Wikipedia:Reference desk/Archives/Science/2012 July 8

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July 8

On Growth and Form

I've heard a lot of good things about 'On Growth and Form', but the book is also nearly 100 years old. Is it still the best text on its topic, or has it been superseded by something more modern? 65.92.7.168 (talk) 00:55, 8 July 2012 (UTC)

It's a standard text like Helmholtz' On the Sensation of Tone which, due to its quality, remains a basic introductory text in its field, and hasn't been supeseded for what it covers, which is the basic geometry of bilogical form. I saw it on the shelves for undergraduate bio courses in the Ivy League schools in the 1990's. For a reader with general interests it's worth getting from the library and thumbing through, not spending money on with the expectation that you need to master it. Of course, developments in embryology and genetics since take the field from the level of what with D'Arcy Thompson is basically an art to one of the most complicated of sciences. The Shape of Life: Genes, Development, and the Evolution of Animal Form was a cutting edge popular work when it was published in 1996, dealing with the comparative genetic regulation of development such as the HOX genes. It's hardly up to date now, but it's still highly recommended. μηδείς (talk) 01:48, 8 July 2012 (UTC)

'On Growth And Form' is a truly marvellous book, IMO. But it is certainly not up-to-date. It was not up-to-date fifty years ago.

In 1961, Cambridge University Press published an Abridged Edition edited by John Tyler Bonner. The introduction to that edition is well worth reading for an understanding of the remarkable nature of D'Arcy Thompson's book. Wanderer57 (talk) 02:23, 9 July 2012 (UTC)

Electrides of elements with Z>173

Untriseptium and unsepttrium both state that unsepttrium is the heaviest possible neutral element.

But couldn't the elements beyond unsepttrium theoretically exist in a quasi-neutral state as their own electrides, such as unseptquadium(I) electride, [Usq⁺][e^-], unseptquadium(II) electride, [Usq²⁺][e^-]₂, and unseptpentium(II) electride, [Usp²⁺][e^-]₂, with the minimum oxidation state of the element in the electride being Z - 173? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:31, 8 July 2012 (UTC)

I won't pretend to know all the physics, but it seems to me that if heavier elements can not hold their own electrons in orbitals, there would be no reason that they could form an electride either. -RunningOnBrains^(talk) 03:07, 8 July 2012 (UTC)

*waits for explanation* Whoop whoop pull up ^{Bitching Betty | Averted crashes} 03:20, 8 July 2012 (UTC)

Well, the binding force for ionic bonds is the electromagnetic force, the same force that keeps electrons in their orbitals, so if an electron can not be bound in an orbital I don't see why it could be bound in a bond. Like I alluded to before though, I am certainly not an expert in nuclear (or quantum) physics.

The problem for the highly charged nucleus is not losing an electron from the outer shell, but that the field around the nucleus is so strong that the vacuum is split into positron and electrons with the resultant destruction of the innermost electron. Alternately I suppose you can think of the potential energy of the inner electron has become so negative it exceeds the rest mass of the electron. It would be like matter falling into a black-hole and crossing the event horizon. see Extended periodic table#End of the periodic table which needs an expert to improve it (not me). However sodium can spontaneously form an electride when it is put under pressure, where you can get black sodium, red sodium and transparent sodium, all electrides. It sounds a good topic for Whoop to write up. This phenomenon could do with more investigation and perhaps more elements can form electrides by themselves. Graeme Bartlett (talk) 07:19, 8 July 2012 (UTC)

Brain dead pregnant woman

What was the name of the pregnant woman who according to this webpage was declared brain dead at 24 weeks gestation but was kept on life support for another 9 weeks to allow the delivery of the baby? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:14, 8 July 2012 (UTC)

Christine Bolden?[1] Not sure it's the same person, but hard to say. That webpage is not a great source of physiologically accurate assumptions in the questions it asks. 71.212.249.178 (talk) 06:45, 8 July 2012 (UTC)

No, the woman in the article I mentioned did not give birth to twins, was kept on life support for twice as long, and was way back in 1988. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 06:58, 8 July 2012 (UTC)

Not answering the question; hatted. Wnt (talk) 20:49, 8 July 2012 (UTC)
The following discussion has been closed. Please do not modify it.
We should list all articles about these incidents that we can find so that maybe we can find out which one that webpage was referring to. (There should already be a list of those somewhere on Wikipedia though...) Whoop whoop pull up Bitching Betty | Averted crashes 07:07, 8 July 2012 (UTC) List of women who were declared brain dead while 24 weeks pregnant and were kept on artificial life support for nine more weeks in order to allow for delivery? Evanh2008 (talk|contribs) 07:16, 8 July 2012 (UTC) WILL YOU PLEASE NOT MAKE FUN OF THIS QUESTION?!?!?!?!?!?!?!?! Whoop whoop pull up Bitching Betty | Averted crashes 07:47, 8 July 2012 (UTC) Why not? Didn't you ask it for time-wasting fun, like most of your questions? Wickwack120.145.35.180 (talk) 12:33, 8 July 2012 (UTC)

I suspect you will not find the name online as all other references seem to derived from a single medical ethics paper (you can see the abstract here) and details of this nature tend to be kept confidential. But if your interests runs deep enough, you can try contacting the article's authors who may have already received consent to share said information Snow (talk) 07:06, 8 July 2012 (UTC)

• The case study is reported in PMID 3392814, available online in full here. The woman is not named, though. Looie496 (talk) 15:59, 8 July 2012 (UTC)

Patients are rarely named in the medical literature. Exceptions are people long gone (>100 years). OsmanRF34 (talk) 19:29, 8 July 2012 (UTC)

about wireless electricity transmission

is it possible to transmit electricity in a long distance? I am working in this project.It will be really beneficial. please give me some suggestions. — Preceding unsigned comment added by 1.38.16.23 (talk) 07:39, 8 July 2012 (UTC)

Yes, you can convert it to methane which can be transmitted in a pipeline. 71.212.249.178 (talk) 07:50, 8 July 2012 (UTC)

You could just transmit the electricity through the pipeline, so long as it's a good conductor and you insulate it properly. — DanielLC 20:26, 9 July 2012 (UTC)

Depending on the distances involved, a synthetic methane pipeline can be more efficient, thanks to improvements in water electrolysis over the past decade. 71.212.249.178 (talk) 01:46, 10 July 2012 (UTC)

Yes, electricity can be transmitted without wires. See Microwave transmission#Microwave power transmission and Wireless energy transfer for details. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 07:51, 8 July 2012 (UTC)

There are four ways (and only 4 ways) to transmit electrical power from one place to another, without recourse to doing non electrical things like produce gas and pipe the gas:- 1) by wires (conduction), 2) by capacitive coupling, 3) by induction, and 4) by radio progagation. Sorry to dissapoint, but misguided but often mentioned efforts by Tesla, and wacky proposals for enormous satelite-to-earth systems notwithstanding, only conduction of wires is any good in practice, and it works really well. Electricity grids traverse netire continents. Capacitive coupling and induction come under the heading of "wireless energy transfer" and is inherently good for short distances only (distance <= diameter of devices). Capacitive coupling has had no significant commercial use as far as I know, but inductive transmission's main applications are swipe cards and RFID identification, and powering implanted medical devices from powered sources worn in clothing. Radio progation requires a transmit antenna, a recive antenna, and a space between the two, and as such is governed by the path loss equation, well known to radio engineers. The physics of the path loss equation is such that while radio waves can be detected at truly enormous distances (of galactic scale), radio propagation is really only practical for transmission of information, and not power. Typical path loss values are of the order of 10's of watts to kilowatts transmitted, and microwatts to picowatts received. If this is for a school project, I suggest you look up the 4 methods, get some undertanding why the physics means only transmission by wires is used in practice, then look at the various refinements of wire transmission, viz: High voltage AC, Extra High Voltage DC, and 3-phase transmission. Transmision of power by light is in some ways more promissing, as lenses and lasers offer much better directivity (ie are better focused into a beam) than do practical radio antennae, but even light transmission is also governed by the path loss equation, and will only be used for specail or niche applications. Keit124.178.37.91 (talk) 10:53, 8 July 2012 (UTC)

Transmission by wire is expressly disallowed by the OP. 84.209.89.214 (talk) 18:34, 8 July 2012 (UTC)

There was a cute project in Popular Electronics (i think) in the 60s, which was a crystal radio with a one transistor amplifier which was powered by the output from another crystal radio tuned to a strong local station. Gzuckier (talk) 05:26, 9 July 2012 (UTC)

That cute principle is covered here, with a reference to Radio-Electronics, 1966. DriveByWire (talk) 14:58, 9 July 2012 (UTC)

Practical transmission by light is used either for communication in optical fibers or in free space for switching tv channels. It is not useful for power transmission. Roger (talk) 14:15, 8 July 2012 (UTC)

Light is not currently used for power transmission (except is a few novel demonstrations, eg powering toy helicopters), but has much greater potential than does radio frequencies, for the reasons given above - this may be more appropriate to what the OP was looking for. Not only is much better beam focussing realisable in practice, but very high power lasers are practical. So in that sense, yes, it IS useful. Keit121.221.215.121 (talk) 14:50, 8 July 2012 (UTC)

Toy helicopters are only controlled, not powered, by light - they have LiPoly batteries on board. The controller works the same way as a tv remote. Roger (talk) 15:10, 8 July 2012 (UTC)

That was my first thought too, but then I remembered that this article in New Scientist covered a small helicopter in which power was beamed to it using a laser. Brammers (talk/c) 16:44, 8 July 2012 (UTC)

Not sure exactly what 'Keit' 121.221.215.121 was referring to there, but Microwaves have been used to power a helicopter, over a short distance and rather in-efficiently "In this experiment, the microwave energy itself was transferred with an efficiency of 51% over a distance of twenty-five feet, and then converted with an efficiency of 50% into DC power of 100 watts which was used to drive an electrical motor. ... A few months after this demonstration in microwave power transfer, personnel of the Raytheon Company conducted experiments with an electrically powered helicopter having rotor blade diameters of four and six feet. These helicopters exhibited an excess lifting capability sufficient to carry a lightweight receiving antenna and a close-spaced thermionic diode rectifier." Ref. "Experimental Airborne Microwave Supported Platform" (PDF). (4.1 Mb) (page 2). Not particularly practical. - 220 of ^Borg 16:53, 8 July 2012 (UTC)

The LaserMotive page may be of interest re. lasers for power transmission.--220 of ^Borg 18:07, 8 July 2012 (UTC)

The sun transfers energy over very long distances and we are able to transform that into electricity using solar cells so yes, wireless long distance transfer of electricity is possible. There are other methods as mentioned above.— Preceding unsigned comment added by ScienceApe (talk • contribs) 15:04, 8 July 2012

Unfortunately, conversion of light to electricity is highly inefficient, with additional inefficiencies added by conversion of the electricity into light at the source and losses during transmission. StuRat (talk) 17:33, 8 July 2012 (UTC)

By the standards of electrical transmission by wires, yes. However, CO2 lasers are available in large powers (~100 kW and more) with a conversion efficiency of up to 20%. Laser diodes are available in powers up to the kW range and somewhat better efficiency. Recoversion at the recived end can be done with photovoltaic cells, which typically have efficiencies of 25%. Laser beams can be highly focused - ending up with a spot only meters in diameter on the moon has been demostrated. Therefore, over significant distance, and end-to-end efficiency of around 10% is possible. That's pretty disgusting compared compared to typical electricity grid routes, but still usuable. Keit60.230.203.147 (talk) 01:44, 9 July 2012 (UTC)

Isn't 20% of 25% already down to 5%, with a further reduction due to absorption or scattering in the air ? Also, unless you happen to have a straight line of sight where you can safely fire hi-powered lasers, you may need to use relay stations, such as a satellite. With just one relay, we are talking less than 5% of less than 5%, or less than 0.25% efficiency, unless you can reflect the laser and reduce the losses in that way. StuRat (talk) 03:59, 9 July 2012 (UTC)

Yes. But my point was that transmission by laser is pretty disgusting efficiency-wise (though heaps better than using radio wavelengths), and you've just reinforced that. I was a bit sloppy in typing - I left out the efficiency possible with laser diodes, reportedly up to 40%. However, I intentionally left out scattering, as the OP is clearly after hypotheticals, and you can reduce the loss due to scattering by optimum choice of wavelength, and reduce it to any desired level by sufficient beamwidth. And in space, scattering should be very low. Keit121.221.86.50 (talk) 11:50, 9 July 2012 (UTC)

OK, using your optimistic 10%, we are down to 1% with a single relay. Unless, as mentioned, the laser can be reflected with more than 10% efficiency. Do you know if this is the case ? StuRat (talk) 17:41, 9 July 2012 (UTC)

Ordinary mirrors are almost 100% efficient, but would require very precise positioning, orders of magnitude better than current earth satellite standards. Doesn't seem at all insurmountable though, except for one critical thing: Precise postioning/aiming of satellites is done by periodic firing of small rocket motors (eg hydrazine jets). Current satellites have a limitted service life due to running out of positiong motor fuel, so if aiming needs to be more accurate, I expect fuel consumption to be prohibitive. Keit124.178.139.176 (talk) 02:07, 10 July 2012 (UTC)

Instead of moving the entire satellite, how about if they just move the mirror, and a counter-weight on the opposite side ? The power to move the mirror and counterweight could be from solar panels (or maybe a small portion of the laser energy). I expect they would eventually need to move the entire satellite, but much less often with this system. StuRat (talk) 04:42, 10 July 2012 (UTC)

Obviously it's more inefficient, but it's wireless. Some things obviously can't have wires. I always imagined that airplanes could be fed electricity via satellites (with solar panels) in orbit to increase their flight time. Such a design could theoretically keep an airplane flying indefinitely. Certainly would have some technological hurdles to overcome though. ScienceApe (talk) 11:51, 10 July 2012 (UTC)

(edit conflict)The OP was specifically asking about electricity transmission, but allowing 'energy' transmission this will pass. ;-) Certainly it is possible to transmit energy (electrical or other) using electro-magnetic radiation over long distances. Somewhat impractical for point-to-point use on a planetary surface though, which is what I think they are getting at. You need a fusion generator the size of a Star to begin with. - 220 of ^Borg 18:07, 8 July 2012 (UTC)

Flow of current by Electric arc is also possible. Air breaks down at about 30 kV/cm so the achievable distance may not be very long, but once established the arc behaves almost as a short circuit through which large power can be transmitted without wire. 84.209.89.214 (talk) 18:34, 8 July 2012 (UTC)

Actually, it's no good. To transmit power from one point to another distance point, you need a return circuit/conductor. So you need two arcs, not just one. Since, for transmission over a distance, the two arcs must have a length vastly greater than their specing, it won't work. An arc seeks out the shortest path, so you'll just get an arc between to two terminals of the transmitter. In any case, an arc is NOT a short circuit - in welding, for example, the voltage drop is of the order of 20V over a few millimeters, and the power lost in the arc is the source of welding heat. Keit60.230.203.147 (talk) 01:51, 9 July 2012 (UTC)

Two arcs are needed, yes (or one with a ground return when the distance is on Earth). The arcs must be spaced by more than double their length, yes (though once struck that requirement is reduced). I said "almost", not quite, a short circuit. Electric arcs have a peculiar negative resistance: the voltage drop goes down as the current increases. I agree electric arcs are much better suited to welding, heating and detonation than wireless transmission of electricity but I think the possibility should be included in your list if it is to be exhaustive. 84.209.89.214 (talk) 02:50, 9 July 2012 (UTC)

Still not quite right. While you can certainly lengthen an arc once it has struck, the two arcs wil be drawn towards each other by magnetic forces (the proximity effect). Or, if an earth return is used (whic I should have thought of), the one arc will be similarly be drawn towards the earth. In any case a requirenet to start with transmitter electrodes further apart than the transmitting distance hardly qualifies as distance transmission - you might as well lay the transmitter "antenna" on its side and be done with it. So, no, it doesn't warant being in the list. Keit60.230.203.147 (talk) 03:18, 9 July 2012 (UTC)

Electric arcs are extremely hot, so the ionized current path rises into an "arch," the word Humphrey Davy used to describe it circa 1811, which he later shortened to "arc." I have seen a lot of electric arcs, and I have never seen one "drawn towards the earth." I agree that if the phase and neutral, or the three phases, were close to each other, they would arc across rather than arcing to the remote "load" unless there were nonconductive barriers between phases, such as the ceramic parts used in utility air-break circuit breakers. Magnetic coils can also be used to steer an arc, as is done in circuit breakers, and as was done in high power arc radio transmitters such as the Poulsen system. A vapor other than air can be used instead of air, as was done in arc transmitter voice radio in the early 20th century. Edison (talk) 19:54, 11 July 2012 (UTC)

If you are going to provide magnetic steering coils along the route, you might as well just make them straight end-to-end wires carrying the electricity. If you are going to have a special gas (and no gas will give anything like a useful advantage over air in this application, you are going to need tubes to contain it in. Might as well use the tubes as conductors. Keit124.182.147.203 (talk) 01:43, 12 July 2012 (UTC)

In this picture current is flowing across the wireless gap between the rail and the pickup shoe and supplying uninterrupted power to the inductive load of the motor. "Distance" is a relative, not absolute, concept. DriveByWire (talk) 15:28, 9 July 2012 (UTC)

Well, yes, but clearly not within the context of the OP's request for "long distance" transmission. Keit124.178.139.176 (talk) 02:00, 10 July 2012 (UTC)

High voltage transformers and overhead lines commonly use electrically- or hand-operated three phase disconnects. They are high above the ground and have a large spacing between phases. Many are non-loadbreak devices, intended to interrupt only capacitive charging current. Typically when they are opening, a piece of metal on the moving part contacts a metal hook and the (small) current then flows from this "whip" to the stationary hook, until it snaps loose, breaking the current. I once saw one accidentally interrupt an unknown number of amps of load current, while in a parallel connection with another networked line. When the whip snapped free, current continued to flow across the gap on all three phases, without a phase to ground or phase to phase fault occurring. The three arcs were bright (blue green as I recall) and loud, and eventually the current stopped flowing when the gap got large enough as the operator cranked the disconnect open. For a few seconds, megawatts of 3 phase 138kv power were flowing "wirelessly" through the arcs. Certainly it would not be a recommended way of supplying current, since it was likely to arc to ground or across phases, and since the high temperature arc was burning away copper from the conductive parts of the switch. An electric arc furnace melts down scrap metal via a 3 phase arc, using perhaps 4kv. Similarly arc welding carries much lower voltage high current electricity to the metal parts being welded. Folks opposed to overhead high voltage transmission lines used to demonstrate that the field below the 345 or 765 kv AC lines is strong enough at ground level to light a fluorescent tube. Near high voltage DC transmission lines, a metal roof has to be grounded to avoid giving someone a nasty shock when they touch it. In an AC transmission switchyard, a few feet of wire quite a distance from the bus can pick up enough stray voltage to make a visible arc. Near a conductor carrying a hundred amps or more, a permanent magnet might vibrate in your pocket like a buzzer from the stray magnetic field. I have heard a crystal radio a mile or more from a radio station drive a loudspeaker to a nice listening volume with no battery powered circuitry. Edison (talk) 19:34, 11 July 2012 (UTC)

Keith Henson is interested in laser transmission of power. That can be more efficient than other wireless and pipelineless methods, but it's still a huge loss and practical applications don't exist yet because of the huge losses, unless you count laser cutting and heating directly. 70.91.171.54 (talk) 22:14, 8 July 2012 (UTC)

Since he just signs his name "Keit", how do you know his full name ? StuRat (talk) 04:08, 9 July 2012 (UTC)

It ain't me - I'm not the slightest bit interested in laser trasmission of power, and my real name is nothing like Keith anything. But as an Engineer, I understand the implications of the well known (to Engineers) path loss equation. I assumed that Keith Henson is some joker known in the poster's locality. Keit120.145.142.105 (talk) 09:26, 9 July 2012 (UTC)

Keith Henson, wikilinked above too. 71.212.249.178 (talk) 01:51, 10 July 2012 (UTC)

OK, just coincidentally similar names. StuRat (talk) 04:37, 10 July 2012 (UTC)

With only 4 letters to go on, how do you know they are similar? Keit120.145.23.26 (talk) 14:49, 10 July 2012 (UTC)

Within the context of one question, having two different names mentioned that happen to start with the same 4 letters seems unlikely. This reminds me of my bank, which, to protect my security, only gives out the last 4 digits of my account numbers when they give me a balance statement. The bad news is, I'm the unlucky 1/10,000th person who happens to have two accounts that end in the same 4 digits. StuRat (talk) 20:28, 10 July 2012 (UTC)

You must be not the unlucky 1/10,000, but something like the unlucky 1/100,000,000th person, as at least one of the last 4 digits is usually a hash digit, hashed from all other digits (same idea as your income tax ID), including the other 3 included, but not the BSB digits. http://en.wikipedia.org/wiki/Hash_function This lets bank clerks detect immediately a typing error, without consulting records. Without hash digits, a percentage of payments would be continually going to the wrong accounts every time somebody made a single typo. Wickwack120.145.199.129 (talk) 07:06, 11 July 2012 (UTC)

Another means of wireless electric transmission exists which is by ground current. It is very inefficient and Keit may not welcome it in the list. Nevertheless, if one drives two rods a distance apart into the ground and applies a voltage between them, not all the resulting earth current flows in a straight line between them. A receiving pair of rods can collect a fraction of the transmitted voltage at a considerable distance, if they are aligned optimally. I once had fun "energising" a large field with music from an ordinary amplifier with the loudspeaker output terminals connected to earth rods a couple of meters apart. The music could be heard anywhere in the field on sensitive headphones connected to a pair of nails pushed appropriately into the ground. DriveByWire (talk) 15:31, 9 July 2012 (UTC)

Many who became interested in electronics, including me, have also had fun doing this. It has been used communication in underground mines. It is actually a form of conductive transmission, which I already included in my list of 4 forms. Ground cuurent transmision is weofully inefficient and good for information transfer, not power transmission. Keit124.178.139.176 (talk) 02:00, 10 July 2012 (UTC)

Perhaps you are already familiar with the early wireless telephone experiments of Nathan Stubblefield, who used inductive transmission as well as conduction through the ground and through water 1892-1908. Edison (talk) 20:11, 11 July 2012 (UTC)

Yet another way is via a truckload of charged capacitors. Some electric vehicles may already have these on board. See supercapacitor. Graeme Bartlett (talk) 22:05, 9 July 2012 (UTC)

Or you could set up a conveyor belt of rechargeable batteries! Good imaginative call, but a pipe carrying gas (see 2nd post) would be a lot simpler, cheaper, and durable. You can also transmitt power via belts or chains. In case someone thinks chain drives are only short distance, I point out that before electricity, some large cities powered their trams by the cable and grip system (http://en.wikipedia.org/wiki/Cable_car_(railway)) - the steam power house pulled cables installed down a slot in the road - each tram clamped a "grip" onto a cable, and released it to stop. Still in use in San Fanscisco when I visited. But is this within scope for the OP?? It has nothing to do with electricity. Keit124.178.139.176 (talk) 02:00, 10 July 2012 (UTC)

• Tesla's proposals to transmit power wirelessly seem to have been dismissed above rather quickly. His work seems to have quite a following in some circles, and more discussion might be appropriate. Edison (talk) 02:26, 10 July 2012 (UTC)

Quite a following in recent fashionable circles not involving qualified engineers! There's plenty here for the OP to chew on, and I see little value in going into why Tesla, who made important contributions to the electrical art, nevertheless promoted something that was completely daft, known to be daft at the time, and known to be daft ever since - such discussion would inherently go off-topic or off on a tangent. However, if you are curious, there is no reason why you can't post a question of your own, such as "Why did Tesla's ideas for wireless power transmission come to nothing?", or "Why did Tesla's financial backing for Wardencliffe fail?" or some such. You might trigger some discussion, but be sure to read the Wikipedia articles on Telsla & Wardencliffe first. Note that Tesla's demonstrations of power transmission without wires involved methods 2 & 3 listed in my first post above and were therefore only very short distance. Keit120.145.175.84 (talk) 04:02, 10 July 2012 (UTC)

Its funny you keep saying Tesla, concepts were daft, considering there was also a "Daft Electric Light Company" in 1892, headed by Mr Leo Daft It's funny reading old court transcripts about the "Daft electric railway. " There are some engineers and physicists today, not just unqalified engineers as you assert, who see some merit in some of Tesla's notions about wireless power transmission. The use of lasers to remotely propel space probes has also had a lot of coverage from seemingly well qualified space travel designers. See [2]. See Beam-powered propulsion. Who cares if the efficiency is 1% or .01%, when the thing is out in space and there is obviously no way to run a cable from the generating station to it? Carrying the fuel off the ground at liftoff of a conventional rocket into space is also very inefficient. Edison (talk) 19:46, 11 July 2012 (UTC)

I entirely agree with your comments ("Who cares....) about laser transmission - that's why I mentioned it in my first post. However, Tesla's ideas are another matter. Can you cite or name a suitably qualified professional Engineer that sees merit in it? Physicists are another matter. The role of a physicist is that of a scientist - explain part of how something might work. He need only focus on one thing. The role of an engineer is much more rigorous - make something work. That means an Engineer must consider everything related. Scientists are optimists; Engineers are skeptics. Keit124.182.27.45 (talk) 03:20, 12 July 2012 (UTC)

However, Tesla's ideas failed largely because electricity generation is expensive, so you can't just give it away for free (as metering would be impossible under such a system) and allow huge portions of it to be wasted. If, at some point in the future, we find a way to produce electricity dirt cheap, in a centralized location (let's say by nuclear fusion), then that equation might change. StuRat (talk) 04:49, 10 July 2012 (UTC)

Yes, we are going off topic, as I expected, but while Stu's revenue reason is often quoted, its not the full story. When profesional radio broadcasting started in Australia (1920's), idiot politicians passed laws to create the "sealed set scheme". Under this system, when you purchased your radio set, it was tuned to the chosen station and sealed. You paid a fee to that radio station, which was government owned. Naturally such a dumb scheme imediately failed - you can't stop people from tuning to whoever they want. However, it was replaced by a scheme where every radio owner was compelled to pay a licence fee just for owning a radio, whether they tuned into the govt station or not, or even whether or not they turned the thing on. That was a simple practical scheme that worked, and stayed in place until the 1960's, when the widespread sale of small transistor radios made it impossible to police - license fees were then abandoned. The moral is that just because something is technically difficult to administer, it doesn't mean it cannot be solved by laws and treaties, though the dumbness of politicians does not make it straightforward. The real problem with Tesla's power transmission scheme is that almost all the transmitted power would have simply dissappeared into "thin air". That's no doubt why, when Tesla's backers backed away, he couldn't find replacement financiers. No doubt if he had been able to show it worked, his next step would be to sell it to govts, either directly or thru a licencing system. Of course, radio being what it is, an even better scheme is possible and became universal - commercial sponsorship. Keit121.221.86.127 (talk) 06:20, 10 July 2012 (UTC)

In Germany, they still do the licensing thing with radio and television. 203.27.72.5 (talk) 07:18, 10 July 2012 (UTC)

Last time I heard, they still do in Britain as well - but the British always were a strange lot, with almost all doing what they are told, just because they were told, and a steady number with radios and TV's not declared. So their Govt had a fleet of "detector vans" that drove round detecting the magnetic field from the TV Cathode Ray Tube scanning coils. Must have been a bit of a blow now that CRT's have been replaced by the various flat-screen technologies (eg LED) that don't have scanning coils. At one time they were detecting back-radiation from the tuners in both radios and TV's, but that became no good with the change from tubes to transistors (in the 1970's for TV's). Keit121.221.79.37 (talk) 10:10, 10 July 2012 (UTC)

But, when they detected a radio or TV in use in a home, then what ? Did the license restrict use to a particular house ? If not, they would have no way of knowing if the device being used in the house was a registered one or not. Or did merely using one constitute adequate cause for them to pound on the door and demand to see a license for the device ? StuRat (talk) 20:35, 10 July 2012 (UTC)

In Australia, it was the responsibility of the house owner or lessor to have a licence to cover for any reciever on the premises (regardless of who owned it), and any reciever installed in a vehicle kept that that address. Hotels were required to have a licence if any guest had a radio or TV with them. According to an article in the journal Wireless World some years ago, the detector crews drove slowly down the street. As they went past each house, and picked up the magnetic scanning field or tuner back radiation (TV users who don't pay the fee tended to use rabbit ears & not an external antenna), they checked against a list of address who did have licences, When they found an unlicenced address emitting a scanning field, they checked the building plan, which they obtained from local government. By elementary direction finding, field strength measurement, and frequency measurement of tuner back radiation if detected, they then could knock on the door, and say something like "You have an unlicenced TV set in the 2nd bedroom switched on and tuned to Channel 4". That, and the sight of the detector van with its direction finding antennae pointing at the 2nd bedroom, was usually sufficient to scare the resident into admitting guilt. If they didn't admit guilt and told the detection officers to nick off, a search warrant, which must be granted by a justice of the peace, as for any police search of a private home, was required. Keit124.178.136.133 (talk) 01:53, 11 July 2012 (UTC)

Wouldn't that give them time to remove the TV or radio from the premises ? StuRat (talk) 18:22, 11 July 2012 (UTC)

Yes. Keit124.182.147.203 (talk) 01:14, 12 July 2012 (UTC)

In Germany the license pertains to the household. Over there they were enforcing it by just coming and checking your house if you don't have a license to make sure you're not watching TV (or listening to the radio) without a permit. In future they're just going to force people to pay for the license irrespective of whether or not they have a radio or TV which also alleviates your concern about the "TV registration office" being a target for invading armies. 203.27.72.5 (talk) 21:31, 10 July 2012 (UTC)

So not having a TV or radio license was sufficient cause for them to search your house ? Apparently the denazification program didn't work. I have no objection to charging everyone a tax, regardless of use, as that's basically what the US does, with taxpayer subsidies to PBS, NPR, etc., although it's not broken down as such on our tax forms. And, realistically, just about everyone uses a radio and/or TV. StuRat (talk) 22:19, 10 July 2012 (UTC)

StuRat, this is Germany we're talking about. They denazified by making thoughts and opinions criminal. Without irony. 203.27.72.5 (talk) 00:02, 11 July 2012 (UTC)

As per usual, wikipedia has an article on this topic. 203.27.72.5 (talk) 20:21, 10 July 2012 (UTC)

However, the article has some serious errors. For instance it includes under Detection a lot of nonsense about the British authorities refusing to disclose the detection technology and claims it has not been demostrated that detection is possible! The technology has been fully disclosed in both prefessional journals and in commercial elecronics magazines, such as Wireless World / Electronics World. Keit124.178.136.133 (talk) 01:53, 11 July 2012 (UTC)

Well, go on Keit. Be bold. 203.27.72.5 (talk) 03:52, 11 July 2012 (UTC)

You would think that Europeans would have learned their lesson, that invading armies can go to the records office, and then confiscate all the radios. This is also true of guns, but, of course, there are more serious consequences to having millions of unregistered guns than either TVs and radios. StuRat (talk) 20:44, 10 July 2012 (UTC)

Don't worry about it. When the Japanese invaded South East Asia during World War 2, they didn't waste time with record offices. They just broadcast a demand that all citizens hand over their radios on pain of severe punishment. Keit124.178.136.133 (talk) 02:00, 11 July 2012 (UTC)

Sure they can, but presumably members of the resistance would keep their radios anyway, unless the Japanese knew just where to look for them. StuRat (talk) 18:16, 11 July 2012 (UTC)

Absolutely! Not only that, resistance fighters and prisoners of war built their own radios, using parts stolen from the Japs. Keit124.182.147.203 (talk) 01:29, 12 July 2012 (UTC)

In South East Asia in the 1940, there wouldn't have been too many locals with electricity, let alone radios. And the European colonialists didn't have to do anything rebellious like hold on to radios to cop a bit of punishment off the Japs. It would have been pretty obvious where to look for people that have underground radios. Hint: they're the same places that you target for pilaging most everything else of value. 203.27.72.5 (talk) 21:11, 11 July 2012 (UTC)

Electricity has little to do with it. In 1940, most rural areas of Australia didn't have mains electricity either, except in town centres. The chicken farming area I grew up in, only 30km from a capital city, did not get electricity until about 1970. But we allways all had radios since broadcasting stated (1920's) - battery powered radios in the house, and car radios in our cars. In fact battery powered radios pre-date mains electricity radios. Keit124.182.147.203 (talk) 01:29, 12 July 2012 (UTC)

Wow, I didn't know compact batteries had been around for so long. But still, surely they would have been quite expensive for south east asian rice farmers. And how many other uses were there for batteries back then? Looking at the houses that have recently purchased batteries would narrow the list a fair bit. 203.27.72.5 (talk) 21:06, 12 July 2012 (UTC)

Seriously, StuRat. Are you purposly steering the conversation on ever increasingly tangential lines just to prove Keit's prediction correct? 203.27.72.5 (talk) 21:26, 10 July 2012 (UTC)

How to change the way the jet stream flows

The jet stream is flowing South of Britain causing bad weather, disrupting Wimbledon and it will likely cause problems for the London Olympics. So, how would one go about pushing the jet stream North? Count Iblis (talk) 15:32, 8 July 2012 (UTC)

At this point in the history of science and technology, and for the next couple of hundred years at least, the only method that has the faintest chance of success is prayer. Dominus Vobisdu (talk) 15:49, 8 July 2012 (UTC)

The only plausible way is by reducing global warming. And that isn't a joke answer: the details are very complex, but in a general way global warming should increase the meander in the jet stream, causing it to make more frequent southward excursions. Looie496 (talk) 15:52, 8 July 2012 (UTC)

This is highly speculative, and I'd like to see if there's any evidence of it. One of the consequences of increasing greenhouse gasses is that the equator-to-pole temperature gradient will decrease (this part is not up for debate, it's simple physics), leading to a weaker jet stream on average, and (here's the speculation on my part) a less meridionally amplified (fewer north-south meanders) Rossby wave pattern. So if my educated guessing is correct, global warming would lead to sunnier summertime weather for the British Isles. This is of course ignoring a huge amount of uncertainty in ENSO and other large-scale patterns. -RunningOnBrains^(talk) 18:48, 8 July 2012 (UTC)

Why would the temperature gradient decrease ? More of a greenhouse effect should make it much hotter where more sunlight hits, near the equator, but not much hotter where no sunlight hits at all, as at the poles on winter. To me, this means a greater temperature gradient from equator to pole, at least in winter. StuRat (talk) 04:27, 9 July 2012 (UTC)

From the article on Venus (which has a runaway greenhouse effect); "The surface of Venus is effectively isothermal; it retains a constant temperature not only between day and night but between the equator and the poles." Compare that to other celestial bodies that have a smaller or absent greenhouse effect e.g. Mercury which has 140K of mean temperature variation from 0°N, 0°W to 85°N, 0°W and it's obvious what effect the greenhouse effect has on pole to equator temperature variation. Those quotes have refs in the articles too. 203.27.72.5 (talk) 21:57, 9 July 2012 (UTC)

I don't think you can assume that just because the overall trend from no atmosphere to thick atmosphere is more even temperatures that this automatically means this trend doesn't reverse itself at any step along the way. Considering the complexity of the interactions involved, I'd be surprised if it was that simple. For comparison, if you noted that the chance a person who is 100 will die that year is higher than the chance that a person who is 0 will die that year, and just assumed that the chance a person will die at each year in-between must therefore steadily increase, then you would be wrong. StuRat (talk) 22:10, 9 July 2012 (UTC)

I didn't make that assumption. You did in your comment above (though with the opposite understanding of the effect). 203.27.72.5 (talk) 22:21, 9 July 2012 (UTC)

I don't know what you're trying to say. BTW, are you RunningOnBrains ? StuRat (talk) 22:33, 9 July 2012 (UTC)

No, I'm not RunningOnBrains. This is what was trying to point out:

RunningOnBrains: From an analysis using simple physics, a stronger greenhouse effect leads to less pole to equator temperature variation.

StuRat: Here is a simple physical mechanism which predicts the opposite.

203.27.72.5: Since we're doing a first order, simplistic analysis, here is a simple model that is consistent with RunningOnBrains' prediction.

StuRat: Your simplistic model is invalid because it's too simple. This is a complex process and needs complex analysis. *says nothing about validity of own simplistic mechanism*
203.27.72.5 (talk) 23:16, 9 July 2012 (UTC)

But my model is less simplistic, as it at least deals with climate examples here on Earth, eliminating variables like tidal locking and variable distance from the Sun, that don't apply to Earth. StuRat (talk) 23:25, 9 July 2012 (UTC)

Here's NASA's take on the matter. 203.27.72.5 (talk) 23:56, 9 July 2012 (UTC)

And to eliminate the variables like tidal locking and variable distance from the Sun, we could use an Earth based model by comparing the Cretaceous with the present. The Cretaceous had "a very gentle temperature gradient from the equator to the poles", 6 times preindustrial CO₂ levels and an average surface temperature 4°C higher. 203.27.72.5 (talk) 00:01, 10 July 2012 (UTC)

OK, that NASA link certainly seems more relevant than the climates of other planets, but I notice they use "could" versus "will" whenever they say anything about the equator-to-pole temperature variance being more gradual, so it sounds like they aren't exactly sure. Then there's those graphs showing the effects of greater temperature variance, which seem at odds with the text. (I realize that the graphs may be temperature variance at one location, versus from the pole to the equator, but, at least now, temperature variation at any point is caused by polar air masses versus equatorial air masses moving into an area, so it is related.) StuRat (talk) 04:29, 10 July 2012 (UTC)

Yeah, I don't get that graph either. It seems to disagree with the notion that the atmosphere would be closer to isothermal overall. 203.27.72.5 (talk) 04:57, 10 July 2012 (UTC)

Whoa, totally missed this branch of the thread, sorry I never responded. That NASA graph has nothing to do with north-south temperature gradients, it's describing the local variation in temperatures, and it's an if graph; each panel shows the effects of one possible scenario. The body of the article does say, however, "Global warming could affect storm formation by decreasing the temperature difference between the poles and the equator".

Here's the simple physics I alluded to (I use the term "simple" liberally): if you trap outgoing longwave radiation (which is what greenhouse gasses do), you are essentially decreasing the rate of cooling of the planet. However, this cooling is actually most efficient in the warmest areas; i.e. the tropics, and less efficient at the poles. This is because the intensity of outgoing radiation is proportional to the temperature to the 4th power (the Stefan–Boltzmann law), so the rate of cooling will increase less at the poles. Note that when I say "rate of cooling" I mean the power of the outgoing black-body radiation, not an actual decrease in temperature. I hope I've explained this clearly, one of my (much smarter) friends was explaining this to me last week and probably put it much better than I can.

As an additional contributing factor, decreasing sea ice from increasing temperatures will decrease albedo in polar regions, which will increase solar heating there, but this is really a less important secondary effect if my educated speculation is correct. I should also point out that so far the greatest warming has been in arctic regions, so recent history supports this notion.-RunningOnBrains^(talk) 05:52, 10 July 2012 (UTC)

Regarding the graphs, even if they are only one possible scenario, their inclusion, and the exclusion of any showing a decrease in temperature variation, seems to show that whoever included the charts think that this is the more likely scenario. The author of the text, on the other hand, went the other way, but seemed rather noncommital about it.

And what about my argument, that greenhouse gases will trap more solar radiation at the equator, where there's more to be trapped, than at the poles, where, at least in winter, there no solar radiation to trap at all ? Perhaps, combining your theory and mine, we will get less temperature variation in summer, but more in winter. StuRat (talk) 06:08, 10 July 2012 (UTC)

This might be the deepest indent I've ever gotten to :)

About the graphs, I think you're confusing variance with gradient. Those graphs say nothing about the pole-to-equator gradient.

And about the GHG-trapping, you're thinking about it too simplistically. You're using the (usually effective) analogy of greenhouse gasses somehow "trapping" solar radiation, which really isn't true; the explanation I gave above is the actual physics behind it. However, now that I've sat down and done some of the math, I am beginning to doubt myself; it's way to late, I'll try to get a better explanation to you tomorrow. -RunningOnBrains^(talk) 07:33, 10 July 2012 (UTC)

You must have missed my earlier comment, so I'll repeat it here: "(I realize that the graphs may be temperature variance at one location, versus from the pole to the equator, but, at least now, temperature variation at any point is caused by polar air masses versus equatorial air masses moving into an area, so it is related.)". StuRat (talk) 20:39, 10 July 2012 (UTC)

The greenhouse effect should dampen out both spacial and temporal temperature variation. You can see this even if you are thinking of solar radiation as being trapped in. It's because the rate of energy being dissipated from the Earth's surface by thermal radiation is effectively slowed, so there is more time for convection and conduction to play a role in determining the surface temperature. Direct solar illumination plays less of a role and mixing of warm and cold gases comes to dominate. If you do take the more accurate approach of realising that GHGs absorb and reemit IR, then you will also see the effect of that radiation going in all directions, and thereby spreading heat to other latitudes and longitudes rather than directly into space or at the surface of the Earth. 203.27.72.5 (talk) 07:49, 10 July 2012 (UTC)

And the best way to prevent weather from interfering with British sport events is to move those events to someplace else with better weather. Wimbledon, in particular, frequently had poor weather, long before global warming became a concern. StuRat (talk) 17:28, 8 July 2012 (UTC)

There is no way to change weather patterns reliably. Rossby waves (the waves in the jet stream flow) are dynamically chaotic, meaning that a small perturbation now will result in large changes in future behavior. That's why weather prediction is essentially useless after 7 days; you driving to work tomorrow could cause a perturbation that would result in a difference of 1000 km of the position of the jet stream two weeks from now. -RunningOnBrains^(talk) 18:39, 8 July 2012 (UTC)

I say we kill all the butterflies, as they are the cause of all this chaos. :-) StuRat (talk) 20:17, 8 July 2012 (UTC)

Tricky. Nice Land Rover ice cream van, though. . . dave souza, talk 20:30, 8 July 2012 (UTC)

Question: If small changes affect the pattern, doesn't that mean that with enough computing power, a humanly achievable input could affect which way it goes? I'm thinking that setting a forest on fire should be about the most we can do; for finer control but much less effect I'd think that a wind farm could be switched to generate power or spin freely on perhaps a second-to-second scale? Wnt (talk) 20:54, 8 July 2012 (UTC)

Setting off thousands of nukes would be the most we could do, but this may not be advisable. :-) Also, theoretically the causes of chaos ultimately reduce down to quantum effects, which are, by definition, random and uncontrollable. StuRat (talk) 21:23, 8 July 2012 (UTC)

To Wnt, no, and you have fallen prey to the same false assumptions that researchers had in the 1950s and 60s. Back then, weather control was a hot ticket, and was beginning to seem feasible with improvements in computer modeling. Famously, Edward Lorenz, a meteorologist and the founder of the field of chaos, discovered that atmospheric flow contained unstable points, where a small perturbations could lead to huge differences in a short period of time. However, when he attempted to show his results to other scientists, and they told him "Oh, you're talking about weather control". But they failed to see (as you do now) that every point in the flow has this instability; any perturbation that you make is insignificant compared to the (literally) trillions of small perturbations that are below the resolution of computer models, and can only be quantified (in a very rough way) by ensemble forecasting. When we say "a butterfly flapping its wings can lead to a hurricane a month later", this is equally true of every butterfly, every person, indeed, everything that can not be represented in the computer model.-RunningOnBrains^(talk) 00:17, 9 July 2012 (UTC)

But if you know absolutely everything about the system's original state, you can predict exactly what will happen. Which includes predicting exactly what will happen after you make just such perturbation. Which means you can figure out exactly how you should perturb the system to, say, move the jet stream north over Scandinavia. For every set of exact initial conditions and one exact time frame, there is only one possible outcome. A mathematical equation always has exactly the same solution; for example, 1 plus 2 always equals 3, and the positive square root of 144 is always 12. Whoop whoop pull up ^{Bitching Betty | Averted crashes} 01:11, 9 July 2012 (UTC)

You're still thinking in terms of classical Newtonian mechanics, where every action has an identifiable cause. In quantum mechanics, this is no longer true, things are truly random. A common example is radioactive decay. While, on the average, it's rather predictable, when we get down to an individual atom we can't predict when it will decay. And things as small as individual atoms eventually affect weather patterns. So, you ultimately can't predict or control the weather with exact precision, but can only do the same type of bulk averaging that gives us the half-lives for atomic decay. StuRat (talk) 03:55, 9 July 2012 (UTC)

It's not even necessary to introduce quantum mechanics; this is a classical mechanics problem with no known solution (see Navier–Stokes existence and smoothness; it's actually one of the last unsolved problems in Newtonian mechanics) -RunningOnBrains^(talk) 15:57, 9 July 2012 (UTC)

Also, by the time you finish running a computer model, the initial conditions have already changed in unpredictable ways. Do you propose that it will ever be feasible to include every molecule of the planet in a computer model; and even if we could (which we won't), how would we manage to get information about the location and momentum of everything? Even if you somehow had perfect weather stations with no observation error (impossible) for every cubic meter of the atmosphere (also impossible) taking measurements every second, you could not predict the weather even one month in the future (from the book "Chaos: Making a New Science", which I highly recommend as one of the best lay-person science books I've ever read). Plus, the equations of motion are nonlinear equations, meaning that they can not be solved exactly by computers, as they require iterative solutions which introduce floating-point errors.

Impossible is not a word I use often (I majored in physics, after all), but perfect weather prediction is impossible. -RunningOnBrains^(talk) 15:55, 9 July 2012 (UTC)

I think some heuristic tricks might be important. For example, just looking at jet stream time lapse, it seems like it comes in very steadily toward the Pacific coast of the U.S., then oscillates wildly as it hits the mountains. So I'd think you could have more impact if you target that spot. I'd think that, over time, you could come up with a sort of "finite state machine" like model for which way the jet stream is going to go if it's going this way at a certain time, and evaluate what circumstances tend to make it shift. And the key instances when you actually want to change the weather aren't when this is too unpredictable, but when it's too predictable - when it always goes the same way and no rain falls in Texas for half a year. I'm not going to say it's possible, but ... I don't know of any theory that says you can't lever a semi rig out of mud pit with a toothpick if you're really, really, really clever about it. ;) Wnt (talk) 16:16, 9 July 2012 (UTC)

Unnoticed effects would eventually cause problems, but as long as we're willing to keep modifying things, we can keep it on the right track. We just have to make sure that the effects we control are at least as large as the ones we don't know about or lack the computing power to predict. I'm not sure how much this is, but I'd bet it's at least in the nuke range. It could very well take more than all we have. Given that "eventually" is a week from now, we'd have to use them that often. — DanielLC 20:21, 9 July 2012 (UTC)

It's true that we could control the weather by your suggested means instead of trying the "small nudge" method which is doomed to fail due to chaos, but then we must compete with the energy scales of atmospheric motions, which are as of now (and the foreseeable future) completely impractical. For instance, a rough approximation of the energy involved in a single hurricane is approximately 200 times the entire world power output. We'd be better off using that energy to moving Wimbledon indoors :) -RunningOnBrains^(talk) 21:05, 9 July 2012 (UTC)

Man...if we had that much energy, we could move Wimbledon so indoors...203.27.72.5 (talk) 22:06, 9 July 2012 (UTC)

Major local forest fires are hard to arrange on a regular basis. The Himalayas and the Rockies play a huge role in the path of the northern jet streams. I suggest building a mountain range or blasting a path through an existing one. Of course valium is probably a much cheaper and effective way to deal with climate change anxiety. μηδείς (talk) 21:05, 8 July 2012 (UTC)

Ah, yes, I've seen this one proposed before. Now where'd I leave the family atomics? :) Hmmm... seriously, though, the part about building a mountain range is interesting. If you lay a series of cables with streamers across a wide mountain pass, can you disrupt laminar flow of the air to create a turbulence that would dissipate a significant portion of the wind's force against the cables or the walls? If you control several such passes in such a way, can you thus change the overall vector of the surface air flow emerging from the far side of the range? Wnt (talk) 21:32, 9 July 2012 (UTC)

Funny I didn't even think of dune, which I have read 5 times. μηδείς (talk) 05:08, 10 July 2012 (UTC)

Ha, I' see I've kicked off a big discussion here :) . What about this variant of Wnt's and μηδείς' suggestion. A huge balloon connected to the ground by cables could be put into the jet stream... Count Iblis (talk) 02:03, 10 July 2012 (UTC)

That's an awful lot of mass to create a very little resistance, given you'd run into a power law relation between the cross section of the balloon and its mass. It would also want to flutter, and would probably end up failing catastrophically. Also, of what use would it be except when the wind were trying to blow through its path? μηδείς (talk) 05:08, 10 July 2012 (UTC)

(edit conflict)

Well, the jet stream doesn't pass near the ground; it's typically from 300-200 hPa, which is around 7-10km altitude. It doesn't pass through mountain passes; it barely grazes the tops of some peaks (and that's just in the Himalayas) Also it is (order of magnitude) 100 km across and 1 km deep (it's actually around 3-5 km deep usually, and its width varies quite a bit). You'd need a helluva lot of balloons to make a significant impact, and the string would have to be incredibly long and incredibly strong, a combination which is not yet technically possible (I'm thinking the realm of carbon nanotubes).

And even with all this you could not predict the impact precisely. I'm going to sound like a broken record or a politician, but Rossby waves are chaotic! I feel like most of you aren't understanding the full weight of this statement. It is no exaggeration to say that the difference in one degree of temperature in one small area can have drastic impacts even in short- to medium-range forecasts. Just look at the image accompanying our article on ensemble forecasting. All those models were given the exact same data; the only differences are in model resolution and the parameterization of small-scale processes. And even at 3 days out, there is a spread of several hundred kilometers in the predicted position of Hurricane Rita. And this was one of the better predictions; just take a look at these model predictions for the recent Tropical Storm Debby (2012). Hilariously uncertain.

I realize that hurricanes are a different phenomenon from what we're discussing, but just look at the current GFS ensemble precipitation forecast for 5 days from now. Each of those panels is the same model, the same data, just with small perturbations introduced to the initial conditions (every ensemble member is a realistic representation of the atmosphere, i.e. consistent with the millions of bits of observational data fed into the model) . I apologize that the image isn't very big, but you can clearly pick out storms that are in different positions, different intensity, or just plain aren't in some of the ensemble member forecasts.

Chaos is impossible to control, we can only hope to understand it enough to suit our own needs. Close-to-perfect 1-day forecasts are certainly feasible, and good forecasts out to 14 days could be in our future (but only in certain flow regimes; some are more unstable than others!), but anything beyond that is asking too much.-RunningOnBrains^(talk) 05:31, 10 July 2012 (UTC)

How (in terms of physical motions and mechanics) does a slug foot walk?

In terms of physical motions and mechanics, how do slugs move about? I note 'succeeding waves of muscular contraction which move down the undersurface of the foot' (http://wiki.answers.com/Q/How_do_snails_move_around) - but how does this work, physically? How do 'succeeding waves of contraction' make the slug move forward? My four-year-old wants to know. (I would love to show him a video of a slug moving its foot upon glass, if this could help us to understand, but I see no such thing.)82.31.133.165 (talk) 19:47, 8 July 2012 (UTC)

Do you know how an inchworm moves ? It's like that, only the "arch" distance above the surface is tiny (and filled with slime), so it's not easy to see. Also, an inchworm actually picks up one end at a time, while a snail or slug just slides it along the surface on slime. Your 4-year old can probably do it too, by putting him in a sleeping bag and having him sit on his butt and feet, and scoot along by pulling his feet close to him, then pushing them away. As he will note, this method of movement is rather slow. But slow can be good for a snail or slug, if it makes them too slow to trigger the motion sensitive vision in predators. StuRat (talk) 20:05, 8 July 2012 (UTC)

This video [3] clearly shows the waves of muscle contraction. I found it by searching "slug locomotion" on youtube. Related is peristalsis, which is basically the same thing, but in a tube. Our article has some nice diagrams that might help explain. SemanticMantis (talk) 20:31, 8 July 2012 (UTC)

LOL, I love the note bellow the video: "Attention: disgust risk!" Notice that the author of the video also includes a description that might be perfect for the OP to use to describe the mechanism to his son: "Their muscles move under their bulky body relatively steadily forward - similar to the chain drive of a big tank!" Snow (talk) 22:08, 8 July 2012 (UTC)

If your son enjoys slug motion he will love that of snakes, which have several different types. Unfortunately our article is rather limited on the topic, but it lists the main types for your further research. See Snake#Locomotion and http://www.youtube.com/watch?v=5CchyctRFrQ. μηδείς (talk) 20:59, 8 July 2012 (UTC)

When was this ice age?

Someone in commons has an issue with a category. I don't speak pre-history though. If someone would like to pop over and help it should be apreciated. I hope science is the correct section here. If not we can close here and open in another desk. http://commons.wikimedia.org/wiki/Category_talk:Ice_age_410k-380k_BP --Canoe1967 (talk) 20:22, 8 July 2012 (UTC)

An interglacial is a warmer period like the present when ice age glaciers have retreated. I have no personal knowledge of whether the period of 410kya to 380kya was an interglacial or not, but the image at the article I linked to seems to imply it was. μηδείς (talk) 20:45, 8 July 2012 (UTC)