Wikipedia:Reference desk/Archives/Science/2013 November 20

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November 20

Unsure how to calculate a percentage of power to create a solution

See talk page
The following discussion has been closed. Please do not modify it.
Note: I have blanked this thread, as it is clearly a request for medical advice. We do not answer such questions. Seek such advice from a qualified medical professional. AndyTheGrump (talk) 03:40, 20 November 2013 (UTC) This blanking is being discussed on the RD talk-page. Please leave it blanked pending that discussion. Many of you are beyond 3RR and WP:CIVIL and will be blocked if this behavior continues. DMacks (talk) 04:47, 20 November 2013 (UTC) Who besides ATG is beyond 3RR or has made an uncivil comment? μηδείς (talk) 22:14, 20 November 2013 (UTC)

halting global warming?

I've looked and I can't find the answer to this question (two parts):

1. If all (or essentially all) of the electricity was produced by means that don't burn fossil fuels, would that be enough to halt global warming?
2. If not, what if all (or essentially all) automobiles didn't burn fossil fuel - would that be enough? Bubba73 ^{You talkin' to me?} 06:20, 20 November 2013 (UTC)

There are also other sources of atmospheric greenhouse gases, like slash-and-burn agriculture. And things like solar panels may not be a solution at all, if it takes more energy to produce them than you get out of them over their lifetime, and this energy comes from burning fossil fuels. StuRat (talk) 07:24, 20 November 2013 (UTC)

Yes, I know, but I saw somewhere that producing electricity was the biggest contributor to carbon in the atmosphere and automobiles were second. Bubba73 ^{You talkin' to me?} 18:13, 20 November 2013 (UTC)

That varies a bit by country. Here is the EPA data for the US in 2011, where indeed electricity (33%) and transportation (28%, note that that includes air travel, shipping, railroads, and trucks) are indeed the largest producers. Attribution of recent climate change has world-wide data for 2000, and for all GHG emissions, not just CO2. Cutting our GHG emissions to about one third would go a long way to reducing the medium-term risk of global warming, but we are already committed to significant future warming, since the planet has not yet caught up to the current imbalance we have created.--Stephan Schulz (talk) 18:31, 20 November 2013 (UTC)

Have a look here [1]. It's not exactly what you are talking about, but very similar. This type of analysis is often referred to as a "wedge" approach to halting/reducing climate change, so that term might help your searches. According to the graph I linked, all renewable and high-efficiency electricity would not halt climate change, but for vehicles they just have an "efficiency" wedge, which I think still means fossil fuels are used. Another thing to keep in mind is that there is a sort of momentum involved with atmospheric dynamics and CO2 emissions. Thus, even if we could halt all CO2 emissions today, the climate would likely still warm for several years, and it would take hundreds to get back to pre-industrial levels of atmospheric CO2. Hope that helps, I can dig up science articles on the topic if you'd like. SemanticMantis (talk) 16:26, 20 November 2013 (UTC)

Even if we were to do nothing more than stop burning fossil fuels today (just so we can all breath cleaner air, if nothing else) the planet will still go through a period of several decades of warming before settling on a new stable, but higher temperature. See this source. Hence we need to put a stop to the pollution and clean it up too ASAP. -Modocc (talk) 19:46, 20 November 2013 (UTC)

Effects of masturbation on sperm count.

What effect does masturbation have on sperm count and the ability to have children? 94.124.154.253 (talk) 07:47, 20 November 2013 (UTC)

According to Masturbation#Evolutionary utility, masturbation can increase the ability to have children, by flushing stale sperm with low motility out of the male's genital tract, making way for fresher sperm with higher motility. Red Act (talk) 08:15, 20 November 2013 (UTC)

Cool! Thanks for that! This non-signed-in user can continue his self-pleasuring habit, safe in the knowledge that it is all in the interests of protecting his progeny. 94.124.154.253 (talk) 08:29, 20 November 2013 (UTC)

Continue that lifestyle and you won't have to worry about any progeny. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:04, 20 November 2013 (UTC)

And it's good for you. AndrewWTaylor (talk) 12:20, 21 November 2013 (UTC)

Why doesn't water vapor always condense in water droplets?

Water will evaporate because the energy is distributed evenly in the water, and as a result some water molecules near the surface will have enough energy to escape the liquid. The water vapor that forms will eventually be at room temperature though. So if the water vapor is below its boiling point, why doesn't the vapor condense into water droplets? Why does it take a certain concentration of water vapor for droplets to form? 74.15.137.253 (talk) 13:08, 20 November 2013 (UTC)

Could it be surface tension based? It might take a certain amount of moisture to be present to cause molecules to come together to form droplets 217.158.236.14 (talk) 13:38, 20 November 2013 (UTC)

Fundamentally the reason is entropy (or, more specifically, Gibbs free energy for your constant pressure/temperature environment): there are more ways to scatter your water molecules around the room than there are to arrange them in water droplets on the floor (nevermind restricting it to the glass), so that's the preferred state. However, if the water takes up any significant fraction of the available (sealed) space — which is to say that there's your certain concentration present — then the space available to the liquid water is comparable to that available to the gas, so the advantage of the liquid state (its lower internal energy) becomes significant and not all of the water evaporates. --Tardis (talk) 14:08, 20 November 2013 (UTC)

Another way to think of it is to consider the Boltzmann distribution of the water molecules at any given temperature. See This image. At any given temperature, molecules of a substance are not all at the same energy. They exist in a distribution of energy states, and some water molecules will always have enough energy to escape the liquid phase. Those that are already in the gas phase will also be in a Boltzmann distribution, that is some number of water molecules will be moving slow enough to be "captured" when the land on the liquid phase, and thus condense. The issue is that at any temperature, you don't have all of the molecules at the same energy. You always have a distribution of molecules at various energies, and some will have enough energy to remain in the gas phase. Notably, we have Ludwig Boltzmann to thank for both the concept of entropy (the explanation given above) and for the explanation I have given here; neither if a "better" reason, and really are just two different sides of the same coin; just different perspectives for looking at the same concept. --Jayron32 00:38, 21 November 2013 (UTC)

I think water vapor does always condense into water droplets, but at the same time those water droplets are evaporating, so you get an equilibrium, and only when conditions are right does that equilibrium favor water droplets large enough to see. StuRat (talk) 06:19, 21 November 2013 (UTC)

Radioactivity of technetium and promethium

Why are technetium and promethium radioactive although they are in between stable elements? Czech is Cyrillized (talk) 13:32, 20 November 2013 (UTC)

To really understand this, we need to explain why any nuclide is radioactive. We can summarize by saying that the nucleus is in an unstable energy configuration, and the release of a particle (by radioactive decay) puts the nucleus into a lower energy state. This is correct, but it's nearly equivalent to saying "it's radioactive because it is radioactive."

What we need is a good model of the energy configuration of the atomic nucleus. It would be great if we could show you an analytic equation, into which you could plug the number of neutrons, the number of protons, and calculate the binding energy of the nucleus. Unfortunately, nuclear chemistry is very much an empirical science. We know the binding energies for various configuration only based on experimental observations. When we try to write analytical equations for small nuclei, we might make a little progress with, say, the quantum mechanical Yukawa potential (that is, if we attempt to express the energy of the strong nuclear force in a quantum mechanically correct way). But for large nuclei - the really interesting ones, particularly those that undergo radioactive decay - these models just don't work. The formulas predict incorrect values, and worse yet, they're entirely unwieldy, because they're set up to handle a small number of particles.

So, we're back to a little bit of hand-waving: some nuclei are unstable; we know they're unstable from lab measurements, but we can't easily explain why. Atomic physics really isn't very intuitive: in the macroscopic world, if you take an unstable physical dynamic system (let's say, a bowling ball glued to a stretched slinky, hanging over a ledge, and oscillating back and forth), you can't make it more stable by adding another bowling ball. One bowling ball is about to break away; two bowling balls are going to break away faster. More mass, more force acting against the adhesive property of the glue, faster "decay rate." Adding mass and energy and momentum in the macroscopic world changes the dynamics, but it often makes an unstable dynamic system more unstable. In the case of nuclei, adding mass and energy and momentum sometimes makes the system more stable. If we had a predictive model explaining why - in the general case - then I never learned about it, and I spend a lot of years studying atomic and nuclear physics. Nimur (talk) 13:56, 20 November 2013 (UTC)

It's certainly empirical like you said, but a useful summary of the relevant ideas is found in the Mattauch isobar rule. You can also start with the very simple observation that even numbers (separately) of protons and neutrons improve stability, in a theoretically-justified manner analogous to electron pairs. --Tardis (talk) 14:14, 20 November 2013 (UTC)

When by itself the Technetium-98 nucleus is stable. And it only changes due to electron capture. In an atom it can captures an electron and decay. Graeme Bartlett (talk) 21:30, 20 November 2013 (UTC)

(Since all isotopes of Sm are predicted to be capable of decay, is Pm really between two stable elements? Just a thought. Might it be better considered theoretically to not so much be unstable among stable elements, but just have a half-life much less than the elements around it?) Double sharp (talk) 14:21, 21 November 2013 (UTC)

Strange columns

Why there are patches of a brick-like surface on columns which appear to be of marble? Is it some other material, that reveals such weird layer when aged? 93.174.25.12 (talk) 15:21, 20 November 2013 (UTC)

You are probably seeing modern-era masonry reinforcement that has been used to re-build the column.

My favorite example of this is Baalbek, which I have visited many times. It's ancient; some of the temples pre-date the Roman era.

People kept destroying the temple, and then rebuilding it; every few hundred years, some messiah or pagan or Jewish revolt would occur, or Persians or Greeks or Franks would invade, and everyone would sack and loot every temple for hundreds of miles. There were periods throughout history during which tourists would have to wait a few decades until the preservationists could rebuild the temples. Around 500 CE, a major earthquake knocked over most of the columns, except for six very tall columns; and the archaeologists and preservationists decided to keep it that way, because the ruins looked "pretty" and "ancient." Unfortunately, there were still a few thousand years of war and catastrophe left for human history to experience; so the ruins had to be re-preserved (back to their ruinous state) following the arrival of the Arabs, and the Crusaders, and Napoleon's army, and a few decades of cold-war era bombings, hijackings, occupations, antiaircraft batteries, airstrikes, and so on.

The last time I went to Baalbek, the columns were still pristinely preserved in their ruinous state, and are usually nicely lit up with colorful electric lighting.

Archaeologists and preservationists at such sites have to be very careful about their strategy; ancient "restoration" work becomes part of the site history; even if it is cosmetically dissonant from the original site. (In fact, to restore Baalbek to its pre-Byzantine glory, we would need to disassemble the Hagia Sophia - the foundations of which were built from parts that Justinian sacked from Bekaa; any proper "restoration plan" would make a lot of people very unhappy).

I would be very interested to read more about Volubilis, if anyone knows a good history book. Nimur (talk) 15:41, 20 November 2013 (UTC)

(For anyone who is interested in some lighter recreational reading on the topic, I highly recommend the art and architecture picture-book series produced by Phaidon Press, a publishing house which was for a time staffed by the better half of the Encyclopedia Brittanica team. This one is particularly worthwhile, though I don't remember if it covered Morocco in great depth). Nimur (talk) 21:53, 20 November 2013 (UTC)