51–60 of 84 posts
Earlier quoted context omitted.
The video says, "Not available in my area"! I don't think they realize I'm in the USA. The U-S-A! Everything is available to me. How could anyone let this happen?!
That's surprising: I thought YouTube's unit of granularity was the country. I'm in the US too and can see the video. I guess this means it's available in some parts of the country and not others. Hurray for being in Boston, then.
"Mirrors don't reverse left and right. They reverse in and out."
Then tell the interviewer that only an idiot would look at a local coordinate frame and think it's a global one. Just what is he insinuating? This had better not be one of those "stress interviews" people talk about. There's no way in hell you're going to work for a company that will screw around with you on day one just to see how you'll react.
Works every time.
Instead, put a paper bag on one hand and stick your hands out. Look in the mirror. Your "bag" hand and mirror you's "bag" hand are both pointing the same way!
Now stick the bag on your foot. Look, mirror you's bag foot and your bag foot both point the same way!
Now stick the bag on your head. Look, mirror you's bag head is in the dark!
But seriously, everything in the mirror is oriented congruently with this "side" of the glass. The appendages wearing a bag always match up. "Bag hand" and "not bag hand" match just like head and feet do.
Oversimplification (ignores angle of light from object observed to eye), but here:
Imagine standing in front of a mirror, both arms straight out. A photon leaves your left index finger, travels straight to the mirror, and is reflected straight back.
Now imagine photons leaving all your parts, traveling to the mirror, and reflecting straight back.
That's all.
Mirror's don't flip left and right. We implicitly compare a mirror image to the original by rotating the object, and naturally we maintain top/bottom orientation, this gives the appearance of "flipping" the object left to right. However, if you use vertical rotation to super-impose the object on its mirror image you'll see that it seems to have been flipped top-to-bottom instead.
The way I see it, the mirror does flip up and down, at least by the measure of the same experiment used to prove that it flips left and right. To prove that it flips left and right, imagine a vertical pole between you and the mirror. The pole has a card attached to it with the front facing the mirror. The two dots, red and blue are painted on the card and you can see their reflection in the mirror. In the reflection,…
This proves that the mirror flips left and right."
All it proves is that you've rotated the card. You've done the flipping, not the mirror.
Now, without doing any rotation to the card, if the card is seen from the perspective of the mirror, the blue dot is on the left, and the red on the right.
Depending on which perspective you're looking at an object from, one side will be on your left, and the other on your right. But no flipping takes place, unless you either move yourself to a different perspective, or rotate the object. A mirror does neither. It just reflects back exactly what's in front of it.. so you see whatever's on your right on your right, and whatever's on your left on your left. There is no flipping.
The same part of your body is reflected at the same side in the mirror (paint your cheeks with different colors; the mirrored cheeks have the same color on the same side as the normal). However, we CALL the cheek left or right depending on where we are facing. The mirrored image reverses the facing so its left and right are ASSIGNED that way, though it's the same physical cheek.
Up and down are absolute regardless of where we face. A mirrored image only changes the "facing" aspect so up and down don't change.
Mirrors don't flip anything. Oversimplification (ignores angle of light from object observed to eye), but here: Imagine standing in front of a mirror, both arms straight out. A photon leaves your left index finger, travels straight to the mirror, and is reflected straight back. Now imagine photons leaving all your parts, traveling to the mirror, and reflecting straight back. That's all.
My high school history teacher asked this same question (yes, it is that old) and my answer at the time was: Left and right are assigned relative to where you are facing, while up and down are not regardless where you're facing. The same part of your body is reflected at the same side in the mirror (paint your cheeks with different colors; the mirrored cheeks have the same color on the same side as the normal). Howev…
I believe InclinedPlane's answer [1] is much better. We implicitly perceive the reflection as having rotated as a human would, by turning around on his or her feet.
However, if instead the reflection is perceived as having rotated vertically, with the human flipping over onto his or her head, the image is actually flipped vertically.
So the answer is actually that the image in the mirror is either flipped horizontally or vertically, depending on one's perception of how the mirror image got there in the first place.
While the local/global orientation explanation does show that there are no inconsistencies, and the lack of a relative orientation for 'up' clouds things a bit, it doesn't actually explain at all why we naturally look at the image and decide it's flipped horizontally.
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> intellectual dickswinging Yes... but not just intellectual.
True. But fortunately that doesn't come up in the BBC interview. Also I don't think swinging is quite the right verb for that area of his pursuits.