Wikipedia:Reference desk/Archives/Science/2010 November 24

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

November 24

Are there any self-sufficient polities left?

Let's set a minimum population of 100,000 to rule out dinky communes and Pacific Islanders and such - are there any truly self-sufficient groups remaining in the world? or has trade (and other things) created interdependence pretty much everywhere? The Masked Booby (talk) 08:06, 24 November 2010 (UTC)

You have to distinguish between "can be" and "is". I bet a lot of groups could be self sufficient if they wanted, but use interdependence to make things easier and more efficient. North Korea has an official policy of self-sufficiency, but as far as I know it doesn't work in practice. Ariel. (talk) 09:25, 24 November 2010 (UTC)

I would particularly if you are considering "can be" suggest you also have to define "self-sufficiency". At a basic level, this would arguably be water, food, some form of energy and perhaps shelter. While things like the internet are sometimes considered important enough to life in the developed world that they may be considered a basic right, it's questionable if the lack of internet access (and computers or something else to use that access) is really enough to make some society non self-sufficient. Then there are of course things like large TVs that wouldn't generally consider a basic necessity at all. On the other hand there are the more iffy things like medical care. Nil Einne (talk) 13:26, 24 November 2010 (UTC)

You could say the combined human population of the Earth forms a self-sufficient polity of 6 billion people. Apart from that, trade has been improving human living standards since at least the Stone Age, so if you defining "self-sufficient" a no trade, then no, no significant subset of the human population is self-sufficient. Physchim62 (talk) 13:32, 24 November 2010 (UTC)

The last really big group of people to be discovered that had previously had no contact with outsiders was people living in the interior of New Guinea [1]. During the 1930s, mining expeditions and such discovered about a million people who had had no contact with people on the coasts. This population was not a single cohesive unit, but rather a smattering of individual tribes or villages, each one maybe numbering in the thousands. There may still be small groups of people who have not been contacted by the rest of the world (in the Amazon, or similar little explored regions), but the possibility of discovering a largish group of people like this is very small. Buddy431 (talk) 18:23, 24 November 2010 (UTC)

Many countries have sufficient natural resources to feed, clothe, house, and keep their citizens warm and in nominally functional economies, but most of the "industrialized" nations have outsourced most of their manufacturing sectors. Germany is an example of a OECD country which still has a very robust manufacturing sector, but I think it imports a lot of energy. At the other end of the spectrum, China is one of the places to where the developed nations have outsourced their manufacturing, so if they became isolationist they can be self-sufficient but it would mean a huge loss of employment for them. Ginger Conspiracy (talk) 05:19, 27 November 2010 (UTC)

Fastest acceleration in the world

Which source produces the fastest acceleration in the world or universe? Can such an acceleration kill by dragging all blood out from some point in the human organism? —Preceding unsigned comment added by 89.77.158.172 (talk) 09:00, 24 November 2010 (UTC)

Well an explosion such as a supernova would certainly take care of the killing bit. Not sure whether that would be the fastest acceleration going on.--Shantavira|^{feed me} 09:25, 24 November 2010 (UTC)

(ec)A wakefield plasma accelerator is probably the strongest on earth. In the universe there are some amazingly intense accelerators though. Magnetars, Pulsars, Black holes. There are two ways to accelerate something. You can accelerate every atom of the object at once, gravity for example does this. If you do that then you feel nothing - every part of you accelerates at the same rate. The second way to accelerate something is to "press" only on the outside of the object - for example a rocket ship presses on the bottom of your feet. In that case you would feel it. The article on G-force may help as well. Ariel. (talk) 09:42, 24 November 2010 (UTC)

I was thinking about this the other day by coincidence. What actually happens at the moment of say Beta decay (or other interactions ) in terms of acceleration for the emitted electron and electron antineutrino or other products ? I got nowhere. Is it even meaningful ? Sean.hoyland - talk 09:44, 24 November 2010 (UTC)

That's a pretty interesting question. I think it has no meaning because of the uncertainty principle. You can't know both Time and Energy at the same time, but when a particle is emitted its energy is very accurately known, this means that time has no meaning, and if time has no meaning neither does acceleration. Ariel. (talk) 10:33, 24 November 2010 (UTC)

I think some of the fastest acceleration is when high energy particles collide in particle accelerators such as the Tevatron and Large Hadron Collider. I do not know how the uncertainty principle affect this. --Gr8xoz (talk) 10:38, 24 November 2010 (UTC)

They accelerate over a large time and distance so the uncertainty principle should not be a problem. I did some calculations for the g-force article. The LHC accelerates protons at 1.9x10⁸ g. A wakefield accelerator is far more stupendous: 8.9x10²⁰ g. Ariel. (talk) 10:50, 24 November 2010 (UTC)

You're looking at the wrong side of the reaction. Gr8xoz mentions the acceleration (or colloquially decceleration) that occurs when particle beams collide. When two high energy particles collide head-on one will have a problem defining exactly what one means by the acceleration during the collision itself, but there will certainly be a large change in the distribution of momentum afterwards, and hence in some sense it is probably fair to say that such collisions involve very large accelerations. Dragons flight (talk) 11:08, 24 November 2010 (UTC)

I was, you're right. But I wonder if you can really define acceleration there, at those energies the protons don't really collide and bounce - they melt, and new particles are generated on the spot. What about when two atoms of air collide? They are traveling at about 1000 miles per hour, and turn around in a very short distance. Assuming they turn around in the distance of the size of an atom, then I calculate an acceleration of 6.22×10¹⁴ g! [2] That's absolutely immense. Ariel. (talk) 12:06, 24 November 2010 (UTC)

Protons in the LHC main loop circulate at a rate of ω ≈ 2πc / 27 km ≈ 70 kHz, and that gives a (relativistic) centrifugal acceleration of γvω ≈ 10¹⁷ m/s², assuming circular motion. In fact the beam path is not a circle and the beams are only bent at certain points, so the maximum acceleration must be higher, at least 10¹⁸ m/s². Presumably an exact figure could be found on the net somewhere. -- BenRG (talk) 01:49, 25 November 2010 (UTC)

In living things, I believe the fastest acceleration is accomplished by the ever-cool mantis shrimp, which can whip its claw though sea-water at a mind-boggling 10,400g (102,000 m/s²), about as fast a .22 calibre gun. Fast enough to generate a shock wave that can kill prey. And don't bother trying to hide from it - it can see from infrared right through to ultraviolet (and polarized light to boot). Matt Deres (talk) 14:37, 24 November 2010 (UTC)

A simple TV CRT can produce immense accelerations. It operates at around 1000V and accelerates electrons across 20 cm, which corresponds to an acceleration of 10^15 m/s^2. --140.180.14.145 (talk) 19:24, 24 November 2010 (UTC)

That's some good examples. Maybe it's worth mentioning the acceleration article, in particular point out the A=F/m equation. This means that Acceleration is proportional to Force and inversely proportional to mass. So applying a larger force to a smaller mass results in a greater acceleration. However, it stops making a lot of 'intuitive' sense when you start talking about relativistic speeds and zero rest mass particles. Vespine (talk) 23:22, 24 November 2010 (UTC)

Relativistic acceleration makes intuitive sense. It's just curvature of the worldline. -- BenRG (talk) 01:52, 25 November 2010 (UTC)

Psychology

What is the name utilized when someone creates traumatic acts so then they can come in & become the hero? Ie: a fireman who sets fires to be the savior or the nurse who doses patients inducing cardiac arrest & then administering CPR. —Preceding unsigned comment added by 99.184.223.44 (talk) 14:47, 24 November 2010 (UTC)

That sounds a bit like Münchausen syndrome by proxy. AndrewWTaylor (talk) 15:51, 24 November 2010 (UTC)

MSbP typically (if there exists such a thing as a 'typical' case) involves someone who is seeking attention and sympathy through assuming a 'victim' role, rather than a 'hero' role. We have an article Hero Syndrome which is directly on point, but the label as used there seems to be mostly a media creation rather than a formal medical diagnosis. (Google searches on "firefighter arson" and similar keywords pull lots of hits, but very little good medical or scientific literature.) TenOfAllTrades(talk) 16:37, 24 November 2010 (UTC)

Actually, that's Munchausen syndrome, where the person hurts themself to get attention. Munchausen by proxy means they hurt someone else to get attention, "by proxy" meaning "designating another person". MSbP often occurs when mothers hurt their children, and then bring them to the doctor, or "save" them themselves, bringing attention for the act. --96.255.208.104 (talk) 21:38, 24 November 2010 (UTC)

Beverley Allitt is an example of this. --TammyMoet (talk) 18:44, 24 November 2010 (UTC)

No air

When exactly did people first discover that space had no air in it, and how was the discovery made / proven? —Preceding unsigned comment added by 91.1.149.157 (talk) 21:01, 24 November 2010 (UTC)

Vacuum says Otto von Guericke is the one. Clarityfiend (talk) 21:15, 24 November 2010 (UTC)

It's a long article, but I don't think it says that - or at least precisely that. Otto von Guericke did work on vacuum pumps, but I don't think he postulated anything about the nature of outer space, which is what I think the questioner is asking about. I may be wrong there; I didn't read the article thoroughly. Matt Deres (talk) 21:33, 24 November 2010 (UTC)

Outer space#Discovery says that Otto von Guericke concluded that there must be a vacuum between the Earth and the Moon. Red Act (talk) 22:17, 24 November 2010 (UTC)

Thanks for the correction; I've struck-through my earlier comment. Interestingly, it seems that it wasn't until the early 20th century that consensus regarding the vacuum of outer space managed to overcome the idea of luminiferous aether - centuries afterwards. Matt Deres (talk) 22:36, 24 November 2010 (UTC)

Peripherally related - long before there were rocket explorations of outer space, radio was used to probe our upper atmosphere. This allows experimental study of the composition of the high atmosphere, which gradually tapers off toward vacuum. The radiosonde article, and the related ionosonde, describe the radio apparatuses that scientifically probe the ionosphere. The realization that the atmosphere becomes heavily ionized as well as very sparse was "mostly accidental." Scientists began to study radiophysics in order to make effective use of the skywave effect and to explain the Luxembourg effect. Nimur (talk) 22:47, 24 November 2010 (UTC)

I got the name from the outer space article, but somehow typed vacuum. Must be one in my head. Clarityfiend (talk) 01:11, 25 November 2010 (UTC)

Even in ancient and medieval times, people were of the opinion that "outer space" had no air in it, though they thought that the realm of air did extend to the orbit of the moon. They thought, following Aristotle, that beyond that was aether. (Despite some confusion in the linked article, based on the similarity of name, this has basically no relation to the luminiferous ether referred to by Matt Deres). Deor (talk) 01:35, 25 November 2010 (UTC)

At some point someone must have measured the velocities and angles of clouds to conclude that they couldn't have been more than a hundred miles up. But clouds aren't air, I suppose. Ginger Conspiracy (talk) 04:16, 27 November 2010 (UTC)