Wikipedia:Reference desk/Archives/Science/2015 October 7

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October 7

Does SETI target stars that could detect us?

It occurs to me that astronomers are really excited about hunting exoplanets using the transit method because they stand a chance of detecting atmospheric content. That means that the plane of the exo-planet's ecliptic more or less intersects the Earth.

It follows that aliens who wanted to find other civilizations to talk to would find our planet by the transit method too...which suggests that SETI should preferentially search for radio signals along the plane of the ecliptic.

Do they actually do that - or do they avoid the ecliptic for some reason? SteveBaker (talk) 05:02, 7 October 2015 (UTC)

The idea has been discussed: http://www.centauri-dreams.org/?p=6652 Don't think Seti@home is doing it specifically, they get the data but don't have control of the telescope; if a signal is found they ask for observation time. Data comes from Arecibo Observatory, which has a 40° cone of visibility around zenith. It's located at 18°22'N so I assume they can observe just above half the region in question? Ssscienccce (talk) 07:50, 7 October 2015 (UTC)

SETI optimism is stimulated mainly by the Drake equation which suggests a finite probability that extraterrestrial civilizations have developed communications which we might detect (without quantifying the probability) but does not give any reason to prefer ecliptic planes.

A planet's ecliptic is an inopportune plane in which to transmit to a very remote destination because of the difficulty for a receiver to distinguish the transmission from the background noise of the star, the star blocks the signal path for part of the planet's year and the signal frequency suffers maximum Doppler shifts. The few tentative (reckless?) SETI transmissions (Active SETI) have all been away from the ecliptic e.g. towards Messier 13 at declination +36° in 1974; a morse message from 1962 has long passed Venus and has surely dissipated on its way towards Gliese 581 declination −08°. As if to emphasize distaste for the ecliptic, NASA has transmitted music by The Beatles to Polaris declination 89° with no reply expected ever. So there is little enthusiasm for focussing the limited SETI radio listening resources on ecliptic directions. However Geoffrey Marcy, an extrasolar planet hunter, examines optical spectra taken during extrasolar planet hunts for a continuous, rather than pulsed, laser signal that has been suggested as a way for alien civilisations to communicate. Bestfaith (talk) 10:30, 7 October 2015 (UTC)

@Bestfaith: Wait... is the background noise for us listening actually worse for stars in our ecliptic than from other locations, provided you're not pointing at Jupiter or something? What does it come from? And our transmission to Polaris would be perfectly OK with the OP's idea -- if it had a transiting exoplanet. And surely there must be a way to compensate for Doppler shifts over the course of a year (and the day) ... if we had an alien signal to listen to for that long! Wnt (talk) 10:55, 7 October 2015 (UTC)

The OP's question is about extrasolar planets that we discover because Earth is in their ecliptic plane; they need not lie in Earth's ecliptic plane. The worst place to detect a weak radio emission is in the same direction as a star, which is generally a powerful wideband emitter. One of the pioneers of Radio astronomy J.S. Hey, a British Army research officer, made the first detection of radio waves emitted by the Sun in 1942. If one could choose a source location, it would be somewhere in "black space" with only the CBR plus our own QRN and QRM for competition. Sources in Earth's own ecliptic might occasionally be received well, the occasions being particular dates in the year when reception is not blocked by Jupiter or a wide array of things such as the Sun, other planets, dwarf planets, asteroids, Kuiper belt and tens of thousands of other space junk that infest the Solar System ecliptic. Doppler shift can indeed be compensated in an active receiver if you have exact ephemeris data on the moving source and if the inconvenient aliens don't confuse the issue by Frequency modulation. I don't see the OP or anyone being serious about NASA contributing to a Beatlemania in year 2442 some 434 light-years away at Polaris which is a 3-star system, but anyone can speculate how well a popular 4-star group will be received there by and by. Bestfaith (talk) 16:48, 7 October 2015 (UTC)

The Op says that if extraterrestrials would send signals (using their own "Arecibo" antenna), they would aim at planets they can see. So the signals will most likely come from planets that can detect us, not planets that we can detect. If they use the same methods, they would detect us when they are in our ecliptic plane. Ssscienccce (talk) 18:54, 7 October 2015 (UTC)

The notion that unearthly beings watch and care what happens here on Earth had more credence when Ptolemy's Geocentric model was in style. Notwithstanding Copernican heliocentrism the OP's prophetic insight into the intentions towards us of said extraterrestrials surely calls more for a Leap of faith than of logic. If we want (and dare) to send a message in our ecliptic plane we may do better optically using a huge dirigible sunshade for semaphore than at radio frequency. Bestfaith (talk) 01:40, 8 October 2015 (UTC)

Aliens with technology more advanced than ours, if they wanted to look for planets around other stars, would probably use space telescopes. There is no serious barrier to building reflecting telescopes a thousand kilometers across, if they are built in space away from planets. That's far larger than needed to directly resolve planets orbiting nearby stars. Any advanced civilization would surely do this as a self-defense measure: they'd want to know who is nearby. Looie496 (talk) 15:14, 7 October 2015 (UTC)

@Looie496: Well, one of the more cogent explanations given for the lack of alien communications is that once a planet starts chirping, berserkers swoop down on it and do something to remedy the problem. In that case, communications might be received only from low-tech planets with limitations much like ours. Wnt (talk) 15:58, 7 October 2015 (UTC)

Yes, there's a whole range of speculative resolutions to the Fermi paradox, this one fits under Fermi_paradox#It_is_the_nature_of_intelligent_life_to_destroy_others. SemanticMantis (talk) 17:07, 7 October 2015 (UTC)

I'm not trying to address the Fermi paradox, I'm just saying that the transit method is only likely to be high end technology for a few decades. Once a civilization has the ability to use the transit method, it probably won't take more than a few decades before it can build 100 meter reflecting telescopes in space. That's sufficient to directly resolve Earth-size planets around at least a few dozen of the nearest stars. (I personally think the solution to the Fermi paradox is that advanced civilizations don't actually want to advertise their presence. We aren't trying to do it, are we?) Looie496 (talk) 17:37, 7 October 2015 (UTC)

Sure, I think that's a fair point, I was just providing a link to our WP coverage of the idea Wnt was getting at. Then again maybe It_is_the_nature_of_intelligent_life_to_destroy_itself and those few decades between transit methods and large space telescopes turn out to be very perilous. As for your question: yes, we have tried a few times to advertise our presence, but perhaps ineffectually. See Arecibo_message which was more of a proof-of-concept than a serious attempt. Other things mentioned at Active SETI. Last Feb. there was a conference session of the annual meeting of the AAAS dedicated to discussing whether we should be attempting this sort of thing, and if so, how to do it properly, etc., so intentional "advertising" of human life on Earth isn't quite off the table [1]. I don't think there's any formal published proceedings of that conference, but a little more info on what was said here [2]. SemanticMantis (talk) 17:58, 7 October 2015 (UTC)

This video from PBS's Space Time channel takes a look at how you might go about effectively signalling other intelligent life. --71.119.131.184 (talk) 07:02, 8 October 2015 (UTC)

In regards to the Fermi paradox, my guess is that we may simply be the first civilization in our galaxy. Sexually-reproducing multicellular organisms took almost 4 billion years to arise on our planet; that's almost a third of the age of the universe. Also, our sun is a metal-rich yellow star outnumbered hugely by metal-poor red dwarfs. For two great explanations as to why civilizations don't get off-planet, read Frederic Brown's seminal short-story, The Waveries (available on line), and Greg Bear's more metaphysically speculative Blood Music in the extended novel-length version. μηδείς (talk) 17:30, 8 October 2015 (UTC)

@SteveBaker: Just saw this report about exactly what you proposed. Also [3][4]. Mentions a paper by Heller and Pudritz in Astrobiology (found it, according to Nature News, except no, I'm not seeing anything from their link - please post if you find it somewhere else) and something called "Breakthrough Listen", which is being advised to concentrate on that sliver of the sky. Wnt (talk) 13:47, 1 March 2016 (UTC) Hmmm, might as well ping the others in case they're interested: @Ssscienccce, Bestfaith, Looie496, Medeis, and SemanticMantis:

Wow! So they only just started thinking about it? Maybe they should have posted a question to WP:RD/S "Where should we look to have the best chance of finding aliens?" - we could have saved them a lot of time!  :-) SteveBaker (talk) 15:25, 1 March 2016 (UTC)

@SteveBaker: ... and now this has prompted a reeely dumb idea of trying to "cloak" the Earth by hiding its transits by compensating with a laser. They're never going to look at the right frequencies to uncover the deception, uh-huh. Note the original is dated March 30, not today. [5] Wnt (talk) 12:29, 1 April 2016 (UTC)

Exploration of the Earth's core

I was just reading some information that Mantle plumes are in fact real, large, and go all the way down to the outer core boundary. They apparently come all the way up to the upper mantle, if not to the volcanoes on hotspots themselves, though they get wiggly above 1000 km. This means that, for the first time, there seems to be persuasive evidence that (with better mapping) a voyage of exploration can be planned clear to the iron core of the Earth. So I should ask...

1) Do we have anything like a 4000-C-able probe? Something that is completely solid, that has relatively constant expansion/contraction coefficients for both temperature and pressure throughout, and can travel without moving parts using magnetohydrodynamic propulsion or something?

2) Do we have a means for it to send back data? I'm thinking there was a recent neutrino transmission/reception experiment, but that required a very big transmitter indeed. Seismic transmission is possible ... but that's low bandwidth. Or it could come back... but that's dicey. Anyone had a better idea?

3) Is it possible for a probe to extract practical amounts of energy from the surrounding rock and temperature/current differentials? Would a small nuclear reactor supply enough power for it to move?

I'm feeling now there must be a way. Wnt (talk) 14:27, 7 October 2015 (UTC)

This reminds me of some articles published back in the 1970's about exploring the mantle. The wonder of the WWW has saved me the effort of climbing up into the attic to dig them out. Radioactive Sinkers – New Scientist Magazine.--Aspro (talk) 15:29, 7 October 2015 (UTC)

I think a more realistic approach might be to drop some solid (tungsten ?) spheres in a location that will draw them down deep into the Earth, then reflect signals off them from the surface (or a mine). This will give us info about the flow patterns. StuRat (talk) 15:46, 7 October 2015 (UTC)

You seem to be imagining mantle plumes as liquid corridors. That's not true. With the exception of places very near the surface with limited local melting, the entire mantle is a solid, or more properly a rheid. Rheids are solids that deform and flow under pressure. You should imagine something like cheese that is a solid but can be permanently deformed by pushing on it. Mantle plumes are solid flows that move at minuscule rates (e.g. 30 cm / yr). If you wanted to move through one you'd have to either drill or melt the rock on the way through it. Dragons flight (talk) 15:52, 7 October 2015 (UTC)

@Dragons flight: Very good point. But can you give a better sense of their viscosity? I mean, I bet you could design a nuclear submersible capable of "swimming" through cheese by some means or other. But according to rheid, granite at STP is also within the definition, and I don't think it will go through that.

Also, the article currently says nothing about rheids/solids/liquids/viscosity/etc., so if you can update it that would be much appreciated! Wnt (talk) 16:05, 7 October 2015 (UTC)

10²¹ Pa-s, give or take an order of magnitude or so. Granite is the right analogy to have in mind. Dragons flight (talk) 16:40, 7 October 2015 (UTC)

That's actually more viscous than granite! I've read of the mantle being "semi-solid", and this is the part of it that is flowing ... never imagined it would be that tough to pass through. Wnt (talk) 18:51, 7 October 2015 (UTC)

Here's a ref that backs up the viscosity given above [6]. Here's one that focuses on the ratio of viscosities between the ambient and buoyant fluid [7]. Seems that sometimes one bit can be several hundred times less viscous than nearby bits. SemanticMantis (talk) 19:00, 7 October 2015 (UTC)

The mantle flows not because it is "soft", but rather because the deforming pressures are enormous. Dragons flight (talk) 20:02, 7 October 2015 (UTC)

The answers to 1, and 3 will be "no". For 2, you could probably send data back via seismic waves, perhaps using a magnetorestrictive material with a pulse of current to vibrate. Neutrinos would require too much equipment to make into a controllable beam. (I suspect I have a spelling error in there) But if the probe can go down, perhaps it can come back up with all the data on board. Graeme Bartlett (talk) 21:32, 7 October 2015 (UTC)

See:Magnetostriction to understand magnetorestrictive. Yet, the amplitude of such a device will be very small and of high frequency, which don’t carry very well over long distances. However, such a probe will only descend slowly, so a piston type seismic transducer (which produces lower frequencies) should have plenty of time to send the telemetry data up very slowly, (providing such a probe could be built),(this is to do with signal to noise ratio and bandwidth, which is why the Voyager space craft can still remain in contact with Earth by sending its signals very, very slowly). The Chines who invented the rock may have never imagined that one day they will go to the Moon, Mars and beyond. --Aspro (talk) 12:47, 8 October 2015 (UTC)

are sexual disorders caused by Fluoxetine usage temporary or permanent

OP wants exhaustive replies with references — Preceding unsigned comment added by Mahfuzur rahman shourov (talk • contribs) 15:38, 7 October 2015 (UTC)

Read Fluoxetine#Sexual dysfunction then follow the references and read those. Ariel. (talk) 16:34, 7 October 2015 (UTC)

more needed, updated ones — Preceding unsigned comment added by Mahfuzur rahman shourov (talk • contribs) 16:45, 7 October 2015 (UTC)

Don't know if you saw the old article about Post-SSRI sexual dysfunction here. See the AfD here for why it was deleted. Seems it didn't have reliable sources. What is known for sure is that SSRI's often cause temporary dysfunction during treatment, prevalence and duration of post-SSRI dysfunction is unknown so far I think. And one more paper. Also found on PUBMed. But primary source. So these probably aren't WP:MEDRS, it seems few researchers or doctors want to do such studies it seems. Ssscienccce (talk) 17:36, 7 October 2015 (UTC)

If humans had remained isolated from each other for longer time, will they evolve into different species?

What if different populations of Homo sapiens never join together? What if one population undergoes a genetic bottleneck or founder effect so it develops different characteristics from another population? A wolf and coyote can mate to form the coywolf. If two humanoid species mate, are they both human or is the offspring a hybrid? 140.254.70.25 (talk) 20:25, 7 October 2015 (UTC)

According to Hybrid (biology): "Modern humans acquired new traits and evolved to the present, very fertile form of the species via hybridization with at least two other hominid species: Neanderthals and Denisovans." Things might not work out if we were further apart than we were, obviously. However, you need a very long time for that. If it happened again, we would have to ask ourselves whether the offspring is human or not. --Scicurious (talk) 21:36, 7 October 2015 (UTC)

To your title question, the answer is "maybe, it depends on how long they are isolated, and how you are defining species." See species problem, species complex, speciation, and allopatric speciation. SemanticMantis (talk) 21:37, 7 October 2015 (UTC)

Timeline of human evolution, Fully (anatomically and behaviorally) modern humans is 200,000 years old. If a generation is roughly 25 years , we're talking about 8000 generations back we're still modern humans. You need to go back millions of years before we stop being "human". Vespine (talk) 21:52, 7 October 2015 (UTC)

Anatomically, pretty much. We've been a little taller and shorter, generally. Behaviorally, those old folks didn't even spend their day farming, let alone pretending to run a virtual farm from their phone. Many "new" languages now, too, including all of them. I'm pretty sure those damn, dirty apes twerked, though, InedibleHulk (talk) 08:24, 8 October 2015 (UTC)

The answer is yes, eventually, but it would take many thousands of years, perhaps hundreds of thousands. Species are defined as groups different enough to be unable to interbreed and produce fertile offspring. That would be bound to happen eventually, but it wouldn't be likely to happen quickly. Looie496 (talk) 21:56, 7 October 2015 (UTC)

No, that's not the definition of species. Or at least not one that is used outside of high school biology classes. Ring species are very common. E.g. many Larus spp. can interbreed and produce fertile offspring, as can many Anas species. For example the blue-winged teal, the cinnamon teal and the green-winged teal are different species by almost any reckoning. They look different, they act different, and yet they can interbreed to produce fertile offspring. They have overlapping ranges, and tend not to interbreed much in the wild, but they can and do. Anas#Systematics specifically mentions how fertile hybrids confound the systematics of that group. The truth of the matter is, there isn't any universally accepted definition of species; the term is simply operationalized as appropriate within different texts and research programs. SemanticMantis (talk) 22:22, 7 October 2015 (UTC)

The best example of this I know are the "Pygmies" of Africa, such as the Twa. While AFAIR some of these groups are genetically close to other Africans, some are notably diverged; it brings sympatric speciation to mind. I find myself fond of the notion that these peoples are preadapted to space travel, though alas we do not have the literal data for how well they stand up to space, having (at least) good intellect for small mass. They also have a huge reservoir of diversity, permitting them to adapt to new environments. As such, I have considered them as the base of a new species, "Homo apotelesmatis", which is - if any is - destined to dominate in an "Out of Earth" scenario. Wnt (talk) 00:54, 8 October 2015 (UTC)

I think (no refs) that developments in biotech (which happen on a distinctly non-evolutionary timescale) may bring about a system in which a small minority who've enhanced and augmented themselves like you've never seen, lords it (more than they do already) over a downtrodden majority, who can't do anything about it (i.e. like pre-1917 conditions, only perpetual) purely because they lack IQ/longevity/concentration/strength/cohesion and whatever else could be an object of artificial enhancement. This is a scenario humanity is exceptionally ill-equipped for, morally. Asmrulz (talk) 02:38, 8 October 2015 (UTC)

That'd be this book, unless this one happens instead. Ian.thomson (talk) 08:07, 8 October 2015 (UTC)

The main hope against that scenario is that the people who play god may not stack up against natural selection. They can try to enforce all sorts of desirable characteristics, but in the end their meddling, their striking out of undesirable characteristics and with it the loss of genetic diversity, dooms their perfect humans to helpless mediocrity. Also, my take on history is that the races enslaved are generally superior to the slavers (for example, Africans brought in to work plantations that whites couldn't) and so the situation is inherently unstable.Wnt (talk) 15:36, 8 October 2015 (UTC)

Also, history shows that regardless of what taboos (or laws) there are against inter-class or inter-racial relationships, there will always be people willing to ignore them. The augmented ruling class are unlikely to be able to keep their enhanced genes to themselves. Iapetus (talk) 14:18, 23 October 2015 (UTC)

There is a bit of a controversy over whether Neanderthal Man was a separate species (its taxonomic name Homo neanderthalensis implies that strongly) or a subspecies of Homo sapiens.

The two species had a common ancestor. Quoting from our article on Neanderthal man:

"From mtDNA analysis estimates, the two species shared a common ancestor about 500,000 years ago. An article appearing in the journal Nature has calculated the species diverged about 516,000 years ago, whereas fossil records show a time of about 400,000 years ago. A 2007 study pushes the point of divergence back to around 800,000 years ago."

So, at some point, physical isolation (along with mutations) may account for there having been two races of man sufficiently different that their DNA genomes are only 99.5-99.9 percent identical - modern man and Neanderthal man. All humans carry some common genetic material with Neanderthal man, non-Africans more so than Africans. loupgarous (talk) 07:35, 8 October 2015 (UTC)

Removing ammonium nitrate stain from phone

Today I got hit in the face with a basketball in gym class. My coach went to get me an instant cold pack. When he returned, he said he had accidentally busted it, but that it would probably be okay because it was just water(he didn't read the label, obviously). It was Equate brand, and they use ammonium nitrate in their ice packs. I wrapped it in a paper towel and put the non-leaking part on my face, but accidently squeezed too hard. Some whitish substance dripped down my arm and onto my pants pocket, which held my phone. I washed my hands, but only discovered the white stain on the back of my phone when I got home. How do I remove it from my phone and jeans?2602:306:CC43:A8A0:C8A1:D21E:F7DC:74C1 (talk) 23:53, 7 October 2015 (UTC)

Ammonium nitrate is water soluable, so removing any residue would just require a rinse. However, I would assume you already tried this, so must conclude that it has oxidized (bleached) the jeans and phone material (plastic ?). I see no way to un-oxidize it, so you may be out of luck. You may need to live with it or replace it. (For bleached jeans, one option is to replace the missing pigment using a marker, but it has to be laundry marker or it washes out, and it never looks quite right in any case.) StuRat (talk) 00:57, 8 October 2015 (UTC)