Wikipedia:Reference desk/Archives/Science/2016 March 18

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March 18

Light path analysis and consequences

It was suggested to repost my question from Talk:Michelson–Morley experiment.

Question

Remark

According 1800s-physicists' thoughts, light propagates through ether in any direction with same speed $c$. So they assume that lamp and its light both goes with initial speed = ether speed, but interferometer goes with Earth speed. Why??? Lamp must go with same speed as interferometer. So light speed in interferometer reference frame must be $c$. So we should have next: - ether with speed = $0$ - interferometer with speed = $u$ (relative to ether) - light with speed = $c+u$ (relative to ether) or $c$ (relative to interferometer). If light has speed $c$ relative to interferometer, then none effects can be found. And Michelson–Morley experiment did not show any effects not due to absence of ehter but due to Galilean velocity addition. Can anybody explain me please, why does Feynman take $c$ as speed of light on every segment e.g. BC', C'B', BE', E'B' and even on BC and BE [ http://www.feynmanlectures.caltech.edu/img/FLP_I/f15-02/f15-02_tc_big.svgz ] ??? And why does he make conclusion that light speed does not depend on reference frame? Experiment just shows that ether could be entrained with Earth or in the last resort does not prove falsity of Galilean velocity addition.

http://www.feynmanlectures.caltech.edu/I_15.html#Ch15-F2

95.134.204.112 (talk) 09:02, 18 March 2016 (UTC)

Your question is legitimate: the interferometer experiment does not rule out the luminiferous ether theory. Specifically, you are describing ether drag. Our article explains several historical attempts to formulate the ether, including drag, so it would be consistent with interferometer and other experiments. But, we now have a simpler explanation (relativity). With this mathematical model, we don't need ether, so we don't need to figure out complex details about how it would get dragged around. Nimur (talk) 09:13, 18 March 2016 (UTC)

Yes, experiment can prove absence of ether wind (and using Ockham's razor we can reject ether at all). But experiment does not disprove Galilean velocity addition. E.g. I stay in center of square closed railway car 10x10 metres, with speed relative to ground $\mathbf {v}$ and throw 2 bouncy balls along and across vector $\mathbf {v}$ with speeds relative to railway car $v_{\parallel }=v_{\perp },\mathbf {v} _{\parallel }\cdot \mathbf {v} _{\perp }=0$. They come back in same time. Why can not be the same picture in the interferometer? — Preceding unsigned comment added by 95.134.204.112 (talk) 10:13, 18 March 2016 (UTC)

Question

Remark

The situation in 1800s was next. Physicists thought that light (like sound) must be waves of some medium (called ether). This ether can not be connected with the atmosphere, as light propagates from sun, stars and from planets as reflected (I'm not sure did physicists know atmosphere thickness and whether sunlight is the same light as from candle. Suppose they did). Therefore ether must fill the space. Light waves must play as sound waves: epicentre of waves is not connected with source and haven't speed of source, but is connected with medium and have speed of medium. Using sound waves we can calculate our speed relative to the air (windspeed). Michelson & Morley constructed such device by which they hoped to get displacement of the interference fringes and measure ether wind. After work with apparatus they found displacement of 0,01 of the distance between the fringes which meant ether wind speed < 1/4 of Earth's orbital speed. Maybe Earth orbital motion accidentally coincide with ether? Michelson & Morley repeated experiment every 3 months. And again found nothing. So hypothesis about ether is wrong. But physicists continued to think light speed doesn't connected with source. Why??? What does the special relativity here? Fitzgerald contraction?

https://archive.org/download/PhysicsForTheEnquiringMind/Rogers-PhysicsForTheEnquiringMind.djvu , pages 476-480 https://www.aip.org/history/exhibits/gap/PDF/michelson.pdf

95.134.204.112 (talk) 19:39, 18 March 2016 (UTC)

The big conceptual axiom is the assertion that vacuum permittivity and vacuum permeability are fundamentally invariant for all observers. This axiom says that these physical properties are more fundamental than relative measurements of time or distance. Everything else - including the invariant speed of light - follows mathematically from these assertions. Most physicists believe these assertions are true because lots of independent experiments can and do verify them. Nimur (talk) 19:53, 18 March 2016 (UTC)

Thanks for info. Do you know any experiment proving directly invariance of light speed, in which source and detector are in different reference frames? E.g. 1st measure of $c$ is made with both source and detector in 1st reference frame, 2nd measure with source and detector in 2nd r.f., but 3rd maesure made with source in 1st r.f. and detector in 2nd. Otherwise any experiment can be explained through Galilean speed addition. — Preceding unsigned comment added by 95.134.204.112 (talk) 20:28, 18 March 2016 (UTC)

The De Sitter double star experiment shows that the speed of light measured by an observer is not dependent on the motion of the emitter. You may also want to look at our article Tests of special relativity. CodeTalker (talk) 22:22, 18 March 2016 (UTC)

"So they assume that lamp and its light both goes with initial speed = ether speed, but interferometer goes with Earth speed." – no, the lamp (light source) moves with the interferometer. "Lamp must go with same speed as interferometer." – correct. "So light speed in interferometer reference frame must be c." – no, the light speed in the interferometer's rest frame is anisotropic (different in different directions). It's the same as a boat moving on the water with a speed less than the speed of surface waves. Waves will propagate outward from the boat in all directions, but the waves ahead of the boat will move away slower (relative to the boat) than the waves behind it. That was the effect they were looking for.

Galilean velocity addition does not really apply to water waves or aether waves, even in a Newtonian universe. The speed of the waves is unrelated to the speed of the thing generating the waves. You seem to be thinking of an emission theory of light where the speed of light is c relative to whatever emits it. That is not an aether theory. It is not ruled out by Michelson–Morley, but it is ruled out by other experiments, such as the De Sitter double star experiment that CodeTalker just mentioned. -- BenRG (talk) 08:09, 19 March 2016 (UTC)

Quote	Answer
That is not an aether theory.	Yep. But if ether theory is wrong, there is no need to think that epicentre of spherical wave is independent from source. However as I can see, there were other experiments proved this. Well, I think I understand my question. * Thank all of you very much. ______ see 20 March

95.134.204.112 (talk) 11:07, 19 March 2016 (UTC)

Evolutionary jump of plastic-eating bacteria

Amid plans to use plastic-eating bacteria for recycling, is there a risk that in case of plastic scarcity they will someday evolutionarily proceed to eat some useful things (similar to HIV, which jumped from African monkeys to humans)? Thanks.--93.174.25.12 (talk) 11:53, 18 March 2016 (UTC)

Currently plastic eating bacteria eat very slowly, and they would need other minerals and water, and possibly other nutrients to do the job. They do not rely on plastic only to feed. At the rate they eat it takes years to chomp down 1 mm. However humans will probably do some genetic engineering to try to improve their rate of consumption, and transfer the genes to other bacteria too. reference: http://nakeddiscovery.com/scripts/mp3s/audio/Bacteria_that_eats_away_at_plastic.mp3 Graeme Bartlett (talk) 12:26, 18 March 2016 (UTC)

The writers Kit Pedler and Gerry Davis explored this risk in the first (1970) episode of their TV series Doomwatch and their subsequent 1971 novel based on it, Mutant 59: The Plastic Eater. Per an earlier question on the RefDesk about using bacteria to eat ocean gyre plastic accumulations such as the Great Pacific garbage patch (which I wasn't able to address at the time): although their scenario – the plastics of a plane being rapidly consumed while it's in flight – is obviously exaggerated for dramatic impact, it does highlight the dilemma – how do you prevent such bacteria spreading from discarded plastic to identical plastic still in use? {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 14:23, 18 March 2016 (UTC)

For bacteria that have to survive "in the wild" (such as would be required to remove plastics from the open ocean), there is certainly a problem. But for bacteria that only have to survive in an industrial context, it's possible to engineer them to require some kind of nutrient that's not found in the natural world. If they ever escape their industrial setting, they'd die from lack of that nutrient. The only slight problem with that is the risk that they might somehow evolve to NOT need the nutrient if (for example) some sloppy industrial company were to try to save money by reducing the amount of that key nutrient that they supply. This would put evolutionary pressure onto the bacteria - which would presumably soon discover that they don't need the nutrient after all - and then any subsequent accidental release into the wild could result in problems. That's why is "Jurassic Park" kind of approach needs to be treated with extreme care.

In the wild, you'd ideally want a kind of bacteria that could only survive in the presence of the plastics they're supposed to digest. That way they'd naturally die out when their task was complete - and any that escape would have no food supply and would simply die off. But there is still a risk that as the plastics food supply dwindles, that they'd adapt to alternative food sources and become a problem. Probably the best way to handle that is to do your initial bio-engineering on an organism that already, naturally, lives in that environment in some abundance - so when your engineered bacteria evolve to 'go native', they aren't that different from the ones that were already out there and no great harm is done.

But either way, you have a problem if you want the plastic digestion to only happen in a particular location - so you want plastics to be digested in the Great Pacific Garbage Patch - but not infect (say) the factory that makes LEGO bricks out of the same exact plastic. The concern then would be that there might be bacteria that are capable of feeding on plastic AND on some natural food source - and now, you've lost all of your control, and Very Bad Things might happen. SteveBaker (talk) 14:47, 18 March 2016 (UTC)

Steve refers to the "lysine contingency" in Jurassic Park, where the dinos where engineered to be unable to produce lysine, an essential amino acid, and thus could not survive without it being supplied to them in their food. However, they evolved to produce it on their own. (In reality no animals can produce lysine, and we all get it from our food, but the concept could be applied to hormones, etc., that we do need to produce.) StuRat (talk) 17:20, 18 March 2016 (UTC)

In all likelihood nutrients will be missing from most plastic objects. How much Na+, Mg++, Ca++, Cl-, NH3+ etc. are present in your computer keys or motherboard? I don't know, but probably some are missing. It seems easier somehow for me to postulate plastic-eating activity in unknown alien forms of life that might have a simpler and radically different biochemistry, which is of course very speculative, but real-world bacteria really want to eat their plastic in a soup of some sort, not dry and standing alone on a clean shelf. Wnt (talk) 18:33, 18 March 2016 (UTC)

^^^ Yes. Keep in mind that we have scads of things that can in principle eat wood. Yet lots of wooden things remain intact for hundreds of years, and 100 years is a good rough estimate for life time of a wood product [1] [2]. So even if we had plastic-eating critters roaming the environement, I think you're right - this would be no great inherent thread to my Lego, no more than Wood-decay_fungus threatens my wooden blocks. 19:29, 18 March 2016 (UTC)

How do you feel about Dry rot threatening your wooden floorboards? (My floorboards and other house components, incidentally, are about 115 years old, but have been specially treated: plastics might not be so protectable.) {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) —Preceding undated comment added 19:37, 18 March 2016 (UTC)

My main point was to counteract an concern I've heard mentioned, and to my eye implicit in some responses here. Something like: "plastic-eating bacteria are very risky and dangerous, because they might destroy our plastic things unintentionally, and then we could not use plastic to make nice things". Of course we do have to worry about wood rotting in many circumstances, and we might have to start treating plastics a little differently, but it wouldn't necessarily be any more challenging than keeping a nice wooden bookcase from rotting over a ~30 year span. SemanticMantis (talk) 14:33, 21 March 2016 (UTC)

Evolution's revenge is always something to worry about - whenever a new species forms, or an existing one expands its niche, there is likely to be trouble. But predicting that trouble may not be easy. Wnt (talk) 17:17, 21 March 2016 (UTC)

While the plastic lacks many nutrients, the microbes may find those in the environment. For example, those eating plastics floating in the ocean might get those nutrients from the ocean or atmosphere. Those eating buried plastics might get them from the soil or water passing through. StuRat (talk) 00:05, 20 March 2016 (UTC)

Believing fiction is real

Is there any specific psychiatric name for when people believe fictional characters/organisations etc are real and affect their lives? 131.251.254.154 (talk) 14:07, 18 March 2016 (UTC)

No. Collect (talk) 14:08, 18 March 2016 (UTC)

In a psychiatric context, an unreasonable belief that someone clings to despite evidence to the contrary is a "delusion". There are a variety of subcategories of delusions, though I can't think of one that exactly identifies with the situation you describe. In general, imagining that other people / organizations affect your life in implausible ways are broadly called "delusions of control", though the imagined actors in such a situation need not be fictional. Dragons flight (talk) 14:23, 18 March 2016 (UTC)

A more cynical and literal atheist than I would probably reply "religion", but that would be unkind. (I actually practice a religion without accepting it to be objectively true, because I think it nevertheless makes me a better person.) The Slenderman phenomenon may be relevant to the OP's question. {The poster formerly known as 87.81.230.195} 185.74.232.130 (talk) 14:30, 18 March 2016 (UTC)

posting by banned user removed. Fut.Perf. ☼ 20:33, 18 March 2016 (UTC)

Lie to children. Robert McClenon (talk) 19:49, 18 March 2016 (UTC)

No. That's the adults. Magical thinking. Robert McClenon (talk) 19:50, 18 March 2016 (UTC)

See Suspension of disbelief. — Preceding unsigned comment added by Baseball Bugs (talk • contribs) 20:36, 18 March 2016 (UTC)

That's not the same, as it only lasts for the duration of the movie, and you still don't really believe it, just pretend that's it's true. StuRat (talk) 03:15, 19 March 2016 (UTC)

Yes. Suspension of disbelief is like the opposite of the delusion the OP asked about. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:24, 19 March 2016 (UTC)

I bet every single one of the posters here who mocked those with religious beliefs has convinced their children that Santa Claus comes down the chimney in December and leaves gifts in return for a glass of wine and a beer. Akld guy (talk) 05:01, 20 March 2016 (UTC)

Northing / Easting Conversion

This site [3] (in German) operated by the government of the German state of Baden-Württemberg lists geographic coordinates as "Rechtswert" and "Hochwert", literally "Easting" and "Northing" respectively. I'd like to figure out how convert these to latitudes and longitudes. My first guess was the UTM coordinate system, but that doesn't seem to be correct. Any suggestions? Is there a Northing/Easting system popular in Germany? Dragons flight (talk) 14:13, 18 March 2016 (UTC)

It appears to be some form of Gauss–Krüger coordinate system, you can use this tool to convert to conventional coordinates, which gets N 48.89922; E 9.17305 in decimal degrees, which is about right for Ludwigsburg. - Lindert (talk) 14:40, 18 March 2016 (UTC)

Thanks. That seems likely. Dragons flight (talk) 15:09, 18 March 2016 (UTC)

What are you supposed to do with desiccants?

What are you supposed to do with desiccants? Keep them or discard them? I have a bottle of aspirin, in which there is a desiccant. Am I supposed to keep it in there, while I go through the bottle of aspirin over the next few months? Or am I supposed to discard it when I open the bottle for the first time? Thanks. Joseph A. Spadaro (talk) 20:34, 18 March 2016 (UTC)

Whichever you like - it isn't going to make any practical difference to the effectiveness of the medication. 109.150.174.93 (talk) 21:10, 18 March 2016 (UTC)

I usually leave it until the bottle is empty. The main things to avoid consuming it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:28, 18 March 2016 (UTC)

Thanks. I guess my question is this: After I open the bottle, is the desiccant still doing anything? Or does it "stop working" after the seal is broken and the bottle opened? Thanks. Joseph A. Spadaro (talk) 21:54, 18 March 2016 (UTC)

It's like a sponge, so (to continue that analogy) it keeps working until it gets "mostly full". Opening the bottle doesn't break the dessicant, and if you open and close the bottle, the dessicant (assuming it still has some power left) can re-dry the newly admitted air. Whether that has a measurable benefit, and how to know when there is no drying capacity left depends on how long you've had it, how often you've opened it, whether you've stored it "in a dry place" vs in the room with your shower, etc. As a teaching example, I use a bottle aspirin many years old that we intentionally stored non-ideally, and there is noticeable evidence of decomposition. But whether that is loss of 1% vs 5%, and the rate of loss, dunno. DMacks (talk) 22:01, 18 March 2016 (UTC)

It has a certain capacity to absorb moisture, and once that is used up, it's done (there are some that can be heated to release their moisture and then reused, but I assume we aren't talking about that here). Every time you open the bottle, more moisture gets in with the air, so I'd leave it in. If you left the bottle opened, though, it would soon use up the capacity of the desiccant and the pills would start to bloat up with moisture. StuRat (talk) 22:02, 18 March 2016 (UTC)

It continues to absorb moisture and will continue to reduce the softening of the aspirin as long as you replace the lid on the bottle. Eventually, especially if you leave the bottle open for long periods in a damp atmosphere, it will become saturated and will cease to be effective. Aspirin tablets will eventually disintegrate if allowed to absorb lots of moisture over a long time, but I don't think moisture makes them significantly less effective, so if you prefer to throw out the desiccant, you will not be harmed. Here in the UK, aspirin are sold encapsulated in foil and plastic instead of using a desiccant in a bottle. Dbfirs 22:05, 18 March 2016 (UTC)

It's not just the tablet losing its structural integrity. As our aspirin article notes with cites, and that I also observe, aspirin does indeed chemically decompose if there is moisture present. Whether salicylic acid has a comparable effect I guess depends on what effect you are trying to accomplish. DMacks (talk) 03:36, 19 March 2016 (UTC)

Salicylates in general are medicinal, but usually far too sweet (see wintergreen). Bayer, by combining that sweetness with vinegar (essentially) made it into a tolerable medicine. Collect (talk) 12:34, 19 March 2016 (UTC)

Do you have a source for them being too sweet (as opposed to just too toxic) to be tolerable ? StuRat (talk) 20:11, 19 March 2016 (UTC)

Put simply - is there any down-side to leaving the dessicants in there? I think not. So even though we may not know whether they still have the ability to pull humidity out of the bottle once it's been opened fir a while - and even though some drugs suffer worse than others from any remaining humidity - you might as well leave the dessicant in there "just in case" because there is no good reason why you shouldn't - and some probability that you should. SteveBaker (talk) 15:35, 20 March 2016 (UTC)

One downside is that it keeps falling out when you pour out your aspirin, and, if you are particularly careless, you might accidentally put it in your mouth. StuRat (talk) 19:15, 20 March 2016 (UTC)

Technically this is improper medical advice, because it's about medicine and you're asking what you should do. But I don't think saying to keep a desiccant that still seems dry in a bottle so it can keep down moisture as intended is really specialized medical advice, at least. One thing I should note is that the main worry may not be how much of the drug you lose to decomposition, but what it turns into. There are a handful of cases - like with tryptophan nutritional supplements - where the result of an unwanted reaction has been notably dangerous. Drug manufacturers usually get around that by putting an expiration date on the bottle. The problem is, if you ignore the expiration date (as most people do with common drugs like aspirin) and then you also get rid of the desiccant, leave the bottle open for long periods, store it at too high a temperature, etc. etc., all while using a drug like aspiring that is known to be dangerous to many people already, then you just keep pressing your luck more and more. There may be studies on the safety of mistreated aspirin, but I doubt it is a big focus of research, so I'd suggest a bit of caution on the small things you can control. Wnt (talk) 17:27, 21 March 2016 (UTC)

Chemical Symbol

The chemical symbol is in Latin. Why Latin? Why not English? Bonupton (talk) 20:28, 18 March 2016 (UTC)

Latin was once the universal language among scientists and mathematicians. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:31, 18 March 2016 (UTC)

Your argument is imprecise. Have a look at our article List of elements. --Cookatoo.ergo.ZooM (talk) 20:38, 18 March 2016 (UTC)

Some of them are of Greek origin and elsewhere, but they are all pretty consistent in sticking with the classic languages. As to "why not English?" it seems pretty obvious. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:27, 18 March 2016 (UTC)

The element symbols are universal, used in all languages, so there's no reason they should be based on English. Some element names and symbols are based on Latin words, some on Greek words, and a few are from other languages; eg. the small Swedish town of Ytterby is the source of the name and symbol for FOUR different elements, Ytterbium (Yb), Yttrium (Y), Erbium (Er) and Terbium (Tb). Actually I think more come from Greek than from Latin. CodeTalker (talk) 22:35, 18 March 2016 (UTC)

And aren't some named for people? Joseph A. Spadaro (talk) 23:28, 18 March 2016 (UTC)

Some of the later ones are, but their names are rendered in Latinized form. "Einsteinium", for example. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:43, 18 March 2016 (UTC)

The -ium ending comes from Latin and is standard for all new elements, but I don't think it adding it should be counted as Latinizing the name. If einsteinium was really Latinized it would be something like unilapidium (from unus lapis, "one stone"). --69.159.61.172 (talk) 00:16, 19 March 2016 (UTC)

According to our article Latinisation of names, Latinization can be done by directly translating the name, but it can also be done by adding a suffix, or changing the pronunciation. Iapetus (talk) 13:25, 21 March 2016 (UTC)

"The element symbols are universal"...now. Plenty of not-very-old German literature (a common language for chemistry) uses "J" for iodine rather than "I", based on a common spelling of the element's name in that language. DMacks (talk) 03:31, 19 March 2016 (UTC)

The original poster asked "Why not English?", but the correct question is "Why not Swedish?"; the system of chemical symbols was invented by Berzelius. --69.159.61.172 (talk) 00:16, 19 March 2016 (UTC)

And that's a Latin name, so all is explained. —Tamfang (talk) 23:51, 20 March 2016 (UTC)