Wikipedia:Reference desk/Archives/Science/2018 January 22

= January 22 =

Pyrogens as alternatives to DNP for weight loss?
People in the past took a chemical called dinitrophenol to raise basal metabolism but it has a narrow therapeutic index and a propensity to cause cataracts, particularly in women. Pyrogens are a type of chemical which includes some proteins made by immune cells which raise body temperature to fight an infection. Could small amounts of a suitable pyrogen have a similar effect to DNP? Would the therepeutic index be just as narrow and dangerous as DNP? --129.215.47.59 (talk) 14:49, 22 January 2018 (UTC)


 * Leukocytic pyrogen is studied in relation to metabolism as well as many other health subjects, such as fever reduction and muscle injuries. 209.149.113.5 (talk) 15:14, 22 January 2018 (UTC)

The history of weight loss drugs is marked by the widespread use of one compound after another that turn out to be killers. See. Even herbal supplements not covered in that publication turn out to be killers, like Ephedra. I can't think of any other area of medicine where a new drug - even one asserted to be safe by government agencies - should be viewed with more trepidation. With that warning out of the way, I should note it is not hard to find people claiming to sell pyrogens for weight loss. There are endogenous cytokines like cachectin (i.e. TNF-alpha) that cause severe weight loss (cachexia). But then again obese people produce lots of TNF-alpha and it is more often blamed for diseases associated with "low-grade inflammation" than cheered on as an effective means of weight loss. Wnt (talk) 16:36, 22 January 2018 (UTC)

Dyson sphere
Hi. I have read the article and still have a question. Why is it necessary to collect the star's energy from artificial objects orbiting it? A planet is an object orbiting the star, why not collect the sun's energy directly from collection devices on the planet instead of building them in space? I would like to understand why a dyson sphere/ring would be an advantage, how collected energy gets transmitted back to the planet, and why that's more efficient than collecting it when it arrives at the planet instead. Ta. 70.67.222.124 (talk) 17:10, 22 January 2018 (UTC)
 * Assuming that more energy is required than can be collected from the star from a planet's surface, a larger surface area could allow more collection. Enclosing the star, partially or completely, would increase this surface area and even prevent radiations from leaking out, permitting even better harvest.  The hypothesis is that such energy quantities could be useful for particular advanced future technologies (perhaps including time-space bending), interplanetary civilizations and industries, etc.  — Paleo  Neonate  – 17:23, 22 January 2018 (UTC)
 * Of course you can collect some of a star's energy from a planet's surface, just like we already do with solar panels on Earth. However, only a small part of the energy/light that a star emits strikes the surface of planets and other natural orbiting objects. Most of a star's light escapes into deep space simply because there's nothing that stops it. The idea of a Dyson sphere is surrounding a star, so that little to nothing of the star's usable energy escapes.
 * As to how energy can be transmitted from collection device back to a planet, there are a number of options, e.g. lasers that are directed at the planet or storing the energy in fuel to transport back to the planet. - Lindert (talk) 17:31, 22 January 2018 (UTC)
 * "I know - lets build a device to collect the entire power output of the sun, and then turn it into lasers and fire it at our home planet! What could possibly go wrong?" Iapetus (talk) 17:29, 23 January 2018 (UTC)
 * Good point, but it doesn't really matter how you transport the energy. People on a single planet simply won't be able to handle all the heat generated by using so much energy. So the Dyson sphere only makes sense if there's a considerable amount of space colonization/exploration. - Lindert (talk) 17:51, 23 January 2018 (UTC)
 * (Whoops -- this is an answer to why it should be a complete sphere ... which wasn't the question. But I hate to delete my fine answer!)  I've never read the original thesis, but I would assume the shell theorem is involved.  A closed sphere will exert no net gravitational pull on the star; hence the star will exert no net gravitational pull on it.  If it can be set up where the radiation pressure and gravity equal one another it might not even need much compressive or tensile strength.  But if there is a hole, some pattern of orbiting is required, and things get (at least) more complicated to arrange with ultra-strong elements or moving parts or something. Wnt (talk) 17:40, 22 January 2018 (UTC)


 * A Dyson sphere is built presuming all the planet is already rigged for solar. It also often comes with an assumption that some kind of actual habitat with people living on it might actually extend all the way around the star, with the solar panels powering their local needs, or beaming the energy to a range of smaller settlements possibly in orbit. Wnt (talk) 17:46, 22 January 2018 (UTC)

The Earth intercepts solar power over an effective surface of about $$A = \pi r^2.$$, where r= about 3963 mi. The area of a sphere at the earth's orbital radius of 1 AU= $9.296 mi$, is $$A = 4\pi r^2.$$. So if you covered the earth with solar collectors, you could capture about ($1.55$)/($3.43$) of the total energy that reached earth's orbital distance from the sun. That's about one part in 500,000,000, or 500 parts per billion. If your civilization needs more solar power, you need to go beyond Earth. -Arch dude (talk) 22:30, 22 January 2018 (UTC)


 * 2 ppb. Sagittarian Milky Way (talk) 05:18, 23 January 2018 (UTC)


 * And I get a 1 AU Dyson sphere area of more than you for 1/2 ppb, not 2 ppb. Sagittarian Milky Way (talk) 05:28, 23 January 2018 (UTC)

Keep in mind that this is a thought experiment at an era where creating the structure is far beyond our capability. 10,000 years ago, imagine cavemen thinking about how to grow trees inside complex cave structures so they would always have firewood. They understand campfires, caves and wood as fuel. With the benefit of hindsight, campfires, trees and caves are no longer our primary habitat. Nor would a 10,000 year old plan to seek out advanced civilizations by looking for signs of giant caves with underground arboretums powered by large campfires be particularly insightful. Dyson spheres are an entertaining thought experiment limited by our current understanding. The assumption is that a civilization may eventually need all of a stars energy output and the thought experiment is how to contain it without simply appearing as a blackbody radiator as we currently do. --DHeyward (talk) 03:32, 23 January 2018 (UTC)


 * Exactly. And the concept of a "whole star energy budget" as described by Dyson is a variation on the theme of the Kardashev scale: it's a thought experiment that models major technology levels by comparing the energy budget of a society to different natural scales.  A small and primitive society increases its energy production until it captures all the energy of its entire home-planet; to get any more, it must do something dramatically different.  For a long time, there can be no progress (measured by growth in energy budget) until some major breakthrough makes off-planet growth practical.  Presumably, the society and its energy use grows steadily, until the next big milestone - capture of the entire energy of the local star.  Then, for a long time, there can be no further progress... and so on.  This entire model of life in the universe is a thought-experiment; the Dyson sphere is a specific detail on the theme.
 * Obviously, this line of reasoning, subject to literary license, is like a great field of wheat: we have the potential to thresh a kernel of scientific insight only if we can discard a great deal of silly scientific-fiction chaff; hence we can mill the science into flour to create space-dough.
 * The famous paper was published in Science in 1960, and it met the bar for peer-review, and it was lauded by many respectable experts. Freeman Dyson did not ever, in his paper, discuss space-dough; but some twenty years later, he did write about space chickens and space eggs.
 * That original paper is the optimist's version of SETI. Quoting Dyson: "The material factors which ultimately limit the expansion of a technically advanced species are the supply of matter and the supply of energy."  In other words, we pesky Earthlings can - in principal - keep growing and progressing and evolving until we eat every single molecule of matter on this Earth, drink every single watt of fresh-squeezed solar power, and distill every last drop of stored fermented energy!  By the end of it, we Earthlings surely won't look like mammals!  And then, we either extinguish, or we find a way to move off-world - to eat and drink every atom and ion and watt produced in the gravitational potential energy well of the local star, perhaps becoming some kind of space-jellyfish.  ... with apologies: "I do not argue that this is what will happen in our system; I only say that this is what may have happened in other systems."
 * The pessimist's version of SETI, largely attributable to Frank Drake's work during that very same era, proposes a different limit to the ultimate expansion of a technically advanced species: as indicated on the great equation emblazoned on the wall at the entry to the SETI Institute, the scale factor L describes the longevity of an intelligent species. Intelligent species seem prone to self-annihilation; it hardly takes a measurable fraction of a Scale I energy budget to destroy intelligent life on a single planet, and I wake up each morning surprised we've made it through another orbit-fraction.  This is one of the most probable resolutions to the so-called Fermi paradox.
 * I met Frank Drake this summer while I was stationed at SETI; and I had the opportunity to ask his opinion on our prospects; but all he wanted to talk about was the proliferation, diversity, and beauty of orchids on planet Earth. I had to acquiesce - of course, as difficult as it is for a self-locomotive mammal-brain to recognize, truly intelligent life is almost certainly autotrophic.
 * Nimur (talk) 06:04, 23 January 2018 (UTC)


 * Without having seen the original paper, I'll go out on a limb and opine that what Dyson had in mind was not "if we build a sphere, we can capture all the sunlight" but rather that, as a civilization grows, it will seek to capture more and more sunlight, with the result (not a goal) that its sun is eventually hidden. —Tamfang (talk) 03:48, 24 January 2018 (UTC)

Thank you all for the thoughtful answers; this has cleared up a lot. You all helped, but Lindert especially got to the nub of my confusion. I've added some text to the article, including the crucial link to "thought experiment". 70.67.222.124 (talk) 16:09, 24 January 2018 (UTC)

Human head hair - changes from child to adult.
I have noticed that human head hair tends to darken as the person gets older, and that curly hair tends to straighten. (This is in people of European descent). What causes this? DuncanHill (talk) 19:44, 22 January 2018 (UTC)
 * You can look at Human_hair_color. Ruslik_ Zero 20:34, 22 January 2018 (UTC)


 * Some information at Human hair color which says "This is caused by genes being turned off and on during early childhood and puberty". This is referenced to Ask a Geneticist: Why does the hair color of children often change color as they grow older? (2010) by Dr. Barry Starr from Stanford University.
 * I also found an article about The HIrisPlex System for Simultaneous Prediction of Hair and Eye Colour from DNA (2013). In Section 3.3 Age-dependent hair colour changes and consequences for hair colour prediction the authors say: "Age-dependent changes in hair colour are evident from anecdotal knowledge. The most often observed age-dependent hair colour changes occurs from light blond during childhood towards dark blond/light brown as an adult, but can also occur from light brown to dark brown/almost black. Suggestions of hormonal changes during adolescence have been advocated as a possible explanation, but the molecular basis are yet to be unveiled". Alansplodge (talk) 20:36, 22 January 2018 (UTC)


 * Thank you, anything about curls? DuncanHill (talk) 00:09, 23 January 2018 (UTC)
 * Why does hair curl with age? says: "Dr. Barry Starr, a Stanford University geneticist thinks (according to an article on NPR.org) that most people’s hair doesn’t change from straight to curly. He doesn’t know why some do have this change and is skeptical that we will ever know! Scientists do know that curly hair follicles have a different shape than straight hair follicles. Therefore, according to Dr. Paradi Mirmirani (dermatologist), if your hair is changing, the follicles must be changing. She thinks it is related to hormones. Dr Val Randall (endocrinologist at the University of Bradford in England – according to NPR) also believes it is hormone related but says there is no evidence to prove it – and she is doing research on hormones and hair. She also claims it doesn’t happen very often!" Alansplodge (talk) 16:02, 23 January 2018 (UTC)
 * My observation is that curly haired children tend to grow into straight haired adults, the opposite of the agingbodies.com question. DuncanHill (talk) 16:30, 23 January 2018 (UTC)
 * The NPR ref does mention children although also with straight hair changing to curly. It also mentions people (well at least one, the other I'm unsure) who have had hair changing back and forth. It also mentions there is a a fair degree of funding for research into trying to change hair shape for cosmetic reasons which makes me think any common childhood changes would have been studied but I couldn't find anything from a quick look earlier. (I also would have expected them to be mentioned in the NPR ref but easily possible for it to be missed I guess.) Nil Einne (talk) 02:36, 24 January 2018 (UTC)
 * Looking a bit more I found [//www.scienceworld.ca/blog/can-hair-change-straight-curly] which also talks about hair changing from straight to curly when people were teens. It does talk a bit about hormonal changes in general (not specifically relating to childhood). This not very good source [//www.naturallycurly.com/curlreading/seniors/this-is-how-your-hair-changes-at-every-age-b] suggest hair gets thicker during childhood which can lead to straight hair becoming curly. I found a case report on a single African-American teen who's hair changed shape after treatment for hair loss due to alopecia areata [//jamanetwork.com/journals/jamadermatology/fullarticle/1105175]. Anyway I mostly mention it because the new hair was straight which is said to be similar to the hair during early childhood, while the hair which wasn't lost was curly, implying his hair changed from straight to curly during childhood. Nil Einne (talk) 12:17, 24 January 2018 (UTC)