Wikipedia:Reference desk/Archives/Science/2015 December 19

= December 19 =

Baumgartner's balloon
Hello! I'm trying to calculate the buoyancy force acting on Felix Baumgartner's balloon at lift-off. However, I get a seemingly unrealistic 8.34 MN. The values I am using are 834.497,16 m3 for the volume of the balloon and 1.127 kg/m3 for the density of air. Is my math correct? If not, what am I doing wrong? Thanks. --Leptictidium (mt) 10:06, 19 December 2015 (UTC)
 * Your math is right, but the procedure is a little different than you might think after seeing illustrations of the enormous balloon next to the Statue of Liberty. High-altitude balloons are only inflated on the ground to a very small fraction of their capacity.  This allows the helium to expand to match the pressure of air and fill the entire volume once the balloon reaches float.  You can read a little about it here, although it's light on details.  Let's say the balloon is fully inflated at 120,000 feet where the air pressure is 0.067 psi  or 0.0046 atmospheres.  Let's also assume that the amount of helium in the balloon is the same at float as it was at the end of inflation on the ground.  (In reality it will lose some helium, but this should be a small fraction of the total.)  Then the volume of the balloon when it is launched should be 834497 m^3 * (0.0046 atm / 1 atm) = 3839 m^3 and the lift would be only about 38000 N.  The total mass of the balloon + payload was a few thousand kg, presumably a little under 3800 kg so that the force of lift would overcome gravity plus a little more to give a gentle ascent. --Amble (talk) 20:20, 18 December 2015 (UTC)
 * You can also see this in photos of the balloon at launch and when it reaches float altitude. At float, the capsule is hanging just under the bottom of the balloon on a short cable .  At launch, it looks like it's at the end of a very long cable .  That "cable" is actually the rest of the balloon, while only a very small portion at the top has inflated so far.  It slowly inflates as the helium gas expands during the ascent. --Amble (talk) 20:32, 18 December 2015 (UTC)
 * @Leptictidium: Your math looks suspicious. 834.497,16 m3? Do you mean 834 497.16 m3? (Let's just say 834 500 m3) What value are you using for the density of helium at sea level pressure? Dolphin  ( t ) 03:30, 19 December 2015 (UTC)
 * @Dolphin51: That's just a difference of notation in what makes a decimal mark. --Amble (talk) 05:46, 19 December 2015 (UTC)
 * Many thanks for that. I wasn't familiar with the decimal comma or the point as a thousands separator until I read your link. However, I'm still suspicious about Leptictidium's math, or should I say his physics. He has quoted the volume and the sea level density of air, and arrived at a force in meganewtons. He hasn't disclosed his intermediate steps and I think they contain at least one error. (Anyone experienced in applied math or physics would not use 8 significant figures in a calculation of this kind.) I have tried a few simple calculations and I don't arrive at 8.34 meganewtons. Dolphin  ( t ) 06:37, 19 December 2015 (UTC)
 * The intermediate step was, quite naturally, the buoyancy force equation: density of the gas displaced in kg/m3 * gravitational acceleration in m/s2 * volume displaced in m3: 1.127 * 9.8 * 834,497.16.Leptictidium (mt) 10:09, 19 December 2015 (UTC)


 * The numbers seem about right although, as explained by Amble, they are for the wrong calculation: Lep has calculated on the assumption that at ground level the balloon is filled with helium. The size of the balloon is confirmed here as "almost 30 million cubic feet": if it was exactly 30,000,000, then that would be just over 849,500 m&sup3;.  The density of air depends on the temperature, but is 1.205 kg/m&sup3; at 20&deg;C; however, the correct value to use for the calculation is the difference between the density of air and the density of helium; at 20&deg;C helium is 0.1664 kg/m&sup3;, so the difference is 1.039 kg/m&sup3;.  By way of comparison, the Hindenburg had about 1/4 that volumne and a fully loaded mass of 214,000 kg on one of its trips (source: The Golden Age of the Great Passenger Airships: Graf Zeppelin and Hindenburg by Harold G. Dick with Douglas H. Robinson), thus requiring 2.1 MN of buoyancy.  (Of course it used hydrogen, but the difference is small.)  Something over 8 MN would be about right&mdash;if it was the right calculation. --76.69.45.64 (talk) 11:11, 19 December 2015 (UTC)
 * The buoyancy force equation, as presented in our article, is relevant to a solid immersed in a liquid. The buoyancy force is only one of two forces acting on the solid (the other force is the weight of the solid object.) In this format the buoyancy force equation is not appropriate to determining the net force acting on a gas-filled balloon. I agree that it is the difference in density that is relevant, not simply the density of air. If a balloon with this volume is filled with CO2 it would displace the same amount of air, but as CO2 is 1.67 times more dense than air the result would not be a buoyant balloon. Quite the opposite. Dolphin  ( t ) 12:10, 19 December 2015 (UTC)
 * The buoyancy force is the same no matter what sort of object is immersed in what sort of fluid. It is indeed opposed by the weight of the object, and Amble's comment below is also correct. --76.69.45.64 (talk) 23:08, 19 December 2015 (UTC)
 * I think Leptictidium was trying to determine the resultant force on the balloon at lift-off. That would be relevant to a lighter-than-air balloon because it would partly determine the initial acceleration away from the ground. I also think his math was deficient because he didn't take into account the properties of helium so he didn't find the resultant force. When a large helium-filled balloon first leaves the ground it accelerates very slowly so Leptictidium was expecting a small force. That is why he was surprised to find such a large force as 8 meganewtons. Dolphin  ( t ) 04:31, 20 December 2015 (UTC)
 * He explicitly said he was trying to calculate the buoyancy force. His calculation was correct assuming the balloon is fully inflated on the ground -- but it isn't. --Amble (talk) 04:41, 20 December 2015 (UTC)
 * You can include the mass of the helium in the total mass of the balloon rather than the buoyancy force, so that's perfectly fine in the OP's calculation. It makes no difference to the buoyancy force calculation whether the fluid is liquid or gas, and whether the floating object is solid or gas-filled. --Amble (talk) 18:39, 19 December 2015 (UTC)

Orion, Sirius, and sunrise on Dec 25
I saw a thing on YouTube that says that the three stars in Orion's belt and Sirius form a line that points to where the Sun rises on December 25. Is that correct? Bubba73 You talkin' to me? 05:35, 19 December 2015 (UTC)
 * Where in the world would that be? Richard Avery (talk) 07:46, 19 December 2015 (UTC)
 * There appear to be some weird things going around about that, but they seem awfully vague. The main thing I would note is that you can use the belt of stars to find Aldebaran, a star in Taurus.   And the Sun isn't in Taurus on Christmas. Wnt (talk) 09:49, 19 December 2015 (UTC)


 * As noted, "where the Sun rises on December 25" is different for every latitude in the world: indeed, there are large areas in the Arctic where it doesn't rise on that date, but Orion is still visible.


 * In addition, alignments like "Orion's belt and Sirius" don't point in the same direction at all times; the place they point to would shift as the stars proceed from rising to setting.


 * In short, there may be some place and time where the claim is true, but in general it appears to be nonsense. --76.69.45.64 (talk) 10:42, 19 December 2015 (UTC)


 * I'm going to go out on a limb and guess this video is from some Biblical literalist trying to prove the Star of Bethlehem was a real event. --71.119.131.184 (talk) 11:50, 19 December 2015 (UTC)
 * No one knows the date or month Jesus was born, so such an effort would be useless. ←Baseball Bugs What's up, Doc? carrots→ 17:17, 19 December 2015 (UTC)


 * The question makes a nice exercise in spherical geometry, although some misunderstandings in the question need to be cleared out first. Any two points on the sky define a great circle, in this case we use Sirius and the central star of Orion's belt (Alnilam). Two great circles intersect in two antipodal points on the sky; in the question, the second circle is the ecliptic, the path of the Sun over the course of a year. It makes sense to ask when the Sun passes through these intersection points. That has nothing to do with sunrise or such topocentric points of time.
 * To do the calculation, take the equatorial coordinates of Sirius and Alnilam and convert them to cartesian coordinates (e.g. x-axis towards the vernal point (α=0, δ=0), y-axis to α=6 hours, δ=0, z-axis to the celestial north pole, δ=90°. This gives two unit vectors. The great circle through the stars is conveniently given by the direction of its pole, this is simply calculated as the (normalised) vector product of the vectors towards the stars. One intersection point of the circle and the ecliptic is now given by the vector product of the unit vectors towards the pole of the circle and the unit vector towards the pole of the ecliptic; the other is just its antipodal point. I find for the relevant intersection point α = 15h58m08s and δ = -20°29′27″. Stellarium puts the Sun in the position on 24 November, a month earlier than claimed. --Wrongfilter (talk) 12:30, 19 December 2015 (UTC)


 * Some of the comments above make it sound like the stars are getting stirred. If the Sun were in Taurus - and that does happen once a year, though not quite on the date the astrologers use - Orion's belt would be pointing at it when it rose, when it set, in London or Baghdad; even at the South Pole though you might need to invent a better neutrino detector to do the observation.  The point where the Sun rises in the East may vary, but the Sun is always there! Wnt (talk) 17:05, 19 December 2015 (UTC)

Thank you for the replies. This is probably one of those things that people make up and hope to spread around. I saw a few seconds of it on a YouTube video, I don't know which one. They seemed to be getting to the point that the three stars in the belt are the wise men and Sirius is the star of Bethlehem, etc. Bubba73 You talkin' to me? 18:30, 19 December 2015 (UTC)
 * Oh, if that's what it's about then one needs to take precession into account. I used Stellarium for today; for 0AD, the sun is in that spot at a different date. If I'm not mistaken, it does take the date into December, although it doesn't reach the 25th. Not that I would support any wild speculations based on that. --Wrongfilter (talk) 18:51, 19 December 2015 (UTC)
 * There is no such date as 0AD. There is only 1BC and 1AD. Akld guy (talk) 21:19, 19 December 2015 (UTC)
 * For astronomical purposes, there is indeed a year zero. --Amble (talk) 21:55, 19 December 2015 (UTC)

This is apparently a bit of nonsense from the Zeitgeist movie. See. --Amble (talk) 19:10, 19 December 2015 (UTC)


 * Probably so because I did see that word mentioned. Bubba73 You talkin' to me? 22:24, 19 December 2015 (UTC)

Truss type
What's that special vertical truss called? I think it has an Italian name. 82.132.223.218 (talk) 15:59, 19 December 2015 (UTC)


 * Have you read Truss? I'm not sure it's in there, but it might lead somewhere. ←Baseball Bugs What's up, Doc? carrots→ 17:13, 19 December 2015 (UTC)


 * If it's not there, can you give a clearer description of what you mean or where it can be found? --76.69.45.64 (talk) 05:11, 20 December 2015 (UTC)


 * I don't know of an Italian term, but do you mean a transmission tower (for electrical wires, etc.), or something like the Eiffel Tower ? StuRat (talk) 05:17, 20 December 2015 (UTC)


 * Piloti. Widneymanor (talk) 16:03, 20 December 2015 (UTC)


 * Those seem to lack the cross-supports I associate with a truss. StuRat (talk) 19:57, 20 December 2015 (UTC)


 * Latticework? as in Lattice truss bridge? Akld guy (talk) 05:17, 22 December 2015 (UTC)

Weather balloons
What pressure differential (between inside and outside) can they withstand before popping ? StuRat (talk) 16:23, 19 December 2015 (UTC)
 * It's the degree of expansion (which is of course related to the pressure difference) that governs the altitude limit - see here for such a calculation. Mikenorton (talk) 16:32, 19 December 2015 (UTC)


 * You may be interested in our article Superpressure balloon. -- ToE 17:38, 19 December 2015 (UTC)

How do evolutionists explain that life appeared just once?
Why wouldn't new living beings be created again and again? However, all living beings are related to each other. You could say the conditions changed, and now, it's not possible to create life anymore. However, why, in the time it was possible, didn't several different life forms arise independent of each other?Scicurious (talk) 20:05, 19 December 2015 (UTC)


 * Life appeared multiply times on earth, but once the first life had a foothold, it became more efficient very quickly and thus out competed (ate) all the other times life appeared independently. Do you have any idea how competitive life is? Compare this with why despite the fact written numeral system appears multiple times independently, the Hindu–Arabic numeral system ate them all up instantaneously. 175.45.116.66 (talk) 22:01, 20 December 2015 (UTC)


 * Who says they aren't? And who says they didn't? ←Baseball Bugs What's up, Doc? carrots→ 20:08, 19 December 2015 (UTC)


 * I don't want to endorse the view the OP appears to be heading to, but Common descent answers your question, Bugs.--Denidi (talk) 20:12, 19 December 2015 (UTC)


 * There may have been other life started that didn't survive. Bubba73 You talkin' to me? 20:26, 19 December 2015 (UTC)


 * Yes, it's difficult to prove that life only originated once. In any case, other life forms didn't survive long. At least we can say that there is one common origin to viable life forms.--Denidi (talk) 20:36, 19 December 2015 (UTC)


 * Perhaps it is extremely unlikely for life to appear on a planet. If it is one in a billion chance then there maybe hundreds in our Galaxy, but probably none where it happened twice. Or maybe the chance is only 1 in 10400, in which case the Anthropomorphic principle ensures that we are on the one place that life appeared in the Universe. Or for life to appear by itself is impossible, requiring special creation, but evolutionists would not claim that. Graeme Bartlett (talk) 21:34, 19 December 2015 (UTC)


 * There's quite a few people who think life and even intelligent life elsewhere in the universe is very probable. I just have this picture of all these missionaries from Earth trying to convince some alien lifeform of why they should follow the teachings of Christ or Allah or the Buddha ;-) Dmcq (talk) 21:36, 19 December 2015 (UTC)
 * Anthropic principle, I think. The anthropomorphic principle is succinctly expressed in Rule 39. Tevildo (talk) 13:56, 20 December 2015 (UTC)


 * As has been mentioned above, it's quite possible that life did arise independently several times, but the earliest life on the scene used its head start to eat all the others. As everything at this point would have been microscopic single-celled (at best) organisms, no fossil evidence of this is likely to have been preserved.
 * A second possibility is that once one form of life had arisen, it ate the chemical precursors that might otherwise have given rise to other forms of life, so they never could.
 * A logical third possibility is that life forms arose several times (not necessarily on Earth) but were repeatedly wiped out by inimical conditions except for the most recent which persisted, giving rise to everythng now living on Earth. {The poster formerly known as 87.81.230.195} 94.10.79.49 (talk) 22:30, 19 December 2015 (UTC)


 * Perhaps multiple early life forms that began on their own merged to form those that survived. For example, Neanderthals seem to have merged with modern humans rather than simply becoming extinct.  Mitochondria may have merged with other single-celled organisms early in the evolutionary process.  Obviously Neanderthals didn't arise independently of modern humans, and mitochondria may not have, either, but there might be some other constituents of modern life that did.  See symbiogenesis.  StuRat (talk) 03:48, 20 December 2015 (UTC)


 * I think it's pretty clear that there are three possible reasons here:
 * The probability of a self-replicating molecule appearing spontaneously could be astronomically unlikely. But the universe is insanely large - and quite possibly infinite - and the amount of time available for this to have happened is insanely long (on the scale of chemical reaction times).
 * If this is the case, then life only happened sufficiently few times that it only ever happened once (and we're obviously the result of that).
 * Or the probability of it happening twice on the same planet is astronomically unlikely - so there is life elsewhere - but we just haven't found it yet.
 * The probability of that self-replicating molecule appearing spontaneously isn't high - but it's common enough to happen rarely over the life of our planet.
 * If this is the case, then perhaps we should expect to see several (or perhaps MANY) kinds of life that are fundamentally incompatible with each other (eg one uses DNA/RNA - and the other uses something completely different).  We don't see that - so if this is what happened, then once one form of life appeared, it somehow suppressed the other forms.
 * ...by consuming the resources needed to build new lifeforms.
 * ...by out-evolving the other forms.
 * ...by changing the conditions sufficiently to shut down subsequent spontaneous formation events.
 * The probability of that self-replicating molecule appearing spontaneously is high. Life has been created multiple times here on earth - but for some reason we haven't recognized or discovered the other forms yet.
 * Maybe the other forms only live in very unusual places (under the ice-caps, in very deep ocean trenches, deep underground, in the ionosphere).
 * Maybe we see them all the time, but don't realize that they are alive because they are so unlike us.
 * Maybe there is only a very small set of initial replicating molecules that can actually produce life - and they all produce identical styles of DNA/RNA so we don't realize that they are the result of separate life-creation events.


 * The thing is - we don't (yet) know which of those things it is - there is research going on - but we really don't know. My money is on (1) because the simplest self-replicating molecules are pretty darned complicated and the probability of such a molecule just randomly appearing from the available raw materials is insanely small - but not zero.
 * There are perhaps ten trillion planets in our galaxy. There are at least 200 billion galaxies - but probably an awful lot more than that.  2x1024 is a good number here.  If 1% of them could support life - we still have 2x1022 of places where life could form.  There have probably been planets in existence for 13 billion years - which is 4x1017 seconds.  If these planets are about the size of ours, and they have similar volumes of water, the earth has 1x1027 cubic millimeters of water.
 * That means that if one complex chemical reaction happens in every cubic millimeter of water every second - then there have been 2x1066 chances for a self-replicating DNA molecule to happen by chance alone somewhere and sometime in the universe so far. Even if the odds of that happening is 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 to 1 against, then that's enough for us to exist.
 * But there have been "only" 3 billion years (1x1016 seconds) and only one set of oceans for life to have formed in here on earth - that's "only" 1x1043 opportunities for life to form.
 * So if the odds of life forming spotaneously in one second and one cubic millimeter of water is worse than 10,000,000,000,000,000,000,000,000,000,000,000,000,000,000 to one but better than 1,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 to one - then it would be no surprise that it only happened once here on earth (so far).
 * Given the complexity of the simplest self-replicating molecules that we know of - I think those odds are quite reasonable. We have created artificial RNA molecules with a couple of hundred base-pairs that come close to being able to self-replicate...so probably the first ever RNA strand was about that length.  With four base-pair "letters", the odds of this strand forming from a set of randomly connecting base pairs is 4200 to one against.
 * That's 1x10100...which suggests that:
 * If one random collection of base-pairs was created in every cubic millimeter of water every second for the life of the universe, then the universe would need to be 1x1044 times larger than the 'visible' universe that we can see. That's perfectly possible...and of course, chemical reactions happen faster than once per second, and many many more than one could happen in every cubic millimeter of water.
 * It's also possible that there are shorter RNA strands that could self-replicate - and they wouldn't have to be much shorter to erase all of those extra zeroes...also, we only have one example of such a short self-replicating strand that's been created in the lab - that doesn't mean that there aren't a lot of other similar ones that would work just as well.


 * It seems plausible - that with sensible guesstimates on the time to randomly create a sequence of base-pairs and a reasonably sized universe and a reasonably simple self-replicating RNA strand - that life could pop into existence just once and never again.


 * The difficulties in finding a mechanism by which life is initially created is easily resolved if the probability of precisely the right molecules colliding in precisely the right way to make an RNA molecule in a protective coat of some kind is really insanely unlikely - but if the universe is truly immense and old, so it happens (rarely). That's a good enough explanation - and it follows Occams razor...which is always a good clue if you don't have a better idea. SteveBaker : &lt;== (That was my 30,000th edit of Wikipedia BTW!) SteveBaker (talk) 15:51, 20 December 2015 (UTC)


 * Many scientists interested in abiogenesis think it's unlikely the first life used RNA, exactly because it's a relatively complex molecule. Life probably initially used something else to store genetic information; RNA and DNA came later. Of course, as with everything in this topic, these are just educated guesses at this point. (See abiogenesis and RNA world for some discussion.) --71.119.131.184 (talk) 13:47, 21 December 2015 (UTC)


 * aren't lichens considered a new life form? They derived after bacteria and fungi were formed. 66.87.80.164 (talk) 20:40, 21 December 2015 (UTC)
 * According to our lichen article: "A lichen is a composite organism that arises from algae or cyanobacteria (or both) living among filaments of a fungus in a symbiotic relationship." - since neither algae, nor cyanobacteria, nor fungi are considered to have derived from a separate abiogenesis event - I'd say the answer was a definite "No!". SteveBaker (talk) 22:07, 21 December 2015 (UTC)


 * My opinion is that we really have very little idea whether life with another chemical basis formed on Earth in the past, and in fact, I think we don't really know if it shares the planet with us now. I can easily picture, say, an oil company discovering tomorrow that pumping oil from one well down another would cause some kind of subtle contagious change in the chemical properties of the recipient well that no one ever noticed, or that some kind of cascading reaction could spread in deep sea clay, or that there is some kind of ongoing competition between circulation patterns in the geodynamo that powers the Earth's magnetic field etc.  The problem is, when we look for life, we look for stuff that looks and acts like the kind of life we know; when we look for it scientifically, we look for DNA.  So I think we aren't addressing the question in any meaningful sense, beyond the commonsense chemistry practice that you should clean your glassware well to make sure nothing unpredictable happens.
 * Another aspect is that life might have become symbiotic after its origin - for example, early on there might have been some kind of limited, self-replicating but poorly controlled protein or lipid chemistry separate from self-replicating RNA, but then the two might have evolved to coordinate their efforts. It's very difficult to research things that happened so long ago and left no large morphological fossils and which in any case occurred in rock that has largely been removed from the surface of the Earth. Wnt (talk) 13:30, 23 December 2015 (UTC)

New charity article may need a look for promoting AIDS denialism
Just seen a newly-created article about a UK charity called the Immunity Resource Foundation. The article so far is entirely written by a user who discloses that they were paid to write the article. I'm concerned that the 'non-incorporated' charity seems to be a front to promote HIV/AIDS denialism and that the article doesn't clearly explain this. Can someone look into this? 85.211.96.114 (talk) 22:50, 19 December 2015 (UTC)
 * WP:FTN might be a better place for this sort of question. The article makes the position of the organization clear, and appears (although I've not checked everything) to be adequately sourced - see WP:FRINGE for the relevant guideline. Tevildo (talk) 22:57, 19 December 2015 (UTC)
 * Article is going through AfD, discuss any issue there.--Bickeyboard (talk) 18:02, 20 December 2015 (UTC)