Cosmology | Lecture 5

[786GuardianAngel]

He made a big jump at one point (around 44:00). What does the fact (pertinent to the stereographic projection) that objects further away from the south pole have a larger projection, have to do with how big objects appear to us from earth.

[786GuardianAngel]

Question from the very first part: Can one describe a circle without resorting to a (Euclidean) two-dimensional embedding space?

[786GuardianAngel]

@786GuardianAngel : OK he answers my question later: one can use a metric. That's a cool idea.

[whotaughtyou]

RECORDING ECARD SADDAM HUSSEIN

[csmcmillion]

There's an old adage in psychology - you can't communicate w/ someone who is more than 25 IQ points different than you. Now, IQ per se is over rated, but I think there is something to the concept. I'm no genius, maybe up around 125 level, but I can tell you that trying to relate ideas to someone who is a 90 is nearly impossible. They just can't grasp the fundamental concepts. Likewise, I have to work really hard to grasp some of Susskind's concepts (esp in GR).

[sbergman27]

@csmcmillion I would disagree with your implied assertion that one can describe intelligence with a single number, let alone measure it. We have some pretty good examples to suggest that we cannot. So-called "idiot-savants", and what are we to make of dolphin intelligence? Bigger brains. More convolutions. Far greater surface area. But we have hands, and that helps. Are hands intelligence? Intelligence is multi-faceted. Your claim of being "up around 125 level" is just meaningless.

[csmcmillion]

@sbergman27 Agreed. That's what I meant when I said it is overrated. Intelligence is a complex beast, and IQ as a metric doesn't mean a lot. I doubt Susskind would actually score all that high - he seems to stumble on some "practical" concepts, and practical problem solving is a large part of IQ testing. I've heard Feynman was around 120(?) yet brilliant in his field. Again, much difference b/t abstract reasoning and other types.

[dmkramerica]

"If I'm dead, hold the class anyway."

[dokaflokajoe]

Wouldn't a -1 sphere be a singularity?

[BigMTBrain]

I HIGHLY recommend (to everyone watching) the 10-part series titled "Geometry Dimensions" which begins at: /watch?v=FTP-H4oFLYc . It starts out slow, but, trust me, when it gets going... it really gets going. It's a brilliant and beautifully produced series. If you have difficulty imagining the geometries discussed here in Lecture 5, The "Geometry Dimensions" series will rid you of that.

[captainhampton]

@BigMTBrain Great suggestion, the video was done excellently!

[PeaceyWeasey]

Thank you very much for these online lectures!

Now I know what a closed (positively curved), open (negatively curved) and flat universe means.

Prof. Susskind is a good lecturer.

[sbergman27]

@PeaceyWeasey Susskind is an incredibly annoying lecturer. Everyone goes on about how fantastic he is. But... he starts a sentence... changes his mind... goes back... forgets what he said... remembers... changes the subject... goes off on a tangent... negotiates some terminology... forgets to use it... apologizes for that... and bids you good bye. Scatterbrain! It's OK if you are addressing other physicists. But it's a shitty way to teach. Walter Lewin is an excellent professor. Susskind is not.

[csmcmillion]

@sbergman27 IT's just a function of the huge gap b/t his IQ and yours.

[sbergman27]

@csmcmillion No. Susskind is brilliant, but comes to class unprepared. I know it is considered cool to drool over famous theorists when then teach a class. But the truth is that preparation for delivering knowledge is more important than the knowledge or brilliance itself. I take Lewin as an example of a good professor, since he rehearses each lecture 3 times in front of volunteer critics before speaking in front of his MIT classes. I would encourage you to look up his YT vids.

[csmcmillion]

@sbergman27 All that being said, beggars can't be choosers. We (and his class) are lucky to have him doing these lectures. Honestly, if I was a scientist in his league I doubt I'd be teaching undergrads, let alone continuing education classes.

[sbergman27]

@csmcmillion Then I suppose we more or less agree. A sincere thank you for the response. My initial post was more provocative than it might have been. But the combination of Susskind's rambling (remember Mr. Kimbal from Green Acres?) and people lording praise for mediocre lectures, when I know better professors are out there, apparently annoyed me, overly, at the time that I made that post. Glad we got to work that out. ;-)

-Steve

[csmcmillion]

@sbergman27 Yes, we agree. Let me add, when I decided to work through this series I pretty much expected what you described (he starts a sentence... changes his mind... goes back... forgets what he said... remembers... changes the subject... goes off on a tangent... etc.). My experience has been that it's how many abstract thinkers function. I would have expected same from Einstein. Lewin, on the other hand, is an EE type - more fundamentally grounded, requiring less interpretation/translation.

[sbergman27]

@csmcmillion Hmm. Let me ask you this. If Susskind wanted to give a lecture which was more clear... could he do it? How hard would it be for him? He gets along OK in a very concrete world. It's not like he's trapped in the abstract. I do not intend this question in a provocative manner. But it *is* worth asking. And, of course, any time that he spends on that is subtracted from his work on the abstract. Susskind does what he does. It's "his business", as they say, and his life.

[csmcmillion]

@sbergman27 Certainly. If he prepared better and worked harder at establishing a concrete foundation first and relating back to it. Just as you and I would have to do if teaching, say, Algebra 1. As you alluded to, I , however, would prefer he focus his time and energy on working on some cutting-edge physics (such as string theory) so we can all figure out how this universe really works. I'm here more for the concepts than the details anyway.

Cheers

[sbergman27]

@csmcmillion A very reasonable response. And cheers to you. ;-)

-Steve

[csmcmillion]

@sbergman27 I've watched Lewin - he is a great teacher. Though Susskind is a great t physicist, I wouldn't classify him as a great teacher. I've done the whole Susskind lecture series up to this point, and I can see where you are coming from (my background is EE, not math). I think the crux of the issue is that Susskind is really an abstract thinker. He's more of a mathematician than a physicist IMO. Let's also consider he is what, 70+ years old, which does not help short term memory.

[MrAytug]

i just got we have 2 billion years to invade milky way hurry up hahahahaha

[UniversumExNihilo]

No. Currently there are no way's for us to manufacture such a device. No one even has an idea for how one might work, especially considering the brain is meant to send signals, not receive them.

We don't even have a full understanding for how the emergent patterns in the brain manifest themselves, and that is crucial for a mind control device.

[flumpyo]

how can the circle shapes (continents) be conserved on the 2 dimensional plane?

surely they would be distorted into "ovals" as you moved northwards up the projection.... hmmmm Leonard I'M NOT BUYING IT...

And what's wrong with England?????!!!!!!

[foketesz]

South America hangs from North America. LOL

[pw3uk]

Cats are female dogs :-)

[t0kt0k]

is "ds" supposed to just mean "distance"?

or does the s mean something?

if not, then what is "d" without the s?

[sikory]

s means distance, ds means a very small (infinitesimal) change in s it is like in calculus, where you have an expression like dy/dx = 2x you keep taking smaller steps for dx and dy. in the limit dx and dy go to zero, meaning a very small number. in the same sense ds is a very small change in s, d by itself does not mean anything, it only makes sense if you put it in front of a variable.

[t0kt0k]

got it :)

thanks