Wikipedia:Reference desk/Archives/Science/2016 June 26

Science desk
< June 25	<< May | June | Jul >>	June 27 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

June 26

Std transmission

Why is it that the incidence of stds spread through oral sex is much lower than that spread through vaginal or anal sex? Shouldn't it be the same given that many diseases spread through the mouth including common colds, stomach bugs etc? 82.17.228.64 (talk) 08:28, 26 June 2016 (UTC)

See Wikipedia:Reference desk/Archives/Science/2015 September 6#Std statistics and Transmission (medicine). Nil Einne (talk) 13:23, 26 June 2016 (UTC)

Maybe that London-based drive-by didn't like the answers he got a year ago? ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:28, 26 June 2016 (UTC)

Well I'm not certain if this is the same editor, even if they're both from the UK. I initially thought this was our friend who liked to ask about stats surrounding STD transmission via oral sex, one of the reasons I searched but after searching wasn't so sure so left a neutral comment. Nil Einne (talk) 14:24, 1 July 2016 (UTC)

Bacteria and viruses have evolved to function in certain conditions - and they do less well if the conditions are different. Bacteria which transmit gastric diseases are happy to be swallowed - the can cope with the saliva and the stomach acid. Other bacteria are much less likely to survive that. In the same way, the organisms which produce STDs have evolved to thrive in the conditions in the genitals. Wymspen (talk) 21:48, 26 June 2016 (UTC)

Well, that's part of the picture, but your last statement muddies the waters a bit on this issue. It's not just a matter of which tissues are viable environments for a pathogen, ultimately--after all, many different parts of the body might play host to the pathogen in sequence. The bigger driver here is the means by which the pathogen infects the body in the first place. In the case of STD's, many have evolved to exploit vulnerabilities in specialized cells which are found only in the surface tissues of the genitals--with anal sex the transmission occurs most commonly from micro (or not so micro) abrasions in the rectum, allowing pathogens direct access to the blood stream. It's also probably worth mentioning that the OP's premise is actually pretty flawed; a great many STDs are quite readily (and constantly) spread via oral sex--they just happen to be different diseases, by and large, from those which are more consistently spread by other sexual acts. Snow ^{let's rap} 00:51, 1 July 2016 (UTC)

2016 HO3

Our article on 2016 HO3 says "...this small asteroid is caught in a game of leap frog with Earth...". Why is this pointed out? Isn't that basically what most moons, including our own, do? I'm having trouble figuring out how this orbit is much different from our moon's orbit. Dismas|^(talk) 13:31, 26 June 2016 (UTC)

As the article explains: In its yearly trek around the sun, asteroid 2016 HO3 spends about half of the time closer to the sun than Earth is (that is, the asteroid is inside the Earth's orbit) and passes ahead of our planet, and about half of the time farther away (crosses outside Earth's orbit), causing it to fall behind. Its orbit is also tilted a little, causing it to bob up and then down once each year through Earth's orbital plane. AllBestFaith (talk) 13:37, 26 June 2016 (UTC)

For some reason our article doesn't mention it, but I've read that 2016 HO3 is well outside Earth's Hill sphere, the region it dominates in the attraction of satellites. The Sun is pulling more strongly on the object than Earth is. So really Earth and the object are simply orbiting the Sun on roughly the same orbit, pulling on each other along the way in such a way that the description quoted by AllBestFaith applies. Loraof (talk) 14:23, 26 June 2016 (UTC)

(ec) I think the issue here is that a quasi-satellite is outside the Hill sphere and therefore is not in a stable orbit around Earth. The best example is 2003 YN107, which went around the Earth like a moon at 0.1 AU, but then transitioned after a few years to a horseshoe orbit like many other quasi-satellites currently have. This satellite likewise, long term, exists in an equilibrium between horseshoe and moonlike orbits. I think the best way to visualize it is by comparing the video diagram for 2016 HO3 to that for Cruithne. Both asteroids have orbits with the same period as Earth; that doesn't change. But what differs is that one is constantly ahead of Earth when the two go near each other, while the other goes ahead and behind. If they were at a different point on their orbits around the Sun - but with the same orbits - they'd change apparent geometry. Wnt (talk) 14:26, 26 June 2016 (UTC)

2016 HO3 is not in Earth orbit, but in solar orbit in a 1:1 orbital resonance with the Earth's orbit, which happens to loop around Earth. It's outside Earth's Hill sphere and not gravitationally bound to Earth. This has an important consequence: 2016 HO3's "orbital period" around Earth of 1 year is far too short for an object at that distance. Edit: this is the synodic period. The siderial period is infinite, which doesn't obey Kepler's third law either. 2016 HO3 is not stationary relative to Earth, so if the sun disappeared it would probably still fly away. If the sun would suddenly disappear, the Moon would remain in orbit around Earth, but 2016 HO3 would fly away. PiusImpavidus (talk) 14:59, 26 June 2016 (UTC)

I'm trying to keep all my best faith that you're not just taking a jab at me by telling me what I've already read.

So, if you combine what I quoted plus what AllBestFaith quoted, you basically get all of what the article states. Great. Fine. Now, how is HO3 different from our own moon in the "spends half the time closer to the sun and half farther" part? Unless I'm wrong, our moon does exactly that. Why go through this leap frog analogy?

And the other explanations here about the Hill sphere make sense, so thanks for that. Dismas|^(talk) 20:25, 26 June 2016 (UTC)

• .

It has been argued that analogies are "the core of cognition", and they are a valuable way to introduce familiarity in technical explanations. The talk page for the 2016 HO3 article is where you try to persuade other editors not to use the "leap frog" analogy that NASA has used. AllBestFaith (talk) 11:35, 27 June 2016 (UTC)

@PiusImpavidus: It think this is a sort of complicated point, having to do with sidereal versus synodic orbital period. For example, the Moon masses 7.342E22 kg, Earth masses 597.237E22 kg, M = Me+Mm = 6.04579E24 kg total. Semimajor axis is 3.84399E8 m. G is 6.674E-11 N m2/kg2. Orbital speed is sqrt ( G * M / r) = sqrt (1049680 N M /kg) = 1024.539 m/s. To go roughly 2 * pi * 3.84399E8 m therefore takes about 2357402 s = 27.284 days, which given the approximation of a circular orbit is pretty damn close to the actual 27.321 day actual sidereal period. But actually look at the Moon and of course it gets an extra revolution a year that changes this value. With the small quasi-satellites, any "true" orbital speed is extremely slow, so this synodic correction dominates. At least, I think that's the explanation. Wnt (talk) 11:16, 27 June 2016 (UTC)

Indeed, the 1 year orbital period of 2016 HO3 is its apparent synodic orbital period around Earth (it slipped my mind in my previous post), which is a retrograde orbit, as much as it's its real siderial orbital period around the Sun. For retrograde satellites the number of synodic revolutions per year is always one more than the number of siderial revolutions (for prograde satellites like the Moon it's one less), and indeed the apparent siderial orbital period of 2016 HO3 around Earth is infinite, which again tells us it cannot be a real orbit. Viewed from Earth, 2016 HO3 is always in the same part of the sky relative to the distant stars. It only orbits the Earth in a rotating frame of reference in which the direction from the Earth to the Sun is fixed.

I hope this explanation doesn't make things even more complicated. PiusImpavidus (talk) 12:45, 27 June 2016 (UTC)

You put your finger on a problem with my explanation. How can 2016 HO3 always be in the same direction from Earth relative to the stars? That would mean the center of its orbit is not the center of Earth's orbit! But actually the asteroid loops around Earth at different distances, and eventually it goes into a horseshoe orbit, and I'm thinking if I played around watching simulations of the orbits it would eventually make sense that this has to happen in order for its orbit to be centered on the Sun, but I'm not at all sure about that.

But the motion also reflects that it doesn't have a real "1 year orbital period" since that orbit does change year to year; I suspect it differs from a stable 1 year orbit by just enough to account for its tiny "true" orbital speed. It varies between 38 to 100 times the distance of the Moon, so its orbital period should be something like 70^3/2 longer than the Moon's, or something like 43 years. Of course, using that simple approximation for a circular orbit in this situation is bonkers, but it's a point of comparison. Apparently it has been thought to have "revolved" around Earth for less than a century and will continue to do so for centuries, so this "period" is (barely) within an order of magnitude of actual relevant changes to its orbit. Wnt (talk) 13:09, 27 June 2016 (UTC)

The Earth's orbit is almost circular, but this asteroid has a distinctively elliptical orbit. The Sun is at one of the focal points of the ellipse, just as Kepler's first law dictates. The semi-major axis of its orbit is the same and its orbital period is too, exactly as Kepler's third law dictates. It is in a 1:1 resonance with Earth. And just as Kepler's second law dictates, it moves faster when closer to the sun than Earth and slower when farther away.

So suppose we look from a great distance onto the Sun's north pole. We put the face of a clock on the Earth's orbit in such a way that 2016 HO3 reaches its perihelion at 12 o'clock. When the Earth is at 12 o'clock, the asteroid also passes at 12 o'clock. As the asteroid is at perihelion, it moves faster than the Earth and overtakes it. At this point, it's below Earth on the clock face. Next, we wait 3 months. The Earth reaches 9 o'clock (moving counterclockwise). The asteroid has overtaken Earth and has just moved to a distance from the sun a bit farther than Earth. So it's ahead of Earth at nearly the same distance from the sun, and on the clock face still below Earth. Wait another 3 months, and the Earth is at 6 o'clock. The asteroid is at aphelion, moving slowly and being overtaken by Earth. It's farther away from the Sun, so on the clock face still below Earth. 3 months later, the Earth is at 3 o'clock, the asteroid is picking up speed and passing behind Earth, still below it on the clock face. Seen from Earth, the asteroid moves a bit to the east and west and to the north and south, in a figure-8 loop, as the orbits are not exactly in the same plane, but it always remains in the same general area of the sky.

2016 HO3 is not bound to the Earth and would, if the Earth, the Sun and the asteroid were the only parties involved, stay forever in this resonance, even if the Earth had no gravity acting on the asteroid. There is some gravitational interaction between both, and that is what locked 2016 HO3 into this resonance and keeps it there despite disturbances from elsewhere. Those disturbances exist, primarily Jupiter's gravity, flexing the asteroid's (and Earth's) orbit so that the apparent orbit of the asteroid around Earth changes. Precession of the orbits, which proceed at different rates for Earth and 2016 HO3, also causes some of the variation.

At some point in the future Jupiter and Saturn might pass at the right point in their orbits just as 2016 HO3 passes the right point in its orbit, which may speed up or slow down 2016 HO3 just enough to break out of its 1:1 resonance. It will then be in an orbit slightly wider or slightly smaller than Earth's orbit. When that happens, the Earth's gravity may put it in a horseshoe orbit, exchanging some orbital energy whenever it comes close. PiusImpavidus (talk) 19:17, 27 June 2016 (UTC)

All this stuff is a little TL;DR for me. Let me give my quick understanding, and someone can tell me if it's blatantly wrong.

• First of all, all these distinctions about which body is orbiting which are a little bit arbitrary, as these are all special cases of the three-body problem or even the n-body problem.
• That said, the difference between 2016 HO3 and the Moon is that, if the Sun weren't there, the Moon would still orbit the Earth pretty much the same way it does now, whereas 2016 HO3 would drift away.
• Defining what this counterfactual means precisely is a little tricky and, again, a little arbitrary. But (at least to a Newtonian approximation) you could probably say something like this: At some times (possibly all the time?) the velocity of 2016 HO3 wrt to the Earth is greater than its escape velocity from the Earth at that position, whereas this is never true of the Moon.

Is that basically right? --Trovatore (talk) 19:36, 27 June 2016 (UTC)

@Trovatore: At least the first thing I looked at makes sense: yes, it is going too fast! According to this site, the grooviest use of a Javascript that I've seen in some time, it is presently going at 3.9 km/s relative to Earth. That is actually 4x faster than the Moon! Every five hours it is moving something like 8.5 arc seconds relative to the stars, so certainly it is not stationary relative to the stars from Earth. I haven't figured out what all this means at this point... Wnt (talk) 14:50, 28 June 2016 (UTC)

If a person gets an orchiectomy & has an extra testicle (plus epididymis), then can this person's vas deferens re-canalize & attach to this extra testicle (or to this extra epididymis)?

Any thoughts on this? Futurist110 (talk) 17:52, 26 June 2016 (UTC)

The article Polyorchidism describes what can be sourced about the rare incidence of more than two testicles. A supernumerary testicle may be functional or non-functional. AllBestFaith (talk) 18:14, 26 June 2016 (UTC)

I am talking about one's vas deferens re-canalizing and attaching itself to one's extra testicle, though. Futurist110 (talk) 19:23, 26 June 2016 (UTC)

This is actually about logic, and the laws of probability, rather than about biology or medicine. It has to be hypothetically possible that this could happen - but that does not prove that it ever has happened or that it ever will happen. The human body is so variable, and unpredictable, that it is impossible to say that a given situation could never possibly happen. However, if you wanted to calculate odds of it actually happening, it would be as near to zero as makes no practical difference. Wymspen (talk) 20:15, 26 June 2016 (UTC)

So, would lifetime insurance for child support in the event that this will indeed occur be extremely cheap? Futurist110 (talk) 23:00, 26 June 2016 (UTC)

This is a question for an Actuary. Vespine (talk) 01:41, 27 June 2016 (UTC)

OK. Also, let me guess--is the question of whether or not it is possible to remove my *entire* vas deferens during an inguinal orchiectomy a question for a doctor? Futurist110 (talk) 02:22, 27 June 2016 (UTC)

I don't think reputable doctors do "elective" orchiectomies, as it's unnecessary surgery.

If so, then I'll go to a non-reputable doctor. Indeed, abortions certainly aren't the only surgeries which can be performed in 'back-alleys"! Plus, in regards to unnecessary surgery, how about doctors stop performing elective cosmetic surgeries, eh? After all, those surgeries are also unnecessary surgeries! Futurist110 (talk) 06:46, 27 June 2016 (UTC)

If you want to be sterilized that's what a vasectomy is for.

Except a vasectomy is certainly an extremely shitty form of birth control due to the fact that vasectomy doctors themselves certainly don't have full confidence in their own surgeries! Thus, how exactly can I have full confidence in these doctors' surgeries? Futurist110 (talk) 06:46, 27 June 2016 (UTC)

Also, I don't think insurers write child support insurance. I've certainly never heard of it. One major reason is probably the inherent moral hazard; someone could get child support insurance, then go out and have a ton of children.

What about Lloyd's, though? Also, how exactly would such fraud work with a prior orchiectomy? Futurist110 (talk) 06:46, 27 June 2016 (UTC)

Why are you so obsessed with child support and sterilization?

Because child support will certainly result in a lot of harm for me. Futurist110 (talk) 06:46, 27 June 2016 (UTC)

If you don't want to have kids, get a vasectomy or use other birth control.

The thing is, though, that all non-drastic forms of birth control can and sometimes do fail. Futurist110 (talk) 06:46, 27 June 2016 (UTC)

The probabilities of a vasectomy or properly-used, high-quality birth control failing are so minuscule they're not worth thinking about. --71.110.8.102 (talk) 05:08, 27 June 2016 (UTC)

Then how about vasectomy doctors man up and agree to pay all of their patients' child support for 18+ years in the event of a vasectomy failure, eh? After all, according to you, "[t]he probabilities of a vasectomy or properly-used, high-quality birth control failing are so minuscule they're not worth thinking about." Futurist110 (talk) 06:46, 27 June 2016 (UTC)

Have to agree with 71 and Wymspen here. You've been told repeatedly that the answers to much of your questions are, "yes it's thereotically possible" because with something as complex as what you're asking about, you can't rule out some real strange stuff happening. However the probability is very low. For some of your scenarios, probably so low that as also pointed out before, it's questionable why you would worry about them when you could theoretically have other strange stuff such as the surgeon impregnating themselves (if female) or someone else somehow or other fantastical scenarios.

Wouldn't a surgeon impregnating herself be impossible considering that one doesn't actually have mature sperm in one's testicles, though? Futurist110 (talk) 06:46, 27 June 2016 (UTC)

You still don't seem to get it. When you're talking about exceptionally low probabilities and complicated biology, nothing should be see said to be impossible. And who said anything about the sperm coming from the testicles anyway? Why are you ignoring the other possibilities like sperm present on the penis or the million and one different other scenarios you can come up with? Nil Einne (talk) 13:22, 27 June 2016 (UTC)

I don't think you can ever hope to have enough info to actually calculate probabilities for many scenarios but logic would suggest some of them are more likely, particularly when combined. I believe you're past puberty, so remember it's theoretically possible you already have a child somehow that you don't know about. (Actually I think this was mentioned before too.) I'm fairly sure that both 71's and Vespine's points on insurance have also arisen before. And I aslo believe it's been pointed out that many failure rates include cases where proper advice wasn't followed by the patient (e.g. on refraining from sexual intercourse and followups) or non pregnancy related failures (detected in the followups) so you should use caution when reading failure rates.

The problem is, though, that apparently unlike many other body parts, the vas deferens--or at least its epithelium--certainly appears to be capable of regenerating and of growing back. Futurist110 (talk) 06:46, 27 June 2016 (UTC)

Sure but you're not just talking about it growing back, but it attaching to an extra testicle and this system (including the testicle) actually functioning sufficiently to result in impregnation. Nil Einne (talk) 13:22, 27 June 2016 (UTC)

Notably, on 71's points, you'll probably find it easy to convince a doctor to do semi-regular checks (i.e. after those normally recommended) to attempt to detect failure than you ever will for an elective orchietomy

The thing is, though, that a doctor certainly isn't going to pay all of my child support for 18+ years for me in the event of a vasectomy failure! Thus, this doctor should certainly stop whining and complaining and instead become willing to perform an elective orchiectomy on me. After all, the only acceptable alternative to this for me is getting an extremely dangerous "back-alley" orchiectomy (in place of a safe orchiectomy). Futurist110 (talk) 06:46, 27 June 2016 (UTC)

You're missing two key points. One is that doctors are bound by medical ethics, not what some random person thinks. Two is that as already explained what the doctor is and isn't willing to pay for is also irrelevant. Your back-alley orchiectomy isn't going to prevent pregnancy, Perhaps your back-alley orchietomy actually has a greater chance of resulting in pregnancy. Who knows?

Also you keep bringing up child support. I initially thought you had some sort of phisophical objection to fathering a child based on things you've said in the past. I'm not sure if you're hanging out in men's rights sites too much or something, but if this is all about money, and your userpage suggests you live in the US, have you considered the possibility that tomorrow you may somehow cause an injury to someone which will result in you having to pay a similar amount for the rest of that person's life which may be longer then the 18 years normal for child support? (E.g. you're too busying fretting about getting someone pregnant that you walk into a ladder and cause a serious spinal injury.) Or the possibility that something which happens during whatever operation could result in something (not pregnancy) which will again similar end up with you winding up with a similar financial burden? Or that these questions may somehow wind up with you incurring such a financial burden?

And maybe I shouldn't say this since I actually agree with Wnt that you're skirting very close to the line here (although not sure it's advice from a surgeon you need), but have you considered that having sex, as with many many things, has many risks of varying probablities besides pregnancy. And that some of these risks would result in a financial burden which in some cases would match child support? And why are you so worried about a financial burden when there are risks, some vastly more likely than some of the stuff you've suggested, of you dying? You're not going to keep your money when you die.

Nil Einne (talk) 13:42, 27 June 2016 (UTC)

and if you're really so concerned, a vasectomy doesn't have to be "or". Nil Einne (talk) 06:12, 27 June 2016 (UTC)

What exactly do you mean by "or" here? After all, even 2+ forms of birth control can simultaneously fail! Futurist110 (talk) 06:46, 27 June 2016 (UTC)

Yes, but as I said when you are talking about exceptionally unlikely probabilities, you need to consider that you could already be a father and that even death and the burning of your body isn't going to rule out the possibility you somehow becoming a father in the future and the millions of other such scenarios. Have you even researched vasectomy failures rates considering the points outlined? What about failures rates of properly used birth control (say condoms + birth control pills used consistently etc)? What about failure rates of tubal ligation? Have you tried to combine these failure rates (bearing in mind their failures should be mostly independent)? Nil Einne (talk) 13:37, 27 June 2016 (UTC)

If you are that worried about the possibility of fathering a child, just don't have sex. That is a 100% guaranteed form of birth control. Wymspen (talk) 07:21, 27 June 2016 (UTC)

According to this well-documented case study chastity is not a 100% guarantee. --Cookatoo.ergo.ZooM (talk) 10:16, 27 June 2016 (UTC)

More seriously, I strongly disagree as already outlined above. The problem is the OP is talking about exceptionally low probabilities in some cases. So low, that the possibility of pregnancy without sex shouldn't be ruled out. For example as I said above, the OP is past puberty. Even without masturbation (and sex), they've surely released sperm. The possibility that one of these could or will somehow impregnate/d someone must surely be very low, especially without intentional action, however it can't be ruled out anymore than some of the other fantastical scenarios the OP has came up with at various times. More likely, although you could say male rape involves having sex, it's not something the OP may ultimately have control over and frankly the probability seems more likely than even the OP's scenario here. In fact the possibility it's already happened and the OP doesn't know may by itself be more likely. Nil Einne (talk) 14:09, 27 June 2016 (UTC)

This has gone off the rails into personal medical advice. It's one thing to speculate about these things in the abstract, but if you want to make decisions about your vas deferans you need to talk to people who have your medical history and situation in front of them. Wnt (talk) 10:43, 27 June 2016 (UTC)

I agree the OP should seek help, but I'm not sure if it's help from someone who specialises in male reproduction. Nil Einne (talk) 13:37, 27 June 2016 (UTC)

Also we should note that child support does not necessarily end after 18 years. In some states, it is 21; in some, college costs must be paid; in some, disabled children must be supported in adulthood.[1] Rmhermen (talk) 22:19, 27 June 2016 (UTC)