Wikipedia:Reference desk/Archives/Science/2015 February 4

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February 4

"Geo warping"

I found this Geo warping article whimpering in a dark corner of the orphanage. No sources, created by an SPA in '07 never to be heard from again, smells like a copyrightvio but I find no evidence of that, perhaps pure original research... I can't find any outside evidence that "geo warping" exists as described in the article (but then science articles make me want to curl up and take a nap...)

Any ideas? Vrac (talk) 00:11, 4 February 2015 (UTC)

Well the lack of sources is pretty bad, but I think this is basically a real thing, as a subfield of GIS and image processing. The page is mostly about "warping" images to properly overlay with different map projections. Georeference is somewhat in the same vein, and a (marginally) better article. I didn't try to search for copyvio. It doesn't seem like it's very standard terminology based on google searches. When I searched /georeference warp image/ I found a few more legit looking and fairly relevant sources, e.g. [1], [2]. So I suspect this is a valid topic, but it badly needs the attention of an expert. It might be a simple as a bad title. SemanticMantis (talk) 00:37, 4 February 2015 (UTC)

I'd suggest Image rectification and Orthophoto. I used to work in this field - and I never heard "Geo warping" as a common term. SteveBaker (talk) 20:08, 4 February 2015 (UTC)

Converting sounds into colors

http://www.lunarplanner.com/Harmonics/planetary-harmonics.html

I'd like to know if this really makes sense. It's a bit difficult for me to imagine that you can convert frequencies into colors. Why do we need to raise the frequency of a piano key by 40 octaves? --2.245.131.73 (talk) 03:10, 4 February 2015 (UTC)

Because the base 2 logarithm of the frequency of visible light divided by the frequency of ordinary piano music is approximately equal to 40. This has no actual useful or meaningful implication, but the author of that page is sort of an artist, and has decided that it's "neat." We shouldn't even need to bring it up, but sound waves and electromagnetic waves (like visible light) are not directly convertible - so there's no physical meaning to this frequency ratio (nor is there any meaning in "transposing up 40 octaves" - except that this is how the math works out). Nimur (talk) 03:41, 4 February 2015 (UTC)

Also note that somebody with synesthesia might convert sounds to colors in their mind. StuRat (talk) 05:59, 4 February 2015 (UTC)

Which is relevant to the question at hand, how? The neuronal associations which cause a perceptive cross-over between the senses in synesthesia -- and, by the by, synesthesia isn't a condition certain people have; we all experience varying degrees of interplay between the senses, to differing degrees in different modalities; in some people it's just sometimes pronounced in some extraordinarily strong or idiosyncratic way -- these associations are formed by the brain's physiology, not by any rational associations or systematic mathematical conversions reflecting the natural properties of the waves... Snow talk 14:52, 4 February 2015 (UTC)

There's a whole field of data visualization, that uses images to help us understand things that are inherently not visual. Your link is sort of going the other way; think of it as a "data sonification" or something. If we have data about a certain light/color, this link is describing a way to present that data as sound (or go the other way, given a pitch, associate it with a color). This specific method might not be especially useful for anything, but it is somewhat interesting in my opinion, and isn't really any different from the many other ways that we manipulate data to change the way that we perceive it. Spectral colors are defined only by their frequency (or wavelength), as is pitch_(music). There are some caveats about how human perception of pitch is not exactly the same thing as the frequency of the wave, but I think we can disregard that at them moment. A similar issue comes up with color perception. Anyway, it really shouldn't be that surprising that there are ways to associate colors and pitches, because the physical phenomena are both waves. No, we are not really "converting" any physical waves, but we can take the data about the wave and present it in many different ways. SemanticMantis (talk) 14:56, 4 February 2015 (UTC)

Along those lines. There's also actually a strong history of research in a related area exploring just to what extent the regions of the brain usually utilized for spatial environment/image construction in vision can be co-oped for utilization in auditory "image" modelling, as in the case of the blind. Though often echolocation is the specific mechanic being explored, rather than a frequency correspondence, be it for spatial purposes or color/luminosity data. Snow talk 15:11, 4 February 2015 (UTC)

The problem at the heart of this is that sound waves are vibrations in the air and light is an electromagnetic wave. We have ultrasound machinery that can generate sound waves in the GigaHertz range - which is the same range of frequency as a UHF radio signal carrying a cellphone conversation. But you can't use those two waves in remotely the same way. The UHF radio signal carries many kilometers - but an acoustic signal with the same power and frequency travels only a matter of centimeters before dying out. Looked at the other way - a radio signal with the same frequency range as a piano would be in the "LF" range - which is used for long distance/low speed communications, such as for aircraft navigation beacons. Those radio waves are likely to be passing through your body all the time - yet you can't hear them because they aren't sound waves.

That said, the frequency of light is indeed around that number of octaves higher than the piano...but it's not like you can compare the two kinds of wave. However, if you get hold of a suitable microphone and a radio transmitter, it is a handy device to convert between them in one direction, and a loud speaker performs the reverse transformation. SteveBaker (talk) 20:04, 4 February 2015 (UTC)

A friend in high school said windowpane could do this, but I guess that's too WP:OR. Short Brigade Harvester Boris (talk) 00:58, 5 February 2015 (UTC)

Deuterium

As a non-scientist, I read this article and was left with the impression that the way we gather heavy water for use is by essentially looking for it in ordinary water, like looking very carefully for a needle in a haystack. This implies to my untrained mind that synthetically producing the substance is impossible theoretically or practically. Is it the latter? --Dweller (talk) 12:36, 4 February 2015 (UTC)

OK, duh, the answer is given in our heavy water article. Sorry. --Dweller (talk) 12:37, 4 February 2015 (UTC)

I have added the information from heavy water to Deuterium. It is uncited, so if one of you clever people could add that (in both articles), that'd be another win for the Ref Desks. Cheers. --Dweller (talk) 12:40, 4 February 2015 (UTC)

Make you a deal: I get the refs, someone else add them? These are both RS that describe the production of heavy water [3] [4]. They may not be the best refs available, but I'm confident they are better than nothing. SemanticMantis (talk) 15:01, 4 February 2015 (UTC)

Thanks. I had a quick look at both and my befuddled non-scientific brain couldn't see the claim that it's more practical to search for Deuterium than artificially synthesise it. Did I miss it? --Dweller (talk) 15:04, 4 February 2015 (UTC)

Oh, sorry, I misunderstood. These refs are suitable for Deuterium#Production, and everything in the first paragraph of Heavy_water#Production except for the last sentence about cost! But the claims about methods of production are still uncited at present. I'm not sure how to find a ref that specifically says nuclear synthesis is not viable. Most people who would research it would see it as obvious, I think. Concentrating heavy water just starts with regular water and uses "normal" chemistry that accomplishes Isotope_fractionation. So it's not so much that we are "searching" for deuterium/heavy water, filtering or concentrating would be better analogies. We know all water has some heavy water, just like most stable isotopes occur in certain ratios of most Earthly elements.

In contrast to the chemical concentration approach, "synthesizing" deuterium out other isotopes of hydrogen requires nuclear reactions. Finally, the first link above at least implies that synthesis is cost ineffective, because it compares the efficiency and costs of several non-nuclear reaction methods without even considering nuclear processes. So I still think these are better than nothing, and can support other claims in the production sections. But now I'm also out of my element as well :) Hopefully someone else will find a better ref that explicitly rules out synthesis via nuclear processes on economic/efficiency grounds. SemanticMantis (talk) 15:23, 4 February 2015 (UTC)

Cost-effectiveness is a tricky matter. If you happen to be Germany in the second world war, then hydrolysis was the most cost-effective approach because the concentrations appearing in the outflow of a fertilizer factory were high enough, and there was essentially free hydroelectric power in the area. (See: Norwegian heavy water sabotage) But if you lack that already concentrated heavy water, and you have an abundant heat source, then distillation may be better - but if you have neither in abundance, but have a nuclear reactor lying around, then maybe irradiating regular water gets the concentrations higher to improve the efficiency of the other techniques. Which of these is "best" depends on what your starting point is and what other resources you may already have. SteveBaker (talk) 19:47, 4 February 2015 (UTC)

Isotopic Separation and Enrichment is a very resent lay-mans understandable article (2014). All I need now, is an explanation as to why the wife's Rock-Cakes are heavier still – does she use uranium concrete?!--Aspro (talk) 23:04, 5 February 2015 (UTC)

Spontaneous Hummingbird Combustion

I have heard it claimed that if a human's metabolic rate was somehow increased to match that of a hummingbird, the human would burst into flames. Is this true, and if so, how was it calculated? And for that matter, what prevents hummingbirds from spontaneously combusting if their metabolism is as high as this claim implies? 75.4.22.29 (talk) 15:19, 4 February 2015 (UTC)

What you've stated is a common misconception. Hummingbirds are bursting into flame all the time. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:20, 4 February 2015 (UTC)

For the last Q, it has to do with the surface area to volume ratio. Small objects cool much faster than large ones. And those frenetically flapping wings have got to provide quite a bit of cooling, too. There's a hummingbird in a South American desert, where the temp drops off dramatically at night, which sits on a tree and stops moving at night, quickly cools to close to freezing, then warms up when the sunlight hits it the next morning and emerges from it's torpor. StuRat (talk) 16:36, 4 February 2015 (UTC)

That makes sense, and it's a factor I didn't think about! But yes, I suspect the idea of metabolically induced combustion is something of an exaggeration (even assuming some way to artificially raise an animal's metabolism). 75.4.22.29 (talk) 18:29, 4 February 2015 (UTC)

You may be interested in reading square-cube law. -- ToE 19:55, 4 February 2015 (UTC)

To answer the first question, read the Wikipedia article titled Hyperbole. Come back if anything in that article doesn't make sense. --Jayron32 16:39, 4 February 2015 (UTC)

You're assuming it's just an exaggeration. It could very well be true. StuRat (talk) 16:41, 4 February 2015 (UTC)

I don't tend to assign true/false values to random statements people make, absent any evidence either way. It's a strange thing to assume that every possible combination of syllables a person utters should be accepted as true without any evidence one way or the other. --Jayron32 16:49, 4 February 2015 (UTC)

No, it could not "very well be true"; plenty of complex organisms require heat regulation of one form or another, but they do this for reasons of homeostasis, to avoid tissue damage -- not because they will burst into flames otherwise. Snow talk 16:49, 4 February 2015 (UTC)

You'd have to assume they meant "if the human metabolic rate was increased to where they burned the proportional energy per second as a hummingbird, with no other changes, then the human would burst into flames". Obviously the increase in metabolic rate would never actually evolve, but you could determine how much heat would accumulate if it did. The statement is rather silly, but that's not the same as untrue. StuRat (talk) 17:20, 4 February 2015 (UTC)

Yes, you are right to be skeptical; that claim betrays a great deal of confusion as to the nature of metabolism. The term is, in this context especially, a cache-all for any number of biochemical pathways, to which abstract notions of "fast and slow" apply with varying degrees of accuracy; some metabolic pathways might be said to be faster or slower in a human or a humming bird, while others that are found in one are entirely absent in another. I'd say it's an apples and oranges type situation, but frankly the hummingbird and the human are significantly farther apart in physiology than any two types of fruit. So already we've run into trouble in trying to establish what the aggregate "speed" of each organism's relative "metabolism" is. There are some measures that might be relevant, such as caloric expenditure over a given period of time relative to the overall mass of the organism. Regardless, even if we go with the generous suggestion that a hummingbird utilizes two-dozen times as much energy in a given period of time than a human, relative to mass, there's still no bio-mechanical or biochemical function by which either species can set itself alight through basic internal stresses or chemical reactions. Snow talk 16:43, 4 February 2015 (UTC)

(edit conflict) Biologist Paul R. Ehrlich wrote on the topic of bird metabolism in his bird book, excerpts of which are available free online. Hummingbirds are already very close to fatal overheating, which is interesting from the viewpoint of evolutionary biology. "Why do birds (and mammals) run these risks of maintaining a high, constant temperature, especially since it costs them to do so?" ... But overheating is not the same as spontaneous combustion.

Thanks for the link! 75.4.22.29 (talk) 18:32, 4 February 2015 (UTC)

I've heard the "combustion" analogy repeated many times before, but it's not a very scientific statement: how do you scale a metabolic rate? Obviously if you select a scaling-methodology that implies a mammal should burst into flames, your methodology runs contrary to empirical evidence. From a viewpoint of biology or molecular chemistry, mammal metabolism is very similar to bird metabolism, appropriately scaled; and yet we do not see combusting wombats. So, although I'm sure you can find this analogy about combusting humans, it's improbable that you can attribute it to a reputable scientist. Nimur (talk) 16:43, 4 February 2015 (UTC)

Random internet numbers suggest that hummingbirds expend roughly 10 kilocalories per day and weight about 10 grams. That's about ~4.2 MJ / kg. Humans are more like 0.12 MJ / kg. So hummingbirds are burning roughly 35 times as much energy per unit mass as humans. Heat dissipation is generally proportional to temperature difference. Let's say the typical human is about 10 C warmer than his environment. Increase the energy output 35 times (by magic) and pretend there are no new sources of heat dissipation or limiting factors, and the human would now equilibrate around 350 C warmer. According to the interwebs, human hair ignites below 250 C, so it does seem plausible that hummingbird-man could autoignite (or at least it would be plausible if the whole thing wasn't completely silly to begin with). Dragons flight (talk) 17:36, 4 February 2015 (UTC)

Sure, but why didn't you divide the absolute temperature by a factor of ${\frac {\pi }{17.2}}$ and add the boltzmann constant? You're already performing totally arbitrary mathematical manipulation.

What I mean to say is, you are not conducting science. Science uses observation to guide our understanding. It's fruitless to start multiplying and dividing stuff just because we want to. Why do you assume energy-per-unit-mass is the appropriate unit? Have you got a testable hypothesis and experimental data to corroborate your approach? Can you refer to published sources that use that approach?

Instead, what you're doing is throwing a bunch of equations at the concept, which perpetuates a widely held misperception of what science actually does. I know that you know better, but you're conveying the wrong message to people who aren't as well-informed about scientific process as you are!

Most problematically, you're falling into the very same trap as StuRat - where are your cited references? You're throwing around quotes and factual assertions and numerical constants and attributing them to "the internet" at large. That's not suitable for our reference desk - we have higher standards than that, and I know that you can do better.

Nimur (talk) 17:48, 4 February 2015 (UTC)

I don't think you're trying to be funny, but I've got to laugh. That's a remarkable uptight comment to leave on a question about whether people with a hummingbird metabolism would spontaneously combust. You know I am capable of writing much more elaborate responses, but I don't think a question like this justifies either the time or energy. If my response bothers you, feel free to give a better one. However, your earlier reply simply dismissed the hypothetical without even considering any numbers, which is really just avoiding the issue. Here is a quote [5]:

"Hummingbird metabolic rates are ..., the highest metabolic rate per unit of body weight in the avian world. ... Hummingbird researcher Crawford Greenewalt said that translates to [humans] eating forty ten-pound bags of potatoes or 1000 quarter-pound hamburgers every single day! It is thought, unbelievably, that this consumption would raise our body temperatures to 750°F (398°C) and cause us to explode."

Greenewalt, was a chemical engineer by training (so maybe not technically a scientist), but he did publish a few academic papers on the mechanics of bird flight and our article claims he was president of the American Philosophical Society for a time. Greenewalt's 1960 book, titled simply Hummingbirds, was published by the American Museum of Natural History and also repeats the 750°F number. In the quote above, also note the use of "metabolic rate per unit of body weight", also known as the "specific metabolic rate", which is a typical way of comparing metabolism across species and equivalent to the scaling I used above. For example, the specific metabolic rate is mentioned in the metabolic theory of ecology. Personally, I think that is a natural scaling to use, for an admittedly silly hypothetical, but you could argue for a different one if you like. Dragons flight (talk) 19:21, 4 February 2015 (UTC)

Thanks. The point stands that if we do some naive scaling in terms of energy output per hour, it would be far too much heat for a human to handle. But as others point out, humans don't work that way, and evolution doesn't work that way, etc. I think Nimur is being a bit too grumpy here; the calculations aren't totally arbitrary. But his point also stands: this isn't really "doing science", and there is nothing particularly valuable or deep about this exercise, other than to point out that hummingbirds are flying pretty hot.

But we have lots of stories like this: "If humans were as a strong as ants, they could lift up full-size trucks over their heads!" or "If humans could leap like fleas, we could jump over a 70 story building!" -- Yes, there are scientific problems with that type of claim and we should be very cautious of "shut up and calculate" mottos. But the point of these quips is not to give a very rigorous lesson in biophysics or metabolism or whatever. The point is get people interested and excited about the natural world and the abilities of organisms, by doing some (often technically sloppy) translating to scales that normal humans are more comfortable thinking in. SemanticMantis (talk) 19:38, 4 February 2015 (UTC)

Many thanks for finding that quote-- it's pretty much the sort of analysis I was looking for regarding this admittedly silly question, a quantification of the metabolic rates and temperatures involved and their possible effect.

Resolved

75.4.22.29 (talk) 19:33, 4 February 2015 (UTC)

Indeed, thanks for following up, and I apologize if I came across as grumpy. I'm glad that we've collectively been able to deliver a set of responses that are much more thorough than the last time I posted. Thanks guys. Nimur (talk) 20:39, 4 February 2015 (UTC)

The point (I think) is that a lot of the pop-sci claims that are out there really don't stand up to even cursory examination ("Humans only think with 10% of their brains" or "Science has proven that a bee can't fly" are classic examples) - and others seem broadly OK. I think this one clearly falls into the second category...sure, it's a hypothetical situation - and a solid scientific answer would need to know how all of this extra energy is being generated...are the muscles bigger...are we ingesting more calories...all sorts of detailed matters the would affect the answer. But that's not the point here. The original inventor of this claim is merely trying to express just how ungodly active these birds really are - and in terms that most readers can comprehend. If it was off by an order of magnitude in either direction - then we might say it's nonsense - but it's clearly in the right ballpark - and that's good enough. It's not like designing an airplane where people's lives depend on you getting it right. SteveBaker (talk) 22:03, 4 February 2015 (UTC)

What do you mean? African or European Hummingbirds? It's a question of weight ratios. really all it means is that we'd have enough muscles and energy to flap hard enough to fly and use the air as coolant. Probably be very fast swimmers too. --DHeyward (talk) 18:32, 4 February 2015 (UTC)

DHeyward, the issue is that the hummingbirds don't combust when they carry a coconut together on a line. Nyttend (talk) 18:31, 6 February 2015 (UTC)

We had a cold snap the other night. The only birds that weren't flash-freezing in mid-flight were the local hummingbirds. New York One news was advising people who found sparrows and other songbirds frozen in mid-air to scoop them up with a fishing net, and microwave them on low for five minutes or so, depending on the make and wattage. μηδείς (talk) 18:44, 4 February 2015 (UTC)

"And as I fricaseed him, he gave out a yell: 'Oy! Willow! Titwillow! Willow!'" --Allan Sherman[6] ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:53, 4 February 2015 (UTC)

Asthma Meds

I have a list of Inhaled Bronchodilators and a list of Asthma Controllers. Both are many pages long (with many medications repeated for each dose/manufacturer). So far, every medication I've found is on both lists. Are these two names synonyms? Are there Inhaled Bronchodilators that are not Asthma Controllers? Are there Asthma Controllers that are not Inhaled Bronchodilators? 209.149.113.24 (talk) 17:44, 4 February 2015 (UTC)

That might be a good question for your doctor or pharmacist. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:45, 4 February 2015 (UTC)

You might find it helpful to read our article: Metered-dose inhaler. Dbfirs 18:06, 4 February 2015 (UTC)

Some bronchodilators can be taken by routes other than inhalation as Asthma#Medications. Some astma controllers work against inflammation pathways rather than strictly bronchodilation. DMacks (talk) 18:20, 4 February 2015 (UTC)

Why aren't baboons extinct ?

As I understand it, most other primates don't compete with humans, since they live in jungles/tropical forests and humans mostly live on savannas/plains (good farming areas). However, I believe baboons live there, too. So, why didn't humans out-compete them or kill them directly, long ago ?

This source seem to imply that they could retreat to tropical forests when under threat: [7]. Is that how they survived ? StuRat (talk) 20:55, 4 February 2015 (UTC)

In evolutionary terms, it's not uncommon for two species to occupy the same niche. Gnu and Zebra on the plains of Africa, for example. Both wander around in herds grazing on the same plants drinking from the same water sources and predated upon by the same predators. Neither has displaced the other. So long as their breeding success rates are kinda similar, it all seems to work out OK. I've gotta say that seems like an unstable equilibrium - but it happens in enough places that it's evidently a common situation. SteveBaker (talk) 21:53, 4 February 2015 (UTC)

Zebra's and Wildebeests don't share the same ecological niche, in any of the senses of that word. They have differences in predation rates, identity of main predators, differences in refugia, differences in plant preference, differences in migration, differences in digestion, and differences in life history. This is a student paper [8], but it cites dozens of real research papers that discuss mechanisms of coexistence relevant to African grazers. Here's a paper that specifically addresses the differences in nutrition and foraging behavior [9] SemanticMantis (talk) 23:10, 4 February 2015 (UTC)

I believe they prefer to be called "zebras and wildebeest". Or they would, if they weren't preoccupied with survival. I'm not being a grammar Nazi, just a concerned mutualist. InedibleHulk (talk) 04:17, 5 February 2015 (UTC)

Ha! That has to be the worst pluralization mistake I've ever made. Don't tell the mouses and deers. SemanticMantis (talk) 15:58, 5 February 2015 (UTC)

First, competition isn't an all-or-nothing thing, and humans absolutely compete with many primates, usually for habitat, in the form of deforestation. There are several ways to quantify competition, but species that compete often coexist, we call it competitive coexistence [10]. Secondly, there's many types of competition - there's resource competition, apparent competition, and all these arise from the degree of niche overlap to consider (see also Limiting_similarity).

But the simple answer to your question is "because in recent ecological past, the force of intraspecific competition is greater than the force of interspecific competition for these two species". This falls out of early work by Gause, now known as the Competitive_exclusion_principle. It also holds true in the Competitive_Lotka–Volterra_equations, and it remains true for most any theoretical model or empirical study. Levin (1970) establishes that complete overlap of niche precludes coexistence. So I can say with some certainty that baboons and humans don't share the same niche. Coexistence can be promoted by even slight differences in predators, slight differences in prey, differences in refugia, things like that. Temporal variation in resources, and species-specific responses to spatial heterogeneity also go a long way (Chesson and Warner, 1981; Chesson 2000, and we even have an article on the storage effect).

So we know why in a general sense, but to get into the proximal mechanisms, we'd have to know more about the fecundity, diets, predation, and migratory patterns of our ancient ancestors, as well as those of ancient baboons. I'm sure people will be happy to speculate on that, but I won't. I will opine casually, that most any baboon could kill most any human without even trying. So our ancestors probably kept their distance :) 23:10, 4 February 2015 (UTC)

The above post is by SemanticMantis μηδείς (talk) 03:58, 5 February 2015 (UTC))

Probably not, if that human had a spear, and modern humans and Neanderthals have had spears for a very long time. StuRat (talk) 23:42, 4 February 2015 (UTC)

• Baboons are rather vicious little monkeys, the largest of the non-hominid primates, omnivorous, swift, living in packs of dozens or scores or more. And adult males are able to intimidate leopards. They are known to kill sheep, goats, and antelope, as well as other monkeys, and rarely, human children. They are eaten as bushmeat, but given the diseases they carry, they may be smarter than their human predators. And they run faster than humans, breed more regularly, and, like the Cape baboon retreat to hills, rocks, and large trees for defense and nesting. They could surely be driven to extinction with modern firearms, but the trend is apparently for them to become scavengers of human settlements, not human prey. μηδείς (talk) 03:53, 5 February 2015 (UTC)

Two separate primatologists have told me their rule of thumb: in a fight, 1 lb of monkey equals 9 lb of human. Apparently a walking stick isn't always enough to keep a feisty 9 lb capuchin from mugging you for your lunch. I've looked for refs but this is obviously just oral lore and anecdote. I wouldn't go near a baboon even if I had a very pointy stick. SemanticMantis (talk) 16:04, 5 February 2015 (UTC)

I believe it. I was slapped on the forearm by a chimp once. I've never tried to pat another since. That's mostly because I haven't met another since, but it was astonishingly hard for a quick one, like if a human his size put the whole shoulder into it. InedibleHulk (talk) 00:24, 7 February 2015 (UTC)

I would put odds on the human with the pointy stick (spear), but of course I wouldn't want to take the chance, since he'd probably only get one chance to impale it. StuRat (talk) 22:37, 7 February 2015 (UTC)

These questions can never be answered appropriately since the observation is always of the past. It's shortcoming of the Theory of Evolution. It's not predictive. It's not that there is anything wrong with theory but the nature of these types of questions are not particularly insightful when answered. The simple truth is that if baboons were extinct there would be a natural selection answer. And since they aren't extinct, there is also a natural selection answer. We can't answer even basic, short time-span questions like "What will be selected in the next 10,000 years" because of the complexity, I don't think it's realistic that very simple answers are forthcoming. --DHeyward (talk) 01:22, 8 February 2015 (UTC)

Can rockets fueled with liquid hydrogen, use the oxygen of the air?

Up to what altitude can it use the oxygen of the air, if at all?Noopolo (talk) 22:45, 4 February 2015 (UTC)

They could, in theory, but none that I know of do. Rockets consume extremely high amounts of fuel. Getting a corresponding amount of oxygen from the environment, compressing it to the required pressure, and injecting it into the engine probably is more trouble than it is worth. Note than most jets are very inefficient at low speed, because the air is not already compressed by airspeed when entering the engine inlet. And that initial phase is when rockets need their oomp most - the longer a rocket stays essentially motionless, the longer it wastes fuel just by keeping more fuel (in tanks) from falling back to earth. --Stephan Schulz (talk) 23:21, 4 February 2015 (UTC)

oomp?Noopolo (talk) 23:33, 4 February 2015 (UTC)

"Oomf" (sp ?) is slang which roughly translates as linear inertia here. StuRat (talk) 23:39, 4 February 2015 (UTC)

The word is "oomph" [11]. Dragons flight (talk) 03:40, 5 February 2015 (UTC)

The problem is that you would need a very different configuration to use atmospheric oxygen than using oxygen from tanks. So, you'd want a big scoop in front for the first part, but not for the second. This might be possible, via a multistage rocket, or perhaps a rocket that launches off the back of a conventional airplane (this option requires a small rocket and huge airplane). StuRat (talk) 23:31, 4 February 2015 (UTC)

It's so different that we have a different name for the thing. It's only called a rocket if it doesn't use oxygen from the atmosphere. If it does, it's a type of jet engine. --65.94.50.4 (talk) 00:18, 5 February 2015 (UTC)

Checking the Saturn V, for example, the stages were fueled by rocket propellant and then by hydrogen. In all stages, liquid oxygen was used as the oxidizer. Obviously, needed in much greater concentrations than the atmosphere could provide. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:22, 5 February 2015 (UTC)

You may wish to read about SABRE (rocket engine), the "Synergistic Air-Breathing Rocket Engine" which would be the engine for the proposed Skylon_(spacecraft) launch vehicle. -- ToE 01:15, 5 February 2015 (UTC)

And for those who just want a quick answer, SABRE, described as an Air/LOX/LH2 engine, is designed to switch over from air to LOX at Mach 5.14, 28.5 km altitude. Note that it is currently a paper rocket engine (though they are doing some development of components) for a paper rocket. -- ToE 01:29, 5 February 2015 (UTC)

Here's a rough attempt to quantify this. I'll outline some false assumptions further down.

1. According to Falcon 9, the first stage of that rocket uses 150,000L of liquid oxygen.
2. According to this book, the concentration of oxygen in air is 9.35 mol/m³.
3. According to Oxygen, the relative atomic mass of oxygen is 16, meaning that one mole of oxygen weighs 16g.
4. According to Liquid oxygen, the density of liquid oxygen is 1.141kg/L.
5. According to SpaceX, the first stage burn time of the Falcon 9 is 180s.
6. From 2 and 3, we can calculate the mass of oxygen per m³ of air. This is 9.35 x 16 = 149.6g/m³.
7. From 1 and 4, we can calculate the mass of oxygen burnt by the first stage. This is 150,000 x 1000 x 1.141 = 171150000g.
8. From 6 and 7, we can calculate the equivalent volume of air required to provide the oxygen requirement of the first stage. This is 171150000 / 149.6 = 1144050m³.
9. From 5 and 8, we can approximate the rate at which air would have to be consumed by the rocket to supply the necessary oxygen. This is 1144050 / 180 = 6356m³/s.

Note some dicey assumptions here:

• I've assumed that the density of the atmosphere is constant. It isn't. The numbers used are approximately the same as surface conditions, but as the rocket goes up, the volume of air required will increase.
• I've assumed that the burn rate of the rocket is constant. I don't think it is, though I don't know. I'd expect that maximum burn rate would occur as the rocket is just leaving the launch pad, ie. the time when it's hardest to ingest air, because you don't get the compression effect of the rocket's motion.

With all that in mind, you've then got to design an air intake to provide the air. According to SpaceX, the rocket itself is 3.7m diameter. Let's be generous and say you build a big, circular air intake on the front of the rocket that takes that entire diameter. That gives you an area of 11.6m². That means that, to provide our 6356m³/s of air, the air through the intake will have to travelling at 6356 / 11.6 = 546.8 m/s, or nearly 2,000km/h. At the earth's surface, at, say, 15 degrees, that's mach 1.6.

So, to do this on the Falcon 9, with an air intake taking up the whole forward-facing profile of the rocket, you need to accelerate the air moving into the engine to 1.6 times the speed of sound before the rocket starts moving, and you have to do it without destroying the vehicle's aerodynamics. This is why they don't do it. GoldenRing (talk) 03:23, 5 February 2015 (UTC)

Well, part of why they don't do it. There is, among other things, also the problem that you either need to somehow separate oxygen from the other 80% of the air before it enters the motor, while it is moving at mach 1.6, or somehow accommodate an extra 5,000 cubic metres of non-reactive gas moving through the motor each second. GoldenRing (talk) 07:27, 5 February 2015 (UTC)

That amount of gas is probably an under-estimate. For one thing, at the temperatures and pressures involved, oxygen will react with the nitrogen in the air which reduces the amount of oxygen available for burning fuel. When you look at all of the various NOx's coming out of a car engine, this should come as no surprise. Also, as altitude increases into the mesophere (the "ozone layer"), the composition of the atmosphere starts to change, you get ozone, atomic oxygen, atomic nitrogen, NO and various other stuff. What that would do to this hypothetical engine is hard to guess. SteveBaker (talk) 15:25, 5 February 2015 (UTC)

The SR-71 operated at a very high altitude and it's engines were most efficient at Mach 3+. There might be a way to stage turbo-fan to jet to rocket like SpaceShipTwo does for suborbital. A turbo jet doesn't necessarily mind supersonic velocities but the compression and slowdown heats the air and engine which has to be managed. I don't think the problem would ever be scoop size since it will most likely be a staged operation as no one will want to drag an air breathing engine into space. Similarly it doesn't make sense to have to burn fuel in non-vertical flight if a rocket with fuel and oxydizer can do the same thing with the same weight of propellant. But I'd rather develop a space launching railgun. Really if we can launch all the non-human cargo by railgun, we can have very small human capsule. Imagine every piece of the ISS being launched by railgun and assembled in space while only needing the small capsule for crew. Right now we have EM launchers for aircraft on aircraft carrier. The miltary is testing railgun sabot projectiles. Personally, I'd rather have NASA solving this rather than talking about human mars missions. Figure out how to launch tons of material at a fraction of the current price. --DHeyward (talk) 06:06, 8 February 2015 (UTC)

The one link that actually does answer the question has not yet been given - Scramjet is clearly the most relevant article. Roger (Dodger67) (talk) 22:54, 8 February 2015 (UTC)