Wikipedia:Reference desk/Archives/Science/2015 May 9

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May 9

Dark Matter

Is Dark Matter death? ? asked by Ed Slater artist from Dumfries

No. --OuroborosCobra (talk) 00:27, 9 May 2015 (UTC)

Says it all, really. Death is a process, whereas dark matter, if it exists, is a substance, so the OP's question can be answered in the negative on purely metaphysical grounds. You can have a bottle of dark matter (how large it would be and what the walls would be made of is another question), but you can't have a bottle of Death. Tevildo (talk) 09:34, 9 May 2015 (UTC)

Duncan MacDougall (doctor) tried to measure a loss of weight from patients/corpses at the moment of death (see also [1]), claiming positive results. If this were taken at face value it might back up a death-based mechanism of dark matter production. However, it's been nearly a century since this was even a sci-fi grade reference, since it is universally assumed that the small sample size and measurement error were to blame. Wnt (talk) 11:34, 9 May 2015 (UTC)

• You can't have a bottle of death, but you can have a charred hunk of evil. (Tevildo's point is actually quite important, and you'll find a lot of the motivation behind drug and gun control legislation is the ideas that those things themselves are evil, not how they are misused.) μηδείς (talk) 18:30, 9 May 2015 (UTC)

I dunno. It's not death as depicted by the Grim Reaper or "souls" as seems to be implied above. However if it's the result of universe expansion and cooling, it could very well represent the death of the stars, galaxies and universe. I suspect there is a volume and temperature that no longer supports stellar formation or any type of coalescence. "Assumed room temperature" may be quite apt description of "death" and if the universe assumes the temperature of dark matter.... --DHeyward (talk) 05:48, 10 May 2015 (UTC)

This is the science death desk, however, not the metaphorical death desk. μηδείς (talk) 14:48, 10 May 2015 (UTC)

Brings to mind a creepy but well-executed little piece by Harlan Ellison, called The Diagnosis of Dr. D'arqueAngel. --Trovatore (talk) 00:11, 11 May 2015 (UTC)

Space elevator

Hi there!
What are the symbols of this formula meaning in the context of the space elevator: dF = (GMρA/r² − ρAv²/r)dr ?
Thank you for your answer!
Calviin 19 (talk) 10:06, 9 May 2015 (UTC)

F is the force on a particular point in the cable exerted on it by the cable below it (which is calculated by integrating the above formula), G is the Gravitational constant, M the Earth's mass, ρ the density of the cable, A the cross-section area of the cable, v the orbital velocity of any part of the cable and r the distance from the Earth's center. - Lindert (talk) 10:30, 9 May 2015 (UTC)

[ec] The equation appears in this paper by Jerome Pearson, where the symbols are explained thus:

G is the gravitational constant

M is the mass of the Earth

ρ is the density of the tower and A is its cross-sectional area

v is the velocity at point r on the tower due to the Earth’s rotation.

It's not explicitly stated in the paper, but dF is the increase in the (vertical) force on the tower for an increase dr in height. Lindert's posting above agrees with Pearson's definitions. Tevildo (talk) 10:37, 9 May 2015 (UTC)

Extinct (planes)

Considering we have not yet found a viable alternative to oil and gas, is it possible that commercial passenger planes could become extinct by the end of this century? 92.25.95.41 (talk) 10:49, 9 May 2015 (UTC)

I doubt it. I web searched natural gas powered plane and came up with [2]; you can repeat for the fuel source of your choice. (In the 50s they even considered nuclear airplanes!) Now powering a plane with heavy, high pressure tanks of combustible gas doesn't sound like the most appealing idea, but people do what they have to. Also see [3] (I think we had a thread on that recently) Wnt (talk) 11:39, 9 May 2015 (UTC)

The weight might be an issue, but as for flammability, the current jet fuel is somewhat flammable, too. Synthetic jet fuel would be the logical replacement. Since it's considerably more expensive, you could expect air travel to reduce, but not end. StuRat (talk) 11:42, 9 May 2015 (UTC)

There are many alternatives, both old and new. Just as we had electrical cars in the 19th century, we also had Rigid_airships crossing the atlantic way back. Hydrogen-powered_aircraft is one of many newer alternatives. Star Lord - 星王 (talk) 13:13, 9 May 2015 (UTC)

Lighter-than-air travel is inherently dangerous, as winds can easily blow the ship off course, make mooring impossible, etc. It's also inherently slow. You might think it would at least be peaceful, but those steering props still cause noise and vibration. I should think travel by ship or train would be better alternatives, should planes somehow become impractical (a decades-long volcanic eruption filling the sky with ash could do it). StuRat (talk) 13:24, 9 May 2015 (UTC)

I'm still holding out for a magic carpet myself - a giant membrane, light as parachute cloth, covering a vast area, with actuators to wiggle it up and down in wave patterns and/or open and close pores in the material, with some kind of howdah in the middle and (of course) exquisite computer modelling to guide it. Wnt (talk) 16:11, 9 May 2015 (UTC)

I wouldn't write off airships just yet [4] [5] although they're being developed for cargo rather than passenger transport. Richerman (talk) 16:46, 9 May 2015 (UTC)

Yea, with some types of cargo scheduling is less critical, so intermittent, slow deliveries might be acceptable. StuRat (talk) 17:49, 9 May 2015 (UTC)

I added to the title to give a clue what the Q is about. StuRat (talk) 13:19, 9 May 2015 (UTC)

Wikipedia is not a crystal ball. Come back in 80 years and we will delighted to give an answer about fin-de-sicle plane fuel. --Llaanngg (talk) 17:51, 9 May 2015 (UTC)

Not likely. Unless batteries with comparable energy density to fuel can be developed, hydrogen or biofuels are the most likely option. Mr.Z-man 23:23, 9 May 2015 (UTC)

No. Oil and gas will be around much longer than the end of this century. Of course, a hundred years ago, if you phrased the question using steam trains and coal: steam trains are all but gone as are trains that run on burning coal directly - nothing to do with supply though. Quite possible that suborbital ballistic transport using rail guns or other technology is available. In that sense, we're not a crystal ball but there's no reason to think it will be limited by supply of oil or gas. --DHeyward (talk) 06:21, 10 May 2015 (UTC)

completely extinct? Almost certainly not. Even in a worst case scenario, enough fuel could be synthesized that the elite could still get where they wanted to go.

Could fuel become scarce enough that middle-class luxury travel goes extinct? Sure. But for the majority of the world's population, airfare is out of reach anyway., so we don't have to work too hard to imagine what that would be like. 75.69.10.209 (talk) 18:28, 10 May 2015 (UTC)

The same processes used for the production of biodiesel can produce fuel suitable for jet engines. The Fischer-Tropsch process for converting gaseous hydrocarbons (biogas is mosly methane) to liquids is also a well established industrial activity. Roger (Dodger67) (talk) 09:48, 11 May 2015 (UTC)

The adipose tissue has the smallest amount of extracellular matrix

We learned that the adipose tissue has the smallest amount of extracellular matrix. What does it mean? 149.78.38.232 (talk) 11:42, 9 May 2015 (UTC)

Adipose tissue, Extracellular matrix. Bus stop (talk) 13:34, 9 May 2015 (UTC)

To put it in context, consider liposuction. It works well enough (though it strikes me as kind of a brutal procedure). But it wouldn't work with a bone, or even most internal organs (though that's kind of hard to evaluate because if you want to remove those usually you need to get every last cell and deal with a much larger blood supply). Adipocytes are huge cells without much structure, separated by narrow gaps, and adipose tissue tends to fit into various spaces whichever way pressure dictates. Wnt (talk) 16:17, 9 May 2015 (UTC)

Why is it more windy over the ocean than it is over land?

Is it simply because of the lack of physical barriers obstructing the wind? Malamockq (talk) 13:39, 9 May 2015 (UTC)

This link gives the math to explain it. >http://www.google.co.uk/url?q=http://www.iawe.org/Proceedings/7APCWE/T2D_5.pdf&sa=U&ei=mB5OVdrFIMLQswHi7oDADw&ved=0CBYQFjAA&usg=AFQjCNEw46UhkdHaqUXR0eOTB20-UPZ9rA< Topographical effects on wind speed over various terrains.--Aspro (talk) 15:05, 9 May 2015 (UTC)

A more direct version of that link: http://www.iawe.org/Proceedings/7APCWE/T2D_5.pdf —Tamfang (talk) 19:07, 10 May 2015 (UTC)

Yes. Trees or even plants slow wind considerably, and hills and mountains even moreso. Completely flat ground with no vegetation, like salt flats, might not. And note that the wind speed difference between land and sea fades with altitude. StuRat (talk) 15:07, 9 May 2015 (UTC)

There's a piece missing as there is off-shore winds that are largely unaffected by the coast and are larger over oceans because of lack of topographical interaction. But there is also diurnal winds (i.e. Sea breeze or on-shore winds) that are caused by the difference in air pressure driven by heat capacity differences of land and sea. It's windier at the beach - both on water near the beach and on shore - because the land heats and cools daily while the ocean temps is relatively constant throughout. --DHeyward (talk) 06:55, 10 May 2015 (UTC)

• Because God was a sailboat-fisherman. μηδείς (talk) 04:02, 12 May 2015 (UTC)

Science and applied science

What's the distance between a natural science, and it's engineering or applied version? Think: chemistry and chemistry engineering, or biology and biotechnology. Is it common to find someone with a pure science background competing against someone with an applied science background? --Llaanngg (talk) 17:59, 9 May 2015 (UTC)

"Applied", meaning using something for a purpose? Maybe see basic science vs applied science or science vs engineering or chemistry vs chemical engineering? There's a lot of overlap, where people working on basic science are still aiming to solve an applied problem (very common, especially to have a "so what good is this new thing?" answer for purposes of getting grants and publications), or working in applied science and still developing new basic science along the way. DMacks (talk) 19:28, 9 May 2015 (UTC)

I don't think it makes sense to put a hard division between theoretical and applied sciences...or between the people who work in them. To pick a well known counter-example: Albert Einstein - probably considered to exist at the extreme theoretical end of the scale of scientific achievement - famously designed the Einstein refrigerator and a hearing aid...both being examples of practical consumer product engineering at the very opposite end of the scale. Is this common? It's a matter of degree - so I don't think it's possible to nail it down. SteveBaker (talk) 20:10, 9 May 2015 (UTC)

• An example: the applied version of biology, chemistry, and in some degree physics, is medicine. --Mr.Pseudo ^{Don't talk to me} 20:13, 9 May 2015 (UTC)

There is often not a clear distinction. If you look at the articles in the Journal of Applied Physics for instance, it can be difficult to imagine a real "application" for all of them. Is the sound velocity of tantalum under shock compression in the 18–142 GPa range really of any industrial interest? Probably not, or else it would be published in a more engineering-focused journal. Research published in something like the Journal of Constructional Steel Research is certainly going to be on the "applied" part of the spectrum, while Low Temperature Physics is more "pure." But most research published is more toward the middle of the spectrum, not "science for the sake of science" but still several degrees removed from any real-world application. Mr.Z-man 23:16, 9 May 2015 (UTC)

You mention chemistry/chemistry engineering and biology/biotech. The way you describe things as "pure" vs "applied", and using the word "compete", I am here assuming you mean lab chemistry and chemical engineering. All have been in labs, but chemical engineers are also trained to put together the industrial side: pipes, valves, pumps, tanks and other chemical machines. There is not a lot of "competition" here. Nor is there much competition between biology and biotechnology. In biotech fields where the science is well known and scalability is a factor, it is often built by chemical engineers. Biologists are usually more interested in animals or plants than any tech. The "purest" forms of chemistry is in my experience performed by physicists and mathematicians. There is overlap among all, but I see a lot more cooperation than competition. There is definitely no general "distance" between "pure" and "applied" in science. Most uses of the word "applied" that I have seen have been for marketing purposes rather than any strict division between them. Star Lord - 星王 (talk) 23:21, 9 May 2015 (UTC)

I've known a couple of people who did maths at university that worked as, or at least, alongside, engineers. I've also known at least one who did pphysics and several who did materials science working as engineers. Greglocock (talk) 00:17, 10 May 2015 (UTC)