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March 18

Positive charge on flying insects?

I was just reading the article in New Scientist 2 march called "Electric plant auras guide foraging bees", and it states "As bees fly through the air, they-like all insects- acquire a positive charge". I can't find any references that discuss this further, is it a well known fact? and what causes it to happen? — Preceding unsigned comment added by 122.108.189.192 (talk) 07:04, 18 March 2013 (UTC)[reply]

This link would suggest that it's true for bees and the cause is given as "frictional electricity" as they fly, and here's another on the subject. Mikenorton (talk) 08:08, 18 March 2013 (UTC)[reply]

Thanks Mike, that last link is fascinating.122.108.189.192 (talk) 07:35, 19 March 2013 (UTC)[reply]

interstellar Bomb

Even if this is not trolling there is nothing going to be solved by this. CambridgeBayWeather (talk) 06:40, 19 March 2013 (UTC)[reply]

The following discussion has been closed. Please do not modify it.

Hello, I want to know, if it is possible to send an atomic Bomb (or any other Device that destroys more than 1 km²) so that it reaches a Star within a distance of about 100 Lightyears not later than in the mid 42th Century in operational conditions. Additionaly the exact orbit properties of the target are unknown, so it is necessary for the Device to determine the exact course within this star system while on flight.

Please take this question seriosly, there is more on stake than you can imagine. (excuse my bad english, it's not my usual language.)--AlaneOrenProst (talk) 08:08, 18 March 2013 (UTC)[reply]

The technology needed for interstellar travel is not available. And the energy needed for interstellar travel cannot be obtained from Earth. So keep your fantasy in the pages of science fiction books. --PlanetEditor (talk) 08:50, 18 March 2013 (UTC)[reply]

just because the necessary technology isn't available now, did not mean it is impossible. The article you linkend already gives some possible ways to acomplish what is necessary.--AlaneOrenProst (talk) 08:58, 18 March 2013 (UTC)[reply]

PS: and, no, this is not a science fiction book. This is reality.--AlaneOrenProst (talk) 08:59, 18 March 2013 (UTC)[reply]

Well I think it is just about possible, at the moment there's no good reason to spend the enormous amounts that would be involved on such an undertaking, but I'd guess in another hundred years it might actually become practical to think about sending off a fast interstellar ship. By the way you don't need a bomb, just don't slow it and aything going at that speed will destroy a wide area. As far a I know there are no current threats from bug eyed aliens that need to be countered so I don't see the point of the 'this is reality' business. Dmcq (talk) 09:24, 18 March 2013 (UTC)[reply]

currently there is no problem, but if we do not act now, the Prophecy will fullfil, and the terrible Event I want to avert will happen. --AlaneOrenProst (talk) 09:30, 18 March 2013 (UTC)[reply]

PS: more exactly spoken: the Event will happen with a probality between 37,5% and 62,5%, acording to the prophecy.--AlaneOrenProst (talk) 09:33, 18 March 2013 (UTC)[reply]

Sure, there doesn't seem to be any scientific limitations on such an idea. Any technology required is not impossible, as noted, it's just not something that humanity currently capable of doing. Plasmic Physics (talk) 09:27, 18 March 2013 (UTC)[reply]

then we have to hurry to get the technology to be capable.--AlaneOrenProst (talk) 09:38, 18 March 2013 (UTC)[reply]

Why the rush? Plasmic Physics (talk) 09:40, 18 March 2013 (UTC)[reply]

Well Plamsa Physics, could you explain where would you get the energy required for interstellar travel? --PlanetEditor (talk) 09:42, 18 March 2013 (UTC)[reply]

@Plasmic Physics: because of the Blackbird-Molotow-Reich-Effect. As more we wait, as harder it gets to escape the prophecy.--AlaneOrenProst (talk) 09:44, 18 March 2013 (UTC)[reply]

Oh the BMRE! I don't see the urgency. Isn't that not for at least a couple millennia? We have plenty of time. Especially since in 3127 we can harness time dilation technology and postpone that event almost indefinitely or at least until 1234567. No worrys. Lets revisit this in a coupe hundred years just in case. Or just tomorrow when you come down.68.36.148.100 (talk) 03:27, 19 March 2013 (UTC)[reply]

If you - or anyone else - can figure out a way to send a probe to a star 100LY distance then I think that guidance should be a simple matter to sort out...

You wouldn't need a nuclear warhead btw - just keep accelerating the whole way and impact the probe into the target. Refer to kinetic bombardment, impact depth and relativistic kill vehicle for more information relating to the power of kinetic energy.

If you could manage an acceleration of just 0.0001G - that is just shy of one mm/s^2 - then the probe would arrive in just under 2000 years with enough speed to punch a sizable hole in a planet. WegianWarrior (talk) 09:46, 18 March 2013 (UTC)[reply]

well, that sounds like something we can work with. But a sizable punch is not needed. I do not want to kill a whole world, the "1 km²" is more or less all the damage needed.--AlaneOrenProst (talk) 09:51, 18 March 2013 (UTC)[reply]

To everyone providing their opinion, the energy required for interstellar travel is not available on Earth. This makes interstellar travel impossible. --PlanetEditor (talk) 09:48, 18 March 2013 (UTC)[reply]

For now. Someguy1221 (talk) 09:57, 18 March 2013 (UTC)[reply]

It most certainly is available on earth as nuclear fuel. Plus they're not trying to send people. I think I'd much prefer a cleaner way than Project Orion though, ion drive has lots of room for improvement and also in the future it should be possible to assemble stuff automatically on say the moon instead so pollution might not be such a worry. Dmcq (talk) 10:46, 18 March 2013 (UTC)[reply]

Yeah, sending a tiny Voyager-like probe to the interstellar space may be possible. It will take more than 80,000 years to reach the nearest star Proxima Centauri. Nearly 3000 human generations. So manned interstellar travel is impossible. --PlanetEditor (talk) 10:52, 18 March 2013 (UTC)[reply]

The qualifier for that statement in the article is a bit ambiguous, it doesn't say how long a reasonable time lasts. Plasmic Physics (talk) 10:57, 18 March 2013 (UTC)[reply]

Actually, sending "a tiny Voyager-like probe to the interstellar space" is certainly possible, because we have already done that (you might quibble if the Voyagers have reached "interstellar space", but there is no reasonable doubt that they will reach it). And I see no hard physical reason why it should not be possible to send e.g. an 0.01c mission out to other stars. If it's economically and politically feasible is another question, but scientifically and technically it shouldn't be that hard. See Project Orion (nuclear propulsion). --Stephan Schulz (talk) 13:31, 18 March 2013 (UTC)[reply]

If we're not worried about 100g type acceleration or stopping at the far end it should be possible to do considerably better than 0.01c.. Dmcq (talk) 16:07, 18 March 2013 (UTC)[reply]

Yeah, what the previous guy said... it isn't named Voyager Interstellar Mission for nothing. If you think about it, once you have attained escape velocity, which we could even manage with a manned capsule, decades ago, you are on an interstellar trip, as long as you have plotted your course so as not to get trapped in the gravity well of another solar system body. If Voyager could do it with flybys through the ecliptic, it shouldn't be very hard if you aim out of the ecliptic. The only additional requirement for your plan is getting there on time, and as everybody knows, in space without drag you can just add acceleration until you get to the speed you need. I'm too lazy to do the math right now, but aside from standard rocket engines, you have the choice of not very advanced technological stuff like nuclear powered ion-drive thrusters, because over a couple of millenia even a tiny fraction of a G of constant acceleration tends to add up. And then there are always the way-out-there drive concepts, like solar sails, possibly with a boost from terrestrial-based lasers, interstellar ramjets, etc. which could be developed into operation in part of the 2000 years you have to spare. Certainly, there is no guarantee that any of these will get you there on time and functional, but there is no hard and fast reason that makes it impossible. And, you could certainly try all of the above, in the hopes that at least one will succeed. You're probably more at risk of failure regarding the control and guidance systems being functional after 2000 years to aim the thing, as you require. Also note that in addition to the plain old impact at that speed being destructive enough to eliminate the need for an explosive payload, as previously mentioned, in fact if you get up to a high enough velocity and you have enough control to steer the thing, all you have to do is flip it over 180 degrees just before you get there as though you were trying to slow down, and the relativistic blue shift of the energy of your engine will do some really serious damage to whatever you're moving towards. Gzuckier (talk) 16:26, 18 March 2013 (UTC)[reply]

ok, that sound's like something basical. Who schould I contact to make this real?--AlaneOrenProst (talk) 17:01, 18 March 2013 (UTC)[reply]

If you really want to go up to 100 lightyears in only 2100 years, then at constant acceleration you'd need to reach nearly 0.1c. You could do it with as little as 0.05c if you mostly front-load your acceleration. A mere 100 kg of projectile going 0.05 c would require no less than 10 petajoules (1×10¹⁶ J) of energy to achieve this (and likely a great deal more due to inefficiencies). Setting aside the fact that a rocket that small could never store that much energy, the amount of energy is "only" about the equivalent of a 3 megaton nuclear bomb, which means it is on the range scale of things humans have achieved. If instead of 10 petajoules, we imagine the inefficient (or larger) rocket actually requires 10 exajoules (1×10¹⁹ J) then that's still only about 20% of global annual electricity production. Finding a way to channel that much energy into a rocket would be extremely challenging, but given one or a few centuries to figure it out and a united global effort to accomplish it, then I don't see any reason it shouldn't be possible in principle. I certainly wouldn't expect to see such an effort in my lifetime though. Dragons flight (talk) 16:42, 18 March 2013 (UTC)[reply]

it should better happen within the next few years. The Blackbird-Molotow-Reich-Effect is already dragging hefty.--AlaneOrenProst (talk) 17:01, 18 March 2013 (UTC)[reply]

Okay, I'll bite. What is this Blackbird-Molotow-Reich-Effect ? Just a pointer to a source or web page will do (maybe one that doesn't use block capitals or flashing neon fonts). Gandalf61 (talk) 17:16, 18 March 2013 (UTC)[reply]

the Blackbird-Molotow-Reich-Effect basicly means, that, on the long run, to change anything in history via timetravel (and the only way I can imagine the Prophecy can be here is that it was send back in time) is impossible. The changes you can acomplish will ever follow a a*t^k*e^-n*t²) formula, so on short you have an exponentionally efect, but on the long run in converges against 0. This efect was discoverd by prof. phy. Molotow, one of the small pack of refuges who made it to the TMSC Hope, and who discoverd the timegate and how it works, dr. hist. Reich, another refuge and as historical advisor member of the time travel commando and cmdr. Kathrin Blackbird, second in command of the TMSC Hope and leader of the time Travel commando, which tried to avert the foundation of the Cygnian empire throgh travveling from 31th Century to 21th Century earth. --AlaneOrenProst (talk) 17:32, 18 March 2013 (UTC)[reply]

I can imagine another way this alleged prophecy could "be here": Someone made it up. Created the idea in their imagination. It happens, you know. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:46, 19 March 2013 (UTC)[reply]

Fine, there is nothing wrong imaging a fantasy future. But from a scientific point of view, let me clarify some points. Predictions sometimes ignore reality and science. For example, A. C. Clarke predicted that dinosaurs will be cloned by 2023, but his prediction was not based on science. There are multiple obstacles to manned interstellar travel which cannot be averted unless you alter biological and physical laws. 1. Microgravity: Humans can stay in microgravity in the ISS for months, but a lifelong stay in microgravity defies human biology. 2. A lifelong stay outside the protection of Earth's magnetic field and exposure to cosmic rays will be disastrous. 3. If humans plan to make a trip to another star, they will need resources (oxygen, food reserve for decades to centuries), health care, repair and maintenance crew. Any possible damage to the starship need to be repaired, necessitating the burden of a repair crew and machinery on board. All these are just impractical and can exist only on Star Trek. 4. At 0.01c, even a tiny atom can do incalculable damage to the spacecraft. Chances of collision with a Small Solar System Body is very high when you are traveling at 0.01c in a gigantic starship through the Oort cloud. 5. Humans can survive short-duration stay in space. But lifelong space journey needs a self-sufficient ecosystem to produce human needs. And an ecosystem can't exist beyond the habitable zone.

So far, humans have been able to visit space with active support from Earth, and with the protection of Earth's magnetic field. Self-sufficiency in space without any contact with Earth is impossible. It is economically infeasible, biologically impossible. --PlanetEditor (talk) 17:03, 18 March 2013 (UTC)[reply]

PS, I think we have been trolled. --PlanetEditor (talk) 17:03, 18 March 2013 (UTC)[reply]

Well, you might be right about that one, but most of the rest is, quite simply, wrong. Microgravity would not be a problem - on the size of an interstellar space ship, you can use centrifugal force as an adequate replacement for gravity. Cosmic rays are a problem, but not an unsurmountable one. For one, we already know how to generate magnetic fields quite well. And the damage done by an atom at 0.01 c is very much calculable - an H atom (the most frequent kind by far) will have about 6.6e-15 J (i.e. not very much). For WIM, the most common kind if interstellar medium, there are about 0.01 ions per cubic centimeter. Going 3000 km/s, the total energy deposited per second per square meter is about 2.2 J, i.e. measurable, but not a problem (for comparison, at 20 degrees centigrade, black body radiation of that square meter is about 400 W). And chances of collision with any solar system body is actually quite low (and, for a given distance, independent of speed). If there were that much stuff out there, we wouldn't see the stars). --Stephan Schulz (talk) 19:37, 18 March 2013 (UTC)[reply]

you seem to ignore the fact, nobody here is speaking about manned interstellar flight except you. And, no, I'm not a troll, I try to avert a catastrophy. --AlaneOrenProst (talk) 17:09, 18 March 2013 (UTC)[reply]

My proposal would be to send a microscopic self-replicating machine to either a solar system that's nearby to the destination or to some planet of that same solar system. The machine will then grow all by itself using solar energy into a nuclear bomb factory and missile factories within a year. It would take only a small amount of energy to send such a factory to the desired destination at a speed close to c. Count Iblis (talk) 17:22, 18 March 2013 (UTC)[reply]

Ok, I've got to ask - what is this catastrophe you're trying to avert? Richerman (talk) 17:41, 18 March 2013 (UTC)[reply]

the multiverse-War, from 4169 onwards, cost 210 billion human lives (217 Billion gross) and ended a milenia long period of peace and prosperity. --AlaneOrenProst (talk) 17:44, 18 March 2013 (UTC)[reply]

Why worry about something 2,000 years in the future, when there's so much stuff to worry about in the here and now? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:48, 19 March 2013 (UTC)[reply]

WP:DENY. μηδείς (talk) 17:46, 18 March 2013 (UTC)[reply]

Putting aside the dull issue of the questioner's motivation, how about the interesting part: is it impossible to power an interstellar manned mission with all the Earth's energy? According to Apollo 13 you can go to the Moon and back in 143 hours - so 72 hours (3 days) to send 43,000 kg including 3 men for something like 380,000 km (10^5). By comparison, Alpha Centauri is 4.36 ly = about 41200000000000 km (10^13). That leaves us with 10^8 times the distance to go. The article doesn't say how long we have, so let's take the OP's figure of 2000 years = 240000 the time to do it in. So the interstellar mission has to have an average speed that is about 400 times faster than that of the space probe, which does indeed suggest the need for 160000 times the fuel (to speed up that much faster and burn that much longer). If I suppose that the giant first stage of a Saturn V was mostly to escape the Earth's pull, and count therefore only something like 600,000 kg of fuel used to get to the Moon, that gets me about 1 trillion kilograms of fuel. Compared to 88 million barrels of oil used daily = roughly 12 billion kilograms? that should be what, 80 days worth, times some factor for the extra energy in rocket fuel. Hmmm.

Now let's just go for raw kinetic energy. We want 43,000 kg travelling at an average 4.12E16 m/6.3E10 s = 6.5E5 m/s. That gives kinetic energy (4.3E4 kg) (6.5E5 m/s) (6.5E5 m/s) = 1.82 E16 kg m^2/s^2 = 18 petajoules. Load up 18 Tsar Bombas and you're set. (Well, 19, let's not forget the one to spread the message of civilization to the stars!) Compare to what joule says, 9.4 E 19 joules used in the U.S. per year.

Either way, we have this huge advantage that we've considered 1/25 the OP's distance - so should pay 625 times more, or 136 years of oil production (if we had it) to go to his destination in his time frame - or we should get to Alpha Centauri in, oh, I dunno, article doesn't say, but let's say 80 years, which happens to be 1/25 of 2000... ditto. That sallot of energy. But it's still 18*625 Tsar Bombas = 11250 of them. Our article says there are 17,000 nuclear weapons in the world ... what a splendid use for them! Pity it would be impossible to get them all on a 50,000 kg mission, though I wonder how many factors shy it need really be. Wnt (talk) 22:25, 18 March 2013 (UTC)[reply]

Wnt, feed the birds, not the trolls! 24.23.196.85 (talk) 00:14, 19 March 2013 (UTC)[reply]

suicide by hanging

whether there is any kind of noise from the mouth of a person who hanged herself or himself. 120.59.132.210 (talk) 08:33, 18 March 2013 (UTC) Saurabh pandey,— Preceding unsigned comment added by 120.59.132.210 (talk) 08:28, 18 March 2013 (UTC)[reply]

How often does it happen with someone else observing? I would think not very often. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:06, 18 March 2013 (UTC)[reply]

Public hangings were once a popular spectacle, so there were plenty of observers. If the hanging is done properly, death is instantaneous and the airway is swiftly closed, so not much chance of a noise from the mouth. But if a suicide is botched and the victim slowly dies of strangulation, they might well make some noise during the process.--Shantavira|^{feed me} 12:30, 18 March 2013 (UTC)[reply]

Some one who commits suicide by hanging is unlikely to use a long drop, so they will die by slow strangulation. There might be some noise from the mouth, but as there would be very little airflow through the constricted throat probably not very much. AndrewWTaylor (talk) 12:42, 18 March 2013 (UTC)[reply]

For more info on noise made by strangulation victims, see Strangers on a Train. 24.23.196.85 (talk) 00:00, 19 March 2013 (UTC)[reply]

Heat flow

If you have two bodies of different temperatures next to each other, what is the rate of heat flow between them? Is it just proportional to the difference between the temperatures? Is there an exact relationship?

150.203.115.98 (talk) 11:02, 18 March 2013 (UTC)[reply]

What you are looking for is Newton's law of cooling, which says that "the rate of heat loss of a body is proportional to the difference in temperatures between the body and its surroundings". Note that this is an empirical law, not a theoretical derivation or definition - however, it is useful because it is approximately true in a wide range of circumstances. Gandalf61 (talk) 12:09, 18 March 2013 (UTC)[reply]

Its dependent on materials and conditions because heat flows different already in single bodies of different materials. Its all exactly described in Thermodynamics. --Kharon (talk) 15:15, 18 March 2013 (UTC)[reply]

If the bodies are in contact (with good thermal conductivity at the contact area), and there is not much heat lost or gained to the surroundings, then Thermal conduction is the main factor in heat flow between them, and this is usually proportional to temperature difference in good conductors. ( I say "usually" because someone will point out exceptions, though I can't think of any.) If the bodies are not in contact, and the main transfer of heat is by Thermal radiation, then this is proportional to the fourth power of absolute temperature, making the rate of heat transfer more complicated because there is radiative transfer with the surroundings. Dbfirs 16:33, 18 March 2013 (UTC)[reply]

I would be remiss, after my elaborate rant above on Fourier's law, if I didn't point out an exception! The infamous Peltier effect, wherein electrical energy is expended to make the heat flow in the wrong direction (against the thermal gradient), is a great exception. Though, if you want to get really really into technicalities, heat is still flowing from hot to cold; but because the material is subject to an electric field and unique material properties, the electron gas has a different temperature than the substrate. All the necessary mathematics work out, anyway; per my standard reference, oh, probably Chapter 4 of Bittencourt for physics of dealing with multiple temperatures in an ionized plasma (though I don't specifically recall any discussion about solid-state "electron gas" plasmas in Bittencourt's textbook). Nimur (talk) 17:15, 18 March 2013 (UTC)[reply]

Thanks, I knew there would be an exception! Dbfirs 17:54, 18 March 2013 (UTC)[reply]

I was mistaken about the chapter; Chapter 7, Section 3, mixtures of different particle species, and derivation of macroscopic variables like temperature. Just noting for posterity, in case anyone looks it up... Nimur (talk) 15:42, 20 March 2013 (UTC)[reply]

Drug Interaction

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

--Jayron32 18:54, 18 March 2013 (UTC)[reply]

A few questions regarding atomic energy levels (1&2) and orbitals (1)

I'm currently working on a paper dealing with aspects of Franck-Hertz experiment, and encountered some puzzling descriptions and symbols in an article published in the past, as follows:

1. The article includes a simplified energy level scheme of mercury. This scheme includes also a 7th & 8th levels, despite the fact that the outermost level in Hg is n=6. Any reason or explanation to this 'odd' diagram ?

2. It's claimed in this article that when a triplet appears it means that the electronic configuration consists of 2 electrons in 6s6p orbitals "giving a total P state where the spins are coupled to a total spin with quantum number S=1". How this 6s6p configuration came to be so ? what's the meaning of the quoted phrase ? - I'm familiar with spin physics, but the quoted phrase is seemingly unclear. It'll great to elaborate on these.

3. d orbital is distributed equally in space: x, y & z axes. However, as it's shown in various textbooks, and Wikipedia isn't excluded, there is a kind of a spatial preference: x & y are populated first, and the 'leftovers' go to z. What's the reason for this spatial asymmetry ? BentzyCo (talk) 14:01, 18 March 2013 (UTC)[reply]

Try these answers on for size

Energy levels exist regardless of whether there are electrons that fill them. Remember that energy levels are merely geometric descriptions of the solutions to the Schrödinger equation, and you can arbitrarily feed any set of quantum numbers into said equation to get the data for any energy level or orbital you wish, those orbitals "exist" in the sense that an electron given enough energy will "promote" to that energy level, even if it isn't the ground state for that atom. There are an infinite number of energy levels, but we generally stop describing them when it isn't useful to use them. For the purposes of the Bohr model (which only strictly works on a "one electron atom", but qualitiatively the principles behind it still hold for all atoms) one will still need to know what the energies of the n=7 and n=8 energy levels are for an atom, because energy imparted to electrons will still cause electrons to jump from the ground state to those higher states, and when they relax back down to the ground state from those higher energy levels, you can use the emissions data to calculate what energy those levels were at.
Triplet state describes the situation. For a two-electron system, if the electrons are in separate orbitals, they exist in a triplet state: Four total spin states, with two degenerate with each other: basically they would be up-up, up-down, down-up, and down-down, with the middle two being degenerate. If the two particular electrons are in the same orbital, their spins MUST be opposed (per the Pauli exclusion principle, so the only possibilities are the degenerate up-down and down-up states; since these are identical in energy this is called the singlet state. What your sentence sounds like is that there is some state of mercury (not familiar enough to know if this is the ground state or an excited state) which has a 6s¹6p¹ configuration, which gives rise to the triplet (the expected 6s² state would be a singlet state).
All the d orbitals are distributed evenly in space, in the sense that all 5 d orbitals, if overlaid and added together, will make a perfect sphere (this is strictly true of all orbitals of the same n and ℓ values). For any geometry higher than ℓ = 1, the complete set of orbitals will not be geometrically identical. As you note, there's one d orbital whose shape does not match the other four; likewise for f orbitals, there will be four of one shape, two of another, and a single of yet a different shape. I'm not completely familiar with how or why this works out that way, or what this means for the "order" that d orbitals fill in; however as far as I know it is completely arbitrary as all 5 d orbitals should be identical in energy. But at this point someone else will need to answer more authoritatively, as I can't quite find the answer in any of my searches, and I've either not known (or more likely forgotten) this little bit of chemistry. --Jayron32 17:38, 18 March 2013 (UTC)[reply]

Re #2, the triplet state is three total spin states, not four. The fourth is the singlet state.

\left|\uparrow \downarrow \right\rangle -\left|\downarrow \uparrow \right\rangle

is the singlet state (ignoring normalization). It has that value regardless of the spin axis you choose, even though the choice of axis determines the meaning of the up and down arrows.

\left|\uparrow \downarrow \right\rangle +\left|\downarrow \uparrow \right\rangle

is one component of the triplet state (note + instead of −). If you rotate the spin axis you will not get that, but rather some combination (superposition) of it with

\left|\uparrow \uparrow \right\rangle

and

\left|\downarrow \downarrow \right\rangle

, which are the other components of the triplet (in one basis, anyway).

Re #3, the orbitals that you see in pictures are just a somewhat arbitrary basis set. As an analogy, try to find an orthogonal basis for the plane x+y+z=0. One possibility is (1, −1, 0) and (1, 1, −2): they both satisfy x+y+z=0 and their dot product is zero. They don't seem very symmetric, though, compared to the plane itself which is symmetric under arbitrary permutations of the x, y, z coordinates (not to mention the much larger group of continuous rotations). That's okay, because no particular vector (except (0, 0, 0)) has that symmetry; it's just the whole collection of vectors that's symmetric, and (1, −1, 0) and (1, 1, −2) is a perfectly good basis for that collection of vectors. Likewise, with the orbitals, the pictures you often see in books are just basis vectors for a space of solutions. The sum of those basis orbitals is still not rotationally symmetric, just like (1, −1, 0) + (1, 1, −2) = (2, 0, −2) is not rotationally symmetric. It's the space of orbitals spanned by the basis orbitals that's symmetric. To put it another way, if you rotate an orbital in this space, you always get another orbital that can be expressed as a sum of orbitals from the same (small, finite) basis set. -- BenRG (talk) 18:27, 18 March 2013 (UTC)[reply]

First, thanks to both of you. I still have to learn your answers here, and make my own comments and also may focus the issue better. In the meanwhile, I've two more points to raise, following further study of the subject:

a. It turns out that what level is excited depends on the mean free path traversed by the electrons, which is inversely dependent on the collision cross section. However, the sublevel that is mainly excited is 6³P₁ (4.89 eV), which belongs to a triplet, while the other two have smaller cross section. Now, this isn't understood: how can the cross section differ for the same specific atom encountered by the electron ? In terms of the mean free path, it's even less understood, since it is related to the average distance between collisions.

b. later. BentzyCo (talk) 13:07, 20 March 2013 (UTC)[reply]

It seems as if my recent response and question dissolved in an immediate sea of other questions, or in other words: "living by the day". BentzyCo (talk) 17:06, 21 March 2013 (UTC)[reply]

Dr Anna L

Hello, I had recently saw on Facebook, under the page Abandoned Asylums, a mansion that was owned by a Dr. Anna L. The pictures are amazing and the contents of this mansion is very dated ie: glass medicine bottles and the containers organs are preserved in etc. It is said that he was killed in a car crash about 20+ years ago. It also states that his family didn't care about the inheritance, this is also odd. There is something most intriguing about this person and would like to know more but I cannot find much except a video footage on youtube under Mansion of Dr Anna L. I don't think he is English but I'm not sure where he is from either. Is it possible that you could find out more about this person? Thanks Michelle Gecas 24.102.51.143 (talk) 14:39, 18 March 2013 (UTC)[reply]

Googling shows that the mansion is in Europe, probably the Netherlands, but it's hard to find search terms that give anything more than that. Looie496 (talk) 16:48, 18 March 2013 (UTC)[reply]

As far as I can see, all text in the Youtube video and the pictures is in German, so it is probably in Germany, Austria or the German-speaking parts of Switzerland, Belgium or Luxembourg. - Lindert (talk) 17:05, 18 March 2013 (UTC)[reply]

A little further research shows that it's in a spa town in the vicinity of Berlin, but the exact location is a secret passed around by word of mouth, no doubt because the place has already been looted to some degree. Looie496 (talk) 17:44, 18 March 2013 (UTC)[reply]

Amount of dissolved salts in a solution

I want to find out the amount of salts and other elements like nitrates, sulphates, chlorides, ammonium, phosphorous, potassium, magnesium, sodium etc in a solution. I guess that I should resort to titration but I am not sure which standard solutions and indicators to use, to find out the concentration of different elements and salts. Is there a web site (or a book) which gives the detailed procedures for finding out the concentration of these? My requirement is very much similar to Water chemistry analysis but that page doesn't give much info. I could pay some labs to do these tests for me but I want to do it at home, as I am likely to repeat the tests many times - WikiCheng | Talk 17:01, 18 March 2013 (UTC)[reply]

Could you please give a complete list of the substances you're testing for? 24.23.196.85 (talk) 00:19, 19 March 2013 (UTC)[reply]

A manual from a university lab course on quantitative analysis might be a good start.--Wikimedes (talk) 00:49, 19 March 2013 (UTC)[reply]

For 24.23.196.85: Here is the list of substances - Nitrates, Ammonium, Phosphorous, Potassium, Magnesium, Sulphates, Chlorides, Sodium, Iron, Boric acid, Zinc, Copper and Manganese. I am basically testing a nutrient solution for plants - WikiCheng | Talk 16:50, 19 March 2013 (UTC)[reply]

This is a big, big list! Do you have (or can you afford) any kind of spectrometry equipment? Because this is the easiest and most convenient way to test for all of these substances -- you just put your solution in the cuivette (or sampling flask), select the wavelength you want, put the sample into the instrument and measure the absorbance (or emittance). If not, then the analysis becomes much harder, because you'll have to take thirteen separate samples and analyze each of them for just one substance. In the case of phosphorus, magnesium, chloride, iron, zinc, copper and manganese, you can perform a gravimetric analysis: chloride with silver nitrate (note this will interfere with your nitrate determination); copper with H2S under acidic conditions (IN A FUME HOOD WHILE WEARING A GAS MASK!!!); iron and manganese together by adding alkali to pH of 8 (this WILL skew at least one of the other analyses); zinc with a sulfide salt under alkaline conditions; phosphorus and sulfate together by adding a calcium salt at pH of 8 or above; and magnesium by EDTA titration after precipitating ALL of the transition metals (iron, zinc, copper and manganese). As for the other substances: you can test for ammonium by adding alkali, absorbing the ammonia gas in boric acid, and back-titrating the boric acid solution with sodium carbonate; for phosphate by adding ammonium heptamolybdate and stannous chloride, followed by colorimetric or spectrophotometric analysis; for sulfate by adding barium chloride; and for nitrate by adding concentrated sulfuric acid, absorbing the gas in alkaline solution, and back-titrating with acid. As for potassium, sodium and boric acid -- sorry, you can ONLY analyze for them using spectrometric methods. (You realize how cumbersome this is if you don't have any spectrometric equipment?) 24.23.196.85 (talk) 02:56, 20 March 2013 (UTC)[reply]

Oh! and Ooops! and Thank you ! :-) So it IS much harder than I thought it would be. In any case, thanks a lot for taking time to answer in this much detail! - WikiCheng | Talk 04:16, 20 March 2013 (UTC)[reply]

I've done this analysis for real quite a few times, so I know first-hand that without our trusty AES (atomic emission spectrometer), this is an absolute nightmare! Thank God for modern technology... 24.23.196.85 (talk) 05:52, 20 March 2013 (UTC)[reply]

Dollar bills and a reflecting telescope.

I was trying the other night to recall an anecdote about someone who placed a surprising amount of dollar bills on a large reflecting telescope to show ??how occluding part of the mirror does not affect the image. Maybe I have the reason back to front, but does anyone recall this story and hopefully provide a link. Richard Avery (talk) 19:21, 18 March 2013 (UTC)[reply]

It's certainly true that you can place things in front of the primary mirror of a Newtonian telescope and not block out parts of the image (although it does "affect" the image by making it dimmer). The mere existence of the secondary mirror (which blocks out parts of the primary) proves that. I'd be very surprised if anyone would be allowed to place dollar bills directly onto the mirror of a large telescope, simply because of the risk of scratching it or leaving some kind of undesirable contaminant behind. But what you describe would certainly work...I just don't see where the anecdote came from. SteveBaker (talk) 16:50, 19 March 2013 (UTC)[reply]

Indeed I'd expect that the damage done by touching the mirror would cost more to repair than the dollar notes used to entirely cover the mirror. If one used $100 bills for the experiment it might cover the costs but singles won't. Repolishing and coating large telescope mirrors costs significantly more than US$0.0624009 per square inch. (If you're wondering where that number comes from: current US banknotes all measure 2.61 by 6.14 inches) Roger (talk) 19:43, 19 March 2013 (UTC)[reply]

OK, thanks for taking the trouble guys. Richard Avery (talk) 22:50, 19 March 2013 (UTC)[reply]

Neutron instability - magnetic field effect

Are there some data (from measurements) concerning the effect of magnetic field to the mean lifetime of a neutron?--5.15.215.42 (talk) 21:37, 18 March 2013 (UTC)[reply]

Data on the number of books published annually in the world, 1950 and 2012

I have heard that data exists to identify the massive growth in books publihed in the last 50 to 60 years. I have found some UNESCO references to Scientific Publications but I was looking more broadly than just this. Is there any data I can readily access? — Preceding unsigned comment added by 124.187.78.18 (talk) 22:43, 18 March 2013 (UTC)[reply]

Some data are in the article "Books published per country per year".

—Wavelength (talk) 23:00, 18 March 2013 (UTC)[reply]

Can the energy needed for interstellar travel be obtained from Earth?

A message for those in the "Interstellar Bomb" section above who claim that "the energy needed for interstellar travel cannot be obtained from Earth":

This is a classic example of misquoting Wikipedia. It is instructive to examine how a good article was twisted into pseudoscience:

The original question asked about the feasibility of sending a few pounds (say, a nuclear artillery shell) on a one-way trip of 100 light-years with a flight time of roughly 2000 years. But of course the false claim isn't just that that trip is impossible, but rather that no trip is possible.

The Wikipedia page that supposedly supports this claim is at Interstellar travel#Required energy. To get the bogus claim, you have to:

Change "trip" to "round trip"
Change "arriving" to "decelerating on arrival".
Change "a few pounds" to "big enough to support a crew."
Change "no time limit" to "a few decades".
Change "available energy" to "actual energy historically produced"

This may be a new record for misusing a Wikipedia page.

Not only is interstellar travel possible, but it has already been done, at least as far as starting the trip goes. It left in 1972. We will have to wait for a while before it reaches another star, but it will do so. --Guy Macon (talk) 23:51, 18 March 2013 (UTC)[reply]

"If deceleration on arrival is desired and cannot be achieved by any means other than the engines of the ship"

Uh, isn't the ship headed into a stellar wind at a considerable clip? Doesn't that count as a nifty power source for planetary encounters? Hcobb (talk) 23:59, 18 March 2013 (UTC)[reply]

Yes, stellar wind and a big sail can give you a considerable amount of braking. There is a limit, though; come in too fast and the sail won't have enough time to bring you to a stop before you blow past the star or hit something. --Guy Macon (talk) 05:50, 19 March 2013 (UTC)[reply]

If you converted the whole mass of the Starship Enterprise into energy (E=mc² etc) it would not go far anytime soon. Look at the math. Bit like saying that Neanderthal cavemen could achieve oceanic voyages by tossing a log into the sea, which washes up (eventually) on some distant shore. [1]--Aspro (talk) 00:02, 19 March 2013 (UTC)[reply]

Actually, it's like saying that no land-based species on earth could achieve oceanic voyages, while ignoring the fact that coconuts do it all the time. --Guy Macon (talk) 05:50, 19 March 2013 (UTC)[reply]

It is the oceanic current that pull off these feats with the coconuts. The coconuts are just joy-riders of this natural phenomena. Likewise, Voyager was just thrown into a gravitational 'current' whereby its rotational velocity was converted, so as to give it in excess of sun's escape velocity. Modern Homo- sapiens knew just where to throw this metal log in to the near shores of the great cosmos. It was the orbital velocity of earth that gave Voyager the initial oomff. The only difference is that Homo- sapiens could throw their robotic coconuts where as the coconuts palms could only drop.--Aspro (talk) 16:15, 19 March 2013 (UTC)[reply]

While I generally agree with your most abstract points above with regard to the general energy needs and logistics, there are some other pragmatics which bear mentioning. Specifically, that Voyager is likely to be slowly annihilated by interstellar debris while en route, as would indeed any ship not rigorously designed (arguably to specs not possible with current materials science) or repaired during the passage. Snow (talk) 11:16, 23 March 2013 (UTC)[reply]

Sounds interesting. What's the Starship Enterprise's total displacement? 24.23.196.85 (talk) 00:29, 19 March 2013 (UTC)[reply]

You probably wont get an answer to that, because it is water bound vessels that 'displace' water at 1gram/cc, whilst space craft displace.. well - just space at ≈ 0 grams/cc.--Aspro (talk) 15:40, 19 March 2013 (UTC)[reply]

All right, then, the maximum gross weight (with full bunkers and magazines, that is)! I figured, if it's a ship, it must have a displacement... 24.23.196.85 (talk) 01:58, 20 March 2013 (UTC)[reply]

And what's the question? I just saw statements and no question, not even an implied one. Dmcq (talk) 00:52, 19 March 2013 (UTC)[reply]

The (slightly ungrammatical) question is in the section header. I don't have a horse in this race (or a good answer), but I can see why the OP is asking for further references/clarification, even if he is sounding a bit pointy. SemanticMantis (talk) 01:02, 19 March 2013 (UTC)[reply]

So completely misrepresenting what a Wikipedia article says isn't disrupting Wikipedia to make a point but talking about the misrepresentation is disrupting Wikipedia to make a point? You learn something every day... --Guy Macon (talk) 05:50, 19 March 2013 (UTC)[reply]

Oops! Left in an extra word. Fixed now. (Note to self: next time, smoke crack after editing Wikipedia...) The question is, "Can the energy needed for interstellar travel be obtained from Earth?". It was raised in the the "Interstellar Bomb" question, and I thought it best to discuss it outside of the material about time travel commandos trying to avert the foundation of the Cygnian empire through traveling from 31th Century to 21th Century earth. --Guy Macon (talk) 02:43, 19 March 2013 (UTC)[reply]

Here are some sources:

[2]
[3]
[4] see the energy section --PlanetEditor (talk) 03:10, 19 March 2013 (UTC)[reply]

...which nicely shows that humans reaching the stars is unfeasible using today's technology or any projected future technology. Robots are another story. We have already launched several with enough velocity to escape the solar system and reach the stars -- but it will take a very, very long time to get there. --Guy Macon (talk) 05:50, 19 March 2013 (UTC)[reply]

I don't have an issue with Robots doing the trip in our place. As long as they are clever enough to build a civilisation upon arrival. --Lgriot (talk) 09:45, 19 March 2013 (UTC)[reply]

Where will they build civilization? --PlanetEditor (talk) 10:03, 19 March 2013 (UTC)[reply]

Alpha Centauri, of course. As everybody knows, Alpha Centauri is just version two of Civilization, but also with robots....and xenofungus. Those were dark times. Nimur (talk) 12:27, 19 March 2013 (UTC)[reply]

Ghandi when asked what he thought of Western civilization 'That would be a good idea'. ;-) You'd want to send robots first anyway to make certain the place was prepared and a good place to go to, I think you'd be talking about hundreds of years at the very least before humans followed or were seeded or whatever. Dmcq (talk) 12:32, 19 March 2013 (UTC)[reply]

Human survival needs Earth's magnetic field, average world temperature, pressure, proper distance from a star like sun, Earth's atmosphere with the exact composition, Earth's surface gravity and escape velocity, biosphere. Even humans would not have survived in the condition Earth was 100 mya. Now where will you get all these? Have a look at Rare Earth hypothesis. Humans can at most be able to set up a moon base or Mars base which will be occupied by rotating crew as the case with the ISS. And they will extract material resources from Mars, Moon, or near-Earth asteroids. --PlanetEditor (talk) 12:54, 19 March 2013 (UTC)[reply]

All good points, but considering that humankind could at best begin feasibly working towards the goal of interstellar travel in the order of centuries (and that assuming we began to make it a priority in the near future, which is far from certain or even likely), who knows what manner of advancements we'd have made in the biosciences, which are already flourishing and arguably adapting at a much higher pace than our space exploration efforts. Sure, there are upper limits to what can be accomplished but I have to imagine the viable candidates will be improved at least somewhat by then. But then I also tend to feel that practical space travel (regular interplanetary travel, let alone interstellar) is likely to take hundreds or even thousands of years longer to develop than the more optimistic minds tend to assume, so that's the scale of time I'm imagining for concurrent developments in all fields relevant to planetary habitability. Snow (talk) 11:37, 23 March 2013 (UTC)[reply]

Why would Humans not be able to survive on Earth 100 mya? Also, why would atmospheric exact composition, Surface gravity and (escape velocity??) be needed? Dauto (talk) 14:45, 19 March 2013 (UTC)[reply]

Hmm, your question is proof that people love to imagine without caring for science. But I made a mistake. I should have said 150 mya, not 100 mya. Because upto the Late Jurassic (that lasted 150 mya), atmospheric CO2 levels were 4-5 times the current levels. Human respiratory system is not designed to breathe is an environment like this. High atmospheric CO2 means low atmospheric O2, so you inhale less oxygen each time you breathe, than what is necessary for your survival. The respiratory system of the genus Homo sapiens is designed to function in the atmospheric composition that you see today, or that Y-chromosomal Adam saw 237,000 years ago.

Human body is biologically designed to function in the gravity of Earth, i.e. 9.81 m/s2. On a long timescale of multiple decades, humans body will not function if the gravity differs too much from the value 9.81 m/s2. Earth's escape velocity plays crucial role in maintaining its atmosphere, and the composition of its atmosphere.. This in turn maintains the proper atmospheric pressure and temperature needed for human survival and the survival of plants (and edible plants). Without this escape velocity, you will not find the atmospheric composition, temperature, and pressure that you need to survive, you will not find the food (the nutrients) that you need to eat for proper nutrition. --PlanetEditor (talk) 15:41, 19 March 2013 (UTC)[reply]

You keep saying the weirdest things with absolute conviction. CO2 is a a critical, but miniscule part the the atmosphere. Over long periods of time, CO2 and O2 are only very weakly correlated. In particular, a CO2 concentration that is 5 times higher will have significant effect on our climate, but is below noticeable level for humans. Concentrations up to 0.5% (5000 ppm) are tolerated for work place conditions, and there usually is no harmful effect on humans even for permanent concentrations up to 3000 ppm. Atmospheric oxygen has likely varied from ~20% to ~25% during the Late Jurassic, which only lasted around 20 million years. Humans are very capable of living and operating at that level of oxygen. I'm not aware about any long-term studies of humans in different gravities - we know that humans work reasonably well at around 10m/s² (although knees and hips and discs tend to fail after "multiple decades" ;-), and we know that long-term microgravity has bad effects on humans. But that's about it - there are no experiments with 0.7g, or 1.1g. --Stephan Schulz (talk) 16:17, 19 March 2013 (UTC)[reply]

Oops, I made a grandiose mistake regarding CO2. Thanks for correcting me. --PlanetEditor (talk) 16:42, 19 March 2013 (UTC)[reply]

We may not have done many experiments at 0.7 to 1.1g - but we know that average adult humans who starve themselves until they weigh less than 100lbs function perfectly well - and even if someone who weighs 150lbs stuffs themselves with pizza and donuts until they are up at 300lbs, we know that they are still able to lead mostly reasonable lives. Sure, there are health issues at those extremes - but not enough to prevent us visiting, exploring and even colonizing a planet with 0.7 or 1.1g's. The effects of too much or too little weight on bones and organs is extremely well studied. I agree that it's uncertain whether we could live under much more or much less gravity - but if there is a problem, it's got to be something very subtle - not just joint and bone problems. SteveBaker (talk) 16:39, 19 March 2013 (UTC)[reply]

When we consider interstellar travel, we ignore the fact that humans are not immune to technological innovation. We'll soon have the technology to make artificial brains, which will radically alter the calculations about interstellar travel. Just like we today send files via email instead of having to physically travel by plane carrying a computer containing the file, in the future we'll travel from one galaxy to another by uploading ourselves to distant machines via radio communications. The more civilizations there are, the easier this way of travel is. If we are alone in our galaxy, then we would have to send some machines via conventional space travel to build up the necessary infrastructure first.

Presumably, members of advanced civilizations already travel this way through the universe, so we could try to download E.T. and make him answer all the Ref Desk questions! Count Iblis (talk) 15:43, 19 March 2013 (UTC)[reply]

"in the future we'll travel from one galaxy to another by uploading ourselves to distant machines via radio communications". Why take so much trouble? Genetically modify humans so that they can travel faster than light, and can live in space, immune to cosmic radiation. Genetically modified Homo sapiens extremophiles. Develop anti-aging science so that humans will eventually become immortal. They will not even need a planet to live in. The GM humans will hover in the vacuum of the space. The easiest way to colonize the Universe. --PlanetEditor (talk) 15:59, 19 March 2013 (UTC)[reply]

What makes you think it's possible to do those things by "genetic modification"? No amount of genetics will get you moving faster than light - that's a physical impossibility...it may be impossible to genetically modify the body to survive for years in space too. Even immortality has limits due to mental problems of being confined for thousands of years in a small spacecraft...you might have to become something non-human (or at least not recognisably or usefully human) in order to survive the trip. Living off-planet could well be virtually impossible due to the lack of material resources. Why try to modify humans to be something so radically different rather than just starting off with something that works from scratch (ie computers and solar panels). We know how to do the latter - but the former is very likely to be impossible. Your ideas simply don't survive what we know of actual science. SteveBaker (talk) 16:23, 19 March 2013 (UTC)[reply]

I thought Count Iblis is joking, so I replied with another joke. Anyway here is an interesting piece. --PlanetEditor (talk) 16:42, 19 March 2013 (UTC)[reply]

Kinetic energy is what's required here and that's just a function of mass and velocity. Hence, the critical questions are:

MASS: What has to do the travelling? A tiny solar-powered computer is a lot easier to ship over there than a bunch of living humans with full life-support systems and food, air and water for the entire journey.
VELOCITY: How much time can it take? Trying to get to the nearest star in a decade or two is vastly harder than if you're allowed to take a 1,000 year trip.

Those two issues each add many orders of magnitude to the energy calculations...issues of whether you need to decelerate or have a return-trip possibility are likely to be factors of two or four - irrelevant by comparison to my two previous questions. Worse still, the two questions are inextricably linked. Taking humans along with all of their support 'stuff' results in a need to get there fast enough for them to live long enough to survive the trip - so the mass you need to take along is gigantically more and the speed also has to be crazily high.

IMHO, the most likely way for "humanity" to reach other stars is to have us either develop artificial intelligence that's as good as our own - or to figure out a way to scan our brains and run our minds on an artificial (software) neural network. In either case, the thing that we really need to be out there (an intelligent brain) is just software. The spacecraft can be tiny...in principle the size of a grain of rice or so. If the "occupant" (be it AI or neural net) is just immortal software, then the passage of time for the trip is largely irrelevant. Hence, with this restriction, you can allow long trip times (of the order of millenia) and low mass (of the order of grams) - which makes it all seem quite possible...and as others have pointed out, we've already sent a couple of spacecraft of more than adequate size at comparable speeds. There are other variants of this - ship a small self-reproducing nanotechnological robot and some human DNA, or maybe a handful of frozen, fertilized ova. Have the robot make humans from local materials on arrival.

The bottom line is the same - it's much easier to ship ourselves as data than as atoms. SteveBaker (talk) 16:23, 19 March 2013 (UTC)[reply]

The short answer to the OP's question is that there is certainly enough energy available here on Earth. In addition to our robotic spacecraft which have been sent on long journeys, passenger ships could be accelerated to near light speed with simply the equivalent of a significant fraction of their rest mass energy, but the energy needed for deceleration, although it could come from earth, will likely be sourced from their destination planets. Furthermore, with evermore powerful mass drivers being built it may even happen! I enjoyed reading the few skeptical references given above, but I should explain how, with some resourceful robots and a few big guns, such travel should be possible, because mass drivers may very well become the real workhorses of interstellar commerce. To put some actual numbers on this idea, first consider that there was an acceleration record (see here) for a mass driver of 5km/s in 1cm length, which is 1.25*10^9 meters per second squared (since v=a*t and d=v*t/2, thus a=v^2/2*d=5000^2/2*.01=1.25*10^9) or a thousand times quicker than most firearms (per[5]) or 127 million g (about sixty to two hundred times greater acceleration than ultracentrifuges!)! To reach a significant fraction of the speed of light, a mass driver capable of such accelerations would need to be a "mere" 36,000 kilometers long ((3*10^8)^2/2*1.25*10^9). Thus, should such long-barrel guns be built by our star-hopping robots, and these guns are busily propelling various robotic payloads as well as robotic fuel tankers to and from our neighboring stars at near light speeds, then the fuel and reaction mass needed to supply the passenger ships' engines can be efficiently accelerated/decelerated by these guns. In other words, these large ships' insatiable propellant/fuel requirements would be obtained via frequent periodic inflight refueling by an extensive fleet of robotic tankers during their acceleration/deceleration periods that occur within a light year of each ship's departure and destination points. For instance, to handle the deceleration of a passenger ship returning home from a time dilated journey to a distant star, a gun stationed in our solar system would send fuel to another gun stationed at a fuel storage depot about a light year away, which would be tasked with sending tankers at progressively faster speeds towards us, each precisely timed to intercept the decelerating ship (note that the slower tankers need to be sent first so they are further along the ship's path). Overall fuel and propellant requirements to produce one g-force on the ships, although large, would therefore be manageable even with today's rocket propulsion systems. And even these current systems would likely become antiquated as even more powerful and efficient mass drivers are built! Again, I do not know for sure if large-scale mass drivers can actually become anywhere near powerful enough (there are "practical engineering constraints" according to the mass driver article!), but hopefully with a long and prosperous future ahead of us, I'm thinking that interstellar travel, by people, could be possible (and meeting up with a few of our distant neighbors' bug-eyed beauties too perhaps...). -Modocc (talk) 01:19, 20 March 2013 (UTC)[reply]