Wikipedia:Reference desk/Archives/Science/2009 January 29

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January 29

Parallel Universes' Laws of Physics

Hello,

According to String Theory ("M" theory in particular), there is the possibility of many other parallel universes just out of our "dimensional reach". Interestingly, The Elegant Universe by Brian Greene, gives rise to the possibility that these universes (if they exist) could reasonably have different laws regarding physics as we know it. My question is how is this possible?

Why would other universes have completely different laws? I can understand that there may be different parameters than ours (temperature, structure, makeup, etc...) but I don't understand that there can be a universe with laws that wouldn't make any sense! For example, if our universe had different laws, such as "F=m/a" or "E=mc", it would fall apart quite quickly, correct? Can universes really exist if they, say, violate the Laws of Thermodynamics? Or am I reading too much into the hypothetical implications to a hypothetical theory?

On a side note, could anyone please provide links or reading from a respectable (read "scientifically accepted") journal, website, book etc... for either the acceptance or denial of the Laws of Physics changing over time? Multiple sources or conflicting viewpoints are fine as well!

Thank you for your time, additional reading or information would be greatly appreciated!

Cheers! ❦ECH3LON❦ 00:28, 29 January 2009 (UTC)

Scroll up and read Cosmic gods Rotational (talk) 13:52, 29 January 2009 (UTC)

I suspect a lot of assumptions are hidden here under the term "laws of physics". Are we talking about "laws" like E=mc^2 or "F=m/a" or are we talking about, say, the number of quarks in existence, the relative strength of gravity, the same bestiary of particle physics? It's easy to imagine a universe where gravity is more powerful than it currently is; it's hard to imagine a universe in which simple relationships were not the same. --98.217.14.211 (talk) 00:43, 29 January 2009 (UTC)

The problem is that any parallel universe which is 'inaccessible' to us is inaccessible to our theories too. So we have no way (even in principle) to probe the other universe to figure out what its' laws are. Do we have any reason to assume the laws ARE the same? Npt really. Heck, we don't even know for 100% sure whether the laws we've worked out apply everywhere in OUR universe. We don't know - we can't know - so the safe assumption is that they could be different. SteveBaker (talk) 00:48, 29 January 2009 (UTC)

Well, I don't know if it's a "safe assumption." I hate invoking anything resembling the anthropic principle, because I find it less than explanatory, but from an issue of pure incidences, we certainly know that our particular configuration seems to work and appear fairly steady. We have no evidence that anything else could be. We have no evidence (and no reason to assume) our particular universe is anything special, that our particular place in it is particularly privileged. So it seems to me like we'd have more reason to assume that things elsewhere are similar to the way they are here. That's no rigorous proof, obviously. But I'm not sure there's any reason to assume they are different elsewhere. I don't see why, in the absence of evidence, it makes sense to assume that something is different than the case we know, even though the sample size is blindingly small (n=1). --98.217.14.211 (talk) 01:41, 29 January 2009 (UTC)

(Edit Conflict) By "laws of physics" (sorry for the vague term), I meant the relationships (mathematically) that we understand. For example, F=ma,

E=mc^2, Laws of thermodynamics, Maxwell's equations, etc... Does this help? Cheers! ❦ECH3LON❦ 00:51, 29 January 2009 (UTC)

If I recall that book correctly, he was talking about different values for physical constants such as c, μ₀, and particle masses, though I might be wrong. They say that if the strong nuclear force were only a few percent stronger than it is, then tetraneutrons could exist, which would make for an interesting universe (and would also throw our notions of radioactivity to hell). There are actually theories that some physical constants might change over time. It's a fun thought experiment to imagine a universe where the speed of light is only a few hundred miles an hour. But I digress.

Any notion of different laws of physics would be completely incomprehensible; asking how other physical laws are possible in other universes is like saying "how is it possible that God exists"? We only say it's "possible" because its outside of the realm of physics to say it's impossible. It's all a thought experiment anyway, like working with four-dimensional geometry. It doesn't exist in any way that we could ever observe it, so it isn't worth worrying about.-RunningOnBrains 01:31, 29 January 2009 (UTC)

Heh, I'm reading that book at the moment too. I wonder if I know you ;) —Cyclonenim (talk · contribs · email) 07:45, 29 January 2009 (UTC)

Unfortunately, I lost my copy of that book years ago (I should buy another one...), so I'm not sure quite what he was talking about. However, things like the inverse square law are easy to change - in a universe with 4 spacial dimensions, you get an inverse cube law (which messes with things like orbits to the point where everything either flies apart or crashes together). --Tango (talk) 13:55, 29 January 2009 (UTC)

Centripetal vs. Centrifugal

Could someone please explain to me the difference between centripetal acceleration and centrifugal acceleration? Also, what is the dostinction between centripetal acceleration and centripetal force? Yakeyglee (talk) 01:58, 29 January 2009 (UTC)

If you swing a mass round in a circle, there must be a force acting on the mass to stop it flying off in a straight line (as per Newton). This force is directed toward the center of rotation and is called the centripetal force. Every action has an equal and opposite reaction (some one called Newton again) so the centripetal force is balanced by the centrifugal force (which is what you feel when in a centrifuge. Force = mass*acceleration (that Newton chap again)--GreenSpigot (talk) 02:17, 29 January 2009 (UTC)

That last part isn't entirely correct. Every action has an equal and opposite reaction, yes, but you're confusing where the reaction is. The string is pulling the mass inwards, and the equal and opposite reaction is the string pulling your hand outwards. (When you're wondering about equal and opposite reactions, it's always best to consider that the forces are almost always applied to different objects, because if they were applied to the same object the equal forces would mean that nothing would ever move). For a better explanation of centrifugal force, see the article linked. It's a tricky one, because many over-zealous physics teachers will tell you that centrifugal forces "do not exist." This isn't quite true, it's just that they only exist in the frame of reference of the object being spun. — Sam 146.115.120.108 (talk) 03:40, 29 January 2009 (UTC)

Our article on inertial frames of reference has a nice explanation too. Basically, if you have to invoke forces that have no obvious physical origin and that act on all particles within a body (like centrifugal force and Coriolis force) then this shows that you are working in a non-inertial reference frame. A hypothetical Foucault pendulum at the North pole illustrates the difference nicely - what causes its plane of oscillation to rotate through 360 degrees every 24 hours ? Non-inertial frame answer - Coriolis force. Inertial frame answer - the plane of oscillation doesn't rotate, the Earth rotates around it. Gandalf61 (talk) 12:20, 29 January 2009 (UTC)

Obligatory xkcd reference. — DanielLC 16:48, 29 January 2009 (UTC)

According to Newton's first law, in the absence of an external force, a body will continue to move with uniform velocity in a straight line. The force that causes a body to deviate from a straight line and move along a circular path is called a centripetal force. However when you make measurements in a frame of reference that is intself rotating (such a frame of reference is called a non-intertial frame of reference), you get a "fictitious force" which is experienced in that non-intertial frame. This fictitious force is called the centrifugal force. So, if you you use an inertial frame of reference you experience a body getting deviated into a circular path due to a centripetal force. If on the other hand you are using a non inertial force which is rotating (revolving?) along with the body, you experience a centrifugal force on everything in that frame of reference. Gosh I always think I will be the first to answer some easy question I can answer but get beaten to it everytime :-( ReluctantPhilosopher (talk) 09:25, 30 January 2009 (UTC)

Actually - it's not a matter of being first - or even being the first to be correct - it's a matter of being the first to be both correct AND sufficiently lucid for the OP to understand what you're saying. I think you nailed that this time. There were other explanations ahead of yours - but I think you was the first that was really clearly explained. Sadly, there are no prizes being handed out (I need to make a T-shirt: "I made 15,000 useful posts and all I got was this lousy barnstar.")!! SteveBaker (talk) 12:28, 30 January 2009 (UTC)

Yes seems a very good answer to me. Perhaps some of the text of this answer could actually be incorporated in the relevant articles as a non technical explanation of this misunderstood topic?--GreenSpigot (talk) 18:42, 30 January 2009 (UTC)

Seeing bubbles on a leaf in water

If I put a leaf in water for a while, I see lots of bubbles. "Weeee!!! The plant is photosynthesizing!" I think, "I'll demo this for my students!" But... then I put a pen in water for a while, and I see just as many bubbles. Hmmm....

1) Why do bubbles build on the pen? Yes, I know there are dissolved gasses in the water, but why to they build on the pen?

2) Does anyone know a good lab that makes it clear that the bubbles on the leaf are being produced by photosynthesis?

Thanks! — Sam 146.115.120.108 (talk) 03:17, 29 January 2009 (UTC)

1) Nucleation

2) Not right off, since leaves are not exempt from nucreation you'd have to separate that out. The article hints that pure water might work, but then how do you prove to your students that they are seeing two different effects. Someone probably has a nicer set up up their sleeve. 76.97.245.5 (talk) 04:01, 29 January 2009 (UTC)

It might work if you degas the water immediately before. I can't comment on if you'd actually see the bubbles from photosynthesis - I'm not much of a biologist. --Bennybp (talk) 04:07, 29 January 2009 (UTC)

I think the water can be degasified by boiling it. Then, of course, let it cool before putting the leaf in. — GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 04:24, 29 January 2009 (UTC)

The leaf will need CO2 to be in the water, so you can't de-gas it. --Milkbreath (talk) 11:50, 29 January 2009 (UTC)

You're right, Milk. Boiling the water will remove the CO2. But that could be the basis of another classroom demonstration. Put a leaf in an inverted test tube full of unboiled water in a beaker of unboiled water. Put another leaf in the same situation with boiled water. Put both beakers under a strong light. I think oxygen bubbles will appear only on the leaf in the unboiled water. This will demonstrate that the leaf takes in CO2, extracts the carbon and keeps it, and exhales the oxygen. Perhaps it could be demonstrated that the gas which collect at the top of the unboiled water test tube is actually oxygen, though I don't know of an easy way to do that. The leaf being under water is not its natural conditiion, but still... - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:34, 29 January 2009 (UTC)

You could show that the gas in the test tube is probably oxygen by putting a heat-glowing stick or cotton swab in the test tube. The glowing item will burst into flame. - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:51, 29 January 2009 (UTC)

(ec)I like it, but how do you convince the kids that boiling removes gasses? (I once lost an eyebrow demonstrating fractional distillation for my step-daughter with a saucepan, some vodka, and a match.) Maybe you could boil some seltzer water and show that it's flat. Also, you'd need to seal the boiled water against the air to keep CO2 from getting into the water, and the plain water, too, for equivalency, which would put a time limit on the effect. I've seen a simple test for oxygen done by introducing a glowing splint of wood, which flares up in the presence of it. If you use a small enough test tube and let it go long enough to get a good amount of oxygen, you could evacuate the water by bubbling air into it through some tubing, leaving the air-oxygen mixture in the tube, hopefully concentrated enough to test positive for O2. --Milkbreath (talk) 18:59, 29 January 2009 (UTC)

(ec)1) Dunno. Maybe the air is coming out of the plastic as the water cools it; maybe the rough surface of the pen is providing nucleation sites for dissolved gases that are coming out of solution as the water comes up to room temperature.

2) Fill a test tube with water and place a sprig of elodea inside. Invert the tube in a pan of water. You might have to set up a clamp or something to keep it from falling over. Do the same with a fake plastic sprig of elodea as a control. Keep the rig well lit and the live elodea should outpace the plastic one in bubble production by quite a lot. --Milkbreath (talk) 04:12, 29 January 2009 (UTC)

I think that nailed it pretty neatly. Does anyone know if the Lotus effect would also work in reverse, i.e. would gas bubbles in water on a lotus leaf behave like water in air? 76.97.245.5 (talk) 04:25, 29 January 2009 (UTC)

Thanks! That sounds like a great setup. — Sam 146.115.120.108 (talk) 12:08, 29 January 2009 (UTC)

The plant doesn't just generate oxygen from nowhere - it converts CO2 to O2 in the presence of light - and reverses the direction of the reaction (O2 to CO2) in the dark. So there needs to be dissolved oxygen in the water in order for you to see CO2 bubbles. De-gassing your water seems like it's going to prevent photosynthesis. SteveBaker (talk) 18:39, 29 January 2009 (UTC)

The process doesn't "reverse" in the dark; cellular respiration occurs at all times, it's just that photosynthesis overwhelms that process during sunlit hours to obscure that fact. </pedant> Matt Deres (talk) 14:20, 2 February 2009 (UTC)

Atomic Bombs and Radiation Burns

On the recent episode of Lost, they make reference to the fact that several people suffered radiation burns/radiation poisoning from an unexploded nuclear weapon (a hydrogen bomb). I was under the impression that the uranium/plutonium used in nuclear weapons is comparatively inert and relatively not that radioactive, at least up to the point it goes supercritical. Given the amount and type of radioactive material in an unexploded nuclear bomb, how close would you have to be to the bomb, and how long would you have to stay there to get enough radiation for acute effects to occur? (The bomb was depicted as leaking, so figures for both with and without typical shielding are appreciated.) -- 76.204.94.153 (talk) 04:46, 29 January 2009 (UTC)

You won't get radiation burns from the core of a nuclear weapon unless it is having some sort of criticality accident (i.e. if a gun-type weapon was submerged in water it could basically become a light-water reactor). But that doesn't sound like the case here—just Hollywood B.S. (no h-bomb would use a gun-type design). (Something similar happens in the film version of Sum of All Fears, if I recall.) To be sure, a hydrogen bomb contains a lot of unpleasant and exotic material, but until it goes critical its hazards are not radioactive (they are toxic, but that's a different issue). If just being near a nuclear weapon would burn you up, you can be sure that a lot of photos would probably indicate that. --98.217.14.211 (talk) 05:02, 29 January 2009 (UTC)

When the last poster writes "its hazards are not radioactive", I'm sure the intended meaning is that there is not enough radioactivity to be an immediate hazard. I mention this because it might be taken as saying that there is no radioactive material in the bomb; and since it contains a fission bomb, that would of course be wrong. --Anonymous, 07:25 UTC, January 29, 2009.

Well, right. What I meant is, "radioactivity is really not your biggest problem in a situation like that." There are far more dangerous materials in an unexploded bomb (high explosives, beryllium, etc.). The radioactivity of an unexploded bomb will only be a problem if, say, the high explosives go off and litter the surrounding area with a nice mist of plutonium, but even that won't give you radiation burns, per se, which is characteristic of highly radioactive material. (Materials of low radioactivity are still dangerous, mind you, but not because they will burn you or give you radiation sickness—they'll get in your lungs and bones and just radiate for ages, and eventually you'll get cancer and die. hooray.) --98.217.14.211 (talk) 12:37, 29 January 2009 (UTC)

But given the timetravel and other such events on the show, I think its safe to say the laws of physics as we know them do not apply to the island and therefore anything is possible. I try to turn the scientific portion of my brain off when watching, since its more of a fantasy setting than sci-fi. I'm not quite sure why bad science doesn't bother me on "Lost" but it does on "Fringe". Maybe its because Fringe acts like it is based on real science while Lost is so far out there they don't even try. -- Mad031683 (talk) 18:21, 29 January 2009 (UTC)

We don't have to even assume different laws of physics, though. We can just assume that it's a really poorly made hydrogen bomb, one that they happened to shove a bunch of raw fission products into. --140.247.243.29 (talk) 18:56, 29 January 2009 (UTC)

Oh lord fringe is so bad. They look at the guy's browsing history or something and get the street address of someone downloading the same thing right now? The platters of the hard drive are fused together but it's ok they have a special program that can recover data? °_o .froth. (talk) 18:44, 29 January 2009 (UTC)

Loss of memory cells

If you lose a lot of blood, will you also lose the immunological memory contained in those memory B cells you lost? Will you be once again susceptible to some diseases you've suffered in the past? Thanks for your answers. --Leptictidium (mt) 10:56, 29 January 2009 (UTC)

Typically you will retain more than one memory B cell per pathogen, so the odds of all of one of a particular type being flushed out – even with extended bleeding and multiple transfusions – is low. Further, at least some cells will likely remain in areas that won't drain readily, including the spleen and lymphatic system. TenOfAllTrades(talk) 14:20, 29 January 2009 (UTC)

Another thing to consider is the distribution of B lymphocytes in your body: Only roughly 2% of your total B cells are at any timepoint in your blood, 98% are in your tissues and lymphatic system. So the chance of completely eradicating a specific memory clone is rather low. In addition, even a heavy blood loss normally leaves several liters of blood even in a smaller human body (otherwise you will die rather quickly). So even the 2% that actually swim in your blood will not be drained completely. TheMaster17 (talk) 14:45, 29 January 2009 (UTC)

The new blood will contain Immune memory of diseases the donor has had. Will the recipient of the blood acquire those immunities? - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 18:55, 29 January 2009 (UTC)

The "new blood" as you call it is not typically whole blood, but only plasma and/or red blood cells. But even in cases where whole blood is given, the few remaining living cells in the "new blood" are quickly eradicated by the recipient's immune system, because they are recognized as foreign antigen. So no "transfer of immunological memory" is possible simply by blood tranfusion. :-) PS: It is considered polite on wikipedia to sign your posts by adding four tildes [~] at the end. TheMaster17 (talk) 19:52, 29 January 2009 (UTC)

(edit conflict)

Donated blood is usually split into two or three components in the blood bank - the red cells, the plasma and often, but not always, the platelets. The plasma may be used either for producing plasma-derived proteins for treatment of specific diseases, or as whole plasma, which is used for stopping bleeding. When asking about the "immune memory" in the blood , you could refer to the T and B lymphocytes, and possibly also to the antibodies in the plasma.

First, the T and B cells: When these are transfused, they do not under normal circumstances transfer any useful immunity to the recipient - on the contrary, they act as antigens in the recipient, and are destroyed. This will lead to the recipient producing antibodies against the Human Leukocyte Antigens of the donor. Such antibodies can cause problems in subsequent transfusions, both febrile transfusion reactions and poor response to platelet transfusions. Very rarely, the transfused lymphocytes survive, and attack the cells of the recipient, causing graft versus host disease. Because of the problems the lymphocytes cause, it is mandatory in many countries to remove the white blood cells by filtering the red cell and platelet concentrates. In addition, for patients that are especially vulnerable (immunosuppressed), the blood bank will irradiate the blood to ensure that white cells that have managed to get past the filter cannot multiply in the recipient.

Second, the antibodies in the plasma: As said above, whole plasma (as well as platelets) is used for stopping bleeding. The amount of antibodies in whole plasma is too small to have any significant beneficial effect in the recipient, and again, it may cause problems. Plasma from a donor of blood group A has antibodies against blood group B, and would cause a transfusion reaction if transfused to a recipient of blood group B. However, as mentioned above, plasma is also used as raw material for industrial production of specific proteins, such as concentrated amtibodies. Such antibody concentrates are used to treat patients with immune deficiencies, and transfer immunity in a passive way.

The procedure of intentionally transferring functional immune cells is called stem cell transplantation, and the stem cells are either harvested from the bone marrow (bone marrow transplantation), or from the blood. However, to get stem cells in any significant amounts to enter the blood stream requires that the donor is treated beforehand, and it also requires that the donor is carefully selected to match the tissue types of the patient. --NorwegianBlue ^talk 20:27, 29 January 2009 (UTC)

Doctors in Médecins Sans Frontières

When Médecins Sans Frontières sends a doctor to say Rwanda, Sierra Leone or whatever, what is the status of this doctor? Does he have a degree to be a doctor in these countries? Is he illegally working as a doctor but since nobody cares, he can get away with it?--Mr.K. (talk) 11:06, 29 January 2009 (UTC)

From the article Médecins Sans Frontières:

Medical volunteers include physicians, surgeons, nurses, and various other specialists, all of whom usually have training in tropical medicine and epidemiology. In addition to operating the medical and nutrition components of the field mission, these volunteers are sometimes in charge of a group of local medical staff and provide training for them.

So the doctors definitely have degrees at least in the own countries. I would assume that they don't have degrees in the countries they are flying to, but I'm not sure why you would call this "illegal." They are not prescribing drugs, and I don't think there are laws that prevent anyone at all from giving medical care, or even performing surgery. If you wanted to reset my broken arm, and I was ok with you doing it, there is no legal reason that you couldn't. — Sam 146.115.120.108 (talk) 12:18, 29 January 2009 (UTC)

This string is a bit off topic but I think the word "volunteers" is a bit misleading since although hats off to them for volunteering to go, AFAICT they are still paid a salary comparable to an expat doctor for a multi-national? However since they are paid by MSF in whatever offshore location they may not have to be qualified to practice (meaning doing paid work) locally. I know plenty of people who were medically qualified in the UK who couldn't work for pay as a doctor in whatever non-Commonwealth country Africa but were welcomed to work as unpaid volunteers there. Paid by an offshore NGO is probably similar--BozMo talk 12:31, 29 January 2009 (UTC)

It should also be noted that MSF tends to operate in areas which are often described as "Failed states" or "failing states". In many of these areas, there are may be so few qualified doctors that there does not exist any real regulatory apparatus; or the government has so little control that any regulation on paper, especially one as esoteric as the regulation of doctors (which the country may not have many of to begin with), is essentially unenforcable. Even if the doctors are not technically "certified" in the states in which they are working, its hard to imagine that, if someone showed up and said "Hey, we want to cure your 3-year old kids of Diphtheria" that anyone would turn them away. It happens (in Rwanda, for example) that sometimes the doctors are unwelcome, and are murdered as such; however in general many places recognize the charity they provide for what it is and raise no objections.--Jayron32.talk.contribs 14:48, 29 January 2009 (UTC)

@Sam 146.115.120.108: I do believe there are laws in many countries regulating medicine in general and not just people prescribing drugs.

There is still a third possibility: there may be a special UN regulation for the case of catastrophic events, and doctors working for a specific international institution only have to be certified at home. MSF - and other international institutions like Red Cross- often works in failed stated, but also in war-torn regions, earthquakes...80.58.205.37 (talk) 15:20, 29 January 2009 (UTC)

AFAIK if there is an de facto government then that gets to decide what foreign help to accept and what not. There have been cases in the past where the local government has turned away help despite their people suffering. (e.g. Myanmar, [1]) Most countries regulate entry of people wishing to work in their country via visas. A government that accepts help from an international aid organization and issues visas to their employees will probably also accept their qualification. 76.97.245.5 (talk) 04:47, 30 January 2009 (UTC)

About Ocean Tides

Moon has less gravitational pull when compared to Earth's gravity.But how it is possible for moon to pull the water body(ocean) of the earth? —Preceding unsigned comment added by 117.200.112.103 (talk) 13:09, 29 January 2009 (UTC)

It's not the gravitational "pull" itself that causes the tides, it is the difference between the pulling forces at that side of the Earth that faces the moon, the centre of the Earth, and the side that faces away from the moon. Those differences are large enough to cause the tides as we see them (locally the effect can be enhanced by resonant and even interferometric effects due to the shape and size of ocean and sea basins). --Wrongfilter (talk) 13:32, 29 January 2009 (UTC)

But, if the Moon had comparable oceans, it would indeed have tides. StuRat (talk) 14:39, 29 January 2009 (UTC)

Even without oceans, the moon can have "solid" tides in the crust or mantle. That's how the moon's rotational energy dissipated to the point that now the moon always shows the same side to earth. Dauto (talk) 15:19, 29 January 2009 (UTC)

Perhaps the easiest way to think about it is that the ocean water that's closest to (vertically below) the moon feels the earth's gravity MINUS the gravity of the moon. That makes the effective gravity (and therefore the weight of the water) be a bit less there. That reduces the pressure of the water - and the higher pressure water off to the sides and further away that aren't feeling the moon's gravity quite so much are able to push inwards towards the point of least "gravity". That causes a bulge in the ocean vertically beneath the moon. It's actually more complicated than that because there are actually TWO high tides per day - one when the moon is overhead and ANOTHER when it's vertically beneath your feet.

That second tide is harder to explain:

Because the earth and the moon are rotating about a common point that's at the center of gravity of the two bodies, the earth doesn't spin perfectly about it's center - it orbits about a point that's a bit closer to the moon than the true center of the globe. So the part of the ocean that's furthest from the moon experiences centrifugal force that's a little higher than for the rest of the ocean. This results in an outward centrifugal force that ALSO causes the water to bulge outwards - but opposite from where the moon is.

To add to the complication, the sun also causes tides - but much smaller ones than the moon. So depending on the time of year and the time of the month and day - the sun's tidal force may add to or reduce the height of the tides. It ends up being rather complicated!

SteveBaker (talk) 18:32, 29 January 2009 (UTC)

Are you sure about that? I don't think it has anything to do with centrifugal force, it's just tidal forces (ie. the difference between the strength of gravity on different parts of the object due to different distances). The bit of Earth closest to the Moon feels the most gravity, the centre of the Earth feels a little less and the bit on the far side of the Earth feels even less, that causes the Earth to be stretched along the line joining the Earth and Moon. Both tides are caused by exactly the same thing. (Low tides are caused by each side of the Earth being pulled towards the centre of the Moon, so they are pulled at slightly different angles, the net result is that they get pulled towards each other.)--Tango (talk) 18:45, 29 January 2009 (UTC)

The viscosity of water has to be taken into consideration. As the moon pulls the ocean toward it, water flows from all parts of the earth to be closer to the moon. But viscosity slows down the flow. This will not produce a high tide on the far side, but it will lessen the high-tide effect. - GlowWorm.

That's not true, the moon doesn't pull the ocean towards it. The Earth and Moon orbit each other, that means they are in free-fall so are weightless. It's tidal forces (the difference in gravity between different points), not gravity itself, that cause the tides. It does take time for the water to move, though, which means the tidal bulges are offset slightly from the line joining the Earth and Moon - this is what causes tidal locking (gravity pulling on the bulge pulls against rotation, slowing it down). --Tango (talk) 19:32, 29 January 2009 (UTC)

It's just a matter of terminology. "Pull" in this context signifies the difference between the earth's gravitation and the moon's gravitation. - GlowWorm. —Preceding unsigned comment added by 98.17.34.148 (talk) 21:44, 29 January 2009 (UTC)

It's not the difference between the Earth's gravity and the Moon's, it's the difference between the Moon's at one point on Earth and the Moon's at another point on Earth (because they are different distances away from the Moon, or the Moon is in different directions). It isn't pulled towards the Moon, it's pulled away from the centre of the Earth in the direction towards the Moon and towards the centre of the Earth in the perpendicular direction. There is absolutely no difference between "directly towards the Moon" and "directly away from the Moon" - the ocean is pulled the same amount in each direction. Our article, Spaghettification, has some good explanation (with diagrams) - the tides caused by the Moon are far less extreme than those described in the article (which is about black holes), but the principles are the same. --Tango (talk) 22:46, 29 January 2009 (UTC)

Crystal violet staining for cell-counting

In a lab where I'm an intern, we perform crystal violet staining of cells for subsequent assessment of cell-growth inhibition of certain compounds. My problem is thus: the current protocol requires the removal of the medium (DMEM, 10% FBS, 1% P/S antibiotics) before addition of the crystal violet/ethanol solution. The methods for currently employed for medium removal are a) shake the (96-well) plate in a large beaker or b) pipette the medium off the bottom. Option a) results in the cell culture leaving the bottom of the plate in a more or less random pattern, leading to large irregular patches of cells disappearing. Option b) results in small marks in almost every well where abrasion by the pipette tip has resulted in removal of cells from the bottom of the plate. My solution is to add 100% formaldehyde directly to the medium without removing first (intended end concentration 10% = 20 ul formaldehyde + 200 ul medium), fixing the cells and preventing them from leaving the plate during the exercise of medium-removal-option a) (shaking the plate). Thus, my question is: will formaldehyde be able to fix cells to the bottom of the plate in the presence of the DMEM? ----Seans Potato Business 14:17, 29 January 2009 (UTC)

Not an answer to your Q, but have you considered using a needle and syringe instead of a pipette ? An even better option may be to put a sterile paper towel at the lower corner of the plate, to absorb the solution. StuRat (talk) 14:37, 29 January 2009 (UTC)

You haven't stated what kind of cells you're working with, but from your description of the experiment and medium removal techniques, it sounds like they are adherent cells. I don't know about formaldehyde, but paraformaldehyde is often use for fixation of cells in suspension before doing flow cytometry. In that setting, the paraformaldehyde does not make the cells stick to the plastic walls of the 96-well plates (or the tubes) that you're working with, at least not to an extent that causes problems. Why don't you try it out experimentally? Take three plates, seed out equal cell numbers in a couple of concentrations with several replicates for each concentration, and then try the three techniques for medium removal, and compare the variances between the methods? It doesn't sound like a difficult or expensive experiment, and you're the one who is in the position to perform it. If the reproducibility is poor, I would consider a redesign of the technique you use for getting a readout, using a staining method that doesn't require that the medium be removed. --NorwegianBlue ^talk 21:41, 29 January 2009 (UTC)

The DMEM probably isn't going to be a problem; the FBS might be. (Typical DMEM composition is here: [2].) Protein in the serum - mostly bovine serum albumin (BSA) - is going to be crosslinked and fixed by the formalin/formaldehyde. This may affect the degree of fixation of your cells, and may also result in a noisy result in your assay (as large amounts of precipitated, crosslinked protein is left behind). You may have to try it and see.

In lieu of violent shaking over a beaker, can you get an equally effective result - that doesn't detach cells - by gently inverting the plate over a stack of paper towels or other absorbent material? Gently refilling with PBS and dumping a second time may be required to clear most of the media before fixation. One last thought - perhaps you could look for 'stickier' plates. Different manufacturers offer tissue culture plates with different coatings; some will hold cells better than others. TenOfAllTrades(talk) 23:32, 29 January 2009 (UTC)

Swollen abdomen in Kwashiorkor

From the article "One important factor in the development of kwashiorkor is aflatoxin poisoning. Aflatoxins are produced by molds and ingested with moldy foods. They are toxified by the cytochrome P450 system in the liver, the resulting epoxides damage liver DNA. Since many serum proteins, in particular albumin, are produced in the liver, the symptoms of kwashiorkor are easily explained. "

Does this albumin deficiency causes the abdomen to swell? Why does it happen? 80.58.205.37 (talk) 16:32, 29 January 2009 (UTC)

According to the german language WP, albumin is mainly responsible for the colloid-osmotic pressure of blood, i.e., its content of solved substances. If that goes down, tissues near the blood will draw water, and this water can't be reuptaken by the veins---which are the most numerous in the belly. --Ayacop (talk) 17:08, 29 January 2009 (UTC)

Hypoalbuminemia (low albumin in the blood) causes transudative ascites. Axl ¤ [Talk] 18:40, 4 February 2009 (UTC)

Cause of death in the ocean

I’m curious as to what the frailest part of a person is while in the ocean. In particular say a person is in the ocean, perhaps a few miles off the coast of Florida, I’m wondering what factor would kill them if they don’t or can’t get help/swim to shore. Presumably the person would be able to float sufficiently well to not drown. And they probably don’t look enough like food to be eaten by something. So I would guess that either hypothermia, dehydration or salt overdose would be the actual killer. Any ideas as to which would come first, or how I would figure this out? Thanks 130.127.186.172 (talk) 17:41, 29 January 2009 (UTC)

In cold water, hypothermia is probably your primary concern. In extremely hot conditions, dehydration would be a problem. In more temperate conditions, exhaustion, leading to drowning, would probably be what gets you (while people float pretty well in salt water, it does take a certain amount of effort to keep your head above water, particularly in rough seas). This is just off the top of my head, though, we don't seem to have a relevant article (at least, not one I can find)... --Tango (talk) 18:00, 29 January 2009 (UTC)

Without flotation aids, I'd expect that both hypothermia and salt ingestion lead to drowning as the immediate cause of death, since those conditions would cause on to lose the ability to keep one's head above water before they actually become fatal. With a life jacket, I'd guess hypothermia is the killer for large portions of the ocean. Dragons flight (talk) 18:16, 29 January 2009 (UTC)

I've often heard "exposure" as a cause of death in those cases, which I would guess is by a combination of severe sunburn, dehydration, and exhaustion (since it would be tough to sleep while keeping your head above water). A lot of times desperately dehydrated people with no survival skills will drink seawater, which leads to confusion, hallucinations, and a fairly quick death.-RunningOnBrains 20:23, 29 January 2009 (UTC)

Guidance required.

Hello all, most initially, sorry for putting such an odd question here. But I want to create a new Project about Development of Science in Ancient India. Can anyone please tell me how should I proceed since I am new to this site? Anirban16chatterjee (talk) 17:50, 29 January 2009 (UTC)

Try the Wikipedia:Help desk for advice on how to contribute to Wikipedia (the Ref Desk is more about helping people get the most out of what is already written). It sounds like an interesting topic to write about - good luck with it! --Tango (talk) 17:54, 29 January 2009 (UTC)

Thank you very much, for rendering your kind hand of cooperation. And, thank you for your best wish! Best Regards. Anirban16chatterjee (talk) 18:09, 29 January 2009 (UTC)

Do you really mean "Project" (as in WikiProject) or do you just want to write an article? Writing an article is very easy and there are lots of tutorials out there. However, if you really do want to start a project (as in a collaboration between a number of editors to write, grade, produce standards and maintain a body of articles relating to a common topic) then I STRONGLY recommend that you write some articles in the areas of your interest, gradually find out who the active editors in those areas are - get to know them and gradually form a consensus to start a 'Project'. If a relative newcomer just dives in and starts trying to do such ambitious things - well, let's just say that it won't end well!

If you do actually just want to write an article then I recommend starting with Wikipedia:Introduction, then Wikipedia:Introduction_2, then go to the full Wikipedia:Tutorial. There are lots of quick guides out there - I'm going to recommend the one on my own off-site Wiki: http://www.sjbaker.org/wiki/index.php?title=The_simplest_possible_guide_to_writing_MediaWiki

There are already a couple of dozen WikiProjects relating to India Wikipedia:WikiProject_Council/Directory/Geographical/Asia#India and also a fairly large and active project that handles issues relating to the history of science in general: Wikipedia:WikiProject_History_of_Science. You might want to talk to the people on those projects about your ideas...I'm sure you'll find them a helpful and useful resource.

SteveBaker (talk) 18:18, 29 January 2009 (UTC)

Tons to kN conversion

I've found a source relating to the collapse of a bridge saying that the wind "applied an estimated lateral force of 90 tons (40 kN)" I pretty sure "kN" is kilonewtons, but which type of ton (short ton-force, long ton-force ect) is given? I have tried converting them myself, but I couldn't get the numbers to match up. --​​​​D.B.^{talk•contribs} 17:58, 29 January 2009 (UTC)

I can't get the numbers to match either... If I'm doing the conversion right (well, typing the right things into google!), 90 short tons-force is 816 kN, 90 long tons-force is 914 kN and 90 metric tons-force (tonnes) is 900 kN. Perhaps tons-force isn't related to tons-mass in the way I would think (1 tons-force being the weight of 1 ton at the Earth's surface). Our article, Ton#Units of force has the necessary numbers, and they give roughly the same answers as I got (the difference is probably because I used g=10m/s², not 9.81), and certainly not anything close to 40kN. I think your source is wrong. --Tango (talk) 18:08, 29 January 2009 (UTC)

It probably was a mistake in their calculations. I went and checked another source and it gives the 90 tons measurement but doesn't provide any conversion. I'm assuming that because it's a U.S. source, it means short tons-force. Thanks for checking. --​​​​D.B.^{talk•contribs} 18:44, 29 January 2009 (UTC)

No problem. --Tango (talk) 19:13, 29 January 2009 (UTC)

Just a thought, might the 40 kN be 40 kn = knots and the wind speed [3]?76.97.245.5 (talk) 05:09, 30 January 2009 (UTC)

NPN transistor as a switch

Would this work? If not, why? Normally the transistor is wired up differently (emitter connected to ground).

File:NPN transistor switch inverse.png —Preceding unsigned comment added by Jcmaco (talk • contribs) 18:36, 29 January 2009 (UTC)

Sure. See "Common collector". --Milkbreath (talk) 18:45, 29 January 2009 (UTC)

If you define "work" and define the "load" more specifically, it will be possible to evaluate your question more rigorously. Nimur (talk) 18:51, 29 January 2009 (UTC)

IMO this is not really a good switch circuit (unless the base voltage is slightly greater than the positive supply voltage) because the voltage applied to the load can only be about 0.6 v below the base voltage and the transistor cannot saturate. Much better to put the load in the collector then you can saturate the transistor and get minimum power loss in the transistor itself.--GreenSpigot (talk) 02:38, 30 January 2009 (UTC)

Space

So far how many countries have succesfully landed on a space using space rockets? who are these countries? —Preceding unsigned comment added by 196.200.102.42 (talk) 18:53, 29 January 2009 (UTC)

If you mean landing (or purposely crashing) on somewhere other than Earth:

• the Moon - U.S., Soviet Union, European Union, Japan, and India
• the International Space Station - U.S., Russia, and the European Union
• everywhere else - see Robotic spacecraft#List of space probes. Clarityfiend (talk) 19:15, 29 January 2009 (UTC)

If you mean landed people, then only the US have landed people on any other world (namely, the Moon). If you count putting people into Earth orbit, then the US, Russia and China have done that. Other countries have sent people into space, but only in someone else's spacecraft. --Tango (talk) 19:28, 29 January 2009 (UTC)

Doesn't it depend what you meanby 'world'? The moon is a natural satellite of earth and is sufficiently large to gravity that you can feel it but it's not a planet by any definition. The space stations are/were artificial satellites and aren't large enough for gravity you can feel. Both artificial and natural satellites could be counted as other worlds or neither. Nil Einne (talk) 17:29, 1 February 2009 (UTC)

Yes, it does depend on your definitions, but it isn't uncommon to call the Moon a "world". --Tango (talk) 19:12, 3 February 2009 (UTC)

It is worth noting that this questioner's IP address maps to Eritrea, and it is probable that she/he is a non-native English speaker. Judging from Languages of Eritrea, it is likely that the questioner will understand at least one of the following articles:

• Veicolo spaziale (italiano)
• مركبة فضائية (Arabic/ عرابي )
• صاروخ

Our English articles, Spacecraft and Spaceflight, are available in many other languages as well. Hopefully this will help... Nimur (talk) 15:52, 4 February 2009 (UTC)

Determing the thermoelectric cooler's current output when using a fan as a load

Through amateur experimentation, I have found that a thermoelectric cooler has a varying current whenever it has a fan attached to it as a load.

These coolers are old technology that are being implemented recently into computer CPUs to recover some of the waste heat emitted as exhaust. While attempting to measure the total power output (I know the Current input, voltage input, and therefore the Power input) the current constantly fluctuates.

I am using a resistor to emulate the CPU and it can produce up to 130degrees C. (Any temperature above 130degrees C. can cause damage to both the thermal probe and my TEC plate.)

When I used a ~5 Ohm resistor as a load, it gave me a constant current allowing me to find my efficiency at 2.25% with a maximum voltage of 2.5V and a maximum current of .5A yielding a power output of 1.25 watts. When entered into the equation: Power Output/ Power input (the input is 56.25W) I obtained my efficiency of 2.25%.

My problem lies in the fact that whenever I change my load from a constant resistor to a fan, I cannot determine the current, yet my voltage has increased to 3.7V and 5.9V (using a small fan on top of the heatsink [3.7V] and a larger fan [5.9V]).

I cannot determine the efficiency because I can't find the current of the output.

It should be noted that the current has very frequent oscillations instead of reading a blank value.

Can you help me?

Thank you. —Preceding unsigned comment added by 24.3.140.186 (talk) 19:46, 29 January 2009 (UTC)

Fans, like other electric motors, have a current roughly approximated by Current_To_Overcome_Friction (small) + Current_For_Acceleration (large and dynamic). It's possible that your fan is not operating at constant speed; a common cause is due to dust or dynamic mechanical behaviors. Nimur (talk) 20:14, 29 January 2009 (UTC)

small computer fans switch the current on and off rapidly. I dont know but I speculate that using current smoothing devices could help give a steady reading. If the speed of the fan is the same as when it is in the open, and the voltage is the rated voltage printed on the fan then the current should also be very close to the rated current.Polypipe Wrangler (talk) 01:39, 30 January 2009 (UTC)

humans ≠ able to tell time

Clocks are very, very simple mechanisms. Small enough to be put inside a very, very small box and be strapped to your wrist, and still be able to tell time. Humans have a very big, very functional brain that is infinitely more complex and infinitely smarter than a standard wristwatch, yet humans cannot accurately keep time. I tried this thing at a museum to see if you could press a button when exactly a minute had passed. I couldn't, and the tour guide said that he couldn't remember a single case where someone could do it more than one time without getting completely off the second time. Why can't humans do this simple task? flaminglawyer 00:20, 30 January 2009 (UTC)

Sure we could, it would just take practice. Here's a guy who memorized the first 67,000 digits of pi. You don't think he could learn to count to 60 reliably? --Sean 23:01, 29 January 2009 (UTC)

What does memory have to do with precision timing? --Tango (talk) 23:05, 29 January 2009 (UTC)

My point is that humans can do all kinds of things with practice. The only thing we can do without practicing is clamber up to a nipple and suck on it. --Sean 13:11, 30 January 2009 (UTC)

Because it isn't a skill that makes you more likely to pass on your genes to the next generation (or, at least, wasn't until the industrial revolution when precise timings became useful), so there is no evolutionary pressure towards developing such a skill. There are other animals that have very precise measures of time, as I recall (fireflies perhaps - do they flash at a very precise rate?) - the skill is useful for them, it isn't useful for us (or, at least, hasn't been for long enough for evolution to have a chance at giving it to us - and given that we've replaced the need for such a skill with technology, it will probably never happen). --Tango (talk) 23:05, 29 January 2009 (UTC)

Any drummer worth their salt should be able to keep to 60bpm for a while.91.109.221.91 (talk) 23:24, 29 January 2009 (UTC)

You don't hang out with many drummers do you:) "How do you know if there's a drummer at your door?" "The knocking keeps speeding up." DMacks (talk) 21:05, 30 January 2009 (UTC)

You can teach yourself - definitely. There is a long section in one of Richard Feynmann's books about how he taught himself to count seconds very accurately. He didn't find that terribly difficult. He then tried to learn to do other things at the same time as keeping track of seconds and was interested to discover that there were some classes of task that he could do while keeping track of seconds accurately - and others where his timing went wildly off whenever he did it. Sadly, I'm not near my books right now so I can't get you the exact title of the book or a more precise description of what transpired. As to why humans can't "just do it" - we had no need to do so throughout the evolutionary process that developed out brains. We probably have a need to look at the sun and the horizon and guess whether we have time to hunt down another mastodon before bedtime - but nothing precise. Even nowadays when it would be exceedingly handy to be able to do it, that ability would be unlikely to get you laid any more often - hence not much evolutionary pressure there. But the brain is amazingly adaptable - and with practice and determination - I bet you could prove the tour guide wrong. SteveBaker (talk) 23:33, 29 January 2009 (UTC)

(sorry, forgot to sign my post up there, I guess Sinebot missed it? <oh no!>) Then why hasn't anyone done it? Surely people have tried (they've tried just about everything else, like that Lu Chao guy, remembering pi), but no one can, so that means that they must've failed. But humans should be able to do it. Think: Computers, like the one you're sitting in front of right now, are displaying Firefox, running an anti-virus scan, maintaining an operating system, etc., yet they still can give you an exact time. (technically, it's beamed in from timeservers, but how do you think timeservers do it?) The human brain is so much more efficient and capable of much greater things (bigger, built with proteins instead of metal, etc.) but it can't even do tell time. So, since no one can do it, I guess it's impossible. Why? My confidence in mankind used to be a bit bigger :( . (sorry for not posting this earlier, but I got e/c'd a couple times and gave up) flaminglawyer 00:20, 30 January 2009 (UTC)

Who says no-one can do it? Steve says Feynmann could do it, and the anon points out that drummers can probably do it. As for why we can't do things computers can - that's because computers are specially built for those kind of things, we're not. My wrist watch is a tiny fraction the size of me and is far far better at telling the time, but it is rubbish at reproducing itself. We're each made for different purposes, so each have different abilities. --Tango (talk) 00:29, 30 January 2009 (UTC)

Feyman could only do it if that was the only thing he was doing. And I'll bet that any drummer would lose his beat if he had to do anything else. Even the simplest of tasks, like drinking coffee. But I get it, so

Resolved

. flaminglawyer 00:36, 30 January 2009 (UTC)

Unresolved

It seems a little arrogant to stick a 'resolved' sticker on an answer when you've just disagreed with a Nobel-winning scientist. You didn't even check the book - or search the web or anything! As you'll see below - you are quite utterly WRONG. A little humility please! SteveBaker (talk) 01:33, 30 January 2009 (UTC)

No - categorically not. Feynmann found that there WERE some tasks he could perform while maintaining his count...but others not. Argh - I wish I could look it up - but I don't have my book collection with my right now. As I recall, he hypothesised that there was some particular brain function of which we only had one that was enabling him to keep good time...so long as the other activity doesn't require that brain function, one may multitask. SteveBaker (talk) 01:16, 30 January 2009 (UTC)

Aha! Google books to the rescue! "The Pleasure of Finding Things Out" - in the chapter called "It's as Simple as One, Two, Three". [4] - He found WITHOUT ANY PRACTICE that he could 'time' 48 seconds plus or minus one second by counting to 60. He found that he could fill out a form and use a typewriter while keeping good time - but he couldn't count things 'normally' - but he could mentally group things into three and tick off three per second and keep good time. He could read a newspaper and keep good time - he could run up and down stairs and keep good time. He could NOT talk and count. Then another guy tries it - and he finds that he CAN talk and keep good time...but he keeps time by visualising a tape with numbers on it scrolling past his mind's eye - so he's not counting. Try as he might, he could not find a way to read out loud and keep good 'mental' time. As usual, Feynmann (who is my personal hero) likes to experiment with the simplest of problems and invariably discovers something fascinating. SteveBaker (talk) 01:29, 30 January 2009 (UTC)

I've been looking for the following anecdote since this question was asked, and I finally googled it loose: Maestro Eugene Ormandy was asked by a radio producer how long a certain piece of music he was to conduct on the radio later would run. He replied that he didn't know, having never timed it, but he spotted someone nearby with a stopwatch and told him to start it. Two phone calls and a couple of conversations later he said stop, right on the money. (One for Ripley, or not?) --Milkbreath (talk) 02:05, 30 January 2009 (UTC)

Yeah - that's exactly the kind of thing Feynmann was saying. Presumably, the Maestro set the music playing 'in his head' and because he's good at it - the imaginary music plays at precisely the right tempo. Evidently he is able to talk and 'play music in his head' at the same time - so it all turned out OK. Feynmann too claimed that he could read and perform various other tasks while counting - but he couldn't speak. Then his colleague reports that he visualises an image of a band of numbers scrolling past in his mind's eye - so he can talk while "watching" the band scroll by - but he can't read. So this anecdote further shows that you CAN produce reasonably precise timings AND do something else at the same time...providing it doesn't use the same part of your brain. Now, if you were REALLY smart - you could count like Feynmann and read a book - then, if the phone rings, stop counting and start scrolling a 'tape' with numbers on it past your mind's eye or start listening to Bach harpsichord music in your head while you talk to the person on the phone - then revert to counting when you sit back down to read. With a big enough range of alternative timing tricks and enough practice that this became automatic - I think you could probably teach yourself to measure time automatically all day long...which would be a neat party trick! I feel an experiment is needed. I'm going to practice listening to Queen's "Bohemian Rhapsody" (which I know well) in my head - and I know it's 5'55" long (I used to be a radio DJ when I was in college - I used to tell my listeners that I put it on so I had time to go outside and wash my car during the show...which wasn't true - but it's a great line!). Anyway - I'm going to listen to it 'in my head' and try to write C++ code at the same time. I'll report back later. SteveBaker (talk) 12:21, 30 January 2009 (UTC)

Anectodally, the music thing works pretty well. When I was a kid, I had insomnia, and to pass the time, I would sing "99 Bottles of Beer" to myself, in my head, and found that it took almost exactly 22 minutes for me to run through the entire song. I then did some math and found meant that meant it took roughly 13 seconds to do one iteration of the song, or that 4-5 iterations was about a minute. Its a skill I lost, but for many years it was how I would keep time while doing stuff where I didn't have a clock to look at, and I found I could keep time to within about 5 minutes in an hour. I would just play the song in my head, and however many bottles of beer were left on my wall, I could quickly estimate how long it took me to do a task. It got to be almost automatic. Came in handy on things like the SAT, where I only had a certain amount of time to complete a task, and I could fairly reliably estimate my mile time when running on my High School cross country team. So, with some training, humans can fairly accurately measure time while completing other tasks, even those (like taking a test) that require some other intense mental work as well. --Jayron32.talk.contribs 17:02, 30 January 2009 (UTC)

More WP:OR: I have found that -- with statistically improbable frequency -- I will wake up exactly one minute before my alarm clock rings if I have set it to some unusually early time the next morning. --Sean 17:59, 30 January 2009 (UTC)

OR results are in. Evidently my head replays Bohemian Rhapsody quite a bit faster than Queen - my five tries to keep it playing in my head while working were very successful - I didn't "lose my place" or pause or anything at any point in my testing. But each time the times were well short of the 5'55" that the tune is supposed to take: 5'22", 5'25", 5'23", 5'27" and 5'20". However - as Feynmann pointed out in his book, that doesn't really matter. So long as you know the factor that you are 'off' by, you can correct for it. That's a variation of +/- 4 seconds - which is about +/- 1% accuracy. That's comparable to Feynmann's figures for counting and reading at the same time. Having a fairly accurate five minute timer in your head is pretty useful - so I'm actually going to figure out whether there is a convenient 24 second-ish chunk I can cut out of the song to make it fit in 5 minutes. Anyway - as the Mythbusters say, this one is "Confirmed". SteveBaker (talk) 20:36, 30 January 2009 (UTC)

That's what I would have expected. The important thing is not that you can reproduce Queen's version of Bohemian Rhapsody, it's that your version is consistant. Which it would appear to be... --Jayron32.talk.contribs 20:44, 30 January 2009 (UTC)

Yep - exactly. SteveBaker (talk) 01:30, 31 January 2009 (UTC)

We're still missing the point. I know that you can measure an amount of time if you know the offset factor, etc., etc. My intention was for the question to say something like, "Why can't humans tell time in their head while doing completely different things?" I realize that this is completely redundant to a wristwatch, but it seems so simple, and so doable... I also realize that this has already been answered (kind of) so I feel that I could correctly stick a {{resolved}} on it. But I won't. I still disagree with a Nobel-winning scientist. flaminglawyer 00:42, 31 January 2009 (UTC)

You aren't just disagreeing with Feynmann. We've shown that (a) Professor Richard Feynmann (Nobel Prize winner)...AND... (b) Feynmann's colleague (c) Maestro Eugene Ormandy (d) Jayron32 (Grand Tutnum, esteemed member of The Bathrobe Cabal and winner of twenty-three and a half barnstars) and (e) Me (someone who now has the bloody 'Bohemian Rhapsody' stuck in his head) - could ALL count time fairly accurately by more than one method whilst simultaneously doing something else. The evidence is IN. This is the science desk - not the ignoring-all-of-the-evidence-because-it-doesn't-fit-our-world-view desk. Are you calling ALL of us liars? If you thought you knew the answer before we started and are going to disagree with all of the evidence then why the heck did you ask the question in the first place?! To say this as clearly as possible: I was EASILY able to keep track of time to about +/-1% precision while simultaneously writing a particularly tricky C++ class for managing shader uniform state efficiently in both OpenGL and Direct3D. We have evidence that at least four others are capable of this feat. So there is really zero doubt that one CAN both keep reasonably accurate time AND perform at least some other tasks at the same time. Dude - I did it...just this morning! SteveBaker (talk) 01:24, 31 January 2009 (UTC)

Now I'll stick a resolved sticker on it so I can quit while I'm only a little bit behind. flaminglawyer 05:45, 1 February 2009 (UTC)

Resolved

Earth without a moon.

Theoretically, what would be the effect if our moon just magically disappered. Would the tides stop and how would this affect sea-life. Would it change the weather drastically? Would our orbit around the sun change?91.109.221.91 (talk) 23:29, 29 January 2009 (UTC)

There was a question about this a while back. The synopsis is: Yes, our orbit would change because we're currently going around the sun in a wobbly orbit - and it would straighten out - but I doubt we'd notice. The majority of the tides would go away - but there are tides due to the sun that would continue (albeit at a much smaller scale). Doubtless that change would have some effect on the weather and to marine-life that depends on tides (eg the kind that live in rock-pools) - but it's hard to predict what that effect would be. If the moon vanished 'abruptly' - much larger and more drastic consequences are possible due to the sudden 'jolt' due to vanishing gravitational fields...but we'll assume you aren't really talking about that kind of thing. The lack of moonlight at night would help some hunters with really good night vision (maybe owls) and worsen the outcome for their victims - other nighttime predators might do worse...again, it's hard to predict because the world is such a complicated place. SteveBaker (talk) 23:40, 29 January 2009 (UTC)

Why would owls hunt better when it's darker? Just because they can hunt in the dark doesn't mean it isn't easier when it's light. Unless they're competing for the same pray with hunters with worse eyesight, I guess... --Tango (talk) 00:15, 30 January 2009 (UTC)

I'm assuming that the owl's reduction in acuity as it gets darker is more than counter-balanced by the lack of acuity on behalf of it's prey. So in moonlight, the owl can see the mouse very well indeed - but the mouse can also see the owl. When it's pitch-black, the owl can still see reasonably well - but the mouse is effectively blind. That may or may not actually be true - but it's certainly a cause to suspect that the lack of moonlight might affect certain aspects of the ecosystem. SteveBaker (talk) 01:12, 30 January 2009 (UTC)

An owl doesn't need to see the mouse in order to catch it. Experiments show that owls can hear the tiny rustlings of a mouse, even under thick leaves or snow. ~AH1^(TCU) 19:44, 30 January 2009 (UTC)

The Moon is presently the largest torque acting on the tilt of the Earth's axis (its obliquity). Because it is so large and so close, the Moon dominates over other perturbations and effectively stabilizes the Earth's tilt with only small variations over time. If you take away the Moon, the tilt of our planet would be expected to slowly random walk over millions of years due to perturbations from the Sun and other planets. (This same process is believed to be ongoing with Mars, which lacks a large moon.) As this occurred it would have the potential to create radical changes in the intensity of the seasons experienced on Earth. Dragons flight (talk) 01:50, 30 January 2009 (UTC)

As noted above, if the moon magically disappeared, there would still be tides but they would be smaller -- less than half of their present size. They would also differ from the present tides in two other ways. First, they would be the same size all the time, instead of varying every 15 days between stronger "spring" tides and weaker "neap" tides. And second, high tide at a particular place would be at the same two times every day, instead of changing every day -- on open coastline it'd be around noon and midnight.

Another thing is that we would have to change the calendar, and there might be detectable changes in the climate too.

As noted above, the Moon causes the Earth to wobble slightly in its orbit: when the Moon goes away, the wobble ends. But this doesn't mean the Earth resumes its average course; rather, it just keeps going in whatever direction it was wobbling in at the time. Now this wobble is small: the Earth's center orbits the Earth-Moon center of gravity at about 25 to 30 mph (depending on where in its orbit the Moon is), which isn't much in comparison with the Earth's orbital speed of about 66,500 mph around the Sun. But still, it's enough of an effect to be detectable.

For example, say that the Moon disappears at full moon. Then its orbital velocity is in the same direction as the Earth's orbital velocity around the Sun, so the Earth itself is wobbling the other way -- moving in its orbit about 25 to 30 mph slower than usual. When the Moon disappears, the Earth will no longer resume its normal speed. Say it's at aphelion when this happens: then the aphelion remains the same but the perihelion becomes lower. I have calculated (when this question was asked in another forum in the past) that the mean Earth-Sun distance will reduce by about 0.1%. Since the amount of sunlight varies as the inverse square of the distance, it would increase by somewhat about 0.2% on the average, with the greatest increase (about 0.4%) in January when the Earth is nearest the Sun. Very likely that is enough to create detectable climate changes.

And this orbital change would shorten the year from about 365.24 days to something more like 365.03 days. We would only need leap years about 3 times per century.

Conversely, if it happened in the opposite set of circumstances, the Earth-Sun distance would increase, the amount of sunlight would decrease, and we would need leap years more often. And in in-between circumstances, there would be other results of similar or lesser magnitude. You get the idea. --Anonymous, 11:57 UTC, January 30, 2009.

Also, there's the problem that it's not the Earth in isolation now that is orbiting the sun, it's the "Earth-Moon system". If the Moon just disappeared, the Earth-Moon system would still need to conserve its momentum, but it would have just lost 1/6th of its mass. The result would be that Earth would speed up in its orbit. This increase in speed would cause the Earth to change its orbit around the sun; possibly outside of the narrow band of "livable distance" we occupy now. --Jayron32.talk.contribs 16:50, 30 January 2009 (UTC)

First, we were told that the Moon was destroyed magically; there was nothing about its momentum being transferred to the Earth or to any other specific body. Obviously the momentum magically disappears.

Second, let's suppose that's wrong and its momentum actually was transferred to the Earth. The Earth now varies between 91,500,000 miles from the Sun at perihelion to 94,500,000 miles at aphelion and therefore, by Kepler's third law, its orbital speed varies by the same ratio, from about 65,520 mph at aphelion to 67,760 mph at perihelion. The Moon has 1/81 of the Earth's mass, so transferring its momentum to the Earth would -- in addition to canceling the effect I described above with regard to the wobble -- increase the Earth's orbital speed by 1/81 or say 820 mph.

If this happened at aphelion, the 65,520 mph speed would become 66,340 mph. This is only about 250 mph above the speed for a circular orbit at that distance. Therefore the Earth's perihelion would rise to give a perihelion speed about 500 mph faster (yes, I know, this is an approximate method, but it's good enough for this purpose) or 66,840 mph; the perihelion would therefore be at 94,500,000*66,340/66,840 = 93,800,000 miles, and the mean distance would be 94,150,000 miles. The length of the year would increase by a factor of sqrt(94.15/93) to about 367.5 days, and the mean intensity of sunlight would drop by a factor of (94.15/93)², or by about 2.5%. That might produce an ice age but I doubt it would leave the planet uninhabitable. But at least February could become a month of 30 or 31 days like all the rest.

If it happened at perihelion, we'd be worse off. Now the perihelion would remain the same but now it would be the aphelion that'd rise, making the orbit significantly more eccentric. The aphelion increase would be by roughly the same amount, so aphelion would be somewhere around 96,800,000 miles. The reduction in sunlight would be the same on average, but now its intensity would increase from July to January by a factor of (96.8/91.5)² or almost 12% instead of (94.5/91.5)² or about 6.7% as it does now, and that might be enough to have additional climatic effects. If it happened in between aphelion and perihelion, of course, the results would be in between.

--Anonymous, 06:23 UTC, January 31, 2009.

Many animals depend on the moon for some activities. Some Religious holidays worldwide are also defined by the phases of the moon. Near-Earth asteroids might also behave differently around an Earth without a moon. ~AH1^(TCU) 19:39, 30 January 2009 (UTC)

Isaac Asimov had some interesting thoughts about what would have been different if the Earth had no moon. 152.16.59.190 (talk) 11:31, 31 January 2009 (UTC)

The tides would drop, as mentioned, to a third of their current level, precession of the equinoxes would stop, there would be no more eclipses, and werewolves would get more sleep. B00P (talk) 13:08, 31 January 2009 (UTC)

Hmmm...according to this documentary [5] the moon actually stabilizes the tilt of the Earth's axis and without it, the Earth would wobble violently. It also states that the Earth would spin much faster resulting in 4 hour days. Our Rare Earth Hypothesis article states the moon "act[s] as a gyroscope, stabilising the planet's tilt; without this effect the tilt will be chaotic, presumably also causing difficulties for developing life forms." A Quest For Knowledge (talk) 17:07, 31 January 2009 (UTC)

A Quest For Knowledge has misunderstood both the question and what must have been presented on the show. The questioner wanted to know what would happen if the Moon suddenly (and magically) disappeared now. That business of a four-hour day refers to the situation if the Moon had never existed. As for wobbling, Venus doesn't have a moon, and it doesn't "wobble violently" nor is its axial tilt "chaotic." Why should Earth behave differently? B00P (talk) 00:53, 1 February 2009 (UTC)

Sure, there'a difference between what would happen if the moon disappeared and if it had never existed, but that doesn't mean that that none of the information in the documentary or Wikipedia article applies. I'm not an astrophysist or a even a scientist for that matter but both say that the moon stabalises the Earth's tilt. Whether they're right or wrong, I can't say; I'm just repeating what they're saying. When I get a chance, I'll watch that documentary again (although by that time, this thread will be long gone out of the main page). A Quest For Knowledge (talk) 15:05, 2 February 2009 (UTC)