)

"Nice planet, mate. Awful shame if somethin' bad happened to it ..." Gandalf61 (talk) 13:52, 12 September 2008 (UTC)

Rather a high level of WP:BITE here: please avoid pejoritives such as "silly," "drivell (sic)," and "irrational" in responses. Lomn has the right idea in providing a reasoned and informative response without insulting the questioner. Edison (talk) 19:01, 12 September 2008 (UTC)

Have any scientists calculated the beam energy scale where we would actually say "Hmm, maybe we better not try that"? Could it be the next machine after the SHLC? Franamax (talk) 19:27, 12 September 2008 (UTC)

Probably somewhere around the Overwhelmingly Large Hadron Collider, which I think comes after the Ginormous Hadron Collider. -- Coneslayer (talk) 19:32, 12 September 2008 (UTC)

I don't know how higher energies are likely to cause problems, regardless of how high they get (assuming the equipment is built to handle that much energy - obviously if the machine explodes that would be undesirable! It wouldn't destroy the planet though, just Switzerland. ;) ). All the fear with black holes is nonsense, it doesn't matter how much energy is involved, black holes just don't behave in ways that would swallow the Earth like that. --Tango (talk) 21:22, 12 September 2008 (UTC)

Yes, I'm not that interested in the MBH hypothesis, for one thing, we now have an experiment underway to test it :)

However, to take a ridiculous example, if you collided two particles with the same energy as the Big Bang, you would end up with a new expanding universe in your lab, which could have undesirable results. Somewhere between there and here must be a line where problems could result.

Wouldn't there be an energy where you made a black hole big enough that it would be a problem? Or a sufficiently energetic strangelet or powerful magnetic monopole that they would do whatever bad things they might do?

How many orders of magnitude are we away from those energies? Franamax (talk) 23:15, 12 September 2008 (UTC)

The energy has to come from somewhere, you would need to extract all energy from the whole universe in order to create an explosion with the same energy as the big bang (and even then, it wouldn't be a big bang - the big bang involved space expanding, not just matter exploding). --Tango (talk) 08:38, 13 September 2008 (UTC)

Well, I suppose I shouldn't have postulated the ridiculous case of the Big Bang. (Though I'm reminded somewhat of an Asimov story where the first computer was asked "can the end of the universe be prevented?" and the last computer solved it, and "the cosmic AC said 'Let there be light' - and there was light").

I will persist in my question though - is anyone aware of scientific calculations as to the energy scale of a collider which could produce particles or states of matter which could pose a planetary threat? I'm pretty sure that every accelerator ever built has had just such a risk assessment - so what was the risk based against? In fact, in the 60's and 70's, I think there was a specific named committee to examine new accelerators.

And as a secondary question, what are the energy scales where we could possibly produce a more stable phase of matter, a cosmic Ice-9 as it were? Obviously these would be theoretical answers - has anyone done the theory? Franamax (talk) 10:27, 13 September 2008 (UTC)

Even in less extreme cases, the energy still has to come from somewhere. I don't think putting lots of energy into a few subatomic particles is going to be any more dangerous that releasing the same amount of energy with a bomb, so you would need to get an amount of energy into the particles comparable to the energy released by several large nuclear bombs - that's very difficult to do. As for your second question, more stable than what? Regular matter is pretty stable... --Tango (talk) 11:21, 13 September 2008 (UTC)

Water bears on Mars

We hear about the harsh conditions on Mars, and how unlikely it is to find life. But Water bears (Tardigrades) have been shown to survive (for 10 days)[1] conditions far harsher than those seen by recent Mars probes, including the vacuum of outer space, temperature extremes, and intense UV radiation.. They can survive ten years without water, temperatures from about absolute zero to 151 Celsius, and 1,000 times the radiation which would kill humans. Could terran Tardigrades survive and reproduce in the Martian polar areas, given that there seems to be liquid water sometimes? (after 6 "database locked" error messages)Edison (talk) 05:16, 12 September 2008 (UTC)

I don't think there's ever liquid water on Mars (currently, that is), the most it does is sublimate. Also, according to this Wired article: "Tardigrades may even provide insights into adaptations necessary for survival in off-Earth colonies, though they could not live actively in the extreme and nutrient-poor environments of Mars or the moon." -- MacAddct  1984 ^{(talk • contribs)} 05:44, 12 September 2008 (UTC)

See Extremophile. Even the limited spectrum of life seen on this planet shows that there is probably no environment too harsh for life to develop. There is a very real chance that space itself is liberally populated by micro-organisms which could very well seed planets, satellites, asteroids and comets with the first steps on the way to macro-organisms - I deliberately avoid use of the word "higher" or "more advanced", as being very subjective. 196.2.124.253 (talk) 06:47, 12 September 2008 (UTC)

The bacteria that can survive in space usually do so by becoming dormant, they need less extreme conditions to actually reproduce. I don't think the surface of Mars ever has conditions suitable for terrestrial life to reproduce, although somewhere underground theoretically could. --Tango (talk) 10:32, 12 September 2008 (UTC)

Maybe deinococcus radiodurans would be a better candidate. -- MacAddct  1984 ^{(talk • contribs)} 14:16, 12 September 2008 (UTC)

If there is never liquid water, coult sometning like a tardigrade live in the water ice layer a few inches below the Martian surface, dormant most of the time, but active and reproducing when conditions are least harsh? Desert plants and animals remain dormant for a year or longer on earth and use the rare less harsh conditions to do their business. Edison (talk) 18:55, 12 September 2008 (UTC)

Earth-derived life seems to requre exactly two things to flourish: liquid water, and an energy source. We've never found life where one or the other is missing, and everywhere we've looked that has both, we've found life. --Carnildo (talk) 21:35, 12 September 2008 (UTC)

If one is speculating about the forms that life might take, then there is no reason to suppose that water is a prerequisite for life to develop or exist. 196.2.124.253 (talk) 19:56, 12 September 2008 (UTC)

There is somewhat of a difference between lasting 10 years and 100000000 years between ice melting. Radiation damage would be far more severe, and any way what is there to eat for those tardigrades on Mars? The perchlorate would poison them anyway! Being animals they also need to respire oxygen . Graeme Bartlett (talk) 22:48, 12 September 2008 (UTC)

Water on Mars? They also recently found wet rivers that dried up I think.

~AH1^(TCU) 23:48, 12 September 2008 (UTC)

Gamma ray bursts and black holes

Gamma ray bursts are a very large release of energy. Assuming black holes have a limited lifetime because of an upper limit to the mass that they can contain, would an explosive release of that mass be of the same order of energy as observed gamma ray bursts? 196.2.124.253 (talk) 06:31, 12 September 2008 (UTC)

Much bigger. Who cares, it will never happen. Next black hole question, please. --Ayacop (talk) 07:56, 12 September 2008 (UTC)

Since no existing theory predicts an upper limit to the mass of black holes, there's nothing we can really say about what would happen when a black hole hit such a limit. Algebraist 09:46, 12 September 2008 (UTC)

Black holes don't explode... very small ones evaporate by Hawking radiation pretty explosively, but all black holes will evaporate at the same rate in their last X seconds of life, regardless of their starting mass (bigger ones will just take longer to get there). --Tango (talk) 10:30, 12 September 2008 (UTC)

This possibility has been explored by scientists, but not for black holes formed from stars since they last very very long, but for smaller black holes created in the big bang. I can't find any references but I think they studied what the signature flash would be like. No sightings so far. EverGreg (talk) 16:03, 12 September 2008 (UTC)

As mentioned, there is no known upper limit, but presumably if a black hole evaporated for long enough, at some point (the Chandrasekhar limit?), gravity would not be strong enough to resist the various forces of matter that enjoy a little lebensraum and it would explode. --Sean 16:40, 12 September 2008 (UTC)

As far as I know, degeneracy pressure doesn't count for anything once it's collapsed into a black hole - there isn't really any matter left, there's just a singularity (of course, our understanding of black holes isn't really up to explaining what happens to the matter). Current theories don't include any kind of lower limit under which black holes explode, there's just Hawking radiation (which grows exponentially, so the last fraction of a second would seem rather explosive). --Tango (talk) 17:42, 12 September 2008 (UTC)

Radioactive decay in materials. Schrodinger's cat

The degree of decay in a given radioactive material is measured in half-life. If this is so, then surely it should be possible to predict the point in time at which a material has sufficiently decayed to an extent that it will trigger the release of a poisonous gas, thus killing an imprisoned cat? —Preceding unsigned comment added by 78.32.39.90 (talk) 08:13, 12 September 2008 (UTC)

Half-life is a measure of a quantity of atoms, i.e., statistical. No way to predict the behaviour of a single atom which is random. Those gedanken experiments you are referring to (see Schrödinger's cat) always involve a single atom, not a quantity. --Ayacop (talk) 08:30, 12 September 2008 (UTC)

The half-life is basically an average, there is plenty of deviation from that average for either small amounts of the isotope or small periods of time. --Tango (talk) 10:27, 12 September 2008 (UTC)

As the others say, the problem is that if it is a single atom you have no way of predicting when it will or won't decay. Half-life does not tell you about that. --98.217.8.46 (talk) 12:37, 12 September 2008 (UTC)

Instead of providing a solution, the statistical nature of half-life is actually what causes the problem. If you have a large quantity of a radioactive material, after one half life 50% of that material will have decayed. Therefore, there is a 50% probability that any individual atom in that material will decay. According to quantum mechanics, that atom actually exists in a superposition of states (decayed/radioactive) until we observe it, at which point our observation collapses the wave function into one state or other. The point of the schrodinger's cat thought experiment was that by including the cat in the system, the cat itself should be thought of as entagled with the atom and therefore as existing in a superposition of states (dead/alive) until we observe it, which is extremely counter-intuitive. Schrodigner originally meant the experiment as a discusison of QM's flaws, but subsequent interpretations of the thought experiment have been used to illustrate how other interpretations of QM operate. Read our article on it, it's not bad. --Shaggorama (talk) 14:18, 12 September 2008 (UTC)

Unsailable Dead Sea

Our Dead Sea article states that the "salinity makes for a harsh environment where animals cannot flourish and boats cannot sail". Why is that? Is it due to high buoyancy or the effect of the salt on the hull of the boats? Or something else? -- MacAddct  1984 ^{(talk • contribs)} 15:12, 12 September 2008 (UTC)

No... I suspect that the article is wrong. Plasticup ^T/C 16:00, 12 September 2008 (UTC)

I've dropped it from the article. Such a surprising claim certainly needs a supporting citation. ike9898 (talk) 16:28, 12 September 2008 (UTC)

Animals not being able to flourish is certainly true (hence the name Dead Sea), but I can't see any reason why boats would have any difficulty, the added buoyancy should make things easier, not harder. --Tango (talk) 17:44, 12 September 2008 (UTC)

The very salty water might promote corrosion of metal hulls, but that's hardly the same as "boats cannot sail". --Anon, 22:06 UTC, September 12, 2008.

The Israel Museum certainly thinks it's possible to sail: [2] Now, they're just showing old anchors, so it's technically possible that all you can do is anchor a boat in the Dead Sea. ;) I would think though that the greater buoyancy would decrease draft and maybe make it much harder to control the boat. You might need so much ballast that your boat would be too heavy for the wind to push. Franamax (talk) 23:00, 12 September 2008 (UTC)

I was thinking that - I think you just need to change the shape of the boat so it has a flatter bottom, that should stabilise it (I've not done much sailing, so I'm guessing here). --Tango (talk) 08:35, 13 September 2008 (UTC)

This convention center advertising touts "sailing on the Dead Sea itself". Clarityfiend (talk) 02:03, 13 September 2008 (UTC)

And in case there's any doubt left at all... Site Matt Deres (talk) 15:25, 13 September 2008 (UTC)

Electroforming solution

Is there anywhere where i can find some recipes for a coppor electrioforming solution. I know that the main components are distilled water, copper suphate and various acids but cannot find any information about quantaties of each. Any help would be very much appreciated. regards Kirk uk —Preceding unsigned comment added by 87.82.79.175 (talk) 16:04, 12 September 2008 (UTC)

here you go. Watch yourself with those acids! Fribbler (talk) 17:53, 12 September 2008 (UTC)

Patella/knee jerk reflex

I've knocking my knees every which way with a finger-long hammer (toy, tool? I know not which) and I'm getting no reflex. I've seen the graphics but can't find the spot. Argh. Imagine Reason (talk) 17:40, 12 September 2008 (UTC)

I think it's just below the knee cap, there's a soft bit. Make sure your knee is bent and you should feel a dip between the knee cap and the top of the lower leg bone (I'm sure someone will tell me what that bone is called, but I don't really care!). I can trigger the reflex by hitting that spot with the side of my hand. --Tango (talk) 17:46, 12 September 2008 (UTC)

Yes, the patellar tendon is the spot, like tango says (above the tibia). You can also try to enhance the reflex by clenching your teeth or trying to pull your clasped hands apart. Fribbler (talk) 17:49, 12 September 2008 (UTC)

Huh. What's that based on? I mean, what makes it work like that? -- Captain Disdain (talk) 17:59, 12 September 2008 (UTC)

Shhhh Captain! :-) Telling you how it works will likely remove some (but not all) of it's effectiveness. It sure works though. I use it regularly. Fribbler (talk) 18:08, 12 September 2008 (UTC)

Oh, good old misdirection. I dig. -- Captain Disdain (talk) 00:11, 13 September 2008 (UTC)

It works better if someone else does it to you. Graeme Bartlett (talk) 22:38, 12 September 2008 (UTC)

chemistry - glassware

I have been working in labs for a couple of years, but I never have understood exactly the qualifications for volumetric glassware to called class "A." Does anyone know what the requirements are? —Preceding unsigned comment added by 204.214.74.84 (talk) 18:12, 12 September 2008 (UTC)

See Volumetric flask. Strawless (talk) 18:56, 12 September 2008 (UTC)

I have read that article but I was wondering if there is a more precise definition of the classifications -- all the article says is that the graduation mark is placed more accurately. This begs the question, to what degree of accuracy? —Preceding unsigned comment added by 204.214.74.84 (talk) 19:55, 12 September 2008 (UTC)

Have a look at this pdf file. It contains a table of how accurate the graduations must be. Fribbler (talk) 20:01, 12 September 2008 (UTC)

PHEV Battery Economics

How can I calculate the following:

• Cost of Plug-in Hybrid Electric Vehicile (PHEV) vs. Internal Combustion Engine (ICE) in cents/mile?
• Total lifetime operating cost of PHEV-vs-ICE, including the decrease in battery capacity and resistance to re-charge with time, as well as the difference in maintenace costs between PHEV and ICE technologies?

Also: Can the batteries proposed for PHEV's be used as a storage system for homes using wind or photo-voltaic power systems? 146.18.173.73 (talk) 18:51, 12 September 2008 (UTC)EC

The Tennessee Valley Authority had a wind generator which charged battery powered vehicles as a demonstration project over 30 years ago, so clearly wind generated electricity could be used to charge the batteries of a plug-in hybrid vehicle. Any source of electricity could be used to charge any batteries, with varying cost effectiveness. As for the other question, experience may not exist yet for lifetime operating cost. What is the lifetime of a vehicle these days? Edison (talk) 01:06, 13 September 2008 (UTC)

angular momentum

Is angular momentum just a manifestation of linear momentum (ie you can treat angular momentum as the combination of thelinear momenta of each of the rotating object's particles)? There's a follow-up question. —Preceding unsigned comment added by 65.92.231.82 (talk) 21:04, 12 September 2008 (UTC)

Short answer, yes. I think it also works the other way around - linear momentum is just angular momentum taken around a point at infinity (don't quote me on that, though!). --Tango (talk) 21:25, 12 September 2008 (UTC)

This is probably a silly question -- I'm trying to make my quota for the week. If linear momentum is angular momentum taken around a point at infinity, is that point on the line of the linear motion, off to the right, downstage left, or?? Wanderer57 (talk) 21:46, 12 September 2008 (UTC)

I haven't heard this interpretation before, but it seems like it ought to be the point at infinity at right angles to the line (which of these two points you choose will just introduce a minus sign somewhere). Algebraist 21:52, 12 September 2008 (UTC)

Wouldn't any point not on the line of motion yield a linear momentum? i.e. hold your reference point steady then allow the mass to continue moving, it's no longer at a right angle but the momentum is still linear. -- Mad031683 (talk) 22:03, 12 September 2008 (UTC)

Yes, but not a constant one. An object moving in a circle does have a linear momentum, but it changes direction as it moves round. If the point is at infinity (and I did have an infinity at right angles in mind, yes) then that change in direction becomes zero (a radius of curvature of infinity corresponds to a straight line). I'm not sure how rigorous all that is, I haven't really heard it before in this context, but it makes sense intuitively (I have heard of translations being thought of as rotations about infinity - momenta are a natural extension of that, I think). --Tango (talk) 08:32, 13 September 2008 (UTC)

Okay, there's a reason I asked this question. If I push against a vertical wall, I will gain linear momentum, right? But the earth in response will start spinning. Isn't the sum of the linear momenta of a rotating body equal to 0 (every point has corresponding point going in the opposite direction). So how is linear momentum conserved? Is the question even valid (a force is acting on each of the rotating particles to keep them in uniform circular motion)? —Preceding unsigned comment added by 65.92.231.82 (talk) 21:57, 12 September 2008 (UTC)

In considering the momentum changes when two bodies interact, you have to use a reference frame based on their common center of gravity. When the objects are you and the Earth, that will be near enough to the center of the Earth. When you push against a wall, you set the Earth spinning and you also set yourself rotating around that center of gravity. The momentum you gain only seems linear because your motion is constrained to be parallel to the Earth's surface and you move a small enough distance that the Earth seems flat. But angular momentum is conserved. --Anon, 22:17 UTC, September 12, 2008.

No. Gravity does not have to have to be intoduced. Besides, you can push strongly enought to surpass the earth's escape velocity. Anyway, even in your example linear momentum wouldn't be conserved. —Preceding unsigned comment added by 65.92.231.82 (talk) 23:26, 12 September 2008 (UTC)

• I did not mention gravity, I mentioned the center of gravity, also called the barycenter or center of mass. My apologies for confusing you by my choice from the three synonyms. --Anon, 21:08 UTC, September 13, 2008.

Ignoring gravity, you push on a wall on Earth's surface and fly off into space. Your push gives Earth some angular momentum (around its center of mass) and also some linear momentum (its center of mass moves away from you as it spins around it). -- BenRG (talk) 10:23, 13 September 2008 (UTC)

Missiles on Main Battle Tanks

Are there any MBT's that mount missiles? Is there a reason why most (if any) don't mount missiles? ScienceApe (talk) 21:36, 12 September 2008 (UTC)

Missile tank. Dragons flight (talk) 21:51, 12 September 2008 (UTC)

Price is a factor: a TOW missile appears to have a unit cost (the missile, not the launcher) of $38,000. The M256 round an M1 Abrams MBT fires costs around $4000. The two rounds have comparable weight and lethality (although the TOW has greater range). That cheaper round means you can have more in inventory and thus don't have to be so careful in deciding what to shoot at (and so can shoot at lower-value targets). -- Finlay McWalter | Talk 21:56, 12 September 2008 (UTC)

Yea, I've considered the costs. Missiles cost so much which is why railguns are so appealing in the future. But missiles can do things that cannons can't. Like being guided. Such a thing would be useful against attack helicopters and such. I would think that kind of extra protection would justify the extra costs. ScienceApe (talk) 22:14, 12 September 2008 (UTC)

But cannon shells can be guided.[3] Once again expense enters into the equation. Rmhermen (talk) 23:48, 12 September 2008 (UTC)

It's always tempting (to generals in particular) to keep adding stuff on (until they've build an Apocalypse Tank). But you get much more flexibility if you build the antiaircraft capability separately, so you can a) defend what you like with it and b) it can be a mile or so behind the dynamic tank battle and still give effective AA protection. The jack of all trades is the (super expensive) master of none. -- Finlay McWalter | Talk 22:33, 12 September 2008 (UTC)

Additionally, you don't really want all your big expensive fragile (and explosive) stuff outside the tank's armor. Even if its destruction won't harm the tank, it's highly vulnerable to soft kills and endangers exposed crew or nearby troops. — Lomn 23:19, 12 September 2008 (UTC)

Eh. I've considered that too, but I would think there would at least be some more experimentation with such a tank. I guess we could assume it would become a jack of all trades, master of none, but without actual testing it's a little presumptuous. ScienceApe (talk) 03:26, 13 September 2008 (UTC)

According to IT-1, "The large deadzone around the tank created by the missiles' minimum range combined with the limited amount of ammunition carried made it unpopular with the military." Clarityfiend (talk) 08:10, 13 September 2008 (UTC)

England MD/MBBS info

Hello every one.I need imformation about England Medical College/Universities for MD/MBBS courses.Please any body tell me the Tuition Fee,Living Fee,visa and other requirement for international students and also scholarship availibility.Any help will be much appreciated.OR someone wantto directly contact me are most wellcomed. thax —Preceding unsigned comment added by 202.125.143.76 (talk) 23:13, 12 September 2008 (UTC)

Hi 202, I googled here[4] then my eyes decided to swim in opposite directions so it's over to you – but it's a start until someone who knows comes by. Julia Rossi (talk) 07:27, 13 September 2008 (UTC)

Hi. Individual medical schools in the United Kingdom all charge different tuition fees, the only way to tell is to look at the individual schools themselves. Try looking at List of medical schools in the United Kingdom, picking a few that sound interesting to you, and going to their websites. They always give details of their international rates, and usually give you an idea of living costs. —Cyclonenim (talk · contribs · email) 08:19, 13 September 2008 (UTC)

This website [5] run by the British Council, has a number of search options for courses, scholarships etc. It would also be worth contacting the British Council, either through the website or through the branch nearest you. DuncanHill (talk) 12:11, 13 September 2008 (UTC)