Wikipedia:Reference desk/Archives/Science/2008 April 28

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< April 27 << Mar | April | May >> April 29 >
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.


April 28[edit]

Website with yellow text on a black background (and some blinking elements)...[edit]

Man, why does that hurt my eyes and screw up my vision so much? I can only look at it for maybe ten seconds before my vision is completely screwed up (blurry and wobbly with 'stars' and intrusive afterimages) and my eyes start watering. --Kurt Shaped Box (talk) 00:13, 28 April 2008 (UTC)

Funny, I heard the same thing the other day from someone whose work essentially requires staring at a computer screen all day long...It has never bothered me, personally. Someguy1221 (talk) 00:25, 28 April 2008 (UTC)
I never usually have problems myself. I do occasionally see afterimages (a bit like if you've been staring at the sun - but less so) if I've been reading bright-on-black text on my screen for a long time - but this was the first page I've ever seen in a long time that actually, literally *hurt* me to look at it. Red-on-navy-blue text (for some reason, that used to be a quite popular choice for personal websites a few years back) is not much fun for me either... --Kurt Shaped Box (talk) 00:42, 28 April 2008 (UTC)
Hi. Black text on white background leaves an afterimage in my eyes too, even if I turn the computer's brightness and contrast to the lowest possible. Also, I think a developer might have changed Wikipedia's background colour from purple-white to blue-white a couple of months ago. Most websites don't *hurt* my eyes, but if I use the computer for too long then sometimes I will get a headache. Thanks. ~AH1(TCU) 00:55, 28 April 2008 (UTC)
Look at Action potential. I'm no expert, but as far as I understand it the chemicals (e.g. electrolytes) in your cells get out of whack and that may cause pain. There are also effects of nerves firing electrical impulses at certain intervals. Photosensitive epilepsy is probably over-reported, but migraines and headache fall well within the spectrum. (Oops had my desks mixed up.) Lisa4edit71.236.23.111 (talk) 04:47, 28 April 2008 (UTC)

Virginian Tree Identification[edit]

Do basswoods grow in Virginia? I'm trying to identify a tree that has heart-shaped leaves with ridged edges, and that narrow into a thin stinger-like point at the pointy end of the heart.

It looks very similar to the picture of the leaf under the basswood article:

http://en.wikipedia.org/wiki/Image:Lisc_lipy.jpg http://en.wikipedia.org/wiki/Basswood 71.174.18.26 (talk) 00:44, 28 April 2008 (UTC)HotSpringsMonkey

According to my Audubon guide, Virginia is at the southern limit of American Basswood and the northern end of White Basswood aka Linden aka Basswood. In my (Ontario) experience, the leaves are quite large, 3-5" across, and the mature trees are often hollow, though still lively. They're kind of a messy-looking tree, unlike, say, a beech or oak.
"Leaves alternate in 2 rows...3 or more main veins from base, often toothed...Flowers in branched clusters...5 petals (sometimes none)". Best I can do! Franamax (talk) 22:21, 28 April 2008 (UTC)

What will happen if scientists ever see the beginning of time?[edit]

Is this possible? Every once in a while I read in the paper that scientists, using telescopes, have went back a few more million years and now see the universe in it's infancy. Is there a limit here? And if they ever do see the beginning of time, can thier minds handle it? Will thier minds shut down, or will it be like peering into subatomic realms, where they know they've seen something but cant explain it? --Sam Science (talk) 02:34, 28 April 2008 (UTC)

Scientists do not see time. They see electromagnetic radiation (of which visible light is a part). When you see that they are seeing far back in time, it means that the particles (or wavicles if you want to be weird) originated a long time ago and are just now making it to Earth so scientists can see it. So, is it possible to see the very first particle ever emitted? Yes. Will we see it? That is a math problem. The particle travels at the speed of light in basically a straight line. Once it passes Earth, it is too late to try and catch it. Of course, this assumes that space doesn't wrap around on itself giving the particle another chance to swoop by Earth. As for your odd pondering about melting minds and whatnot... It is not reasonable to assume that seeing an electromagnetic particle will melt anyone's mind. It is just a little speck of energy. The importance of the speck (being the first one created) is placed on it by those doing the research, not the speck itself. -- kainaw 02:58, 28 April 2008 (UTC)
So no face melting?--Shniken1 (talk) 05:25, 28 April 2008 (UTC)
There is a limit of electromagnetic viewing, as the universe was originally opaque. -mattbuck (Talk) 11:16, 28 April 2008 (UTC)
The cosmic neutrino background gets you back much further, if we ever manage to detect it. Algebraist 11:23, 28 April 2008 (UTC)
The universe is the same everywhere, and there will always be light from any era that was emitted at just the right distance away to be reaching us right now. The reason we can't see the earliest photons is not that they've passed us but simply that they were long ago reabsorbed. As mattbuck said, the universe was opaque (to electromagnetic radiation) until about 375,000 years after the big bang. We've already seen light from that era (the CMBR), and we'll never see any earlier light because unlike the CMBR it didn't survive to the present era. -- BenRG (talk) 12:08, 28 April 2008 (UTC)
"The very first particle ever emitted" implies a level of synchronicity which is not currently consistent with theory of space-time. See our article on relativity of simultaneity for an introduction to this sort of mind-bending topic. Briefly, "the first particle ever emitted" is a different particle for two different observers, in different reference frames (depending on where you are and how you're moving). This sure does make it difficult to define how the universe started! There are some limits, imposed by causality, though, so some particles are definitely precursors to other particles; nonetheless, the "first event in the universe" is probably not the best way to think about the early universe. Nimur (talk) 13:39, 28 April 2008 (UTC)
Actually in cosmology there's no congruence of different notions of simultaneity the way there is in special relativity. There's a privileged time coordinate called cosmological time which can be used to order events that aren't causally connected. The special relativistic notion of "observer" doesn't really carry over to general relativity. People do use the word "observer" in general relativity, but they mean something completely different by it (in special relativity it's usually a global inertial reference frame, in general relativity it's usually a worldline). I agree that "the very first particle ever emitted" doesn't make much sense, but that's for quantum mechanical and quantum gravitational reasons. -- BenRG (talk) 19:38, 28 April 2008 (UTC)
The article Cosmology says the universe is ~13.7±0.2×10^9 years old. Age of the universe says "13.73 billion years, with an uncertainty of about 120 million years," which overlaps the other article but is a more precise claim. The Hubble space telescope has reportedly [1] "seen" ancient white dwarf stars which are 12 to 13 billion years old. We non-astronomers get the impression that astronomy is creeping closer and closer to the "first light" of the universe, emitted some time after the "big bang." In 2001, astronomers said [2] that after the big bang the universe was too hot for complete atoms to form, but that after 300,000 years hydrogen atoms could form, and that half a million years later, light-emitting objects could form. By subtraction, 13.73 billion -.8 billion yields 12.93 billion years (+/- yadda yadda) as the oldest light emitting objects. Is there any reason one might not read in science news one day that we have now observed these first light emitting objects? Is it possible that Hubblle's light from 12 to 13 billion years ago includes some of the first light emitting objects? Edison (talk) 00:44, 29 April 2008 (UTC)
I found a 2003 article which seems to say the Hubble 'scope saw these first light emitting objects. The light was emitted when the hydrogen atoms filling the universe was ionized enough to permit light to propagate. The estimated there weree 400 million "proto-galactic objects" in the universe at that time, when the "dark ages" of light absorption by hydroegn atomes ended, which the Arizona State University scientists estimated to be about 1.3 billion years after the big bang. The numbers seem rather imprecise from various sources. Edison (talk) 00:59, 29 April 2008 (UTC)
Simplified timeline is as follows:
  • Recombination - approx 300,000 years After Big Bang; universe has cooled enough for neutral hydrogen and helium atoms to form; photons that we now see as cosmic microwave background were last scattered at this time; these are the "oldest" photons that we will ever see.
  • Dark ages - approx. 300,000 - 100m years ABB; universe is filled with neutral hydrogen and helium; photons that will form CMB propogate freely; no stars/quasars have yet had time to form.
  • First quasars and Population III stars form - approx 100m years ABB; Spitzer Space Telescope may have captured photons emitted by these objects; Keck II telescope has captured images of proto-galaxies from 500m years ABB.
  • Reionization - starting approx. 150m years ABB; photons emitted by first stars and quasars ionise neutral hydrogen atoms in inter-stellar space; universe is filled with low-density plasma; most CMB photons are unaffected, but some Thomson scattering can be detected; plasma absorbs light from first stars and quasars at hydrogen line wavelength. Gandalf61 (talk) 10:00, 29 April 2008 (UTC)
It won't happen. Unfortunately, we didn't exist back then, and there is a limit to how far back the observable radiation can go. There was a Scientific American article a few months back about this. It was titled somthing like "The End of Cosmology" and focused mainly on how evidence of the Big Bang will gradually fade away as the Universe expands. Soon (cosmologically speaking, anyway) scientists won't be able to observe event he background microwave radiation for some reason or the other. Then there's redshifting, and stuff. And, once galaxies are moving away from each other faster than the speed of light (yes, it is possible, each one goes half the speed of light, so technically the distance between them is expanding at the speed of light) we won't be able to see them at all. Ilikefood (talk) 16:29, 4 May 2008 (UTC)

Day on Mercury[edit]

How long is "day" on Mercury? Night? How long does it take for Mercury to rotate around its axis? —Preceding unsigned comment added by 24.7.54.224 (talk) 06:56, 28 April 2008 (UTC)

Have you seen our article on Mercury (planet)? If the article doesn't answer your question, feel free to come back here and provide some more detail on what you're looking for. Thanks, Confusing Manifestation(Say hi!) 07:32, 28 April 2008 (UTC)
Mercury rotates around its axis, relative to the fixed stars, once in about 58.7 Earth days. It revolves around the sun exactly 2/3 as fast, or once in about 88 Earth days. To an observer on Mercury, the Sun moves across the sky with the difference of these rotation rates, resulting in a day (sunrise to sunrise) of 3*58.7~176 Earth days. "Day" (sunrise to sunset) and "night" are of course each half as long. --mglg(talk) 00:26, 29 April 2008 (UTC)
The relative length of day and night would depend on where on the planet you stand when. --Lisa4edit (talk) 00:55, 29 April 2008 (UTC)
See Mercury (planet)#Spin–orbit resonance for an explanation of why the day and year have an exact 3:2 ratio. Also see the last paragraph in Mercury (planet)#Orbit and rotation for a description of an interesting phenomenon (the Sun sometimes "turns around and goes the other way" when viewed from Mercury). StuRat (talk) 05:08, 29 April 2008 (UTC)

Generational LEDs[edit]

I was looking into emergency lighting for my car and came across the LED lit ones being listed as "Generation I LEDs" or "Generation III LEDs". I've never heard of different generations of LEDs before, is there any difference between them? -- MacAddct  1984 (talkcontribs) 15:02, 28 April 2008 (UTC)

Are you sure your not getting confused by something like [3]? This is referring to the generation of the device given by the flashlight company, not the LED per se. Generally speaking, LEDs, as with most electronic devices are getting all the time. LEDs in particular are getting more efficient (which I believe includes brighter for a given voltage level, brighter overall and better luminous efficacy) as well as cheaper to produce. IIRC the Colour Rendering Index is also being improved as well as different Colour temperatures so they are suitable for people with different preferences (both probably not that important for a flash light) Nil Einne (talk) 17:44, 28 April 2008 (UTC)
That's what I had thought at first, but the descriptions certainly seem to imply different models of LEDs. Compare: [4] and [5]. "66 Hyper Bright 5mm Generation I LEDs" vs "Generation III LED's" -- MacAddct  1984 (talkcontribs) 18:03, 28 April 2008 (UTC)
It seems to be mostly a marketing term. Manufacturers group their products by specs like operating voltage, color, composition and light output. Generation III is usually used for LEDs that produce bright "white" light and are used to replace lightbulbs. Generation II seems to be a company specific term (http://compoundsemi.com/documents/view/generic.php?id=709). This http://olla.ichf.edu.pl/lect/SS2005/H_Boerner.pdf may contain an explanation or may refer only to a specific type. --Lisa4edit (talk) 21:48, 28 April 2008 (UTC)

Medical explanation.[edit]

Is there a medical explanation for as to why someone is obsessed with religion and philosophy? I have been studying "Biology and human behavior" and the man lecturing claims that it has to dd with an imbalance in the brain. Could someone please elaborate on this for me? Thanks. —Preceding unsigned comment added by 72.40.54.255 (talk) 20:31, 28 April 2008 (UTC)

Mixing science and religion is always a recipe for murky results. What your lecturer might have been referring to is Obsessive-compulsive disorder. But the phrase "obsessed with religion" is usually not understood as referring to the medical disorder, but more to a psychological state (or disorder) Obsessive love is an article that could shed light on some of the issues involved, but I wouldn't call it a collection of well established facts. As with most psychological issues there is a fine line between common and accepted and harmful and pathological. If someone spends all their free time meditating on the deeper sense of being that's o.k. If they can't sleep because of it and skip work or don't eat and don't socialize, that's reason for worry. If they start harming others or themselves that's pathological. There may be a "chicken and egg" causality though. E.g. if you don't sleep you can develop symptoms that are indistinguishable from bipolar disorder, but bipolar disorder can/does cause insomnia. Chemical imbalances in the brain can be caused by the system not being set up correctly or by it being knocked out of order.--Lisa4edit (talk) 21:17, 28 April 2008 (UTC)
There are two uses for the word "obsession": the clinical disorders mentioned by Lisa4edit above, plus the more general layman's term to refer to preoccupation or fascination with a subject. Neither are restricted to religion and philosophy: clinical obsessive disorders can vary in subject and severity. As for the second, it is perhaps difficult to ally with specific scientific reasons. We all have interests and things we enjoy thinking about: science, philosophy, sport, archeology, Wikipedia, stamp-collecting, bird watching, and so on; some of us are more "obsessed" by our interests than others. An elite sportsman, for example, is extremely single-minded. Would you class that as a pathological imbalance in the brain? Or just a response of natural talent and application? An academic scientist is driven to investigate, observe, study, research and develop ideas and natural phenomena. Some people spend much time considering metaphysical matters. It is entirely natural. Gwinva (talk) 05:31, 29 April 2008 (UTC)

LHC[edit]

When in May does the LHC start up. Is is midnight May 1 or later? Thanks *Max* (talk) 21:14, 28 April 2008 (UTC).

Judging by this http://cerncourier.com/cws/article/cern/33789 looks like it'll be June. They have to cool the ring before they can inject the first beam. I guess that would be what you call start up. --Lisa4edit (talk) 21:31, 28 April 2008 (UTC)
...But that doesn't mean they start collecting data in June. According to Peter Woit's blog they're planning a physics run at 5 TeV starting in September, and at 7 TeV in April 2009. I'm not sure where he got those dates (he cites two sources, but I can't find them in either one). -- BenRG (talk) 21:56, 28 April 2008 (UTC)
You're right. That's when it starts getting interesting. (Remember though that LHCb already got nice data from cosmic rays during the equipment testing.) But things don't usually happen when they are supposed to. I could get at the sources but they had nothing really interesting on dates, except that the June date for injection might be "late" June. They plan to run it at 5TeV and then shut down around X-mas to get it ready for 7 TeV. I'd say keep and eye on the Cern Courier and that blog but don't hold your breath. boredom - anticipation - frantic exhilaration, repeat  :-) —Preceding unsigned comment added by Lisa4edit (talkcontribs) 22:28, 28 April 2008 (UTC) oops--Lisa4edit (talk) 22:30, 28 April 2008 (UTC)

Helium: Lewis Structure[edit]

Hello. Why are helium's valence electrons paired to the right in the Lewis dot diagram? Can helium's valence electrons be paired to the top? Thanks in advance. P.S. May you please name some ionic compounds in which carbon is a cation? --Mayfare (talk) 22:50, 28 April 2008 (UTC)

I vaguely remember there's a rule about where the pair goes, but you'll rarely find a high school teacher and never find a professor and/or chemist who actually cares. The point is that there are two valence electrons in the same orbital, so as long as that's clear...As for carbon being a cation, there is the general class of molecules called carbocations. Most of these that you find in chemistry are merely reactive intermediates, but some can be isolated, especially certain aromatic carbocations, such as many salts cotaining tropylium. Someguy1221 (talk) 23:00, 28 April 2008 (UTC)
Lewis diagrams are a useful tool, but they are a tremendous simplification of very complicated physics. Like someguy said, the important thing is displaying the number of valence electrons. Their position on the atom is irrelevant, since the electrons are in constant motion. Also, due to the uncertainty principle their location is best described as a cloud of probability density. Finally, if you just rotate the atom in your lewis diagram 90 degrees, then their paired on the top. --Shaggorama (talk) 06:48, 1 May 2008 (UTC)

Aurora borealis from space?[edit]

Is this photo (from WikiCommons) real or fake? According to its deletion request page, it cannot be real because of the location of the sun and where the aurora seems to be over. Kreachure (talk) 23:18, 28 April 2008 (UTC)

According to the info sheet it was taken from Atlantis. Maybe you could ask NASA for more details (http://www.nasa.gov/help/contact/index.html). Science photos are often "enhanced" to show details or make a point. There was quite a bit of shouting back and forth about red tints in photos of some planets while back. There are instruments/cameras that collect "image data" outside of the human visual spectrum. If you assign a color we can see to that information and overlay it over a visual spectrum image that would not be a "fake", but humans would not get the same image if they looked at it. --Lisa4edit (talk) 00:34, 29 April 2008 (UTC)

The thing is that the image has a delete proposal because it's not certain that it's from NASA. I was expecting aid that didn't involve contacting a U.S. government agency :P. Their contact page says that they're not too worried about answering inquiries such as this one; so maybe someone here can help? Kreachure (talk) 15:03, 29 April 2008 (UTC)

I'll see if my astronomer can help out, but that will take a while and he may not be able to say anything definitive. Meanwhile since NASA is up to it's usual "impressive efficiency" because they have to shovel all their "leadership", you might have more luck e-mailing these guys with your picture and question: editors@SkyandTelescope.com I've met a couple and they are nice folks and helpful. Just tell the deletomanicas to hold their horses. --Lisa4edit (talk) 22:07, 29 April 2008 (UTC)

Follow the "see also" link from the deletion request page and you'll see a message from NASA saying why the picture must be a composite. The aurora is too bright, the wrong color, and probably in the wrong place. --Anonymous, 00:22 UTC, April 30, 2008.

Well, apparently NASA did send a response. (I'm impressed ;-) I think there is a way to move the image to your user page. That way it would not be "lost". Since NASA confirmed it to be a composite why not label it as such. With a title like "artist rendering of an aurora viewed from space" or "composite modeling aurora effects above the atmosphere" people would know what it is. I don't think you'll be able to put it back into commons until you've found the "copyright owner" though. BTW it might well not be NASA but ESA or one of the others. --Lisa4edit (talk) 03:59, 30 April 2008 (UTC)