1670: Laws of Physics

Explain xkcd: It's 'cause you're dumb.
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Laws of Physics
The laws of physics are fun to try to understand, but as an organism with incredibly delicate eyes who evolved in a world full of sharp objects, I have an awful lot of trust in biology's calibration of my flinch reflex.
Title text: The laws of physics are fun to try to understand, but as an organism with incredibly delicate eyes who evolved in a world full of sharp objects, I have an awful lot of trust in biology's calibration of my flinch reflex.

Explanation[edit]

Black Hat, being Black Hat, is deliberately perverting a classic physics demonstration. In the normal version of the demonstration, a heavy ball on a pendulum is pulled to one side until it is almost, but not quite, touching the demonstrator or volunteer's nose or chin. When the ball is released at rest, it swings down and away, then back up to (almost) the same distance in the arc from where it started — but never (by the laws of physics) farther than where it started. As long as the demonstrator doesn't lean in or push the ball, it's impossible for it to strike them. It's a natural instinct to move away or protect yourself if you see a heavy object moving quickly toward you, but confidence in the physics of the demonstration means there is no reason to flinch. (Sample videos: [1], [2].)

In this comic, Cueball is not standing at the beginning edge of the ball's movement, but rather at the base of its swing, meaning that the ball will strike him at its maximum speed. Presumably, Black Hat is entirely aware of this and is hoping that Cueball's understanding of physics is insufficient to see through this prank. Judging from the "slack" of the rope, the ball should not hit Cueball in the head but would almost certainly hit him in a lower, and quite painful, place...

The title text refers to the fact when someone flinches during the pendulum experiment, they are commonly accused of not having faith in the laws of physics. Randall is rebutting this argument by stating that, rather than not having faith in science, he is actually in tune with it, specifically the biological processes that led to the flinch reflex. His eyes and his flinch reflex have been calibrated through millions of years of evolution. To instantly dismiss his body's natural reaction when a heavy object comes quickly towards his face does not give enough credit to these mechanisms that successfully kept him (and every one of his ancestors) alive. In other words, while flinching may indicate doubt of the laws of physics, it may equally well indicate trust in the laws of biology.

The idea of hitting someone else with a pendulum is also the topic of 755: Interdisciplinary.

Transcript[edit]

[Black Hat is standing on a ladder, holding a heavy ball attached to a line from above. Cueball stands beneath, where if the ball swings it will smack him right in the face.]
Black Hat: Okay, hold still.
Black Hat: And remember, if you really believe in the laws of physics, you won't flinch.


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Discussion

This was demonstrated nicely by Neil deGrasse Tyson in episode six of the new Cosmos. [3] .42 (talk) 15:18, 20 April 2016 (UTC)

Another demonstration: [4] ;) --198.41.242.240 16:06, 20 April 2016 (UTC)
This youtube video with Neil deGrasse Tyson has been modified heavily from 6 secs to the end and no longer represents true psychics. Is this video here as a joke or should it be removed? --108.162.214.197 22:19, 20 April 2016 (UTC)
Richard Dawkins demonstrated this as part of his Royal Institution Christmas Lectures in 1991. This is shown at the start of his video interview describing the experience of presenting the lectures. [5] He also discusses it in the second volume of his autobiography Brief Candle in the Dark Ericmberg (talk) 01:01, 15 June 2016 (UTC)

I believe that the line about having faith is also supposed to be a dig at magical thinking in science. Cueball may "know" that the experiment works because he's seen it done, but he hasn't thought it through enough to realize that it doesn't work from the other direction. 173.245.54.252 16:32, 20 April 2016 (UTC)

I concur. "if you really believe in the laws of physics, you won't flinch" seems like Black Hat teaching a very important lesson to Cueball about trusting appeals to science. Not kindly. 162.158.255.103 (talk) (please sign your comments with ~~~~)

Could it also be interpreted that Black Hat is talking to himself, instead of Cueball?

108.162.237.221 17:29, 20 April 2016 (UTC) Brian
Black Hat being Black Hat, I very much doubt that. 162.158.150.219 19:53, 20 April 2016 (UTC)
He could be reassuring the ball. Elvenivle (talk) 03:49, 21 April 2016 (UTC)

The comic is in 2d. Are we sure that Black Hat will release the ball in a plane that actually runs through the volunteer? If the plane is actually just in front of the volunteer's nose, then he will not be hit (okay, there may be precession, but that will only come into play after a while). In that interpretation, the volunteer still needs trust, but not only in physics, but also in Black Hat's ability to release the ball in a suitable plane. --Markus (talk) 17:47, 20 April 2016 (UTC)

There's slack in the line. Assuming the ball swings, a rough measurement seems to position it below Cueball's chin. Elvenivle (talk) 03:49, 21 April 2016 (UTC)
Around this location actually; I bet that smarts. Elvenivle (talk) 05:11, 21 April 2016 (UTC)

Inocalash: Assuming that the line is not a bungee cord. otherwise knowing black hat he might of set this off in a very well calculated bouncing action that will actually not hit Cueball. as if the balls weight was just right it would bounce over Cueball's head. as the start height is indeed above Cueball. 141.101.98.85 (talk) (please sign your comments with ~~~~)

Possible reference to #755? 108.162.222.143 03:27, 21 April 2016 (UTC)

It does seem his head is tilted towards the ball. Elvenivle (talk) 03:49, 21 April 2016 (UTC)

This experiment is in the novel "Contact" by Carl Sagan. Chvsanchez (talk) 06:09, 21 April 2016 (UTC)

In that demonstration the tested subject flinches and her companion notes "You have a lot of trust in science, but not total trust" (or something along those lines), upon which she answers "No, that’s not it: that was a million years of brain fighting a few billion years of evolution." – which is imho the same topic as Randall's title text. 162.158.150.137 12:06, 22 April 2016 (UTC)
Definitely reference to "Contact". It should be mentioned. 162.158.238.22 11:33, 19 January 2017 (UTC)

Could the joke also be that flinching won't help Cueball much at all when he gets creamed by a bowling ball? 173.245.54.31 21:18, 21 April 2016 (UTC)