Uploaded October 2023 | Updated September 2026, 2 weeks ago
The painter's paradox, a.k.a. Gabriel's horn paradox a.k.a. Torricelli's horn paradox has been done to death on YouTube. So why do it again? Well, being all about some remarkable features of 1/x, this topic nicely complements the previous two videos that were also dedicated to 1/x. Now the first Mathologer trilogy is complete! Also, I thought of a couple of nice twists to make this treatment of the painter's paradox really stand out from the crowd (I hope :)
00:00 Intro
02:59 What's that horn?
07:09 A 700 year old trick
12:26 What's the volume exactly?
16:33 What paradox?
18:17 Fun fact.
20:12 Thanks
Must check out.
Wiki page on the horn: en.wikipedia.org/wiki/Gabriel%27s_horn
(also has a nice discussion of the converse of the paradox at the end)
Wiki page on Torricelli: en.wikipedia.org/wiki/Evangelista_Torricelli
(the anagram that featured in the video also gets a mention on this page)
Very nice write-up of the history of the horn by Paolo Mancosu and Ezio Vailati jstor.org/stable/233514 tinyurl.com/3rff7ubb
Wiki page on Oresme: en.wikipedia.org/wiki/Nicole_Oresme
(has a page from one of his books with some graphs. Somehow overlooked this one. Would have been nice to flash this in the video :(
Stanford Encyclopedia of Philosophy entry on Nicole Oresme (in particular, see the section on math) https://plato.stanford.edu/entries/nicole-oresme/#maths
Wiki page on the Method of shells: en.wikipedia.org/wiki/Shell_integration
Fun/intersting: The opposite of this is a vuvuzela, which is a horn with finite surface but infinite volume (as in loud)
One interesting observation is that both area and volume being finite or infinite is independent of what unit we use. Therefore it does make sense to compare finite/infinite volumes and surface areas of shapes. And one interesting observation in this respect is that solids of infinite volume and finite surface area don't exist. On the other hand, that also means that areas and volumes scaling differently is not part of the resolution of our paradox which only depends on the volume being finite and the surface area being infinite.
Music at the end: Young rich pixies - Year of life
T-shirt: TONEWAVE Music Tee Geometric Overtone Frequency Musician Sacred Geometry Tshirt etsy.com/ca/listing/212767891/unisex-tonewave-music-tee-geometric
Enjoy!
Burkard
The painter's paradox, a.k.a. Gabriel's horn paradox a.k.a. Torricelli's horn paradox has been done to death on YouTube. So why do it again? Well, being all about some remarkable features of 1/x, this topic nicely complements the previous two videos that were also dedicated to 1/x. Now the first Mathologer trilogy is complete! Also, I thought of a couple of nice twists to make this treatment of the painter's paradox really stand out from the crowd (I hope :)
00:00 Intro
02:59 What's that horn?
07:09 A 700 year old trick
12:26 What's the volume exactly?
16:33 What paradox?
18:17 Fun fact.
20:12 Thanks
Must check out.
Wiki page on the horn: en.wikipedia.org/wiki/Gabriel%27s_horn
(also has a nice discussion of the converse of the paradox at the end)
Wiki page on Torricelli: en.wikipedia.org/wiki/Evangelista_Torricelli
(the anagram that featured in the video also gets a mention on this page)
Very nice write-up of the history of the horn by Paolo Mancosu and Ezio Vailati jstor.org/stable/233514 tinyurl.com/3rff7ubb
Wiki page on Oresme: en.wikipedia.org/wiki/Nicole_Oresme
(has a page from one of his books with some graphs. Somehow overlooked this one. Would have been nice to flash this in the video :(
Stanford Encyclopedia of Philosophy entry on Nicole Oresme (in particular, see the section on math) https://plato.stanford.edu/entries/nicole-oresme/#maths
Wiki page on the Method of shells: en.wikipedia.org/wiki/Shell_integration
Fun/intersting: The opposite of this is a vuvuzela, which is a horn with finite surface but infinite volume (as in loud)
One interesting observation is that both area and volume being finite or infinite is independent of what unit we use. Therefore it does make sense to compare finite/infinite volumes and surface areas of shapes. And one interesting observation in this respect is that solids of infinite volume and finite surface area don't exist. On the other hand, that also means that areas and volumes scaling differently is not part of the resolution of our paradox which only depends on the volume being finite and the surface area being infinite.
Music at the end: Young rich pixies - Year of life
T-shirt: TONEWAVE Music Tee Geometric Overtone Frequency Musician Sacred Geometry Tshirt etsy.com/ca/listing/212767891/unisex-tonewave-music-tee-geometric
Enjoy!
Burkard








![What does this prove? Some of the most gorgeous visual shrink proofs ever invented
Bit of a mystery Mathologer today with the title of the video not giving away much. Anyway it all starts with the quest for equilateral triangles in square grids and by the end of it we find ourselves once more in the realms of irrationality. This video contains some extra gorgeous visual proofs that hardly anybody seems to know about.
0:00 Intro
0:47 First puzzle
2:24 Second puzzle
3:50 Edward Lucas
4:41 Equilateral triangles
13:15 3d & 3rd puzzle
19:52 30 45 60
29:31 Credits
Here are links to/references of some of the things I mention in the video:
Joel Hamkins blog posts that inspired this video:
http://jdh.hamkins.org/no-regular-polygons-in-the-integer-lattice/
http://jdh.hamkins.org/no-regular-polygons-in-the-hexagonal-lattice/
There is also a whole chapter about all this and much more related maths in his new book
https://www.amazon.com/Proof-Mathematics-Joel-David-Hamkins/dp/0262539799
Here is another really good article which includes a nice characterisation of the triangles that can be found in square grids plus a very good survey of relevant results:
Michael J. Beeson, Triangles with Vertices on Lattice Points, The American Mathematical Monthly 99 (1992), 243-252, https://www.jstor.org/stable/2325060?seq=1
Scherrers and Hadwingers articles:
Scherrer, Willy, Die Einlagerung eines regulären Vielecks in ein Gitter, Elemente der Mathematik 1 (1946), 97-98.
https://tinyurl.com/y45p64t7
https://gdz.sub.uni-goettingen.de/id/PPN378850199_0001?tify={%22pages%22:[101]}
Hadwiger, Hugo Über die rationalen Hauptwinkel der Goniometrie, Elemente der Mathematik 1 (1946), 98-100.
https://tinyurl.com/yx98kkqt
https://gdz.sub.uni-goettingen.de/id/PPN378850199_0001?tify={%22pages%22:[102],%22view%22:%22info%22}
Another, nice paper on rational (and algebraic) cosines
https://arxiv.org/pdf/1006.2938.pdf
Here is a solution to the first puzzle (one way to find the general formula):
https://nrich.maths.org/657/solution
The music in this video is by Chris Haugen, Fresh Fallen Snow (playing in the video) and Morning Mandolin (for the credits)
A couple of remarks:
1. Probably the simplest way to deduce the sin and tan parts of the rational trig ratio theorem is to realise that they follow from the cos part via the trigonometric identities: sin(x)=cos(90-x) and tan^2(x) = (1-cos(2x))/(1+cos(2x)). Note that the second identity implies that if tan(x) is rational, then cos(2x) is rational (if tan(x)=c/d, then tan^2(x)=c^2/d^2=C/D and cos(2x)=(D-C)/(D+C)).
2. Bug report.
a) Here I redefine cos(120◦) = 1.
https://youtu.be/sDfzCIWpS7Q?t=1362
Remarkable :(
b) This transition to the good stuff I clearly did not think through properly.
https://youtu.be/sDfzCIWpS7Q?t=1018
Its possible to make this work for all regular n-gons. There is only one complication that occurs for ns that are of the form 2 * odd. For the corresponding regular n-gons, if you pick up the edges in the order that they appear around the n-gon and assemble them into a star, things close up into (n/2)-stars. For all other n, things work exactly as I showed in the video. Having said that you can also assemble the edges of one of the exceptions into stars. Have a look at this https://imgur.com/68A3fEe and youll get the idea. Anyway lots more nice side puzzles to be explored here if you are interested :)
Enjoy!
Burkard
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14. Sep. 2021: Thank you very much Michael Didenko for your Russian subtitles. What does this prove? Some of the most gorgeous visual shrink proofs ever invented](https://i.ytimg.com/vi/sDfzCIWpS7Q/mqdefault.jpg)

