
Round Peg in a Square Hole [video] - xbryanx
https://www.youtube.com/watch?time_continue=2&v=AvFNCNOyZeE
======
OskarS
I love Tadashi Tokieda so much, he's just one of the most delightful human
beings I've ever seen. I highly recommend all of his Numberphile videos, and
you should also check out his Toy Models lecture [1]. It's so much fun to see
him show some weird phenomenon with marbles or magnets or whatever (that
should be seemingly simple to explain with mathematics and/or classical
physics) and then say "There is no theory for this. We have no idea why this
happens. I'm working on it though".

[1]:
[https://www.youtube.com/watch?v=pkfDYOZ1p4Y](https://www.youtube.com/watch?v=pkfDYOZ1p4Y)

~~~
luisb
Tadashi is awesome! I love his video explaining how someone found a prime that
looks like the Arms of Trinity Hall [1]. Highly recommend all videos from
Numberphile [2] and Fermat's Library [3].

[1][https://www.youtube.com/watch?v=fQQ8IiTWHhg](https://www.youtube.com/watch?v=fQQ8IiTWHhg)
[2][https://www.youtube.com/channel/UCoxcjq-8xIDTYp3uz647V5A](https://www.youtube.com/channel/UCoxcjq-8xIDTYp3uz647V5A)
[3][https://www.youtube.com/channel/UCSD2RxaYn2Nxkm41gp-
eKfA](https://www.youtube.com/channel/UCSD2RxaYn2Nxkm41gp-eKfA)

~~~
imglorp
If you aren't convinced rolling downhill is complicated, physicist Walter
Lewin has a demonstration involving cylinders, no fluids this time.

[https://www.youtube.com/watch?v=cB8GNQuyMPc](https://www.youtube.com/watch?v=cB8GNQuyMPc)

~~~
arbie
That was incredible. Every combination hypothesized, then experimented with,
ending with an intuitive explanation.

~~~
lisper
I'm afraid I have to dissent here.

Compare the footage at 2:10-2:15 with that at 3:20-3:25. He _wants_ the result
to be that the box starts sliding at the same angle in both cases, and that's
what _should_ happen if what they teach in physics 101 is correct, but that is
_not_ actually what happens in the video. In fact, the box starts to slide
noticeably earlier in the second case (which is exactly what the off-screen
crew members predicted). But he simply glosses over this and says "within one
degree the same". What is what _should_ have happened, but is not what
actually happened. This is a very unscientific attitude, and I think this does
a tremendous amount of damage to the popularization of science, particularly
in the face of accusations that science is just another religion with its own
dogmas, high-priesthood, etc.

The correct reaction here would have been, "Hm, that's interesting, it started
sliding earlier. That's not what I expected, and is not what theory predicts.
Let's see if we can figure out why this happened."

It's also kind of lame that we have to rely on his callouts to know what angle
the board is at. It would have been trivial to set up a pointer that would
have been visible to the camera.

P.S. Yes, I know that he "explains" the discrepancy at 3:40, but his
explanation is bogus. First, the discrepancy is much bigger than the "half a
degree" that he explains away. And second, his explanation is actually a
hypothesis that is easily tested: just run the experiment multiple times. He
could easily have done this and again demonstrated how science is actually
supposed to work, but he didn't.

P.P.S. He does it again at 7:02 where the longer cylinder is clearly beating
the shorter one by nearly a full cylinder radius right before he proclaims "no
difference".

~~~
baddox
I understand your complaint, but this isn’t a formal proof or a research paper
seeking peer review. This is an educational demonstration of physics concepts
that have already been very well-established through the much more rigorous
methodology and peer review you are asking for. Of course the educational
demonstration won’t have the same rigor, and it shouldn’t be expected to.

~~~
sago
With respect, I don't think that was his complaint.

The problem is pretending to demonstrate by experiment something that involves
abstractions to the real world.

It's the same thing with 'demonstrations' that a heavy object will fall at the
same speed as a light object where inevitably its 'close enough,' but not
actually true (they do in perfect vacuum, but not in a simple experiment).

This happens a lot in demonstrating science, because science is really messy.
And even relatively simple physical phenomena we don't understand fully (a
recent topical example is we don't properly understand why curling stones curl
the way they do).

The problem is pretending the answer is simpler than it is. Which inevitably
leads to motivated 'pseudo-experiments'.

~~~
lisper
> The problem is pretending to demonstrate by experiment something that
> involves abstractions to the real world.

Not quite. My complaint is pretending that the result of an experiment was
something other than what it clearly was and saying, implicitly, "despite the
fact that you could plainly see that the result of this experiment was NOT
what I said it would be, you should nonetheless believe what I tell you about
the laws of physics because I'm the professor and you are the student and I
know what's what and you don't. Pay no attention to the actual outcome of the
experiment that you saw with your own eyes and instead trust my authoritah."

> This happens a lot in demonstrating science, because science is really
> messy.

That's no excuse here IMO. In this case the demo was simply very poorly
designed. It's just not that hard to construct a friction and moment-of-
inertia demo that actually shows what it is intended to show.

~~~
exodust
Obviously he is gearing up to demonstrate the significant difference between
hollow and solid cylinders. It's the only race out of all that anyone could
place a confident bet on the outcome, and this is what matters. Kids learn
that weight and size make no difference. Kids would probably call out the
differences on the day and then that could be explained and repeated if
needed.

~~~
Judgmentality
I think you're glossing over something very important though - which is that
he visibly demonstrated that he was wrong. I understand his intention and how
he was building up towards the end, but this video makes me question
everything he says rather than believe him. He is very much telling us to
ignore what we saw with our eyes because it disagrees with his prediction,
with very little explanation as to why. He made a prediction, he demonstrated
for us that his prediction was wrong, and then he told us he was still right.
If that's not an appeal to authority then I don't know what is.

~~~
baddox
I just don’t think it’s anywhere near as egregious as you make it sound. If he
had literally told us to ignore our eyes, yes that would be bad. But he
explicitly said that things were close, and that variations in the plank can
cause slight differences, and that averaging a few trials would show extremely
close results. Sure, you have to “take it on faith,” but it’s a very
reasonable explanation, and by the end of the demonstration (when you see the
much larger difference with the hollow cylinders) it becomes clear (or at
least extremely easy to believe) that the tiny variations in earlier
experiments were indeed the result of “impurities” in the physical medium
rather than attempts to conceal inaccuracies in the physics claims being
demonstrated.

~~~
Judgmentality
I admittedly could be wrong, but I feel you're approaching this video from the
assumption that he is a physics professor and what he says must make sense. I
suspect you've already taken physics at some point and this reinforces what
you've already learned.

Consider this from the perspective of someone who knows nothing of physics and
is skeptical of science and academia. Here is a person that shows us he is
wrong, does almost nothing to rectify this (there is a very brief explanation,
but why not more demonstrations? Or really, why not just prepare a better
demonstration that doesn't have these problems?), and then continues to
pontificate as an authority figure.

If his goal is to offer a refresher to people that already know the physics,
okay I guess this makes sense, but I sure as hell would've liked a refresher
on the equations personally (so I am not the target demographic). If his goal
is to teach people that know nothing of physics, he really could've done a lot
more to actually teach and explain things.

Getting back to my first paragraph though, I feel like this comment thread
might be a great example of humans being humans - everybody is susceptible to
confirmation bias (again I could be wrong, but that hypothesis makes the most
sense to me). If you didn't already understand the physics and you didn't take
him at his word because he is a college professor, honestly his tutorial is
unconvincing. He completely ignores the scientific method!

------
wolfgke
To me this is not very surprising to me, since in Germany there exists a well-
known children's game called "Durch eine Postkarte steigen" ("step through a
postcard"), where - as the naming suggests - you have to step through a
postcard while you are only allowed to use scissors to cut the postcard in a
clever way.

Here a German YouTube video that shows how it is done (you don't have to
understand anything that is spoken, since I think the video is quite self-
explanatory):

>
> [https://www.youtube.com/watch?v=ynoLSTsrRhs](https://www.youtube.com/watch?v=ynoLSTsrRhs)

~~~
jonshariat
I think the reason the example in the video is so interesting is that its non-
destructive. It only involves bending and the paper and coaster remain intact.

~~~
wolfgke
> I think the reason the example in the video is so interesting is that its
> non-destructive. It only involves bending and the paper and coaster remain
> intact.

There is a quadratic hole cut into the quadratic paper (which I would clearly
call "destructive"). It is just not shown in the video how the quadratic hole
is cut into the quadratic paper.

If this argument does not convince you, here is another one: Also for stepping
through a postcard after the hole is cut it is just bending the paper.

~~~
Too
Ehh. They way you initially cut the paper constraints how you later can fold
it. If the square was cut any smaller you wouldn't be able to fit the coaster
through no matter how you try to fold the paper. The square and its size is a
constant in this problem, using a scissor to make the square bigger after its
given to you would be considered destructive. In the postcard problem there is
no such constraint as you are allowed to cut in whichever form/size you want.

------
thegabez
Goes to show how poorly adapted our intuition is in manipulating space across
dimensions. Its scary to think about how much ground breaking science is still
left uncovered because of this blindspot.

~~~
joenathanone
The only thing I found surprising about this was that you were expected not to
have known how it worked. It's the same sort of thing as trying to move a
couch and having to angle it to fit it through a door, it's how 3D space
works.

~~~
itg
I think the equivalent would be a door that is too small now matter what angle
the couch is in. The only way to get it through would be to "stretch" the door
in 4-d space and collapse it back into 3-d to allow the couch through.

------
ghostwreck
If you like the idea of solving problems using extra dimensions, Diaspora [1]
takes the idea in some really interesting directions. Just be prepared to
fight through a few sections of intense Riemannian geometry to bring you into
that world.

[1]:
[https://en.wikipedia.org/wiki/Diaspora_(novel)](https://en.wikipedia.org/wiki/Diaspora_\(novel\))

~~~
mirimir
This is probably my favorite novel by Greg Egan. Most of its central
characters are AIs.

------
Starwatcher2001
Love it. It's stuff like this that got me interested in science. I remember
seeing the same thing (larger object through a smaller hole) demonstrated on
"How" in the 1970s, which was a TV show with a quirky mixture of science and
fun. It was aimed at children, but didn't talk down to them.

Here's a ransom episode for those who remember that show.

[https://www.youtube.com/watch?v=rsDd_9VpzHE](https://www.youtube.com/watch?v=rsDd_9VpzHE)

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kamranjon
so cool - I also like the term 'ambient 3rd dimension'

~~~
wereHamster
But let's not hijack a perfectly well understood technical term and give it
another meaning. "isomorphism" in the javascript community, I'm looking at
you.

~~~
ape4
Programs do well defined things in their space but are sometimes aware of
stuff outside their space - eg if another program slows down the machine
exposing a timing bug in the first program.

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runeks
Seems obvious to me: you have a square with four sides of length _n_ , and
when you fold the paper, the four-sided square with a circumference of _4n_
becomes a slit of length _2n_.

------
tomtimtall
You can fit any object at any size through a an arbitrarily small and
arbitrarily shaped hole. Just blend it an send it through as a stream with the
same cross section as the hole. The naysaers will say that this is cheating
because you are changing the shape of the object, but the trick mentioned here
is just changing the shape of the hole from a square of one perimeter length
into a rectangle with the same perimeter length. Similar yet simpler trick for
those who don’t have a blendtec ready at hand.

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aidos
Someone posted this in a comment on HN during the week and I subscribed
immediately. Soooo wonderful. I'm definitely going to give this a shot with
the kids tomorrow. Thanks for reminding me.

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sackeyj1
Didn't think I'd really be that interested in this. Kind of made me excited.
Thanks.

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andy_ppp
I think about the analogy of folding spacetime when I see things like this...
what could you used to fold a 4d region of spacetime into a fifth dimension to
create a “wormhole” and where would it lead? I’m not even sure what this would
mean!

------
jonplackett
Never heard of Tadashi Tokieda before so THANKS!

------
Slansitartop
Great video, but I think it would have been better without the cartoons. They
were distracting and added nothing.

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sillysaurus3
I wish HN would loosen up and admit that videos are a new medium, worth taking
seriously. It might bother us that longform writing is dying, but when the new
generation decides that this is the way new ideas should be communicated,
we'll be left with no audience.

For example, I've been working on an essay for some time now, but I'm
seriously considering making it into a companion video. I have no video
experience whatsoever, so that's a tall order. But what are you to do? If you
want to make an impact, are you sure it's still possible to do it by writing
173 essays over 15 years? It used to be, but the world seems to be changing.

(This is mostly a reaction to this post being one of the rare videos Deemed
Worthy to be on the front page, when there are tens of thousands of others.
It's not a good idea to mix up the content too much, but there really are a
lot of quality videos and no central curation mechanism. Unlike articles.
/r/videos is for mainstream content, like
[https://youtu.be/kJGGlVg5PpY](https://youtu.be/kJGGlVg5PpY). There really
isn't any place that collects intellectually gratifying content like the
current submission.)

~~~
stochastic_monk
I typically don’t have the patience for most videos. I want information, and
much of the time, the information bandwidth or payoff is too low. I think
video can be great auxiliary, supporting material, but there should usually be
a textual component when trying to inform.

~~~
__s
I get around this by watching videos in fast forward

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neogodless
Ahhh Easter Egg! Firmware version! Love it!

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IshKebab
Thought this was going to get clever but... it didn't.

