Wikipedia:Reference desk/Archives/Science/2011 August 30

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August 30

Negative matter

I remember Michio Kaku's book, Physics of the Impossible stated something along the lines of the statement that one could use matter with negative mass to hold the wormhole in the singularity of a black hole open for long enough to stabilise it for something to enter it. But since negative mass is supposed to be repelled by gravity, and nothing can escape a black hole, shouldn't the negative matter be unable to enter the black hole, as the hole's gravity will push the matter away infinitely? --Σ _{^talkcontribs} 00:04, 30 August 2011 (UTC)

Negative mass is such a fanciful concept that we can't answer questions about it. However, I'm going to say yes anyway. 99.36.74.131 (talk) 00:52, 30 August 2011 (UTC)

According to the equivalence principle, even negative mass would be gravitationally attracted to a black hole, but other than that you're basically right. There are mathematical theorems in general relativity that say that without exotic matter you can't make a traversable wormhole. That doesn't imply that with exotic matter you can make a traversable wormhole. There are a few other hurdles to be surmounted first, such as making sure the stuff goes where it needs to go and stays there. Realistically, none of this is possible. -- BenRG (talk) 01:26, 30 August 2011 (UTC)

Actually the negative mass is repelled from the black hole ... it's just that the repulsive force causes it to fall in. F=ma and all that. ;) Wnt (talk) 02:14, 30 August 2011 (UTC)

Indeed. The reason everything falls at the same rate, regardless of its mass (Galileo dropping cannonballs off the Leaning Tower of Pisa, and all that), is because the m's in F=GMm/r² and F=ma cancel. They still cancel if they are negative. --Tango (talk) 11:46, 30 August 2011 (UTC)

While we're on the subject, what is theorised to happen if you push such a thing? Surely it can't move right through your hand – or maybe it does? Grandiose (me,talk, contribs) 12:19, 30 August 2011 (UTC)

Surely when you push something the forces involved are electrical, not gravitational? Stanstaple (talk) 18:05, 30 August 2011 (UTC)

Exactly, so the force away from you would result in an acceleration towards you. The force on you (equal) would accelerate you back, but if you're more massive, then less, so... Grandiose (me, talk, contribs) 18:12, 30 August 2011 (UTC)

@BenRG What do you mean by impossible? All you have to do is get something that doesn't exist and stabilize in a intrinsically unstable configuration in a completely inaccessible position. Dauto (talk) 13:02, 30 August 2011 (UTC)

Why isn't there an X-Ray Structure of Bovine Serum Albumin?

Or any other structure of BSA for that matter? There isn't so much as a homology model out there. Seems odd, since it's so cheap you'd think someone would have given it a shot. It can't be because it's not interesting enough, or there wouldn't be so many structures of lysozyme (arguably one of the least interesting [and easiest to crystallize] things to ever have a structure solved). It can't be that hard to crystallize since there's a ton of deposited structures of Human Serum Albumin (HSA), and you'd think they'd be homologous. Anyone have a definitive answer? Or even some well sourced idle speculation? Thanks --Chemistry-grad-student (talk) 02:32, 30 August 2011 (UTC)

It has been done a number of times for human serum albumin but apparently isn't all that easy -- the only account I can find for bovine serum albumin is this thesis report from 2004. There are lots of other descriptions of the structure relying on simpler methods than crystallization. Looie496 (talk) 02:47, 30 August 2011 (UTC)

The 2004 paper describes considerable effort to get good crystals - the problem is likely, as the author says, the crystals don't diffract very well "probably due to three-dimensional flexibility in some flexible regions (such as N-terminus or C-terminus regions) of BSA that causes crystal lattices in these regions disordered." Bear in mind that albumin, as the major serum protein in a mammal, has a very special role, transporting hormones and drugs; it needs a certain special character about it, which apparently involves a certain amount of cussedness. While it's possible that the people who crystallized human albumin just did a really good job, it's also quite possible that the bovine form is just more flexible. Wnt (talk) 04:08, 30 August 2011 (UTC)

Thanks for the responses. I suppose there's no rule that homologs have to crystalize under the same or similar conditions or even have comparable dynamics. Was wondering if there was another obvious explanation (other than 'hard to crystalize'), I suppose not. Thanks again. (chemistry grad student) I(q) = User(q)·Talk(q) 00:56, 31 August 2011 (UTC)

Dizziness caused by a somersault

I was demonstrating an underwater somersault (forward roll), during which I suddenly felt an awfully strong dizziness and vertigo. That left me with a nauseous feeling for the rest of the day. As a child, I could do as many rolls as I pleased, one after the other. I never had any head injuries in the past. What could that be? Gil_mo (talk) 05:35, 30 August 2011 (UTC)

You should see your doctor for medical advice because there are many possible causes, but you might also wish to read our article on Balance disorder. Dbfirs 07:00, 30 August 2011 (UTC)

I don't consider dizziness during a somersault to be abnormal. On the contrary, those who can do gymnastics without becoming dizzy are abnormal, but in a good way. StuRat (talk) 07:15, 30 August 2011 (UTC)

Dizziness during a somersault doesn't sound abnormal at all. Nausea for the rest of the day, though, does. It's worth talking to a doctor. --Tango (talk) 11:49, 30 August 2011 (UTC)

Discuss Hypotension with your doctor. Cuddlyable3 (talk) 09:04, 30 August 2011 (UTC)

In a similar situation, I noticed that amusement park rides I used to enjoy in my youth now make me nauseous. Maybe it has something to do with age? Although somersaults under water have always given me a brief sense of vertigo, I don't notice any lasting effects even when I do them now. ~Amatulić (talk) 16:13, 30 August 2011 (UTC)

A quick google on "inner ear ageing" throws up many references around the increase of dizziness because of age-related changes to the balance mechanism. --TammyMoet (talk) 18:15, 30 August 2011 (UTC)

What injuries can be instantly healed?

The title's not exactly what I mean to say, but I couldn't think how to phrase it.

I write stories, and I like to injure my characters. However, I prefer injuries that can be instantly healed. For example, dislocated shoulders can be popped back into place and the character is right as rain (I know, not in real life, but its believable enough that Willing-suspension of disbelief discards it.)

Basically, I want injuries where the problem can solve itself using little to no 'medicine' or recovery time. So, not things like gunshot wounds or broken bones.

Can anyone think of anything? Remember that since it's fiction, you've got a bit of leeway regarding how incapacitating it would 'actually' be. ~~Ye Olde Luke — Preceding unsigned comment added by 70.179.55.4 (talk) 07:00, 30 August 2011 (UTC)

Well, simple bruises administered by blunt instruments will basically heal themselves over time (the no-medicine requirement), but it will not be instant - hours to days depending on severity and impact force. --Ouro (blah blah) 07:06, 30 August 2011 (UTC)

For a nice gross one, how about an eyeball popped out of it's socket, then popped back in ? Or maybe a tooth knocked out, then pushed back into place. StuRat (talk) 07:11, 30 August 2011 (UTC)

For truly sadistic inspiration see John and Lorena Bobbitt. Cuddlyable3 (talk) 09:01, 30 August 2011 (UTC)

Sorry, but that doesn't qualify as "instantly healed". 67.169.177.176 (talk) 05:36, 31 August 2011 (UTC)

A splinter, thorn, or other irritant that doesn't penetrate deeply could be most of the way fixed simply by removing whatever is causing the problem. Dragons flight (talk) 11:40, 30 August 2011 (UTC)

A fairly small cut that you can just apply pressure to for a few minutes and then put a plaster/band-aid or a dressing on and then leave alone could count. The injury is still there, but you can ignore it once it is dressed. If it's bad enough to need stitches then, if you don't get the medical treatment, you'll probably end up with a really nasty scar, but that might not be a problem depending on your story. There are also issues with infection, but you can just assume they get lucky and the wound isn't infected. --Tango (talk) 11:53, 30 August 2011 (UTC)

Getting the wind knocked out of you --Digrpat (talk) 13:18, 30 August 2011 (UTC)

About 90% of the injuries sustained on a soccer field, apparently. --TammyMoet (talk) 13:51, 30 August 2011 (UTC)

A minor electric shock. Googlemeister (talk) 13:57, 30 August 2011 (UTC)

A spinal misalignment that slips back into place, no longer impinging on the nerve ? StuRat (talk) 19:12, 30 August 2011 (UTC)

Not medical advice, and don't try this at home: Getting the wind knocked out of you as was mentioned above seems to fill the bill. A kick in the nuts is debilitating, and people seem to get over it, but it could certainly cause permanent damage to the reproductive system. "Nursemaid's elbow" occurs when someone lifts a small child by his arm, causing some kind of painful dislocation in the child's elbow. A pediatrician said it is pretty easy for a layperson to fix if the pe4rson is shown how by the doctor. (Once it happens, it is likely to recur). I've seen a football coach fix a dislocated finger. A martial arts teacher once said that men have had their testicles driven up into the abdomen by a kick and that they could sometimes be restored to their normal place without medical intervention. From personal experience, a "basket handle tear" in the knee can result in painful locking of the knee in a bent position when one puts pressure on the knee in certain ways, like standing up with the "trick knee" bent back under the front of the chair. Sometimes it can be "unstuck" in a short while. A "punch in the breadbasket" can somehow injure the diaphragm so it is hard to breathe, and this has typically corrected itself quickly. Any "charleyhorse," cramp or muscle spasm could be crippling for a short while: is there a way to induce one? Aren't there some martial arts pinches which cause paralysis of a limb for a bit? And don't forget the dread {Icecream headache]], an intense pain in the roof of the mouth which feels like a brain freeze, also typically self correcting in a short while. (Make the victim eat ice cream?) Eating a very hot pepper can cause intense pain, sweating, eyes watering for several minutes, as can pepper spray or tear gas. A Taser knocks a person down, and typically they get over it, though some die. Edison (talk) 20:38, 30 August 2011 (UTC)

Dr. Hibbert: "Worst case of brain freeze I've ever seen, get me 50 cc's of hot fudge, stat !" StuRat (talk) 21:51, 30 August 2011 (UTC)

Cracking your knuckles. ~AH1 ^(discuss!) 20:23, 31 August 2011 (UTC)

That's not really an injury. 67.169.177.176 (talk) 05:29, 1 September 2011 (UTC)

A whip or rope lashed around the neck,( perhaps while dangling from a balcony) which with great dexterity can be removed shortly prior to asphixiation etc. etc.190.56.115.105 (talk) 22:48, 31 August 2011 (UTC)

Seperatism...One foot tied to a ship, the other to the dock as the ship sails away. More dexterity, or perhaps weak roap.190.56.115.105 (talk) 22:56, 31 August 2011 (UTC)

I forgot ask. Can these misfortunes be purposely inflicted,, or must they be accidents?190.56.115.105 (talk) 23:00, 31 August 2011 (UTC)

Air embolism from diving or other causes, handled in a pressurized chamber. Wnt (talk) 23:18, 1 September 2011 (UTC)

Sound transmission and atmospheric pressure

So, there's no sound transmitted in a vacuum, or presumably in the near vacuum of space, while it transmits fine at both standard atmospheric pressures, and, AFAIK, at the reduced pressure atop Mount Everest. So:

1) At what pressure does it fail to transmit ?

2) Is it a sharp point or a gradual transition ?

3) Does the volume just decrease or is there a shift in frequency, too ? StuRat (talk) 08:16, 30 August 2011 (UTC)

1) Zero

2) Gradual

3) Volume decreases. Frequency is unchanged. Cuddlyable3 (talk) 08:58, 30 August 2011 (UTC)

In general, efficient sound transmission requires a wavelength that is much larger than the mean free path of the gas it is travelling through. Dragons flight (talk) 11:36, 30 August 2011 (UTC)

Are there any estimates on the mean free path of the smattering of molecules (1) on the moon and/or (2) in space? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:15, 30 August 2011 (UTC)

The article has a table of values at several orders of magnitude and the formula to calculate it at any arbitrary one you like. DMacks (talk) 14:42, 30 August 2011 (UTC)

Exactly why couldn't Jurassic Park happen?

This may sound like a crazy question, but precisely what park of the dinosaur cloning process from Jurassic Park is impossible? As far as I know, there really were dinosaurs. There really were mosquitoes. Some of those really were preserved in amber. That blood really could contain "Dino DNA". That DNA surely could really be cloned and implanted into an egg?

So basically, which of those is not true? Many thanks, Prokhorovka (talk) 10:55, 30 August 2011 (UTC)

To my surprise, this isn't discussed in the article Biological issues in Jurassic Park, which merely talks about inaccuracies in the representations of the dinosaurs. Well, one problem with resurrecting extinct species from DNA is the need for a suitable womb: it seems like it would be simpler for egg-laying species, but still doubtless very difficult to find a suitable surrogate. I suppose issues might include the yolk, the egg size, the temperature, and I don't know what else - perhaps something more fundamental than any of that. I also suspect the mosquitoes preserved in amber would not contain blood with DNA in it, since during formation amber is pressure cooked. Dinosaur#Soft_tissue_and_DNA says that we're not doing very well at finding any. Oh, and I found the section Jurassic_Park_(novel)#Biological_issues_and_accuracy, which is where the feasibility of getting the DNA is discussed.  Card Zero  (talk) 11:12, 30 August 2011 (UTC)

DNA at room temperature will break down spontaneously, even if you seal it away air tight. People can work with degraded DNA, but generally put a limit at 20-100 thousand years for getting any useful DNA under good conditions. Under absolutely ideal condition in very cold ice, you could perhaps reach one million years, but that's pretty much it. When you are talking about dinosaur age fossils, we simply don't expect there to be any DNA remaining. Maybe someone will come along and prove that wrong, but right now we don't know of any way to get dino DNA. Dragons flight (talk) 11:28, 30 August 2011 (UTC)

One of the big issues with the cloning as displayed in the film is the role that epigenetics plays. In nearly every example of cloning of multicellular organisms I can think of, the genetic material is hosted in a cell from the same, or very closely related, species; that is we take a cell and swap out the DNA for the DNA from a very closely related individual. For dinosaurs, the closest relatives (birds) are probably too distantly related for this to work effectively. --Jayron32 12:32, 30 August 2011 (UTC)

In principle, one might solve the host problem by bootstrapping. Use a currently-living animal (bird) as a host for a two-million-year-old extinct species' DNA; use that animal as a host for four-million-year-old exctinct species; and so forth. (This presumes a method to acquire, sequence, and synthesize suitable ancient DNA.) TenOfAllTrades(talk) 13:35, 30 August 2011 (UTC)

DNA is a very large molecule, and like most macromolecules, very unstable. It will eventually degrade even if only from background radiation. Estimates of eventual destruction of DNA like Dragon's Flight mentioned, is max 1 mya (thus definitely no dinosaurs, the last of which died out ~65 mya). Thus, claims of recovery of older DNA is sometimes viewed with suspicion, as they may be, in actuality, contamination of the samples with modern DNA or ancient microbial DNA. But who knows, there may be a way they actually survive that long through some unknown process. Endospores for example, are highly resistant, and may be enough protection. See example of 40-million year old DNA from an apparently still living bacterial spores recovered from a bee trapped in amber. Or claimed recoveries of 121 to 250 million (!) year old revived (!!!) spores of the archaean Halobacterium salinarum.

Anyway, in order to 'build' an organism you need the full DNA, and DNA even from specimens only a few thousand years old are usually only found in fragments or are not found at all. What DNA fragments that are recovered are like very complex blueprints with almost all of the pages missing, torn pages with no page numbers, ink stains, and written in a language we do not understand. Jurassic Park (at least the novel) had that premise. That only fragments were recovered, but were then somehow reconstructed by using DNA from extant animals to fill in the blanks. But gaps like that aren't really that easily filled, it must be sequenced, and there's the possibility that you could mix up DNA from two or more organisms from the samples if you're only getting fragments, and even just a minor mistake can mean one dead lizard with an arm growing out of its nose. And then yeah, there's the problem of actually implanting it in a viable egg and finding a surrogate mother.

We're probably centuries behind any technology like that, and even then, it's probably only feasible for recent extinctions in which we can recover intact DNA from. But I hope it's eventually possible. There are some research projects dedicated to this goal, particularly of the thylacine and mammoths. See Cloning#Cloning extinct and endangered species.

But we do retain ancient traces of our ancestors in our DNA. Unexpressed but still there, a sort of biological arsenal that manifests as vestigial traits (like gill slits in human embryos) or once in a while as (usually nonviable) mutations, specifically regressions(tails in human babies, scaly skin, etc.), but still important somewhat for adaptation and evolution. So... maybe we could go the other way around and reverse engineer birds? :P Though like Jayron said, birds are way too far down the ladder already.

But yeah, for dinosaurs... probably not ever. See Are Movies Science? Dinosaurs, Movies, and Reality from the University of California Museum of Paleontology -- Obsidi♠n Soul 13:33, 30 August 2011 (UTC)

So to summarise, it breaks down at the DNA stage since the amber would not in fact contain any or at best sufficient "Dino DNA". Even if this weren't true, going from cloned DNA to Dinosaur is fraught with difficulties. Thanks everyone, very interesting and comprehensive. Prokhorovka (talk) 19:14, 30 August 2011 (UTC)

In summary, too much frog DNA and your T-Rex croaks. ~AH1 ^(discuss!) 20:16, 31 August 2011 (UTC)

Errrrr

Sometimes when a person has to think for a period of time to produce an answer or continue a sentence, they make a noise like "errr", "errrm", "ummmm". Is this an innate or learned phenomenon? Does it vary between countries/cultures? Is there an article? --129.215.47.59 (talk) 15:04, 30 August 2011 (UTC)

Umm... Speech disfluency? Jebus989^✰ 15:11, 30 August 2011 (UTC)

And specifically see also Filler (linguistics), which discusses different fillers in different languages. They are considered by linguists to be meaningful parts of language — they mean, "I am still talking." I suspect (just guessing) that the use of them is innate, but the specific expression is certainly learned. --Mr.98 (talk) 15:28, 30 August 2011 (UTC)

Usage varies a lot between languages. I don't mean just the specific sounds. In Italian, if you quit making sound, other people will assume you've finished and start talking, even if you obviously haven't finished your thought or even sentence. So if you're not sure what to say next, you have to draw out the final vowel of the word you're on. Luckily, most Italian words do end in vowels. --Trovatore (talk) 18:04, 30 August 2011 (UTC)

If William ... SHATner were Italian, he'd never finish a ... SENTence. --Trovatore (talk) 19:00, 30 August 2011 (UTC)

See mental block and writer's block. Also this. ~AH1 ^(discuss!) 20:10, 31 August 2011 (UTC)

ET phone home ......... from L2?

• Lagrangian point

Currently several spacecrafts have been or are around the L2.

How do they phone home if the beautiful moon gets in the way?

Could they use long wave radio? Or do they need one or more communication satellites around the moon to relay the signal? -- Toytoy (talk) 15:13, 30 August 2011 (UTC)

Halo orbit--Aspro (talk) 15:29, 30 August 2011 (UTC)

Oops! My fault!

The moon could not block the spacecraft's view of earth if it is not exactly between the earth and the spacecraft. EVEN IF THE SPACECRAFT IS EXACTLY ON THE L2.

Even if the moon blocks the view, it is not large enough to fully block the whole earth. The earth and the spacecraft can still have visual contact.

The moon can only block the view of the earth if the spacecraft is within about 22000 km from the moon.

Earth ----- 60000 km -------> Moon --- 22000 km ---> Spacecraft -- Toytoy (talk) 15:32, 30 August 2011 (UTC)

(ec) The Moon's orbit is inclined to the plane of the Earth-Sun system (the ecliptic), which means that most of the time the Moon actually doesn't come between the Earth and L2 anyway—it passes above or below. Also, the satellites 'at' L2 (like WMAP) are actually usually in orbits around the L2 point, not stationary on it; the moon eclipsing such a satellite will be a rare occurrence, and could (in principle) be avoided entirely by careful tuning of the satellite's stationkeeping. Even if such temporary eclipses were unavoidable, most scientific satellites are capable of storing data on board for later transmission.

All that said, I've just looked at our articles on Lagrangian point and Moon, and noted that L2 is about 1.5 million km from Earth, while the Moon is just about 400,000 km from Earth; that puts the Moon 1.1 million km from L2, at its closest. The Moon's diameter is about 3000 km, so it actually doesn't cast a 'shadow' on Earth that's wide enough to completely obscure the L2 point; the Moon will only obscure a disc about 4000 km across as seen from L2. Since the Earth's diameter is about 12,000 km, there will always be spots on Earth that have a direct line of sight to L2, even when the Moon is in the worst possible place. TenOfAllTrades(talk) 15:42, 30 August 2011 (UTC)

Uh... The Op seems to believe that those spacecrafts are in the Earth-Moon L2 Lagrangian point. They are actually in the Sun-Earth L2 Lagrangian point. Dauto (talk) 16:10, 30 August 2011 (UTC)

In fact if you look at List of objects at Lagrangian points, only ARTEMIS is listed to ever have been in the Earth-Moon L2 point. Dauto (talk) 16:13, 30 August 2011 (UTC)

Evolution in animal thinking

From my understanding, humans had evolved from apes and primates. If this is the case, I have to questions.

1. If evolution from apes to proto-humans happened, why didn't all of the apes evolves into humans?
2. The process of this evolution also lead to evolution of our brains and how we think. If this is true, why don't other animals brains evolve to produce abstract thought?

Thanks! 64.229.155.210 (talk) 15:40, 30 August 2011 (UTC)

Q1 is the simplest: we didn't evolve from apes (at least not modern-day apes); we share a common ancestor. This ancestor more closely resembled a modern day "ape" than a modern human but the idea that half of all Gorillas suddenly became human, and the others were left scratching their heads and eating a banana is a common misconception. You can probably find more info at objections to evolution. For the details of why lineages diverge, see speciation. Jebus989^✰ 15:50, 30 August 2011 (UTC)

When told that the Spanish language evolved from Latin would you ask why in other regions Latin didn't evolve into Spanish? For instance, in the Italian peninsula Latin evolved into Italian which different from Spanish. Clearly the same way that one language can evolve into many languages over time, it is also to be expected that not all Apes should evolve into humans. Dauto (talk) 16:02, 30 August 2011 (UTC)

Well, while that may be the case, the only reason I asked is because wouldn't it be beneficial for all of our common ancestors to evolve into humans? While it wouldn't have been at first as humans haven't developed abstract thought thousands of years later, wouldn't evolution have it that the animals catch up to us? 64.229.155.210 (talk) 16:13, 30 August 2011 (UTC)

No, that's not how evolution works. Evolution is historic, just like the evolution of Spanish is historic, and cannot be replicated. Human evolution is one of a kind and will never happen again. Dauto (talk) 16:20, 30 August 2011 (UTC)

You have the misconception that evolution is a process of constant improvement. It isn't. Rather, it's a process of adaptation. If there is no environmental pressure for a population to evolve adaptations to give a survival advantage in that environment, then there is no need for the population to evolve. The thought development displayed by gorillas and dolphins, for example, is quite suited to their respective natural environments. ~Amatulić (talk) 16:33, 30 August 2011 (UTC)

Here's another way to think about this: if human beings kill off all species of primates other than themselves within the next 100 years or so (a not completely unrealistic possibility), will primates have all evolved into human beings? This highlights that when you say "evolved into" what you're really saying is "was outcompeted by." Homo sapiens sapiens (and its predecessor species) did out-compete most other large primates, as far as we know. Those that exist today are in niches that somehow were self-sufficient despite the fact that human beings took over in a major way. (And yet some species are highly endangered as a result of this competition, at the moment.) --Mr.98 (talk) 17:21, 30 August 2011 (UTC)

Since most other primates occupy arboreal niches (they live in trees), and we don't, we tend not to compete with each other. We more directly compete with large animals which live on the plains, and we've killed off many of those, such as the saber-toothed tiger and mammoth. StuRat (talk) 19:07, 30 August 2011 (UTC)

FWIW, we may have actually out-competed another sapient species. For a certain time period, modern Humans (Homo sapiens) and Neanderthals (Homo neanderthalensis) coexisted in Europe. Neanderthals went extinct, possibly out-competed or even directly decimated by interspecies warfare with Humans emerging from Africa. Though genetic studies have confirmed that a small percentage of Europeans and Asians still have traces of Neanderthal genes, also suggesting absorption to a certain degree as another possibility.-- Obsidi♠n Soul 19:25, 30 August 2011 (UTC)

The basic answer to the original question, I think, is that brain tissue requires a tremendous amount of energy to operate. Homo sapiens evolved in a region of the east African savannah where large amounts of rich food were available to animals with the lifestyle of our ancestors. For other species, the costs of very large brains, in terms of energy needs and the anatomical problems produced by large head size, appear to have exceeded the benefit. This is a speculative answer, of course, but I believe it follows the current mainstream line of thought. Looie496 (talk) 21:23, 30 August 2011 (UTC)

Few creationists find it objectionable that we're no longer bacteria. Imagine Reason (talk) 00:14, 31 August 2011 (UTC)

Standard model vs GR

Is the treatment of mass in the standard model of particle physics consistent with general relativity? If not, does it mean that only one model is right? --41.135.50.237 (talk) 17:58, 30 August 2011 (UTC)

It is not inconsistent. Dauto (talk) 18:26, 30 August 2011 (UTC)

The Dirac Equation expresses the wave function for a general relativistic particle. You should be pretty familiar with quantum mechanics before you try to understand the Dirac equation; it's somewhat complex. The relativistic compensations are expressed as the matrices α and β in our article's presentation; otherwise, as you undoubtedly instantly recognized, it's nothing more than the standard Schrodinger equation. Our article proceeds to translate the Dirac equation into a more generalized coordinate scheme; but this is not really useful for any practical purpose. I highly recommend the Shankar and the Griffiths' textbooks; they are more comprehensible than Dirac's original work. Nimur (talk) 22:00, 30 August 2011 (UTC)

Just making sure the information above is clear, the Dirac equation is used to describe relativistic particles that have spin 1/2. Particles with spins other than 1/2 are described by different equations. Dauto (talk) 17:21, 31 August 2011 (UTC)

Mammals physically capable of sticking their head up their bottom?

Do any mammals exist who are capable of sticking their head up their bottom, putting things as civily as is possible? My friend wants to know. Obviously it doesn't have to go all the way. My personal guess is that a duck billed platypus could at least touch their bottom with their beak, but I don't have one at hand to check (and I suspect even if I did it wouldn't cooperate, no matter how persuasive I was) Egg Centric 18:13, 30 August 2011 (UTC)

With or without assistance? 76.254.20.205 (talk) 18:28, 30 August 2011 (UTC)

You mean poppers? The animal would need to have a very small cranial-rectal ratio, so either a tiny head or a very broad rectum. It would need to have a great degree of control over the muscles in that region, or else it might suffocate or strangle itself, leaving a toroidal corpse. It would not necessarily require a long neck. Rabbits are capable of eating pellets directly from their own anuses, so that level of flexibility is not unheard of in mammals, even stocky, short-necked ones. Mammals' large skull size would make the feat difficult. (It is comparatively easy to imagine a ratite or reptile stuffing its smaller head into its relatively large cloaca.) The only insurmountable problem is ventilation. With the head completely enclosed, there would be no way for the animal to breathe. Of course, if you're assuming human assistance, and if you don't demand that the animal survive the procedure, then there's no problem at all. Any small mammal could, under heavy sedation, be forced into this configuration. I wouldn't be surprised if some taxidermist hadn't created such a specimen at some point, as a tacky novelty. LANTZY^TALK 19:25, 30 August 2011 (UTC)

I would expect heads to be much bigger than rectums, in all mammals. Perhaps an animal with a long, narrow snout, like an anteater, could jam that up there, if the motivation struck. StuRat (talk) 19:01, 30 August 2011 (UTC)

Ok so ignore the insertion issue...

Ignoring the head/rectum problem, what mammals can get their head down to their anus comfortably? Egg Centric 21:52, 30 August 2011 (UTC)

Let's see. Cats and dogs certainly can, and routinely do. And rabbits, as I mentioned. Probably most rodents can. It might be easier to come up with a list of mammals that almost certainly can't accomplish the feat: elephants, manatees, ungulates, hominids... LANTZY^TALK 22:42, 30 August 2011 (UTC)

I'm actually curious what the "head/rectum problem" is? lol... Vespine (talk) 23:54, 30 August 2011 (UTC)

Ok, I wrote that before reading the comments immediately above! Forget I asked, and in fact I wish I hadn't! lol Vespine (talk) 23:56, 30 August 2011 (UTC)

Could be that the OP was told he/she had his/her head up his/her ass. 67.169.177.176 (talk) 05:44, 31 August 2011 (UTC)

Helium ionization detector

Dear all, kindly note that,the article Helium ionization detector, the content is not correct. Most of the HIDs not using any radio active substances. This is with reference to VICI detectors. Please note that this is a nondestructive detector. Please update the article if i am correct... — Preceding unsigned comment added by 89.211.137.39 (talk) 18:22, 30 August 2011 (UTC)

Can you provide any reliable sources to prove that ? Also note that the article's talk page is the best place for such comments. StuRat (talk) 18:57, 30 August 2011 (UTC)

Chocolate bars

Moved from WP:HD#Chocolate bars. —Akrabbim^talk 18:59, 30 August 2011 (UTC)

On BBC News there is a title on EATING CHOCOLATE saying that for the hearth is good to eat one CHOCOLATE BAR a day but on WIKIPEDIA I could not find anywhere how much is the weight of one bar of chocolate, so please help me to understand, many thanks.- — Preceding unsigned comment added by 79.42.125.144 (talk) 16:51, 30 August 2011 (UTC)

Have you tried Wikipedia's Reference Desk? They specialize in knowledge questions and will try to answer just about any question in the universe (except how to use Wikipedia, since that is what this Help Desk is for). Just follow the link, select the relevant section, and ask away. I hope this helps. – ukexpat (talk) 17:00, 30 August 2011 (UTC)

(edit conflict)Wikipedia does not give medical advice, but if you look again at the BBC news item you will see that it gives a link to the BMJ report so you can read it for yourself. - David Biddulph (talk) 17:03, 30 August 2011 (UTC)

I have read many of the peer-reviewed journal articles on the topic. They are referring to the nasty bitter dark cocoa powder, not the candy you buy at the store. However, people WANT to hear that eating candy is healthy, so the news purposely implies that you should run out and stuff your head full of chocolate bars. Naturally, Wikipedia shouldn't repeat such misinformation. -- kainaw™ 17:16, 30 August 2011 (UTC)

Please continue this on the Reference Desk where it belongs. ---— Gadget850 (Ed) ^talk 18:08, 30 August 2011 (UTC)

Some people (like me) like the nasty bitter powdery stuff better than the candy. Dauto (talk) 19:12, 30 August 2011 (UTC)

I haven't read any of those, but I read the BBC article, which says they "compared the risk to the brain and heart in groups of people who reported eating low levels of chocolate, fewer than two bars per week, with those eating high levels - more than two bars per week." The word reported there (and the word bar) implies to me that in this study they are in fact talking about the delicious kind of chocolate, which people eat by choice, rather than recruiting test subjects and feeding them spoonfuls of cocoa powder. They go on from this to give what struck me as some very odd advice: although they apparently found eating chocolate to be (statistically) good for the heart, they didn't advise anybody to start eating it. I have to wonder whether they would have advised the same caution if they had made the same discovery about something foul-tasting and fat-free. It seems most unscientific. Presumably this is because those genetically predisposed to it would be more likely to get Type 2 diabetes if they started eating more sugary snacks: but why advise "those who do eat chocolate" to eat "small amounts on a regular basis"? Why not "large amounts on a regular basis", since that's where the study showed the benefit is?  Card Zero  (talk) 19:39, 30 August 2011 (UTC)

A chocolate bar can be healthy, in moderation, provided:

1) It doesn't contain any added trans-fats, like partially hydrogenated vegetable oils.

2) It contains a high cocao content, on the order of 75-85%. (Note that this means it won't be very sweet, since it can't be more than 15%-25% sugar, and cocao is bitter.)

If the bar isn't labelled for these items, don't eat it. StuRat (talk) 19:17, 30 August 2011 (UTC)

Thanks Dr. StuRat! We all appreciate your medical advice. --Mr.98 (talk) 20:07, 30 August 2011 (UTC)

You're welcome, but, of course, dietary recommendations are not medical advice. StuRat (talk) 20:08, 30 August 2011 (UTC)

Statements about what is healthy and strong statements about what one should or shouldn't eat are not medical advice? Seems to be riding an awfully fine line there, especially for someone who has not cited anything to back up their assertions. --Mr.98 (talk) 20:47, 30 August 2011 (UTC)

As you know, medical advice is that which seeks to diagnose and treat a specific medical condition. And whether one cite's sources is quite irrelevant to whether something is medical advice. If I don't cite sources on how to build a bicycle, does that make it medical advice ? StuRat (talk) 21:07, 30 August 2011 (UTC)

Surely you can't be telling me that obesity is not a medical condition (a medical condition whose primary treatment IS dietary). Googlemeister (talk) 12:53, 31 August 2011 (UTC)

First, there was no mention of obesity in this question. Secondly, I wouldn't consider obesity a medical condition as long as it still can be handled by diet alone, until it becomes morbid obesity of a degree requiring medical intervention, like gastric bypass surgery. And don't call me Shirley. :-) StuRat (talk) 02:57, 1 September 2011 (UTC)

Well if you don't cite sources, your instructions could result in anything, for all we know. Perhaps some abomination of a medical chocolate bicycle.  Card Zero  (talk) 21:32, 30 August 2011 (UTC)

It's a meta-analysis of seven studies:

Levels of chocolate consumption included the consumption of chocolate bars, chocolate drinks, and chocolate snacks (including confectionery, biscuits, desserts, nutritional supplements, and candy bars). All the studies reported chocolate consumption in a different manner: three categories (never, once a month to less than once a week, and once a week or more); two categories (less than once a week, once a week or more); four categories (never, less than once a month to less than once a week, once a week, and more than once a week); thirds of cacao intake; five categories (none, 1–3/month, 1–2/week, 3–6/week, and >1/day); fourths of chocolate consumption (ranging from 1.7 g/day to 7.5 g/day); and four categories (none, 1–3/month, 1–4/week, and >5/week). Considering the heterogeneity in reporting and measuring chocolate consumption, we decided to use the lowest and highest categories to measure the association of chocolate consumption with cardiometabolic disorders.

I'm not sure which of those "manners of reporting" the BBC picked up on when it said "more than two bars per week". I suspect they in fact were referring to one of the "how often do you eat chocolate products?" studies, rather than the one which specified (quite small) weights, and that's why the BBC didn't specify a size of a bar.  Card Zero  (talk) 20:11, 30 August 2011 (UTC)

I think the question was simply "how much does a chocolate bar weigh?" perhaps you could go to a store and read the wrapping.190.148.132.191 (talk) 23:50, 30 August 2011 (UTC)

Chocolate bars come in a wide variety of sizes. StuRat (talk) 05:53, 31 August 2011 (UTC)

I think these studies are still at the levels of correlations and vague assertions like "polyphenols are good for you" (an offshoot of the even vaguer and less well-founded belief that "antioxidants are good for you"). It's a happy finding that chocolate eaters seem to have some health advantages, but I don't think anyone has ruled out e.g. that people who can regularly afford chocolate have better health coverage, or have a less stressed attitude, or avoid potato chips, or any of a thousand explanations other than a longevity chemical in the chocolate. Wnt (talk) 00:19, 31 August 2011 (UTC)

In the US, at least, chocolate bars are quite inexpensive. StuRat (talk) 05:53, 31 August 2011 (UTC)

I'm adding a third thing you should look for in your chocolate bar:

3) It shouldn't contain milk products (that is, no milk chocolate). In addition to this meaning it would have less cacao, milk also seems to somehow cancel the anti-oxidant benefits. This also means you shouldn't consume the chocolate along with milk products. StuRat (talk) 05:56, 31 August 2011 (UTC)

And, to go along with your chocolate bar, I've broken off a little section of an article for you to digest: Types_of_chocolate#Dark_chocolate_health_benefits. StuRat (talk) 06:03, 31 August 2011 (UTC)

Stu, you haven't read the meta-analysis have you? Regardless of what you think the results should have been, it actually found that the benefit didn't specifically attach only to dark chocolate, or high cocoa solids, or chocolate taken without milk. This means that the benefit was probably not due to anti-oxidants (which are blocked by milk), or polyphenols. The effect was present for people who ate chocolate biscuits, or chocolate-covered toffee, or milk chocolate, or white chocolate. So it doesn't actually matter what weight of chocolate you ate, because it isn't really an effect from a dose of some substance. It seems to be a more fundamental benefit of regularly eating something nice which makes people feel happy and relaxed, regardless of the apparent health drawbacks of sugar and fat. If I were to step beyond the reported stuff, I would also say that regularly eating chocolatey things probably means you aren't dieting or worrying too much about food, which is healthier and less stressful. 86.163.211.187 (talk) 14:48, 31 August 2011 (UTC)

Yes, but I'm expanding beyond that article to describe how to best take advantage of all the benefits of chocolate, including the anti-oxidants. StuRat (talk) 03:03, 1 September 2011 (UTC)

Well, as described at Antioxidant, the idea of antioxidant supplements as some kind of cure-all is really not holding up - it never really had that much evidence supporting it beyond wishful thinking. Wnt (talk) 00:23, 4 September 2011 (UTC)

I remember reading somewhere that the beneficial cardiac effects of chocolate are due to stearic acid. 76.254.20.205 (talk) 19:08, 31 August 2011 (UTC)

Since women have longer life expectancy, could this simply be the case that women are more likely to eat chocolate regularly? Anonymous.translator (talk) 00:33, 1 September 2011 (UTC)

Self-reports are extremely inaccurate, and observational studies can usually only tell correlation, not causation. I wouldn't trust the results of this study at all. To me it was a waste of money and resources. Imagine Reason (talk) 03:35, 1 September 2011 (UTC)

I wouldn't call it a waste of time and money. You can't tell which way the train went by looking at the track. But you have a lot better odds of figuring out where the next one is headed if you know where the tracks are. Wnt (talk) 23:14, 1 September 2011 (UTC)

Io and Pulsars.

Around 1610 A.D it was noticed that the orbit of Io Around Jupiter changed in time depending on where the earth was around the Sun . I think I may be able to understand this , its a "time dilation" effect.

However I do not understand why Pulsars keep perfect time in relation to us moving around the Sun or indeed the galactic center. — Preceding unsigned comment added by 92.30.154.8 (talk) 23:30, 30 August 2011 (UTC)

I don't think it's a "time dilation" thing at all, it's a simple "speed of light" thing.. When the earth is closest to Jupiter (893 million km ), say (from earth) you observe IO crosses Jupiter at exactly 12:00 (hypothetically), when the earth is furthest away from Jupiter (964 million km ), you still expect Io to cross at exactly 12:00, but instead you observe it crosses at 12:03. This was puzzling until they worked out that light took an extra 3 minutes to cross the extra distance. As for pulsars, they weren't discovered until 1967, so i think speed of light was already figured into the observations as a matter of course, i don't think they're immune from the extra time it takes to reach the earth depending where we are in orbit around the sun, but there was nothing "surprising" about it by that stege. Vespine (talk) 23:46, 30 August 2011 (UTC)

In 1610 Jupiter's moon Io had only just been reported by Galileo. The modern value for its orbital period is 42.459 306 86 hours, see Io (moon), which resonates with the orbits of Europa and Ganymede, see Io (moon)#Orbit and rotation. What source claims an observation of a time dilation effect in 1610? Wikipedia has an article about Pulsars that cites a source for some pulsars having rates as regular as an atomic clock and describes studies of their regularity such as Pulsar timing array projects. Cuddlyable3 (talk) 00:04, 31 August 2011 (UTC)

See speed of light#Astronomical measurements. It describes quantitative measurement of the speed of light by observations of the periods of Jupiter's moons, but not until 1675 by Ole Christensen Rømer. (Actually we have a whole article Rømer's determination of the speed of light. But measuring it in 1675 is still quite impressive! Wnt (talk) 00:13, 31 August 2011 (UTC)

It's not a time dilation effect. It's a Doppler effect. Dauto (talk) 01:01, 31 August 2011 (UTC)

Not at all. The Doppler effect is caused by the relative velocity between two objects; the effect discussed here depends on their distance. It is strongest between those times when the distance between Earth and Io/Jupiter is maximum and minimum. At these times, the velocity is perpendicular to the line joining them, hence the Doppler effect is zero. In principle, the effect should be present in Pulsar data as a modulation of the arrival time of pulses; whether it matters for the measurements depends on the measurement method. Because pulsar periods are short, they can be measured over a short time span, hence there is no need to observe or predict pulse timing over the course of an entire year. In case it does matter, one would take it out of the raw data - scientific work uses reduced data where effects that are well known but unimportant to the scientific question are corrected for. --Wrongfilter (talk) 06:51, 31 August 2011 (UTC)

It is a Doppler effect. The Doppler effect shifts all frequencies equally—not just the frequency of the light but also the orbital frequency of the moons. When Earth is moving away from Jupiter the observed orbital period is longer, and that adds up to an overall delay of the eclipse times when Earth is farthest from Jupiter compared to when it's closest. There are other ways of looking at it, of course. The same thing happens to pulsar signals. -- BenRG (talk) 09:56, 31 August 2011 (UTC)

There is a Doppler effect due to Earth's motion about the Sun, but that was definitely unobservable in the 17th century. The orbital speed of the Earth is 30 km/s. That modulates the observed orbital period by a factor v/c = 0.0001. In Io's orbital period that is presumably unobservable even today; it may be in pulsar periods. The effect that Ole Romer observed is due to the fact that light from Io has to travel a further 2 AU when Jupiter is in conjunction with the Sun compared to when it is in opposition. That effect gives a difference of about 16 minutes, not in the period, to be precise, but in the phase of the orbit. --Wrongfilter (talk) 10:16, 31 August 2011 (UTC)

This shift in the phase is nothing more than the accumulation of the Doppler effect over a period of six months. It is a Doppler effect. Dauto (talk) 14:17, 31 August 2011 (UTC)

Ah, okay, now I see what you are talking about, thanks for the clarification. I was slightly worried and confused about having to distinguish between the phase and the period. So, the Doppler effect itself is unobservable, but its integrated effect is. The integration also explains the phase shift between Romer's observation and the instantaneous Doppler effect. There is an interesting parallel to the cosmological redshift, which can also be constructed as an integrated Doppler effect. --Wrongfilter (talk) 14:29, 31 August 2011 (UTC)

Hang on, is saying doppler effect the same as my 1st answer? I don't think "red shift" or anything "relative" has anything to do with what was described back then. Vespine (talk) 00:37, 1 September 2011 (UTC)

Yes, it is the same thing. The 17 minute delay is given by the integrated Doppler effect over six months. Dauto (talk) 13:09, 1 September 2011 (UTC)

Well, yes, the effect can be thought of as a generalised Doppler effect if you think of the rotation as a "wave", but this rather unusual interpretation was certainly not used centuries before Doppler was born and is not really helpful for a first understanding of the effect when the explanation of extra distance is so much simpler. Dbfirs 23:02, 1 September 2011 (UTC)