Wikipedia:Reference desk/Archives/Science/2011 March 24

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March 24

Falling of the Newton's Apple

As we all know the reason of the falling of the Newton's apple on earth is that it's  acceleration towards earth is greater than the acceleration of earth towards apple. 

Therefore would Newton's apple fall OR accelerate towards earth if it's  size (both mass and volume wise) increased exactly to size of the earth?

An increase an extra mass might shift them to new orbit But would they have weight pressure on each other as both equal and opposite accelerations cancel each other?74.198.150.220 (talk) 00:13, 24 March 2011 (UTC)Eccentric Khattak#1-420

The acceleration of the apple is due entirely to the mass of the Earth. It is unrelated to the mass of the apple insofar as all objects at the Earth's surface accelerate at 9.8 m.s^-2, regardless of their mass. Similarly, the acceleration of the Earth towards the apple is due entirely to the mass of the apple and is unrelated to the mass of the Earth.

If two planets of equal mass are close enough to influence each other to a measurable degree, both would have the same acceleration, but in opposite directions. There is no science behind the idea of equal and opposite accelerations cancelling each other. If two objects are gravitationally attractive and have equal accelerations in opposite directions, they collide! Dolphin (t) 00:47, 24 March 2011 (UTC)

I think the problem here is the common misconception of action and reaction forces "cancelling" each other out. That isn't the case. When an object gravitationally pulls on another object, the reaction force is that second object pulling back on the first object. The end result is the exact same - the two objects accelerate toward each other and collide. 99.236.18.156 (talk) 01:25, 24 March 2011 (UTC)

What people said above plus weight is not a pressure, it's a force. Dauto (talk) 01:37, 24 March 2011 (UTC)

Also, it's only your perception that the apple is the one object "falling", because you're sitting on the ground and the apple looks so small compared to the earth. As far as you perceive, "you and the earth" could be very light and falling towards a massive apple composed of white-dwarf matter. It's all about your frame of reference regarding relative motion of the apple. DMacks (talk) 09:09, 24 March 2011 (UTC)

I thought that acceleration was absolute? In other words, it really is the case that the apple is accelerating much more than the Earth, not just one's perception... 109.153.232.142 (talk) 18:43, 24 March 2011 (UTC)

It's true that proper acceleration is absolute. For example, if there are two rockets in deep space that are approaching each other at an accelerating rate due to one of the rockets having its thrusters on, it's possible to perform a local experiment (an experiment involving only short distances and times) to determine whether you're on the rocket with its thrusters on, or on the rocket that's coasting. Indeed, the experiment is trivial; you don't really even need an accelerometer: If you're pressed up against a surface of the room you're in, then you're in the accelerating rocket, but if you're floating around in your room, then you're in the coasting rocket.

However, gravity does not involve a proper acceleration, because gravity in reality is a fictitious force. Regardless of whether you're in a room attached to the apple, or in a room at the center of the Earth, you're just going to float around in the room, because you aren't undergoing any proper acceleration either way. (If you're in a room attached to the surface of the Earth, then you will be pressed against the floor, but that's because you're undergoing a proper acceleration upward due to the non-fictitious intermolecular forces the floor is imparting to the bottoms of your feet, that prevent your comoving frame from being an inertial frame of reference.) Red Act (talk) 22:11, 24 March 2011 (UTC)

How about this. You and I are in two rockets at a great distance from the Earth-apple system, such that the gravitational effects are negligible. Using a powerful telescope, you operate your rocket so as to keep level with Earth (specifically, so that a line from you to Earth is at right-angles to the Earth-apple axis), and I do the same to keep level with the apple. Would we not be able to tell that I have to accelerate more than you? 86.176.210.13 (talk) 12:38, 25 March 2011 (UTC)

DMacks' post doesn't seem to me to be a very good one, because it seems to be implying that there is no difference gravitationally between a system consisting of a small-mass apple and a large-mass Earth, and a system consisting of a large-mass "apple" and a small-mass "Earth". That isn't correct. Although no local experiment performed in the apple's frame of reference will detect any acceleration of the apple, if distances involved are large enough, a nonlocal experiment in the vicinity of the apple can detect a tidal force due to the Earth, that's vastly greater than the tidal force that the Earth experiences due to the apple.

I probably should never have even brought up gravity being a pseudo force that doesn't really cause an absolute acceleration, since the topic being discussed here is Newtonian gravity. In the Newtonian view, gravity is a force that's every bit as real as any other force, and it produces an acceleration that's absolute, in that the magnitude of the acceleration is invariant with respect to any Galilean transformation, and the direction of the acceleration is invariant with respect to any Galilean transformation that doesn't involve a rotation. General relativity views matters differently, but getting into that here would be an off-topic digression that would be unhelpful to the people using this thread to better understand Newtonian gravity. Red Act (talk) 17:29, 27 March 2011 (UTC)

You'll note that I specifically framed my response as exactly the local experiment. I did so because that's how the classic apple-falls-from-tree experiment is usually described. With substantially larger distances, or impartial (external) observers, obviously things are different than for observer as part of one of the close bodies. DMacks (talk) 20:33, 28 March 2011 (UTC)

OK, thanks for the clarification. Your intended point wasn't clear to me from my reading of your earlier post. Red Act (talk) 02:46, 29 March 2011 (UTC)

What will be  their weight force (w=mg=mg) on each other for settlement analysis? OR they will be weightless 96.52.178.55 (talk) 05:35, 25 March 2011 (UTC)Eccentric Khattak#1-420

The force on each will be identical and opposite, the magnitude given by Newton's law of universal gravitation (I'm assuming the Newtonian model; don't ask me about relativity!). Whether they have any "weight" as they are falling depends on the definition of "weight", I think (whether it is defined as the gravitational force or the reaction force against some supporting surface such as the ground). By analogy with astronauts in orbit, who are usually termed "weightless", any falling object would also be "weightless". 86.176.210.13 (talk) 12:46, 25 March 2011 (UTC)

Several responses but still not sure  which one of the following is  the true representation of Newton gravitation? 

1- According to Newton's law of gravitation the force of attraction between aforementioned masses; F = G (m)*2/(Diameter)^2= some figure

2-According to their separate analysis the  weight of aforementioned masses over one another are just the meeting of heads of two  arrows (equal in magnitude but opposite in direction). Say these two arrows represent two point loads which may cancel each other.

So according to separate analysis of the theory can I assume that weight of a 1 kg of a sphere on earth decrease by increasing it's mass till it becomes weightless when it's size reached exactly to the size of earth (both mass and volume wise)  -  Although common sense is opposite 74.198.150.216 (talk) 23:26, 25 March 2011 (UTC)Eccentric Khattak#1-420 ¶ GO

As the mass of the sphere increases, the gravitational force attracting it to Earth increases too, in proportion, according to Newton's law. If the sphere is resting on the ground, then this gravitational force is exactly balanced by the reaction force of the surface that the sphere is resting on. The sphere is not subject to any net force, but it still has a weight, which is equal in magnitude to both the gravitational force and the reaction force. If the sphere is falling towards Earth then, depending on one's definition of "weight", it may be considered weightless. 02:16, 26 March 2011 (UTC) —Preceding unsigned comment added by 86.160.211.9 (talk)

Sex in Space

Hi, I was wondering, has anyone, or anything, been known to have sex in space, be they human or animal. And would our biological reproductive systems work in the same way, say for example on baord the International Space Station? —Preceding unsigned comment added by 85.210.94.143 (talk) 02:42, 24 March 2011 (UTC)

There are indeed problems with reproduction in space. See Sex in space, in particular the "Physiological issues" section. Red Act (talk) 03:13, 24 March 2011 (UTC)

What's striking about that page, and the "Physiological issues" section in particular, is how monumentally bad it is. I don't see one claim regarding the physiology of sex in that section that is supported by a reliable source. There are a few statements about rodent development in microgravity that have some support, but that's not the subject represented by the title. -- Scray (talk) 04:22, 24 March 2011 (UTC)

Has it happened? There's an old saying - "Gentlemen don't tell" HiLo48 (talk) 03:46, 24 March 2011 (UTC)

After 9 months the little secret would be out. Cuddlyable3 (talk) 13:41, 24 March 2011 (UTC)

What? There's no article for 400 Mile High Club?!? Kingsfold (Quack quack!) 19:37, 24 March 2011 (UTC)

I saw a science program on TV that considered this. One thing they suggested was a sort of hammock, but with a top on it too, so the parties involved wouldn't float away from each other. Then there's the hygiene issue, with bodily fluids floating around. StuRat (talk) 05:04, 24 March 2011 (UTC)

The ref desk gnomes have considered this long and hard on several occasions. Just search the ref desk archives for sex in space.--Shantavira|^{feed me} 10:18, 24 March 2011 (UTC)

This Cecil Adams article is also good : The Straight Dope : Has Anyone Ever Had Sex in Space.

APL (talk) 14:17, 24 March 2011 (UTC)

Long and hard? That's what she said. (Sorry. Couldn't resist.) Kingsfold (Quack quack!) 19:37, 24 March 2011 (UTC)

What is this owl?

http://hungoverowls.tumblr.com/post/3839474990/look-i-know-alright-well-at-least-have-enough Sancho 03:04, 24 March 2011 (UTC)

I cheated flagrantly on this one and clicked-through the original image to find out it was taken in Malaysia. Searching Google Images I decided it looked like a Malaysian Bay Owl. Searching that term, I got back to the original image which says that it is "Taken in Bird Park Penang, Malaysia. Oriental Bay Owl (Phodilus badius). Thanks bubo_strix for ID." ... which is a wrap --- provided bubo_strix is the right person to copy off of at exam time ;) Wnt (talk) 03:37, 24 March 2011 (UTC)

: Cheated?? No you didn't, you thought it through and used a successful strategy to achieve the goal and attributed the image. No one was hurt, humiliated or robbed. Contrary to some people's opinion this is not a competition arena. Well done! Richard Avery (talk) 08:11, 24 March 2011 (UTC)

Well, I cheated in the sense that I didn't learn anything about the taxonomy of owls, and if I see another photo like this that doesn't offer more information on click-through, I'll be clueless.

Heh, was anyone else here expecting another thread about those really creepy-looking polymorphic Japanese owls? --Kurt Shaped Box (talk) 09:02, 24 March 2011 (UTC)

Time dilation 2

Hi. In this page, there is a simple "derivation" of time dilation with 2 identical clocks - one in a rocket and one in lab (with both being observed from the lab). My question is: wouldn't length contraction cause the lab to observe the length of the clock (L) to be different in the moving rocket than the clock in the lab? That derivation assumes that the length (according to the lab) doesn't change. Is that true? 163.202.48.108 (talk) 10:19, 24 March 2011 (UTC)

If I'm interpreting the diagrams correctly, the 'clocks' in each frame (lab and rocket) are both oriented perpendicular to the direction of the rocket's travel. The Lorentz contraction only occurs in the direction of travel, so the clock doesn't get narrower. TenOfAllTrades(talk) 13:17, 24 March 2011 (UTC)

Thanks very much. 41.135.50.122 (talk) 20:34, 24 March 2011 (UTC)

Identifying sperrylite ore

Few months ago, I received an ore from my uncle, who is geologist. He claims that the ore he gave me is sperrylite (platinum arsenide). The ore looks somewhat golden-gray in colour, while many samples on the internet is silvery white. This make me curious.

Thus I conduct some experiment, the other possible ore that look like this is pyrite, but it is much more golden. When I put in in hydrochloric acid, it produce few tiny bubbles and change the hydrochloric acid to slightly yellowish in colour. If it was pyrite, I expect it to bubbles more.

So I decided to show the ore's photo here and hopes wikipedians will help me identify it better. And ends my curiousity. The picture of the ore and its streak can be viewed here,in my blog:

http://kimiajawi.blogspot.com/2011/03/3-gambar-platinum-arsenide.html

Hope you can identify it. —Preceding unsigned comment added by 60.54.63.64 (talk) 10:34, 24 March 2011 (UTC)

Did u check Mohs hardness (Quartz and porcelain streak plate (bottom of dishes)) and specific gravity? [1] [2] [3] --Chris.urs-o (talk) 12:54, 24 March 2011 (UTC)

I do not have equipment to find its specific gravity,but with porcelain streak plate (which I use bottom of my porcelain crucible) it did produce black streak,the picture of it can be viewed at my blog.So,does this confirm the material I have is sperrylite? —Preceding unsigned comment added by 175.140.146.69 (talk) 13:24, 24 March 2011 (UTC)

As Chris.urs-0 says it would be good to check the hardness, if it is Sperrylite you would expect it to be able to leave a scratch on a penknife blade. Mikenorton (talk) 13:48, 24 March 2011 (UTC)

Also did your uncle say where it came from? If someone gives me a lump of something to identify (half the time it's a lump of slag), that's the first question that I ask. Mikenorton (talk) 14:06, 24 March 2011 (UTC)

Sperrylite has a specific gravity of 10.6 - roughly the same as lead - so dense that even without proper equipment it should be possible to make a rough estimate that rules it in or out. Just measure the ore like a block, in three dimensions, and compare the volume that gives you to its weight. If this crude estimate comes in around 7 or higher, then it's not galena, and you know it must be something good.

And I'm sure everyone wants to know exactly where this chunk of platinum came from. ;) Wnt (talk) 00:10, 25 March 2011 (UTC)

Materials with the same hardness don't leave a streak on each other, but sperrylite can be hardness 6 to 7. Sperrylite has a poor cleavage, and its polished surface has a metallic lustre. Arsenic is poisonous, don't forget to clean the porcelain, pls. --Chris.urs-o (talk) 06:04, 25 March 2011 (UTC)

Triggering an earthquake

Suppose an earthquake is about to happen that would release X joules of energy. We trigger the earthquake prematurely by detonating nuclear devices with total energy Y, with Y much less than X. Is there any way, even in theory, for the resulting earthquake to release much less than X joules of energy? Or will the released energy be closer to X-Y? --140.180.18.11 (talk) 17:21, 24 March 2011 (UTC)

Some seismologists have suggested that the common occurrence of foreshocks before many large earthquakes (about 70 % for M>7 events) suggests that they are part of a preparation process in which a series of smaller earthquakes (which would be similar to the nuke in your question) form a sort of cascade continuing until the mainshock is triggered. However many foreshocks seem instead to be just indicators of the enhanced stress levels that eventually trigger the mainshock, this is supported by an observed relationship between the rate of foreshocks and the rate of aftershocks. In this case the foreshocks (or any other source of energy) do nothing to trigger the mainshock. Mikenorton (talk) 17:44, 24 March 2011 (UTC)

In my lifetime, seismologists seem to have become less certain about the possibility of precise earthquake prediction. How would you know where to do your nuclear detonations? HiLo48 (talk) 17:50, 24 March 2011 (UTC)

Mystery mountain

Hi, can anyone please tell me what mountain this is? I just went to Alouette Lake and got a whole bunch of pictures of it, but I don't want to upload them until I can find out what this is. Thanks, --T H F S W (T · C · E) 19:42, 24 March 2011 (UTC)

It appears to be 'Evans Peak' just in front of 'Alouette Mountain', and with Edge Peak in the distance. Mikenorton (talk) 20:04, 24 March 2011 (UTC)

Right, that's what I was about to say. Looie496 (talk) 20:08, 24 March 2011 (UTC)

Which is which? Is Alouette Mountain the large, blunt-topped one? --T H F S W (T · C · E) 20:20, 24 March 2011 (UTC)

The nearest peak is Evans Peak, almost completely obscuring Alouette Mountain - check it out on google earth (which is what I did), the shape is distinctive. Mikenorton (talk) 20:28, 24 March 2011 (UTC)

Body heat sun's heat

Is it true that the human body produces more heat than an equivalent volume of the sun's matter. As Dr. Al Khalili states. Sounds improbable. Phalcor. — Preceding unsigned comment added by Phalcor (talk • contribs) 20:23, 24 March 2011 (UTC)

I think that would depend on what part of the sun. At the core, I don't think so: 150 g/cm³ at 13.6 million kelvin. At the corona, however, it may reach similar temperatures, but it so thin that the same volume will actually contain less overall heat than the human body. --T H F S W (T · C · E) 20:29, 24 March 2011 (UTC)

Yes it's true. The sun is very dilute - but enormous. Take a look: power per mass for sun = 1.934×10^(-4) W/kg power per mass for human = 1.6 W/kg. (A human outputs an average of 100 Watts per day[4]). A human can put out 8,000 times more power than the sun - and that's a resting average. At peak power a human can do about 9 times as much, so 75,000 times as much as the sun. But the sun is absolutely stupendous in total mass, so even as dilute as it is it puts out a huge amount of power. Also, be aware that all the power in the sun is generated in the core, so calculating just in the core gets 0.0088 W/kg (at most), which is still tiny compared to a human. Ariel. (talk) 20:36, 24 March 2011 (UTC)

As above, depending on what you mean, it's plausible. The sun's output is about 4*10²⁶ J/s, whereas a human's output is around 100 J/s (assuming about 2500 kcal fully converted to heat -- it's probably wrong, but I don't think it's orders of magnitude wrong). The sun is about 10²⁷ m³ in volume, a human about 0.1 m³ (all numbers from Google searches). Dividing those pairs of numbers, the sun radiates 0.4 J/sm³ while a human radiates 1000 J/sm³. So humans are stupendously more heat-producing per unit volume! Well, if you compare a human (where all of the volume is producing heat) with the sun (where only a small portion -- the core -- of the sun is actually producing heat). I've little doubt that the numbers would swing if restricted to the portions of the sun where fusion actually occurs. — Lomn 20:39, 24 March 2011 (UTC)

I just added numbers from only the core to my reply above. And they are so small I wonder if we can ever make fusion power work! The sun's core has a density 100 times that of water, and yet produces power so slowly, how can we hope to beat it? Ariel. (talk) 20:52, 24 March 2011 (UTC)

The reaction that happens in the sun is different from the reaction that happens inside a fusion power plant. The sun fuses Hydrogen. A power plant fuses deuterium and tritium. Dauto (talk) 22:53, 24 March 2011 (UTC)

One minor thing: you're listing power per mass rather than power per volume -- adjusting that, the human body only has a 2:1 edge. Not quite the swing I was expecting, but back into the realm of cautionary notes about back-of-the-envelope calculations. — Lomn 21:17, 24 March 2011 (UTC)

Thank you. Then what is the size of the core compared to the whole sun.Phalcor (talk) 21:00, 24 March 2011 (UTC)

About %20 (but depends on if you measure by mass, volume, or radius). See Solar core. Ariel. (talk) 22:19, 24 March 2011 (UTC)

Just one last crazy thought on this subject. If we could find a way to artificially duplicate the heat production efficiency of the human body in a machine, perhaps we would have an efficient power plant. Comment not seriously expected. Phalcor (talk) 21:29, 24 March 2011 (UTC)

We do it every day, with all normal fuel burning power plants. Ariel. (talk) 22:19, 24 March 2011 (UTC)

Why iodine from nuclear reactor?

As far as I know nuclear reactors do not have iodine or even iodide in them. So how has the Japanese nuclear disaster resulted in radioactive iodine in tap water? How did it get there, where did it come from? Thanks 92.24.188.210 (talk) 20:50, 24 March 2011 (UTC)

Iodine-131 is a major fission product of uranium and plutonium. Mikenorton (talk) 20:54, 24 March 2011 (UTC)

BTW, Iodine-131 has a half life of only 8 days, so the damage will be limited. The other main product is Cesium-137, which lasts a lot longer, but unlike iodine has no biological role, so is not stored by the body. Ariel. (talk) 20:57, 24 March 2011 (UTC)

If it has a short half-life, that means it gives off all it's radiation in a short period, making it even more dangerous if it's in your thyroid during that period. Also, if it causes DNA changes, those could then take years to progress into cancer. StuRat (talk) 23:09, 24 March 2011 (UTC)

Our article on ¹³⁷Cs says that it does mimic potassium...it's not stored (highly incorporated into biochemical/biophysical structures) but it sure does pass through lots of pathways before clearing (which takes several months). DMacks (talk) 21:26, 24 March 2011 (UTC)

The main difference is that the radiation from cesium is spread out in the body, rather than concentrated in the thyroid, so it's far far less harmful. (The body can handle low levels of radiation, but the concentrated radiation from iodine in the thyroid causes more harm than would be expected by the low dose.) Ariel. (talk) 22:27, 24 March 2011 (UTC)

I think Iodine-129 is also an isotope of concern. It has a much longer life. --Mr.98 (talk) 00:56, 25 March 2011 (UTC)

Yah, although probably not for the water in Tokyo. It's yield in reactors is low (about 1/3 of I-131), it's half life is so long that it's not very radioactive - it's almost 1 billion times less radioactive than I-131, and when it does decay the decay energy is low and is less harmful (about 1/10 of I-131). Overall while I-129 is carcinogenic, I-131 has not been found to be[5]. (With a biological half life of 11 days to a few month, the I-131 is cleared out of the body before it can do much harm.) Ariel. (talk) 01:17, 25 March 2011 (UTC)

That sounds a little like you've mixed up the two isotopes in the last two sentences? I-131 has a shorter radioactive half-life than the 11 days, so I don't know why you'd focus on that. It's true that the PDF claims that I-131 has not specifically been found to cause cancer, but I'm not sure what they mean by that (the increase in child thyroid cancers from nuclear testing and Chernobyl is pretty well-documented, I think, and for the reasons you yourself give, it's more likely to have been I-131 than I-129). --Trovatore (talk) 18:31, 25 March 2011 (UTC)

Thanks. What happens to the fission products when the reactor it working normally? Where do they go? Do they eventually end up in landfill, for example? 92.24.188.210 (talk) 21:16, 24 March 2011 (UTC)

In the US after reprocessing and extraction of plutonium and uranium for further use they might end up in Yucca Mountain nuclear waste repository. Not an exactly a landfill, but also not much different.--Stone (talk) 21:43, 24 March 2011 (UTC)

Quibble: I don't believe the Yucca Mountain plan involves any reprocessing; as the Yucca Mountain nuclear waste repository article states, the US doesn't possess any nuclear reprocessing facility at all, except that the military does, for creating nuclear weapons. Comet Tuttle (talk) 22:11, 24 March 2011 (UTC)

Comet Tuttle is correct; the US doesn't do any civilian reprocessing of spent fuel. It was considered at one point but killed in the 1970s because of the security implications. (Inventory control is a very serious problem with reprocessing. In a large plant like the Rokkasho Reprocessing Plant in Japan, the amount of "material unaccounted for" is, no matter what you do, going to be on the order of several Nagasaki-sized bombs per year. That means you essentially cannot detect theft or diversion through inventory control alone, which is rather unsettling. This isn't a matter of building better instruments — there is some inevitable loss in the process that you cannot account for, even at best times, and that adds uncertainty in your ability to track it. It may only be 1-2% of lost material, but when that material is plutonium, "a dab'll do ya".) We don't even do waste disposal at the moment. Things are stuck in a really horrible political/legal/technical situation and there has been little progress so far. There is currently a Blue Ribbon Commission that is supposed to be figuring this out. Good luck to them. --Mr.98 (talk) 00:54, 25 March 2011 (UTC)

In the US, they stay in a swimming pool there at the reactor, for at least 5 to 20 years (see spent fuel pool), then they may stay in the pool forever, or may be pulled out and put into dry cask storage. The Yucca Mountain plan was formed because there was no US national policy to deal with spent nuclear fuel. As the Yucca Mountain article states, the US still has no functioning policy; it's sort of cut off or suspended at the moment, and court challenges are ongoing. Comet Tuttle (talk) 22:14, 24 March 2011 (UTC)

Highly radioactive fission products have short half lives, and decay relatively quickly into more stable things. So your immediate waste is very hot, but after a year or five in the spent fuel pool, they cool off pretty considerably. The problem is that the "more stable" things are still radioactive — and because they are more stable, they stay that way for thousands of years. But the stuff that ends up in the waste site (in countries that actually have waste sites) is not as "hot" as the stuff that comes right out of the reactor, or is stored in the spent fuel pool. --Mr.98 (talk) 00:54, 25 March 2011 (UTC)

Is there a country operating a long term waste storage site for comercial nuclear waste? I know that Germany, Finland, Sweden try to find one or already built tunnels for storage, but operational is non of the facilities.--Stone (talk) 09:33, 25 March 2011 (UTC)

Here's a story complaining that French nuclear waste is being sent to Russia for reprocessing but a lot is just dumped in Siberia. Comet Tuttle (talk) 21:20, 25 March 2011 (UTC)

Is it just me or is nuclear power just ridiculously irresponsible? I mean, is it so important to have power that making more and more super-toxic waste is somehow an acceptable outcome? Yes this is a moral question, not a technical one. But I'm still interested in others' opinions. Vranak (talk) 18:15, 25 March 2011 (UTC)

Other forms of power source either contribute to global warming and pollution or are not economically robust enough. Actually nuclear power is considered widely as relatively "greener" than other conventional sources.--Netheril96 (talk) 18:26, 25 March 2011 (UTC)

Netheril96's last claim is incorrect, at least the word "widely". Environmentalists are painfully split on whether nuclear power is better or worse than the alternatives. Here's a recent Greenpeace press release renewing their call for the phaseout of nuclear power. Comet Tuttle (talk) 21:20, 25 March 2011 (UTC)

Is there anyone who understands the science and still thinks that solar, wind, etc. can replace fossil fuels without nuclear? As far as I can tell, Greenpeace's belief in renewables is a matter of faith. Their whole existence as an organization depends on the viability of renewables; therefore, renewables must be viable, from their perspective. Kind of like the right doesn't believe in global warming because it's inconsistent with the optimality of the free market. It is difficult to get a man to understand something when his salary depends upon his not understanding it, as someone once said. -- BenRG (talk) 21:59, 25 March 2011 (UTC)

I think the Greenpeace people would suggest that the answer is renewables plus a radical restructuring of society to use less energy. Which could work from a technical point of view. But shows little evidence of political traction. If you look at the kind of world that Greenpeace people imagine, it's smaller — more local, shorter distances, less reliance on technological advance. It's not an ugly world in many ways (though we need to recall that the "good old days" of smaller living were not so great for the vast majority), but I don't see any evidence to think that the trends of the world are going in that direction. --Mr.98 (talk) 22:28, 25 March 2011 (UTC)

Nuclear power itself isn't irresponsible, but some of the issues surrounding it are. Building a plant in a populous area without adequate safeguards is irresponsible. Building a plant without a long-term storage solution (already prepared) for the nuclear waste is irresponsible. StuRat (talk) 22:39, 25 March 2011 (UTC)

coriolis effect in deep space?

the coriolis effect on water down the plug hole due to the rotation of the earth seems easy to grasp, but when I look at Hubble deep space photos of spiraling/spinning galaxies, all of those I've seen seem,(from the telescopes view point) to be spinning in the same direction. Given the apparent random nature of the universe it seems that coincidence is unlikely. Could the universe, as a whole, be spinning, having the same effect on the galaxies? And if so, could that cause the red shift effect attributed to universal expansion. Phalcor (talk) 22:56, 24 March 2011 (UTC)

1. Water down the hole does not spin because of Coriolis.
2. The galaxies don't all spin the same direction.

Dauto (talk) 23:05, 24 March 2011 (UTC)

It would be interesting to see numbers on how many galaxies observed are aligned with the Milky Way (or some other axis) vs. opposite to it. Wnt (talk) 00:02, 25 March 2011 (UTC)

Anything except 50/50 would be quite a big deal. See here for more. Ariel. (talk) 01:21, 25 March 2011 (UTC)

Hmmm, proving that their Galaxy Zoo annotators are biased isn't quite the same as proving that the galaxies are truly unbiased. We have the precedent of matter vs. antimatter to suggest that tiny asymmetries can exist and become very important, so I'll hold out for a truly reliable count of all the visible galaxies. ;) Wnt (talk) 08:06, 25 March 2011 (UTC)

It would be very remarkable if spiral galaxies showed a preference for one orientation as viewed from the Earth, because this would mean we occupied a privileged position in a non-isotropic Universe. Our spiral galaxy article says that there is some evidence that the axes of spiral galaxies tend to be aligned with their local galaxy filaments, but there is no mention of any correlation of spin direction. Gandalf61 (talk) 10:14, 25 March 2011 (UTC)

I don't see why it would imply we were in a privileged position. As an extreme example, suppose all galaxies had their spin axis pointing in the same direction. You'd be able to see that from anywhere in the universe, not just here. Or am I missing something? --Trovatore (talk) 22:20, 25 March 2011 (UTC)

If all galaxies had their axes pointed in the same direction, we would see some of them winding clockwise and others winding counterclockwise, depending on whether they are "above" or "below" us with respect to the universal axis. If we were really seeing more clockwise than counterclockwise galaxies, there would need to be something very spooky going on. It wouldn't necessarily place us exactly at a globally privileged position unless the tendency towards clockwise were equally strong in all areas of the sky, but it would kill isotropy. –Henning Makholm (talk) 23:27, 25 March 2011 (UTC)

Well, but we don't have to assume we're stupid. If we see all the galaxies in one direction spinning dweezil and all those in the other direction going widdershins, then we get fifty-fifty in terms of total numbers, but we're allowed to say that's strange, and it already means there's a preferred axis to the universe (or at least the part of it we can see). --Trovatore (talk) 01:20, 26 March 2011 (UTC)

I'm unsure what it is you're arguing for here. Gandalf said that if we were to get total numbers different from 50-50, that would be very remarkable, and it looked like you disagreed with that statement. Now you seem to be saying that some conceivable observations could total to 50-50 and still be remarkable -- which is true, but does not oppose Gandalf's original statement. Am I misunderstanding you somehow? –Henning Makholm (talk) 16:03, 26 March 2011 (UTC)

To be clear, I was only interested in the spin relative to a specific axis, but a significant error rate in spin determination relative even to the original photograph pretty much kiboshes any further working of the data. Wnt (talk) 21:48, 26 March 2011 (UTC)

An ESO VLT ground-based image.

By the way, can we reliably observe which way distant galaxies spin? It's often easy to see visually which way the spiral arms are curled, but how well is that known to correlate with the kinematics of the disk? I suppose we can measure the Doppler shift of spectra at different ends of the major axis of the galaxy's elliptical image in the sky, but that does not seem to resolve the question unless we know somehow which end of the minor axis is closer to us. –Henning Makholm (talk) 16:03, 26 March 2011 (UTC)

True, and that can be easily seen from the fact that interstellar gas obscures the further side. see for instance the picture of the sombrero galaxy that I included. Dauto (talk) 17:45, 26 March 2011 (UTC)

Sure -- but on the other hand, I cannot see the spiral arms in that image. Are there angles under which a typical spiral galaxy shows both clear spiral arms and clear occultation of the far side? Have enough of those been surveyed that we can say with certainty that spiral galaxies predominantly spin with the arms leading or arms trailing? If so, which one is true? And how common (or not) are exceptions? –Henning Makholm (talk) 14:34, 27 March 2011 (UTC)

I never did find a clear statement of which way the arms of a spiral galaxy point, but I found Spiral_galaxy#Alignment_of_spin_axis_with_cosmic_voids which is interesting. But this suggests that galactic spin axes are influenced by the proximity to the void, rather than some universal spin. While it hints that galaxy spin axes might be nonrandom (for example, if the voids were aligned with one another) it would further conceal any universal spin. Wnt (talk) 23:22, 27 March 2011 (UTC)

I don't know anywhere to point you for this. But isn't it intuitively obvious? Stars closer to the center move faster; that's just ordinary orbital dynamics. So the arms trail the spin. --Trovatore (talk) 05:33, 28 March 2011 (UTC)

It's not obvious to me: the spiral arms are supposed to be density waves whose macroscopic movement differs from that of the actual stars in the galaxy. And if the spiral arms participate in the galaxy's differential rotation, then they ought to be wound so tightly they would be smeared out completely by now -- unless there's something that periodically creates fresh spiral/radial structure. –Henning Makholm (talk) 03:31, 29 March 2011 (UTC)