Wikipedia:Reference desk/Archives/Science/2007 November 30

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November 30

MO theory

Hey, I'm in Chem II and we are doing MO theory. We did easy ones in class like O₂ and N₂ and the n=2 elements. But I have no clue how to do like Al₂³⁺! Does the d orbital even have anything to do with MO theory? Thank you! —Preceding unsigned comment added by HALPpls (talk • contribs) 02:04, 30 November 2007 (UTC)

I assume you're referring to molecular orbitals. However, I still have no idea what exactly you're trying to do. Someone versed in the field might understand your question as asked, but it might be a good idea to explain your goals more precisely. For example, are you looking for a qualitative statement or a quantitative calculation? Algebraist —Preceding comment was added at 03:11, 30 November 2007 (UTC)

d atomic orbitals are quite important for the molecular orbitals for some bonds and molecules. It would be hard to get 10 (!) bonds from the central iron atom in ferrocene with just s and p. At the level I think you're working, I think you do Al₂³⁺ the same way you have done other examples (that's how things are usually taught, no?): list the atomic orbitals of each atom, hybridize and mix'n'match them by symmetry. Perhaps you could tell us how far you've gotten on your own and what specific problem you're having? DMacks (talk) 03:19, 30 November 2007 (UTC)

It's a way of telling what electron configuration of a molecule is most likely, and how stable it is, if it exists at all. It uses quantum mechanics. —Preceding unsigned comment added by HALPpls (talk • contribs) 03:31, 30 November 2007 (UTC)

Aluminium doesn't have d electrons!!! Valance electrons are 3s2, 3p1. So... You will have a filled bonding sigma orbital and a fill antibonding sigma orbital. Plus one filled pi orbital. But that is for Al₂.

Don't know what you mean by Al³⁺ Is it a bond between Al and Al³⁺? —Preceding unsigned comment added by Shniken1 (talk • contribs) 04:00, 30 November 2007 (UTC)

Al₂³⁺ doesn't say anything about where the charge is…that's one of the things that MO theory can help determine. You just line up the molecular orbitals in order of energy, then start adding as many electrons as you have in total. Each Al would contribute 3 valence electrons if this thing were neutral; it's a net +3 charge, so it has overall 3 less electrons than that. DMacks (talk) 04:13, 30 November 2007 (UTC)

Even though Al doesn't have any d electrons, it can indeed use d orbitals to make bonds. Anyway, however I have only known aluminum to do this when forming complex ions. Just treat like you'd treat anything else, but with three electrons. Someguy1221 (talk) 08:04, 30 November 2007 (UTC)

An example of an answer:

O₂ Bonding electrons: 8 Anti-bonding electrons: 2

Likelyhood: 6 - very likely

O₂^1- Bonding electrons: 8 Anti-bonding electrons: 3

Likelyhood: 5 - likely

O₂⁴⁺ Bonding electrons: 4 Anti-bonding electrons: 2

Likelyhood: 2 - semi-likely

I don't know how to show my work on here, because it involves pictures...--HALPpls 22:29, 30 November 2007 (UTC)

You're problem is using the electrons on only one atom to make the bonds. You must use all valence electrons on both atoms. And remember that a diatomic molecule can make as many molecular orbitals as it can atomic orbitals, so this also means dioxygen has twice as many available orbitals as a lone oxygen atom. Think about this, and maybe you'll see where you're going wrong. Someguy1221 22:37, 30 November 2007 (UTC)

I take that partially back, I'm not sure where you got your total number of electrons from. Just sum up all the valence ones...Someguy1221 22:45, 30 November 2007 (UTC)

I'm looking for the likelihood of binary molecules that have a d orbital.--HALPpls 12:02, 1 December 2007 (UTC)

I₂ is a diatomic molecule composed of atoms that have d atomic orbitals. Not sure (i.e., depends how carefully you analyze and how literally you define your terminology) whether one would consider them to be involved in molecular orbitals vs being "just lone pairs" on each atom. DMacks 07:09, 3 December 2007 (UTC)

Light green slime

What metal would react with human sweat/salt to give a light green colored slime. i just scraped some off my glasses frame wher they contact the side of my head.--TreeSmiler (talk) 03:34, 30 November 2007 (UTC)

Anything with copper in it will produce a green "slime" when it is in contact with sweat. You mention glasses though. It is common for glasses to go day after day in contact with the skin (dirt and sweat) without being cleaned. So, just about anything can grow on them. I found that boiling my glasses once a week helped a great deal - more often during football season. -- kainaw™ 03:39, 30 November 2007 (UTC)

Hmm dont seem to look like copper, looks more like nickel. Could be some form of cupro-nickel I suppose--TreeSmiler (talk) 05:06, 30 November 2007 (UTC)

Be careful with this boiling. Once when I was trying to fix some broken glasses I got some glue on the lens. To try and help clean it off, I was using boiling water. But I found out the coating was not resistant to such high temperatures (I presume) and so was damaged and the glasses became unusuable. I.E. You should check first that your lenses will not be damaged by the boiling water (I just did a few searches and it appears adhesion after exposure to boiling water to be a common test/feature for coatings so I would presume it's not an uncommon problem although new and more expensive coatings will probably be fine). Nil Einne 10:39, 3 December 2007 (UTC)

Planet Venus

If the poisonous gases and voilent weather did not exist on Venus, what would happen to you if you landed on Venus?--WonderFran (talk) 03:40, 30 November 2007 (UTC)

You would be crushed by the atmosphere that is 300 times as dense as the Earth's. Oh and it is a bit warm there so pack your shortsShniken1 (talk) 03:43, 30 November 2007 (UTC)

What would the pressure be like compared to the deepest part of the ocean? --WonderFran (talk) 03:45, 30 November 2007 (UTC)

Read the article on Venus. This is a direct quote from it: "...a pressure equivalent to that at a depth of nearly 1 kilometer under Earth's oceans." -- kainaw™ 03:46, 30 November 2007 (UTC)

The New York Times today ran a science article [1] saying that the latest results from observations by the Venus Express probe imply that it had origins very similar to Earth, and that it once could have had oceans. The two planets were described as "twins separated at birth." Venus is about the same size and mass as Earth. Its present inhospitable atmosphere took eons to develop, as the water evaporated and the hydrogen dissipated into space, leaving the oxygen combined into carbon dioxide. So what might Venus have been like on its most Earthlike day? Could it have been like early 20th century sci-fi writers and scientists imagined it, with tropical jungles? Edison (talk) 04:28, 30 November 2007 (UTC)

Still, we are doing our best to make the twin planets identical again.  :-( SteveBaker (talk) 04:33, 30 November 2007 (UTC)

Venus does not have (and there is no sign that it once had) a magnetic field strong enough to block radiation. It would be difficult for life to survive while constantly bombarded by high amounts of radiation from space. Perhaps it could develop in the deep water (as it did on Earth), but not on the surface. -- kainaw™ 04:35, 30 November 2007 (UTC)

It's basically a myth that the Earth magnetic field is directly critical to life. The Earth's field collapses to near zero every once in a while, and there has never been an unambiguous impact on the fossil record. The atmosphere itself is far more critical to blocking radiation on our planet. Dragons flight (talk) 08:15, 30 November 2007 (UTC)

While Venus's lack of a strong magnetic field certainly contributed to its current situation, getting twice as much sunlight just might have played a big role. Someguy1221 (talk) 08:18, 30 November 2007 (UTC)

It's not how much sunlight you GET that matters - it's how much you KEEP. With no green plants turning its CO2 into Oxygen, CO2 buildup from things like volcanoes is no small matter. With the ultimate in global warming and absolutely nothing there to reverse it - this is what you get. As the temperature rises, the oceans evaporate - water vapor is even more potent as a greenhouse gas than CO2 - so once things get just so hot, you get to a point of no return. At high enough temperatures, the water dissociates into hydrogen and oxygen - the hydrogen drifts away and the remaining oxygen gets turned into CO2 too. CO2 is a lot heavier than air - and pressures also increase with temperature - so you get an amazingly hot, dry planet with off-the-chart atmospheric pressure. If green plants had appeared on Venus, the extra sunlight would have been tolerable. After all, there is a much more than 2:1 variation in amount of sunlight we get at the equator than at the higher latitudes. SteveBaker 18:18, 30 November 2007 (UTC)

Mmm, but you needed the initial high levels of CO2 to have a reducing atmosphere necessary to spark life. THEN after you had the spark going, could you afford high oxygen levels. Elle _{vécut heureuse} ^{à jamais} (Be eudaimonic!) 02:28, 5 December 2007 (UTC)

How much sunlight you get does matter when you consider the effects it has on the atomospheric conditions of a planet with large water oceans :-p Don't take my word for it, read the nytimes article linked to above. Someguy1221 19:35, 30 November 2007 (UTC)

Can dolphins and whales REALLY talk in some way that humans do?

I am a talking dolphin / whale sceptic, big time. I don’t believe that whale songs that repeat long and complex sequences over long periods of time constitute “talk” in any way that we humans understand it. Human language involves transmission of complex and finely nuanced information. To do this, we have labels (words) for just everything we have encountered. With this, we can convey very detailed information using those words in a structured way. The other day, I saw a Chinese newsreader on ethnic TV, and she was going full blast. I don’t have a word of Chinese, but the sound of it was like no animal noise. Common sense would tell you that the more you repeat the same phrase, the less information you are giving out, not vice versa. If whales could really communicate, they would have organised a boat tipping sortie in the old days and capsized the rowboats with their harpooners. I honestly cannot see how, historically, whale reaction to whale hunts has been any different to the reaction of any game animals that have been hunted by humans.

And I am puzzled as to why data on this question seems to be so murky. There are any number of good experiments I can envisage which could go a long way to answering the question, but no one else seems to be bothered. For example, you could have a pair of dolphins in one section of a pool which has another adjoining section. One dolphin has to swim to the second section where he can see three apertures in a wall, all designed to look different, e.g. one looks like a mound of seaweed, the second a rock, and the third a ball. A light appears above the aperture which holds the food treat. The only way the dolphin can get the treat is to swim back to the other dolphin (who cannot see into the second pool section) and “tell” her which aperture holds the food. Then the second dolphin is allowed to swim into this section and touch the food aperture, releasing the food. But she only has a certain amount of time to do this, and if she nudges the WRONG aperture, the treat is forfeit. Can the dolphins communicate to the extent of “select the seaweed thingy”, or not? Because if they can’t, then I would be loathe to say they can communicate in any way analogous to humans, who have, in every culture and for at least 60 thousand years been able to do things like that from eqarly childhood.

There are many such possible experiments. Is there any consistent research been done on such topics? I am sick and tired of hearing New Age types waxing fulsome on cetaceans being another intelligent species, with very little evidence to show for it. Myles325a (talk) 05:13, 30 November 2007 (UTC)

I don't think that many argue that cetaceans have anywhere near as complex a language than humans do. I don't wish to imply that intelligence is unconnected with language, but language is not the end-all, be-all of intelligence. These matters and others are discussed in our article on cetacean intelligence.--Fuhghettaboutit (talk) 05:34, 30 November 2007 (UTC)

First of all, there are a number of ways in which your experiment could fail, not least of which would be the utter confusion of being placed in an unfamiliar experiment setting. Specific instructions can also be difficult linguistically, as if the situation is less common then the potential for miscommunication or misunderstanding becomes very high. I was very briefly involved in research on dolphin communication, and everything was done with data from wild dolphins who were observed while communicating. In the first stage of analysis, the data was going to be analyzed in a blind fashion to see how different sounds corresponded to different behaviors. There would then be a breakdown of signals into principal features which would then be analyzed to see if there is a component structure to the communication. The last thing to analyze would be the arbitrariness of the components to determine if the language was in fact symbolic. So far, I think it's still at the first stage. SamuelRiv 15:12, 30 November 2007 (UTC)

Your post about language not being everything reminded me of this bit from a Douglas Adams book:

Man had always assumed that he was more intelligent than dolphins because he had achieved so much — the wheel, New York, wars, and so on — whilst all the dolphins had ever done was muck about in the water having a good time. But conversely, the dolphins had always believed that they were far more intelligent than man — for precisely the same reasons.

 :) --Sean 16:18, 30 November 2007 (UTC)

I don't know about dolphins, but my understanding of whale "communication" is that it has some features of what we would call language but missing some other parts that are vital (and I think the experiment laid out would fail to show any sort of communication). Personally, I would call what they have "proto-language" or "pre-language" since it is more than the biologically ingrained noises (such as that of dogs or cows) but does not have the complex (and arguably ingrained) features of human language. If I recall correctly, whale researchers have found that different pods will have different "song dialects" and that closely related pods will have similar dialects (see historical linguistics for the human language analogue).

The main problem with our understanding of whale songs is that if there's any meaning behind them we really don't know what they're ever saying. Ƶ§œš¹ _{[aɪm ˈfɻɛ̃ⁿdˡi]} 01:40, 1 December 2007 (UTC)

I doubt any other animal REALLY talks in the same way that humans do, to use the OP's words. But whether other animals "talk" depends on what one means by talk, and language. Dolphins and whales certainly seem to be contenders. The Orca article (a dolphin-related species) has a few teasers on this. Many bird species also seem contenders, depending on how you define "language". See Crow#Behavior for example. And crows are neophytes compares to some birds. In my personal experience, crows seem to communicate some fairly complex ideas between one another. Of course none of these examples are talking like humans REALLY talk. But they clearly, to my mind, indicate intelligence and rather sophisticated communication skills. Pfly 03:47, 1 December 2007 (UTC)

It could be that humans have frontal lobes, and no animals do. The frontal lobe is what helps you use logic. They probably communicate, but it's probably more like voice tone communication. RJRocket53 02:59, 2 December 2007 (UTC)

OP myles325a responds to Pfly. I don’t see how you make your point any clearer by capitlising REALLY when you write “I doubt any other animal REALLY talks in the same way that humans do…” especially when you add in the next sentence that “Dolphins and whales certainly seem to be contenders [for animals who “talk”]. Melodious, harmonious chanting is NOT a fundamental characteristic of human communication. How much of it do you do, for example? It is the non-repetitive, staccato bursts of words, full of complex semiotic input, which others can act on, often in seconds. My reasoning is that if animals were really exchanging complex and specific data in this way a) the language would be anything BUT mystical long-chain mantras and b). the consequences of such exchanges would have enormous effects on group behaviour, as in my example of how whales could have upturned harpooners’ rowboats if they could communicate. To say that dolphins communicate in “voice tone” is to say that they communicate the way just about all other mammals, and indeed birds do.

And to SamuelRiv I described the proposed experiment very briefly. Of course, the dolphins would be acclimatised to working with humans in similar scenarios, and there would be a number of transition steps before the research proper began. These would include game-play in the 2-pool set up, with the dolphins pressing the food apertures when they have a full view of them. Only later would the game become more challenging. Such procedure are already followed in many similar experiments.

I am beginning to think that much of the material written on the intelligence of dolphins comes from essentially science-loating new age types, and people who think that cute and friendly equals “intelligent”. Such people are sure that their ever-lovin’ pooch is really intelligent because the highlight of his day is when he can just lie on your lap and slobber all over you. In truth, wolves are much more intelligent than such infantilised dogs, and they would rather eat than lick you. EQ is not IQ. Myles325a (talk) 01:42, 6 December 2007 (UTC)

Long acting injectable drugs

I had a couple questions about long acting injectable drugs. Lets say you have testosterone enanthate or cypionate.

1. Why do they have to suspended in oils? 2. What happens if its not in an oil? Like in a liquid like bacteriostatic water 3. What happens if its not put into a muscle and just under the skin? —Preceding unsigned comment added by 76.167.132.90 (talk) 05:58, 30 November 2007 (UTC)

1. The oil is the means by which the long-acting effect is achieved. 2. It would last a considerably shorter time. 3. Again, it would last a considerably shorter time, and would also hurt like hell. - Nunh-huh 13:09, 30 November 2007 (UTC)

1 & 2: Considering testosterone, I guess it's not much better soluble in water than cholesterol (0.095 mg/l), and esterification with relatively hydrophobic acids won't change much. So if you have got a solution of water and testosterone it has to be very dilute or the testosterone will separate (and it's solid at room temperature). Icek 13:16, 30 November 2007 (UTC)

I just discovered that testosterone can practically be applied as a suspension in water[2], so forget my previous comments. Icek 18:31, 1 December 2007 (UTC)

Vandalism?

Is there really a medical problem called "Seradocious Lupius canaralium", or is this (as I suspect) vandalism of James Francis Smith? Clarityfiend (talk) 08:00, 30 November 2007 (UTC)

Since google shows nothing medical related for even one of those words, I'm going to guess vandalism, and about the oldest lingering vandalism I have ever seen. Someguy1221 (talk) 08:11, 30 November 2007 (UTC)

Unless Leonhard Euler is in fact known for "loving toast real good", the vandalism wouldn't be out of character for that IP. jeffjon 13:50, 30 November 2007 (UTC)

Either way - if there isn't a good reference for it, you are justified in removing it on suspicion alone. SteveBaker 17:59, 30 November 2007 (UTC)

Why does poliovirus preferentially infect motor neurones

The article on Polio states that motor neurones are preferentially infected - why is this? —Preceding unsigned comment added by 81.179.82.224 (talk) 12:02, 30 November 2007 (UTC)

This is an area that is incompletely understood, but poliovirus receptor and host factors, as well as type I interferon response, are believed to play roles in the neurotropism of virulent strains of poliovirus. [3] - Nunh-huh 13:07, 30 November 2007 (UTC)

Interesting. Thank you for your answer!

splitting atoms

How do you go about splitting an atom and what are the results of doing so? (aside from the obvious of coarse) —Preceding unsigned comment added by 59.101.238.31 (talk) 12:31, 30 November 2007 (UTC)

Have you read our article about Nuclear fission?

Atlant (talk) 12:57, 30 November 2007 (UTC)

The easiest way to split an atom is separating one or more electrons from it, creating an ion. But you probably mean splitting an atomic nucleus; Atlant already linked to the relevant article. Read it and come back if you have further questions. Icek (talk) 13:02, 30 November 2007 (UTC)

It's pretty much what you'd expect. You whack the atom with something really hard and fast (like a high speed charged particle in a particle accellerator) - it breaks - and you end up with one or more smaller atoms and some debris. That debris is in the form of left-over neutrons and such. If you hit a big, fat atom then the resulting matter will weigh less than the original atom and because of e=mc² you'll get some energy out too. (You could also put this another way and say that some of the debris you got out was in the form of photons...light, radio waves, etc). When you hit a Plutonium atom with a fast-moving neutron, you get energy AND some more fast moving neutrons. If there is enough plutonium around, those neutrons will probably hit more plutonium atoms and make yet more energy and yet more free neutrons - and before you know it...KERPOW! SteveBaker 17:57, 30 November 2007 (UTC)

No No No. A hammer and chisel will do.

Why does lightning shock you even if you are ungrounded?

Still a little confused on this, so if someone can explain in layman's terms, that would be great. You can touch a power line, and not get shocked if you are ungrounded. But if you are hit by lightning you will be shocked whether you are grounded or not. Why is this? 64.236.121.129 13:58, 30 November 2007 (UTC)

"Grounded" isn't an all-or-nothing concept; whatever insulator is keeping you ungrounded can break down if the voltage is high enough. For example, the rubber soles of your sneakers might (might!) keep you ungrounded against your 110 V home outlet, but could break down and provide a path to ground if you touched a high-voltage transmission line. Similarly, if you were hovering 10 feet above the ground, that 10 feet of air might keep you ungrounded if you touched a transmission line, but a lightning bolt is capable of ionizing and traveling through that air. (After all, it can travel through air the whole way from the cloud to the ground.) -- Coneslayer 14:14, 30 November 2007 (UTC)

What if you shoot a taser or electrolaser at a bird or someone who happens to be floating in the air (for whatever reason). 64.236.121.129 14:52, 30 November 2007 (UTC)

The relevant potential difference in a taser is between the two terminals of the taser. It does not require an earth ground to operate. (Same idea as a battery, for example. If you short the terminals of a 9 V battery with a paperclip, you'll see a spark. No connection to earth ground is required.) -- Coneslayer 14:58, 30 November 2007 (UTC)

I see. What about an electrolaser? 64.236.121.129 15:12, 30 November 2007 (UTC)

I don't know anything about them, but I think the article answers your question directly:

To complete the electric circuit, there must be either a second laser beam, or a ground return, from the target to the last transformer in the step-up series.

-- Coneslayer 15:19, 30 November 2007 (UTC)

No, there doesn't. It depends on the frequency of the source and the impedance match of the target. Energy will be directed and reflected back. The plasma channel supplies both the forward (S12) and return (S21) path. --DHeyward 15:44, 30 November 2007 (UTC)

It's a matter of completing the circuit from source to ground. Let's imagine three cases:

1. You are wearing a jet-pack and you fly up to a 1000 volt overhead power line and grab hold with one hand. To be clear, this is not one of those insanely high voltage wires...but it's enough to kill you if you mess up.
2. You do the same thing but grab hold with both hands.
3. You are flying along in your jet-pack and you get struck by lightning.

In the first case, the wire doesn't have enough voltage to arc down though the air to hit the ground - we know that for sure.

When you touch the wire, you are at 0 volts, the wire is at 1000 volts and very briefly, a small (hopefully) current flows to bring you up to 1000 volts - but it can't go anywhere because it's still not strong enough to break through the air to the ground - so no massive amounts of current flow through your body and whilst you might feel it - it won't kill you because this is like static electricity. If the voltage on the wire is really high though, that initial transfer to get you up to the voltage on the wire could still kill you. When you touch the wire with both hands, electricity could theoretically flow up one arm, across your chest and back down the other - but it's not going to do that unless your body has a higher electrical conductivity than the wire itself - which it doesn't. The current prefers to take the easy route...so not much voltage passes through you and you're OK still.

When you get struck by lightning, the critical differences are that the voltage is more than enough to allow the lightning to break down the air and reach the ground - so there is no problem with the lightning hitting your head, passing through your body and exciting at your feet - then carrying on to complete the circuit through the air to the ground. The other thing is that your body (being mostly made of salty water) conducts electricity better than air - so unlike case (2), the electricity prefers to flow through your body than through the air - so you are definitely dead. SteveBaker 17:36, 30 November 2007 (UTC)

Interesting, thanks steve. Few questions. You said that the wire is 1000 volts. If you touch it with one hand, it will bring you up to 1000 volts. But how many amps is the wire, and how many amps are flowing through you if you are ungrounded and touch with one hand? How many volts and amps would flow through you if you touch the same wire while being grounded? If your body for some reason had higher electrical conductivity than the wire, and you touched with two hands, how many volts and amps would pass through you then? 64.236.121.129 18:50, 30 November 2007 (UTC)

(I just picked 1000 volts - real power cables have all sorts of different voltages, many are MUCH higher than that!)...I don't know how many amps the wire could deliver - but will be a lot more than it'd take to kill. If you are holding onto the wire and are not grounded then ZERO current is flowing through you. If you are grounded then we can use Ohms law (V=IR) to calculate the current (I, in amps) from the Voltage (V in volts) and the resistance of your body (R in ohms). Most people's bodies have a resistance of about a half to two MegaOhms - but most of that resistance is due to your skin - beneath the skin you are made of salty water - which conducts electricity extremely well. Since even a brief jolt of 10milliAmps to serious damage to you - and only 100 milliAmps will kill - you can tell that a voltage of only 500,000 x 0.01 = so 5,000 volts is a problem. However, that assumes your skin is intact. If your skin is broken, then your body resistance is very low indeed - 100 ohms perhaps. Then 100 x 0.01 ...ONE VOLT is enough to do it! If this seems unlikely to you, check this out: Courtesy of the Darwin Awards [man electrocuted by 9v battery]. This is why just 110 volts from a US wall outlet is enough to kill you if you take it for long enough to damage your skin. SteveBaker 22:00, 30 November 2007 (UTC)

That's interesting how you can have voltage, but not current (amps) running through you. If you were to use the water analogy, how would that work? It would be like there's a mysterious pressure running through the ground, but no water... Malamockq 00:28, 1 December 2007 (UTC)

Take a stream -- that's your wire. Dig a small hole beside it -- that's you. Dig a shallow trench connecting the two -- that's your hand. The brief inrush of water is the "ow shit" feeling you get as you grab the wire, but once the hole fills with water, nothing more flows -- you're now at the voltage potential of the wire. --Carnildo 01:25, 1 December 2007 (UTC)

You know, now that I look back on this question, http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#Power_lines.2C_and_electric_shock Steve Summit said that there will be a small influx of current when you touch a powerline while ungrounded. So maybe the current isn't quite zero? Malamockq 00:34, 1 December 2007 (UTC)

It isn't quite zero. There's a small transient current, corresponding to the self-capacitance of the human body. But that capacitance is extremely small, so the transient current approaches zero very quickly. --Trovatore 00:40, 1 December 2007 (UTC)

(ec) Current only flows when there is a voltage (potential) difference across you. Current flows when you're grounded because the ground and the wire are at a different potential, and it decides to use your body to make the trip. When you touch a wire, like Steve says, your body is at a different potential, so current will flow. But it only takes a teensy tiny amount of charge to bring your body to an equal potential. You get electrocuted when that tiny amount of charge can then leave your body, and more comes in behind it (quickly). Someguy1221 00:44, 1 December 2007 (UTC)

Oh, I hadn't noticed that the original question specified a 1000-volt overhead power line. That's alternating current, not direct. So I was wrong -- the current is not actually a transient that approaches zero; there's a tiny current that will flow in and out of your body for as long as you hold on to the wire. Presumably the impedance article will tell you how to calculate it, once you find a numerical value for the self-capacitance of the human body. --Trovatore 00:49, 1 December 2007 (UTC)

I would like to point out a detail that I'm surprised this wasn't mentioned in the earlier thread. Yes, if you touch a live object, and you're not grounded, there will be a brief influx current as your body matches the voltage. But if that object is live with AC, like a typical power line, its voltage is constantly changing, and your body has to keep matching it. So the influx current continues flowing back and forth as long as you're touching it. As previously noted, we are talking about a very small current, nothing like what you'd experince if you were grounded, but I don't know how small. --Anonymous, 00:54 UTC, December 1, 2007.

I would beg to differ with the original questioner in that it is, in my opinion, quite possible to get shocked/killed etc whilst 'ungrounded' but swinging from (or being in close proximity to) a high voltage overhead power line. This is because the electric field strength (esp on 132 kV and above) can be great enough to cause lethal currents through the body. This is also why linesmen working on live overhead cables wear conductive equipotential suits to ensure that no dangerous current flows within their bodies.--TreeSmiler 01:37, 1 December 2007 (UTC)

That's true - and we discussed that in detail in an earlier question. I deliberately chose to use a (possibly mythical) 1000v powerline in order to avoid that complication. The OP is already pretty confused and we need to break the explanation down into easily digested chunks. So what you say is true - but not for my deliberately simplified example. SteveBaker 05:52, 1 December 2007 (UTC)

how tall is the talest dwarf

Wikipedia article dwarfism says: "The Little People of America (LPA) defines dwarfism as a medical or genetic condition that usually results in an adult height of 4'10" (147 cm) or shorter." So the answer to your question is 147 cm - that is, if you mean living people and not a fantasy creation. Lova Falk 15:19, 30 November 2007 (UTC)

...such as Carrot Ironfoundersson, the 2m tall dwarf (adopted, fictional). Gandalf61 15:35, 30 November 2007 (UTC)

Or the seven-foot dwarfs of the Kingdom of Loathing. Algebraist 04:56, 1 December 2007 (UTC)

Bone marrow transplant and DNA

Yesterday we watched a whodunit on tv in which the rapist/killer had got a bone marrow transplantation as a child, and because of this, the dna of his sperm was different to the dna of his blood. The sperm had his own dna, but the blood had the donor's dna. Is this really possible?? Lova Falk 15:32, 30 November 2007 (UTC)

I don't know about the transplant case, but it can happen due to having an undeveloped twin: see Lydia Fairchild, chimera, teratoma. It seems plausible. --Sean 16:28, 30 November 2007 (UTC)

This is absolutely true. The circulating cells in the blood all come from the stem cells in the bone marrow; see haematopoiesis for details of this process. If a patient's bone marrow cells are wiped out using chemicals and/or radiation (for example, to treat leukemia: a cancer of the blood) and replaced through a transplant, the patients blood will contain almost exclusively the donor's DNA. TenOfAllTrades(talk) 16:50, 30 November 2007 (UTC)

I thought red blood cells don't have DNA in them, so this is a non-issue. – b_jonas 09:08, 2 December 2007 (UTC)

Fully developed red blood 'cells' in humans are annucleate so lack DNA. However the vast majority of cells in human blood would I presume originate from the bone marrow which is why it's a problem. Obviously the DNA in human blood most come from somewhere I'm guessing it's from WBC, perhaps immature RBC and platetlets ... Nil Einne 10:30, 3 December 2007 (UTC)

I don't know if it's the same case but this was mentioned in New Scientist recently [4] which was picked up by multiple other news sources Nil Einne 10:30, 3 December 2007 (UTC)

What's the largest galaxy that we know of

^Topic 64.236.121.129 18:43, 30 November 2007 (UTC)

Galaxy IC 1101. Someguy1221 19:07, 30 November 2007 (UTC)

Zero-point energy and manipulating objects

I read the article on 0 point energy, and I don't understand most of it. In the game Half-Life 2, a zero-point energy device can manipulate, levitate, and throw objects without touching them. Is this a real potential ability zero-point energy can do? How can it do this? 64.236.121.129 19:00, 30 November 2007 (UTC)

In a word, "no". For more words, see Zero-point energy.

Atlant 19:01, 30 November 2007 (UTC)

Haha, being terse I see. I don't really understand the article, I already said that. 64.236.121.129 19:06, 30 November 2007 (UTC)

Zero-point energy is the lowest amount of energy a quantum mechanical system can contain. Since it's the lowest amount possible, you can't remove it from the system, and thus you can't ever do anything with it (well, you can do some fun things with the Casimir effect, maybe). As for the zero-point energy device, it was in severe violation of the law of conservation of momentum. It has no basis in reality, some guy (but not this guy) just made it up. Someguy1221 19:28, 30 November 2007 (UTC)

Some people think that it may be possible to use the Casimir effect to extract actual useful energy from absolutely nothing. Serious scientists get palpitations at the mere thought of it. Hence science fiction writers like to use it as a plot device to allow spaceships to zip around the place without needing tediously difficult things like fuel. As irresponsible as this is of sci-fi writers, video game writers are even less likely to be bothered with reality. So if you want to describe how some handy in-game gadget works, feel free to grab any set of random science-words and string them together. I want one of those nanotech quantum gravity tachyon crossbows - it fires this pinkish-green ball lightning stuff and turns anything it hits into blue Play-Doh! (See how easy that is? I can (and indeed, do) do this kind of thing all day!) SteveBaker 20:51, 30 November 2007 (UTC)

Along the lines of sci-fi and video-game dialog and "explanations", folks may want to see our Treknobabble article.

Atlant 22:36, 30 November 2007 (UTC)

Is there some connection to The Incredibles here? Pfly 04:23, 1 December 2007 (UTC)

Sure. The movie, like many other sci-fi things, uses the term "zero point energy" to mean "scientific magic". The whole point is that real-life zero-point energy has little to nothing to do with how the term is used in science fiction. It's the modern version of the term "atomic energy" which was used to basically explain away any magical technology in works of the 1940s, 50s, and 60s before it became more mundane and less mysterious. Obviously there was such a thing as "atomic energy" but it had nothing to do with the ways the term was often used in fiction. --24.147.86.187 19:45, 1 December 2007 (UTC)

White holes attract matter?

The article on white holes says both black and white holes attract matter. But white holes spit out matter. I don't really understand the statement in the article. How can it attract, and spit out matter? Does it just mean, it attracts matter because it has gravity, but it also spits out matter from its event horizon? So does that mean, the matter it spits out, it also attracts with its own gravity? 64.236.121.129 19:05, 30 November 2007 (UTC)

The article makes it clear that matter is attracted to the white hole but never crosses the event horizon. -- kainaw™ 19:20, 30 November 2007 (UTC)

Yea, but it doesn't make it clear as to how this works. Does the white hole look like a donut then? Does it spit out matter similar to a polar jet? Since it spits out matter, and attracts matter, does it suck it's own matter back into it? What would it look like? 64.236.121.129 19:24, 30 November 2007 (UTC)

A lot of physicists say it doesn't look anything different from a black hole. Maybe if you hopped in you'd find out, but I wouldn't recommend it. Someguy1221 19:29, 30 November 2007 (UTC)

As exciting as this topic may be - it is vitally important to point out that we've never found any hint that white-holes actually exist. The only reason we even bother to think about them at all is that they show up in some of the relativity equations. I think most cosmologists would say that they do not - nor cannot - actually exist. SteveBaker 20:42, 30 November 2007 (UTC)

Yes, the matter that the white hole spits out is attracted to the hole. So is Hawking radiation, but it escapes to infinity anyway. To understand where the distinction between black and white holes comes from, consider the graph of $r(t)={\sqrt {k+(ct)^{2}}}$ for different values of $k$. ($c$ is the speed of light and $r$ is a kind of radius.) For $k>0$ this is a nice smooth curve (half of a hyperbola). This is the surface of an ordinary gravitating spherical object in Kruskal-like coordinates. For $k=0$ it reduces to $r=|ct|$, which has a sharp 90-degree turnaround in the middle where $r(t)$ goes from "inward at the speed of light" to "outward at the speed of light." The inward half is the white hole horizon and the outward half is the black hole horizon. All of the usual "black hole" solutions to general relativity (like Schwarzschild and Kerr) are really gray holes with both black and white hole horizons in them. More realistic classical models have only the black hole horizon. But the whole business seems rather artificial -- maybe the correct description is more like the $k>0$ case, where the white-black distinction is inherently absent. Hawking radiation makes this more plausible -- maybe it is the time reversal of absorption in quantum gravity. -- BenRG 23:55, 1 December 2007 (UTC)

Black holes attract matter, which passes through a wormhole and exits via a white hole. However, Einstein's gravitational field equations only predict this if the mass of the black hole is 0, which is obviously impossible since black holes form from star collapse. Also, if anything with any mass enters a massless black hole, its associated wormhole and white hole will immediately cease to exist. In other words, white holes don't exist. --Bowlhover 16:12, 2 December 2007 (UTC)

I don't see the article on white holes, saying they don't exist. Before we can say something exists or not, it has to be accepted in the scientific community. 64.236.121.129 15:33, 4 December 2007 (UTC)

The most destructive thing in the universe?

Are supermassive black holes the most destructive thing in the universe? 64.236.121.129 19:13, 30 November 2007 (UTC)

You must first define "destructive". Do you mean the ability to rip a spaceship apart? Do you mean the ability to destroy planets? Do you mean the ability to tear atoms apart or smash them together? -- kainaw™ 19:16, 30 November 2007 (UTC)

Uhh I'm not sure. I guess the ability to destroy planets, stars, and if applicable, galaxies. 64.236.121.129 19:18, 30 November 2007 (UTC)

Well, there's not much else that can consume a galaxy. A hypernova, or a very powerful gamma ray burst could do a nice job wiping out all life in a galaxy. And if you believe in the big rip, then dark energy is the most destructive force in the galaxy. Alternatively, you could say the hypothetical big crunch, caused by gravity, is just as destructive, although this might recycle everything into a new universe. Someguy1221 19:22, 30 November 2007 (UTC)

How long does a hypernova last? Like from the beginning to the end, when the hypernova is considered "over". 64.236.121.129 19:27, 30 November 2007 (UTC)

Well, we obviously don't have data yet, but this paper [5] shows a light curve for a very massive blue supergiant supernova, which shows about a 100 day peak from rise to fall and another 300 day-long tail "plateau" of intense emissions, and after that the explosion itself continues indefinitely with a long tail of emission from the ejected matter. The actual detonation, though, lasts only a few seconds, depending on how you define the beginning and the end (a hypernova is believed to emit a "long" >2sec gamma ray burst on detonation). SamuelRiv 20:23, 30 November 2007 (UTC)

Bah. The ability to destroy a planet is insignificant when compared to the power of the Force. Confusing Manifestation(Say hi!) 22:10, 2 December 2007 (UTC)

I would suggest that the single most destructive thing in the universe would be the Big Bang. However, it is interesting to note that not only is it destructive, but creative and fertile as well... --Saukkomies 19:37, 2 December 2007 (UTC)

I'm sure human stupidity can compete with any natural phenomenon. Peter Grey 18:26, 3 December 2007 (UTC)

How can you say a hypernova lasts 100 days or what? Obviously time doesn't fly by equally fast where the hypernova is than over here? I don't understand. I thought days and years were only applicable for people at sea level on planet earth? — Adriaan (T★C) 15:41, 5 December 2007 (UTC)

Time is the most destructive force in the universe. Second law of Thermodynamics makes it so. --DHeyward (talk) 18:11, 5 December 2007 (UTC)

Is it possible for a Terrestrial planet to be as large as a gas giant?

All the terrestrial planets that we know of are quite small compared to gas giants. Is it possible for a terrestrial planet to be as large as a gas giant? Like say, Jupiter? Is there anything preventing this from happening? 64.236.121.129 19:17, 30 November 2007 (UTC)

This article [6] is about a newly discovered planet: "With a mass of only 14 times the mass of the Earth, the new planet lies at the threshold of the largest possible rocky planets", which suggests (but doesn't explain) that there is a limitation for the size of a terrestrial or rocky planet. jeffjon 20:02, 30 November 2007 (UTC)

Well, as far as I can tell, nothing catastrophic would occur. Gravity would be much stronger (about 3-5g) on a giant terrestrial planet of the same size as Jupiter because Jupiter is only slightly denser than water, whereas Earth is composed mostly of heavy elements (excluding the atmosphere). Another comparison: Jupiter is 1000 times larger by volume than Earth but only 300 times more massive. Then there's radiation and tides: the amount of pressure in the center of such a planet would give you a large, dense, solid core that may have significant effects on the magnetic field. There would be a lot more heat radiated from the planet (Jupiter radiates more heat than it receives from the sun) as residues of its formation, and any object nearby (such as another planet or moon) would feel significant tidal effects (something that causes friction against their rotation and revolution - so something like the Earth's moon would end up always orbiting above the same spot very quickly). Surface pressure would be significant due to a large, thick atmosphere and stronger gravitational pull, so I would estimate it at around 10atm. Finally, the rotation of such a planet would probably be very slow, because, all else being equal, angular momentum must be conserved so the angular velocity must fall with the square of the radius. This makes avoiding getting burned or frozen much more of a hassle.

As far as formation goes, there you would have problems in the currently accepted Nebular hypothesis of planetary formation. Basically, terrestrial planets only reach a certain size in the primordial accretion disk due to some basic nucleation properties of the swirling matter and the chaotic gravitational interaction of nearby protostars and Jovian planets. They end up clearing all matter in their orbit eventually, but there's only so much dense matter than can be taken up and the sphere of influence of a planet is only so large, as it drops with the square of distance from the center of the planet. Finally, if such a planet existed, its density would be such that we would probably have seen it through current extrasolar planet surveys. SamuelRiv 20:00, 30 November 2007 (UTC)

Just a small note, Earth's atmosphere is composed of heavier elements than Jupiters. Ours is O2 and N2, Jupiter's is H2/He. Shniken1 13:06, 1 December 2007 (UTC)

I'm not sure if this is Kosher, but this question prompted me to come up with another directly related question, which I'd like to addend onto this one: Would a rocky/irony terrestial planet the size of Jupiter begin to have nuclear fission due to the incredible pressures in the core? And if so, since iron is unable to sustain this sort of reaction, would it more or less go nova? -- Saukkomies 19:252 Dec 2007 (EST)

Nope. Dense-metal fusion is only possible within the cores of supergiant stars, which are orders of magnitude more massive than our terrestrial Jupiter. I forget what I calculated the core pressure to be for this model, but it's no more than 1000GPa, whereas the pressure necessary for fusion is nearly 1000 times that. SamuelRiv 09:07, 4 December 2007 (UTC)

Manipulating objects without touching them

Lets say you have a plastic ball on a table. You want to pick it up, move it around, spin it around, bounce it on the ground, and put it back on the table without ever physically touching it. Is there any force in science that can possibly do this? 64.236.121.129 19:35, 30 November 2007 (UTC)

If you're looking for the force, no. Objects can only be realistically manipulated from a distance using electromagnetic force. So actually, if you allow the ball to actually be built into a small radiocontrolled helicopter, then there's a definite yes, but I'm going to assume that's not what you were looking for ;-) You can use static electricity to push or attract an object from a relatively short distance, and the same with magnets (these both act through specific aspects of the electromagnetic force). So I can concoct a system of magnets within and outside a plastic ball to make it hop up, spin around, and fall back down, but nothing that would work in general on any given object. Someguy1221 19:52, 30 November 2007 (UTC)

Isn't plastic diamagnetic? 64.236.121.129 19:56, 30 November 2007 (UTC)

Everything possesses diamagnetic character, but that doesn't help you unless all you want to do is push it. You can't get more complex motions out of it, as the sole reaction of a diamagnetic object to a magnetic field will be to feel a force in whatever direction the field weakens most quickly (down the gradient of the field (you have to ignore the directional component of a magnetic field to define a gradient, but that's ok (nested perentheses, wow))). Someguy1221 20:01, 30 November 2007 (UTC)

(EC) It should be diamagnetic (but not everything is diamagnetic - they can also be ferromagnetic, ferrimagnetic, or paramagnetic). That means with a strong enough magnetic field, you can repel any diamagnetic object by diamagnetism or attract any paramagnetic object by paramagnetism, in spite of what you might think intuitively. See Magnetic levitation. SamuelRiv 20:06, 30 November 2007 (UTC)

Use gravity! Take a black hole, pour electrons into it until it builds up a nice large negative charge. Now you can move it around using some handy positive charges you might have in your garage. Now, suspend it above the ball. Gravity will pull the earth, the table and the ball towards the black hole because of its gravitation - but tidal effects will make the ball fall faster towards the hole than the other things (because it's closer) - so gradually, the ball will lift off the table - as it does so, move your star-stuff further away and you've managed to grab the ball without touching it. ('Caution: Wikipedia would like to point out that this is a THOUGHT experiment and any actual attempt to perform this trick could be considered harmful.)

Personally, I find connecting the hose of your shop-vac vacuum cleaner to the output instead of the inlet hole is a great way to play with a ping-pong ball without touching it - and it's a lot easier than the first way I suggested! It's amazing that the ball stays held in the air stream rather than being blown off to one side.

20:29, 30 November 2007 (UTC)

There is a very new and exciting technology that can accomplish exactly this. Friday (talk) 20:46, 30 November 2007 (UTC)

The glove would be physically touching the ball. 64.236.121.129 18:33, 3 December 2007 (UTC)

Moving air could probably assist here, especially when combined with the Bernoulli effect used for attractive purposes. Depending on your definition of "not touching", a pool cue may also be useful, especially when combined with chewing gum. Failing all that, work on developing telekinesis.

Atlant 22:45, 30 November 2007 (UTC)

The cue stick is physically touching the ball. 64.236.121.129 18:33, 3 December 2007 (UTC)

You can do what magicians and movie people do: put a little piece of very fine thread on it, the attach said thread to your glove or something. Poof, magic, just like in the movies! --24.147.86.187 03:29, 2 December 2007 (UTC)

The thread is physically touching the ball. 64.236.121.129 18:33, 3 December 2007 (UTC)

Hire a janitor, and ask her to put the plastic ball back after cleaning the table. Spinning and bouncing around is left as an exercise to the reader. – b_jonas —Preceding comment was added at 08:51, 2 December 2007 (UTC)

I said without physically touching it. The janitor is touching it. 64.236.121.129 18:33, 3 December 2007 (UTC)

Maybe it would be simpler to just anchor yourself to the Earth's crust and move the Earth relative to the ball. Peter Grey 19:56, 4 December 2007 (UTC)

If you're going to eliminate all physical contact, you're limited to (essentially) electrostatic forces and, somehwat harder to manipulate, gravitation. Then again, we could argue whether even physical contact actually touches anything at the atomic level; it's another example of electrostatic forces at work ;-).

Atlant (talk) 17:32, 5 December 2007 (UTC)

Andromeda-Milky Way collision

Hi. I have a few questions about this theory. First of all, it says that the chances of some stars colliding are remote. However, any lifeforms within the two galaxies exsisting at the time will likely be more prone to extinction than before the collision. The thing is, the new galaxy will likely have about 600 billion stars within the main galaxy, surrounding clusters, and orbiting satellite galaxies. Surely at least a few thousand, if not a few million will collide? The merging of the galaxies will probably cause countless new gravitational changes that were not present previously, correct?

Now, if some stars are flung into space, it will likely slow down before it leaves the local group altogether, as there is an enormous envelope of dark matter surrounding both galaxies at the moment. Now, when the galaxies collide, the dark matter will probably be attracted toward the new galaxy, correct? So, if it is attracted toward the new galaxy, it will probably "push" the parts of the galaxies towards each other, and cause a farther merging. If the galaxies are to merge, then the cores will be affected by each other. This should bend each core's path around each other, potentially locing each other's core in an orbit around each other held together by the surrounding envelope of matter.

If a large galaxy usually swallows up an approaching smaller galaxy, why is it that when two large galaxies of about the same mass are expected to collide, they expect the galaxies to miss each other altogether? I know that in three-dimentional space, two objects approaching each other, in this case the galactic cores, rarely, if ever, hit each other head-on. So, since the stars near the centre of the galaxies are more tightly closer together, and the ones near the edges are farther spread apart but still orbit as quickly, is it accurate to say that the stars near the centre of the galaxies have a better chance of collision?

Now, if there are lifeforms living within the galaxies at the time, a higher chance of supernovae nearby and dense intergalactic clouds should cause a higher extinction rate, correct? Now, the Triangulum galaxy is not far in the sky from the Andromeda. Also, it is closer to us than the Andromeda. This places it roughly between the two galaxies. So, when the Milky Way and Andromeda collide, is there a good chance the Triangulum could join in as well? The Milky Way, Andromeda, and Triangulum galaxies are the three largest in the entire local group! In addition, the three combined probably have a few dozen orbiting companion galaxies. So, if the three galaxies merge before they have a chance to disperse, might their companion galaxies, as well as some of the dark matter, start moving toward, rather than away, from the new galaxy, due to a relatively sudden increase in gravitational attraction?

If they eventually do start to "fall" in towards the trio, they will probably come close to the centre. Could this, along with the surrounding dark matter, which is about 10 times more massive than the entire cluster of merging galaxies, trap the group of galaxies inside each other? Now, would some of the heaviest stars in the galaxies now be at the centre, since they would be more attracted by the dense centre that has now formed? So, we can now assume that the densest material will now be at the centre of the new large galaxy. So, the cores will likely still be trying to escape each other through centrifigual force, giving time for more nearby surrounding galaxies to start to be attracted by this increase in gravity, merging into the gravity feild of the group.

However, as gravity only travels at the speed of light, and decreases by the square of distance, only the nearest galaxies will likely become attracted into the group. Eventually, might we have perhaps a dozen galaxies, big and small, within the new galaxy, which will likely now be elliptical, as the new forces will likely have destroyed its former arms. So, as the galaxy is still being held tight, the galactic cores will likely rotate around each other, spinning more and more rapidly, but probably increasingly being attracted toward each other with the new material caving in. By now, I think tens of millions of less affected stars will likely have left the galaxy, perhaps being absorbed by surrounding galaxies, affected and unnafected, while proabably tens of thousands more will already have either collided with other stars, or destroyed by the immense gravitational forces and nearby eruptions.

Now, I imagine that several hundred black holes, both supermassive and mini-sized, will have been caught by the increasing gravitation at the centre. As more massive stars will likely be at the centre, and since areas close, but not too close, to large black holes are good formation centres for massive stars, due to the more concentrated gravitational fields, the leftovers from massive stars that have decayed over this time, some of which are bllack holes, will likely keep joining the ever-increasing gravitational centre, bringing yet more stars and very close companion galaxies and their dense cores toward the centre.

By this point, will the gravity have increased so much that even centrifugal force can no longer stop it? If so, the now-very prominent core, illuminated by occasional explosions, will likely start collapsing in on itself, much like the way that the cores of massive stars and very close binary stars start allowing gravity to beat centrifugal force, tearing matter toward each other rather than away. Now, eventually the supermasive black holes will likely be the closest to each other from the reasons that they have more gravity on each otehr and are the first to merge into this group in the first place. What will happen then? Will the cores of the most supermassive black holes start moving closer and closer together, reaching their orgasm climax of gravity, and eventually colliding so that they explode in an enormous explosion, wiping out the stars and black holes closest to the centre?

Will the explosion have enough energy to travel at nearly the speed of light, pushing intergalactic material, such as nearby dwarf galaxies, stars, and dust clouds, superheating them and adding them to the shell of explosion? How bright would this be when it reaches a planet, say, 1 billion light years away? Would it be visible to the equvalent of the naked (human) eye? Would the now diluted gas and dust and radioactive matter cloud brighten the sky at this site, or perhaps interfere with lifeforms, or would it just be too dilute at this distance for any of this?

So, what do you think, is some of this plausible? Why has the scientific community not considered all these potential factors? Do I just have an overactive imagination? Are there too many "what-if?'s" in this scenario to be plausible? Would Hubble shift prevent some of this from occuring? Or would hubble shift not have increased that much within this timeframe? Are the mentioned bodies (objects) too far away from each other to have much gravitational effect on each other before hubble shift combines with centrifugal force to tear the objects away from each other? However, if this is the case, why did they consider the collision of the two galaxies in the first place; wouldn't the hubble shift along with dark energy dominate over the non-increasing gravitation between the two galaxies and tear them apart before they start moving towards each other?

If even the meeting of the two galaxies in the first place is plausible over such a great distance in non-increasing non-densifying gravity, shouldn't the events mentioned above be plausible under smaller distances and continously increasing and densifying gravitation? Or has too much speculation been put into this senario? Am I asking too many questions (the way I usually do)? Is the theory of the collision and related matters too early in its infancy to approve of all these potential future fators? Are there just too many possible factors that anything could happen? Thanks. ~AH1^(TCU) 22:35, 30 November 2007 (UTC)

Okay, the overarching question has to do with supermassive black hole collisions, which could in principle happen, with enough counteracting matter to slow them down, but this process would take a very long time (given the momentum of the black hole). You seem to be ignoring the fact that when one object is moving and gets attracted to another object by gravity, it goes into orbit. Unless there is friction, it will not collide (unless its orbit intersects the object's radius). Black hole coalescence on smaller scales may be the cause of gamma ray bursts, but we don't know.

Now let's take this from the beginning. When galaxies collide, and they have many, many times in our universe, we have never, not once, seen stars collide. The stars are much more disperse than galaxies, even in the densest regions (you are looking at over 10^6 stellar radii cubed of empty space around each star, versus 10^1 galactic radii of empty space around each galaxy in a cluster). If they did collide, believe me, we would know it.

Current simulations of galactic collisions with dark matter show basically the same result as without dark matter. Just remember that if dark matter works how we think it might, it will not "push" other objects together. It will, by definition, not interact significantly in any way other than gravitationally. Stars do get flung out into space as large, irregular groups after galactic collision: these are called irregular galaxys.

What I'm leading up to here is that it is very likely that Local Group galaxies collided or came close to colliding at one point in time, and will likely collide again in the future (by the way, the Andromeda Galaxy is closer than the Triangulum Galaxy). This probably resulted in the Magellanic Clouds and a newly-discovered third irregular galaxy around us, all of which orbit harmlessly around the galaxy as it is now. Again, let me stress that gravity causes moving objects to orbit, not collide.

Life on Earth is about 3.5 billion years old. If a galactic collision occurred since then, then it didn't do much to life. It would likely result in an increase in large star formation and thus supernova activity, which may have caused mass extinctions in the past, but nothing of the scale that you're talking about.

At this point, pretty much everything afterwards is invalidated. Hypothesizing is good, but just remember: always check your assumptions. In this case, your assumptions about gravity's attractive nature were the fatal blow to this line of thought. SamuelRiv 23:31, 30 November 2007 (UTC)

A back-of-the-envelope calculation shows why galaxies can collide, but stars hardly ever do. Consider a sun-like star falling through the core of the Milky Way, which is about 3,000 light years across with an average density of about 2 stars per cubic light year. The star is 1e6 km across, which is about 1e−7 light years. In falling through the core, it can collide with stars whose centers lie in a cylinder of volume about 1e−10 cubic light years, so it expects to hit on average about 2e−10 stars on its journey through the core. Its odds of hitting another star are billions to one against. (And passing through the core is very much the worst case: the spiral arms are several order of magnitude less dense.) Gdr 12:31, 1 December 2007 (UTC)

Hi. Thanks for your helpful answers, but there are still a few things. I know that gravity causes not collision, but orbitation. In fact, I know that gravity usually cuases objects to depart rather than attract each other via centrifugal force. However, the stars near the core are more dense, so they should have some attraction between the cores, possibly stabilising the orbit, and possibly attracting the cores gradualy and very slowly toward each other, instead of away from.

Also, could the Triangulum galaxy eventually start slowly orbiting the Andromeda, and eventually start orbiting the newly collided galaxy, and perhaps eventually join? The Milky way is already expected to swallow the Magellanic Clouds within 10 billion years if it is not disturbed, indicating that the gravity of the Milky way alone is enough to allow closeby galaxies to move toward, rather than away from, the Milky way. So, if the two galaxies collide, the total gravity should be stronger, and there will likely be more companion dwarf galaxies in total, so eventually a few galaxies should fall into the new galaxy. Well, if the two galaxies collide, the resulting new galaxy should probably be elliptical because it will attract its former arms more inward. So, being elliptical, it will likely be denser.

Also, your calculation of billions to one against, still do not mean that no stars at all will collide. In fact, if the orbits of the two cores hold each other and stabilise enough, some stars might expect to pass not one, but perhaps dozens of times through the centres. So, let's say that there are about 500 billion stars within the elliptical galaxy alone, and since their orbits will likely be distrubed by the new gravitation in opposing forces, and because the stars might pass through the galaxy's centre many times, and because the central reigon will likely be denser than it is today and there is more than one dense area, let's say that about 50 billion stars will find itself passing through the core. Of course if one star collides, the other star it's collided with has also collided. So, assuming that the centre is quite dense, and a star might pass through the core more than once, due to the gravity of the centre which will likely keep in an orbit (albeit a very haphazard one), the chances of a random one of these stars colliding is a billion to one. So, that means about 50 stars will have collided.

Also, by now the triangulum galaxy will likely be caught up within the gravitation of the new epliptical, and so will some smaller dwarf galaxies, that some stars might end up passing through dense reigons while outside the centre. However, probably more stars will have been thrown away than collided. Since there might be many centres, and this tug-of-war might last billions of years if the galaxies catch each other, and because whatever star a star collides with is also collided, let's raise the total number of collided stars to 300, before either the galaxies escape each other or their cores get caught up and collide. So, assuming that there will be about 100 000 stars within 500 light-years of the collided stars, which if those stars harbour solar systems which harbour life, would cause extinctions. So, assuming that there are about 2000 out of those 100 000 stars that have lifeforms, and that there are an average of 10 000 lifeforms per star, and that roughly an average of 1/10 of the lifeforms will go extinct within this reigon, we could be looking at roughly 2 million extinctions with the collision of just one star.

Now, multiply that up, and we could have 200 million extinctions caused by collisions alone within the two galaxies. Now, factor in all the other more common causes, such as supernova explosions, dust clouds, new asteroids, etc, and we could have about 10 billion extinctions related to the collion of the two galaxies. So, maybe it isn't so safe after all, astronomy within 3-5 billion years? So, if gravity causes the galaxies to orbit, will the orbit eventually become larger and larger before escaping each other's grasp, or will they tighten before eventually a collision occurs?

I now understand this isn't very likely, but if the galaxies were to collide, and their centres were to collide as well, about how bright would it be if it were viewed from 1 billion light-years away, factoring all the triggered collisions, stars destroyed by the burst of explosion, clusters of stars and whole galaxies pushed by the shell of gas? If this were to happen, would the now dispersed shell of gas brighten the sky at this distance? Keep in mind that a marshmellow dropped on a neutron star will release about as much energy as an atom bomb on Earth. Collide two neutron stars, you get even more energy. Collide two black holes, yet more energy. Collide two or more supermassive black holes, and let the explosion push and swallow stars, yet more energy.

Would the radiation at one-billion ligh-years, in the unlikely scenario that this were to happen of course, cause extinctions, or would the radiation be too dispersed, decayed, and old, to cause any damage? Could the heavier particles collide with the observer's planet's atmosphere and cause a radioactive meteor shower? Keep in mind that the most common type of uranium, a common radioactive element, takes 4.5 billion years to halflifeanate, about the same time it would take for this hypopthetical shell of radiation and matter and stargas to reach the observer's home planet.

Do any epliptical galaxies right now look like they might have been caused by the fusing of two or more spiral galaxies? Again, would hubble shift quickly tear the orbits apart and prevent this from happening? As a side note, after half an hour of searching using a detailed star map book, I finally found the Andromeda galaxy through binoculars. It was so cold and windy that, although I was wearing gloves - two pairs of them - my fingers got so cold they hurt down to the bone. Well, I don't think I'm going to be able to do that tonight: nearly a foot of snow may be expected by the end of the storm coming tonight! I found the Andromeda by rotating my head to Cassiopia looked like an M, then followed it "up" so that there are three stars in a row "above" the M, with the one farthest "left" "higher" than the one farthest "right"; I looked "down" from the middle star, leaning my FOV toward the "right" to another star, continuing "down", this time leaning "left" before I saw a fuzzy patch. Well, it looks like I always need to keep changing my countless hypotheses to suit new information. So, can someone answer my few remaining questions? Thanks. ~AH1^(TCU) 16:40, 1 December 2007 (UTC)

Please read my previous answer again. I need to make this abundantly clear. No star collision has ever been observed in galactic collisions (which are quite common), and it would be very obvious if we had observed it. Orbits are stable. They do not fly apart or come closer together. They stay in the exact same position forever. It's the same reason why planets do not collide with the sun. It is centripetal force, not centrifugal force, that counteracts the attractive force of gravity - just note that the two are different manifestations of the exact same force, so they counteract exactly in a complete orbit. The centers of galaxies are not very dense. Again, 1 star has about 10^6 radii cubed of clearance, even in the center, so the chances of collision are about 1/10^18, or one in a billion times a billion. Galaxies are generally moving fast enough relative to one another and have enough gravitational influence from other nearby galaxies that they do not form stable rotations. (Andromeda and Triangulum are moving on the order of 100km/s toward us after correcting for the rotation of our galaxy (with some additional unknown tangential component, so they are probably not on a direct collision course)). SamuelRiv 18:26, 1 December 2007 (UTC)

I don't disagree with your point that no collisions have ever been observed, but I don't think your calculation of the probability of collision is correct. It's the size of the swept path that needs to be considered. So you can't cube the clearance, you can only square it. Gdr 18:37, 1 December 2007 (UTC)

You're right, my bad. I was considering it from a stochastic motion perspective, not a linear motion, which works for collisions in condensed matter but not in astrophysics. SamuelRiv 20:58, 1 December 2007 (UTC)

Supposing that vampires existed and had the same basic daily calorific needs as regular humans...

How much human blood would a vampire need to consume per day in order to remain healthy? --Kurt Shaped Box 22:50, 30 November 2007 (UTC)

According to [7] and [8], it takes ~600 Calories to regenerate the constituent parts of a pint of blood (a remarkably large number). Assuming your vampires could extract energy from it with perfect efficiency, they would only need 3-4 pints per day. I will note though that most vampires of legend also ate traditional food in addition to drinking blood, so it would appear that blood was not envisioned as a primary food source.

So, Kurt, how many gulls would a vampire abstaining from humans need to eat? Dragons flight 23:03, 30 November 2007 (UTC)

Dunno. Has anyone here ever read the nutritional information on those little bottles of supermarket gull blood? ;) So, an exclusively blood-drinking vampire would need to kill a *lot* of people, as I thought (one every two days or so?). Not exactly going to remain inconspicuous for long, is he? Even moreso if he has to hunt for virgin blood (I know that some vampires are very specific about this). --Kurt Shaped Box 23:39, 30 November 2007 (UTC)

He could just hunt children in that case. He could also store unconsumed blood in a cooler. Yet further, knowing that Vampires are cold-blooded and spend much of the day motionless in a coffin, they may have considerably lower daily caloric requirements than a live human. Someguy1221 00:46, 1 December 2007 (UTC)

Well, wiki tells us that the birth rate is ~20 per 1000 people per year. And the death rate is about 9 per 1000. So that gives an excess of 11 snackable humans per 1000 per year to maintain a fixed population size. So, in order to eat one every two days, each vampire would need a feeding ground of at least 16,500 people. If your diet calls for only nubile virgin girls, then perhaps at least 50,000 people per vampire. So a major metropolitan area could easily support twenty or more vampires. However, they would probably need to work out a way to dispose of their bloodless victims. (Lots of neck wounds might look suspicious.) At that end, going into the mortuary business might be a good idea. What's one more corpse at a funeral home? Not to mention the convenient supply of beds. Dragons flight 01:19, 1 December 2007 (UTC)

Well, in Asian supermarkets they do sell cow blood and stuff. If a vampire was running short on virgins, they could always disguise themselves and buy themselves a pint or two. bibliomaniac15 01:23, 1 December 2007 (UTC)

...but can't vampires just turn themselves into vampire bats and find their own cows rather than having to rob the dead or actually run a funeral home or do whatever else to pay with cash? 71.100.1.143 07:27, 1 December 2007 (UTC)

If a vampire in bat form eats enough to fill its (bat-sized) stomach, is it still full when it takes its much larger human form, or does it become hungry again? If it stays full, it could feed that way :) 98.196.44.210 02:01, 4 December 2007 (UTC)