Wikipedia:Reference desk/Archives/Science/2008 January 31

From Wikipedia, the free encyclopedia
Jump to: navigation, search
Science desk
< January 30 << Dec | January | Feb >> February 1 >
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.

January 31[edit]

Cause of gravity- what is it?[edit]

I was watching a tv program a few days ago where Dr Brian Cox (quantum physicist) first said gravity was due to the bending of spacetime as per Einsteins theory, but then said it was due to gravitons which haven't yet been seen. So which is it really--TreeSmiler (talk) 00:57, 31 January 2008 (UTC)

An experiment in the new supercollider is supposed to find proof of gravitons and strings. I thought it was supposed to already have taken place, but we would have heard about any proof or lack of proof found. Personally, I do not believe in gravitons in any way. It isn't a scientific theory based on experiment. It is just that there is nothing observed in gravity that requires gravitons. Therefore, I see no reason to assume that gravitons exist. -- kainaw 01:14, 31 January 2008 (UTC)
So you think its bent spacetime?--TreeSmiler (talk) 01:19, 31 January 2008 (UTC)
It's not so clear that the two things are different. Ideally a theory of quantum gravity would be something that describes gravity such that, when you look at it one way, it's an exchange of virtual gravitons, and when you look at it another way, it's curvature in the metric tensor. As far as I know, no one has yet come up with anything very satisfactory along those lines, but that's what I think physicists want. --Trovatore (talk) 01:24, 31 January 2008 (UTC)
This is like asking whether a zebra is black with white stripes or white with black stripes. When the electrons in an antenna wiggle back and forth in response to a passing radio wave, is this because they are responding to oscillations in the electromagnetic field or because they are interacting with a stream of photons ? It's both - these are just two different descriptions or models of the same physical phenomena. In the same way, you can describe gravitational force as a bending of spacetime or as an exchange of gravitons. For almost all purposes the bending of spacetime model is adequate and simpler to use (in fact, for many purposes, the "force at a distance" model of Newtonian gravity is adequate and simpler still). It's only when you are looking at very high energy densities and very small scales that the behaviour and interaction of individual gravitons becomes significant. This is when you need a consistent theory of quantum gravity (which we don't yet have). Gandalf61 (talk) 10:46, 31 January 2008 (UTC)
  • Switching from physics to zoology, if you look at how the stripes end you can see that zebras are white with black stripes. Sorry, couldn't resist. --Anon, 07:30 UTC, February 1, 2008.
Unfortunately for the theory, gravitons (unlike photons) have yet to be detected. Why is that?--TreeSmiler (talk) 13:50, 31 January 2008 (UTC)
Perhaps because we don't have the right instruments, or the right experimental setup, or perhaps because they don't exist. No firm answer for this can be given. You may be interested in reading about the Higgs boson, a theorized particle with much wider acceptance than the graviton which is also still undetected. — Lomn 14:24, 31 January 2008 (UTC)
Our graviton article says that gravitons (if they exist) interact so rarely with matter that it would be very difficult (and perhaps impossible) to build a detector that could directly detect individual gravitons. I imagine this is connected with the fact that gravity is very much the weakest of the four fundamental forces. The best we can do with present day technology is to try to detect gravitational waves with experiments such as LIGO. Finding out more about the properties of gravitational waves might allow us to confirm or rule out the existence of gravitons. Gandalf61 (talk) 14:22, 31 January 2008 (UTC)
Hmm. If gravitons dont interact with matter much, how can they be responsible for the effect of gravity. Yes I believe LIGO has had no success either. So if gravity waves dont exist either, what then?--TreeSmiler (talk) 16:13, 31 January 2008 (UTC)
Gravitons don't need to interact much with matter because gravity is very very very weak compared to the other fundamental forces. If gravity were as strong as the electromagnetic force then anything with a mass more than a few grammes would collapse into a tiny ball of neutronium under its own self-attraction.
We know, indirectly, that gravitational waves exist because the orbital decay curve of certain binary star systems can only be explained if the system is radiating gravitational energy in accordance with the predictions of general relativity - see binary pulsar and Hulse-Taylor binary. What we haven't done yet is detect a specific gravitational wave event. An analogy is that you know someone is raiding your fridge if food goes missing, even if you haven't caught the culprit in the act. Gandalf61 (talk) 16:48, 31 January 2008 (UTC)
So if its invisible gravitons and gravity waves, how does space time get bent by these?--TreeSmiler (talk) 02:00, 1 February 2008 (UTC)
A gravitational wave doesn't cause the bending of spacetime, it is the bending of spacetime. An analogy is that a water wave doesn't cause a disturbance in the water, it is the disturbance in the water. A water wave is a time-dependent change in the water level, and a gravitational wave is a time-dependent change in the curvature of spacetime.
Gravitons are an alternative view or model of the same thing - when a particle of matter interacts with a passing graviton, it behaves as if the curvature of spacetime in its vicinity had changed. The problem with most versions of the graviton model is that gravitons also interact with other gravitons, giving rise to runaway calculations that lead to "infinities".
I realise this is all a bit vague, and answers that describe gravitational waves and gravitons as if they were water waves and tiny ball bearings are bound to be incomplete and inaccurate at some level. To get the real McCoy you have to get into the advanced mathematics of Riemannian geometry, general relativity and quantum field theory, which is a long and difficult journey. Gandalf61 (talk) 10:15, 1 February 2008 (UTC)
Yes but we can see the so called bending of space time by the orbits of moons and planets and by gravitational lensing, but we cant see either the gravitational waves, or the gravitons that 'cause'it. Is that what you are saying? Hmmm!--TreeSmiler (talk) 17:52, 1 February 2008 (UTC)

I must point out that gravitons are entirely hypothetical. They are no more factual than tachyons, in the sense that they don't violate any scientific laws, but don't necessarily exist. Einstien's theory of general relativity covers why gravity occurs. In short, objects with mass make dents in space-time. The more massive the object, the larger the dent is. The larger the dent, the larger the effect of gravity is. (talk) 17:09, 1 February 2008 (UTC)

Gravitons are indeed hypothetical, but they seem to a hypothesis with a high degree of necessity. We know for certain that general relativity is not the last word on the subject of gravity, because it is an entirely classical (i.e. non-quantum) theory. Some form of graviton is a key component of each of the currently proposed flavours of quantum gravity, AFAIK. Our quantum gravity article says: "If the graviton turns out not to exist, it will render all work based on quantized macroscopic physics flawed, and destroy virtually all the accepted notions of a unified theory of physics since the 1970s". Gandalf61 (talk) 17:55, 1 February 2008 (UTC)
So gravitons are to gravity, what photons are to light (em radiation). And gravity waves are to gravity, what em waves are to em radiation. BUT gravity waves are so weak and feeble, and gravitons are so rare, that we have difficulty in detecting either of them? Is that right?--TreeSmiler (talk) 18:02, 1 February 2008 (UTC)
Yes, I would say you have got it right. One minor correction - it is not the gravitons themselves that are rare, it is their interactions with matter (which is the only way we can detect them directly) that are rare. In physics-speak we say that gravitons have a very low cross section. Gandalf61 (talk) 09:11, 2 February 2008 (UTC)

Quantum Physics[edit]

I have an equation here in which I am having a very hard time getting both sides of the equation to equate to one another. The answers I have been getting are radically different where they should equate. This equation is supposed to relate the radius of a quantum dot to the frequency of light it emmits. I ordered this kit from Cenco Physics so I assume all of the values are correct. It would be great if someone could point out how to get the sides to equate. (Please include steps).

In which:

Dirac's constant


Planck's constant


speed of light in vacuum

For clarity:




Zrs 12 (talk) 01:41, 31 January 2008 (UTC)

It seem to comes out about right with n=1. I get about 3.3×10−19 J on each side using Google Calculator. I'm not sure how to break this down into steps; you just regularize the units and then do the arithmetic. Maybe you're missing a unit conversion factor somewhere? -- BenRG (talk) 20:09, 31 January 2008 (UTC)
Thanks. What units did you have to convert, though? I have just been plugging the values in as are (which is probably the problem). Zrs 12 (talk) 20:27, 31 January 2008 (UTC)
For one thing, if you're going to use J and kg, to be consistent you'll need to use m for the radius, not nm as listed. Also, make sure you use m/s units for c, and J s units instead of eV s for h and . MrRedact (talk) 05:52, 1 February 2008 (UTC)
Oh O.K. thanks. I bet that solves the problem I've been having. Zrs 12 (talk) 14:06, 1 February 2008 (UTC)

Songs written by drummers[edit]

Why is it that songs written by drummers tend to be worse than songs written by a band's singer or musicians, anyone else in the band in other words? I know that there's been exceptions but more often than not, it seems like the tracks I often end up skipping on albums have been filler tracks written by the drummer. —Preceding unsigned comment added by (talk) 02:28, 31 January 2008 (UTC)

There is a stereotype, of course, that drummers are stupider or less musical than the rest of the band members. I've no idea if there's any truth to that but of course there are a lot of notable exceptions. It could be that they've never been the centerpiece of the band and so have less experience with writing songs than the other members. Who knows. It might just be that the bands you listen to have drummers who are bad songwriters. -- (talk) 02:54, 31 January 2008 (UTC)
I've also heard that drummers tend to be more explosive. Meanwhile, Phil Collins seems to be an argument against 81.77's theory.
Atlant (talk) 13:02, 31 January 2008 (UTC)
As is Don Henley and others. Though they are, of course, the very notable exceptions to the general rule, I think, that drummers aren't the real songwriters behind the band. -- (talk) 14:30, 31 January 2008 (UTC)
Hmmm. This isn't really a scientific question, is it? At least not in the way that "Who the hell decided that making the drums sound like they were made out of rubber and wet cardboard on songs produced in the 80s was somehow cool?" is... ;) —Preceding unsigned comment added by Kurt Shaped Box (talkcontribs) 01:40, 1 February 2008 (UTC)
Our article on The Yardbirds says that their drummer, Jim McCarty, was involved with the song writing.
Atlant (talk) 13:16, 2 February 2008 (UTC)
Old joke: "What do you call a guy who likes to hang around with musicians but can't play anything? A drummer". Gzuckier (talk) 19:27, 6 February 2008 (UTC)

Shower mold[edit]

What are the common species of shower mold? I am most interested in the "orange, very hard to scrub off but not rust" variety. Also can one identify molds at home? -Ravedave (talk) 02:30, 31 January 2008 (UTC)

In the U.S., both Home Depot and Lowe's sell mold detection packages that you mail in and a lab sends back a mold identification. You can do specific samples or a basic air sample. -- kainaw 02:33, 31 January 2008 (UTC)
Really? Wow. I might have to grab some of them to test my friends. SGGH speak! 11:22, 31 January 2008 (UTC)
All of our home supply stores have them in the air filter section. It is a little pack with a petri dish, instructions, and an envelope to mail it to the lab. -- kainaw 15:23, 31 January 2008 (UTC)
Your friends are molds? Clarityfiend (talk) 20:58, 31 January 2008 (UTC)
Maybe he's just not sure if his guy friends are fun or not...Tuckerekcut (talk) 22:19, 1 February 2008 (UTC)
There aren't a lot of red/orange molds that I know of; might be Neurospora crassa. That's a tough customer.Gzuckier (talk) 19:28, 6 February 2008 (UTC)

minerals and rocks[edit]

A____________is a mixture of solid particales called grains. —Preceding unsigned comment added by (talk) 04:42, 31 January 2008 (UTC)

Rule #2 above: "The reference desk will not give you answers for your homework", and this looks like a homework question to me. -- HiEv 04:59, 31 January 2008 (UTC)
I think we can bend the rules here, the answer is granola Mad031683 (talk) 20:29, 31 January 2008 (UTC)
I assume the "grain" here is part of the etyomogy of the word "granola"? That doesn't make any sense though, because then "villain"→"vanola", yet vanilla-white is the color of the good guy, not the villain. I knew there's a reason I went into science not language-arts. DMacks (talk) 20:36, 31 January 2008 (UTC)
bit too keen to say 'homework' above I think - could be a crossword clue.. How about "granular agglomerate".
I the original questioner could give us a little more context to the question a better answer might develope. The answer could be 'sandstone' for example? (talk) 20:44, 31 January 2008 (UTC)
Context would indeed help. Clastic rock could be the answer tho'. DuncanHill (talk) 01:29, 1 February 2008 (UTC)
A granular mixture of particles is a mixture of solid particles called grains. − Twas Now ( talkcontribse-mail ) 02:26, 2 February 2008 (UTC)
breakfast cereal? Gzuckier (talk) 19:29, 6 February 2008 (UTC)

Sick again[edit]

In instances where I've gotten a cold from a friend or vice versa, I've found that increased exposure to said friend can result in a sort of relapse of sickness when I'm starting to get better. This has happened more than a few times, despite people telling me that this is not very likely and that I probably got sick from something or someone else. What's the scoop? What's the likelihood of this sort of thing happening? — Ƶ§œš¹ [aɪm ˈfɻɛ̃ⁿdˡi] 05:20, 31 January 2008 (UTC)

This is very close to the "Don't ask or give medical advice rule" but you don't seem to asking anything specific. What I'd wager is that you are giving your cold to your friend, and due to the virus' ability to mutate quickly it is mutating within his system to the point where your immune system is unable to defend against it well, causing you to catch the cold off him again. TheGreatZorko (talk) 08:42, 31 January 2008 (UTC)
It doesn't need to involve mutation. There are lots of different viruses that cause colds, and you can be getting over one of them when you catch another from your friend. - Nunh-huh 18:43, 1 February 2008 (UTC)
Absolutely. We tend to think of pure cultures, like in bio labs, but in fact in nature nothing is pure, every culture is a mixture of strains and species. If you culture somebody with the flu or a cold, there will be plenty of other organisms enjoying the free ride, in addition to the main infection; and the main infecting organism often changes with time, as when a bacterial infection like pneumonia arises from a viral infection like the flu.Gzuckier (talk) 19:31, 6 February 2008 (UTC)


What would make a star change colors rapidly?-- (talk) 14:01, 31 January 2008 (UTC)Tyler J Long

I think you mean "astronomy" rather than "astrology" in the title. Viewed from Earth, a twinkling star (which can appear to change color) is exhibiting scintillation. A star like the sun can, over a long period, exhibit color changes as a function of surface temperature as outlined in stellar evolution. Finally, a nova or supernova can result in a sudden massive change in a star's appearance, color included. If, on the other hand, you really did mean "astrology", changes can be explained by anything you choose. — Lomn 14:21, 31 January 2008 (UTC)
(ec) Usually the apparent colour of a star depends on its surface temperature (the spectrum of a star is very close to that of an ideal blackbody). Our article on stellar classification delves into this in some detail.
Changes in apparent colour come about in a number of different ways. Our article on variable stars is extremely thorough. Depending on what you mean by 'rapidly', there are processes that act on timescales anywhere from minutes to years. (All might be considered 'rapid' on astronomical timescales.) TenOfAllTrades(talk) 14:27, 31 January 2008 (UTC)
Though they are not stars, some of our neighbor planets appear as stars from Earth. One of the main differences between them and stars when viewed with the naked eye is that the planets twinkle more and sometimes appear to change color. -- kainaw 15:29, 31 January 2008 (UTC)
Um, planets don't twinkle anywhere near as much as stars do. That's a good way to tell they're planets. I can't find a reference for that in Wikipedia, but if it's a clear night where you are you can see for yourself. --Milkbreath (talk) 16:35, 31 January 2008 (UTC)
Phil Plait to the rescue—here's a reference on planetary twinkling: [1]. TenOfAllTrades(talk) 17:18, 31 January 2008 (UTC)
I was typing one thing and thinking another completely. My point was that the planets appear as steady stars - no color change. This would make the stars that twinkle seem odd in comparison. But, since the planets aren't stars, the twinkling stars are normal. But, I typed the exact opposite. In my defense, I'm at home today taking care of a 13-month old with molars coming in. It is difficult to think when a baby is screaming non-stop all day. -- kainaw 18:39, 31 January 2008 (UTC)
I figured it must be something like that—pack of rabid wolves trying to get in, killer bee attack, arterial bleeding, squalling baby.... Just wanted to keep things straight for the questioner. --Milkbreath (talk) 19:03, 31 January 2008 (UTC)


carried by cats that changes mouse brain —Preceding unsigned comment added by (talk) 20:45, 31 January 2008 (UTC)

Toxoplasma gondii (not a virus). Сасусlе 21:50, 31 January 2008 (UTC)

Square drums[edit]

Why are drums round, rather than square? --Carnildo (talk) 21:19, 31 January 2008 (UTC)

I would imagine it is so that they give the same sound at equal distances from the central point, and so that the skin isn't stretched too tight at corners and things. A square has four corners which are points of weakness. It could also be for acoustic reasons. -mattbuck 21:28, 31 January 2008 (UTC)
Also, I'd say from the constructional point of view - a round drum will be stronger than a cubical drum made of similar materials. I think. --Ouro (blah blah) 21:40, 31 January 2008 (UTC)
Sometimes, they are hexagonal.  ;-) --LarryMac | Talk 21:50, 31 January 2008 (UTC)
...or octagonal. -- (talk) 22:59, 31 January 2008 (UTC)
Mathematics has gone a long way. Try to read hearing the shape of a drum article. Cheers, --Dr Dima (talk) 08:27, 1 February 2008 (UTC)
There's also the traditional element - drums used to be made by stretching skin over pots or wooden bowls, which are much easier to make round (using a pottery wheel or lathe) than square. Laïka 09:44, 1 February 2008 (UTC)
One argument *for* using square drums would be that it would enable the drummer to more easily count to four without error. All you'd need then is some method of stopping him soloing inappropriately and a bucket to catch the drool.
Ahhh. What would a drum-related thread be like without at least one drummer skit? ;) --Kurt Shaped Box (talk) 13:29, 1 February 2008 (UTC)
  1. Stress risers.
  2. a circle has one resonant frequency due to uniformity of dimension, a square has a few since the diagonal is a different length from side to side, for instance.Gzuckier (talk) 19:32, 6 February 2008 (UTC)

carbon dioxide[edit]

Why cant we just put up a bunch of carbondioxide filter things and use the carbon they filter to make carbon fiber then put that carbon fiber on cars making them lighter and more fuel effitiont or houses or what ever? —Preceding unsigned comment added by (talk) 21:54, 31 January 2008 (UTC)

In a word, expense. Filtering carbon dioxide can be costly, and manufacturing carbon fiber is certainly costly. Even with increasing eco-friendly interests, the market won't support it. — Lomn 22:41, 31 January 2008 (UTC)
As you said, they would filter out carbon dioxide, which would require a lot of effort and expense to convert into carbon fiber. They are different compounds, not just easily interconvertable forms of the element "carbon". DMacks (talk) 22:48, 31 January 2008 (UTC)
And in particular, converting carbon dioxide to carbon would consume more energy than was released by burning the oil, coal, gasoline, or whatever generated the carbon dioxide in the first place. -- (talk) 22:54, 31 January 2008 (UTC)
I've done a lot of contract work for a paper company that plants tons of carbon dioxide filters (trees) and turns them into paper (which is technically carbon-based and fibrous). Of course, one of the major byproducts of the process is production of carbon dioxide. -- kainaw 01:33, 1 February 2008 (UTC)
Beside, you don't make carbon fiber that way, you make it out of polyester fabric or some such which you then cook the hell out of until nothing is left but the carbon. Gzuckier (talk) 19:35, 6 February 2008 (UTC)

August eclipse times[edit]

Hi. I'm just wondering, when does partiality end for the following cities for the solar eclipse on August 1, 2008, local daylight savings time?

  • Rimouski, Quebec
  • Gaspé, Quebec
  • Fredricton, New Brunswick
  • Saint John, New Brunswick
  • Halifax, Nova Scotia
  • Yarmouth, Nova Scotia
  • Sydney, Nova Scotia
  • Charlottetown, Prince Edward Island

I don't want the times for totality, because totality will not even be occuring in those reigons. I think I might be able to find this, so so far my searches with Yoursky have made the sun and moon too big, but perhaps I can find it eventually. I realize that the eclipse ends at sunrise for some of these places, so don't give me a time without mentioning that it ends before sunrise if that is the case, but I wish to know when the edge of the moon completely leaves the sun in these places. Also, if possible, try to include the elevation (altitude) of the sun at these times, but this is not nessecary because if you can give me a time, I could look up the coordinates and input the time on Yoursky. Thanks. ~AH1(TCU) 23:15, 31 January 2008 (UTC)

Fred Espenak at NASA maintains a great set of pages about eclipses. This PDF file contains all sorts of details about the eclipse. On PDF page 42 (page 34 as marked on the page), Table 9 contains contact times for various points in Canada, including five of the eight places on your list. In all five places the eclipse begins before sunrise and reaches maximum extent before sunrise, but does not end before sunrise. The specific time you're asking about is called "fourth contact". The table gives it only given in UT; I'll convert them to local time myself, but you should check the original document to make sure I haven't miscopied from it. I'll add Chicoutimi, the nearest place they give to Rimouski, which you asked about. I assume it's on Eastern Time, unlike all the other places listed here.
     Chicoutimi ....... 09:34:25.0 UTC (05:34:25.0 EDT) altitude 2°
     Charlottetown .... 09:26:01.3 UTC (06:26:01.3 ADT) altitude 4°
     Fredericton ...... 09:27:28.5 UTC (06:27:28.5 ADT) altitude 2°
     Halifax .......... 09:22:59.2 UTC (06:22:59.2 ADT) altitude 3°
     Saint John ....... 09:25:45.0 UTC (06:25:45.0 ADT) altitude 2°
     Sydney ........... 09:24:17.3 UTC (06:24:17.3 ADT) altitude 6°
Now look at Figure 2 on PDF page 55 (page 47 as marked). You might want to enlarge it to see the relevant region more easily. Clearly, the further northeast you are in this region, the more of the eclipse you see (weather permitting) time-wise, and the further northwest you are, the greater the fraction of the sun that is eclipsed. So if the weather is clear everywhere, Gaspe would be the best choice of the places you mentioned.
--Anonymous, 00:28 UTC, February 1, 2008.