Wikipedia:Reference desk/Archives/Science/2006 July 20

Humanities Science Mathematics Computing/IT Language Miscellaneous Archives

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Spliting The Atom

Has anyone tried to split other atoms, and would the yield of energy be worth it?

Er, confusing question? I guess if splitting other materials than uranium and what-have-you wouldn't be worth it, or we'd have tried it already. On the other hand, we have such an incredible desire to a'splode the universe in the name of science. :P Vitriol 00:58, 20 July 2006 (UTC)

It depends what you mean by "other atoms" and what you mean by "split the atom". If you mean nuclear fission, there are a number of isotopes which can be subjected to fission by means of slow neutrons. The Curve of binding energy is probably relevant reading here. Elements at the low end of the curve can be fused together to get energy, and elements at the high end of the curve can be fissioned. Things toward the middle can't do anything (i.e. iron). --Fastfission 01:54, 20 July 2006 (UTC)

Yeah I was asking if anything smaller than uranium had been fissioned also has any other elements besides hydrogen been fused together?

I'll fission YOU !! Vitriol 06:14, 20 July 2006 (UTC)

Definately. For an easy to think of example, take Carbon-14, whose nucleus degrades on its own. We use Uranium and Plutoniom because they have a much shorter half-life. As for fussion, the article Nuclear fusion seems to say that you can fuse other elements, but that only the small ones do so exothermically. registrar

Nuclear decay is not the same thing as fission—a nucleus ejecting a particle or two is not the same thing as it breaking into two pieces. Nothing smaller than uranium undergoes fission by slow neutrons, and only specific isotopes of uranium even do that. --Fastfission 14:42, 20 July 2006 (UTC)

Hydrogen fusion is not fission. Surprisingly. Philc _T^E_C^I 14:06, 23 July 2006 (UTC)

Thanks

Yes. o_o --Proficient 02:54, 22 July 2006 (UTC)

Integer Sorting using Pointers

Hello everyone, if you remember I had put up a question about bubble sort some time ago. Here is another problem I am encountering about sorting. The problem is from a book probably titled "Structured C programming", I dont remember the author. The problem is like follows: 10 Integers are to be taken from the user and stored in an array Now this array has to be sorted in ascending order, but without creating any new integer array.

The hint given is : use array of pointers. This array initially would hold the addresses of the integers in the order entered by the user. Now sorting would be done by changing the addresses held in the pointer array. That is, the the original array would not be manipulated, but the addresses held in the pointer array would be manipulated in ascending order. I hope I succeed in explaining the situation to you.

I have used the following code to do it, and I think the logic is correct, but its somehow not working. Can somebody help? - Nikhilthemacho

#include<stdio.h>
#include<conio.h>

void main()
{
int arr[]={10,44,12,99,66,84,45,59,128,1,27,33};
int i,j,n;
int *pasc[15],*pdsc[15],*porig[15];

clrscr();


printf("Original Series : \n");


for(i=0;i<10;i++)
{
porig[i]=&arr[i];
pasc[i]=&arr[i];
printf("\n(orig)Number %-3d : %-3d,address : %-7u || ",i+1,*porig[i],porig[i]);
}



for(i=0;i<n-1;i++)
for(j=i+1;j<n;j++)
{

if(  *pasc[i] > *pasc[j] )
{
pasc[i]=&arr[j];
pasc[j]=&arr[i];
}//end of if

}//end of j loop

printf("\n\nafter sorting:\n");
for(i=0;i<10;i++)
{

printf("\nNumber %-3d : %-3d,address : %-7u",i+1,*pasc[i],pasc[i]);
}

getch();
}//end of main

You need to be careful about what you sort.

#define N 12
	int *ptemp;

	for(i=0 ; i<N ; i++)
	{
		for(j=i+1 ; j<N ; j++)
		{

			if(*pasc[i] > *pasc[j])
			{
				ptemp=pasc[i];
				pasc[i]=pasc[j];
				pasc[j]=ptemp;
			}

		}
	}

Cheers, --Kjoonlee 05:29, 20 July 2006 (UTC)

I think thats wrong bcoz u r not using the "&" operator to get addresses of elements. Example, if you use ptemp=pasc[i], it wouldnt work, you will have to put it as ptemp=&pasc[i]. Secondly, here you have misunderstood the requirement of the problem. Here we dont have to sort the pointer array, but change the addresses stored in these pointers so that they point in ascending order. That is, the first pointer should point to the least , then next pointer to the next higher number. We dont have to sort the pointer array. Hope someone can fix this one. Bye - Nikhilthemacho

No. The & operator was previously used (pasc[i]=&arr[i];) to assign the addresses of elements. ptemp=pasc[i]; works because they were declared as int *ptemp; and int *pasc[];. I have tested the loop I quoted together with the whole program and I can tell you, it works.

The pointer array contains addresses; sorting the contents *is* sorting the addresses. --Kjoonlee 08:01, 20 July 2006 (UTC)

Whole source:

#include<stdio.h>
#define N 12

int main(void)
{
	int arr[]={10,44,12,99,66,84,45,59,128,1,27,33};
	int i, j;
	int *pasc[12], /* *pdsc[12],*/ *porig[12];
	int *ptemp;

	printf("Original series:\n");

	for(i=0 ; i<N ; i++)
	{
		porig[i]=&arr[i];
		pasc[i]=&arr[i];
		printf("Original number %-2d: %-3d, address: %-8p\n", i+1, *porig[i], porig[i]);
	}



	for(i=0 ; i<N-1; i++)
	{
		for(j=i+1 ; j<N ; j++)
		{

			if(*pasc[i] > *pasc[j])
			{
				ptemp=pasc[i];
				pasc[i]=pasc[j];
				pasc[j]=ptemp;
			}

		}
	}

	printf("\nSorted series:\n");

	for(i=0 ; i<N ; i++)
	{

		printf("Sorted   number %-2d: %-3d, address: %-8p\n", i+1, *pasc[i], pasc[i]);
	}

	//getchar();

	return 0;
}

Results, with Cygwin GCC:

Original series:
Original number 1 : 10 , address: 0x22ee90
Original number 2 : 44 , address: 0x22ee94
Original number 3 : 12 , address: 0x22ee98
Original number 4 : 99 , address: 0x22ee9c
Original number 5 : 66 , address: 0x22eea0
Original number 6 : 84 , address: 0x22eea4
Original number 7 : 45 , address: 0x22eea8
Original number 8 : 59 , address: 0x22eeac
Original number 9 : 128, address: 0x22eeb0
Original number 10: 1  , address: 0x22eeb4
Original number 11: 27 , address: 0x22eeb8
Original number 12: 33 , address: 0x22eebc

Sorted series:
Sorted   number 1 : 1  , address: 0x22eeb4
Sorted   number 2 : 10 , address: 0x22ee90
Sorted   number 3 : 12 , address: 0x22ee98
Sorted   number 4 : 27 , address: 0x22eeb8
Sorted   number 5 : 33 , address: 0x22eebc
Sorted   number 6 : 44 , address: 0x22ee94
Sorted   number 7 : 45 , address: 0x22eea8
Sorted   number 8 : 59 , address: 0x22eeac
Sorted   number 9 : 66 , address: 0x22eea0
Sorted   number 10: 84 , address: 0x22eea4
Sorted   number 11: 99 , address: 0x22ee9c
Sorted   number 12: 128, address: 0x22eeb0

If you're unsatisfied with my solution or explanations, at least you know where to start from: n was uninitialized and the wrong things were being sorted. Also, you might want to overhaul the code to eliminate *porig[]. --Kjoonlee 09:07, 20 July 2006 (UTC)

Well kjonlee, thanx for attempting it. And definitely you have got the answer. But the requirement has been bypassed. I will try to explain it to you again. See, when you are sorting the "pointer array", you are actually changing the order of the "elements" of the "pointer array". But the program requires that the "addresses" to which the pointers are pointing should be swapped. Example: consider three integers array int arr[]={55,2,87}. Consider int *parr[]. Now, parr[1] would contain address of arr[1]. parr[2] would have address of arr[2], and parr[3] of arr[3]. So after sorting, what should happen is that parr[1] should have address of arr[2], parr[2] of arr[1], and parr[3] of arr[3]. Hope I have cleared this example this time.

COREX SYRUP

Que: After how many days or months or years will corex start showing its effects on kidney if taking in high quantities? And what are the other negative effects. Explain in detail . —Preceding unsigned comment added by 202.177.148.100 (talk • contribs)

Our article on Corex needs work. You may get a better idea by looking at its ingredients, chlorpheniramine maleate and codeine phosphate. - Nunh-huh 04:41, 20 July 2006 (UTC)

Please consult a doctor if you are concerned. Because Wikipedia can be edited by anyone, and changed maliciously, you should never use it as a source of medical information. Notinasnaid 09:33, 20 July 2006 (UTC)

Integration!

Why there is a need of integration when Addition is there and wat integration do the same as simple addition?

My question is wat is the basic purpose of integration ?? and in it is most commonly used(i mean in which field)?

To do the mathematical function. That's like asking "what is the purpose of addition". It's commonly used in any field requiring calculus. — Lomn | Talk 05:26, 20 July 2006 (UTC)

A common example is that you have a function that you can graph which shows how a rate changes with time, for example, you might have a record of how fast a car was moving over a period of an hour. If you integrate the rate over some period of time, you find the cumulative effect at the end of the time. For example, if you integrate the speed of the car over the hour that you have a record for, you find out how far the car moved during the hour. Integration is also often thought of as finding the area under a curve. Gerry Ashton 05:41, 20 July 2006 (UTC)

Integration is another form of addition. It is used where you need to add the data which changes continuously. Say you want to find out the area of a circle. One way is to devide the circle into small strips, find out the area of each strip (each strip resembles a rectangle. Smaller is the width of the strip, better is the approximation) and add the areas of all strips to get the total area. With integration, you can do it in one shot. You integrate the area of one strip with the curve (the circle in this case) as the limits. See Integral --Wikicheng 07:19, 20 July 2006 (UTC)

In many ways, integration isn't used in real life (i.e., engineering). Structures are too complex to develop a solvable equation. Instead, numerical computing methods are used like FEA. Basically, the problem is chopped into little tiny pieces which are easily calculated and then summed. This is iterated to come to a solution approaching the real solution. Calculus is still, generally, required to develop the math to use FEA, but once you're working in the field, you don't have to do integrals any more. —Bradley 15:42, 20 July 2006 (UTC)

Air to water

When I enter a swimming pool, the water at first feels cold, unless it is heated, then it feels warm. Is there any possible water temperature relative to air temperature that would make the water seem devoid of temperature change? Hyenaste ^(tell) 05:23, 20 July 2006 (UTC)

I think it has more to do with skin temperature v/v water temperature, rather than air temperature v/v water temperature. Spending time in the water cools your skin temperature, which makes the air seem warmer when you get out of the water.--Anchoress 06:06, 20 July 2006 (UTC)

You can test this for yourself by slowly adding hot water to a bowl of cold water and testing it with your hand. As Anchoress says, it's all to do with skin temperature. Assuming your hand is warm, i.e. just below blood temperature, you will cease to feel a sensation of hotness or coldness when the water reaches the same temperature as your hand. Other parts of your body will respond at different temperatures depending how warm they are in turn.--Shantavira 06:53, 20 July 2006 (UTC)

Water conducts heat better than air. So when you enter water with a temperature below body temperature it will feel cool. After a while the water around you will heat up - there would be a thin layer of slightly warmer water. Unless you start moving around, but even then a (thinner) warm layer would 'stick' to your skin. I suppose that if the water were at body temperature it would at first feel 'neutral'. But then, pretty soon, the body would be presented with the problem it can't lose its heat, so you'd get pretty hot (and start sweating, but the sweat couldn't evaporate, aggravating the problem). DirkvdM 09:29, 20 July 2006 (UTC)

Although the point about water conducting heat better than air is important, the rest of the comment is somewhat misleading. Both water and air at or above body temperature will feel quite warm; the "neutral" temperature is the one, somewhat below body temperature, where the heat loss from the skin exactly balances the heat gain from metabolism; this will be closer to body temperature for water than for air, thanks to the better heat conduction of water, but for the same reason the margin will also be narrower. So it is possible to have water that feels neither warm nor cold at all, but you need to adjust the temperature carefully to make it so.

What makes the situation more complicated, as has been alluded to above, is that both the heat loss from the skin and the heat production from metabolism are variable. The human body reacts to cold by increasing its metabolic rate and by reducing blood flow to the skin, thus reducing heat loss; in a warm environment the reverse occurs. When you step into a swimming pool that is at the same temperature as the air, the leat loss will initially increase due to the better heat conduction of water, making it feel cold, but your body will soon adjust and the water will start feeling neither warm nor cold. To make the water feel neutral as soon as you step in, its temperature would have to be at just the point between air and body temperature to make the heat loss from your body to the water, even with the increased conductivity, exactly the same as from your body to air.

The layer of warm water around your body, mentioned above, does exist, but it's generally not very significant; even in a swimming pool, the water will normally be moving around enough that, even if you stay completely still yourself, the layer will nonetheless be quite quickly dispersed as it forms. Still, cold water does feel colder if it's flowing rather than still, as you may easily observe: just fill a cup with cold water from a tap, and hold one hand in the cup and the other under the running tap. You'll notice the the difference after a while.

Of course, as soon as you get out of the swimming pool, the water on your skin will immediately start evaporating, temporarily increasing the heat loss from your skin a lot, making you feel cold again. This will happen regardless of the water (or air) temperature, although it can actually be more noticeable if you're feeling a bit cold already. The movement of the air (wind, that is) does however have a significant effect here, since it not only increases the heat conduction but also the evaporation rate.

(Whoa, that was long.) —Ilmari Karonen (talk) 21:39, 20 July 2006 (UTC)

Jeez, that was a lot more complicated than I expected it would be. Thanks all for explaining. :) Hyenaste ^(tell) 22:15, 21 July 2006 (UTC)

Why when you are in front of a switched on fan you experience more cold?

Shouldn't it be otherwise, if a lot of particles hit you at high speeds? Thanks.

Evaporation of sweat takes energy because a liquid is changing into a gas. This energy comes from your body heat.Under still conditions the air near your body will become saturated with water vapour that has evaporated from your body, this slows down the rate of evaporation. A fan constantly blows a stream of relatively dry air at you, this speeds up evaporation and cools you down. Theresa Knott | Taste the Korn 06:31, 20 July 2006 (UTC)

See wind chill. Isopropyl 06:33, 20 July 2006 (UTC)

The speed of air flow has nothing to do with the speed of molecules. Molecules move chaotically with speeds about $v\sim {\sqrt {\frac {kT}{m}}}$, where $k$ is Boltzmann constant and $T$ is an absolute temperature (in Kelvins) (the strict formula depends on a type of gas). So, if the temperature is, say, 300K, the molecules' average speed is a few hundreds of m/s, whereas the speed of air flow is just a few m/s. And you experience more cold not because this particles stuff, but because air flow constantly blows off a thin layer of warm air (which is warm because your body heats is).--Ring0 06:46, 20 July 2006 (UTC)

It's the wind chill factor. Once, when standing on a windy cliff, I felt very cold. All I had left to put on was a thin plastic poncho. I put it on nevertheless and instantly felt warm. DirkvdM 09:47, 20 July 2006 (UTC)

Infinitely Variable Transmission

how does an infinitely variable transmission work?i hear there are model cars being developed that use IVTs,how do they work? —The preceding unsigned comment was added by Chiwaye (talk • contribs) 09:22, July 20, 2006 (UTC).

An IVT is an extension to a continuously variable transmission which allows forward as well as reverse gears. The article on CVTs should answer most of your questions - if you have any other questions after reading the article, feel free to come back here and ask again! — QuantumEleven 08:51, 20 July 2006 (UTC)

DAF's Variomatic (see the Dutch article for schematics) has been around since the late 1950's, so it is hardly something new. See the DAF Trucks article for some more info plus an image of the car. This transmission works the same both ways. So these cars go just as fast in reverse as they do forwards. In the Netherlands, there used to be a 'backwards driving' race for some years. Because the DAFs outraced all the other cars, they were put in a separate category. These cars were very small (easily mistaken for Ladas), but here, they were the formula one. :) DirkvdM 09:44, 20 July 2006 (UTC)

Music software (open source?)

Are there any free / open source softwares that converts a music into a score? For example I have a piano song, I put it into the software and the software inteprets it and produces a piano score? Thanks! —The preceding unsigned comment was added by 219.78.204.234 (talk • contribs) 10:29, July 20, 2006 (UTC).

In general, that sort of thing is very difficult to do, especially for a computer. If the song in question only has one instrument playing and is of high quality, then you might have a chance, but as soon as you have lyrics, percussion, or multiple instruments at the same time, there's not a chance, it's almost impossible to pick out the individual instruments. Do some Google searching and you'll find some programs that offer free trials (like this one), but I haven't personally used any of them, so I can't vouch for their performance. — QuantumEleven 08:48, 20 July 2006 (UTC)

If you mean music you play yourself and you have a midi keyboard (can be really cheap if you use it just for this purpose), it isn't quite that difficult to translate midi to musical score. Have a look at the Scorewriter article. The major problem is that musical notation puts the notes on the exact beat, which you don't (can't, but wouldn't want either). So you'd have to 'quantise' the recording (as it's called in Cubase), which shifts each note to the nearest beat. For this to work you need to play very 'dull' (on the beat) and specify the right grid for quantisation. But I suppose the software documentation will explain al that. DirkvdM 09:58, 20 July 2006 (UTC)

I don't know about open source, but if you are willing to pay for music notation software, Finale and Sibelius are in general the two professional standards (although others exist). —Mets501 (talk) 12:53, 20 July 2006 (UTC)

I think that there may be some misunderstanding - to the original poster, did you mean you have a song (eg as an MP3 file) which you wish to convert to a piano score, or can you play a song on a piano which you wish to convert to a score? In the latter case, you first need to connect a digital piano / keyboard to your PC with a MIDI interface - and I would imagine the MIDI interface card probably comes with some basic software. If not, go with Mets501's suggestion, or take a look at scorewriter, which has a list of software. — QuantumEleven 15:17, 20 July 2006 (UTC)

Plasma Cooling

What if we superheat hydrogen to get plasma and isolate the contents(protons and electrons) and individually particle accelerate 4 protons to just the right amount that they fuse(NOT collide),then would not we have had our first fusion reactor?

Hmm...if your design were to succeed, it would not be the first fusion reactor - see fusion power. There are many fusion reactors around the world already. When you "superheat" hydrogen, you are in fact "particle accelerating" all the protons and electrons, because heat is a measure of average kinetic energy - when things are very hot, everything is whizzing around fast; that is how current fusion reactors work. They heat up the gas until it is a hot plasma, and then the particles are going so fast that they sometimes collide and fuse. However, proton-proton fusion is not the main fusion reaction going on - that's the reaction that powers the sun, but the activation is too high for terrestrial reactors. Usually it is deuterium-tritium. Also, I'm not quite sure what you mean by fuse, but not collide. In order to fuse, they pretty much have to collide. As a side note, proton particle accelerators already have been made, for instance the Bevatron. --Bmk 13:35, 20 July 2006 (UTC)

Hmm... again... fusion without collision.. interesting, couldn't some form of tunneling work, on a very small scale system, bypass the activation energy completly, and never require physical contact. Is that what's being asked?--152.163.100.74 13:39, 20 July 2006 (UTC)

Even when tunneling through the coulomb barrier occurs, it's still a collision; it's just a collision that happens when the kinetic energy isn't high enough for the collision to occur classically. That could be what the anonymous fellow is suggesting, though. --Bmk 14:02, 20 July 2006 (UTC)

The Dust Bowl, man made?

Isn't it a bit far fetched to suggest that a natural climate condition could have been affected so quickly by human actions? A few farmers not plowing their land well enough isn't exactly going to affect a thousand year old cycle of climate change in the midwest, I mean it used to an inland sea, and now it's dry and arid, obviously there haven't been human beings living there the whole time doing it, so why attribute it to human actions? It seems like this was more of an excuse for FDR to get the federal government involved in the personal affairs of farmers, then a serious study. So the question, in light of current science, does FDR's theory of 'Over farming' still hold water?--Dusty Bowls 12:38, 20 July 2006 (UTC)

• True, a few farmers not plowing well won't do much. However, thousands upon thousands of farmers getting rid of vegetation that holds in the topsoil and then abandoning the land (since the drought came before the dust storms) is obviously going to lead to desertification or something like it. That combined with heavy winds is a recipe for disaster. I'm speculating wildly, but I think the farming was the straw that broke the camel's back. Besides, it's weather. Chaotic system, no? Butterfly in Peking, eh? Deltabeignet 13:22, 20 July 2006 (UTC)

You say "there haven't been human beings living there the whole time doing it", which is part of the answer. People come somewhere, find good soil, start using it, and then suddenly the soil disappears. How much of a coincidence it that? I don't know how long that soil has been there, but probably thousands of years (if not tens or hundreds of thosands of years). Then humans come along and a few decades later it's gone. Coincidence? DirkvdM 13:58, 20 July 2006 (UTC)

Maybe I'm missing something in your question, but the Dust Bowl article is very clear that it's a combination of natural forces and human effects; namely, a drought (natural) plus overfarming (human). I don't find it unreasonable at all that people could chew up the land quickly enough to exacerbate an otherwise natural condition. The original question, on the other hand, seems to work on the assumption that people caused the drought, but I just don't see that point of view appearing anywhere. — Lomn | Talk 14:24, 20 July 2006 (UTC)

Just for the record, there were plenty of humans in North America for millenia before the Dust Bowl. It was agriculture that was the novel factor. --Ginkgo100 ^{talk · contribs · e@} 19:37, 20 July 2006 (UTC)

Drought may or may not be something humans can cause (some have suggested that the Sahelian drought of the 70s and 80s was triggered by pollution from Europe), but the removal of vegetation can reduce transpiration, which generates a lot of rain locally. But poor farming practises can cause the dust storms - vegetation binds soil, which is why California has mudslides after fires. Prairie grasses have very extensive root systems - agriculture removes those root systems. The Dust Bowl would not have happened (or would not have been as severe) if the native grasslands had been intact. On the other hand, it wouldn't have happened either if there hadn't been a drought. Guettarda 14:51, 20 July 2006 (UTC)

nuclear physics

I would like to know, what a hindered transition means. For eg. 103Rh, which is an E3 transition.

The theoretical transition probablity / exptl gives the value ~400. Theoretical value is obtained by uisng the single particle estimate for E3 35(A^2)(E^7) s-1 and exptl value by using the relation ln 2/[(t1/2)(1+Tot. ICC)] Tot. ICC is the total intenal conversion coefficient.

So, what does this mean.

• I think it means you should do your own homework--152.163.100.74 13:35, 20 July 2006 (UTC)

I don't think this is homework, but it's way over my head.

• It does look like homework, but on second glance it doesn't seem to be asking for the answer, although this is probably PHD work, so also over my head--152.163.100.74 13:59, 20 July 2006 (UTC)

New computing reference desk

Well the title says it all really. This is to announcement that there is a new section of the reference desk devoted to software, hardware and computer science at Wikipedia:Reference desk/Computer so that those of you who want to can add it to their watchlists. if you want to comment on the wisdom/stupidity of the move please don't do it here do it here Theresa Knott | Taste the Korn 15:31, 20 July 2006 (UTC)

• I'm I the only one who thinks 'Tech Support' would make a better name for it? I mean that's what it is, isn't it--64.12.116.74 18:36, 20 July 2006 (UTC)

Woot! My Internet connection is slow and the Science Reference Desk takes ages to load; removing the computer questions (which I have no expertise to respond to) will improve things dramatically. Also, I think "Computer" is an appropriate name, as it is more consistent with the names of the other RDs -- they all refer to a broad subject, not a function. --Ginkgo100 ^{talk · contribs · e@} 19:40, 20 July 2006 (UTC)

Speaking of which, is anyone planning on archiving the reference desk again? ever? It hasn't been archived in weeks, the page length is a killer, even on a DSL--64.12.116.74 20:45, 20 July 2006 (UTC)

The bot which did the archiving (Crypticbot) is dead, and the one which replaced it (Werdnabot) isn't set up to archive the reference desks. --cesarb 16:14, 21 July 2006 (UTC)

Is anyone planning on writing an archiving script? I can do it if necessary. --Kainaw ^(talk) 17:32, 21 July 2006 (UTC)

I asked Werdna648 if Werdnabot could do something like this. I'm waiting for a reply. —Mets501 (talk) 17:43, 21 July 2006 (UTC)

Ophthalmology

I am getting an eye exam monday at 2:00, but I have a bike race at 6:00, and I was wondering how long it takes for the pupil dilation to wear off. AdamBiswanger1 17:28, 20 July 2006 (UTC)

You need to ask your Eye Doctor. My guess is it takes a long time, ask if you can wear dark glasses for the bike race.

It shouldn't last that long. The effect should wear off after an hour or two. (Don't try to drive yourself home from the appointment!) Ask your eye doctor, of course, to be certain. TenOfAllTrades(talk) 18:40, 20 July 2006 (UTC)

It depends on the drops used for the dilation. They have a wide variety of different durations of actions, so there is absolutely no way of predicting the duration until you know which ophthalmic preparation will be used. Those with shorter durations tend to be preferred, but you have to ask to be sure. - Nunh-huh 18:47, 20 July 2006 (UTC)

The reason they dilate your eyes is that they want to increase the size of your pupil in order to see your retina better and look for any disease/damage to your retina. There are now cameras that can get a good image of your retina without dilating your eye at all.[1] The best of these are digital so they can take both eyes in rapid succession and view the images instantly on a large computer screen.[2][3] Ask your eye doctor if he has the right camera to avoid needing to dilate your eyes. Johntex\^talk 21:25, 20 July 2006 (UTC)

I had mine dilated last week. It took me about three hours before i was able to see adequately outside (with sunglasses) and maybe 5 or 6 before i felt completely back to normal and was able to see in sunshine without sunglasses. It was a really sunny day, though. Rockpocket 21:52, 20 July 2006 (UTC)

Thanks for the input--From what you guys have told me, I'm just going to assume that I'll be able to see, but it won't be quite as comfortable as normal--If he dilates the pupil at all. AdamBiswanger1 12:58, 21 July 2006 (UTC)

Dell Vs Gateway Vs Mac Processors

I am in the process of purchasing a computer and have heard varous opinions about Dell, Gateway, and Mac. I wanted to compare the processors and the cost of the three to make my decision. If you have any information or could guide me in the right direction, I would appreciate the help.

They all use Intel processors. Dell does have a few AMD offerings, but not enough to be concerned about. Intel is Intel. You want a fast chip, dual-core if possible. --Kainaw ^(talk) 18:03, 20 July 2006 (UTC)

While Macs now use Intel processors, this is a fairly recent development. --ColourBurst 18:31, 20 July 2006 (UTC)

It depends largely on the components that are in the computer rather than the company. You might want to wait until Conroe becomes more widespread before you start buying a computer. I advise you to save money and build a computer yourself, as there are many tutorials online. --Proficient 02:59, 22 July 2006 (UTC)

Spectral Equivalent to the Sonic Boom Phenomena

Would there be a spectral equivalent to the sonic boom phenomena, if a vehicle could travel faster than the speed of light.

If so what would it look like, assuming you could see it and negating any physical limitations preventing you from seeing it.

See Cerenkov effect. TenOfAllTrades(talk) 18:39, 20 July 2006 (UTC)

Right - this phenomenon does occur when particles are travelling through a material faster than the speed of light in that material. Note though that the word "spectral" is not specific to or indicative of electromagnetic radiation.

So what would happen to the image of the vehicel travelling faster than the speed of light?

If you're talking about the speed of light in a vacuum, then it's very difficult to say. When special relativity is applied to superluminal speeds, it seems that matter travelling faster than light would travel back in time. I suppose that would look like the vehicle disappearing instantaneously! However, there are serious concerns with this being possible deriving from causality; if the vehicle travels back in time, it affects the future, and could therefore interfere with the event of going back in time, leading to a paradox. --Bmk 06:40, 21 July 2006 (UTC)

The Universe

Can someone answer this question very simply: Leaving aside spiritual ideas, which is more reasonable: (1) the universe goes on forever, or (2) the universe has borders? If scientists believe in situation (2), what is just past the borders? Please - serious answers only. 66.213.33.2 18:51, 20 July 2006 (UTC)

Both always struck me as being unreasonable but I don't see any other options. However if the universe has boarders there simply is no "just past the boarder". Theresa Knott | Taste the Korn 18:53, 20 July 2006 (UTC)

There is another option: The universe curls back in itself. So, if travel in what you feel is a straight line you will eventually end up back where you started. To simplify, imagine walking around the moon (I use the moon, because I want to ignore the issue of walking across oceans on Earth). You walk in a straight line and eventually walk all the way around the moon and end up at the same place. That is because your "straight line" was actually curved in a circle around the moon. Expanding this concept to space, the universe's three dimensions that we use to measure space could be curved around some extra-dimensional artifact into a big sphere. --Kainaw ^(talk) 19:22, 20 July 2006 (UTC)

The serious contenders are (1) an infinite universe (maybe the same as your number 1), and (2) a finite universe without boundary, as Kainaw described. There are some great popular books that discuss these, e.g., Brian Greene's The Fabric of the Cosmos. (Cj67 20:24, 20 July 2006 (UTC))

not an expert on this, but surely a universe with borders is the logical proposal? the universe would radiate outward from some point, with a radius of 4.5 billion light years? Xcomradex 22:46, 20 July 2006 (UTC)

Maybe there's a third choice? One that we haven't discovered yet. There are a lot of things we don't know. --Yanwen 02:48, 21 July 2006 (UTC)

Logic is not of much use here. I've never been able to conceptualise a universe that has borders (although there are plenty of boarders scattered throughout). If that were true, what's outside is "nothing", not even space. If you remove space from where it currently is, what's left? More space. I just can't get my head around the possibility of a spaceless void. Yet we're told this is a serious possibility. JackofOz 05:43, 21 July 2006 (UTC)

I would just like to add to Kainaw's response. The BOOMERANG project demonstrated that the curvature of the Universe is zero (it's flat). From this we know that the Universe could not curve back on itself in exactly the same way as a sphere as a sphere has a positive curvature. For the Universe to curve back on itself and maintain a zero curvature it would have to take on a toroidal shape (I'm not sure off the top of my head if there are other shapes that would suffice). Basically, if you can keep travelling in a straight line round the Universe and end up where you started it's because it's doughnut shaped!

Mine disaster survival

Astronauts in space survive for weeks, even months, breathing the same air over and over. Why can't the technology used to remove carbon dioxide from air be used in mining shafts? Is it too costly?

If you're talking about mine disasters, it is carbon monoxide, not carbon dioxide that is poisonous and causes problems. —Mets501 (talk) 20:05, 20 July 2006 (UTC)

No, what I think he's asking is.. if you get trapped in a mine with a car, and can't get your keys out of the ignition, how do you remove all the carbon monoxide... on a less sarcastic note, don't they usually have CO2 scrubbers in mines anyway?--64.12.116.74 20:18, 20 July 2006 (UTC)

Z machine

Where did the name come from?--64.12.116.74 20:02, 20 July 2006 (UTC)

Have a look a bit further into the article. The passage that begins "It gets its name because..." is the one you're looking for. Cheers! TenOfAllTrades(talk) 20:17, 20 July 2006 (UTC)

Ok, I feel silly--64.12.116.74 20:19, 20 July 2006 (UTC)

Horse Fly

As a kid I got bitten whilst fishing by an insect which I commonly called a horsefly (UK). It was quite large - substantially bigger than a mosquito and had a long proboscis which folded under its body with a joint, like an elbow. Over the last few days working I have been bitten repeatedly by what I now know is a horsefly - 'Tabanus'. What was I getting biten by as a child?

Colloquial terms can get quite confusing. That is why we have binomial nomenclature. Do you have any more description of the event? Where were you? Bibliomaniac15 00:34, 26 July 2006 (UTC)

Where do enzymes in Biological Washing Powder come from?

As my school biology teacher pointed out longer ago than I'd care to remember, enzymes are proteins and nobody (as far as I know) has synthesised a protein yet. So where do the enzymes come from?

Thanks. --62.253.52.155 20:50, 20 July 2006 (UTC)

(duplicate question removed). I can't fully answer your question, but the enzyme article says that biological detergents can be from one of (at least) four classes. One class, proteases, are produced in an extracellular form from bacteria, says the article. Likely many enzymes are extracted from or produced by bacteria. Digfarenough 21:07, 20 July 2006 (UTC)

A minor note—technology may have advanced a bit since you studied biology in high school, and the in vitro (in glass, as opposed to in vivo, in an organism) synthesis of short polypeptides is routine. Some small proteins can also be prepared this way. (Peptide synthesis has more information.) That said, the easiest way to create large quantities of a protein is to crank it out in bacteria as noted above. TenOfAllTrades(talk) 21:44, 20 July 2006 (UTC)

as far as i know, the enzymes are produced using genetic engineering. is generally far simpler to prepare proteins on a large scale by getting biology to make them for you. Xcomradex 22:52, 20 July 2006 (UTC)

How many planets in the solar system?

You're going to tell me that this depends upon how you define a planet.

Second question - how many 'things' (technical term) are there in solar system that it might be worth having a space staion on in the future, say at least 500 miles long in their longest dimension?

Thanks. --62.253.52.155 21:03, 20 July 2006 (UTC)

You already answered your first question. As for the second, all the traditional planets as well as many (but not most) moons exceed your requirements. It appears that only one of the noteworth asteroids, Ceres, that we have listed exceeds 500 miles in diameter. So that should be most of them. Digfarenough 21:13, 20 July 2006 (UTC)

Oops, 90377 Sedna is big enough as well. Digfarenough 21:14, 20 July 2006 (UTC)

So you didn't dig far enough the first time. :) DirkvdM 08:28, 21 July 2006 (UTC)

I'm not actually sure how many "traditional" planets there are nowerdays, as there seemed to be two different planets discovered at about the same time, and then some people are saying that Pluto should no longer be regarded as a planet.

(M u s t r e s i s t......the urge to say that its a pity that the tradition of naming planets after cartoon characters has not been continued with, as someone will report that the cartoon was named after the planet; and that the planet was named by a little english girl.)

Yep Pluto isn't a planet it's a Kuiper belt object. So that makes eight planets. Theresa Knott | Taste the Korn 22:05, 20 July 2006 (UTC)

Wheather or not Pluto and 2003 UB313, also known as "Xena," are planets is really a matter of personal opinion at this point. The International Astronomical Union's defintion of "planet" is due out this fall (probably September). Whatever they decide though, the controversey will most certainly not end. Personally, I don't really care because the term "planet" has virtually no scientific meaning. A more sensible (in my opinion) alternative would be to have different types of planets. For example, we could have the terrestrial planets (Mercury, Venus, Earth, and Mars), the Jovian planets (Jupiter, Saturn, Uranus, and Neptune), the trans-neptunian planets (Kuiper Belt objects such as Pluto, Xena, Sedna, Quaoar, etc.), and minor planets (which could include any of the asteroids larger enough to pull themselves into a roughly spherical shape like Ceres). All that is unlikely to happen though. Anyways, just had to insert my two cents worth :-) --Nebular110 22:22, 20 July 2006 (UTC)

Trivium: 'planet' literally means something like 'moving object' and referred to celestial objects that moved against the background of stars. So, originally, the Sun was called a planet (and Earth wasn't). DirkvdM 08:28, 21 July 2006 (UTC)

Definition of planet is a featured article - read it :). The definition I prefer is that it is a body massive enough to be sphereoid as a result of its own gravitational pull. Raul654 08:33, 21 July 2006 (UTC)

Yes, but that would include a lot of moons too, wouldn't it? — QuantumEleven 08:19, 25 July 2006 (UTC)

Well I don't know if it's true or not, but an astronomer friend told me that a joke among his colleagues says that the definition of our solar system is 'a star with one planet and a lot of space junk', due to the overbearing size of Jupiter in comparison to everything else in the system.--Anchoress 05:21, 25 July 2006 (UTC)

Isaac Asimov, among others, argued that Earth and its moon should be regarded as a double planet, rather than a planet and its moon--due to the fact that the gravitational attraction between the sun and the moon is stronger than the attraction between the moon and the earth, and apparently Earth's moon is the only "moon" in the solar system for which this is true. Chuck 20:35, 27 July 2006 (UTC)

Will our robots survive us?

Nothing lasts forever. At some time far in the future humans as a species will die out. By that time technology should have advanced enough to make the autonomous and concious robots of science fiction an everyday reality. Being non-biological, and cleverer than us, they should survive whatever it is that kills us. So they will live on as a kind of new robot species, while our human species has gone into history. Thanks. --62.253.52.155 20:57, 20 July 2006 (UTC)

• They're really not all that clever--64.12.116.74 22:53, 20 July 2006 (UTC)

The stuff of surviving intelligence will need to live on something that lasts longer, or can regenerate itself and pass on like genetic memory so the child knows what the parent knew. Look at where history is recorded. Not even carvings in stone survive the millenia. User:AlMac|^(talk) 05:19, 21 July 2006 (UTC)

Considering how much our technology has progressed in the last few decades and how much more time we will have to progress even further (milennia? millions of years?) it makes sense that hopes are high. But we haven't a clue how far away the target is (if we did we'd probably have the answer already :) ), so whether machines will ever become intelligent (whatever that is) is pretty much unanswerable. And our definition of 'intelligence' will probably change with that progress (most probably to exclude machine intelligence).

As for their survival of whatever kills us, that's would probably be the result of having a completely different physical basis, not so much their intelligence. But then, what do I know with my limited intelligence? DirkvdM 08:35, 21 July 2006 (UTC)

• This question was answered in 1952, in City (book by Clifford D. Simak). Notinasnaid 12:26, 21 July 2006 (UTC)

How could we make a robot thats cleverer than us? Philc _T^E_C^I 14:15, 23 July 2006 (UTC)

We've certainly got computers that are cleverer than us: chess programs can be cleverer than almost all chess players, while software that plays Reversi (also known as Othello IS cleverer at playing the game than all humans so far. And I consider software such as that implementing Arima to be cleverer than humans within its limited domain. Perhaps the Space shuttle could be looked on as a robot, as I understand that it would be impossibly difficult for a human to land it without computer help.

It would be interesting to see what happens when computers (incl. software) get clever enough to design other computers that are cleverer than they are.

They are not cleverer than us, they are just faster. For example reversi programs probably just consider all options and choose the best one based on what it was programmed to be the best one, probably the one which gains the most pieces. The chess program deep blue lost several times before eventually winning, and still lost the series 4-2, not what I would say is better than all humans. So far all computers are only capable of performing calculations that they have already be programmed to perform. No computers really learn anything. The closest they can come to learning is associating different inputs, and outputs. Thats why I think robots could not surpass us, because as far as I know, they can only apply set parameters and rules. They are not capable of original thinking. Philc _T^E_C^I 21:47, 23 July 2006 (UTC)

"Probably"? So, you don't actually know how the Reversi program works? Neither do I, since I've never heard of it before, but I know enough about the AI used in strategy games to know that that probably isn't how it works. Also, given the number of possible arrangements of pieces on an Othello board, even for an excellent computer it'd be fairly impractical to solve the problem with nothing but brute force. By "no computers really learn anything", I assume you ignore the major strides that have been made in recognition software of all kinds, for instance running empty neural nets through numerous examples of human speech until they adjust themselves to recognize words. No you don't actually, you mention "associating different inputs and outputs". In what way is that not learning? They evolve, from no other basis than an efficient general learning system and their own environment, optimal procedures to achieve a goal, and remember them for later use. Black Carrot 14:03, 24 July 2006 (UTC)

The problem is that we anthropomorphize computers far too much when you get into AI discussions. Yes, neural nets "learn", but they're also bound by programming. A computer programmed to evaluate the universe based on Newtonian mechanics can't spontaneously evolve Einsteinian relativity, it can only say "this is not correct." It is of paramount importance to remember and understand the differences in "learn", "adapt", and "evolve" as applied to human thinking and computer programming. — Lomn | Talk 14:50, 24 July 2006 (UTC)

Gulls vs. Humans

Summing up what's been said here recently - is this right?

Gulls:

Have better eyesight than humans Have better hearing than humans Have more efficient respiratory/circulatory systems than humans Have stronger immune systems than humans Have stronger bones than humans, size for size Can swallow more food than humans in one go Have faster reflexes than humans

Why is it then that gulls are not ruling the world?

Because they are bird brained. Theresa Knott | Taste the Korn 22:02, 20 July 2006 (UTC)

Cross the intellect, social nature and opposable digits of an African Grey Parrot with the toughness, predatory instinct and adaptability of a gull, wait a few million years and you might have a contender... --Kurt Shaped Box 22:44, 20 July 2006 (UTC)

Actually they did try a while back, but as their army marched on human civilisation someone threw a fish into the middle of it and they fell to squabbling amongst themselves. They've never tried again. DJ Clayworth 18:02, 21 July 2006 (UTC)

Because thats just about all they've got going for them. Humans:

are more intelligent

have better problem solving skills

have the ability to use tools

have a perception of groups, i.e. stick up for each other

have better spacial thinking

have digits perfected for multi-use

are pack hunters

thers blatently more, but I can't be bothered. hehe. Philc _T^E_C^I 14:14, 23 July 2006 (UTC)

How to make DIY ear plugs or ear protectors?

I have an incredibly noisy computer - it is almost as bad as sitting next to a vacuum cleaner. I've had it for four or five years, and I often work on it for 8+ hours a day.

I have begun to wonder if this long exposure could be damaging my hearing, as although I think I normally have good hearing, I've noticed that when it is very quiet, such as at night or when I wake up in the morning, I often hear a sort of white-noise in my ears. I wonder if this is the first signs of tinnatus (sp.?) and deafness.

Rather than paying out many pounds for ear protectors, which may be uncomfortable, or disposable ear-plugs, I am thinging about making my own ear plugs out of two very short pieces of wood dowel about 10 or 12 mm in diameter. Does anyone have any other suggestions please?

Thanks --62.253.52.130 22:15, 20 July 2006 (UTC)

Don't. Wood earplugs won't fit well enough to provide any hearing protection, and will damage your ears. Instead, try placing the computer in a noise-reducing box -- cardboard lined with packing foam should work. Make sure you include large vent slots in the box, and have a fan to keep the air circulating so the computer doesn't overheat. --Serie 23:10, 20 July 2006 (UTC)

Another option is to replace the fans with quiet ones. As noisy as he claims it is, cheap $3 fans will be quieter. I have to wonder if this is a server and not a 'personal' computer. Servers have a lot more fans and make a lot more noise and, by function, belong in a server room, not on a desk acting as a personal computer. But, I can't throw stones. I spent three years working in a server room full of noise. At least it was nice and cold. --Kainaw ^(talk) 23:27, 20 July 2006 (UTC)

Or none at all. There are fanless computers available now (Google is your friend!). I do not use one so cannot say anything about their usability or durability. But take care of your hearing, by the time you notice any damage it is too late, hearing damage is incremental and only increases with time.

You are probably right about wooden earplugs - one hears about people who pernamently damage their ears by sticking things in them, especially those little sticks with cotton on the end.

I have bought some proper earplugs (after shopping around found some half the price of the ones I'd first seen). Wearing just ear plugs doesnt remove all the noise, but wearing earplugs and ear-protectors (like ear muffs) does. It feels rather absurd to be wearing them, and makes my ears hot, but the white-noise sounds seem to have decreased.

I have just an ordinary computer, not a server. The computer model on display where I bought it seemed perfectly silent. It really is very noisy, and I'd appreciate any help on how to identify the particular replacement fan I need, and where to buy it by mail order, preferably in the UK.

Thanks.

Has it always been this noisy, or has it happened recently? I made a fool of myself when my work computer got upgraded by calling the maintenance man out because the fan was so noisy. Turned out I had a cable dangling into its path and just shifting it a bit would have solved the problem. Skittle 12:36, 24 July 2006 (UTC)

Open it up and listen while it's running - move your ear closer to the various component (being careful not to touch anything!) to try and identify where the sound is coming from. The most likely sources of noise are the fans (power supply, CPU and case - your PC may not have a case fan) and the hard disks, although the fans tend to prevail. When you identify the culprit, take a look at its specifications (CPU fans are designed for the CPU socket they're attached to, for instance) and shop around for a quieter one (manufacturers give noise ratings, these could be an indication). In the UK, try online shops like dabs.com. — QuantumEleven 08:17, 25 July 2006 (UTC)

Heart Attack

I am researching a novel in which a person with a weak heart, due to a serious heart attack in the past, is stalked by an assassin who injects a chemical into his bloodstream that would cause him to have another heart attack, killing him.

After reading the heart attack article, I have discovered that Antiplatelet drugs such as aspirin or Glyceryl trinitrate are used to treat heart attacks.

Then, in the platelet article, I discovered there are chemicals that (sometimes massively)stimulate the production of platelets such as Thrombin or Convulxin.

So, if a person with a weak heart was injected with platelet stimulating drugs, would it cause them to have a heart attack? Is that logic correct?

--69.138.61.168 22:24, 20 July 2006 (UTC)

think simpler, say ~100mg/kg potassium chloride would do the trick. Xcomradex 22:57, 20 July 2006 (UTC)

Assuming the person with a weak heart is taking blood thinners (which is normal), Viagra would lead to a much more interesting story. Note the commercial's disclaimer: "If you are taking blood thinners for high blood pressure or because you have had a heart attack, please consult your physician before trying Viagra." --Kainaw ^(talk) 23:30, 20 July 2006 (UTC)

How do you liquify Viagra? User:Zoe|^(talk) 02:34, 21 July 2006 (UTC)

Yes, I figure liquifying Viagra to the point that it would be injectable using a syringe would be quite hard, unless you simply forgot the pill and just used the active ingredient. Thanks for everyone's responses. --69.138.61.168 03:12, 21 July 2006 (UTC)

I don't see why Viagra would be any different than any other drug. Grind it down to a power. Put it in a spoon with some saline solution. Heat it up. If it is a torture situation, the long process adds to the suspense. --Kainaw ^(talk) 12:52, 21 July 2006 (UTC)

Looks like the victim will end up as a stiff (groan) Sum0 12:13, 22 July 2006 (UTC)

May I ask how the assassin plans on getting the poison into the victim's bloodstream? Is the victim hospitalized? Is the assassin going to restrain the victim and then place an intravenous line? (Just asking out of curiosity.) — Knowledge Seeker দ 05:27, 21 July 2006 (UTC)

Ooh - here's a good plot twist. Your hapless victim with a weak heart could also be quitting smoking, so he's on the patch. You could have your assasin lace a box of nicotine patches with some deadly chemical and switch them with the victim's patches, so the victim is slowly poisoned and ends up with a heart attack. --Bmk 14:52, 21 July 2006 (UTC)

• I've once seen a detective in which the victim got in a car accident. The ambulance doctor was his son and had a grudge against him, so he made the guy OD on his diabetes medication. I think that could work just as easily with Glyceryl trinitrate. - Mgm|^(talk) 20:23, 21 July 2006 (UTC)

Knowledge Seeker - the victim, since he has heart problems, will have a Port-a-Cath or other similar device implanted in his chest, of which the assassin is aware. --69.138.61.168 20:51, 26 July 2006 (UTC)

The Sun

If the sun's light takes 7 minutes to reach us than are we seeing the sun relative to when the light reached us? (are we seeing the 7 minutes behind?)

you are seeing the sun as it was 7 minutes ago (although i thought the number was 8 minutes). Xcomradex 23:00, 20 July 2006 (UTC)

And if the sun explodes you have approximately 8.31689813 minutes to live (the distance to the sun divided by the speed of light) —Mets501 (talk) 00:56, 21 July 2006 (UTC)

Well, there are two issues here. The image of the sun you see, such as (if you were using appropriate equipment) sunspots and such, are 8.3 minutes old. However, sunrise and sunset still occur at the same time, regardless of how long light takes to travel. This is because at sunrise, for instance, your part of the Earth is rotating into space that is already lit; that light left the sun 8.3 minutes ago, even though your part of the earth was not in line-of-sight at the time. If the speed of light suddenly became 10 times as slow, well, there would be all sorts of problems in physics that I wouldn't begin to understand, but that aside, you would still see sunrise and sunset at basically the same time, even though the light now took almost an hour and a half to reach earth. — Knowledge Seeker দ 05:12, 21 July 2006 (UTC)

Can I clarify what I think you mean, KS? At the moment the tip of the sun appears above the eastern horizon at sunrise, you're saying the sun is actually already "8.3 minutes" or about 2 degrees above the horizon. Likewise, at sunset, the moment the last bit of the sun sinks below the western horizon, the sun is already about 2 degrees below the horizon. Is that right? I don't really get what you mean by "sunrise and sunset still occur at the same time". JackofOz 05:28, 21 July 2006 (UTC)

Actually, Jack, that's not quite right. It's a very common fallacy; I believe it arise from the erroneous modeling of the sun orbiting the earth instead of vice versa. If the earth were stationary and the sun orbiting it, then you would be correct. At the instant you saw the first rays of the sun (ignoring atmospheric refraction, which causes sunrise to occur earlier and sunset later), you could in your mind trace the ray back, at the same 0° elevation, 1 AU back to the sun; the trip would have taken 8.3 minutes. Now fast-forwarding back to the present, as the ray travels 1 AU back to your eye, the sun continues to rise, and so it'd be two degrees above the horizon by the time you see it just rising. It seems logical, but it's not quite right. Instead think of the sun as stationary and the earth rotating 1 AU away. The sun is shining and the space all around is lit, with the exception of the shadow caused by the earth. You're in that shadow. At the instant you rotate out of the shadow, you rotate into a region where light is already present. Now at that instant, the sun is also exactly at 0°. If you rewound time back to when the ray of light left the sun, the earth would rotate backwards, and you'd find the beam of light originated when the sun was 2 degrees below the horizon. It doesn't really matter whether light travels instantaneously, very fast, or very slow. It could take a year to reach earth (ignoring earth's revolution around the sun) and this wouldn't change. Note that I'm ignoring some relativistic concerns, one of the most significant being that there is no such thing as "absolute time", so it doesn't make sense to talk about where the sun is at the same instant I'm seeing its rays here. Does this make sense? — Knowledge Seeker দ 05:51, 21 July 2006 (UTC)

No. :) That is, I don't follow your reasoning. But I get the impression you are talking about a difference between the light of the Sun versus the image of the Sun. The light of the Sun is always there, so how long it takes to get here doesn't matter for sunrise and sunset. I still can't visualise that difference between light and image, though. And I don't see how the Earth rotating around its axis or the Sun rotating around the Earth would make any difference. I'll have to think about this a bit more. DirkvdM 14:54, 21 July 2006 (UTC)

Ah, ok, I get it. Your many words made me search too deep. :) The image may be 8 minutes old, but that does not delay the sunrise. Even if the light were to take hours to get here, sunrise (and sunset) would still be at the same time. We wuld just be seeing an older Sun. But that would also be the case if the Sun rotated around the Earth, so I don't get that bit. DirkvdM 15:01, 21 July 2006 (UTC)

I apologize for my verbosity. For an analogy (assuming classical physics), imagine standing in a very large sink. If the faucet is trickling water and someone slowly swivels it, eventually it will pass over you. By the time the water reaches you, though, the faucet will have moved on. If the water is moving extremely slowly (if for instance gravity were weaker), the faucet may be much farther away; that is, you getting wet is extremely delayed from when you and the faucet were in line. If, however, you're walking towards where the faucet is dripping, at the instant you get wet, you're right under the faucet, regardless of how slow the water falls. Either way the water you feel is x minutes "old", but in the latter case, you have "sunrise" (getting wet) right when the faucet really passes over you. There is no speed of water delay. Again, this ignores relativity. Was I anymore clear? — Knowledge Seeker দ 03:36, 22 July 2006 (UTC)

I'm still not sure I agree. If the Sun instantaneously changed colour to purple, we would not be aware of the change until 8.3 minutes after the event, due to the time it takes for the light to get here. That is, we never see the sun as it is right now, we only ever see it as it was - and, more importantly, where it was - 8.3 minutes ago. Why wouldn't that principle apply to sunrises and sunsets? JackofOz 04:03, 24 July 2006 (UTC)

It does apply to sunrises and sunsets. It's just that the sun is in the same place it was 8.3 minutes ago, so it appears to be in the same place it really is. The sun only appears to move in the sky because the earth is rotating. Chuck 20:45, 27 July 2006 (UTC)

I get it. If the light took 5 times longer to reach us, sunrise would be at the same time but would show an older sun rising. Earth is moving through space that is effectively bathed in light. No matter how long the light takes to reach us, one half is still constantly bathed in light. When our part of the Earth reaches the line where it faces the sun, the old light is already there, waiting. You really do have to picture the Earth in orbit, turning in space. Skittle 12:42, 24 July 2006 (UTC)