Science desk
< August 20	<< Jul \| August \| Sep >>	August 22 >

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

August 21

Are individual photons visible to the dark-adapted naked eye?

Reading the double-slit electron question above, reminds me of something I wondered about some time back, but couldn't find an answer to. I was discussing physics with a friend, who commented that subatomic particles seemed to be entirely imaginary, in that nobody had ever seen one. I pointed out that to the contrary, the only things I'd ever seen were subatomic particles - photons. This raised the obvious point - can you actually see a single photon? (statistically speaking, I mean, to get around the uncertainty principle, and questions regarding the extent to which photons are real). To put it another way, are the light-sensitive cells in a human eye sufficiently sensitive to detect a single photon, under ideal circumstances? AndyTheGrump (talk) 03:19, 21 August 2011 (UTC)[reply]

Answered here with some references. -- BenRG (talk) 03:35, 21 August 2011 (UTC)[reply]

Interesting - thanks. So the answer seems to be that the cells (rods) can detect individual photons, but they are filtered out - you need to detect several (around 9 on average, according to the link, if I understand correctly) to be aware of them. This experiment was done with human subjects of course - perhaps other, more nocturnal, animals have a lower threshold? AndyTheGrump (talk) 03:49, 21 August 2011 (UTC)[reply]

It's often said that the eyes of frogs and toads can detect single photons, though I can't find a good reference. Here [1] is a page which makes it sound reasonable (frogs use their very sensitive eyes for detecting more than for seeing), but doesn't explicitly say they can do it. Here [2] is a chapter called "Photon Counting in Vision" from an apparently unfinished book. It goes into a lot of detail: if you search for "frog" you'll find that one advantage they have is that they are cold blooded, which means you can cool them to reduce the thermal noise on their sensors. I still can't find the part where it actually says that they can see one photon, though. Card Zero (talk) 10:26, 21 August 2011 (UTC)[reply]

How do seeds know which way is up?

I was thinking about a tree at the bus stop the other day, and I wondered how it is that the trunk grows more or less directly upward. I've looked at the germination article in an attempt to answer this question, but I don't see anything there that really gives a satisfactory answer (though File:Mung bean germination.ogv is pretty fascinating). Obviously (?) part of the answer is "gravity," but how, exactly? I understand that plants grow toward the light because cells on the shaded side grow faster than cells on the lighted side—right? Are plant cells really sensitive enough to gravity that they adjust their individual growing speeds so that the stem grows upward? What's the cellular mechanism for this? —Bkell (talk) 04:08, 21 August 2011 (UTC)[reply]

See Gravitropism. --Jayron32 04:16, 21 August 2011 (UTC)[reply]

Ah, thank you. —Bkell (talk) 04:19, 21 August 2011 (UTC)[reply]

Also the previous mechanism you described is called Phototropism (more accurately positive phototropism). And no, it's not the result of the lighted side growing faster, in fact it's the opposite. The cells farthest from the light reacts to the absence of light by becoming more 'elastic' and elongating (due to the presence of auxin), therefore 'bending' the plant towards the source of light in the process. Other more dramatic plant 'movements' is Heliotropism exhibited most famously by sunflowers.-- Obsidi♠n Soul 04:27, 21 August 2011 (UTC)[reply]

Oops. Scratch that. Misread your OP, ^-^ Need moah coffee.-- Obsidi♠n Soul 04:29, 21 August 2011 (UTC)[reply]

And what happens when there's no gravity? Quest09 (talk) 14:04, 21 August 2011 (UTC)[reply]

Then there is no up. Cuddlyable3 (talk) 14:34, 21 August 2011 (UTC)[reply]

Weird things. To generalize from those two articles, if it the gravitropism is exhibited by the entire plant (roots and stems), then it goes in random directions. If it is exhibited by individual cells (as in the case of molds or things like that), then you get crazy patterns (probably, I would guess, because each cell is getting its idea of gravity from its surrounding cells, which probably leads to weird regularities despite them all being confused about the actual direction of gravity). --Mr.98 (talk) 14:46, 21 August 2011 (UTC)[reply]

Total lunar eclipse at December 31

Which year has the next total lunar eclipse on December 31? 123.24.96.94 (talk) 10:13, 21 August 2011 (UTC)[reply]

NASA has a page which should answer your question, although you will have to look around a bit. Jc3s5h (talk) 10:35, 21 August 2011 (UTC)[reply]

December 31 where? There is a total lunar eclipse (71 minute totality) on 31 Dec 2028 at 1653 GMT, and will thus be visible throughout most of asia, but not Europe and the Americas. The OP's IP geolocates to Vietnam, TZ +0700, so the new year will occur just minutes after the time of greatest eclipse (when the moon is closest to the center of the Earth's umbra). Depending on your location of interest, you may also wish to search for eclipses on 30 Dec and 01 Jan. For instance, the next total lunar eclipse visible in the United States on 31 December will be the eclipse of 01 Jan 2048 at 0654 GMT (56 minute totality). With West Coast U.S. Standard TZ -0800, the totality will be complete a good half-hour before midnight on 31 December 2047. -- 110.49.249.165 (talk) 12:57, 22 August 2011 (UTC)[reply]

Information on linitis plastica, a form of stomach cancer

I have read the article on linitis plastica, which I understand is a form of stomach cancer, but the article is really only a stub. I have a friend disgnosed with the condition (yes, he is being treated by a qualified professional) and I'd like to understand more about the disease - stages, treatment methods (chemo? radio? reasons for using each), etc. I am not seeking advice on what will happen for him specifically or his prognosis, I'm just looking to understand better without pestering him with a whole bunch of questions he may not want to answer. Being pointed to other good sources of information would be great, or anything anyone can contribute. I am scientifically literate but not medically trained, so can cope with a reasonably technical responce. Many Thanks. — Preceding unsigned comment added by 121.218.222.153 (talk) 13:43, 21 August 2011 (UTC)[reply]

I'm sorry to here about your friend. If you Google 'treatment of linitis plastica' you'll get quite a few hits, for instance like this one Best. Richard Avery (talk) 14:50, 21 August 2011 (UTC)[reply]

I found one clinical trial recruiting at [3] - you might search other synonyms ("stage [X] stomach cancer", etc) based on his specific diagnosis. I'm can't tell you whether this is a good idea, just putting it out as a possibility. Wnt (talk) 16:55, 21 August 2011 (UTC)[reply]

Tossing and turning

When one can't sleep, it's not uncommon to toss and turn. My experience of it is that suddenly being in one position (lying on my left side, for example) becomes unbearable uncomfortable, and turning over fixes it.. until that becomes unbearably uncomfortable, requiring turning again.

(This is not a request medical advice whatsoever — I'm assuming this is fairly common, hence the common phrase of "tossing and turning.")

What's the reason for this? Why does one side feel so fine, and then so horrible? Why does this only seem to occur when one is fitfully not able to sleep? I find it an odd habit — it strikes me as odd that there is so much movement involved (and annoying to anyone else sharing the bed). --Mr.98 (talk) 15:12, 21 August 2011 (UTC)[reply]

It's explained in this article: Restless legs syndrome. Dominus Vobisdu (talk) 16:43, 21 August 2011 (UTC)[reply]

I don't think that is what Mr 98 is referring to. RLS is a specific neurological disorder that causes an irresistible urge to move during any period of inactivity e.g. when sitting, not just when trying to sleep. Gandalf61 (talk) 17:26, 21 August 2011 (UTC)[reply]

Yes, I know exactly what Mr.98 is talking about, and it is not restless leg syndrome, which I have seen others suffer. There is no actual physical discomfort like a pain, just a strong urge to switch sides which, when one overcomes inertia and gives into it, gives an immediate comforting relief. The problem is that making the effort to turn over repeatedly can bring you up out of the sleep mode. I normally expect to shift like this an average of 2-4 times before I nod off. If I do it more than six times I usually find it is better to get up and read than to keep tossing and turning. My guess has long been that the ultimate cause is restriction of blood flow, but that's a guess. μηδείς (talk) 18:54, 21 August 2011 (UTC)[reply]

Yes, definitely not the same as restless leg syndrome. My guess is that, for some reason, one becomes over-sensitive to the pressure on one side. The pressure is reduced when the body relaxes and spreads its weight on falling asleep, but tends to become uncomfortable when awake because the body is held in some tension when "trying to get to sleep". Dbfirs 19:40, 21 August 2011 (UTC)[reply]

We also periodically must switch positions while seated (I hate bucket seats in cars, since they prevent this), since otherwise pressure points can restrict the flow of blood and lead to limbs "falling asleep". If we didn't switch positions, the blood would pool, seep out of the capillaries, form a bruise, and eventually become infected and cause death. Bed sores are common in hospital patients who can't switch position and in people who are paralyzed.

So, why does it seem like people toss and turn more when they can't get to sleep ? Part of it might be perception. That is, you might toss and turn just as much when asleep, but you are unaware of this. Also, you might actually toss and turn more when awake. That is, when you have nothing else to do, you might as well change position when the first sign of discomfort occurs. There might also be a subconscious thought that "I could get to sleep if I was more comfortable".

Of course, having a comfortable sleeping environment is important, so no bed with springs poking you, for example. A comfortable pillow, and maybe an extra one between the knees, can help. The room must be dark and usually quiet, although some like certain "sleep sounds" such as white noise. And the temperature and humidity must be comfortable and there can't be any unpleasant smells, like skunk or ciggy smoke. StuRat (talk) 19:57, 21 August 2011 (UTC)[reply]

[If someone finds the answer, the information can be added to the article “Sleeping positions”.]

—Wavelength (talk) 20:21, 21 August 2011 (UTC)[reply]

The symptoms are not exactly like the need to shift positions while sitting. There is no tingling, just a general discomfort not tied to any localized physical sensation. I can lay in the same position for a long time reading, yet have to switch from left to right as often as every few minutes while trying to sleep. (It's hard to be sure of the time, since you are trying to fall asleep.) I have a very comfortable bed, plenty of pillows for support, sleep with a fan for white noise, and have almost no sense of smell after having nasal polyps cauterized at age 18. Even then, perfectly comfortable, with no tingling limb itself "falling asleep" I myself never expect to fall asleep before turning at least twice. μηδείς (talk) 20:53, 21 August 2011 (UTC)[reply]

It's your body testing to see if you're asleep before entering sleep paralysis. If you are awake, you will turn over. If you are asleep, you won't and the body enters sleep paralysis. If you are awake but resist the urge to turn, you enter sleep paralysis fully concious and have a lucid dream 82.43.90.27 (talk) 16:49, 22 August 2011 (UTC)[reply]

Well, no. But that certainly was entertaining.

phenobarbitol/ataxia

Is it possible that phenobaritol taken as a young child for several years could cause ataxia and other neurological deaseas as you age? — Preceding unsigned comment added by BurtLauna2 (talk • contribs) 15:31, 21 August 2011 (UTC)[reply]

The drug is phenobarbital. Conceivably yes. But that would only be given to somebody with epilepsy, and untreated epileptic seizures have quite a high probability of producing permanent neurological damage. And in any case I don't see how one could with any confidence assign blame to the drug given that the person has an underlying epileptic disorder. (Note: I don't view this as a request for medical advice, because it isn't asking how to treat a problem.) Looie496 (talk) 17:25, 21 August 2011 (UTC)[reply]

Soymilk makes boobs bigger?

I was at a party the other day and some people were talking about how soymilk increases the production of estrogen, and if males or females drink it on a regular basis, it will make their boobs bigger. Is this true? ScienceApe (talk) 16:25, 21 August 2011 (UTC)[reply]

Soy milk doesn't increase estrogen production: it actually contains phytoestrogens. Anecdotally, at least, it is said to cause gynecomastia if consumed in excessive amounts, though I'm not certain how well this claim has been studied. - Nunh-huh 17:05, 21 August 2011 (UTC)[reply]

Hmmm... anecdote at PMID 18558591. Wnt (talk) 18:22, 21 August 2011 (UTC)[reply]

That is an interesting anecdote. In reply to that case report, there was a letter (PMID 18558589) by Braunstein (chair of Medicine at Cedars Sinai) noting that the association between ingestion of soy milk and gynecomastia remains unproven when studied carefully, as in PMID 15055353. The letter by Braunstein also contains a nice review of environmental causes of gynecomastia. -- Scray (talk) 11:38, 22 August 2011 (UTC)[reply]

I think recent research has shown that soymilk is harmful to health. Milk, after all, is not as good as commonly believed. Imagine Reason (talk) 19:31, 22 August 2011 (UTC)[reply]

I haven't gone into this properly because the studies I'm finding are a bit exasperating - looking at things like breast epithelium at two years or the volume of aspirated fluid, which I can't easily turn into a cup size. But there are a whole lot of papers and I didn't skim over half the abstracts. My feeling is that normal levels of consumption might indeed have little effect, but that anecdote was about someone drinking three liters a day. As I recall conjugated linoleic acid has an opposite effect; maybe you can work a hex on your neighbor to shrink his daughter's breasts in the womb by feeding his cow safflower oil. (But reducing her risk of cancer). But I don't know. Life has its little mysteries. ;) Wnt (talk) 02:54, 23 August 2011 (UTC)[reply]

nova & dwarf nova difference?

what's the difference between nova & dwarf nova? nova also happens in white dwarf only. then what's the difference? please answer me in my talk page--tenkasi subramanian (talk) 19:17, 21 August 2011 (UTC)[reply]

Your question is answered in the first paragraph of an article which by coincidence is also named Dwarf nova. Dauto (talk) 19:53, 21 August 2011 (UTC)[reply]

Does JPL's default simulation accurately depict the orbit of asteroid 2010 SO16?

Does http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2010+SO16&orb=1 (requires Java) accurately depict the horseshoe-shaped orbit, relative to Earth, of 2010 SO16, or do such orbits fall under the "planetary encounter circumstances" mentioned on the JPL page? 76.254.20.205 (talk) 22:38, 21 August 2011 (UTC)[reply]

No, the applet is not trying to show the asteroid's 'horseshoe-shaped orbit, relative to Earth', but rather its elliptical (though nearly circular) orbit, and also those of Earth and the other innermost 5 planets, relative to the stationary Sun ~~and to each other~~. The caution ". . . should not be used for determining accurate long-term trajectories (over several years or decades) or planetary encounter circumstances." means that it uses simplified mathematical methods that cannot reliably give very accurate results as to exactly when and where two bodies -in this case the asteroid and Earth - will get closest to each other approximately once per year, or where all these bodies will eventually be over longer periods: much more complicated calculations and hence more data and computing power would be required for that.

The "Horseshoe orbit" of the asteroid is calculated relative to a supposedly stationary Earth, and shows how the asteroid's position relative to Earth gradually drifts over many years/orbits.

Think of it like two cars racing in the Indianapolis 500. From the point of view of a stationary spectator (the Sun) in the middle of the oval (or a spectator in the external grandstand that is also stationary), the two cars (Earth and asteroid) go round and round the track at similar though not identical very high speeds. From initially close positions the asteroid-car may gradually drop back nearly a lap from the Earth-car over tens of laps, and then nearly catch up again over more tens of laps, before the Earth-car starts pulling away once more (let's assume no pit stops!), but all the time they're both moving very quickly. Seen from the Earth-car's onboard camera, however, the asteroid-car seems to be barely moving second-by-second, and vice versa. If you plot the asteroid-car's position round the track once per lap every time the Earth-car crosses the finish line, it will gradually trace out a "horseshoe" with the Earth-car in the gap. Of course, from the asteroid-car's camera the Earth-car does exactly the opposite, and if you plotted the Earth-car's position every time the asteroid-car crossed the line, you'd get a similar looking result. {The poster formerly known as 87.81.230.195} 90.197.66.149 (talk) 08:48, 22 August 2011 (UTC)[reply]

I agree, but the fact that SO16 is currently "rounding the bend" around the solar L5 point.... 76.254.20.205 (talk) 08:15, 23 August 2011 (UTC)[reply]

How far is asteroid 2010 SO16 from the ecliptic plane currently?

How far from the plane of the ecliptic is asteroid 2010 SO16 at present, and how far is it from the solar L5 point? 76.254.20.205 (talk) 08:15, 23 August 2011 (UTC)[reply]