tag:blogger.com,1999:blog-5303246073824127471.post2696427612012956450..comments2024-03-28T08:17:02.778-04:00Comments on Multiplication by Infinity: The Privileged Character of 3+1 SpacetimeSteven Colyerhttp://www.blogger.com/profile/10435759210177642257noreply@blogger.comBlogger3125tag:blogger.com,1999:blog-5303246073824127471.post-74176898519333793032020-01-07T11:42:28.979-05:002020-01-07T11:42:28.979-05:00Saying that time is "unidirectional" is ...Saying that time is "unidirectional" is just a way of saying there's one dimension different than the rest, i.e. we're in the (-+++...+) or (+--...-) cases. If we were in a (++--) universe neither time nor space would be "unidirectional", and there might even be no fundamental difference between time and space. Greg Egan has a novel about such a world, called <i>Dichronauts</i>. You can read about the physics of that world <a href="https://www.gregegan.net/DICHRONAUTS/00/DPDM.html" rel="nofollow">here</a>. <br /><br />On the other hand, physicists like to study the (+-) universe, where both time and space are "unidirectional".John Baezhttps://www.blogger.com/profile/11573268162105600948noreply@blogger.comtag:blogger.com,1999:blog-5303246073824127471.post-44216737268754801332012-01-02T12:12:36.400-05:002012-01-02T12:12:36.400-05:00The case T=3 and N=1 is essentially the same as th...The case T=3 and N=1 is essentially the same as the case T=1 and N=3. It is merely a change in convention from the Lorentz metric having signature (-+++) (making spatial distances positive) to having a signature (+---) (making energies positive). In fact the latter convention is often used in the particle physics literature where it is convenient to have the energy and the mass of a particle come out as a positive.<br />By the same token N space and T time dimensions differ from T space and N time dimensions only by a change in convention on the "Lorentz" signature<br /><br /> fact many papersRogier Brusseehttps://www.blogger.com/profile/09202922971663241521noreply@blogger.comtag:blogger.com,1999:blog-5303246073824127471.post-77387499753157731752011-12-29T07:13:17.265-05:002011-12-29T07:13:17.265-05:00http://www.matpitka.blogspot.com/2011/12/latest-ma...http://www.matpitka.blogspot.com/2011/12/latest-matrix-model-hype.htmlUllahttps://www.blogger.com/profile/16634036177244152897noreply@blogger.com