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The Quintic, the Icosahedron, and Elliptic Curves [pdf]

106 点作者 mathgenius大约 1 年前

6 条评论

n4r9大约 1 年前
Back in my undergrad days, there was a second year course titled &quot;Groups, Rings and Modules&quot;. The lecturer (NSB) was notorious for his very dense and formal delivery, which left a lot of work to the reader. Another - much more popular - professor (IL) decided to offer an alternative version of the course during the same timeslots in a friendlier style. Despite NSB&#x27;s absent-minded nature, it cannot have escaped his attention that ~10 people attended his lectures while the bulk of the year group queued up outside a different hall. Some friends and I attended NSB&#x27;s lectures out of bloody-mindedness. We anticipated (correctly, it turns out) that if you managed to understand his notes, then you <i>really</i> understood the topic.<p>The reason I&#x27;m reminded of this is that one of the big theorems of the course is the simplicity of A5. I vaguely remember that NSB provided the icosahedron-based proof that&#x27;s mentioned in the linked article, whereas IL provided a more intuitive and sensible proof.<p>One of the perks of being the official lecturer is that you set the exam questions. Imagine our delight when we opened the paper and saw the question: &quot;By considering the rotations of an icosahedron, prove that the group A5 is simple&quot;!
ykonstant大约 1 年前
What a great exposition; very happy this dear topic of mine garnered some interest from HN folks.
joecarmody大约 1 年前
Nice to see some Riemann Academy on the front page of HN...
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JadeNB大约 1 年前
See also the lovely discussion by Baez at <a href="https:&#x2F;&#x2F;classes.golem.ph.utexas.edu&#x2F;category&#x2F;2017&#x2F;12&#x2F;the_icosahedron_and_e8.html" rel="nofollow">https:&#x2F;&#x2F;classes.golem.ph.utexas.edu&#x2F;category&#x2F;2017&#x2F;12&#x2F;the_ico...</a> .
ocfnash大约 1 年前
You can see Klein&#x27;s work in action in Python here if you&#x27;re interested:<p><a href="https:&#x2F;&#x2F;github.com&#x2F;ocfnash&#x2F;icosahedral_quintic">https:&#x2F;&#x2F;github.com&#x2F;ocfnash&#x2F;icosahedral_quintic</a>
empath-nirvana大约 1 年前
&gt; In 1963, the Russian mathematician Vladimir Arnold gave an alternative topological proof of the unsolvability of the quintic in a series of lectures to high school kids in Moscow.<p>...<p>&gt; Arnold’s insight was to show that if there is a radical formula for the roots of a general polynomial, then the “dance of the roots” cannot be overly complex, in the sense that the image of the monodromy map must be a solvable subgroup of . But, for example, the 1-parameter Brioschifamily of quintics () = 5 + 103 + 452 + 2, ∈ ℂ has monodromy group 5 (see Figure 1), which is certainly not solvable since it is simple, as we will see by relating it to the icosahedron in the next section. Hence the unsolvability of the quintic.<p>...of course, well within the reach of most high school students.
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