Wikipedia:Reference desk/Archives/Miscellaneous/2015 April 3

= April 3 =

Eyesight
This is not a request for medical advice. I went to an optometrist yesterday for a routine check, and she said that my eyesight had improved since my last visit (something which I didn't think was possible). I have not had any change in diet or anything (except that I am eating fish more regularly these days), so what could have caused this? KägeTorä - (影虎) ( もしもし！ ) 05:54, 3 April 2015 (UTC)


 * Let me guess, are you nearsighted and middle-aged ? People's vision often drifts towards farsighted as they pass middle age, and those who start out nearsighted can actually see a small improvement when this occurs. StuRat (talk) 06:07, 3 April 2015 (UTC)
 * . Writing that doesn't mean you're wrong.  It means you need to back up what you say with references.  -- Jayron 32 06:17, 3 April 2015 (UTC)


 * You'd have to ask the doc what she meant by that. There are googlable focusing exercises one can do meant to improve nearsightedness and farsightedness.  Heinlein mentions this somewhere, either biographically or in one of is juvenile stories--somebody wasn't able to get into the military until he improved his eyesight.  I notice my eyesight adjusts according to whether I am inside all day on a computer, or out driving and seeing long distance for hours. μηδείς (talk) 06:20, 3 April 2015 (UTC)


 * Apparently, I was originally short-sighted, but became normal in the last few years. I am not particularly bothered about it, because my glasses are perfect (and make me look really good as if I have pockets full of money, because they are reactives, which are really expensive, and the girls like men with pockets full of money), but I was just wondering how this change could happen? Is it because I am using the computer all day, and need to focus on Japanese/Chinese (my job)? I doubt it, but it's a possibility. KägeTorä - (影虎)  ( もしもし！ ) 08:01, 3 April 2015 (UTC)


 * Possibly Age-related Long Sight--Phil Holmes (talk) 09:21, 3 April 2015 (UTC)
 * We have (brief) coverage of it Presbyopia. LongHairedFop (talk) 10:57, 3 April 2015 (UTC)
 * Not really. That says people with myopia have a protective affect against developing presbyopia. But it also says that their myopia doesn't disappear. It doesn't particularly say it doesn't improve, but it doesn't suggest it does. (And realisticly, if it improves there would surely be people with limited myopia for who it would disappear.) It also mentions how people who get refractive surgery may find this puts them at a disadvantage later because they may be more likely to develop presbyopia, but again nothing to do with their vision improving. The last point on astigmatism is unclear whether it means their near vision is better than it was before or akin to their original point, i.e. that their near vision is better than it would be if they didn't have myopia. My strong suspicion is the later. The point is because people with myopia may have a focal ability much more on the near range, presbyopia takes longer to develop. However the development of presbyopia doesn't improve their far sight because what happens is people simply can't focus so well on things that are close without an improvement in their ability to focus on things that are far. I.E. It's not that their focal range is moving to further way objects, it's that their focal range is becoming more limited. (Terms may be not entirely accurate but hopefully people get the idea.) Nil Einne (talk) 14:13, 3 April 2015 (UTC)

Why are humans so badly designed. How did we survive.
Ok here's one I've been wondering for since a kid.

Why, how did we ever get this far despite being so physiologically backward. Look at women for instance. They have to go through periods which cause a range of highly unpleasant symptoms. Whereas, other mammals appear to not have any such issues at all. The process is way more streamlined. I won't even go into childbirth.

And look at how badly humans cope with defecation. Being upright with large upper hamstrings/glutes (the crack arrangement) means passing stools are more likely than not to cause a mess on oneself. And of course, in the animal kingdom toilet paper aisles are non existent. Anyone for crippling rashes that prevents walking (starvation) and/or potentially deadly skin infections?

So how an earth did we end up making it this far with such massive anatomical and physiological disadvantage. — Preceding unsigned comment added by 95.219.29.8 (talk • contribs)


 * How do you know that 'childbirth' is not painful for other mammals? You try getting a baby horse out from between your legs, and then decide. As for defecation, I have never seen a single human shitting standing up. We either sit down or squat. And who says that animals don't go through periods? Chickens lay eggs - that is exactly the same thing (OK, they are not mammals, but anyway).

We survived because standing upright gave us less pressure on the blood-flow to the brain, and we started eating everything else (including each other in some cultures). Also, one of our ancestors was born with a mutated thumb, on each hand, and still managed to get a girlfriend and then created a whole new race of people with mutated thumbs, enabling his descendants to create and use tools, something which is difficult for most animals, due to their physical characteristics. KägeTorä - (影虎) ( もしもし！ ) 12:03, 3 April 2015 (UTC)


 * The difficulty of human childbirth is a consequence of the size of the human cranium, which is correlated with human brainpower, which has allowed our species not only to overcome such physiological disadvantages but to outcompete other species for use of the planet's resources. Marco polo (talk) 13:14, 3 April 2015 (UTC)


 * I've heard this before and it does make sense. However, that doesn't address why human infants can't just be born smaller and grow more outside the womb. For example, polar bear cubs are born weighing just over a pound, much smaller than human infants, but they grow up to be far larger than human adults and have a brain size that's about their entire birth weight. I guess it has to do with the womb providing more safety in the early stages of development, but that's true regardless of cranial size. Besides, the head is not always the widest part of the baby; when I was born, I broke my collar bone. - Lindert (talk) 14:18, 3 April 2015 (UTC)

--The mistake you are making is to assume that we are designed. We aren't; we evolved. We are the way we are because each little evolutionary change gave us just enough of an advantage over our immediately preceding form (and over enough of our rivals) that we were able to survive in the environment at that time. Each change had to be made on the basis of everything that had gone before, so we're just stuck with any inconvenient bits left over from earlier in our evolution. Women's periods, or inconveniences in the way we defecate, or our tendency to get appendicitis because we're stuck with an organ we no longer need, arise from the fact that at some earlier stage in our evolution these features were helpful in some other way, but as we've evolved have become less helpful and more tiresome - just not tiresome enough to actually give us an evolutionary disadvantage yet. As soon as these become actively unhelpful for our survival, they'll evolve away. It's the fact that we're imperfectly functioning, rather than perfectly functioning, that proves we evolved, rather than were designed by some god.
 * This same defecation related question was posted yesterday by an IP traced to Sofia, Bulgaria which has been reported as a source of forum spam.  Today's defecation related question comes from Riyadh, Saudi Arabia. μηδείς (talk) 13:15, 3 April 2015 (UTC)


 * This short video pretty much sums it up. We made ourselves welcome. InedibleHulk (talk) 15:35, 3 April 2015 (UTC)


 * I will try to address some of the specific questions. First, all mammals have some form of estrus.  In some mammals it is known as "heat".  Menstrual periods are distinctive to great apes as "cryptic estrus".  That is, ovulation occurs in the middle of the month, and does not result in any obvious symptoms.  I don't know the exact reasons why apes have this reproductive rhythm, but that is a characteristic of apes.  (Research on female fertility cannot be done on lab animals other than great apes.)  Second, as to childbirth, human childbirth is more difficult than that of other mammals, because human babies have large heads, and human babies have only had large heads for a short period of time in a biological time scale.  I disagree with the comment that one of our ancestors had a mutated thumb that was transmitted to offspring.  The changes and improvements to human hands compared to other primate hands have been gradual.  Monkeys have opposable thumbs too.  It is just that humans have even more flexible hands than flexible monkey hands or chimpanzee hands.  Those are a few answers.  Robert McClenon (talk) 20:40, 3 April 2015 (UTC)


 * It's a tradeoff.  Humans found it advantageous to walk upright, but that meant the birth canal was no longer straight.   This means that sometimes an infant has to tuck his head in a bit or he won't be able to get through.   Humans are far more complex than other mammals, hence the large size of the head at birth compared to the rest of the body and infants being completely helpless when born. 87.81.147.76 (talk) 11:30, 7 April 2015 (UTC)


 * Walking upright lets us outwalk most creatures on this planet. We hunted stuff by just following it like The Terminator.  Humanity used to hunt by making its food run itself to death.  Ian.thomson (talk) 11:36, 7 April 2015 (UTC)


 * That's interesting.  I always thought being two - legged slowed us down.   For example, a horse can gallop at 30 m.p.h., which is a mile in two minutes, but the best athletes can only do a mile in just under four minutes.   Wasn't that why they began breeding cattle in captivity, because the hunt was too much hassle? 87.81.147.76 (talk) 11:41, 7 April 2015 (UTC)


 * Persistence hunting is a more informative link for humans. It includes a marvellous reference Kenyans chase down and catch goat-killing cheetahs. PrimeHunter (talk) 12:14, 7 April 2015 (UTC)

Suicide off the empire state building.
How many people would need to jump off the top before being unable to fall far enough to die? — Preceding unsigned comment added by 86.24.128.230 (talk) 17:50, 3 April 2015 (UTC)
 * People survive falling out of planes. KägeTorä - (影虎)  ( もしもし！ ) 20:13, 3 April 2015 (UTC)


 * Even if the bodies pile up so you only drop a few feet, you could still skewer yourself on somebody's exposed bone. Richard-of-Earth (talk) 20:16, 3 April 2015 (UTC)


 * Assuming the bodies pile up into a cone, with perhaps a 45 degree slope (what is the angle of restitution for corpses?) then if the pile has to come to within (say) 30 meters of the "architectural" height of the building (which is 380m) - then the volume of the pile of corpses would be pi x r2 x h / 3...around 40 million cubic meters. I'd guess that a typical corpse would occupy maybe a tenth of a cubic meter - so you're looking at maybe 4 million people...or a quarter million...or 50 million...there are a lot of unknowns here.  The height of the fall that would kill you is critical because the number of bodies is proportional to the cube of the height of the pile - do small differences in that number make MASSIVE differences to the answer. SteveBaker (talk) 20:32, 3 April 2015 (UTC)


 * Angle of repose, not "restitution". Dragons flight (talk) 20:44, 3 April 2015 (UTC)
 * Steve: "...around 40 million cubic meters. I'd guess that a typical corpse would occupy maybe a tenth of a cubic meter - so you're looking at maybe 4 million people..."  4E6 m^6/person?  Perhaps you should have divided by 0.1 m^3/person instead of multiplying. -- ToE 14:04, 4 April 2015 (UTC)


 * You'd also need to take into account that the empire state building isn't an isolated structure. So, nearby buildings would fill in parts of the "cone". StuRat (talk) 20:38, 3 April 2015 (UTC)


 * After a certain point, you'd also start compressing the corpses at the bottom and losing the fluids. Dragons flight (talk) 20:44, 3 April 2015 (UTC)


 * This is obviously either a late April Fool's joke, or trollery. There is no "empire state building". There is an "Empire State Building", but the superficial similarities between these two titles would trick only the meanest of intellects.  Even a lowly Probationary Acting Assistant Reference Desk Officer Grade I is more than a match for that sort of thing.  :)  --   Jack of Oz   [pleasantries]  21:38, 3 April 2015 (UTC)


 * Depending on wind currents, the answer can be "one". Some decades back, someone climbed over the rail and jumped, only to be slammed against the building by the updrafts, and landed on a ledge, with a broken leg or such. Presumably she then thought better of jumping, and rescuers were able to pull her inside. ←Baseball Bugs What's up, Doc? carrots→ 22:20, 3 April 2015 (UTC)


 * The volume of a cone is 1/3 of the area of the base times the height. If we are assuming they are jumping from the 1250 foot roof (not the tip of the antenna), that gives a base of a radius of 625 feet.  The area of the base is π(r^2) or 390,625 x pi = 1,227,185 sq. ft.  This gives a volume of 511,327,083 cubic feet.  Now, if we ignore the volume of the building itself and the surrounding buildings, which is not easily calculable, and assume the average human weighs 180lbs (according to this, and assume the density of the body to be the same as a water, 62.4lbs/cubic foot, we get about 3 cubic feet per person, then the number is 511,327,083/3 or 170,442,361 people. (Probably with a sig fig of less than 170 million given the rounding.) μηδείς (talk) 22:25, 3 April 2015 (UTC)


 * This would be a good question for xkcd What If. Staecker (talk) 12:33, 4 April 2015 (UTC)


 * Just to complicate it even further: remember that the Empire State Building doesn't have simple straight sides the way the World Trade Center did, but has a stepped design with multiple setbacks. To model a person jumping off it, you need to take into account their horizontal speed to know how far they will fall without obstruction from a setback.  In addition, people have talked about adjacent buildings interfering with the formation of a cone of bodies, but the Empire State Building itself would interfere more significantly, and in a complicated way because of the setbacks. --65.95.176.148 (talk) 16:15, 4 April 2015 (UTC)


 * I specifically said, "Now, if we ignore the volume of the building itself...." μηδείς (talk) 17:25, 4 April 2015 (UTC)


 * The world long jump record is less than 25 feet: One can use that information to calculate a person's likely horizontal velocity when leaving their ledge. Sketching the parabolic path a person would take on their trip to the ground given an initial horizontal velocity is a trivial calculation any high school physics student should be able to do.  -- Jayron 32 16:41, 4 April 2015 (UTC)


 * Of course there are all sorts of complications, people don't tumble freely or uniformly, the cone would slump, uncompressed bodies at the top would take up more space, blood would leak from the bottom of the cone, the ground under the bodies would compress.... The doable calculation is how many bodies would you need to fill a cone 1,250 feet high with a 45 degree slope.  If you want an actual answer you'd need a grant to do the research and data we probably don't have about the compressibility of bodies and the actual behavior of bodies tumbled in a heap.  In any case, you're looking at at least about 170,000,000, which is more than the populations of Mexico, Japan, Russia or Bangladesh. μηδείς (talk) 17:25, 4 April 2015 (UTC)


 * Perhaps it's silly being a stickler over math in a problem like this where there are so many unknowns, but if you really intended a 45° slope, then the radius of the base of the cone should be equal to its height. You used half the height, giving a steep cone with a slope of atan(2) ≈ 63°.  That is why your answer was so much smaller than Steve's (approx 400 million people, once his arithmetic was corrected), despite Steve choosing a shorter cone, only reaching to within 30 m of the architectural height of the building. -- ToE 18:47, 4 April 2015 (UTC)


 * Yes, I made the stupid mistake of assuming the cone would be both the rotation of a right triangle, as well as an equilateral triangle, which would give a sum of 270 degrees for the internal angles, rather than 180. I am sure in some universe highly curved in a higher dimension this must be possible.  My mistake illustrates the wisdom that it doesn't matter how smart you are if you don't check your math.

This has got to be one of the BEST refdesk qs in a long, long time. Anyone care to non? — Preceding unsigned comment added by 86.24.128.230 (talk) 19:21, 4 April 2015 (UTC)

Imaginative certainly, but a best question in my opinion needs to be based on a more realistic scenario. Richard Avery (talk) 07:31, 5 April 2015 (UTC)


 * This reminds me of another unrealistic scenario I once thought of and made some loose calculations on: If the human population continues to grow at the current rate and we spread at the speed of light in all directions then when will we run out of mass to convert to humans and how many will there be? Ignore relativistic effects. PrimeHunter (talk) 13:57, 5 April 2015 (UTC)