Editing 1145: Sky Color
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| date = December 10, 2012 | | date = December 10, 2012 | ||
| title = Sky Color | | title = Sky Color | ||
− | | image = | + | | image = sky color.png |
| titletext = Feynman recounted another good one upperclassmen would use on freshmen physics students: When you look at words in a mirror, how come they're reversed left to right but not top to bottom? What's special about the horizontal axis? | | titletext = Feynman recounted another good one upperclassmen would use on freshmen physics students: When you look at words in a mirror, how come they're reversed left to right but not top to bottom? What's special about the horizontal axis? | ||
}} | }} | ||
==Explanation== | ==Explanation== | ||
− | The point of this comic is that often, curious children ask their parents simple questions about understanding how the world works. | + | The point of this comic is that often, curious children ask their parents simple questions about understanding how the world works. [[Randall]]'s hobby is to make those questions significantly harder to stump the parents and make them uncomfortable. |
− | + | Another point of this comic is that we often think that we understand a scientific phenomenon (e.g. why is the sky blue?); however, a certain simple question (e.g. why isn't the sky violet?) can often uncover large gaps in our actual understanding. One interpretation is that this second question is the "tricky" one. | |
− | + | {{W|Rayleigh scattering}} is the phenomenon that explains the color of the sky, where light of every wavelength gets scattered in the air by the inverse quartic (fourth power) of its wavelength as given in the comic. In the {{w|visible spectrum}}, blue light has a wavelength of 450–495 nm while violet has a shorter wavelength of 380–450 nm. Violet light does indeed get scattered more than blue light, however the lower portion of the spectrum for sunlight consists of blue light and eyes are much more sensitive to blue light than violet light. This leaves the impression of a blue sky. A good explanation, including why blue and not violet, can be found in [http://math.ucr.edu/home/baez/physics/General/BlueSky/blue_sky.html Usenet Physics FAQ :: Why is the sky blue?], but note that human color perception [http://blog.asmartbear.com/color-wheels.html is more complicated] than described there. | |
− | {{ | + | The title text refers to a {{w|mirror image}}, and is discussed by the famous American theoretical physicist {{w|Richard Feynman}} in a famous BBC documentary [http://www.youtube.com/watch?v=6tuxLY94LXw], as one of the problems which he used to have fun with first years (British English for first year student or freshman). |
− | + | A mirror image is a virtual image produced by the reflection of light on a mirror. In the mirror image, only front and back are switched around - like a printing press or a rubber stamp. Left and right are still left and right in an absolute reference frame - wave your left arm in front of the mirror and the "mirror person" also waves the arm on the left side. It is only when using "personal" reference frame - tied to the individual - that we can say that the "mirror person" is moving their right arm. The apparent inversion comes from the fact that the mind projects itself onto the person in the mirror. | |
− | + | To help understand why this effect happens, imagine that you are holding a sign which says "MIX" and facing a mirror. Initially, you face the sign towards you. The M is on the left and the X on the right. Now, you turn the sign around so that the sign faces the mirror. Now, even without paying any attention to the mirror, simply because you have turned it around, now the M is on the right and the X is on the left and if you could see through the back of the sign, it would say "XIM" from your perspective. When you look at it in the mirror, you are now able to see that orientation and it appears to read "XIM". If instead of turning the sign around horizontally to look at it in the mirror, you flipped it vertically and looked at it in the mirror, it would appear to say "WIX" in the mirror. Thus the mirror is only revealing how the text is oriented relative to your eyes. Or, to put it more succinctly: mirrors ''don't'' reverse left to right, ''turning around'' does. | |
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==Transcript== | ==Transcript== | ||
− | :[ | + | :[Girl and her mother, Megan. Megan is at a desk and facing the girl.] |
− | : | + | :Girl: Mommy, why is the sky blue? |
:Megan: Rayleigh scattering! Short wavelengths get scattered ''way'' more (proportional to 1/''<span title="lambda">λ</span>''<sup>4</sup>). Blue light dominates because it's so short. | :Megan: Rayleigh scattering! Short wavelengths get scattered ''way'' more (proportional to 1/''<span title="lambda">λ</span>''<sup>4</sup>). Blue light dominates because it's so short. | ||
− | : | + | :Girl: Oh. |
− | : | + | :Girl: So why ''isn't'' the sky violet? |
:Megan: Well, because, uh... ...hmm. | :Megan: Well, because, uh... ...hmm. | ||
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:My hobby: Teaching tricky questions to the children of my scientist friends. | :My hobby: Teaching tricky questions to the children of my scientist friends. | ||
{{comic discussion}} | {{comic discussion}} | ||
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[[Category:Comics featuring Megan]] | [[Category:Comics featuring Megan]] | ||
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[[Category:Physics]] | [[Category:Physics]] | ||
[[Category:My Hobby]] | [[Category:My Hobby]] |