Wikipedia:Reference desk/Archives/Science/2014 September 22

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September 22

Why do we sleep

I recently read this. I don't understand why is it still a mystery to science. It even states in the article that "sleep is the time when our bodies repair tissues and perform other maintenance activities..." That's 'the reason' why we sleep, simply as that. What more evidences do they want? What is really the mystery behind sleep that we can't explain with science right now? Thanks! 146.151.82.248 (talk) 01:02, 22 September 2014 (UTC)

Part of the reason is that we do not have a good scientific theory of sleep. Theories are explanations (or more properly explanatory frameworks) that have evidence to support how or why something happens. There is a hypothetical theory that proposes that sleep's purpose is to allow maintenance, or to allow neural connections to strengthen, or any number of explanations. The problem is not the lack of explanations, it's the lack of experimental verification of the explanations. A good theory has lots of evidence. The current set of theories are still hypothetical theories because, while logical, there isn't a lot of good evidence that indicates their validity. They may actually be correct. But compared to other theories which we use all the time in science (like evolution, or atomic theory, or general relativity) there isn't a lot of good solid evidence one way or the other to explain why we need sleep. We do know we need it, there's lots of pathologies that result from lack of sleep, but beyond the simple relationship of "no sleep = unhealthy in specific ways" we don't have much to explain why functions that seem to occur during sleep couldn't occur while we are awake. --Jayron32 01:14, 22 September 2014 (UTC)

I found it hard to believe that we can't prove what is going on in our brain during sleep. I believe it has been proven that our brains do in fact in maintenance during sleep. As i can see we have a pretty good theory so far about it. With that theory, i can say that we need sleep because we need our bodies to be repaired before it's broken. 146.151.85.154 (talk) 08:05, 22 September 2014 (UTC)

You misunderstand. We can establish what is happening. We don't have a good explanation for why it happens during sleep (as opposed to simply all the time while we are awake). --Jayron32 10:51, 22 September 2014 (UTC)

We do know that sleep is pretty much universal in the animal kingdom; this universality then suggests that it has nothing to do with biology, it is a consequence of mathematics. If you and I have a system that can only function at a certain level for that to be sustainable, and I operate it at that sustainable level then you can easily outcompete me by operating your system at a higher level, and then letting it take a rest during which the focus is on self maintainance. Also, by tweaking the system you can let the self-maintaince be performed more efficiently during the downtime which then allows the system at the active phase to perform even better. This is a universal feature of almost any system from biological to simple machines like your pc. Count Iblis (talk) 02:01, 22 September 2014 (UTC)

So is this your theory of why we sleep?146.151.85.154 (talk) 08:05, 22 September 2014 (UTC)

Yes, but note that many universal phenomena require mathematical explanations that go beyond the particular subject matter. They tend to be mysteries for a long time because people seek an explanation in terms of the concepts of the subject matter which often isn't appropriate. E.g. Von Neumann made an important discovery about the way DNA works, long before the structure of DNA was discovered by Watson and Crick, see here: "Von Neumann's crucial insight is that part of the replicator has a double use; being both an active component of the construction mechanism, and being the target of a passive copying process. This part is played by the tape of instructions in Von Neumann's combination of universal constructor plus instruction tape.

The combination of a universal constructor and a tape of instructions would i) allow self-replication, and also ii) guarantee that the open-ended complexity growth observed in biological organisms was possible.[3] The image below illustrates this possibility. This insight is all the more remarkable because it preceded the discovery of the structure of the DNA molecule by Watson and Crick, though it followed the Avery-MacLeod-McCarty experiment which identified DNA as the molecular carrier of genetic information in living organisms.[5]" Count Iblis (talk) 18:38, 22 September 2014 (UTC)

My PC doesn't self-maintain when it is switched off. AndyTheGrump (talk) 05:07, 22 September 2014 (UTC)

My PC spends an annoyingly large portion of its processor time on self-maintenance when I want it to be doing useful work, but I accept that this is just a disadvantage of "Windoze". (It's time I replaced it!) Dbfirs 07:41, 22 September 2014 (UTC)

I don't know anything about this, but surely the mystery is why we have to be unconscious for a significant fraction of our lives. It would seem to be a huge adaptive disadvantage in almost any situation. At the very least you'd expect it to be healthy but optional, skippable if you really need to stay alert. But you can't stay alert for long without sleep. What happens in the brain during sleep that's so important that it counterbalances those disadvantages? Also, some animals can sleep one brain hemisphere at a time; why don't all animals at least have that option, given that it could probably save their lives in some situations? -- BenRG (talk) 06:51, 22 September 2014 (UTC)

Probably because evolution selects the animals who sleep and able to repair and perform better than those who don't. The fact that most animals need sleep prove that sleep-animals outperform no-sleep-animals. No-sleep-animals probably died off ages ago because of evolution.146.151.85.154 (talk) 08:05, 22 September 2014 (UTC)

Related to that hypothesis, it's useful to observe the effects on those who cannot sleep, as in Fatal familial insomnia. The end result is typically dementia and death. It's clear that the brain requires some down time. BenRG asks why we have to be unconscious. Keep in mind that our (un)consciousness level during sleep rises and falls, it's not a steady level. If you've ever taken a "cat nap" while watching TV or whatever, sometimes you just barely slip into unconsciousness. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:49, 22 September 2014 (UTC)

I could have asked any question about biological systems and you could have said "the fact that evolution selected for it proves that it's better". That's a wakalixes answer. It's not wrong, just devoid of useful information. What is the advantage of being mostly unaware of your surroundings while healing, versus keeping an eye on your surroundings while healing, that led to the former being preferred by evolution? (I think the correct answer is that there is no advantage, and sleep is not actually about healing, as SteveBaker said below.) -- BenRG (talk) 19:09, 22 September 2014 (UTC)

I heard a scientist on RadioLab say that sleep patterns were related to Predation risk. It does seem that the option to forego sleep for much longer than is currently possible would have survival value regardless of predation risk, though. OldTimeNESter (talk) 15:41, 22 September 2014 (UTC)

It's true that we really don't know for sure - and certainly we don't have all of the details down. But it seems that it's something like this:

First, consider that animals like Dolphins which would drown if they ever fell completely asleep. They often sleep with one hemisphere of their brains at a time, so they always have enough brain power to do things like swim and breathe. That's also true of sharks - which have to keep water flowing over their gill-slits. Some perching birds have an interesting behavior where a group of birds will perch together on a branch and the birds at each end of the row sleep with just the hemisphere of their brains that allows one eye to keep watching for attack from their exposed side - while the birds in the middle of the row can fully sleep with both hemispheres.

These examples indicate that sleep isn't so that our bodies can perform repairs - at least not muscles and bones and other major organs. If that were the case then continually swimming sharks and dolphins would never have time for those repairs - yet their bodies do just fine. So this is best thought of as "brain maintenance" - and that starts to make a lot of sense. But even so, our brains are obviously still active as we sleep...we have dreams - and MRI studies show that there is plenty of activity. If you play music to a sleeping person, the areas of their brains that light up when they listen to music while awake also light up while they're asleep. So if it's "brain maintenance" then it's not that the brain is turning off so that physical structures can be maintained. It's more like the "software" of the brain undergoing some kind of special maintenance.

Consider this: We continually take in and record sounds, images, text and other stuff which we sometimes remember. Yesterday was my granddaughter's 3rd birthday party - and even though it was flushed out of my short-term memory after 20 minutes or so, I recall most of what happened. But when I think back to her 2nd birthday, I only recall a few highlights. Looking back 10 years, I no longer have any memory about my son's 12th birthday - beyond that we went to some kind of indoor rock climbing thing. My memories of these events have slowly faded. But this fading is highly selective. There are things like my son's birth, where every detail is still fairly sharp. So fading memories isn't a kind of dumb, automatic thing like the decay of a banana...it requires selectivity. We lose the memories we don't "need".

There are many, highly divergent, estimates for the capacity of the human brain for memory - but a typical estimate (eg [1]) is that the number is a couple of petabytes - which, in computer terms is about 1000 modern 1 terabyte hard drives. That's a VERY small amount considering that we have decades of video and audio stashed away in there. A low resolution video of the events of that birthday party would be many, many gigabytes. So clearly, this business of selectively (and gradually) 'softening' memories, making them more and more blurry is essential to keeping our brains working.

The best guess for what sleeping brains do while we sleep is that we're dealing with memory reorganization. It seems likely that dreams happen because of this. When a memory needs to be simplified in order to take up less space, we are (perhaps) pulling it into short-term memory, then saving it back out into long-term memory in a simplified way. Consider the analogy of running out of space for photos of some long-ago holiday on your PC. You might pull each photo in turn into Photoshop, reduce the resolution of the image and increase the JPEG compression level - then save it back out again. When we wake up in the middle of a dream, we have all sorts of little snippets of memory from who-knows-where sitting in our short-term memories, seeming like it all just happened. We rapidly turn that into some kind of bizarre story and then (mostly) completely forget it again. All of this makes perfect sense in computing terms.

Of course we know that memories aren't saved as pictures and videos - but as collections of interlinked concepts - but at that higher level of abstraction, we're still editing our memories down to save space.

Further evidence of this is that people's memories get bad if they don't get enough sleep...makes sense if there is insufficient time for the brain to do the necessary housekeeping...and in the extreme case of Fatal familial insomnia when people don't sleep at all for weeks or even months - the consequences of being unable to perform brain maintenance is clear. Memory fails, we run out of space to store things - and the results are predictably disasterous.

The best computer analogy is probably 'defragging' a hard drive - something that users of older versions of Windows are probably familiar with. This is the process of having the system reorganize the files ("memories") on the hard drive ("brain") for more efficient access. The computer shuffles files into and out of RAM memory and puts them back onto the hard drive in a more logical order. If it were possible to have software that uses those files be running while this rearrangement was going on, the results would be a chaotic mess, not unlike dreaming. It's not true in practice, but naively, you could be editing a WORD document, and while you were editing it, bits of other documents could be dumped into that place on the disk drive and the resulting documents would be a weird mix of bits of old documents, stuck together in a strange order. Sounds just like a typical dream - right?

So we don't allow that - other programs should not be running while you're doing a defrag. In the human brain, that option is "sleep" - and we also do things like shutting off muscle control in order that we don't try to act out our dream states...and failures of that mechanism are things like sleep-walking or talking in your sleep. It's fascinating that dogs seem to has a more limited version of that shut-off control and almost always act out their dreams with little twitches of their feet and jaws and small, quiet, barks and growls.

SteveBaker (talk) 15:45, 22 September 2014 (UTC)

WP:TLDR

The human "brain" consists of well over a dozen organs, such as the various lobes of the cerebrum and their subsections, such as Broca's and Wernicke's lobes, the rest of the sensory and motor cerebrum, the cerebellum, the thalamus, hypothalamus, amygdala, pineal gland and its various parts and so on and so forth.

The brain has two major modes, wakefulness, modulated by serotonin, and sleep, especially REM sleep, modulated by acetylcholine. There is also D sleep.

During serotonin mediated wakefulness we are conscious and our working memories are at full capacity.

During ACh mediated REM sleep we dream and our brains lay down permanent memories as mediated by acetylcholine.

The neurons that have fired due to serotonin during the day (and norepinephrine, AKA adrenaline) during the day connect at night during the ACh phase.

Sleep is a state of the various organs of the brain which allows the retention of emotional, verbal, and kinetic memories to be laid down as permanent memories, rather than daily experiences. Refs avail on request. μηδείς (talk) 03:00, 23 September 2014 (UTC)

does the moon's pull affect river

Does the moon's pull affect river currents and river waves? — Preceding unsigned comment added by 199.7.159.41 (talk) 03:50, 22 September 2014 (UTC)

If you mean the tidal force resulting from the Moon's gravitation, yes it affects them - in as much as it affects everything on Earth (though the force involved is very small - the lunar tidal acceleration at the Earth's surface along the Moon-Earth axis is about 1.1 × 10−7 g, where g is the gravitational acceleration at the Earth's surface). In terms of being able to actually measure the direct effects of the tidal force, I don't think this would be possible except in 'tidal' portions of rivers, where the rise and fall is the result of tides out to sea causing the outward flow to stop and reverse. Such effects can be very pronounced, however - see for instance the Severn bore, where the shape of the estuary causes a dramatic upstream-moving wave under the right conditions. AndyTheGrump (talk) 04:59, 22 September 2014 (UTC)

Get your exponents right. It's 1.1 × 10⁻⁷ g.

But yes, the tidal effects on rivers are negligibly small. Not only is the force quite small; it affects two points of the same river to a similar extent, and most things we could observe rely on the difference between forces acting on separate points, not the forces themselves. For example, the Moon even attracts the terrain surrounding the river, another effect which is often overlooked.

The strong tides of the Severn bore are almost purely secondary effects: it's the tides of the ocean which get channeled upstream into a narrower basin, where the reduction in width translates into more height (Kudos to Andy for that example). - ¡Ouch! (^{hurt me} / _{more pain}) 07:58, 22 September 2014 (UTC)

Another well-known example is the "Reversing Falls" of New Brunswick. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:37, 22 September 2014 (UTC)

I'd like to explain why tides are so much smaller on rivers, since the tidal force exerted on a river is the same as on the ocean. It has to do with the depth of the body of water. You can think of water like a coil spring, which compresses a tiny amount when more force is applied, and extends a bit when less force is applied. The tides are caused by the addition and subtraction of the Moon's (and to a lesser extent, the Sun's) gravity to the Earth's. Since the Earth is so much closer to the water, it's gravity is far greater. Now the deeper the water (the longer the spring) the more the water (spring) moves up and down at the top. Rivers just aren't deep enough to have much of an effect, except, as noted previously, where the tides from a much deeper body of water spill over into them. Lakes are in-between, and deep lakes might have a noticeable tide, but still less than oceans. And, again, note that the lake doesn't need to be deep right where the tide is measured, since the water will spill over from where it rises in the deep area.

Sturat. Are you suggesting by "You can think of water like a coil spring, which compresses a tiny amount when more force is applied, and extends a bit when less force is applied" that tides are the result of the volume of water varying locally due to gravity induced compression? Could we have a reference for that? This is a long from my understanding. 2A01:E34:EF5E:4640:C5F3:58BA:E680:C3A2 (talk) 18:05, 22 September 2014 (UTC)

Well, see: Properties_of_water#Compressibility. Admittedly it's not very compressible, but even a slight compression and expansion of a 7 mile tall column of water should change the height by a noticeable amount. Can somebody do the math, using those numbers ? StuRat (talk) 22:45, 26 September 2014 (UTC)

Another factor that affects tides is the shore geometry. If the shore is absolutely flat and at low tide level, then the water that spills over will move far inland, but not raise much in height, since the water is spread out over such a large area. StuRat (talk) 13:27, 22 September 2014 (UTC)

How large is the "tide" on the world's largest (somewhat) isolated bodies of water, such as the Great Lakes? Edison (talk) 12:35, 22 September 2014 (UTC)

According to NOAA, the tides on the Great Lakes are only a couple of inches, and local weather has a much greater impact on lake levels than tides do. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:40, 22 September 2014 (UTC)

• Tides affect everything including the land, buildings, and your body, although in small solid objects, the stretching is microscopic and only noticed in suche cases as approaching neutron stars and blackholes (spaghettification). The tide does affect the land and crust, but Spain doesn't "fow" into Portugal or New Jersey into Pennsylvania because these are solids. Liquids flow freely, however, and ocean tides in effect have a greater fetch over which to build up, meaning a more dramatic effect. The westward pull of the moon doesn't cause the North-South running Nile and Delaware rivers to flow up dramatically onto their western banks the way a very small part of the very large Atlantic ocean does. The tidal effect on the Delaware, which is felt as far north as Trenton, is due to ocean water pushing up the delaware bay, not due to any direct effect on the river water itself, which again would be microscopic were the river a canal with a closed southern end. μηδείς (talk) 17:31, 22 September 2014 (UTC)

But there are people that claim that if there's no measurable tide the stream high tide (besides the full moon, hour, season and weather) still makes it better to fish, even if it's New Moon. Sure fish are sensitive but is there any possible way they could feel a river tide? Or maybe they just claim the moonlit tide, if night is low predator but they often can only use their other senses (water would only transmit moonlight well a few hours a night), the fish might gain lunar day (24.8 hour) sleep patterns and bite best near full moon when it's high in the sky. And maybe it's optimal for fish to eat a second time a day and they minimize hunger and/or digest slowly? Ed:thus explaining the non-moonlit high tide eating peak, if that was indeed what was claimed Sagittarian Milky Way (talk) 01:21, 23 September 2014 (UTC)

I'll just assume you are trolling us with bullshit as usual, but no, of course fish in small bodies with tides that affected their bodies to the same amount as the water itself would not be able to detect the few nanometers stretch that affected them or the water they were in, unless you believe in psychic fish? In which case, why are you asking here? We deal with facts and you obviously have too many. μηδείς (talk) 02:44, 23 September 2014 (UTC)

Remember to be civil, medeis199.119.235.162 (talk) 03:10, 23 September 2014 (UTC)

(edit conflict) I hadn't done the math, and didn't think of how water-like a fish's body must be for very tiny stretches. (Fish can detect very small water pressure changes on their body, and I subconsciously misremembered the ounce lunar pull on a man at the Lagrangian point as at Earth, giving me the wrong idea). Of course I don't believe in psychic fish, but building their circadian rhythm around feeding when moon angles with low water albedo appear could be a means which doesn't require nanometer precision. Anglers who claimed this thought inland tides would not lag the Moon like sea tides (probably true?), making this more likely. Sagittarian Milky Way (talk) 04:50, 23 September 2014 (UTC)

IIRC, fish detect minute pressure changes using their Lateral line. --Jayron32 16:45, 23 September 2014 (UTC)

Lateral lines detect acute water pressure changes caused by nearby stimuli, other fish wagging their bodies, or water flowing over rocks. (Hearing evolved from this.) The fish's body can, for all intensive purposes, be treated as water, since it has almost the same density and is largely made of water or hydrated molecules. As the tide ebbs and flows the water will change in depth, so the water pressure at a given spot will change. THat may very well influence a fish as a sign of a daily change. But This is not a question of the fish noticing its own body has stretched or compressed by the width of a few hydrogen atoms. I suspect that if anything it's the direction of flow of inshore waters that matters in regards to tides and fishing. μηδείς (talk) 03:03, 25 September 2014 (UTC)

Polarity of Electret Microphone?

[[2]]

i want to know which is the Ground (GND) terminal of Electret Mic? one of its two terminals carries mark beside it--- is it GND or +VE ? pls help... thnk u. — Preceding unsigned comment added by 101.210.20.198 (talk) 11:34, 22 September 2014 (UTC)

If the microphone has a metal case, that will almost certainly be grounded. So you could use a multimeter to measure resistance between each pin and the case - if either of them is a dead short, then that's the ground pin. The photo at the top of our article shows that one of the two pins is obviously connected to the case...but your actual device may be different. SteveBaker (talk) 14:57, 22 September 2014 (UTC)