Sunday, July 21, 2013

Now you see me, now you don't. (Stupid Questions)


I took the boys, Mr F and Mr Bunches, to the swimming pool yesterday.  That in itself was not unusual and is only a lead-in to this post, because absolutely nothing remarkable occurred while we were on the way to swimming, while we were swimming, or on the way home from swimming.  In fact, the swimming thing is really irrelevant to the post, as the inception of this post could have come anywhere, or everywhere, but in this case, it happened at the pool, where I was, yesterday. Swimming.

Here's what happened while I was swimming: I was looking a bit at the way the water reflects off the pool and watching Mr Bunches swim all the way across the pool, which he can do now, and I thought to myself

Stupid Question #1: Why can't we see air?

I mean, all my life I've been told that the sky is blue because light bounces off of it, or refracts, or something, that in essence light is bouncing off the sky and we are seeing the blue light, the rest of it being absorbed by the sky, which, as I sat in the pool playing "Sea Turtle & Sloth" (that will require an explanation some other day) began to bug me more and more, in that the sky is made of air and so why can we see the sky when it's way up there, off in the distance, above the trees and above the Ace Hardware and above airplanes, but we can't see the sky when it's right down here on top of the pool?

And, for that matter, Stupid question #2 Why does the sky reflect all the same uniform shade of blue, instead of slightly different colors because the sky is made up of different atoms or molecules or something of air, and why would nitrogen reflect the same color of blue as oxygen?

 So I kept thinking about it, as I swam and played "Up!" with Mr F (not the movie; while we play lots of movies, those are mostly with Mr Bunches and mostly involve the scenes where two characters fight, like when the chef tries to kill Sebastian in The Little Mermaid, which seems pretty horrible the first time around but becomes much more horrible later, because the first time at least you could think that the chef, who appears to enjoy his job chopping off fishes' heads a little too much, thought he was only killing dumb animals, but later on, having been made aware that the sea creatures are sentient, thinking, feeling beings, the chef still wants to kill Sebastian, so he is just a serial killer. Puts a different spin on that movie, doesn't it?

As I kept thinking about it, I was thinking, too, how water's surface looks that peculiar, awesome way, and that it must be because we are seeing the reflection of only some of the light, because water lets light pass through it, only bending it slightly, but if water passed light through entirely, we wouldn't be able to see it, at all.

That got me thinking -- and this, I imagine, is how scientists like Ben Franklin and Aristotle did 'science' back before you could just google stuff, my being in my swimtrunks in a pool and then walking home being the equivalent of being in the Middle Ages, because while I could have gotten out and checked it out on my phone (Imagine: I carry with me at all time a computer that can answer almost any question! I Love Living In The Future!), I didn't do that, because Mr F was as I said making me play "Up!" which is where I pick him up and almost throw him and then put him back down.  He does not, unlike Mr Bunches, want to be thrown, and his game is much harder than when Mr Bunches asks me to throw him, because I have to lift both up and down for Mr F, so it's a real upper-body workout.

Using my old-fashioned science, I tried to work it out.  If water can be seen, sort of, and air cannot, then that means that light passes entirely through air and only partially through water; it is light beams reflecting off of things that allows us to see them, so if we can see the water in the pool, that means that the light is bouncing off of it.

Which didn't explain why we can't see air, though, as (A) we can, remember, we can see the sky, even if it just seems to be a big blue sheet hanging somewhere up there,and (B) even if air is less densely-packed with molecules or atoms or whatever than water, which was my next hypothesis, that didn't mean that we shouldn't be able to see some air, whenever the photons hit an air molecule near our eyes, for example.  After all, if a dust mote drifts near my eye I can see that, so shouldn't all the little molecules of helium near my eye be visible, too?

Which led to a new hypothesis: maybe it was that there are impurities in the water and that is what we're seeing when we look at water: not the water itself, but the chlorine, or the dust, or... let's not think of any other impurities that could be in water.  Let's leave it at dust and chlorine.  After all, there are supposed to be spots in the ocean that have superclear water where you can see the bottom of the sea 20 feet down, and just because I've never seen them doesn't mean that everyone's lying about them.  (I secretly suspect everyone is lying about them, so I'm going to suspect that you, and you, and even you and all of you over there are liars unless you arrange to send me on an all-expenses-paid factfinding trip-not-vacation to such a place. For two weeks. In January.  Put your money where your mouth is, liars.)

I was doing all this thinking because I still like to exercise my thinking muscle, or 'brain,' before actually looking up the answer, and also because: swimming in a pool.  But that was what I came up with: we are actually seeing impurities in the water, and hence the air, which we see as blue because of impurities?

Didn't seem right, even though that would account for days that are 'hazy,' and fits in with things like when you see smog or fog, too, when the air becomes visible because it has more 'impurities' in it.

Now, then, sitting here this morning with my coffee and my computer and the invisible air all around me, I can check out those answers against 'real' "science", by which I mean the kind of science that even though we generally believe it still does stuff like "makes up dinosaurs that never existed and then pretends they were real," so let's take "real" "science"'s answers with a grain of salt.

First, I googled

Stupid Question #1: Why can't we see air?

I got, with that answer, to a site called "Quora," which is apparently new and which I see on Slate a lot, even though I don't read Slate anywhere near as much  as I used to because Slate honestly is becoming just more and more personal blogs and less and less actual reporting or analysis.  I'd say about 75% of Slate's content is no better or worse than this blog -- things I think about stuff, with some googling thrown in, which is okay if you're writing a blog for fun, but not as okay if you  are purporting to be a serious news source.  It says something when I feel like I get more hard news from HuffPo than from Slate, and that is how I feel.

Anyway, I got to Quora where I had to sign in and create a password to see answers to questions! Oh, good! Another password!  That's awesome!  I love having to constantly have a list of identities with me just to read a #(#%*$ question on the Internet!  I know, you use my email to sell to direct marketers and that's how your website becomes free, I get that's the tradeoff I'm making: I can read your website and you can use my email to have me sent "Groupons" or something, but understanding that, why do I have to have a password? Are we worried that someone will use my email to sign in to Quora as me, passing themselves off as me on a site where they can ask questions about stuff?  That's a fear I can live with.  If the worst thing an identity thief can do with my identity is ask questions in my name, I think I'll survive.

(Side note: given my credit rating, I have a standing offer to identity thieves: If you can qualify for credit using my identity, I'll split the credit with you and not press charges.)

Having signed in and created another junk password that I won't remember so that the next time I use this site 30 months from now I will have to have it "send me a reminder," or something dumb, I got to an answer that I couldn't tell if it was by a scientist or not -- it seemed to be but then again it seemed not to be, which is part of the problem with googling stuff: you never know whose answer you're getting.

In this case, the top answer seemed to be from a guy who billed himself as "not a physicist":



but who still seemed more credible than "Karl Malcolm, scientist, academic, guitarist."



What three things would you want the world to know about you if you were trying to convince them that you were smart? "The ability to play hot guitar licks" is definitely near the top of the list, although people who can do that probably don't advertise it.

The top answers I got from skimming those three entries and then ignoring Karl Malcolm's answer because he said air does not absorb light in the visible spectrum and therefore cannot be seen and even I know that's incorrect, that it is the reflection of light that we see, not the absorption, is that we cannot see air because for the most part, air is too small to interact with light.

(Another problem with the internet? "Science" is not a popularity contest. Having regular folks -- or regular folks with an email address and a willingness to use the phrase "CheezDoodle" as their password -- "vote" on what the "best" answer to a question "is", is not science, or even fact.  The popular answer may or may not be right.  I recall once looking at the question "What flavor are white jellybeans?" The top answer was something like "I don't know, but they are delicious," which, while factually accurate as far as the answerer's own state of mind went, was not really the answer to the question, at least not the way we traditionally think of "answers" as "answers.")

It was actually answerer number 2 on that site that gave me the most insight, as he explained the four ways light interacts with junk:


When light passes through an object, one of four things can happen:
1. Absorption: this occurs when the photons of light interact with the electrons in the material and the photon gives up its energy to the electron. The result is that the electron moves to a higher energy level, and the photon disappears.  This makes objects look opaque. The color of an opaque object is dependent on the range of frequencies that it did not absorb.
2. Reflection: this occurs when the photon gives up its energy to the electron, but another photon of identical energy is emitted.
3. Transmission: the photon doesn't interact with any electron in the material and light exits the material at the same frequency that it came in.
4. Scattering: as Joshua Engel mentions, the light interacts with matter or structures in the matter, being absorbed and re-emitted in a different direction. Earth Science: Why is the sky blue?
Air molecules are sparsely distributed, so light passing through air has a small (but non-zero) chance of interacting with air molecules along its trajectory.  However, if there's a lot of air (imagine a 50-mile stretch), lots of these improbable interactions add up, and the effect of the air molecules becomes visible.  Rayleigh scattering, which is the phenomena causing the sky to be blue, favors light in the blue / violet regions and occurs when interacting molecules are much smaller than the wavelength of light.

That guy goes on to explain that we also 'see' light when there is a temperature differential causing the light to change its path: light goes in a straight line through air but temperature can make it change direction, which is why light appears to shimmer above a hot highway, because the air is hotter just above the tar than it is three feet up, so when the light hits it it changes direction and we see what looks like water above the road.


Which made me think that you could make yourself invisible if you could alter the temperature around your body enough to completely bend the light away -- you would appear as a shimmer, like Predator, maybe, but you would be more or less invisible.

Or would you?

Stupid Question #3 If you could have the air immediately around your body be a superdifferent temperature than the air just past it, would you be invisible?

I'll get to that in a bit.  For now, back to #1:


Stupid Question #1: Why can't we see air?

We can't see air because it's not interacting enough with light: air molecules are (relatively) far apart compared to, say, pizza molecules, which are densely packed (yum!).  That and air molecules are smaller, in many cases, than the light waves/photons (light is a both a wave and not, remember), which means that when light interacts with air, it first has to hit some air, and that's hard to do because air is so small and so far apart (relatively speaking, again.)  When light DOES hit air, because the air molecule is (usually) smaller than the light wave/photon, it undergoes "Rayleigh scattering."


Rayleigh scattering, named after the British physicist Lord Rayleigh,[1] is the elastic scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The particles may be individual atoms or molecules. It can occur when light travels through transparent solids and liquids, but is most prominently seen in gases. Rayleigh scattering results from the electric polarizability of the particles. The oscillating electric field of a light wave acts on the charges within a particle, causing them to move at the same frequency. The particle therefore becomes a small radiating dipole whose radiation we see as scattered light.

(That's from Wikipedia.)(Quora: your site is less helpful/believable than Wikipedia.)  Rayleigh scattering also has to do with the softness or hardness of the particle.  That's measured by the refractive index:

n= c/v,

where v= the speed of the light through your substance, and c= the speed of light in a vacuum, so that's the same "c" as in E=mc(squared).

Rayleigh scattering is, by the way, why we see the sun as yellow, which

Stupid Question #4 WAIT WHAT I THOUGHT THE SUN WAS YELLOW ALL THE TIME EVEN IF I SAW IT IN SPACE, OR DID SUPERMAN LIE ABOUT THAT TOO?

So we do see air, it's just that we don't see very much of it and the parts we do see are the results of miles and miles of air being piled on top of us (300 miles, total), so we're seeing the results of billions upon billions of extremely rare interactions as the light gets Rayleighed all the way down to us, and by the time the light is near our eyes there's relatively few atoms of air to bounce off of, but if there were lots of them you'd probably see a blue haze around your eyes.

Why blue? That brings us back to

Stupid question #2 Why does the sky reflect all the same uniform shade of blue, instead of slightly different colors because the sky is made up of different atoms or molecules or something of air, and why would nitrogen reflect the same color of blue as oxygen?

 Remember wavelengths of visible light: ROY G BIV or "Richard Of York Gave Battle In Vain," as our British friends like to remember it.  Light goes from very long wavelengths -- 'very' again being relative, okay, everything's relative keep that in mind -- at the red end (650 nanometers) to very short at the blue end (400 nanometers.)

A nanometer is 1/1,000,000,000th of a meter, so you would have to line up 2,500,000 violet light photons in a row to make a yardstick, which I was going to say meterstick but that's dumb, even if it's a meter long we'd still call it a yardstick.

That would be a cool yardstick, though. It would look like a lightsaber.

The important thing to remember here is that how much something Rayleigh scatters is inversely proportional to the fourth power of its wavelength, so the SMALLER the wavelength the larger the scatter, which is why blue and violet light scatter more than red and orange.

Okay, so

Stupid Question #2A why isn't the sky violet then?

Mostly because we breathe oxygen, and partly because of the color of our sun.  Oxygen tends to absorb light near the ultraviolet end, so that reduces the amount of violet we see, and there is more of the kind of light needed to make blue in the spectrum that comes from the sun.  (This caused me to remember when we would burn salts in chemistry to see what spectrum of light they threw off in order to identify them.  I did NOT pass that test.)

Our sun is a 'yellow sun' because of the spectrum of light it gives off. That means that it looks yellowish to us on the Earth, I gather, because if you look at the sun from space, the sun is white.  Also you would be blind, so use sunglasses.

(The sky is of course black in space.)

The sun looks yellow to us because when we look in the direction of the sun (NEVER look directly at the sun although once I did during an eclipse in fourth grade, and I'm still here, so just don't do it for very long) there is less scattering: the rays hit us more directly and we see more of the red and yellow and orange, which is why sunsets aren't blue, either -- it's the way the light is passing through the atmosphere.  At noon, when you look up at the sun (AGAIN NOT FOR TOO LONG) the sunlight comes shooting straight at your retinas from 93,000,000ish miles away and you see most of the spectrum and it evens out to a yellowish-white.  Looked at from the side (i.e., sunset) you see more reds.

As for the rest of question 2, the answer is that the atoms DO refract different colors.  So do larger particles, like smog.

Here is something you didn't know, I bet, and I know I didn't know it: Moonlight is blue, too. Moonlight is just reflected sunlight, but we don't see it as blue because we use rods, not cones, to see at night and rods see only black and white.  If you lived in an area with enough light pollution -- that is, other light to activate your cones -- you'd see the moonlight as blue.  A blue moon is possible all the time!



Then it's on to

Stupid Question #3 If you could have the air immediately around your body be a superdifferent temperature than the air just past it, would you be invisible?

The answer is "yes."  This site explains that carbon nanotubes can conduct heat quickly and efficiently so that a device or cloth made of them would make you invisible.

Or watch this video:



3 comments:

Pat Dilloway said...

Cool, I'm going to wait for my invisibility cloak now.

Andrew Leon said...

Oh, man, I was gonna tell you about the invisible threads thing! I featured that in one of my 2012 a-to-z posts.

I'll tell you the real reason we can't see air; it's not, I bet, because it's not possible, but because we'd freak out. Like our hearing: we can hear down in range to just above the noises our muscles make when we move around. Can you imagine if we could hear into that range? You'd hear everything you do. Everything. Breathing. Blinking. Your heart. Which you can hear, but you don't hear the muscle noise, just the pumping noise. Imagine if you could hear your heart beating ALL THE TIME. So we can't hear that stuff. I think seeing must be the same way. We can't see small enough to inhibit our functionality. I mean, imagine if you could SEE all the microscopic bugs crawling around on your skin. Or the food you were going to eat. Or that tissue you just blew your nose into. And if you could see air? It would be like walking around with a static screen television wrapped around your head. Everyone would go insane.

Liz said...

The sky isn't a uniform blue. Next time the sun is out, look around. Certain parts of the sky are bluer than others.

And the sky does get violet. Sunset.