I find this quite surprising too and wonder if Brent could weigh in as I'm out of my league on that stuff.
Terren On Oct 25, 2014 12:23 AM, "Peter Sas" <peterjacco...@gmail.com> wrote: > Wow... That's quite shocking! I see I have to be much more careful in > taking over what the pop science writers say... > > Unfortunately, physics is a subject where the text books tend to carry > >> more weight than the popular presentations. The text books show that the >> claims about the zero net energy of the universe made by people such as >> Hawking and Krauss in popular presentations are wrong. The interesting >> question is why undoubtedly clever people such as Krauss and Hawking >> would make such fallacious claims. I suppose simplification can >> sometimes be indistinguishable from over-simplification -- or else >> people become more susceptible to brain farts as they get older..... >> >> Bruce >> >> >> >> > >> > So what gives? I wish you physicists would make up your mind ;) >> > >> > Perhaps it has to do with the fact that most physicists just calculate >> > (not that there is anything wrong with that, of course, math is the key >> > to modern science). But when it comes to explaining what these >> > calculations mean, things get tricky, and you find physicists claiming >> > different things. Perhaps this (positive energy vs. negative energy) >> > could be one of those things? >> > >> > Peter >> > >> > The idea that the positive mass-energy of the universe is balanced >> by >> > the negative energy of gravitation is quite common in the popular >> > science literature -- the idea is that one can then get zero total >> > energy and explain a universe coming from nothing. >> > >> > The trouble with this idea is that it is flatly contradicted by >> general >> > relativity. There are two main points here. First, in the >> cosmological >> > models of GR, energy is not generally conserved. Energy >> conservation on >> > the large scale depends on the existence of a time-like Killing >> vector >> > field, and no such field exists in the general non-static >> spacetime, >> > such as an expanding universe. The question of the total energy of >> the >> > universe simply has no answer -- no such total energy can be >> defined so >> > it has no value -- zero or anything else. >> > >> > The second point is that GR is based on the idea that energy, of >> > whatever form, is a source term for gravity. The equations of GR >> have >> > the geometry of spacetime depending solely on the stress-energy >> tensor >> > containing all mass, energy, stress, pressure and other physical >> terms. >> > There is no term for negative gravitational energy in this tensor. >> > Negative gravitational energy does not affect the geodesics of the >> > spacetime, it does not affect the orbits of distant satellites, for >> > instance. So, in a very real sense, it does not exist. It can be >> > described only by what is commonly called a pseudo-tensor. That is, >> a >> > quantity that does not transform as a tensor under coordinate >> > transformations. One can always find a frame in which so-called >> > negative >> > gravitational energy vanishes, so it is not physical. >> > >> > Hope this helps clear up a few confusions. >> > >> > Bruce >> > -- > 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 everything-list+unsubscr...@googlegroups.com. > To post to this group, send email to everything-list@googlegroups.com. > Visit this group at http://groups.google.com/group/everything-list. > For more options, visit https://groups.google.com/d/optout. > -- 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 everything-list+unsubscr...@googlegroups.com. To post to this group, send email to everything-list@googlegroups.com. Visit this group at http://groups.google.com/group/everything-list. For more options, visit https://groups.google.com/d/optout.
