Science desk
< August 10	<< Jul \| August \| Sep >>	August 12 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

August 11

A question of perception

First of all, this is not a medical or similar question. It is simple curiosity. Often when I am typing on the keyboard I pause to read what I have written. I have noticed many times over the years that when I look at the cursor, it appears to stop blinking for rather long periods of time (I have had the same experience looking at the blinking on my clock). Clearly the blinking has not "stopped" as it appears to have. I am curious as to whether there is an explanation for this perception (any localized space-time anomalies notwithstanding, of course). 173.35.158.194 (talk) 03:45, 11 August 2013 (UTC)[reply]

1) The cursor does sometimes stop blinking for me, when my PC is busy.

2) A blind spot might hide some of the blinking. You aren't aware of it normally, but your vision has lots of missing bits in it, say where you looked at the Sun once. Your brain fills in the missing bits as best it can, but if the entire cursor is in a blind spot, it won't recreate a blinking cursor, but will rather recreate it however it last appeared. StuRat (talk) 03:54, 11 August 2013 (UTC)[reply]

Thanks StuRat. I was pretty sure that there was nothing wrong with the space-time thingy! lol173.35.158.194 (talk) 04:13, 11 August 2013 (UTC)[reply]

I seriously doubt that blind spots have anything to do with it. The effect that you are perceiving is known as chronostasis. As that article explains, it is a result of the weird stuff that the brain does during and after eye movements. Basically the brain blanks out the visual system during a saccadic eye movement, but prevents a gap from being perceived by time-warping perception shortly before and after it. Looie496 (talk) 04:22, 11 August 2013 (UTC)[reply]

This sounds similar to some of the stuff they talked about on a recent cable TV series called "Brain Games". I forget which channel it was on (maybe NG), but a frequent topic was how our eyes deceive us, or more to the point, our brains deceive us. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:54, 11 August 2013 (UTC)[reply]

Long ao I noticed a similar phenomenon: when I looked at the second hand of a ticking wristwatch, it seemed to hold its position for longer than a second before it moved again. This had nothing to do with saccadic blanking, and nothing to do with the blind spot. It lasted longer than another complete saccade would have taken. It seemed to be a selective attention phenomenon. Edison (talk) 13:58, 11 August 2013 (UTC)[reply]

Did you read the chronostasis article? "When eyes execute a saccade, perception of time stretches slightly backward.[2] The viewer's brain registers that they have been looking at the clock for slightly longer than they really have, producing the illusion that the second-hand is frozen for more than a second." In other words, the brain alters its own memory of the past to make it seem like during the saccade, it was perceiving the clock, even though it was perceiving nothing at all. This rewriting of history is IMO one of the creepiest functions of the brain. --Bowlhover (talk) 14:10, 11 August 2013 (UTC)[reply]

I don't think that phrases like "rewriting of history" and "our brains deceive us" are the right way of thinking about this sort of thing -- both of them are implicitly dualistic. I've been working for some time on a book about consciousness and the brain (working title The Virtual Self), and the view I try to develop is that the mind is essentially a virtual entity. The relationship between perception and the brain mechanisms that implement it is complex and indirect in the same way that the relationship between what you see on a computer screen and the code running inside the computer is complex and indirect. What we are seeing in phenomena like chronostasis is the traces of that indirectness. Daniel Dennett's ideas run in the same direction. Looie496 (talk) 15:31, 11 August 2013 (UTC)[reply]

Whatever you choose to call it, it's undeniable that perception conflicts with reality in this case. The brain thinks it sees a continuous stream of images during a saccade, when in fact, it sees nothing between the initial and final head positions. The brain thinks that a clock's hands freeze right after a saccade; in reality, the clock is ticking along at the same rate it always does. --Bowlhover (talk) 07:05, 12 August 2013 (UTC)[reply]

This sounds like a plot. You ought to see the Doctor. μηδείς (talk) 16:37, 11 August 2013 (UTC)[reply]

In school I felt like it was possible to predict success at math contests ahead of time by the degree of subjective slowing of the flashing : on a digital watch shortly beforehand, so I suspect there's a way to get at it by some similarly designed experiment. No idea if anyone has though. Computer cursors, on the other hand, are often too unreliable to say much about. Wnt (talk) 06:36, 12 August 2013 (UTC)[reply]

science )How did big bang occur?)

How did big bang occur? 223.223.150.82 (talk) 12:37, 11 August 2013 (UTC)[reply]

See our article on the Big Bang, but note that "the Big Bang theory cannot and does not provide any explanation for such an initial condition; rather, it describes and explains the general evolution of the universe going forward from that point on." — Lomn 13:16, 11 August 2013 (UTC)[reply]

See Inflation (cosmology) and False vacuum. Count Iblis (talk) 15:38, 11 August 2013 (UTC)[reply]

There is a strong possibility that we may never know the answer to this question - because all of everything was reduced to a singularity (a zero-sized dot) at the instant of the Big Bang, any information about any previous state would be destroyed. We may (possibly) be able to deduce what we think must have happened - but we'll probably never know for sure. SteveBaker (talk) 16:45, 11 August 2013 (UTC)[reply]

It was the hand of God. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:49, 12 August 2013 (UTC)[reply]

And before you ask, I'm defining "God" as creative energy in the universe. In short, it's the same as the other answers: We don't know and never will know what started it all. If we invented a backward-time-travel machine that could travel billions of years in a reasonable time, we might be able to arrive at the starting point - just before being sucked into the singularity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:53, 12 August 2013 (UTC)[reply]

I believe it is too soon to say categorically we WILL never know. I agree it is possible that we MAY never know, but I think it is too soon to discount all possiblility. The LHC recreates conditions moments after the big bang, i don't see why it would be impossible to recreate the conditions before the big bang, even if only in computer models or something. We might never be able to prove with certainty that it IS the way it happened, but a lot of our models are "best fit" interpretations of the evidence, and the big bang left LOTS of evidence :) Vespine (talk) 23:51, 12 August 2013 (UTC)[reply]

We can theorize, but we can't know for sure, we can only infer. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:05, 13 August 2013 (UTC)[reply]

That's basically Deism, Bugs. God created evolution, saw that it was good, and went on vacation to await the results. I don't think anyone except a fundamentalist is going to demand an explanation. μηδείς (talk) 01:20, 13 August 2013 (UTC)[reply]

The OP demanded (or asked for) an explanation. Don't know if he's a fundamentalist. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:05, 13 August 2013 (UTC)[reply]

A whole buncha stuff about the big bang makes more sense if you transform your time coordinate by taking it to be the logarithm of the time after the big bang. We (well, not me, but somebody) can talk intelligently about what might have happened 1 sec after the big bang, or 0.1 sec, or 10⁻³⁵ sec, but not at the big bang — that's meaningless, or if not meaningless, then at least we haven't developed the theoretical framework to make sense of it.

So the big bang theory talks about all these things that happened very short times after the big bang, but it really doesn't talk about the big bang "itself", in the sense that we've been led to understand, with everything proceeding from a literal mathematical point. You can very reasonably take the position that the big bang, in that sense, never happened at all (which is not to say that the big bang theory has anything wrong with it, just the popular presentation of it). --Trovatore (talk) 01:37, 13 August 2013 (UTC)[reply]

I like Trovatore's explanation.

My view is that the phrase "big bang" is meant to disparage (not to explain) the theory of the expanding universe, by drawing attention to the least-intuitive consequence of the model. If we assume an expansion is always occurring after t=0, then the limiting case at t=0 is sort of a conundrum. At the initial time, the whole universe is all scrunched and squished into an infinitesimal point. Theoretical people like Einstein found this notion to be preposterous.

Today, most scientists consider the expansion model to be the most plausible explanation for the universe as we see it today. Theorists are progressively getting better at describing how the early universe evolved, and as the models improve, we can explain more quantitative details about events at times closer to zero. But as we get arbitrarily close to zero, there's very little to predict: everything is all in one place, and very few of the fundamental interactions are meaningful over such miniscule timescales. All that is really relevant, when describing a densely-packed miniature universe, is some pretty abstract physics related to the way that symmetry of fundamental interactions changes at incredibly high energy densities. Nimur (talk) 12:22, 13 August 2013 (UTC)[reply]

Well, these things leave their signatures in the the cosmic background. E.g. you can observe from the cosmic backround alone that the traditional Big Bang model is wrong and that inflation theory is far more likely to be correct, despite the fact that the photons from the cosmic background that you observe come from an epoch when the inflationary epoch had long ended. Count Iblis (talk) 13:01, 13 August 2013 (UTC)[reply]

State of matter of large biological molecules

I suppose most large biological molecules like proteins and enzymes are rarely or never found in isolation. But if you could purify them into a macroscopic quantity, is it safe to say that they would invariably be solid at standard temperature and pressure? If not, how can one determine the state of matter for such compounds? It seems the Wikipedia articles for such compounds never list this information. —Psychonaut (talk) 17:09, 11 August 2013 (UTC)[reply]

They are, in fact, going to always be solid. For any molecular substance, the predominant forces on the molecules working to hold it together are going to be london dispersion forces and dipole-dipole forces. In small molecules, london forces are relatively weak, but they increase roughly with molecular mass; because molecular mass roughly correlates with polarizability. That is to say that larger molecules are more polarizable, so will be more subject to london dispersion forces. Even for a relatively non-polar molecule like a hydrocarbon, any molecule larger than about Icosane (C₂₀H₄₂) is going to be solid. Icosane has a molar mass of less than 300 g/mol. Any biological macromolecule will have masses in the tens or hundreds of thousands; at room conditions any pure substance composed of molecules that large will be a solid. --Jayron32 17:39, 11 August 2013 (UTC)[reply]

It is routine to determine the structure of proteins by purifying them to produce crystals, and then to use X-ray crystallography. — Quondum 19:40, 11 August 2013 (UTC)[reply]

Thanks, Jayron32 and Quondum, for the explanations. You say that any molecule larger than about C₂₀H₄₂ is always going to be solid. What about smaller molecules like C₆H₁₂? There are about two dozen different isomers; are they always going to be liquids, or might some of them be solids or gases? —Psychonaut (talk) 20:34, 11 August 2013 (UTC)[reply]

The hexenes are liquids at standard temp and press. Eg 1-hexene melts at 133 K, boils at 336 K; 2-hexene melts at 130 K and boils at 342 K. All the hexenes melt in the range 130 to 134 K and boil in the range 335 to 347 K. See Chemspider and NIST data. 121.215.13.245 (talk) 00:49, 12 August 2013 (UTC)[reply]

To get an intuitive grasp, consider that Tungsten hexafluoride is one of the heaviest gasses at room temperature, and while pentane boils between 9 and 36 centigrade, hexane is a liquid at room temperature. (Make sure you look at the articles and molecular diagrams). μηδείς (talk) 01:02, 12 August 2013 (UTC)[reply]

There are a few good examples, like powdered milk which is largely casein, contact lens cleaner tablets made out of subtilisin or pancreatin (a mixture) - I think the widest range can be found in Japanese cooking which seems to have really gotten into the idea of isolating enzymes and predigesting food with them, but I don't know much about that - and (in wet form) the crystallins making up much of the cells of the lens of the eye ... anyway, by and large these proteins and proteins in the lab tend to end up looking like white powders, with some colorful exceptions like myoglobin which is ruddy from the heme (also I suppose dried blood is probably >50% hemoglobin come to think of it, but I haven't verified that). Wnt (talk) 06:08, 12 August 2013 (UTC)[reply]

Can a zebra be ridden like a horse ?

Not having seen this (except in the movie Sheena, where it was probably just a painted horse), I assume there's some reason why this doesn't work as well as riding a horse or donkey. StuRat (talk) 19:15, 11 August 2013 (UTC)[reply]

I imagine that there is indeed a reason, and that wild horses can't be ridden for the same reason. In other words, I don't think a zebra would allow a human to mount it and ride it. The domestication of the horse didn't occur overnight. Surtsicna (talk) 19:25, 11 August 2013 (UTC)[reply]

See Zebroid for attempted workarounds. Hcobb (talk) 19:32, 11 August 2013 (UTC)[reply]

Here's a video of a horse trainer using Monty Roberts' "horse whispering" method on a zebra on the fourth day. (Monty can "break" wild horses on the first day.) I don't have a good source, you can google "horse versus zebra"; but horses tend to live in packs like dogs, with an alpha member, while zebras live in large herds and are more skittish and less interactive. μηδείς (talk) 22:02, 11 August 2013 (UTC)[reply]

Zebra#Domestication says "Attempts have been made to train zebras for riding, since they have better resistance than horses to African diseases. Most of these attempts failed, though, due to the zebra's more unpredictable nature and tendency to panic under stress. For this reason, zebra-mules or zebroids (crosses between any species of zebra and a horse, pony, donkey or ass) are preferred over purebred zebras."

I vaguely recall reading that the WWI German Army attempted to domesticate Zebra for military uses in Africa with very little success. They simply haven't had the thousands of years of selective breeding that produced the modern domesticated horse. SteveBaker (talk) 03:49, 12 August 2013 (UTC)[reply]

See http://www.dailymail.co.uk/news/article-1190753/Racehorse-trainer-rides-pet-ZEBRA-pub.html . The greatest thing about biology is that it just plain doesn't know theory, no matter how hard you try to teach it. Wnt (talk) 06:11, 12 August 2013 (UTC)[reply]

No. Zebras' backbones are not like horses'. The former can bend down and the latter locks when you put pressure on it. — Preceding unsigned comment added by 83.60.174.74 (talk) 11:10, 12 August 2013 (UTC)[reply]

Can you give us a source for that? If true you would think it would be more widely reported. μηδείς (talk) 16:44, 12 August 2013 (UTC)[reply]

I've heard the same thing, apparently zebras can't handle the physical strain of added weight during riding. I suppose they can handle a light-weighted person. However, they are still useful for pulling weight as the photo suggests. Sorry, I have no reference. Plasmic Physics (talk) 01:11, 13 August 2013 (UTC)[reply]

I believe that even I have heard the same thing. But I spent a good while looking for sources when this was posted and came across no such comment. I don't remember Gould mentioning it in his essay on What is a Zebra either. I suspect it's an old wives' tale. μηδείς (talk) 01:17, 13 August 2013 (UTC)[reply]

OK, thanks all. So, alas, no zebra polo games. :-( StuRat (talk) 07:49, 15 August 2013 (UTC)[reply]

Low testosterone in women and low estrogen in men

I was wondering what the term is for when a man does not have estrogen and a woman does not have testosterone. Is it seriously Low-T and Low-E? I thought Low-T was a term made up by advertisers. Also; if someone had literally no amount of the opposite sex's primary sex chemical in there body; would that person have to be dead or dying? — Preceding unsigned comment added by 174.16.180.165 (talk) 20:38, 11 August 2013 (UTC)[reply]

Hypogonadism, hypoandrogenism, hypoestrogenism.

As for losing all trace of testosterone or estrogen: It is relatively easy for people of either sex to lose their gonads, but searching "extraovarian estrogen" I pull up lots of sources like [1] and likewise for "extratesticular testosterone" [2]. Mostly the adrenal but apparently also various GI tract tissues. The other way is to lose the enzymes to make them: apparently some of these lead to genuinely no detectable testosterone [3]. Wnt (talk) 06:31, 12 August 2013 (UTC)[reply]

is this poison ivy???

hello, can someone please help me identify this plant? -->http://i.imgur.com/OhPITzn.jpg my dad thinks its poison ivy, but i think its just a weed wrapping around the rake. this is near ottawa, ontario, canada. thanks. 208.96.87.57 (talk) 20:43, 11 August 2013 (UTC)[reply]

I would expect a glossier, shinier leaf on poison ivy; so I would suspect that is some other plant with similar leaf shape. If you aren't sure, err on the side of caution. Nimur (talk) 21:16, 11 August 2013 (UTC)[reply]

It's poison ivy all right, a fine healthy specimen (pretty, isn't it?). While poison ivy leaves can be glossy, it's not diagnostic. Mature leaves tend to be shinier and more potent. Handle with care, wear disposable gloves, and wash everything including yourself, don't touch your eyes, face, etc. I've learned to identify poison ivy from repeated, itchy personal experience. Acroterion (talk) 21:23, 11 August 2013 (UTC)[reply]

my guess is Hog peanut Amphicarpaea bracteata--Digrpat (talk) 23:22, 11 August 2013 (UTC)[reply]

Hog Peanut looks correct. Hog peanut has two large side veins that branch out from the base of the leaf forming a hen's foot, while poison ivy has about a dozen indented veins at right angles from the main vein like comb tines. Of course it is not worth the risk, so just treat it as if it were poison ivy. μηδείς (talk) 00:30, 12 August 2013 (UTC)[reply]