So after watching the famous video on youtube How to turn a sphere inside out I noticed that the sphere is deformed into 8 bulges in the process. Is there something special about the number 8 here? Could this be done with any number of bulges, including 2?


enter image description here

Video: How to Turn a Sphere Inside Out

  • $\begingroup$ I don't understand in this matter much, but as far as I know, the process would be much faster using 8 bulges rather than 2 $\endgroup$ – DanielY Aug 25 '13 at 14:26

No, 8 isn't special beyond it being the choice they made for that specific video.

The software the group wrote to make that video allowed you to choose that parameter arbitrarily. I bet if you spent some time digging you could find that software somewhere on the internet, and create your own eversion videos with a different choice of the number of corrugations.

You can find a (modified) version of the source code here: http://profs.etsmtl.ca/mmcguffin/eversion/

as well as commentary from Silvio Levy on the choice of number of strips.

  • 1
    $\begingroup$ So if I'm interpreting this correctly, it's an open question? There could exist eversions with fewer bulges but no one is sure? $\endgroup$ – Kieran Cooney Aug 27 '13 at 17:58
  • 1
    $\begingroup$ Such eversions exist but whether or not the software actually produces them is not known. If you think through the argument Thurston gives in the outside-in video, it works with any number of corrugations. But the software has limitations so what it does exactly if you specify only two, I don't know. I think I used to know but I've forgotten! $\endgroup$ – Ryan Budney Aug 27 '13 at 18:01

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.