Christopher Sykes
3 HN recommenders · recommended in 3 months, 2012–2024
3:16 · 600K views · May 26, 2008
Richard Feynman, in a clip from the BBC series Fun to Imagine, takes on the puzzle of why mirrors seem to swap left and right but not top and bottom.
Cited as the best explanation of mirror reversal.
3 comments from Hacker News
1. Feynman explains it best this video 3. They approach one another at 30000 mph = 500 miles per minute, so two minutes before they collide they are 1000 miles apart, and who cares that they start out 1317 miles apart? 8. The balloon rushes forward, and gets pulled toward the inside of the curve. The best reasoning is via the equivalence principle: acceleration and gravity feel the same, and the fact that the balloon is buoyant in air means that it should rush away from whatever direction gravity is pointing. 9. It floats at the same location, by Gauss' theorem.
Since left and right and up and down are both the same, it's essentially as though you're looking through the back of the object. Imagine if you made a sign clear and looked through the back. Even though no reversal has taken place, the text looks backward. This is why things appear reversed. If you are confused about how left and right are not actually switched, I would say the easiest way is to think in absolute terms, not relative. That is, don't think about left and right, think about east and west. Face north and paint your east (right) hand red. Now when you look at a mirror (you're still facing north), your east hand is red, but the reflection's east hand (think in real world terms here) is also red. That's because the reflection's horizontal aspects have not been reversed. Richard Feynman enjoys discussing this: this video
> One thing I do remember though is how odd it felt looking at yourself in a mirror without your image being mirrored. Not sure my brain was ready for that one after thousands of years of looking at itself in mirrored surfaces. Feynman has a good explanation for that: this video But it doesn't go deeper as to why we're perceiving ourselves that way, for that we have to dive into biology, neurology, bilateral symmetry, and the fundamentals as to how, as bilaterally symmetric beings, we're able to orient ourselves in a 3D world. (I recall reading a paper or watching some video about that, but can't find it anymore)