On Thursday, January 16, 2020 at 2:02:22 PM UTC-7, John Clark wrote: > > On Thu, Jan 16, 2020 at 1:25 PM Alan Grayson <[email protected] > <javascript:>> wrote: > > >> as Sean Carroll says "*the manifestation of spacetime curvature is >>> simply the fact that space is expanding*". >> >> >> *> If curvature is caused by energy and momentum in space-time, Carroll's >> statement doesn't make sense. AG* > > > Has it ever occured to you that if a professor of physics at one of the > best universities in the world makes a statement about physics that makes > no sense to you it might not be because he is talking nonsense but because > you don't understand something? It makes no sense to you because you assume > spatial curvature and spacetime curvature mean the same thing. But you're > wrong, they don't. And they don't because the time dimension behaves in a > fundamentally different way than any of the 3 spatial dimensions do; more > specifically if you want to use Pythagoras theorem in space*TIME *(not to > be confused with space) to calculate a distance in space*TIME* then you > have to stick in a minus sign that Euclid and Pythagoras knew nothing about. > I f > John K Clark >
*You're referring, of course, to the Lorentz metric with the minus sign. Yeah, I've heard of it -- used in pseudo Riemannian manifolds, and without it those space-time causal cones wouldn't make sense. But I read again and again that "curvature" of space-time is caused by the presence of mass/energy, so I find Carroll's comment puzzling. He seems to be saying that expansion is caused by curvature, when it's generally thought to be caused by dark energy. Also, as you know, I am not an enthusiast (to put it mildly) of the Many Worlds theory of Everett, but Carroll is. So I don't pray at the feet of physicists, even those from prestigious universities. AG* -- You received this message because you are subscribed to the Google Groups "Everything List" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/703d049d-99e0-4531-b454-226083da9c2e%40googlegroups.com.
