Wikipedia:Reference desk/Archives/Science/2011 September 23

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September 23

Neutrinos

(I've taken the liberty of merging this section to #FTL neutrinos below) Wnt (talk) 17:54, 23 September 2011 (UTC)

Photon Mass?

So, I heard that, even though photons do have zero rest mass, they have relativistic mass due to their motion. Could anyone care to explain this in wide detail? Thanks.186.29.118.196 (talk) 01:45, 23 September 2011 (UTC)

Sure. Energy is mass. As long as a photon has energy, it has mass. QED. See mass-energy equivalence and relativistic mass and rest mass for more details. --Jayron32 02:24, 23 September 2011 (UTC)

Any given photon has EVERY mass value from the tiniest amount above zero to as high as you want to count. The observed mass is purely in the eye of the beholder. (Pun intended.) The electron is different. Each electron can be found at any mass level from the base "rest mass" to as high as you want to count. It all depends on who catches it. Hcobb (talk) 02:34, 23 September 2011 (UTC)

If, indeed there is more than one electron. Maybe, there isn't. --Jayron32 03:15, 23 September 2011 (UTC)

That's it. I'm going to start engraving my initials on all of my electrons to make sure I don't lose any. (Shock!) What size font should I use? Hcobb (talk) 16:17, 23 September 2011 (UTC)

Bode phase plot guidelines

(I'm not sure if this might belong in Maths). I've got a set of Bode plots for a bunch of different circuits. On each one, I am supposed to (by analysing the transfer function) "sketch the Bode amplitude plot asymptotes and phase guidelines". However, I have no idea what "phase guidelines" are, and Google is unhelpful. Does anybody here know? --130.216.55.172 (talk) 03:24, 23 September 2011 (UTC)

Yes! Have a look at how to draw a Bode plot by hand. You need to decompose the transfer function into poles and zeros, usually by factoring the denominator of your transfer function. There are many related techniques to accomplish this - partial fraction analysis is the most common - have you covered any of these methods before?

This section explains the rules of thumb for a phase plot. All these "rules" are derived from more rigorous mathematical analysis (frequency-domain analysis, formally by taking the partial derivative of phase and amplitude of the transfer function with respect to frequency. By writing the function in canonical form, you can just churn out the various asymptotes and estimate the value of the phase for any frequency, without ever having to crunch it computationally. Nimur (talk) 04:32, 23 September 2011 (UTC)

Electra 10-E

Does anyone here happen to know where to find a maintenance manual for the Lockheed L-10 Electra? I'd like to know how to (non-fatally) sabotage and then repair one (for a writing project, of course), and for that I'd like to know how the mixture control linkages are arranged on that aircraft. (Don't worry, I'm not trying to sabotage an actual aircraft, just trying to arrange a malfunction and consequent forced landing as a plot device...) 67.169.177.176 (talk) 06:42, 23 September 2011 (UTC)

Does this relate to your shabbat navigation? What are you trying to do, find some way to kill a kharedi? :p Sir William Matthew Flinders Petrie | ^{Say Shalom!} 24 Elul 5771 06:45, 23 September 2011 (UTC)

No, no, no. The only thing these two questions have in common is that they're for the same writing project. And BTW, didn't I specify that the malfunction and force-landing would be non-fatal? Just for the record, I don't want to kill my characters in this case, but I want to have them force-land in a hostile area after running out of fuel (this condition caused by the mixtures sticking in full-rich position) and barely escape with their lives. Any deaths (if such there be) can wait until later. ;-) 67.169.177.176 (talk) 06:56, 23 September 2011 (UTC)

You could go for the simpler approach: have your saboteur drain some of the fuel pre-flight. According to the forums of people asking the same thing as you, there was one website that had the information, but I can't get it to load. It's [1] in case the problem's on my end. You're probably best off tracking down an enthusiast and asking them. Teshmanesh (talk) 08:10, 23 September 2011 (UTC)

I can't get it to load either, and the reason is that it's members-only. 67.169.177.176 (talk) 20:13, 23 September 2011 (UTC)

I would hope that the pilots would notice the fuel level was lower then expected before it was enough of an issue to cause a forced landing. Googlemeister (talk) 13:23, 23 September 2011 (UTC)

Hmmm, would it work to dump a bunch of golf balls down the fuel intake? (I assume they'd fit?) Wnt (talk) 16:48, 23 September 2011 (UTC)

Nah, draining fuel would be too obvious. Second of all, I want the crew to have to get spare parts upon arrival -- that's supposed to be part of the action too. Finally, when I said "sabotage", that was a figure of speech: I meant that I, as the author, want to create this malfunction, but not necessarily by having an actual (well, fictional) saboteur do it. In fact, the plane doesn't get truly sabotaged until reaching Pakistan, and the malfunction of the mixture controls is planned to happen naturally because of worn-out/defective parts. So obviously there's no way to drain fuel "naturally" (barring a leak in the fuel tanks). As for the golf ball idea, it would simply plug the lines and cause engine failure. And as for the pilots noticing the low fuel level, here's the situation: they're flying nonstop from Addis Abeba to Calcutta, so even after noticing the high fuel consumption, they still hope to make it to Ahmadabad, but run out of fuel over the coast and have to dead-stick into Karachi instead. 67.169.177.176 (talk) 20:12, 23 September 2011 (UTC)

Just remembered from one of those Discovery Channel programs: water in the aviation fuel. See [2] [3] etc. Wnt (talk) 15:09, 25 September 2011 (UTC)

Wouldn't this cause engine failure shortly after takeoff, as opposed to many hours later? 67.169.177.176 (talk) 04:00, 27 September 2011 (UTC)

I should admit, I have no idea. I vaguely recollect reading in some planes there are various different fuel tanks - maybe the pilot switches from one to the other and gets a surprise? Or maybe the water can pool somewhere and only come through later? Waving my hands here. Wnt (talk) 12:44, 27 September 2011 (UTC)

I remember being told during flight training that water contamination usually causes engine failure during takeoff/climb to altitude, not during cruise flight. As for the Electra, it has four wing tanks and ten fuselage tanks with a total capacity of roughly 1100 gallons, and the normal procedure is to draw fuel from the fuselage tanks first (because they mess up the trim) and then switch to wing tanks. Anyway, water in the fuel is a "no spares required" emergency (provided that the pilot can safely make a dead-stick landing -- and in my case she indeed can with her level of expertise), and I want the crew to have to get spare parts. 67.169.177.176 (talk) 23:38, 27 September 2011 (UTC)

Do you disagree?

The law which prevents doing anything in the past is the law which states a distance above zero can not be traveled in zero or less time rather than the distance light travels in unit time can not be exceeded. In other words light might get somewhere faster than sound and warn of an explosion faster but that does not mean light (compared to sound) can send information into the past and to do that requires time reversal not speed faster than light. --DeeperQA (talk) 07:35, 23 September 2011 (UTC)

If I understand what you're getting at, see tachyonic antitelephone.

Summary: Sending information faster than the speed of light in your frame of reference doesn't send it backwards in time, in your frame of reference. But it does send it backwards in time in some other frame of reference.

If the mechanism by which you can send the information faster than light is frame-invariant and isotropic, that is if it works the same in everyone's frame of reference and in all directions, then you can combine forces with someone moving quickly with respect to you, to send information backwards in time even in your own frame of reference.

It takes two steps: You send the information to the other party. This takes positive time in your frame, but negative time in his. He repeats the trick, sending it backwards in time in your frame. --Trovatore (talk) 07:53, 23 September 2011 (UTC)

This can be demonstrated using sound in the place of light as the fastest possible means of communication and light as the newly discovered faster than fastest method. What I want to confirm is that the true basis for not being able to go back in time is that no distance can be traveled in zero or less time which time travel or travel to an earlier time would require. --DeeperQA (talk) 10:49, 23 September 2011 (UTC)

No, the speed of sound and the speed of light are fundamentally different. The laws of physics have the same form in all inertial frames of reference. The speed of light is the same constant value in all inertial frames of reference. The speed of sound is not the same constant value in all inertial frames of reference. The speed of light is special.

It isn't necessary to have instantaneous travel, or "faster than instantaneous" travel, in order to travel backwards in time. If something looked like it's travelling faster than the speed of light in some inertial frame of reference, then there exist other inertial frames of reference in which it would look like it's travelling backward in time. All inertial frames of reference have an equally valid perspective, so travelling faster than the speed of light is equivalent (in a different, but equally valid inertial frame of reference) to travelling backward in time. Red Act (talk) 11:49, 23 September 2011 (UTC)

I think it's important to emphasize the two-step nature of the process. In one step, you get information travelling backwards in time in someone's coordinate system. Who cares? That's just a number (the time coordinate) going down.

It's not actually interesting unless the information can be sent back to an earlier time at the same point in space; that is, unless you can get a causal loop. For that you need more than a coordinate system. That's where the two-step process comes in. --Trovatore (talk) 19:08, 23 September 2011 (UTC)

Unfortunately going back in time at the same place in space implies that events which happened there like burning a candle can be reversed since the same point in space can be occupied by only one object at any given time. --DeeperQA (talk) 16:45, 24 September 2011 (UTC)

exceding speed of light

(Merged to #FTL neutrinos Wnt (talk) 17:57, 23 September 2011 (UTC) )

To whom who knows about genomic databases

a. Where can I find genomic databases, to the level of the (DNA) bases ? In particular, I need the human one and that of SV40 virus.

b. Where do I find, there or elsewhere, details regarding the integration sites of SV40 in the human genome ? Thanks, BentzyCo (talk) 08:33, 23 September 2011 (UTC)

Looks like you will need to learn how to navigate either the NIH's genome database or the corresponding UK/EBI genome database. You can get the complete SV40 genome sequence here. The human genome is considerably larger, but you can also download it by following links from either of the sites I gave. Another great resource for visualizing the genome is the UCSC Genome Browser, which provides a user-friendly interface. With regard to question (b) you can do a Google Scholar search on "SV40 human genome integration sites" which yields a few promising looking hits about mapping SV40 sites in the human genome. --- Medical geneticist (talk) 10:18, 23 September 2011 (UTC)

Remote controlled lighting etc.

Typically, I see remote controlled lighting and music systems (as simple as a remote control or merely button somewhere else) sold as part of high end systems. But how difficult would it be to find something to attach to a light and control it from the other end of the room; how costly? Grandiose (me, talk, contribs) 09:35, 23 September 2011 (UTC)

Not that expensive on cost of parts eg http://www.maplin.co.uk/remote-control-lamp-holder-with-dimmer-339239?c=froogle&u=339239&t=module - that's a dimmer. I've seen remove control plugs (4 sockets) selling for about £15. Switching relays can be very cheap eg http://www.maplin.co.uk/ultra-miniature-high-power-mains-relay-218688?c=froogle&u=218688&t=module (this is overspecced for light) - as for the remote control system - I don't know prices - but electronics as well established and simple as this is going to tbe dirt cheap.Imgaril (talk) 10:38, 23 September 2011 (UTC)

I have a remote control outlet that came with my garage door opener. I believe the idea is you use it to turn on a light (plugged into the controlled outlet) when you arrive home at night. StuRat (talk) 15:41, 23 September 2011 (UTC)

I bought a power bar that came with a remote control a year or so ago. The remote allows the outlets on the power bar to be turned on and off. It was marketed as a "green" thing, so that you could unpower your entertainment system when you are going out (preventing consumption of energy in standby mode). Caveat: the remote didn't work well for me. After a month or so, I could no longer reliably turn the power on and off from any significant distance. --Srleffler (talk) 16:28, 26 September 2011 (UTC)

Wifi and cell-phones on board of a plane

Cell-phones are (or were) banned on flight, however, I don't remember any wifi prohibition. Although I don't believe that either could interfere with flight instruments, why was the former banned and the latter not?Quest09 (talk) 11:17, 23 September 2011 (UTC)

Because cellphones are older and is responsible for the persistant myth. Average people aren't smart enough to know that it uses the same technology, so the myth hasn't carried through. Plasmic Physics (talk) 11:45, 23 September 2011 (UTC)

The onboard wi-fi system is fully tested for safety issues, and presumably the aircrew have some control over it, which is not the case with cell phone signals. See this fact sheet from the FAA.--Shantavira|^{feed me} 11:59, 23 September 2011 (UTC)

I didn't mean that "WiFi in the Sky" system, just a plain laptop with WiFi on (even if there were no hotspot to connect to). Airlines never complained, never banned it, never went on the completely secure side. Quest09 (talk) 12:42, 23 September 2011 (UTC)

The last time I was on a flight, which was admittedly about two years ago at least, the stewardess asked for all electronic devices to be turned off. Dismas|^(talk) 12:51, 23 September 2011 (UTC)

Does that include pacemakers? Plasmic Physics (talk) 14:31, 23 September 2011 (UTC)

Don't WiFi adapters transmit at a lower effect and use other wavelenghts than cell phones? Sjö (talk) 13:14, 23 September 2011 (UTC)

The norm I believe is to turn off all electronic devices before take off. Certain devices can be switched on again when the aircraft reaches cruising altitude. They should be switched off again whenever an instruction is given, which includes before landing. IIRC we've discussed this before. I believe the reason is because of the greater risk of things going wrong, not just of any minute risk of interference but also because the devices themselves are a hazard as they can go flying. It also reduces the number of distractions so they are more likely to have your attention if something goes wrong (the onboard entertainment systems are under their control although you could be reading or sleeping with ear muffs). As Sjö mentions wifi which uses the public frequencies generally transmits at a far lower power (as they are limited by the regulations surrounding unlicensed devices) than mobile phones which use licenced frequencies (see dBm and remember mobile phones on planes will at least briefly likely to operate at max power as they attempt to find a network).

Wifi devices also don't tend to have the risk of causing problems for stuff on the ground because of the low range (it's commonly suggested one of the reasons to limit mobile phones on planes is because of the effect on base stations of the rapidly moving transceivers).

And to state the obvious, one of the biggest differences is before smart phones and in the absence of microcells on planes, there was little use to mobile phones on planes other then the silly games and checking or composing existing messages (except if you did happen to get a signal from the base stations but as mentioned that would usually not be something the mobile operators liked). In this smart phones era, most have a flight mode. There were of course some early smart phones as well as semi-smart phones which support J2ME apps and have cameras and music or other media without a flight mode but I don't know how often this was really an issue. Laptops on planes have plenty of uses without wifi including for the higher end clientele and most people would have little idea how to turn off their wifi. So telling people to turn off their mobile phones was often an acceptable tradeoff far less so than telling people to turn off their laptops, and telling them to they can use their laptops but should turn off their wifi is a recipe for confusion.

Nil Einne (talk) 14:41, 23 September 2011 (UTC)

In case I didn't say it before, the ban is a result of a myth. There is no justifiable reason for issueing such a ban. Plasmic Physics (talk) 14:31, 23 September 2011 (UTC)

There are two justifiable reasons. First, there has been recorded coincidences between aircraft control anomalies and use of electronic devices. Second, many people strongly support the ban simply to keep people from using cell phones on an airplane. -- kainaw™ 14:33, 23 September 2011 (UTC)

I would be interested in seeing some of the references on the recorded coincidences you mention Kainaw. Googlemeister (talk) 16:12, 23 September 2011 (UTC)

This is Wikipedia. See mobile phones on aircraft. Make sure you don't incorrectly translate "coincidences" as "causes". -- kainaw™ 16:19, 23 September 2011 (UTC)

Not sure about your experience, but back in the days before in-flight wifi, I clearly remember flights where they instructed us that devices with active wifi connections could never be used on planes. In general, it is still usually the case that all electronic devices must be turned off during take-off and landing. Dragons flight (talk) 16:36, 23 September 2011 (UTC)

I can understand why they would want you to turn off anything that transmits communications, especially during takeoff and landing. What I don't see is why they also make you turn off non-transmitting devices. I have a rather irksome fear of flying that usually only bothers me during takeoffs and when the flying is in what I would call "a hazardous situation" (like the one time a plane I was on had to fly right in between two thunderstorms). One of the things I have found to be an immense comfort during such situations is watching the plane's altitude, speed, and location on my GPS receiver (I'm not sure, but I think it comforts me because I would be able to see abnormal changes in them). I've always wondered why I'm not allowed to use a GPS receiver given that it doesn't transmit any signals and thus couldn't interfere with the aircraft. Ks0stm ^{(T•C•G•E)} 16:51, 23 September 2011 (UTC)

[4] mentions a case where the navigational system of a Boeing 737 stopped working but started again after a passenger was asked to turn off his hand held receiver. [5] (from 1997) notes possible interference from AM/FM radios and CD players Nil Einne (talk) 17:33, 23 September 2011 (UTC)

I suppose the problem is that many receivers also accidentally transmit on another frequency and this accidental transmission could, just possibly, with unfortunate positioning and inadequate shielding, just possibly interfere with some over-sensitive equipment on the plane. I can't imagine how a GPS receiver alone (without other functions) could possibly transmit anything measurable beyond a few centimetres, but the aircraft staff don't have the expertise or equipment to check that the receiver is not combined with some other transmitting equipment. Dbfirs 09:14, 24 September 2011 (UTC)

All, or at least nearly all, radio-frequency receivers also emit radio-frequency signals to some extent. This is because they use superheterodyne technology, generating a signal that they allow the incoming wave to interfere with, and measuring the beat of the combined signal. The power, I expect, is rather low (well, it would have to be; my GPS receiver will run for 24-48 hours continuously on two AA batteries) but I can't guarantee a priori that it's impossible for it to interfere with airline equipment. I'm pretty skeptical though.

My cynical theory about why some airlines don't want you to use the GPS is that they don't want you to have a record of the plane's track, in case that could somehow be useful to you in a lawsuit. A lawsuit about exactly what, I'm not really sure. --Trovatore (talk) 09:23, 24 September 2011 (UTC)

About missing an important business meeting because the flight was diverted? 67.169.177.176 (talk) 19:19, 24 September 2011 (UTC)

Definitely NOT that. Airlines do not guarantee their service, in the fine print it says that they can't beheld liable (above the cost of the ticket) for any delays or cancellations, even if it is their own fault. If you could sue airlines for being late, they would have all been out of business a long time ago. Skeptoid did an episode on cell phones in airplanes. I'm a fan of skeptoid but I have to say, Brian's Libertarian outlook colors this episode more then most, I think the commentary is more just as interesting as the episode. Vespine (talk) 22:41, 25 September 2011 (UTC)

Airlines, definitely, can be held liable for being late, even if it's not their fault (!). They might not be liable of any damage caused by their poor service, but they have to compensate you up some number of hours of delay. (at least in the EU). Wikiweek (talk) 19:12, 26 September 2011 (UTC)

Yes, sorry I should have been more specific, yes they can be liable for things like transfers and hotel accomodation and incidentals arising from delays; what I specifically meant is that you can't sue them for damages (as you state), like "if you miss a very important meeting" and it costs your company millions of dollars, as the post above mine seems to suggest. Vespine (talk) 22:34, 26 September 2011 (UTC)

It's worth remembering the Ks0stm was talking about the ban on all electronic devices, including GPS receivers, during take off and landing which is different even if related to what Trovatore is talking about. As I mentioned above, I believe on of the possible reasons for the ban is because many electronic devices make good missiles so it's preferred if they are stowed during such criticial times. (Of course there's also concern about possible interference.) From [6] it seems the majority of airlines allow GPS receivers during the flight (excluding when it's disallowed by the pilot). Also some phones allow GPS in flight mode [7] [8] [9], I wonder whether they actually mention the ban on GPS during the flight and if not, whether someone using such a phone is likely to appreciate the ban. Speaking on both the ban during criticial times and a general ban, the possibility of intereference may be tiny but I don't think it's that surprising some some airlines would be concerned since the risks to them from problems can be rather severe. In other words, IMO they're far more likely to be concerned about lawsuits if one of their planes crashes (although yes I'm aware there are various laws limiting their liability). As I also mentioned, they are far more likely to be willing to take the risk when they can see an advantage to them, this is there for laptops (although again not enough for them to allow them during takeoff and landing) but with GPS receivers it's far less obvious since it's only the geeks and those like the Ks0stm who are likely to care much. Oh and as for people like Ks0stm, there is the option of the inflight entertainment system which often shows info from the planes internal navigation system, even for more budget airlines some may have it as an optional extra (and if it does cost which one do you think they'd rather you use?). As someone mentioned, it's also difficult for the flight attendant to know if the device is an active transmitter (as opposed to something which has some minor incidental transmissions), modern GPS receivers often have bluetooth and some even have a mobile data connection. There are of course those reports of apparent interference (or problems that were resolved when the devices were switched off) which don't help. I couldn't find any more specifics on the GPS case (I did look before my first post) so the details aren't clear but of course such stories are likely to raise concern (and some of the people making the decisions probably don't know all the details either). BTW, it's worth remembering as for the hypothetical advantage to the passenger having their own GPS track, it would only seem to be an advantage if the passenger either wouldn't know to (because they're not aware of the issue), or wouldn't bother to (because of cost or whatever), or wouldn't manage to (i.e. a court wouldn't allow it) to subpoena the airline's own track of the flight which is the obvious recourse if you want a track. Well unless you come up with conspiracy theories involving either an inaccurate or a modified track from the airline which seem a little far fetched. Nil Einne (talk) 11:46, 27 September 2011 (UTC)

Heavy metal concentration

How can I measure the concentration of heavy metals in a water sample? --70.134.53.27 (talk) 14:54, 23 September 2011 (UTC)

Mass spectrometry, I think is the usual way. Looie496 (talk) 15:05, 23 September 2011 (UTC)

X-ray fluorescence is also usual, as can be X-ray absorption spectroscopy. There are quite a few ways in fact. You really need to search and narrow the field "heavy metal water determination" is a good start, as will be "heavy metal water quantitative analysis". It may also depend on the expected concentrations what methods are best.Imgaril (talk) 16:11, 23 September 2011 (UTC)

Here I was hoping this was a question about doing homework while listening to Opeth. Vespine (talk) 22:42, 25 September 2011 (UTC)

Seriously?

I just saw something that almost made me vomit: a woman with facial hair. I'm not trying to sound mean, but it was disgusting and odd. Earlier today, I saw a young woman with hair on her chin. How is it possible that a female can have facial hair? Is something wrong with her hormones? That's not normal. B-Machine (talk) 15:11, 23 September 2011 (UTC)

Yes, there's something 'wrong' with her hormones: she has too many of the masculine kind. Wikiweek (talk) 15:14, 23 September 2011 (UTC)

All women have hair on their faces. See Facial_hair#In_women. I'm sure at least some of them also find your appearance "disgusting and odd" (I'm not trying to sound mean). Perhaps this person is a female with a hormone imbalance. Perhaps she is intentionally pursuing hormone therapy as a part of gender reassignment. Perhaps she was born with male sex organs, but lives and presents the female gender. Get used to the fact that human bodies come in magnificent variety, and we don't all share your particular set of social norms and gender norms. SemanticMantis (talk) 15:28, 23 September 2011 (UTC)

Also see hirsutism, which explains this rather better.--Shantavira|^{feed me} 15:29, 23 September 2011 (UTC)

Many women have some visible facial hair, or would, if they didn't remove it or bleach it. So, the unusual thing about women who retain visible facial hair isn't that it grows, but that they choose not to do something about it. StuRat (talk) 15:35, 23 September 2011 (UTC)

What is it about American society (and others?) and phobia about hair on women? I mean, even hair on the legs and under the armpits, where it's supposed to be in the sense that most women have it, some kind of fashion junta treats as if unfeminine. Is this unattractive? How did such a phobia ever get started? Wnt (talk) 15:37, 23 September 2011 (UTC)

It started in the 1920s if I recall. Googlemeister (talk) 16:10, 23 September 2011 (UTC)

In general, regardless of society, women are competitive when it comes to beauty. One woman claims to be more beautiful because she shaves her legs. Another says she is more because she shaves her armpits. Another claims she is more beautiful because she shaves her pubic hair. It doesn't need to be hair. It could be skirts in the 60s... Mine's shorter. No, mine's shorter. No, mine's shorter. It could be lace in the 80s... I got lace braided in my hair. I got it on my wrists. I got lace gloves. I got lace legwarmers. In none of these cases are men asked what is beautiful, but all men are blamed for all the "work" required to become beautiful. -- kainaw™ 16:45, 23 September 2011 (UTC)

I've heard it suggested by a psychologist friend that the fashion trend towards no body hair on both males and females is a trend towards paedophilia, i.e. a preference for an impossible look that only exists before puberty. Please discuss. HiLo48 (talk) 20:50, 23 September 2011 (UTC)

...with references. —Akrabbim^talk 21:07, 23 September 2011 (UTC)

That notion is rubbish. Also, wikipedia is not a discussion board. SemanticMantis (talk) 21:08, 23 September 2011 (UTC)

I could turn it into a question... It's a more rational position than vomiting upon seeing hair on woman's face. Whatever would P T Barnum have done without bearded ladies? HiLo48 (talk) 08:36, 24 September 2011 (UTC)

See also: Bearded lady. Mitch Ames (talk) 06:11, 24 September 2011 (UTC)

'Almost made you vomit'? *rolls eyes* I bet seeing a vagina with hair would make you faint. -- Obsidi♠n Soul 07:40, 24 September 2011 (UTC)

Before you people start accusing me of something I'm not, let me clarify what I did here: I was joking. I didn't really see a woman with facial hair. I was bored, so I made this up to see what kind of reaction I would get. Very funny. And as for the accusations, no, I'm not a pedophile (are you sick?), no, I'm not gay, and yes, I like a hairy vagina. I prefer women to have hairy vaginas over shaved vaginas. B-Machine (talk) 22:57, 24 September 2011 (UTC)

If you feel it's funny to make up a question, feel free to also enjoy the attributes we make up to apply to you. HiLo48 (talk) 23:01, 24 September 2011 (UTC)

Calm down, man. I was joking. Can't you take a joke? B-Machine (talk) 23:25, 24 September 2011 (UTC)

Strictly speaking, vaginas typically don't have hair, vulvas do. Mitch Ames (talk) 12:16, 26 September 2011 (UTC)

Whatever the troll's intentions, I am surprised no one mentioned drag kings. I personally know a rather militant lesbian who glues clippings of pubic hair to her chin as a form of transgressivism. I find it kind of sexy in her case. μηδείς (talk) 01:54, 26 September 2011 (UTC)

FTL neutrinos

Is it true? What are the implications for physics? --70.134.53.27 (talk) 15:27, 23 September 2011 (UTC)

Presumably you're interested in recent announcements by CERN, as reported in this BBC article - Speed-of-light experiments give baffling result at Cern? Here's the official press release, OPERA experiment reports anomaly in flight time of neutrinos from CERN to Gran Sasso. If you're interested in the implications, consider reading the papers linked from that, or watching the broadcast seminar, featuring a QA session.

Here's the pre-print, Measurement of the neutrino velocity with the OPERA detector in the CNGS beam. The claim is that tau neutrinos arrived 60.7 ns earlier than they should have, after a flight of 730 km. Unfortunately, as always, high energy physics is much more complicated than that: the tau neutrinos did not fly the entire distance; they are produced somewhere en-route out of muon neutrinos. If you want to understand the details, ... the research is outlined in the paper and websites.

In my opinion, the best way to assess the "implications" of the experiment is first to establish an understanding of the sources of error, and the methods used to control those errors. As a skeptical scientist, I believe it is more probable that a large team of physicists measured time and distance incorrectly, as a result of invalid statistical data processing; but it's also possible that the behavior of 15,000 neutrinos did actually violate all other known physical observations. After you review the data and experimental presentation, and if you believe all experimental errors are accounted for, the next step would be to undertake an explanation for the speed. Finally, you could proceed to derive physical consequences that follow from this apparent violation of the "speed limit." Nimur (talk) 16:47, 23 September 2011 (UTC)

I have to correct you on the tau neutrinos - as far as I know only a single tau neutrino has so far been seen at the OPERA detector (I remember reading that they expect a total of only 11 tau neutrinos over the several years of the research project). Many more muon neutrinos have been detected, and the recent preprint on arXiv states that there were "about 16000" neutrino events detected by OPERA. And since we know about neutrino oscillation, we actually shouldn't talk about tau neutrinos, muon neutrinos and electron neutrinos but about ν₁, ν₂ and ν₃; then e.g. beta decay creates a certain superposition of the 3 neutrinos characteristic for the electron, and there is another superposition for the muon and another one for the tauon. Icek (talk) 18:48, 23 September 2011 (UTC)

(Merged from "Exceeding the speed of light" above - Wnt (talk) 17:59, 23 September 2011 (UTC))

[10] Now i am not a science guy but nothing could exceed the speed of light right?but than whats this? — Preceding unsigned comment added by 175.110.242.217 (talk) 08:10, 23 September 2011

(Merged from #Neutrinos above - Wnt (talk) 17:55, 23 September 2011 (UTC))

Sorry to be the first cranky neutrino question after the CERN release of data, and this is probably a very stupid question. Is there a good reason to think that neutrinos must have a positive mass? I'm sure there must be, but I can't see it in our article neutrino. Our article says that neutrinos must have a non-zero mass, and that our main source of information on the masses depends on the squares of the masses (if I'm reading that right)? Please disappoint me with a reasonable explanation, or I'll be too excited to sleep :P 86.164.78.26 (talk) 21:59, 22 September 2011 (UTC)

Okay, we need to distinguish three different things here:

1. Negative mass. This has nothing directly to do with tachyons. Tachyons don't have negative mass.
2. Negative mass-squared (also called imaginary mass) in classical relativistic particle theory. Classical particles with negative m² go faster than light.
3. Negative mass-squared in relativistic field theory. This is mathematically related to the classical particle case, but the practical upshot is very different. In a field theory, the mass-squared behaves like a spring constant—if you think of the field as a rubber sheet then the higher the mass, the more resistant the sheet is to stretching. If the mass-squared is negative, then not only does the sheet not resist stretching but it actually pushes in the same direction you pull it, leading to an exponential feedback loop if the field is even slightly disturbed. The only way for this to make any sense is if there's a counterbalancing effect that comes into play at larger amounts of stretching, so the sheet only stretches to the point that these opposing effects balance each other. This actually happens in the Standard Model with the Higgs field, and is called tachyon condensation. The result is a field that behaves for practical purposes like it has a positive mass-squared.

I know nothing about this new announcement from OPERA except that they claim to have found actual superluminal propagation. This sounds like the second case above, but modern particle physics is built on quantum field theory, where the second case is irrelevant; "tachyons" don't propagate superluminally in quantum field theory. So, if this is real, it would pretty much require rebuilding modern particle physics from the ground up. It could be a quantum gravity effect, and this might give a hint as to the right theory of quantum gravity. But more likely it's experimental error. -- BenRG (talk) 23:05, 22 September 2011 (UTC)

Might you be referring to the Reuters article that they are travelling faster than light? I just got it linked to me. Excitement should be withheld as it's almost certainly an error, but honestly, given the fact that the scientists aren't crackpots, my heart did rush a little when I got to the end of the article without indication that they're crackpots. SamuelRiv (talk) 23:21, 22 September 2011 (UTC)

[11]. Nil Einne (talk) 00:54, 23 September 2011 (UTC)

Here's the preprint. The official announcement doesn't happen until 4PM Friday in Geneva (13 hours from now). As that blog post says, it's way too early to get excited about this. -- BenRG (talk) 01:01, 23 September 2011 (UTC)

Note from some reports [12] [13] it appears that while the team think there is a possibility their results are correct and would be confirmed by independent replication and that would obviously be their preference, they think the more likely explanation is there's an error they didn't notice. Some further comment on the Sn1987A neutrinos [14] Nil Einne (talk) 01:08, 23 September 2011 (UTC)

The news reports on the report said the neutrinos travelled through the Earth faster than the speed of light in vacuum. What would be the speed of light through dirt and rocks, ignoring the fact that dirt and rocks would absorb the light? Edison (talk) 14:13, 23 September 2011 (UTC)

Can one talk about the speed of light through totally opaque media? Whatever the answer is, it's not faster than it would be a vacuum, so how would that get you anything? --Mr.98 (talk) 19:29, 23 September 2011 (UTC)

opacity is not an absolute characteristic, it is relative. Even dirt and rocks allow EM to propagate through it, albeit not very well, but there is still a "speed of light". —Akrabbim^talk 19:44, 23 September 2011 (UTC)

Well, that's true. I was thinking only about visual frequencies, which are not very penetrative, but of course there are lots of forms of EM. But either way, it's going to be slower than in a vacuum. --Mr.98 (talk) 22:57, 23 September 2011 (UTC)

http://xkcd.com/955/. Deor (talk) 14:36, 23 September 2011 (UTC)

Perhaps they pass through the 8th dimension. Wnt (talk) 17:32, 23 September 2011 (UTC)

Just as likely as The 5th Dimension. Edison (talk) 17:45, 23 September 2011 (UTC)

Ah, but the neutrino oscillation overthruster allows it to tap into the dimension of space inside solid matter.^[15] ;) Wnt (talk) 18:07, 23 September 2011 (UTC)

Perhaps even the Sixth dimension? Hot damn! SamuelRiv (talk) 18:19, 23 September 2011 (UTC)

All kidding aside, I almost wonder if there could be something to this idea. The passage with solid matter is what distinguishes these neutrinos from the ones from distant supernovae. Now a standard force like electromagnetism, so far as I understand from a previous discussion here, can be modeled as an extra dimension, a bending of space just like gravity. But neutrinos ignore this force, so they shouldn't be slowed by the Earth's optical refractive index. Is it conceivable that some obscure force acting on the neutrino could have a different kind of refractive effect, where passing through solid matter actually makes them go faster than passing through empty space? As if there were some other dimension in which space could be bent, but one which is bent in the vacuum, but which can be straightened out by matter? (Almost surely this is bogus - yes, I know that calculation is quite indirect and errors or unspectacular physics oddities could slip in in many places, but if we want to imagine a way to explain the result if it were real...) Wnt (talk) 02:35, 24 September 2011 (UTC)

Err, don't most neutrinos detected go through a lot of solid matter? My understanding is that most neutrino detectors are deep underground to avoid cosmic ray contamination. I don't think passing through matter (which is an imprecise way of saying "didn't interact with any matter", right?) is really the distinguishing factor here. The distinguishing factor is that these guys claim to know when they created the neutrino, precisely, which is exactly what we don't know with regards to supernovae or stars. Right? --Mr.98 (talk) 04:45, 24 September 2011 (UTC)

While the neutrinos measured from SN 1987A did travel a relatively long path through the Earth (if you look at the 3 neutrino detectors mentioned in the article, they are all so far north that the supernova couldn't have been visible from their position at any time of day; and for neutrino detectors with direction sensitivity the neutrinos from above are usually discarded as far as I know, because there is more background of muons being created when cosmic rays hit the atmosphere), that wouldn't have much effect on the average speed from the Large Magellanic Cloud to the Solar System.

Maybe it is some kind of near-field effect like it also occurs in electromagnetic dipole radiation, but that's just something that came to my mind now without any calculations to back it up. In any case, if information really travels faster than light, then causality is broken or special relativity is wrong. Icek (talk) 13:26, 24 September 2011 (UTC)

The world's observatories did a great job on some of these supernovae, but 60 ms precision is surely beyond them! However accurately the neutrinos speed was measured relative to their travel time to Earth, any small variation within the Earth would have gone unnoticed, I would say.

It doesn't break causality or special relativity to go faster than the speed of light, if that speed is measured in water, glass, etc. Only the speed of light in vacuum counts, because it is the fastest and most fundamental speed. But what if it isn't? What if there's some slightly faster speed of light that applies in this case? Wnt (talk) 14:27, 24 September 2011 (UTC)

Of course I mean the speed of light in vacuum. Assuming that the Lorentz transformation is correct, then you could indeed send a message into your own past (you only need a neutrino emitter in the vicinity of the neutrino detector which receives the information from the neutrino detector; the neutrino emitter has to be moving at a very high speed away from the original neutrino source and emit neutrinos towards a detector close to the original source; from the rest frame it will look as if the neutrinos from the fast moving emitter are moving backwards in time).

If you think there is some slightly faster "speed of light" applying in this case (because there is actually no way that light moves in a straight line from CERN to Gran Sasso?), then what would happen if you build a long straight tube from CERN to Gran Sasso? You could repeat the Michaelson-Morley experiment with light sent through the tube and with the interferometer traveling at various speeds (obviously there are many practical problems with these experiments, but in principle they can be done). Would the neutrinos travel slower because the tube exists, or what else would happen (things could be arranged so that the measured neutrinos would move through the soil close to the tube, but not through the vacuum inside the tube)? Icek (talk) 14:58, 24 September 2011 (UTC)

To disclose fully, I don't know (but ought to) whether the Lorentz transformation or electrical formulas involving c would be noticeably inaccurate if they should be using the hypothetical super-fast c accessible to neutrinos passing through solid matter, but instead are using a somewhat slower measure of light passing through a vacuum. On the other hand, since I'm just handwaving anyway, for all I know the neutrino path might be one of these straighter-than-straight non-Euclidean geometry things in 11 dimensions. Alas, my imagination has gotten beyond what I know. But I'm skeptical that the Michaelson-Morley experiment applies, because you can't use it to come up with anything important when a medium slows the speed of light, so why would you be able to use it if it speeds it up? Wnt (talk) 03:41, 25 September 2011 (UTC)

Nature News has printed the extra dimension idea (citing a professor emeritus......)^[16] but without the assistance of Buckeroo Banzai they still have failed to make the connection with the space inside solid matter. ;) Wnt (talk) 17:00, 25 September 2011 (UTC)

—Wow, only on weekends!  :) All kidding aside, I think that this discovery may actually be slightly less revolutionary than it first appears.

It was always my understanding (please feel free to correct me, if I err) that Albert Einstein theorized that the speed of light in a vacuum was a universal speed limit, by claiming that as something approached light speed, the flow of time—relative to it—would proportionately slow down, or "dilate." By extension, as said object hit light speed, time would stop, rendering any further acceleration (speed / time) impossible. There are two "gaps" in this hypothesis, however.

1.) Einstein himself never said that something couldn't travel faster than light speed if it were ALREADY moving that fast when it was created.

2.) Niels Bohr (to whom we owe the current atomic model, along with Ernest Rutherford) in one of his arguments with Einstein, even went so far as to propose that a particle travelling at, say, 9/10 of light speed, may even be able to "quantum jump" to 1-1/10 of light speed.

Long story short, I don't believe AT ALL that Einstein was mistaken in his theories; rather, CERN may have just confirmed the existence of the very first Tachyon! Pine (talk) 21:00, 24 September 2011 (UTC)

As I said above, tachyons are violating causality. For a tachyon at speed v you only need a tachyon emitter traveling faster than ${\frac {2v}{1+{\frac {v^{2}}{c^{2}}}}}$ (a speed which is below c). Send a tachyon from a stationary tachyon emitter to a tachyon detector traveling along the moving tachyon emitter. When the moving tachyon detector detects a tachyon, the moving tachyon emitter shall emit a tachyon back at the stationary tachyon emitter, and it will arrive there before the original tachyon was emitted, as can be calculated using Lorentz transformations. Icek (talk) 22:13, 24 September 2011 (UTC)

This is a really problematic argument because it makes an assumption about emitter vs receiver that isn't even logically coherent. It assumes that you can always choose to emit a tachyon going "forward in time", where "time" is for some reason the coordinate time of your rest frame. I see no reason why the world should work that way in any case, but a more serious problem is that the tachyon's worldline can go forward in time with respect to the rest frames of both endpoint labs, i.e., it can be "emitted" on both ends by this definition. Obviously this makes no sense from a causality perspective. The most obvious solution is to impose some kind of global Lorentz-violating causality relation, perhaps coincident with the rest frame of the cosmic microwave background. But if you do that then of course your procedure for sending a signal into the past no longer works. -- BenRG (talk) 22:54, 24 September 2011 (UTC)

Special relativity, as it existed in 1905, could accommodate faster-than-light travel in a certain limited sense, if you didn't worry too much about causality. But a lot has happened since then. As I said earlier in this thread, quantum field theory, which is the foundation of modern physics, can't deal with faster-than-light particles. It does have a concept of "tachyons," but they don't go faster than light, despite the name. If this phenomenon is real then it undermines the foundations of quantum field theory and everything is potentially up in the air, even basic concepts like "mass" and "speed". -- BenRG (talk) 22:54, 24 September 2011 (UTC)

I'll just note a disagreement with the idea that FTL must equal time travel - this assumes that relativity always applies, but FTL is clearly beyond relativity anyway. I am rather fond of the idea that an absolute rest frame can be defined at any point in space; most of the matter we see stays within 0.1c or so of this rest frame. Provided that under hypothetical new laws of physics an FTL particle is never permitted to move backward in time relative to the locally defined rest frame, it could never possibly move in a complete closed circle in spacetime. Of course there is no shred of evidence for this, but we cannot dismiss FTL a priori based on time travel paradoxes. (And it is also very much possible that time travel is possible, and the single past and the single future simply reconcile their fates as best they may) Wnt (talk) 03:48, 25 September 2011 (UTC)

Here's a good readable summary of the experiment, by Chad Orzel. -- BenRG (talk) 23:17, 24 September 2011 (UTC)

Nature News has a lot of people coming out of the woodwork, you might say.^[17] I am curious about one poster there who has spun a Dutch blog about it^[18] citing an obscure quantum theory of gravity by Vasily Yanchilin. I don't understand the argument but it sounds juicier than its hundred rivals. Wnt (talk) 03:25, 27 September 2011 (UTC)

Relative risk of tuna

There's a warning that canned tuna may contain mercury. However; beef, pork, and chicken definitely contain unhealthy substances like animal fat and cholesterol, in greater quantities. So, my question is, what's the total relative health risk of all of those ? That is, are you likely to live longer by choosing canned tuna over those other options, and ignoring the mercury risk ? (Obviously there are even healthier alternatives, but I don't want to discuss those here.) StuRat (talk) 15:27, 23 September 2011 (UTC)

(comment - I don't think I properly answered your question below - the issue is that - mercury tends to send you mad, not necessarily put you in an early grave)

I read up about this a few months ago when I was feeling quite peckish towards tuna salads, tuna sandwiches etc..

Firstly different tunas have different quantities of mercury. Secondly other seafish and creatures are just as bad, some are worse -halibut, shark etc can be problematic to name just two. Also some crustacae have issues like this, whilst others are relatively metal free.

Also note that mercury is not the only 'toxin' - cadmium is another problematic element- and there are several others.

I'm concerned that what I will say next will be construed as medical advice but here goes - 1 tin of tuna a week should not be a problem (according to the accepted limits for mercury intake) eg - 1 tin a day in the long term will (or is likely) to start to affect you .. that could be as minor effect as friends noticing that you are "acting a bit strange" - people really do start to go a bit loopy if they get too much.

A shame because I find it absolutely delicious.

Also see Mercury in fish, this table is usefull too http://www.fda.gov/food/foodsafety/product-specificinformation/seafood/foodbornepathogenscontaminants/methylmercury/ucm115644.htm Imgaril (talk) 16:20, 23 September 2011 (UTC)

A lot of it comes down to who you are, too. Young children eating tuna is a big deal, someone in their 50's isn't going to be affected by trace amounts of methyl mercury. Cholesterol is actually healthy in proper amounts, some people get paradoxical cholesterol problems by not taking in enough (the body isn't always sensible with synthesis), and fat is necessary at a basic level due to fat-soluble vitamins. The fat in fish is actually deficient in certain diets and may actually be healthy. Certain foods can be very bad for certain people (e.g. phenylketonuria because I'm staring at a can with a warning label, food allergens are another very situational problem). Is eating tuna or pork "better" is an impossible question, whether it's better for you is an answerable one, but it's basically medical advice. If you're seven years old, tuna should be beaten away with a very large trout. If you're seventy, it might be the ideal thing for your diet. SDY (talk) 21:38, 23 September 2011 (UTC)

In 22 documented cases, pregnant women who consumed mercury contaminated fish showed mild or no symptoms but gave birth to infants with severe developmental disabilities. Cuddlyable3 (talk) 23:00, 23 September 2011 (UTC)

Out of curiosity, does anyone know the mechanism of how the Hg causes damage? Does it block a specific reaction? The mechanism section of our articles on Mercury poisoning and Minamata disease give no information? SDY (talk) 00:32, 24 September 2011 (UTC)

This video [19] shows a mechanism by which mercury causes neural degeneration. --173.49.15.225 (talk) 17:38, 24 September 2011 (UTC)

Thanks for the answers so far. I haven't seen any comparison of the relative risk of eating canned tuna versus chicken, beef, and pork, though. StuRat (talk) 02:54, 25 September 2011 (UTC)

The answer, overall, is that there is no answer. Comparing tuna to beef/pork/chicken, the relative risk of contributing to heart disease is lower, relative lisk of developmental abnormalities is astronomically higher, though beef could nominally contribute vCJD, which is only "developmental" in a literal sense. SDY (talk) 06:41, 25 September 2011 (UTC)

Since genetic factors influence your likelihood of heart disease, cancer, and many other ailments, it's impossible to say which is healthier for you to eat. --Colapeninsula (talk) 16:31, 26 September 2011 (UTC)

I didn't ask about me. Just use the typical non-pregnant adult as your model. StuRat (talk) 20:41, 27 September 2011 (UTC)

Human Organ Importance Essay

This is a question about a website resource that I cannot locate.

Several years ago I saw a long, text essay by a physician (I believe internal medicine resident) that listed human organs in importance and he explained why each one was--in his opinion--at that level of importance. It was just fascinating, edifying read and gave a great description of each organ and why it's important. Brain, heart, lungs, so forth.

Have any of you come across such a website or know of a better way to possibly locate this resource (other than Google)? I thought it was possibly a Google Answers response but from what I can remember it might be on a science message board archive site, usenet archive, or something like that. It was a great read.

Thanks for any help on this. — Preceding unsigned comment added by 198.146.5.4 (talk) 16:01, 23 September 2011 (UTC)

I suggest you try to recall some unique phrase from the essay and google it as a strict search. There is nothing in your question which suggests wikipedia can provide an answer for you. μηδείς (talk) 21:28, 23 September 2011 (UTC)

Neurobiology

while study about the "Giant squeed axon" experiment, i learned that when the Axon was in Resting potential., it's ECF was at the electric measure of 0 mv. but the ICF was at -70 mv.

did i understand that correctly?., and another question please; does the Extra-cellular fluid always like that? (0 mv), even in living organisms?.., or it's unique to the experiment..?.

much thanks guys. 79.180.14.78 (talk) 16:44, 23 September 2011 (UTC)

That's the squid giant axon. It is correct that the membrane potential (the voltage difference between intracellular and extracellular points) was about -70 mV. And yes, that is a typical value for the resting potential of neurons in living organisms.

Membrane potential is often a difficult concept for beginners to understand. It might help to look at our membrane potential article. One of the most important facts is that a voltage is always a difference between two points. It does not mean anything to say that the extracellular voltage is 0 mV, unless you specify the reference point used for making measurements. It does mean something to say that the voltage difference between the intracellular and extracellular areas is 70 mV. Looie496 (talk) 17:18, 23 September 2011 (UTC)

is it right that the membrane potential is always 70mv less than the ecf's voltage?. 79.180.14.78 (talk) 17:36, 23 September 2011 (UTC)

No. You are not using the words correctly. This is a difficult concept, and I am afraid your English is not good enough to understand an explanation. If you think you can, please read Membrane potential#Voltage. Looie496 (talk) 18:02, 23 September 2011 (UTC)

I don't think he's wrong. If you define the ECF potential at 0, then the ICF potential is at -70 mV ... provided the axon is at a resting potential. Once depolarization occurs as part of an action potential things can change. See the graphs in action potential for how the ICF reading can vary over time. Wnt (talk) 02:46, 24 September 2011 (UTC)

(ec, and the other editor may have done a better job ;) You're speaking of the giant axon from a species of Loligo, most likely. Note it's a giant "squid axon", not a giant squid axon. ;) Squids, unlike vertebrates, don't use myelination, so if they want to send a nerve signal a long way really fast, they have to resort to making a really huge axon. (the bigger the axon, the faster the transmission speed) These huge axons happen to be convenient for teaching young experimenters in neurophysiology. Now when dealing with electrical potential, the zero point is really quite arbitrary - generally we define it as ground (electricity). As I understand it the potential of "ground" can change greatly as, say, a thunderstorm passes overhead, but all the other potentials change with it. (Why? Because as weak as the current from a neuron or a battery may seem, when that current flows one way without opposition, it adds up quickly to a huge potential difference) So the ECF electrode is set, somewhat arbitrarily, to 0 because it's the electrode which is physically sitting in a conductive saline solution in which the neuron is immersed, where any ground electrode you might have would sit. The ICF electrode will be the one poking through a cell membrane into an electrically insulated environment whose potential can change. Wnt (talk) 17:26, 23 September 2011 (UTC)

How giant is a giant squid giant axon which a giant squid acts on? But seriously, how big is it in a giant squid? SamuelRiv (talk) 19:05, 24 September 2011 (UTC)

As our article says, the squid giant axon reaches 1 mm in diameter -- about the thickness of a pencil lead. Very convenient for experimental work in the 1940s. Looie496 (talk) 19:50, 24 September 2011 (UTC)

Thought experiment regarding an closed and expanding universe.

Presuppose that the universe is a closed manifold universe, so if you travel in a straight line long enough, you'll end up back at your starting location. What if one were to build a solid rod, perfectly straight, so that it "looped" around the universe and connected with itself (never mind how you'd do it). What would happen as the universe expanded? Would the rod necessarily break apart (let's also assume it's made of ultra-strong unobtainium)? Would it heat up? Would the universe expand like a balloon being pinched by a ring? --Goodbye Galaxy (talk) 17:00, 23 September 2011 (UTC)

A strain would build up in the material, which could lead it to break. Compare to how minigrail works. Free test particles would move due to a passing gravitational wave, but a solid material will resist this, leading to strains building up in the material, which give rise to an accoustic signal. Count Iblis (talk) 17:11, 23 September 2011 (UTC)

If you actually had a rod solid enough to apply tension to the universe, it would act as some kind of cosmological constant and affect the size of the universe (at least in that direction?). See dark energy, etc. But the details get me confused every time. Wnt (talk) 17:28, 23 September 2011 (UTC)

Iblis is right, assuming there were some force requiring it to stretch along a great circle path in higher dimensions. In such a circumstance it would break once the increase caused sufficient strain on the atomic bonds holding the rod together. Or, more likely, it would simply "fall off" the universal great circle to one "side" and simply become a great loop. μηδείς (talk) 21:25, 23 September 2011 (UTC)

With a sphere, it could "fall off". If the universe were a torus (or any other non-simply connected space) then you could build the rod in such a way that it couldn't. I agree that, in that case, the rod would eventually break. Does anyone know what would happen if is were a cosmic string that was wrapped around the universe? Can they break? --Tango (talk) 16:14, 24 September 2011 (UTC)

Actual doing of experiments seeing if more oxygen causes larger insects

The fossil record shows that there were larger insects during the carboniferous period when oxygen levels were believed to be around 35%, which is higher than it is now. I'm not aware of a plausible sequence of events that would cause insects to grow larger in a richer oxygen environment, but it seems like an easy enough experiment to do, that is, creating a large terrarium of sorts, maintain an internal atmosphere with a high oxygen content, like 35%, and supply plants, water, sunlight, etc. and maintain many generations of a relatively short-lived species of insect like fruit flies for a couple of years and track the average mass of the flies at death to see if any measurable increase is occurring.

Pick apart the idea if you must, but I don't care so much about anyone's thought experiments determining whether they'd grow or not. I only want to know if it has been done/tried. 20.137.18.50 (talk) 18:45, 23 September 2011 (UTC)

I used Google Scholar to search for drosophila+enriched+oxygen and found thousands of research papers. There are many results indicating physiological changes and adaptations, including mass changes. Nimur (talk) 18:50, 23 September 2011 (UTC)

Those species had evolved over aeons in conditions of higher oxygen and their genotypes were adapted to the conditions. It wasn't the presence of oxygen which made what would have been smaller insects grow large, but the presence of oxygen which allowed species to evolve to larger sizes. Contemporary insects would not all of a sudden become giants if given higher levels of oxygen during development. Their genes don't code for such a response. But were there a sufficient number of generations raised in such high-oxygen conditions, and some sort of significant evolutionary pressure encouraging an increase in size, then you might see a trend toward increase in size over time among such experimental specimens. μηδείς (talk) 21:20, 23 September 2011 (UTC)

" and some sort of significant evolutionary pressure encouraging an increase in size " Maybe "breeders" only letting the largest of each generation survive to reproduction age? Those breeders would then unabashedly stop being scientists and start being just guys who want to see a bigger bug testing to see the effects, if any, of increasing oxygen level alone. Peter Michner (talk) 21:41, 23 September 2011 (UTC)

One can be both. Cuddlyable3 (talk) 22:21, 23 September 2011 (UTC)

I've been trying to re-create Arthropleura from millipedes for some time now, but so far no success :( . Count Iblis (talk) 23:06, 23 September 2011 (UTC)

I think this is less a matter of looking for oxygen to create a selective pressure toward large size than looking for lack of oxygen to create a pressure toward small size. In theory, if our biggest bugs are limited by the amount of oxygen in our air, putting them into an environment with somewhat lower oxygen should force a decrease in size relative to controls with a normal atmosphere. Wnt (talk) 03:33, 24 September 2011 (UTC)

Charge of a magnetic field to repel a positron?

Okay, so just checking, since I'm years out of basic Physics: if you want to repel an electron, you can repel it using a negatively-charged magnetic field. If you want to repel a positron - which is positively charged - you use a positively-charged magnetic field. Have I got that straight? --Brasswatchman (talk) 18:50, 23 September 2011 (UTC)

Not correct at all. Magnetic fields do not have charge. Magnetic fields do not repel electrons; they exert a force on the charged particle proportional and perpendicular to electron velocity. A stationary electron remains stationary in a static magnetic field. A positron experiences an opposite force compared to an electron in the same magnetic field, because it is oppositely charged. Nimur (talk) 18:52, 23 September 2011 (UTC)

All right. So how do magnetic mirrors work, then? Is this merely a result of a magnetic field being strong enough / arranged in such a way that it appears to reflect a high-velocity particle? --Brasswatchman (talk) 19:12, 23 September 2011 (UTC)

Read the article you linked... the positron will merely gyrate the opposite way in the magnetic field, but it will be repelled as well (because its charge is also of opposite sign, so the Lorentz force from the radial component of the converging field lines still acts in the same direction). Icek (talk) 19:47, 23 September 2011 (UTC)

Reading the article is one thing. Understanding it is another. So, basically - magnetic fields in general repel charged particles? Regardless of what charge they (the particles) have? --Brasswatchman (talk) 20:37, 23 September 2011 (UTC)

(ec) No, that's still incorrect. In general, magnetic fields exert a force only on charged particles that are moving. This works for any charged particle (positive or negatively charged; electron, proton, positron, muon, ... anything with electric charge). And, just to reiterate - the force is only present when the charged particle is moving relative to the magnetic field.

The details of the geometry of relative motion between a field and a particle are actually somewhat complicated, and require a little advanced mathematics to explain totally. Those mathematical descriptions are summarized as Maxwell's equations. Particles that move very fast still obey these equations, but you would need to use relativity to get the geometry correct.

But to answer your original question, in plain, simple terms: magnetic fields do not repel charged particles. Magnetic fields affect the motion of charged particles. Nimur (talk) 21:15, 23 September 2011 (UTC)

(edit conflict) No. magnetic fields generally cause moving charged particles to curve. try this needs java

Or try these videos [20] Imgaril (talk) 21:14, 23 September 2011 (UTC)

Okay. So it sounds to me like the whole "magnetic bottle" metaphor mentioned in the article I linked to above is a lot more accurate than "magnetic mirror." Since what it sounds like you're really doing is using a set of magnetic fields to keep high-energy/high-velocity particles curving around and around within the "bottle," thus containing them. Do I have that right, or at least right enough? --Brasswatchman (talk) 22:38, 23 September 2011 (UTC)

okay, think I get that. Did some more reading, and felt like I started to remember something -- so magnetic fields don't have charge. Do *electromagnetic* fields? --Brasswatchman (talk) 21:59, 23 September 2011 (UTC)

Check the article on Electric field which may be what you are thinking of. Cuddlyable3 (talk) 22:18, 23 September 2011 (UTC)

No. Neither electric nor magnetic fields have charge. An electric charge may be thought of as the end point of a field line. In other words, a point-like electric charge (like an electron) creates a field directed towards the charge or away from the charge (depending on the sign of the charge), with the strength of the field being proportional to the inverse of the square of the distance from the charge.

Magnetic field lines on the other hand are always closed loops, thus there are no magnetic charges and no endpoints of magnetic field lines (as a sidenote, there also are electric field lines which are closed loops, in addition to those ending at charges). Icek (talk) 22:21, 23 September 2011 (UTC)

Hmm. Okay. So would the electric field generated by a sufficiently large mass of protons repel a positron? --Brasswatchman (talk) 22:41, 23 September 2011 (UTC)

Yes — and even one proton is sufficiently large. --Tardis (talk) 01:15, 24 September 2011 (UTC)

just wanted to thank everybody who put up with my very basic questions tonight. You've been a big help. --Brasswatchman (talk) 02:13, 24 September 2011 (UTC)

eka-radon at 0 °R

in theory; properties at 0 °R and can eka-radon Perpetual Motion spontaneous fission A half-life fussion of one to another eka-radon — Preceding unsigned comment added by 207.6.211.175 (talk) 23:13, 23 September 2011 (UTC)

You might want to look at our article on Ununoctium. SpinningSpark 00:43, 24 September 2011 (UTC)

Nothing in the theory of fusion or fission allows for perpetual motion (unless you have a perpetual supply of nuclear fuel, that is). Wnt (talk) 03:16, 24 September 2011 (UTC)

I think the question is whether, at absolute zero, could you have an element that would fission and then re-fuse again, and then fission and re-fuse again, and so on. The problem is that you're losing energy with every fission and fusion. So it can't possibly go on indefinitely, especially since both fission and fusion require a little energy in the first place. I suspect that after the first fission you'll just have two fragments that won't fuse without introducing (a lot) more energy into the system. --Mr.98 (talk) 14:44, 24 September 2011 (UTC)