Wikipedia:Reference desk/Archives/Science/2008 March 24

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[edit] March 24

[edit] Mean tropical year

Is the "mean tropical year" the average of the four tropical years measured respectively starting at the vernal equinox, summer solstice, autumnal equinox and winter solstice, or is it based on a mathematical "continuous" averaging taken over all possible tropical years through the four seasons? I have seen it described in both ways -- does anyone have a definitive answer? 86.134.46.159 (talk) 01:02, 24 March 2008 (UTC) (BTW... I should mention that the Wikipedia article Tropical year contradicts itself in this respect. In one place it says one thing and in another place it says another.)

[edit] how do i become taller?

ow i'm over 20 and my height is 5'4" so i want to more tall than before so how can i do? besides go living in asia 141.149.55.113 (talk)

(moved from WT:RD) :D\=< (talk) 04:45, 24 March 2008 (UTC)

There's nothing you can do.. try wearing shoe inserts or buy shoes with thick soles. There is distraction osteogenesis, but it's stupid and, well, absolutely insane. :D\=< (talk) 04:49, 24 March 2008 (UTC)
Aren't you the same person who asked the same question back in January? Do reread the answers at that link. Also read the "Cosmetic lengthening of limbs" section in the distraction osteogenesis article Froth referenced. —Steve Summit (talk) 05:07, 24 March 2008 (UTC)
I'm over 20 and my height is 5'4" so what's the problem? Why would you want to be taller? I think that I'm the perfect height, don't you? Are you saying that I should want to be shorter or taller? Why the hell would I want to be what I'm not? I also don't write poetry - should I worry about that and want to be a poet? Look 141..., you're asking a question like "I am white and I want to be black" or some other such other bullshit. You can and should develop the things that you are good at and not concern yourself with those things over which you have no control. And, asking the likes of us to address the things over which you have no control is really stupid. --hydnjo talk 05:56, 24 March 2008 (UTC)
No use berating the guy for asking a question. Perhaps he thought there might be an easy way to increase his height. (Certainly several completely bogus 'herbal' products are advertised.) Perhaps he has some legitimate and practical reason for wanting to be taller. (Just because we can't think of one off the top of our heads, doesn't mean it can't be true.) Most of all perhaps the guy was just curious. There's nothing at all wrong with that. The point is that it's crazy to rant at someone based not on what they said, but based on your opinions of what you suppose their motives for saying it might be. 72.10.110.107 (talk) 13:50, 24 March 2008 (UTC)
You know, this question was once asked the Cecil Adams on The Straight Dope. He gave some good answers; I'd recommend reading it. Neal (talk) 16:26, 24 March 2008 (UTC).
There is no available drug therapy which can help you grow taller except for in paediatrics where growth hormone therapy can be used, but in adults this is useless. Other than using the |rack, I think you're stuck at 5'4". CycloneNimrod (talk) 17:55, 27 March 2008 (UTC)

[edit] Bamboo

I would like to know the kinds of bamboos. Please!

Is there somthing within the Bamboo article that you don't understand? --hydnjo talk 05:59, 24 March 2008 (UTC)

I mean kinds of bamboos! Names of them!I searched in Bamboo but I didn't see that! so....!

The bamboo article says bamboo's in the subfamily Bambusoideae, which has a list of a bunch of kinds of bamboos. It looks like it lists them all, but may be not(?) -Haikon 06:23, 24 March 2008 (UTC)
) thanks u so much! To u all!

[edit] How come so many invasive species come from Japan?

...to the United States and Europe? May be "so many" is an exaggeration. I can only think of two, those ladybugs and kudzu, but if you think of Japan as a group of Pacific islands, two is a lot. I mean you probably couldn't import an invasive species from New Zealand or Hawaii if you tried. And given some of the peculiar animals native to Japan, it would seem like that ecosystem would be more on the receiving end of pest invasion.

Anyway, I'm trying to find general rules or theories regarding invasive and non-native species to answer this question, and I'm not coming up with much. (Except a "Baker's rule", and I haven't even found that really, not stated by Baker him/herself anyway.) A lot of isolated ecosystems have been screwed up because of non-native species, and in each case it's understood pretty clearly how and why, but I can't find an explanation of how any why this would happen in general, not just in a given case. Anything at all like an answer or points in the right direction would be greatly appreciated. -Haikon 06:44, 24 March 2008 (UTC)

Your first statement appears to be slightly flawed. New Zealand plants are a problem in other countries, e.g. [1], [2]. It is of course true that exotic plants are more of a problem in NZ then NZ plants in other ecosystems, but then nothing you've said suggests that this is any different from Japan except that the Japanese invasive species are more widespread, but then again, the Japanese ecosystem was always a lot less isolated then NZ or Haiwaii (meaning it was a lot less different). BTW, from what I can tell it is inaccurate to call the Harmonia axyridis a Japanese invasive species. It may be native to Japan but from what I can tell it is also native to other countries. It appears even more clear cut with the kudzu. All these two examples really tell you is that the Japanese ecosystem was not that isolated. You could just as well say any species which is native to Bali or some other small island and invasive comes from a tiny island even if in reality it is native to a lot of places. To answer your second question, in general a species will become invasive if it is able to better fill a niche then any of the existing native species. Countries with highly isolated ecosystems such as New Zealand tend to have a lot of niches which can be more effectively filled by something from somewhere in the very wide world out there. Consider New Zealand for example where the lack of large ground based predators meant that most native animals particularly birds obviously were adapted to such a situation leaving it ripe for invasion by ground based predators. Obviously for very diverse, non-isolated ecosystems like Europe, Asia or whatever, it is unlikely that there will be many niches left unfulfilled or that there will be a whole lot of invasive species coming from the small number of isolated ecosystem which are able to better fill a niche. Nil Einne (talk) 09:16, 24 March 2008 (UTC)
Good answer, Nil. And of course we have an article on Invasive species, which is immensely improved from when I last saw it a couple of years ago. --Allen (talk) 17:04, 24 March 2008 (UTC)

[edit] Big bang expansion thing

Okay, space is expanding so from my head it appears my head is the center of expansion. Got it. But am I to understand that at the atomic level space is not expanding? Electrons are not getting further away from the nucleus and the space between atoms and molecules is the same density and the distance between them is the same but what about the distance between planetary orbits? Is that expanding as well? If so by how much in a billion years? 71.100.1.65 (talk) 10:11, 24 March 2008 (UTC)

Short answer is no, space is not expanding at the atomic level because the dominant force that determines the interactions betweens atoms is the electromagnetic force, not gravity. Space is not expanding at the scale of planetary orbits either because the simplifying assumptions on which the Friedmann equations are based are only physically correct on scales of millions of light years or more. For the long answer see this question and its answers on March 21 above, and our metric expansion of space article. Gandalf61 (talk) 13:07, 24 March 2008 (UTC)
Okay, so only gravitational space is expanding? 71.100.1.65 (talk) 20:26, 24 March 2008 (UTC)
Wow, we've got a lot of questions on this lately! --Captain Ref Desk (talk) 14:30, 24 March 2008 (UTC)
Going back to the dots on the balloon analogy in our previous attempt at this question. Draw dots on the balloon, lets call those dots galaxies. Now inflate the balloon - dots get further apart. Now draw some more dots, lets call these dots atoms. take some short pieces of wire and glue the ends to adjacent atoms. Lets call the pieces of wire atomic bonds or crystal lattice. Inflate the balloon again. Do the atoms get further apart? Now give the 5 year old their balloon back. SpinningSpark 23:12, 24 March 2008 (UTC)

Right. Space is expanding on subatomic levels, but nothing is getting farther apart as such things are, in one way or another, stuck together. But if space were expanding fast enough, you might get a big rip. Someguy1221 (talk) 23:33, 24 March 2008 (UTC)

Not sure that we do know that space (or, more precisely, the space-time metric) is expanding on subatomic levels. I see three problems with this:
  1. The Friedmann equations, which are used to model the large scale expansion of space, are derived by assuming a homogeneous and isotropic distribution of matter and energy. This is only physically realistic (even as an approximation) on supra-galactic scales of millions of light years or more. The Friedmann equations certainly do not apply to anything smaller than a galactic cluster.
  2. The large-scale expansion of space does not have to imply a homogeneous expansion at all places and scales. How do we know that the expansion is not confined to intra-galactic space, for example ? AFAIK, there is no evidence or conclusive argument that says the expansion of space has to be homogeneous.
  3. To even begin to model the behaviour of the space-time metric at sub-atomic levels would require a theory of quantum gravity, which does not yet exist. Gandalf61 (talk) 09:51, 25 March 2008 (UTC)

[edit] Forgive me for asking a homework question, but how many different hormones are there in the human body?

Discovered at least -- I've searched this all over, and it seems a particularly pointless question to ask (given that we also have to detail every petty step in various signal transduction pathways), but alas, I can't seem to find a source that lists *every* single human hormone, or at least one that tells me that this is every single human hormone discovered so far (and numbers them). John Riemann Soong (talk) 14:33, 24 March 2008 (UTC)

There are hundreds, are you sure this isn't specific to a certain syllabus? --Mark PEA (talk) 16:13, 24 March 2008 (UTC)
Way too numerous to list - there are literally dozens and dozens of small hormones secreted along with the major ones where the physiological function is poorly under stood. However, the predominate hormones are the following (off the top of my head):
  • Epinephrine
  • Norepinephrine
  • Dopamine
  • TSH, T4, and T3, Calcitonin
  • Parathyroid Hormone
  • FSH, LH for reproduction
  • The androgens for sexuality and reproduction
  • Growth Hormone
  • Prolactin
  • Oxytocin
  • Antidiruetic Hormone
  • The hypothalamic tropic hormones (also known as releasing factors)
  • Glucagon
  • Insulin
  • Somatostatin
  • Secretin
  • Gastrin
  • Aldosterone
  • Cortisol
  • Corticosterone
  • Vitamin D3

There are more, but I can't rack my brain any longer Wisdom89 (T / C) 18:01, 24 March 2008 (UTC)

Well this is precisely my problem -- I don't want to list them all, I just want a nice (2-digit? 3-digit?) number. John Riemann Soong (talk) 18:16, 24 March 2008 (UTC)
Yeah, extremely difficult per my first comment. Physiologists and endocrinologists incessantly disagree about what substances (mostly small peptides) even constitute a hormone. If I had to give an educated guess (and it is educated) for the major hormones, it would be around 120. Wisdom89 (T / C) 18:24, 24 March 2008 (UTC)
here is another list of the major ones, but as others note, some hormones, like the various melanocortins are cleavage products of a pro-hormone (in their case, Proopiomelanocortin). How many different hormones there are from each pro-hormone differs by which criteria you wish to use. Do you wish to count the pro-hormone as 1 or do you wish to count all the possible cleavage products? If you wish to use conservative criteria, there may be around 50, if you wish to include anything anyone has ever called a hormone, perhaps 100-150. Rockpocket 18:45, 24 March 2008 (UTC)

[edit] Movie science: what can or can't you tell about a torpedo from its sound?

In the movie The Hunt for Red October, there's a scene in which a sonar operator reports that an incoming torpedo "went active the moment it was launched" and that the torpedo has acquired its target. Is it real science, or is it just artistic license taken by the moviemakers, that a sonar operator is able to tell if a torpedo is armed and has a lock on its target just by listening to its sound? --71.162.242.38 (talk) 16:25, 24 March 2008 (UTC)

I asked myself the same question. A torpedo can be sent out running slow and quiet so that its target might not know it's there until it's too late. Subs maneuver slowly when they aren't going anywhere in a hurry, so the torpedo doesn't need to go very fast to get over near its target. A wire-guided torpedo will be steered by the attacking sub to get it near its target, at which point it will told to turn on its own sonar and home on that, what the movie called going "active", I guess. Faster torpedo propellor speed means higher pitch and louder. (If the torpedo hasn't hit anything after a certain amount of time has passed, and the wire isn't connected any more, it will conduct a search pattern automatically, at which time the attacking sub had better have gotten its butt out of the area.) I would guess that the search sonar and the final homing sonar would differ in some audible way, so that you'd be able to tell when it had "acquired" its target by merely listening. As for whether the torpedo is "armed", I think we're supposed to imagine that Jonsey knows a hell of a lot more about this whole business than we ever will and that some combination of indicators and knowledge of the workings of Russian torpedos clues him in, so just sit back and enjoy the show. --Milkbreath (talk) 16:48, 24 March 2008 (UTC)
As for "has a lock" -- yes, that's easily determined. If you have a bearing to a sound source (e.g. a torpedo) and that bearing doesn't change, the torpedo is on a collision course with you. If the bearing changes, it's heading somewhere else. As far as arming, I'll just go with Milkbreath's encouragement to enjoy the show -- active sonar corresponding with armed torpedo is a reasonable assumption, and I don't recall the dialog precisely enough to nitpick anyway. — Lomn 17:00, 24 March 2008 (UTC)
As said by MilkB, most torpedoes, eg Mark 37 torpedo don't turn on the active sonar until they are close, so when you hear that happen you want to try not to be where the torpedo is going. A sonar operator can tell the difference between a "search" and "tracking" pattern in the same way that an aircraft can tell the difference with radar. A search pattern sweeps the transmission through 360o, or at least a wide angle. Tracking sweeps over a narrow angle, trying to keep the target illuminated constantly. The military consider tracking an aggressive act and cause for shooting back by the way. So basically, if the sonar operator can hear all the enemy pings or chirps hitting his vessel with no gaps (there would be gaps while the search sonar is pointing somewhere else if it was not tracking) then he can conclude his ship is being tracked. SpinningSpark 19:34, 24 March 2008 (UTC)

[edit] arsenic weight per gallon

I am desining an arsenic treatment plant for a small town in CO and I was crious to know how much a gallon of arsenic would weigh?

Thank You,

Michael miklroy04@yahoo.com

The article on Arsenic_contamination_of_groundwater might provide a good place to start. It looks as if most arsenic is in the form of dissolved arsenic salts, and therefore the weight of material to be removed may be dominated by the substance used to remove the arsenic, not by the arsenic itself. JohnAspinall (talk) 16:53, 24 March 2008 (UTC)
1 gallon (US) = 3.785411784 litres, Density of arsenic 5.727  g·cm−3, 1litre = 1000 cm3
So 1 gallon weighs 3.785411784 x 5.727 x  1000 =21679g = approx 21.7kg (that's about (under) 48 pounds)87.102.16.238 (talk) 16:56, 24 March 2008 (UTC)

[edit] collapsible longboard???

I heard that some yuppies use a longboard for transportation, which I might be interested in doing also, since I walk for 7 minutes to the metro dozens of times a day. Is this is a nutso idea? Why?

are there any collapsible longboards? THank you!

The positive is it might be slightly quicker, if the pavement is smooth and level. The negatives are that you are more likely to fall or trip other people, you have more weight to carry when not skateboarding, it may be illegal in certain areas, people may view you as childish or a menace, and you won't get as much exercise. I'd say the negatives win. StuRat (talk) 20:03, 24 March 2008 (UTC)
Are people still using folding aluminium micro-scooters in the city? Julia Rossi (talk) 02:15, 25 March 2008 (UTC)
A much easier idea is a moped. ~user:orngjce223 how am I typing? 16:38, 26 March 2008 (UTC)

[edit] Static zappage

I work in a library with very fuzzy carpeted floors and metal on the door handles. I am getting shocked almost every time I get up and touch things. It seems that most of the other employees don't get shocked. Are there people who have a higher potential for being shocked? Is there anything I can do to cut down on the number of times I get shocked? I'm starting to get nervous before I open the doors...

It also depends on the clothing you wear - that could be a disparity between you and the other employees. Wisdom89 (T / C) 17:54, 24 March 2008 (UTC)
Try comparing the types of shoes you and the others wear, especially the soles. I'm betting that's the answer, as different types of soles pick up a charge more as you trot about. --Captain Ref Desk (talk) 18:09, 24 March 2008 (UTC)
I agree with the previous answers. Also, perhaps your job tends to keep you in one room and/or you walk around on the carpet more, so that a higher charge builds up before you touch the door handles. You might want to intentionally touch the door every few minutes to prevent static buildup. Then again, maybe you are the subject of a secret psychological experiment the other librarians are performing and that would invalidate the results. :-) StuRat (talk) 19:55, 24 March 2008 (UTC)
Leave your hand in contact with something grounded, like a metal lamp, when you get up out of your chair. Carry something metal with you to draw the arc with before you touch the doorknob, maybe a coin or paper clip. Much of the pain of such zaps is actually from the momentary heating of the skin where the arc occurs, and if the arc hits the paper clip first you won't feel that part of it. --Milkbreath (talk) 03:27, 25 March 2008 (UTC)

[edit] Why is violet reddish?

Why does violet look more red than green, even though green is closer in wavelength? My first thought was that the higher frequencies of violet are an octave of the lower frequencies of red. However, the shortest wavelength of violet is 380 nm and 740 nm as the longest for red, so the octave of violet is not visible. --196.209.178.23 (talk) 20:13, 24 March 2008 (UTC)

It is because the red receptor in the human eye has a slight response to second harmonic wavelength also. This happens to peak towards the high end of the blue spectrum which causes us to interpret light of this wavelength as violet. SpinningSpark 20:26, 24 March 2008 (UTC)
Oh sorry, I did not bother to read all your question. I have some plots of human eye response somewhere from BBC colour vision research which definitely show a second smaller peak in the red response. Of course, you can never find this stuff when you need to answer a question. I assume you got your figures from the color vision article which seems to fail to show this second peak. Possibly the other figures there are non too accurate. SpinningSpark 20:38, 24 March 2008 (UTC)
Image:Human RGB response.PNG

Take a look at this, you can just see the second peak, it is very small, the plot is relative level instead of dB as any sensible engineer would have done. But you are right that it is well off the second harmonic. SpinningSpark 21:16, 24 March 2008 (UTC)

[edit] Cladistic definition of crown groups

Let's imagine metatherians and prototherians become completely extinct in a few years, and eutherians are the only surviving mammals. Cladistics define the class Mammalia as:

"the last common ancestor of all living mammals and all of its descendants"

In this imaginary situation, this would mean "the last common ancestor of all eutherians and all of its descendants", thereby declaring marsupials and monotremes as non-mammals! Isn't this a little absurd? How do you solve this paradox? -- Leptictidium (mammal talk!) 20:14, 24 March 2008 (UTC)

After reading Tudge The Variety of Life I came to the conclusion that all of cladistics is absurd. Non-avian dinosaurs, "no such thing clade as fish" - really whatever next. SpinningSpark 21:21, 24 March 2008 (UTC)
I think the cladistic definition would simply be changed to "the last common ancestor of metatherians, prototherians, and eutherians". It might be stated that way in some technical definitions even now. Note that the ICZN does not currently regulate taxa above family level, so classes, etc. are in flux anyway.
Cladistics only makes sense if you accept that the goal of taxonomy is to reflect evolutionary relationships. As Spinningspark points out, fish are actually 3 or 4 separate clades [depending whether you put hagfish and lampreys together; I'm used to 3 clades, jawless fish, cartilaginous fish, bony fish]. Vultur (talk) 22:16, 25 March 2008 (UTC)

[edit] Balloons and teleportation

I'm writing a story in which one of the characters can teleport instantaneously from place to place. At first, I intended this to be silent, but my brother has pointed out to me that her sudden appearance would result in some pretty intense displacement of air, so the sound of her teleporting should be a lot like that of a very large balloon exploding.

I think this is kind of awesome, but I want to make sure it's right before I use it. What do you all think? --Masamage ♫ 21:07, 24 March 2008 (UTC)

I assume that when you say teleport instantaneously you mean not only that the travel time is zero but the rematerialization period is also zero. If the rematerialisation period was longer (i.e. star trek) there would be no massive displacement of air, ir would be gradual. Anyway, I doubt there would be a sound akin to an exploding balloon. The balloon sounds like that because it is a large amount of air being released from a small area having previously been under very high pressure. To suddenly materialise in air (assuming that all the air is deflected away from you from your centre, rather than being trapped between your particles as you materialise?) would produce something akin to a sudden rush of wind, as the amount of air in the space now occupied by your character has been pushed outwards. The speed of which would, in theory, only be enough to get it out of the way (maximum distance is the same as the dimensions of your character) and the air would probably not go very far before hitting other air molecules. Less of an exploding balloon, I'd say, and more of a sudden, thick but short gust of wind? That is again, of course, depending on the speed of your materialisation. SGGH speak! 21:26, 24 March 2008 (UTC)
Yes, you have it about right for how fast I was thinking she would materialize (although the idea of slow, Star Trek-style beaming is interesting, too). So then, if I understand you right: the displaced air isn't under enough pressure to make that loud and sharp of a noise, so in actuality all that would happen is a sort of fwoosh sound, and maybe nearby people's clothes wafting a little in the wind. And a similar thing would happen to fill the space where she left, right? --Masamage ♫ 21:36, 24 March 2008 (UTC)
(ec) It depends on the mechanism you've chosen for your particular fiction. If air is forced out of the volume to be occupied by the incoming traveller extremely rapidly (as with a near-instantaneous teleportation) then it will generate a shockwave as it moves—a small sonic boom. It will, indeed, be loud.
Now, your teleporting individual would be in a world of hurt if they don't materialize from their center out—that would trap air molecules within the body. Very messy. Slow materialization could be problematic, too—what happens if the character moves during teleportation? A bit of liver here, a bit of lung over there, blood flows down the left leg and back up the right, no problem....
Of course, you could always choose a mechanism where a 'swap' takes place. Simultaneously beam in your character, and beam out the air. If done correctly, it's quiet at both ends. TenOfAllTrades(talk) 21:43, 24 March 2008 (UTC)
Since the method of travel has some air of unfeasability or even ridicule to it, I'd personaly go for a more humoristic sound like a pop or plop or even a whizz or shebang. Anyways. Think too that you could make the business of teletransportation easier if instead of moving just the physical person, you define a volume (a la Terminator) of air emveloping that person. Since it teletransports indiscriminatly a volume of space it can even be used as a plot twist in a story. See you later. Shwabwabwabwabwaaawawawa ... piuut, pop. 200.127.59.151 (talk) 21:44, 24 March 2008 (UTC)
One more thought, depending on whether you're doing science fiction or fantasy. You could generate a 'force field' or something of that sort at the reception point to move the air out of the way slowly; by 'slowly' I mean the field boundary doesn't expand faster than the speed of sound. Your character (with air from his departure point around him) can just pop into the premade vacuum as quick as he likes. Again, nice and quiet. TenOfAllTrades(talk) 21:47, 24 March 2008 (UTC)
Rematerialization time cannot be zero, because the air molecules can't move faster than light to get out of the way. If you got them moving close to the speed of light, I think you'd have a pretty violent event, especially if the teleportee resembled John Goodman. Either the machine would have to force the air molecules aside before materializing the person where they had been, or the person would have to materialize from the center out, in which case they would be subjected to whatever force was needed to move the air. On the sending end, no such problem, and I'd expect a rather soft unidentifiable slap or pop sound. How about you take the air from where you're going and put it back where you came from; swap the person and the air? --Milkbreath (talk) 21:50, 24 March 2008 (UTC)
Hmm, okay. So one vote for a windy sound, one for a sonic boom, one for a patooie, and one for it not even being possible. Also, two votes for swapping the person with the air; my brother had suggested that, too. The weird thing about that, though, is that anything in the air gets popped over, too; dust, smells, poison gas, etc. Also, if the places had different barometric pressures, there still might be some wind. (And if she teleported into a wall, she'd leave a statue behind.) --Masamage ♫ 21:56, 24 March 2008 (UTC)
Note that apparently this was followed in the recent film Jumper, though I haven't seen it. I read an interview with the director in Entertainment Weekly where he talked about the whoosh you'd hear by suddenly creating a little vacuum where you once were. He was quite proud of himself for figuring that one out. --Captain Ref Desk (talk) 22:00, 24 March 2008 (UTC)
too bad he couldn't figure out how to make a good movie --LarryMac | Talk 15:39, 25 March 2008 (UTC)

Of course, you could always decide that the teleportation mechanism is a swap rather than a one-way jump. If the teleporter jumps from A to B, the volume of air that she displaces jumps simultaneously from B to A. Then it could be totally silent -- although of location A is far enough away that the barometric pressure is different there, then there might be a small sound at location A.

And, doing it this way, what if there is water or a solid object at location B? Then perhaps a person-sized hole would appear in that water or object, and a corresponding chunk of water or other material would be transported to B, where it would fall to the ground with an almighty crash or splash. And if that material was part of a living thing, it could get rather hideous.

Just a thought -- you are welcome to use it if you like it. --Anonymous, 23:11 UTC, March 24, 2008.

According to our lexicon (and also the Jargon File), the sound of teleportation is "bamf", and this comes from the Marvel Universe. Also, in Sam Hughes', "Fine Structure" stories, teleporting sounds like a thunderclap. – b_jonas 18:04, 25 March 2008 (UTC)
well, if you're going to be serious about it.... you've obviously got to deal with the air or whatever occupying your target zone, and displacing it causes a lot of problems, so swapping it makes the most sense.

but also, conservation of momentum; if you're getting teleported from Australia where you're whipping along with the surface of the earth, to the US where the surface happens to be heading in the opposite direction at equal speed, you're going to appear with a net relative velocity of like 1500 mph. this will cause a certain amount of noise, depending on what you smack into, including just the air. Gzuckier (talk) 18:42, 25 March 2008 (UTC)

The conservation of energy issue has come up in fiction before. I recall a murder-mystery-science-fiction story (probably by Asimov, as he liked that sort of thing) in which a key plot point dealt with teleporter travel between points at different altitudes. In the book's early-model teleporters, excess gravitational energy would show up as added heat in the teleported person or object. (My back-of-the-envelope calculations put the temperature change of a human body at about 2.5 degrees Celsius per kilometer of altitude, or about 1.3 degrees Fahrenheit per 1000 feet.) Round-the-world teleportation (and the associated problems of relative velocity) were not addressed. TenOfAllTrades(talk) 16:38, 26 March 2008 (UTC)
b_jonas, Sam Hughes used the swapping method, but the person was teleported into space (technically, they were teleported into a coal seam, which was then teleported into space), so it sounded like the one-way version. 67.182.186.132 (talk) 23:03, 25 March 2008 (UTC)
It certainly wouldn't be a really loud crack/pop, but it could be a bit of a whoosh. Quite unlike Ms. Rowling's Harry Potter. ~user:orngjce223 how am I typing? 16:42, 26 March 2008 (UTC)

[edit] More Teleportation

In Robert Heinlein's Stranger in a Strange Land Michael idly toys with the idea of destroying the solar system by teleporting a piece out of the centre of the sun. Although capable of doing this he does not actually go ahead so we never got to see how it would turn out. Would this work, and how big a piece would be necessary? SpinningSpark 23:47, 24 March 2008 (UTC)

I can't see it destroying the solar system unless enough was transported out to alter the gravitational system into essentially a binary star system. However, if a sizable chunk of the Sun's interior was transported onto Earth, it could probably destroy the planet. StuRat (talk) 03:26, 25 March 2008 (UTC)
Not sure, but I think the idea was that the consequent collapse into the now empty space would cause some kind of nova followed by crispy planets. Would it? SpinningSpark 07:47, 25 March 2008 (UTC)
Wouldn't taking out a significant chuck of the core of the Sun effect its fusion reactions as "the core is the only location in the Sun that produces an appreciable amount of heat via fusion: the rest of the star is heated by energy that is transferred outward from the core"? I guess that would be the destruction of the solar system, but certainly life on earth. -- MacAddct  1984 (talk • contribs) 14:07, 25 March 2008 (UTC)
If you removed enough fuel from the core it would prematurely become a red giant. That would destroy the earth, not sure about planets at more distant orbits.
What about the effect on orbits? if any?Gzuckier (talk) 18:36, 25 March 2008 (UTC)
As the sun loses mass its gravitational force weakens, causing the planets to move to higher orbits. This paper discussed in the NY Times suggests that even despite the higher orbit, a red giant sun will still swallow the earth.66.152.245.18 (talk) 19:05, 25 March 2008 (UTC)
An abrupt change in the Sun's mass would convert each planet's orbit into one that was higher on average, but still passed through the point where it was at the time of the change. So if the planet happened to be near perihelion, its aphelion would get higher but its perihelion would stay about the same: it would be a more eccentric orbit. If it was near aphelion, the orbit could become less eccentric than before (depending on how eccentric it previously was, and on the amount of mass change). --Anonymous, 23:33 UTC, March 25, 2008.
This just reminded me of the Stargate episode, Exodus where a Stargate connected via a wormhole to another stargate that was orbiting a blackhole was shot into a star. Mass from the star was sucked through the wormhole by the black hole and the star went supernova.--Shniken1 (talk) 23:52, 25 March 2008 (UTC)