Wikipedia:Reference desk/Archives/Science/2012 September 7

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September 7

Hormonal contraception and pregnancy

So while hormonal contraceptives are relatively decent at preventing pregnancy, what happens in the event that either the woman becomes pregnant sometime between soon before starting taking them and when they become active or while actively using them? What effects do the contraceptives have on the pregnancy? Ks0stm ^{(T•C•G•E)} 01:55, 7 September 2012 (UTC)

The pill (in various versions) doesn't necessarily work by preventing pregnancy. It can work by causing menstruation whether or not fertilization or implantation have occurred. It is an abortifacient. μηδείς (talk) 04:35, 7 September 2012 (UTC)

That was news to me, Medeis. I am having difficulty in finding any mention in the articles you reference to this function of the pill. One only menstruates on stopping taking the active-component pill, which is the purpose of the placebos in most monthly packs. And the primary mechanism of the pill is the prevention of ovulation. See:

Combined oral contraceptive pills were developed to prevent ovulation by suppressing the release of gonadotropins. Combined hormonal contraceptives, including COCPs, inhibit follicular development and prevent ovulation as a primary mechanism of action

What have I missed? Bielle (talk) 04:50, 7 September 2012 (UTC)

Indeed. This seems like a complete fabrication. Combined_oral_contraceptive_pill#Mechanism_of_action mentions nothing at all about "causing menstruation whether or not fertilization or implantation have occurred." Indeed, AFAIK, many hormonal-based birth control stops menstruation by stopping ovulation altogether, though many formulations use placebo pills to allow normal menstuation at times when ovulation isn't happening. Extended cycle combined hormonal contraceptives don't have any menstruation at all. It should also be noted that this is often called "withdrawal bleeding", as it isn't true menstruation, as no ovulation occurred. I'm quite interested where Medeis got their information from, as birth control is half a century old, and its mechanisms have been known for quite some time. --Jayron32 04:58, 7 September 2012 (UTC)

Back to the original question: according to the Mayo Clinic web site, the likelihood of a detrimental effect on the pregnancy or the foetus is small. However, the linked article suggests stopping taking the pill if you believe you are pregnant until you know for sure, and use other birth control methods until you do. Bielle (talk) 04:58, 7 September 2012 (UTC)

Oh yes, and the article also says: See your doctor. Bielle (talk) 05:01, 7 September 2012 (UTC)

Haha fortunately that won't be necessary given my gender prevents me from getting pregnant (supposedly). But thanks, that was pretty much the information I was looking for. Ks0stm ^{(T•C•G•E)} 05:11, 7 September 2012 (UTC)

From the NIH[1]: "Combinations of estrogen and progestin work by preventing ovulation (the release of eggs from the ovaries). They also change the lining of the uterus (womb) to prevent pregnancy from developing..." I had always thought that was the "main" mechanism, but preventing implantation is obviously a hugely important mechanism. μηδείς (talk) 16:18, 7 September 2012 (UTC)

Ok, but nowhere in there does it use the term "abortifacient," nor does it indicate that such birth control leads to the abortion or miscarriage of an already formed embryo, fetus, or even fertilized egg. It says that it prevents pregnancy from developing, which is just a tautological definition of birth control. --Jayron32 18:58, 7 September 2012 (UTC)

Well, I did use the word abortifacient meaning only that it will effectively expel a fertilized egg, rather than letting it implant or remain implanted. The rest, embryo, miscarriage, is what you have apparently read into it. I nowhere said it gets to that stage. That does clarify to me why you accused me of "complete fabrication". Next time please only make that charge on what I have myself actually said, or perhaps be polite enough to ask for a clarification? μηδείς (talk) 20:53, 7 September 2012 (UTC)

This appears to be rapidly heading into serious error. Medeis, your first response to the question consisted of three sentences:

The pill (in various versions) doesn't necessarily work by preventing pregnancy. False. Preventing pregnancy is exactly the way it works whether the prevention is due to the principle mechanism of prevention of ovulation, or secondarily, by the prevention of the formation of a lining to the uterus.

It can work by causing menstruation whether or not fertilization or implantation have occurred. False. It prevents menstruation because it has prevented ovulation.

It is an abortifacient. False. Even the National Catholic Register is clear on this. From the article What an abortifacient is -- and what it isn't:

The most important point that emerges from all of this research is that, so far, there is no scientific evidence that any FDA-approved contraception is capable of destroying an embryo. To say that any of these drugs are abortifacient is not only misleading, it does a profound disservice to women who find themselves in a situation where they might have to use one of these drugs or devices. In short, if it isn't at least an embryo, it cannot be aborted. Bielle (talk) 21:39, 7 September 2012 (UTC)

Equating the contraceptive pill (which includes the morning after pill) to an abortifactant is grossly misleading. Depending on which hormones, contraceptive pills work by suppressing luteinizing hormone release and inhibiting ovulation. Progesterone also decreases the chance of fertilization itself by decreasing the effectiveness of sperm and inhibiting implantation.^{ISBN 0323033091, page 390} In other words they prevent ovulation itself.^{Tekoa King, Mary C. Brucker, Pharmacology for Women's Health, page 885.}

As to the original question, there are cases of pregnancy before the pill takes affect. The reasons that they fail when being taken correctly are complicated and I think not well understood. Shadowjams (talk) 22:45, 7 September 2012 (UTC)

Indeed. I know personally of at least two people who were born while the mother was taking contraception as indicated. Me and my brother. It is rare, but it happens. --Jayron32 23:03, 7 September 2012 (UTC)

Wow, there seems to be a lot of underlying emotion here. I don't give a fuck whether anyone wants to define something that kills a fertilized egg an abortifacient or not. I am not interested in debate. I think I have clarified my point not only enough, but too much. This is not the place for debates. Let's try to get back to sources please. I am not one. μηδείς (talk) 23:06, 7 September 2012 (UTC)

Just an aside: you do little to dispel the notion that you are not yourself emotionally attached to the answers by putting in curses in italics and all bold. As far as I can tell, you're the one using emotional language here — everyone else is, fairly calmly, just trying to tell you that you're incorrect. To this disinterested reader it appears you are the one who is reacting to this emotionally, not the others. --Mr.98 (talk) 01:34, 8 September 2012 (UTC)

The pill doesn't kill a fertilized egg. That's the point, and a fact, and supported by the unemotional sources, one of which is not me. Bielle (talk) 23:17, 7 September 2012 (UTC)

Yes, that's absolutely right. But I am not aware of anything, actually, that directly kills a fertilized egg as such, and I don't think I said it did so. By abortifacient I meant what the word seems to mean at that stage (and as it is used re RU486, a name which will show my age, I guess), it causes the zygote to be aborted rather than implanted. μηδείς (talk) 01:18, 8 September 2012 (UTC)

RU486 is an abortifactant and there's a large difference between its mechanism of action and the contraceptive pill's. RU 486 works well past implantation, whereas progesterone based pills do not. Shadowjams (talk) 06:04, 8 September 2012 (UTC)

The fact that it also works as a medical abortifacient for two months past fertilization in no way negates the fact that it prevents implantation if taken early enough. This is logic 101. You might as well say a herbicide doesn't kill acorns because it also kills oaklings. μηδείς (talk) 06:16, 8 September 2012 (UTC)

From some reliable sources:

Gabbe: Obstetrics: Normal and Problem Pregnancies, 6th ed., 2012: Oral contraceptives use before or during pregnancy is not associated with fetal loss. The same applies for injectable or implantable contraceptives. (from Chapter 26)

Martin: Fanaroff and Martin's Neonatal-Perinatal Medicine, 9th ed., 2010: Oral contraceptive agents | No association between first-trimester exposure and malformations. (from Table 38–5, Effects on the Fetus of In Utero Exposure to Physician- or Self-Administered Therapeutic Agents)

Garfunkel: Pediatric Clinical Advisor, 2nd ed., 2007: Hormonal contraception inhibits ovulation, thickens cervical mucus, inhibits sperm capacitation, slows tubal motility (delaying sperm transport), disrupts transport of the fertilized ovum, and causes endometrial changes that hamper implantation.

These and other sources I've reviewed lack strong evidence of significant effects on a fetus; in contrast, oral contraceptives can prevent implantation of a fertilized egg, as noted above by others. The original question was broader, i.e. "effect on the pregnancy", and I have found no evidence of adverse effects on the pregnant mother. It is clear that oral contraceptives can increase a woman's risk of blood clots, and pregnancy can have this effect, too. -- Scray (talk) 02:46, 8 September 2012 (UTC)

Regarding the controversy above, we do seem to have a relevant article: Beginning of pregnancy controversy. This section of that article describes statements from major medical associations defining uterine implantation as the beginning of pregnancy (i.e. that prevention of implantation would not be considered abortifacient). -- Scray (talk) 03:00, 8 September 2012 (UTC)

I'm not a doctor or expert, but from answering this question and other sources I've looked at, the primary mechanism of progesterone based pills seems to be preventing ovulation in the first place, which means an egg isn't ever even fertilized. There is some suggestion that implantation is impeded by the same too, although at much less frequency. It should be noted too that fertilized and implanted eggs are regularly dispelled by the body. And by no modern definition is a fertilized egg considered an embryo absent implantation. I'm aware certain doctrines believe conception to be the critical moment in terms of life, but even those definitions don't regularly call a fertilized egg an embryo. Shadowjams (talk) 06:00, 8 September 2012 (UTC)

Implantation has nothing to do with it being called an embryo, Shadowjams, just cell division. See embryo and embryo transfer. μηδείς (talk) 06:08, 8 September 2012 (UTC)

Does the egg divide before implantation? Shadowjams (talk) 06:11, 8 September 2012 (UTC)

Yes - implantation occurs during the blastocyst stage, after 6-7 rounds of cell division (cell divisions have actually ceased to be synchronous at that point, so giving an exact number is not possible). Someguy1221 (talk) 06:16, 8 September 2012 (UTC)

See also Implantation (human embryo). μηδείς (talk) 06:20, 8 September 2012 (UTC)

I don't want to get too much in to this dispute, but from what I can tell, this hasn't been mentioned yet. The claim that preventing implantation is an important part of the mechanism of COCP seems to be directly disputed by our article, supported by a reliable source:

Insufficient evidence exists on whether changes in the endometrium could actually prevent implantation. The primary mechanisms of action are so effective that the possibility of fertilization during COCP use is very small. Since pregnancy occurs despite endometrial changes when the primary mechanisms of action fail, endometrial changes are unlikely to play a significant role, if any, in the observed effectiveness of COCPs.

I didn't look at the sources presented above but from what was presented here, it sounds like they are just suggesting the possibility rather then implying it's a significant part of the mode of action.

Nil Einne (talk) 15:40, 8 September 2012 (UTC)

• Our article Morning after pill#United States legal and ethical controversies suggests that the Catholic church has been maintaining a doctrine that several methods of emergency contraception can cause abortion if the initial contraceptive function fails - citing e.g. [2]. Now that publication arouses a certain degree of skepticism when it uses a 1968 reference for its statement! What this source identifies as problematic is progestagens, Depo-Provera, Norplant, and intrauterine devices. At present I have not evaluated these claims in detail; as they concern the fate of rare eggs which escape the initial contraception to become fertilized, I'm not sure how easy it will be to find information about them. Wnt (talk) 21:06, 11 September 2012 (UTC)

One Severe Pain + Self-Applying Pain elsewhere = Less Pain Overall?

In the subject/headline, I am talking about how, when one is in severe pain, if he or she applies pain elsewhere, let's say, by biting his finger, the first pain seems to become less severe. In theory, kind of mathematically, applying the second pain would make a person's overall pain rating higher, but, in practical terms, it seems to help. So, why is this the case? Any help would be appreciated. Thanks. — Preceding unsigned comment added by 99.124.131.25 (talk) 04:52, 7 September 2012 (UTC)

What you describe is reminiscent of gate control theory of pain - that thicker, slow nerve fibers carrying pressure, vibration, and/or dull pain might inhibit thinner, fast nerve fibers carrying "sharp" pain. The article I linked, and those linked from there, may interest you. -- Scray (talk) 05:27, 7 September 2012 (UTC)

I can't say I have a reference for this but I thought it was simply a question of "attention", by biting your finger you are drawing attention away from the other pain. Not the same thing but possibly related I've read that post operative children who are allowed to play video games request far fewer doses of pain medication then kids who do not have access to that kind of distraction. Vespine (talk) 06:17, 7 September 2012 (UTC)

This one [[3]] looks about right as far as I know. Of course a smarter person would achieve the same thing by clenching their fist on an icecube... pain can be gated by cold. --BozMo talk 10:05, 7 September 2012 (UTC)

It's kind of like bandwidth but the "newer" pain gets priority, at least momentarily.165.212.189.187 (talk) 12:27, 7 September 2012 (UTC)

If you want to do some reading, the phenomenon is known in the literature as pain-induced analgesia. It is widely recognized, but its mechanism is not all that clear. This paper provides some evidence that the effect is mediated by the brain's intrinsic reward circuitry. Looie496 (talk) 00:07, 8 September 2012 (UTC)

The "gating" Scray referred to may play a part, but the OP was specifically asking about novel pain's effect on existing pain. So Looie's reference may be more specific to the question. Another term, covering this question is Diffuse noxious inhibitory control. -Anthonyhcole (talk) 06:36, 8 September 2012 (UTC)

Agreed - your response and Looie496's are much more direct answers. I meant for my response to make it clear that what I was describing might interest the original querent, but was not the same thing. -- Scray (talk) 23:10, 8 September 2012 (UTC)

Feces and STDs

I apologize for the disgustingness of this question, but this is a serious and legitimate scientific question:

Can one get STDs (such as AIDS and other STDs) from having one's feces accidentally get inside one's urethra? For the record, this question is purely hypothetical and assume that the person in my hypothetical scenario does not have any STDs at all. Futurist110 (talk) 05:47, 7 September 2012 (UTC)

You can get infections from getting feces in your urethra; bacteria that thrive in the colon, like E. coli, can cause urinary tract infections. Parents of girls are reminded, when changing diapers, to take care when wiping to avoid exactly this problem. However this is not STDs. AFAIK, if you have a sexually transmitted disease, you can't give it to yourself. If the particular disease you have is transmittable by your feces, you can't then give it to yourself through your urethra if you already have it. Some STDs may be transferable to other people through feces, though it sounds like you are asking if you can give yourself an STD this way. You can't give it to yourself unless you already have it, and thus, if you have it, you aren't giving yourself something you already have. My head hurts trying to figure out exactly what you are asking. I apologize if I misunderstood your question, but it sounds like nonsense as it is written. Could you clarify? --Jayron32 05:55, 7 September 2012 (UTC)

I'm asking a hypothetical scenario:

A person who doesn't have any STDs at all accidentally puts some of his own feces inside his own urethra. Both the feces and the urethra came from his own body. Can he get any STDs or any other serious health problems this way? Futurist110 (talk) 05:59, 7 September 2012 (UTC)

You can most certainly be a host to many diseases in your feces without actually being "infected" by those diseases. So definitely YES to the 2nd question, serious health problems yes, as jayron mentions, feces in urethra is definitely not good, it's a very common (probably most common) and easy way to get a urinary tract infection. However, whether any of those diseases which you can carry around in your feces are actually STDs, that sounds far less likely... Vespine (talk) 06:08, 7 September 2012 (UTC)

Sorry, that first sentence is very poorly worded by me, you don't have diseases in your feces, you have bacteria in your feces some of which are potentially infectious and disease causing. Vespine (talk) 06:12, 7 September 2012 (UTC)

Yeah, that's what I thought you meant, Futrurist. In that case, if a person doesn't already have the infectious agent inside their body, then that infectious agent cannot get into their feces. If the infectious agent can't get into their feces, it couldn't get into their urethra from that feces. If they already had the agent that causes the STD, then they already have it. To put it simply: you can't give yourself the clap, because if you don't already have it, you can't pass it on, and if you do already have it, then you already have it. Logically, it makes no sense the scenario you are asking about. --Jayron32 12:46, 7 September 2012 (UTC)

The article on STIs, also known as STDs says: In general, an STI is an infection that has a negligible probability of transmission by means other than sexual contact, but has a realistic means of transmission by sexual contact (more sophisticated means—blood transfusion, sharing of hypodermic needles—are not taken into account). Thus, one may presume that, if a person is infected with an STI, e.g., chlamydia, gonorrhea, genital herpes, it was transmitted to him/her by means of sexual contact. That would seem to be a "no" to the original question with respect to STDs. Bielle (talk) 06:17, 7 September 2012 (UTC)

There is exactly one disease I know of that you can "catch" from your own feces - pork tapeworm, which is far more harmful if the eggs in the feces are ingested causing cysticercosis than initially when pork meat is eaten causing taeniasis (adult parasites in the intestine which lay those eggs). Of course, I don't know every disease! But I haven't heard of a STD like that. But there are examples of intestinal worms being transmitted sexually, [4][5]; also intestinal protozoa can be STDs [6] and some protozoa have interesting life cycles, so I can't rule out the possibility such a thing could happen - I just haven't heard of it. Also, the scenarios I've described of are for infection by mouth - I don't know if any of these can be caught via the urethra. Wnt (talk) 16:05, 7 September 2012 (UTC)

To be fair, a point Bielle raised above needs to be re-raised: an STD/STI is generally limited by definition to a disease whose mode of transmission is of a sexual nature only. To quote it again as Bielle has done "an infection that has a negligible probability of transmission by means other than sexual contact, but has a realistic means of transmission by sexual contact". The "negligible probability of transmission by other means" would preclude infections that you can catch otherwise that also one could catch sexually. Intestinal worms can be transmitted by other means, so the fact that you could catch them through some form of sexual activity doesn't make them an STD, at least by the definition we're working with above. which also raises the question of how one could have sexual contact between one's own feces and urethra. I've been told to do that many times in my life, but I never thought it physically possible. --Jayron32 18:53, 7 September 2012 (UTC)

The point Bielle raised is incorrect (no fault of Bielle's - it's our article that is wrong). If you look at the linked article, that statement is unsupported by any source. I started to make a long list of Pubmed IDs as evidence for my claim, then realized that links to relevant pages at the CDC, WHO, and Mayo Clinic should suffice. Listed STD/STIs there include HIV, HAV, HBV, HPV, Shigella, Cryptosporidium and Giardia lamblia all of which are often transmitted non-sexually. A better definition: "Sexually transmitted diseases (STDs) are infections generally acquired by sexual contact." Perhaps we should improve our article. -- Scray (talk) 01:04, 8 September 2012 (UTC)

Discoveries in space (not just developed for the space exploration)

What, if any, are the discoveries made because humankind can travel to space? Excluding discoveries made to travel to space. OsmanRF34 (talk) 13:26, 7 September 2012 (UTC)

Effect of spaceflight on the human body has some important stuff. None of these developments could have been made had people not actually been in space. Most of the technologies used to get to space already existed on Earth for other purposes: for example, many of the rocket engines used for spaceflight were adapted from weaponry. See Redstone (rocket family), which shows how the first rockets for manned spaceflight developed from ballistic missle rockets. But there have been numerous experiments done in space, such as longterm effects of Weightlessness on various biological and non-biological processes, that could not be done elsewhere. --Jayron32 13:38, 7 September 2012 (UTC)

Didn't it confirm that all objects fall at the same rate? When a feather and heavy object were dropped on the moon - not sure on the details, although I was shown the clip in class. 86.138.171.71 (talk) 14:58, 7 September 2012 (UTC)

Well, but that has also been trivially shown to be the case on earth. Dropping two objects in a vacuum can be done on Earth as well as the moon. That's a fairly trivial experiment. There have been a lot of data gathered on physiological changes to living things: plants, animals, and humans, and on the changes in how many chemical reactions happen in weightlessness. But dropping a ball and a feather is hardly a significant scientific discovery from space travel. --Jayron32 15:03, 7 September 2012 (UTC)

Is the question intentionally limited only to discoveries related to manned spaceflight? Many robotic probes established basic scientific facts - like the characterization of the magnetic field of Jupiter by Voyager - that would not have been possible using Earth-based observation. Nimur (talk) 15:07, 7 September 2012 (UTC)

Nimur beat me to the gun with his question. Space research is one place to look but are you meaning to restrict to discoveries arising from research by or on humans while they are in space? Does being on the Moon count as "space"? A good deal of our knowledge of the geology of the Moon has come from the Apollo program. The Voyager program and Hubble Space Telescope have made a large number of discoveries in astronomy but perhaps they are not what you mean. Thincat (talk) 15:12, 7 September 2012 (UTC)

The question is not limited to humans, just excluding things discovered on Earth for leaving the same. OsmanRF34 (talk) 15:50, 7 September 2012 (UTC)

A good place to start would be our article on Scientific research on the International Space Station. Most of that article except the introduction appears to unfortunately be a list of red links, but each one has a reference to a webpage describing the experiment if you are interested. For a general overview the introduction seems reasonable. Equisetum (talk | contributions) 17:56, 7 September 2012 (UTC)

coffee buzz

I've got a cup of coffee on my desk, made with a drip brewer with a paper cone filter, from dark roasted beans ground maybe a little bit finer than usual for drip brewing, with a few ml of ultra-pasteurized half-and-half stirred in. The damn thing is making a periodic buzzing sound like some kind of insects, definitely audible if I put my ear next to the cup. The buzz starts around 1 khz and descends over about 1-2 seconds to about 500 hz, then jumps back up to 1 khz. (The pitches are rough guesses based on comparing with the 440-hz dial tone from my phone).

What is going on??? I have heard buzzing coming from coffee before, but sort of steady, and I noticed it most when the coffee had powdered creamer, and I figured it was gas bubbles escaping from the creamer. But this has liquid cream and I've never heard this periodic repeating before. I might try making an audio recording and uploading it.

A quick web search about coffee noise finds mostly hits about noisy coffee-making machines.

67.119.15.30 (talk) 17:25, 7 September 2012 (UTC)

I had a similar experience once (with tea, not coffee). The cause turned out to be a tiny, almost-invisible, crack in the cup that the hot liquid was trying to squeeze through. AndrewWTaylor (talk) 17:59, 7 September 2012 (UTC)

If the bottom of the cup is wet, and it is resting on a smooth surface, you may be hearing a sound caused by the air trapped under the cup expanding as it gets warmed, and finding a way out as a stream of tiny bubbles. I've noticed a similar effect with a cold drinks can - though presumably the air would have been going the other way. AndyTheGrump (talk) 18:05, 7 September 2012 (UTC)

Most common cause of this is the cup, not the coffee. One end of the handle has cracked, possibly by a void during manufacture, and there is air trapped inside. Water from its last washing forms a seal. When you add hot liquid inside, the trapped air is heated, expands and is forced out through the crack. This blows bubbles through the water seal, which are just about audible. As they're small bubbles, this is quite a high frequency. Sometimes you can see it happening. Andy Dingley (talk) 18:09, 7 September 2012 (UTC)

While I think the explanations above are the most likely, another possibility is that the coffee-filled cup is just at the resonant frequency to magnify some random vibration in the office, thus increasing the magnitude to the point where you can hear it. StuRat (talk) 18:36, 7 September 2012 (UTC)

Andy's idea about the cup resting on a surface definitely isn't the explanation. The sound didn't change when I lifted the cup to listen to it. I have doubts about the other explanations but can't rule them out. This was a ceramic cup that might have some invisible cracks. I may try some other time with a plastic cup. The sound did get quieter and lower pitched as the coffee cooled down to drinking temperature. 67.119.15.30 (talk) 21:14, 7 September 2012 (UTC)

OK, sounds like you have eliminated the possibility I mentioned, as well. StuRat (talk) 21:16, 7 September 2012 (UTC)

1 Photon in all 360 degrees

When something emits one photon in empty space does that only go out from origin in 1 specific directional line or spherically in all directions like an explosion?165.212.189.187 (talk) 17:47, 7 September 2012 (UTC)

In the particle model, it goes in one direction only. However, the wave-particle duality of light means that it can sometimes be thought of as a wave, which can be focused in one direction, but spreads out from a line. See double-slit experiment for a discussion of this weirdness. StuRat (talk) 18:34, 7 September 2012 (UTC)

Light is neither a particle nor a wave. It is just light. In some situations, it is helpful to model light like a particle, so we have photons for those situations. In some situations, it is more helpful to model light as a wave. The situation StuRat notes is but one example of where both models break down. All models are inadequate in some way, and neither the photon model nor the wave model are, of themselves, capable of adequately covering all of lights behavior. To the OP's question: a single electron can only emit a single photon in a single direction, so all photons have directionality. An object that contains umteenmillions of electrons will emit in all directions, giving the effect of spericality the OP indicates. So, one needs to be very careful how one defines the terms. If we're talking about the sun giving off light, it is most helpful to think of it as non-directional: the light goes out in all directions. If it is a single electron emiting a single photon, then we have a different situation. --Jayron32 18:47, 7 September 2012 (UTC)

It also helps us to refine the model: why is something emitting a photon? Often, a photon emission is stimulated by an external event. If so, the symmetry of the problem can be well-defined; the directionality of the source will have some correspondence to the direction of the emitted photon; calculating that correspondence is a scattering problem. In other cases, a photon is emitted spontaneously. If the source emitting the photon is an idealized, spherically-symmetric object, then the photon is equally probable to be observed in any direction. Where it will actually be observed is a different question altogether - and there's where we wrap up all the complexity that we call wave-particle duality. When lots of photons are emitted, we can discern a radiation pattern, which gives us information about the process that is causing the energy to be emitted; this may reveal structure and other physical information about the source. Nimur (talk) 19:07, 7 September 2012 (UTC)

Well, that gets down to the difference between properties of quantum behavior as observed in the bulk versus observed individually. An event, like the spontaneous emission, that you note will have an equal probability in all directions. Such an event, when it occurs a gajillion times in one place, will result in spherical emission of light equally in all directions, but when observed per particle, each one emission will have directionality. Lots of quantum mechanical behavior has this problem that the behavior on the individual level is not particularly helpful when trying to figure out the behavior of a system of events. The aforementioned double slit experiment is a classic example of the sort of apparent paradoxes this sort of thinking introduces. --Jayron32 19:30, 7 September 2012 (UTC)

The model I prefer is that a photon, or any other subatomic particle, is a particle, but with a probability function associated with it. This allows you to say it is more likely to be in some spots than others, but you still never know exactly where it is. And note that the probability may not just apply to the three physical directions, but possibly also to temporal dimensions and dimensions beyond those we are familiar with. StuRat (talk) 20:31, 7 September 2012 (UTC)

Yeah, that works except when it doesn't. Particles don't diffract, for example. Only actual waves do that. That's the problem with any model of light: None of them work all the time. There are some really obvious times when thinking about light as a particle leads you to very wrong places. And other times where it is the only reasonable conclusion. The answer, from my perspective, is to not try to force the answer. Recognize that all human knowledge is a model, even down to the most fundemental level (in a way, that's what knowledge is: the construction of models of the world inside our brains), and that with light, we're stuck with the fact that nothing in our sensory experience prepares us for light, so there is no good single analogy. So we need to use different models for different applications. Yeah, it sucks, but it is what it is. We marry the models with concepts like Debroglie wavelength and wave particle duality, but a lot of that stuff is just the mathematical way of saying "We don't have a good single analogy to make this work for us." In many ways, the exhortation to "shut up and calculate" is valid. In other words, ours is not wonder why, ours is just to do or die. It is what it is. --Jayron32 21:58, 7 September 2012 (UTC)

It's not necessarily true that particles don't diffract. There are some highly contrived theories of QM that include diffracting particles, and the few physicists who prefer them do so because they hate the idea of waves being a physical thing. Even Isaac Newton's Corpuscular theory of light accurately predicted the brightest diffraction line in something reminiscent of the single-slit experiment, that was popular circa 1700. I don't have links for this because it's something I read in a book when I was in college. The purely-particle QM theory has an article somewhere on Wikipedia. Someguy1221 (talk) 06:29, 8 September 2012 (UTC)

Well, let me clarify a bit. No particle you have ever had sensory experience with has ever diffracted. That is, part of the normal working definition of "object" for people doesn't include the property "can diffract". The very fact that you call the models "highly contrived" is a clue that it is basically playing fast-and-loose with the definitions. Sure, I can invent a thing that I call a "diffracting particle" and then work with that, but once you redefine common terms, you haven't really changed the models, you've just redefined the language used to describe it. If having a "diffracting particle" makes a model work for whatever purpose, that's fine, but it doesn't make it a more accurate model, per se, nor does it make it any better at describing light. --Jayron32 14:37, 8 September 2012 (UTC)

As far as I recall though for an individual quantum particle the 360 degrees bit is wrong, its 720 for a quantum particles isn't it? something to do with the double cover of SU2 by SO4. Or put it another way a 360 degree rotation is not topologically equivalent to staying still whereas a 720 rotation is. So you can only be sure you are back where you started if you turn around twice and it has to go in all 720 degrees of possibility. --BozMo talk 21:04, 7 September 2012 (UTC)

I think you may be over-analyzing the Q a bit. StuRat (talk) 21:11, 7 September 2012 (UTC)

I think, you're thinking of spinors and spin 1/2 particles. That 720 degrees isn't directly relevant to what is being discussed here.Phoenixia1177 (talk) 00:54, 8 September 2012 (UTC)

• Here's a way to focus on the weirdness: if you don't know what happened to the particle(s) that emitted the photon, then you view it as a wave (indeed, one which can diffract with itself, as has been said). But if you know what happened to that particle, then you know by conservation of momentum which way the photon went. And photons that you know where they went ... won't diffract with each other (the double-slit experiment) So not only is the light initially seeming to move in a spherical wave... so is the particle. Wnt (talk) 23:47, 7 September 2012 (UTC)

There is more than just the 360° too, it is actually 4 pi steradians of solid angle. The wave is not confined to two dimensions. And one interpretation of this situation is that until the photon is absorbed you cannot know which direction it has traveled in. The direction of recoil of the the emitter is entangled with the changed momentum of the absorber of the photon. You can also look at the Uncertainty principle with this. With a spherical wave you have the maximum uncertainty in direction . But if you know exactly which atom absorbs the photon you have a very precisely defined direction for the momentum vector, but at the expense of a very uncertain position. Graeme Bartlett (talk) 23:37, 8 September 2012 (UTC)

The whole 720 degrees thing isn't really relevant to this question; not to mention that he is asking about a photon which is spin 1, so this wouldn't even apply to it even if it was relevant (fermions are what you are thinking of.) For more information look up spin, spin statistics theorem, the Wigner D-Matrix.Phoenixia1177 (talk) 09:25, 10 September 2012 (UTC)

So could it be that we can't detect in any observable way some objects in space simply because they do not emit any radiation to our discrete loaction in space?165.212.189.187 (talk) 13:42, 10 September 2012 (UTC)