Wikipedia:Reference desk/Archives/Science/2011 February 14

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February 14

Sulfur hexafluoride boat

If you had a large enough tank filled with SF₆, could a boat with a person in it float on it? Would you be able to move by paddling with the oars? --75.15.161.185 (talk) 00:19, 14 February 2011 (UTC)

Yes and yes, though the scales would need to be rather large and your person would need breathing gear for safety. For the latter part particularly, consider the general nature of propellor-driven aircraft. — Lomn 00:41, 14 February 2011 (UTC)

You'll need much more gas than Mythbusters used. Clarityfiend (talk) 00:52, 14 February 2011 (UTC)

From the Sulfur hexafluoride, we have an SF₆ density of 6.12 g/L or 6.12 kg/m³. From Density of air we have 1.29 kg/m³. The difference gives us a net of 4.83 kg/m³ buoyancy. If we needed to float 50kg (say a 40kg person in a 10kg boat), the boat would need to displace about 10.4 m³. Contrast with water displacement, where only about 0.05 m³ (50 liters) need be displaced to float that same 50kg. -- Tom N (tcncv) talk/contrib 01:10, 14 February 2011 (UTC)

I would just mention that, while the videos look very cool, sulfur hexafluoride is a very powerful greenhouse gas. I'd love to try the thing where you breathe SF₆ and talk (it's the flip side of the helium thing) but I'm not sure I can justify it ethically. --Trovatore (talk) 01:13, 14 February 2011 (UTC)

Wow, you're not kidding! 23,900 times more efficient than CO2 on a 100-year time scale, 32,600 times more effective on a 500-year time scale. (Though at least that's not by weight!, but by parts per billion, which according to Parts-per_notation#Air_measurements seems to be a volume-based measurement.) My, I wonder if you can find sulfur and fluorine on Mars...^[1]

In terms of size, this would be more like and airship than a boat. The volume required to lift a person would still be much lower than helium baloons in air, though. — Preceding unsigned comment added by Roberto75780 (talk • contribs) 12:41, 14 February 2011 (UTC)

Youtube video - mechanical glitch, other artifact or mysterious unreflective object?

Hi. I recently came across this Youtube video showing images of a dark object detected by STEREO but according to an astronomer referred to in the comments is not visible on LASCO. I would be interested to know what it is. I realize the video description and annotated text could be exaggerated and jumping to only one conclusion but can a glitch persist for a month and change in size? Thanks. ~AH1^(TCU) 00:21, 14 February 2011 (UTC)

If you want to be taken even remotely seriously, do not get your STEREO data from Youtube.com. NASA makes the STEREO data available to the public at the official spacecraft webpage, STEREO, hosted at Goddard Space Flight Center. You can download the official data. If a "glitch", image-processing artifact, or astronomical observation of any significance were present in the data, it would not be reported through pseudoscience-crank-videos on Youtube.

Although, if NASA was in on the conspiracy, they might have distorted the images in the official database. We can only presume that if it is the case, and NASA has covered up these glitches by doctoring the official data, that the author of the Youtube video was able to independently acquire the unadulterated raw video, with glitches intact, by operating his own Deep Space Network-sized ground stations; and that he has the scientific expertise to interpret and analyze the images and ascertain the presence of a mystery-object. As an anonymous Youtube-author, though, the uploader of that video has a bit less credibility than NASA.

If you are actually interested in the scientific explanation for image artifacts, NASA's official page has an entire set of explanations for each type of artifact on each instrument on the STEREO spacecraft. Image Artifacts, from NASA, with various subpages.

Here are some nice examples of internal reflections of Venus. These sorts of optical artifacts are very common. If you've ever photographed through a fancy compound optics system, you know how much of a problem internal refractions/reflections/distortions can be. I can personally attest to some funny optical trickery back in December while I was photographing Venus in the early morning. I could have sworn I saw a spurious bright spot - a "UFO," or a moon, hovering just off the limb of Venus. So here was this bright shiny object that I could see, plain as day through my eyepiece, but was completely immune to being photographed! Magic! Or perhaps alien technology! What actually had happened was that my camera, having been sitting right next to my warm cup of coffee, had developed some "fog" or dew on one of its internal optical surfaces (probably the mirror) while I changed lenses; and I got a very nice bright spot that was showing up only through my eyepiece (and never in my photographs). After a few minutes of thermal acclimation, the foggy layer dissipated and my "UFO" disappeared (and I was unable to claim discovery for a moon of Venus). Nimur (talk) 00:58, 14 February 2011 (UTC)

(The specific "glitch" reported in the Youtube video was an example of the long-exposure noise reduction algorithm - it is a digital postprocessing artifact. This effect only shows up on certain data-products. Scientists studying STEREO data will usually obtain low-level data products (the rough equivalent of "shooting raw images") and apply a smarter noise-reduction method. I apologize if my earlier anecdote implied that the "dark spot" was some type of optical effect - I only meant to emphasize that astrophotography is full of "spurious data." Nimur (talk) 13:48, 14 February 2011 (UTC)

Nimur, that is an outstanding response. Thank you for taking the time to write it, and I especially enjoyed the artifact links you included. You are a credit to your species. The Masked Booby (talk) 00:58, 15 February 2011 (UTC)

Antibacterial gels vs iodine

Hi all,

Is there any difference between using antibacterial/antiseptic gels such as Neosporin vs. old-fashioned iodine (or even rubbing alcohol)? Is one better in some cases than in others? Thanks! — Sam 63.138.152.135 (talk) 14:49, 14 February 2011 (UTC)

Non-iodine is better in cases where the patient is allergic/sensitive to iodine. --Sean 15:45, 14 February 2011 (UTC)

And conversely for patients allergic/sensitive to neomycin. Iodine in general can some adverse effects (scarring and interference in healing) depending on formulation. Alcohol evaporates and then it's gone with no lasting effect. Some pathogens are particularly sensitive or insensitive (or worse, develop resistance) to specific agents (especially because some agents are broad-spectrum and others are more mechanism-specific in their mode of action). Hard to answer the question specifically because "in some cases" is pretty vague...includes everything from playground scrapes to surgical incisions to cases of MRSA. DMacks (talk) 18:15, 14 February 2011 (UTC)

It depends a bit on why you're using it. The modern version of good ol' fashioned iodine is Povidone. One important difference between the two is that if you where to use an iodine preparation on a daily basis, one would eventually absorb too much through the skin. However, for some indications it is certainly better. In the first world war, alternatives to iodine was garlic and cannabis --Aspro (talk) 20:21, 14 February 2011 (UTC)

Neosporin also contains a skin protectant and the antibiotic in it is benign, it doesn't cause cell death. The AMA is no longer recommending you use alcohol or peroxide on wounds (not sure about iodine I know it's used in medicine still for example prior to catheterization in a female), the fact it kills cells means that it does more harm than good. 65.29.47.55 (talk) 22:31, 14 February 2011 (UTC)

Atomic structure

When one atom moved away from anywhere very time atomic level are not same but it more equilibrium than other for fixed position with some wave not particles very much to minimum ways series.Reaction position are not same means the wave are not similar for bad condition create some how. — Preceding unsigned comment added by Vowies (talk • contribs) 17:53, 14 February 2011 (UTC)

I'm sorry, but don't think I understand you. Can you try writing that again using proper grammar and punctuation? Dauto (talk) 18:59, 14 February 2011 (UTC)

Or, if English isn't your first language, please write in your first language and someone will translate. Or, see if there is a reference desk on the Wikipedia in your first language. --Tango (talk) 23:17, 14 February 2011 (UTC)

The Ever Eluding Question

Do plants feel pain?? Dutch scientist Marcel Dicke, of the Agricultural University in Wageningen, Holland, found evidence that all plants perform similar actions to the trees, when under threat from predators. Indeed, the level of sophistication in this process is made all the more remarkable by the fact that the these ‘signals’ encourage production of substances tailored to specific pests! An example of this would be the lima bean. When attacked by spider mites, the plant releases a chemical attractant for other types of mite, which prey on the attackers. Some plants help others, as in the case of cabbages, which release foul smelling isothiocyanates, discouraging aphids from attacking neighbouring plants like broad beans. —Preceding unsigned comment added by 1.23.10.106 (talk) 18:14, 14 February 2011 (UTC)

I agree these are survival mechanisms and nowhere close to "animal" like senses but how to concisely refute the theory that plants feel pain in? —Preceding unsigned comment added by 1.23.10.106 (talk) 18:19, 14 February 2011 (UTC)

Plants do not have pain nerves or a brain to receive signals from the pain nerves. To claim that plants feel pain will require defining what you mean by pain in such a way that it is not dependent on the biological process of receiving and processing signals from pain nerves. -- kainaw™ 18:36, 14 February 2011 (UTC)

Nociception may be one such term - for example, Paramecium displays nociception, trying to back off and evade a fine needle.^[2]

One way in which Temple Grandin concludes that many (not sure about all) insects do not feel pain is that they will walk on broken limbs, which no vertebrate will do. Just putting that out there. From Animals in Translation. --Mr.98 (talk) 18:58, 14 February 2011 (UTC)

Here's a related question: how do you concisely show that human beings (other than yourself) feel pain? It's entirely possible that you're the only sentient human, and that all other humans are robots without any consciousness. If you punch a human, how would you know whether that human is responding because he has the subjective experience of "pain", or because he's hard-wired to respond to harmful stimuli so as to minimize that stimuli.

In this case, you might use induction to argue that because you feel pain, and because other humans have nearly identical biochemistry, organs, nervous systems, and reactions to stimuli, they probably feel pain too. However, you can't conclude from this that plants don't feel pain, because you can't prove that the mammalian body is the only system that can feel pain. In fact, it would be very surprising if this were true: why should this one path that evolution semi-randomly decided to take be the only one that leads to the subjective experience of pain? --99.237.234.245 (talk) 20:20, 14 February 2011 (UTC)

As stated above - you need to define what it means to "feel pain" as you are purposely not using the biological definition. -- kainaw™ 20:43, 14 February 2011 (UTC)

Pain: the conscious, subjective experience that something unpleasant or harmful has happened. I think this definition is much closer to what people usually mean by "pain". Since the OP obviously isn't asking how to prove that plants have no nerves or brains, I assumed that he meant "pain" in the everyday sense of the word, and was not using the biological definition. --99.237.234.245 (talk) 23:03, 14 February 2011 (UTC)

I don't think plants can be considered to do anything "consciously". That would require a central nervous system. --Tango (talk) 23:22, 14 February 2011 (UTC)

There is no evidence that a central nervous system is required to be conscious. The fact that humans have a central nervous system means only that the one evolutionary path Earth's animals happened to follow can lead to consciousness. It does not imply that this is the only path, or the most likely path, or the most common path. For all we know, sentient alien creatures might have an entirely chemical "nervous system", transmitting chemicals along structures similar to Earth plants' xylem and phloem. --99.237.234.245 (talk) 01:15, 15 February 2011 (UTC)

Not to detract from the scientific interest of the question, but maybe you might ask for modern philosophy references from the humanities desk. The reason I suggest this is that beyond what we know about nervous systems and empirical science (and I think Temple Grandin's comment is an excellent empirical argument), there is an existential element of the question to which our backgrounds might not do justice. To that end, check out Bentham's animal rights philosophy, and this nice response with lots of links (but from an MA only, so take appropriate salt). And of course our paranormal plant perception article goes into the actual arguments a bit as well. SamuelRiv (talk) 00:03, 15 February 2011 (UTC)

I've read that some trees produce a toxic substance when animals eat their leaves. This prompts the animals to move to the next tree. You could perhaps consider this as an algorithm executed by the tree to protect itself. Arguably, pain is the running of any type of algorithm that overrides/restricts normal function. Count Iblis (talk) 01:02, 15 February 2011 (UTC)

You jostle a car and an alarm sounds. It is an algorithm, perhaps a basic sort of nociception, but does the car feel pain? In truth we have nothing resembling a theory of consciousness. We say that certain neural pathways carry pain because individual persons say they don't feel it when they are anaesthetized or severed. But how do you know even that what a person feels is only what they say? How do you know that the person who comes out of the operation in twilight sleep isn't saying he's alright, but somewhere "unconsciously" he has been in agony? Can you generalize further to say that people are the only consciousness, and no other pathway can feel pain? I don't see a scientific basis to disprove that the clouds feel pain when an airplane flies through them. Wnt (talk) 15:22, 15 February 2011 (UTC)

That is the problem here. In order to claim that plants feel pain, the definition of pain is being generalized to purposely include plants. The side-effect of that is that other things (like cars) get included in the generalized definition. So, it is not a discussion about feeling pain. It is a semantic argument about how to purposely include plants without including other things - which is not in any way science. -- kainaw™ 15:26, 15 February 2011 (UTC)

I agree, but then one can always assume that a conscious entity is identified with an algorithm that is running. This is equivalent to the strong AI hypothesis. So, Wnt is generated whenever we run that particular program that is currently implemented by the neural network that his brain is running. Any entity that is experiencing pain clearly has its normal algorithm being interfered with by the running of an emergency algorithm. In case of a car, you have to assume that without the alarm going off, there is an algorithm running and from the perspective of that algorithm, the alarm going off, is restricting things in some way. Of course, this approach can be criticised as being not very scientific. However, it may be that deep down all that exists are algorithms, i.e. that all that exists is simply a mathematical multiverse. It then makes sense to talk about the world that any given algorithm subjectively perceives as a mathematical representation of the algorithm. Count Iblis (talk)

You are touching on the philosophical question of "Other Minds." There has a rich tradition going back at least to Descartes. A good introduction is the Brain in a vat article. —Preceding unsigned comment added by 12.186.80.1 (talk) 16:19, 15 February 2011 (UTC)

Time dilation measured by radioactive decay

I have a question concerning my better understanding about time dilation. I am wnadering if it is just mathematic aspects or it does really have physical meaning.

Supose the experiment with two observers. One in land, stationary with no movement. The other is travelling inside one rocket with speed around 0.8 light speed (c). If they have the same amount of radioactive matter, uranium or others. What we would observe when the rocket return to start point after one travel that had taken 01 thousand years. Would they see different carbon contents in these two samples or it will be the same. My question is based in the fact that time dilation always has been explained using the time interval between events. This trial has different concept.

Obs: I am not english native. — Preceding unsigned comment added by Futurengineer (talk • contribs) 20:18, 14 February 2011 (UTC)

This experiment doesn't have a different concept. If the time interval between individual particle decays dilates, the half-life must get longer, because the sample is now decaying more slowly. If you put uranium on a spaceship and make it travel at high speed, the spaceship sample will decay more slowly as seen from Earth than an Earth-bound sample, by a factor of gamma=1.67. --99.237.234.245 (talk) 20:36, 14 February 2011 (UTC)

The basic answer is yes, it has real physical meaning. It can be measured a number of ways to prove that this is the case. It is not just a mathematical construction. --Mr.98 (talk) 20:54, 14 February 2011 (UTC)

And to answer your question more directly: There will be more radioactive material left over in the spacecraft sample (as compared to the earth's sample) because a smaller amount of time has elapsed in the spacecraft than on earth. Dauto (talk) 21:43, 14 February 2011 (UTC)

For example, in introductory physics, a common homework problem requires application of relativistic time dilation to explain the arrival rate of muons originating from cosmic rays. These muons decay too quickly, and they have no business arriving at Earth's surface as frequently as they do; but because they are traveling at relativistic speeds, the decay half-life measured in the laboratory is not the same as the decay half-life measured in the co-moving frame of the muon. A model of cosmic ray production in the upper atmosphere, from SLAC, works the math properly for you, and explains the physics of muon production as a result of cosmic hydrogen ions colliding in the thermosphere. Nimur (talk) 23:25, 14 February 2011 (UTC)

Magnetic confinement fusion

After reading this article, I still have no idea how it's supposed to get fusion to occur. Is the idea to get hot plasma as dense as possible and loiter it around each other until the particles can quantum tunnel through and produce fusion? ScienceApe (talk) 21:23, 14 February 2011 (UTC)

Fusion is actually the trivial part: heat hydrogen enough and it just happens. The hard part is making it continue to happen: as soon as your fusing plasma touches any normal-temperature material, its heat is sapped away and the reaction stops; similarly if it spreads out too much. Thus "confinement"; magnetic confinement is just the clever application of magnetic fields to hold the fusing plasma in place for a "sufficient" time to be interesting/productive. --Tardis (talk) 21:40, 14 February 2011 (UTC)

Couple of questions. How do they heat it in magnetic confinement? I know they use lasers in inertial confinement (usually). Why is the torus shape preferable over a spherical shape? Would this be easier to do in a zero gravity environment like outerspace? ScienceApe (talk) 21:45, 14 February 2011 (UTC)

I think it's usually RF heating: the plasma is conductive and can receive energy like an antenna. Torii are good because the magnetic field is solenoidal: the field lines have to form loops, so it makes sense to make the device a loop as well. I don't think gravity is a problem: one ought to be able to counteract it with a static electric field (and a slightly charged plasma). --Tardis (talk) 21:54, 14 February 2011 (UTC)

Watson the computer system

Would the Watson computer system likely be capable of passing the Turing test? Googlemeister (talk) 21:46, 14 February 2011 (UTC)

No. Dauto (talk) 22:01, 14 February 2011 (UTC)

(EC) Presuming you mean Watson (artificial intelligence software), that seems rather unlikely. Amongst other things, if it could you would think IBM would be making more noise about that rather then hyping its Jeopardy! skills... Nil Einne (talk) 22:05, 14 February 2011 (UTC)

IBM isn't even claiming that their system is "turing-test ready." They're simply advertising that it has sophisticated capability for answering questions (or ... questioning answers) posed in natural language format. (I'll also comment that those East-Coast intellectuals seem to have designed a nerdy operating system. Out here in California, our robots are free-range outdoorsy-types who enjoy hiking and long walks on the beach... not crashing out in front of the TV watching Jeopardy. Nimur (talk) 22:33, 14 February 2011 (UTC)

The article you linked has a section on the [Prize], for which "the first contest was won by a mindless program with no identifiable intelligence that managed to fool naive interrogators into making the wrong identification," which is particularly evident in Turing competitions where they have ordinary citizens as judges. But for some perspective on what the Turing Test actually means in terms of consciousness, maybe check out both recent and early transcripts of the Loebner competitions. For all of Turing's genius, his test appears to be short-sighted - perhaps we should start thinking about an improved version video? SamuelRiv (talk) 00:39, 15 February 2011 (UTC)

There is no "official" Turing Test, so the question is unfortunately a little too vague. The Loebner Prize above has tried to make itself into the "official" test, but it's not a test that any scientists participate in, only chat-bot writers with lots of time on their hands. (And they are still pretty terrible -- here's the transcript from the 2009 winner. Really no different from the early Eliza programs.)

One answer might be "Does Watson play Jeopardy in a human-like manner?" That is, might you think a human was giving those answers? If so, Watson has passed a very limited Turing Test. Watching the game last night, the answers were very good, unlike a few months ago when the answers didn't match the questions. So it may have passed this Turing Test. In terms of conversational ability, however, it's not even trying. Therefore, it wouldn't pass the Turing Test as normally envisioned. — Sam 63.138.152.135 (talk) 14:43, 15 February 2011 (UTC)

There is already a method which can answer questions given sufficient information in the query and the database. An example would be if you asked, "What country is known by a pattern of 13 alternating red and white stripes with 50 white stars on a blue background in the upper left hand corner?" or similar question. (this example) Notice that an item (flag in this case) can be identified with far less information after it is classified and then the database optimised. --Inning (talk) 17:43, 15 February 2011 (UTC)