A while back we introduced you to Zogg the alien from Betelgeuse. Zogg has been busy helping aliens understand bizarre human concepts like “rituals” and “vision”, but he took a side journey to help everyone understand the geometry of the Universe. What does it mean to have a flat, finite Universe? How could you travel in one direction and return to your starting point?
The first episode was fantastic, and now serves as my favorite link to send people when they’re having trouble wrapping their head around the concept of a finite Universe. How the Universe can be expanding, without expanding into anything. Seriously, if you haven’t seen Part 1, stop and go watch it now.
True to his word, Zogg released this second episode, detailing the geometries of the Universe. What do cosmologists mean when they say the Universe is “curved” or “flat”. What could the curvature look like.
Watch it and enjoy. I can’t wait for Part 3.
I will remember to stay alien, because I’ve just got youtubed: an odd event. =D
Well, I can’t add a large comment after that. I think the series is well produced, and I certainly like the humor – I’m an avid watcher.
What I can do is to recommend watching Susskind’s cosmology lectures series [youtube] as a complementary (but unfortunately much longer) view. I suspect both series are the better for having that contrast.
Susskind, perhaps arguably, dismisses torus topologies (in one of his two lecture series) as a) non-observed and b) non-isotropic: the repeat distances are different in different directions.
The latter is a serious problem for alternatives I think, because we only know how to do cosmology in so called Friedmann universes, and they are homogeneous and isotropic. In practice it means universes are large compared to a Planck volume, and they have a causal structure from having a general relativistic spacetime.
Also, a possible nitpick: If I remember correctly on the many hours of video Susskind also notes that the cosmological principle is nowadays an observation (within at least a volume 1000 times the observable universe due to observations of cosmic variance).
And one should argue also a theoretical constraint (for all of it) rather than a principle, see above.