Wikipedia:Reference desk/Archives/Science/2011 October 8

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October 8

T power?

Hi, I got a little stupid question. Why all of the objects in the universe move in the same direction on the time dimension? I mean why in the space dimension every object is relativity free to move, and on the time dimension in some speed they all move fowards? Exx8 (talk) —Preceding undated comment added 13:50, 8 October 2011 (UTC).

Not a stupid question at all! Some of the greatest minds in history have struggled with it. Short answer: nobody knows for sure. See arrow of time for an overview and some history. SemanticMantis (talk) 15:08, 8 October 2011 (UTC)

I don't think it's clear that everything does move in the same direction. With a subatomic particle, for example, how could you tell ? StuRat (talk) 17:19, 8 October 2011 (UTC)

The concept of "moving through time" is a loose way of speaking that doesn't actually make sense. Moving in space means having different positions at time 0 and time 1. What would moving in time mean? It must mean having different times at time 0 and time 1. Well, duh. Looie496 (talk) 22:59, 8 October 2011 (UTC)

The arrow of time is due to a low entropy initial condition. But if you wait long enough, you'll see arbitrary large downward fluctuations in the entropy. It turns out that such fluctuations away from thermal equilibrium to a lower entropy state are most likely just the time reverse of the evolution back to thermal equilibrium starting from that low entropy state, see here for details, including an example of the most likely way a piano can appear out of a gas of photons and neutrinos. Count Iblis (talk) 00:42, 9 October 2011 (UTC)

Cosmology fact checking

"The universe will expand, then it will collapse back on itself, then will expand again. It will repeat this process forever. What you don't you know is that when the universe expands again, everything will be as it is now." Is that right? (from K-Pax (film)). Quest09 (talk) 16:13, 8 October 2011 (UTC)

As far as we can tell, the universe will not collapse back on itself. It used to be a close call (the universe looks "flat", i.e. as if it would expand at an increasingly slower speed, approaching zero expansion as time goes towards infinity), but we now believe this is an accident of observation time. According to our standard model, the universe will now continue to expand at an increasing rate due to dark energy. See also our article on the ultimate fate of the universe. --Stephan Schulz (talk) 16:22, 8 October 2011 (UTC)

Agreed. The oscillating universe model seems to be out of fashion, these days. StuRat (talk) 17:15, 8 October 2011 (UTC)

Have a look at [1] citing [2] for dark flow. Dualus (talk) 04:03, 9 October 2011 (UTC)

See the ekpyrosis of Stoic physics and Nietzsche's eternal return. μηδείς (talk) 18:10, 8 October 2011 (UTC)

The jury is still out on eternal bleakness. The further out and back, the harder it is to see, and the big bang is in the way, even if it only turns out to be something like a local ultranova. Dualus (talk) 04:12, 9 October 2011 (UTC)

Even if the universe did collapse in on itself, why would there be any reason to assume that the next "big bang" would result in a repeat of the previous one? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:21, 9 October 2011 (UTC)

The stoic and Nietzschean ideas are widespread mystical ones, not scientific. The screenwriter was obviously familiar with them.μηδείς (talk) 15:10, 9 October 2011 (UTC)

That movie (which I haven't seen) came out in 2001, only a few years after the first evidence for accelerating expansion from supernova observations and two years before it was independently confirmed by WMAP. The traditional cyclic universe model seemed more plausible then than it does now. -- BenRG (talk) 08:31, 10 October 2011 (UTC)

Why must it be this set of solutions?

Dear Wikipedians:

While trying to solve the following force diagram scenario:

(Ignoring all vertical forces exerted on pulley by gravity, etc.)

I was able to figure out the following relationship:

${\frac {150-5a_{p}}{2}}=10a+F_{f}$

where a_p is the acceleration the pulley experiences, a is the acceleration the 10 kg mass experiences, and F_f is the force of kinetic friction which I calculate to be 39.2N.

However, the problem with this is that multiple sets of a_p, a, and T (tension in string) would satisfy the relationship above. The official textbook answer is:

a = 3.18m/s², a_p=1.59m/s², T = 71N which would of course satisfy the above relationship, but I have calculated an alternative set a = 3m/s², a_p=2.83m/s², T = 69.2N which would also satisfy the above relationship. Of course there are an infinite number of other sets that would also satisfy the above relationship.

Am I missing something?

Thank you for your help.

L33th4x0r (talk) 17:06, 8 October 2011 (UTC)

Well, more force produces more acceleration, of course. They usually specify the desired accel to restrict it to one answer. That 2nd answer seems wrong, though, as the accel on the pulley should always be half that of the mass, unless we are stretching the cable. StuRat (talk) 17:10, 8 October 2011 (UTC)

Hmm...but 1.59m/s² is not half of 5 kg either... But thanks for your help, I'm all ears for more information. 70.31.153.136 (talk) 17:35, 8 October 2011 (UTC)

1.59 m/s^2 is half of 3.18 m/s^2, which is what he means. $a=2a_{p}$. Dragons flight (talk) 17:41, 8 October 2011 (UTC)

Oh yeah! That was the elusive 2nd restraint that I was looking for!!! In order for the cable to remain rigid body this restraint must be there!!! Thanks so much. 70.31.153.136 (talk) 17:46, 8 October 2011 (UTC)

Resolved

Defibrillation

Can a downed power line be used as a defibrillator? --70.129.191.75 (talk) 17:18, 8 October 2011 (UTC)

No, pounding on their chest and administering CPR would be far better. StuRat (talk) 17:26, 8 October 2011 (UTC)

Not that that will re-start their hard heart (except on very rare occasions). CPR just keeps their brain from dying while you wait for a defibrillator to arrive. --Tango (talk) 17:50, 8 October 2011 (UTC)

Their hard what ? :-) StuRat (talk) 18:04, 8 October 2011 (UTC)

That's a strange typo... not even close! --Tango (talk) 21:37, 8 October 2011 (UTC)

I often make that type of mistake, where I type a word that sounds like the word I meant, even though it may not be spelled anything alike or mean anything similar. It seems to me that this shows something about how our brains work. We must first think of the words as audio, then convert it to writing in our minds. I wonder if those who have been deaf from birth are immune to this particular type of error. StuRat (talk) 02:11, 10 October 2011 (UTC)

No. There is a chance it could work, but it's highly unlikely. The voltage is completely wrong, you won't be able to accurately apply it to the right place and, without the ECG that's built into a defibrillator, you won't know if it is appropriate to shock the casualty at all. --Tango (talk) 17:50, 8 October 2011 (UTC)

No. Defibrillators use a charge of direct current stored in a large capacitor to apply current through electrodes which spread out the current to reduce damage to the tissues. A power line would supply alternating current, found in the 1880's to cause electrocution rather than to revive people. Edison (talk) 19:32, 8 October 2011 (UTC)

LOL Joepnl (talk) 21:40, 8 October 2011 (UTC)

MacGyver would manage that. Wikiweek (talk) 21:45, 8 October 2011 (UTC)

Chuck Norris can do it. Plasmic Physics (talk) 23:13, 8 October 2011 (UTC)

No, he can't. Only MacGyver can.Wikiweek (talk) 00:59, 9 October 2011 (UTC)

Chuck Norris would probably favour the precordial thump. --Tango (talk) 01:13, 9 October 2011 (UTC)

Jack Byrnes defibrillates himself using household-mains power (I think that's the source, or maybe from something else in his home, but definitely not overhead-transmission). But MacGyver can build an AED out of a downed power line and two scratch&sniff stickers. And Chuck Norris doesn't need to use an AED machine--he has electricity in his hands. DMacks (talk) 17:02, 9 October 2011 (UTC)

You guys act like it takes a wonder person to build a defibrilattor out of some random AC power source. It's not, even Mr. Bean can do it. The difficult part is remembering not to shake the person's hand with the jumper cable when you're done. Nil Einne (talk) 22:08, 9 October 2011 (UTC)

Clearly you are biased against the high frequency power-to-heart aerial transmission system. Dualus (talk) 03:38, 9 October 2011 (UTC)

Study claiming immortality bad for evolution

Did the simulation model used for the study described in this article assume, as those I've seen do, that behaviour is entirely genetic and individuals can't learn? NeonMerlin 17:56, 8 October 2011 (UTC)

It wouldn't need to make any such assumption. This newspaper article has the common flaw of articles based on press releases: it takes an idea that has been around for ages and pretends that it is brand new. The idea that immortality is bad for evolution is obvious as soon as you assume that individuals cannot change their genes -- whether they are capable of learning is irrelevant unless tjhe learning can be passed on in the genome. Looie496 (talk) 23:20, 8 October 2011 (UTC)

Immortal beings would not need to reproduce, and true evolutionary change occurs through reproduction. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:24, 8 October 2011 (UTC)

It's impossible for a reproducing species to be immortal in a finite world. If they were indeed immortal, their population would increase exponentially with time and all of the world's resources would quickly disappear, at which point they can't possibly obtain resources to survive.

Note that it IS possible for a species to have biological immortality, which is just the absence of cell senescence. Those organisms still die due to predation, starvation, disease, natural disasters, etc., just not due to old age. --140.180.16.144 (talk) 06:28, 9 October 2011 (UTC)

Like plants that put out shoots, maybe? That raises a possibly interesting question: Does anyone know what the oldest known domestic plants are that are the result of taking "cuttings" and rooting them? ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:44, 9 October 2011 (UTC)

Baseball Bugs: look at our List of long-living organisms. – b_jonas 09:43, 9 October 2011 (UTC)

This is a bit speculative, but: Without addressing "immortality" per se, a long lifespan tends to allow a long time for mutations to accumulate in the germline. Natural selection can only remove a certain amount of undesirable mutation per generation, depending on its intensity (i.e. the number of offspring - though certainly I'd expect the competition of sperm and atresis of eggs to be most helpful). It follows that there are limits to lifespan for a species to survive in the long term, though these limits are somewhat elastic. I suspect it would be interesting to see whether slow-dispersing organisms in places like Ramsar, Mazandaran evolve a shorter lifespan, and if so what genes are involved. Wnt (talk) 11:42, 9 October 2011 (UTC)

Hearing loss

Is there a term for someone who seems to generally have good hearing, yet is unable to distinguish the voice of the person they are conversing with from other background noises, as in a crowded restaurant ? StuRat (talk) 18:03, 8 October 2011 (UTC)

Cocktail party effect describes the ability to filter out irrelevant background noise, but the article doesn't seem to have a name for when this fails. AndrewWTaylor (talk) 18:14, 8 October 2011 (UTC)

Auditory processing disorder may be what you are looking for 86.189.14.58 (talk) 19:34, 8 October 2011 (UTC)

That term seems to be a catch-all for many different conditions, of which, King–Kopetzky syndrome seems to be the one I mean. StuRat (talk) 19:42, 8 October 2011 (UTC)

Reading that article (and I must admit I had forgotten all about that condition) it seems K-K syndrome is also an umbrella term for several possible pathologies. There is so much about APD and auditory neuropathy that we just don't understand 86.189.14.58 (talk) 19:56, 8 October 2011 (UTC)

Remediation using directional microphone ?

This is a follow-up Q. I've seen ads on TV for a directional hearing aid specifically designed to isolate the speaker from background noises. Are there any studies measuring the effectiveness of this strategy ? StuRat (talk) 19:46, 8 October 2011 (UTC)

Indeed there are. The hearing aid industry is a very lucrative and competitive market, and the effectiveness of a manufacturer's directional microphone is a big selling point. Directional microphones do significantly improve the signal to noise ratio. I found an article on it from Audiology Online; I don't know how to link to it but googling "polar plot hearing aid" returned in on the first page 86.189.14.58 (talk) 20:03, 8 October 2011 (UTC)

This is a medical question which should be directed to a professional who can perform both hearing and physical examinations because the decision tree is likely to require essentially all the information in a hearing test and physical. The details of the physical would be pertinent if a cochlear implant is indicated, and they are increasingly performing above all other options for a wide variety of hearing issues. Please see the heck also http://io9.com/5846275/ Dualus (talk) 03:46, 9 October 2011 (UTC)

Can Mount Teide really be seen from the African coast?

Canary Islands in pre-colonial times contains the (unsourced) claim that it is possible to see the peak of Mount Teide from the African coast (no specific location is named, though) – presumably from ground level. I find that claim quite implausible. I even tried Google Earth and it does not support the claim at all – Fuerteventura and perhaps Lanzarote or Gran Canaria I could believe, but Teneriffa is too far away from the coast. Anyone being able to provide calculations or real-life experiences, perhaps? --Florian Blaschke (talk) 21:17, 8 October 2011 (UTC)

I calculate that the line of sight from sea level to the peak falls below the horizon at a distance of less than 150 miles, and it's almost 200 miles from the peak to the nearest point on the coast -- also the coast is pretty much flat in that vicinity. So I don't see how it would be possible. Looie496 (talk) 22:40, 8 October 2011 (UTC)

Could mirage be an explanation? 86.189.14.58 (talk) 23:02, 8 October 2011 (UTC)

The article horizon gives several formulae to calculate the distance to the horizon. The distance to the horizon from the top of Mount Teide at 3718 meters should be between 218 and 235 kilometers, if my calculations are right. Let's say it is 235 kilometers for further calculations. If, from a point on the African coast you would see a horizon that is closer to Mount Teide than 235 km when looking in the right direction, you should also be able to see the top of Mount Teide. The distance from Tenerife to the closest locations in Africa is approximately 350 km 320 km (measured using google earth). So if you are at an altitude where your distance to the horizon is 320 - 235 kilometers = 85 km, and are looking towards mount Teide, you should be able to see its top. That would require that you are standing on a hill that is 485 meters above sea level, by the same calculations. The highest point in West Sahara is 805 meters, but appears to be quite a bit from the ocean, increasing the distance considerably. So I find the claim somewhat dubious not necessarily impossible. Given special atmospheric conditions, it might be possible. edit: The horizon article mentions that atmospheric conditions tend to increase the distance to the horizon compared to a straightforward geometric calculation, but I was using a formula that was supposed to take this into account. --NorwegianBlue ^talk 23:05, 8 October 2011 (UTC)

The typical conditons near the coast may lead to favorable atmospherical conditions. Inland it is very warm while on sea it is a lot cooler. The warm air from the land rises above the colder air from the sea, creating an inversion. That's why it's bone dry so close to the ocean there. This inversion layer can reflect light back to the ground. Count Iblis (talk) 15:22, 9 October 2011 (UTC)

This book says African can reputedly be seen from the summit of Teide on a clear day. μηδείς (talk) 19:15, 9 October 2011 (UTC)

I'm not seeing the assertion in that linked entry, μηδείς, although neither do I have any reason to contradict it. With respect to seeing Tiede from the African coast, I have read that characteristic clouds often form above islands, particularly mountainous ones, and this is sufficiently common for it to have been used in antiquity to aid navigation in various parts of the world (it's briefly mentioned in Polynesian navigation), so anyone familiar with such clouds (one of whose properties being that they reflect the colour of the vegetation, sand or rock beneathe them distinguishably from clouds above bare ocean) would be able to deduce that an island was present even if the mountain itself was not quite visible. {The poster formerly known as 87.81.230.195} 90.193.78.18 (talk) 23:33, 9 October 2011 (UTC)

The book μηδείς apparently means is the second book appearing in the list, "Astronomy now: Volume 7". The snippet view says: Tenerife is dominated by the majestic snowbound peak of Mount Teide and at 12177 ft it is classified as the highest peak in ... From the summit all the remaining islands and the African coast are reputed to be visible on a clear day.

Fascinating. Thanks, everyone, for your calculations and explanations. I feel much enlightened. --Florian Blaschke (talk) 20:14, 10 October 2011 (UTC)

That's very interesting, about standing clouds over mountain formations. I had not heard of it even though demic expansions are an interest of mine. Thanks. μηδείς (talk) 20:40, 11 October 2011 (UTC)

Egg ID (snake?)

Hello, looking for help on identifying this egg. My cousin thinks it's from a snake. It is large, ~3 in long, pale translucent green & feels rubbery. Found in the past few weeks in NE Ohio. Picture found here [3]. Not sure how many are in nest, but can find out if that will help. Thanks! SemanticMantis (talk) 22:15, 8 October 2011 (UTC)

Actually, it looks like a "witch's egg", which isn't an egg at all, but the immature underground form of a mushroom called the stinkhorn. Check that article out and type "witch's egg" into google images for more pictures. Dominus Vobisdu (talk) 22:55, 8 October 2011 (UTC)

Thanks, but we're pretty sure they are eggs (I have not personally investigated). A fungus would change appearance over a 2 week period, and these have remained more or less the same. SemanticMantis (talk) 23:00, 8 October 2011 (UTC)

Maybe place the egg under a chicken and see what develops. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:18, 9 October 2011 (UTC)

AFAIK, no reptile lays that kind of smooth, shiny, translucent bright green eggs. :/ Reptile eggs are usually chalky white to a dirty kind of yellow and leathery, not rubbery. Unless these have a bad case of DDT poisoning or something. Moreover, at three inches, that's huge. Can you roll it around to see if it's attached to the ground? Are you sure there are others near it? Are they all similarly round and large? It could be some kind of fruit or industrial waste. Or it could be aliens! :D -- Obsidi♠n Soul 11:02, 9 October 2011 (UTC)

If it's translucent, i.e. light shines through it, put it over a strong light source and see what is inside. Maybe take a picture and upload it if you can? --TammyMoet (talk) 10:46, 9 October 2011 (UTC)

Frankly, the image looks like one of Easter Eggs. μηδείς (talk) 20:42, 11 October 2011 (UTC)

"choked with a board"

how exactly would someone be killed by being "choked with a board"? I am aware it is a serious murder but don't really understand how it is done! Harley Spleet (talk) 23:06, 8 October 2011 (UTC)

Are you sure it's not "choked on board"? Wikiweek (talk) 23:38, 8 October 2011 (UTC)

Hmm.. I'm begining to regret trying to help with this one. I assume this refers to John Wayne Gacy who would abduct youths and boys; "Once back at Gacy's house, the victims would be handcuffed or otherwise bound, then choked with a rope or a board as they were sexually assaulted." This article says that Gacy confessed that he would "kill them by pulling a rope or board against their throats." Don't try this at home. Alansplodge (talk) 00:04, 9 October 2011 (UTC)