On Friday, October 4, 2019 at 4:31:31 AM UTC-5, Lawrence Crowell wrote: > > On Thursday, October 3, 2019 at 8:13:22 PM UTC-5, Alan Grayson wrote: >> >> >> >> On Thursday, October 3, 2019 at 7:05:12 PM UTC-6, Lawrence Crowell wrote: >>> >>> On Thursday, October 3, 2019 at 8:01:49 PM UTC-5, Lawrence Crowell wrote: >>>> >>>> On Thursday, October 3, 2019 at 6:59:35 PM UTC-5, Bruce wrote: >>>>> >>>>> On Fri, Oct 4, 2019 at 9:54 AM Alan Grayson <agrays...@gmail.com> >>>>> wrote: >>>>> >>>>>> >>>>>> ISTM, that the argument the universe was NOT in thermo equilibrium >>>>>> just before inflation is alleged to have begun, is extremely WEAK. Thus, >>>>>> it's illogical to claim that inflation "smooths out" the alleged NON >>>>>> thermo >>>>>> equiiibrium just before inflation begun. AG >>>>>> >>>>> >>>>> That is essentially what I said. Lawrence is just replacing one set of >>>>> unknown initial conditions with another, equally unjustified, set. >>>>> >>>>> Bruce >>>>> >>>> >>> In below & means δ. I forgot to replace them. >>> >>> LC >>> >>> >>>> >>>> The entropy is S = A/4ℓ_p^2 + quantum corrections, where these >>>> corrections are ~ (&S/&h^a)k^a. Here h^a is tangent to the horizon and k^a >>>> is normal. This condition coincident on a null surface can appear on a >>>> quantum extremal surface with null tangent g^s so that (&S/&h^a)k^a ≥ >>>> (&S/&g^a)k^a by subadditivity. However, this surface occurs inside the >>>> cosmological horizon. This means there is no equilibriium. Equilibrium is >>>> only approximated by stretching the horizon out to enormous distance after >>>> the spatial surface has inflated. >>>> >>>> It is the case that inflation does not tell us the whole story prior to >>>> inflation. So one can say there are equally unknown initial conditions. >>>> However, the details of those are less important as the spatial manifold >>>> is >>>> stretched out. That means inflation does provide at least a working >>>> system. >>>> >>>> LC >>>> >>> >> Assuming the universe was incredibly tiny prior to inflation, and was >> therefore causally connected, isn't it reasonable to assume that it had >> reached thermo equilibrium *prior* to the onset of inflation? AG >> > > Thermal equilibrium is not possible with quantum fields in curved > spacetiome, nor is is likely in quantum gravity. The reason is not too hard > to see. Suppose you have a black hole in a thermal background with the same > temperature as its horizon T ~ 1/8M. The black hole has an equiprobability > of absorbing or emitting a photon with energy δM The temperature then > adjusts as T - δT ~ 1/8(M + δM) or T + δT ~ 1/8(M - δM) and is shifted away > from thermal equality. This will then enhance the probability the black > hole either then grows by absorbing more photons or by emitting them. There > is no thermal equilibrium. Quantum gravitation is likely the same, for the > effective specific heat of event horizons is negative. What I wrote above > is in effect a more general form of this. > > Now a gemish of particles or a gas can be in thermal equilibrium in > spacetime. That was what was set up with inflation. The whole process of > the early expanding universe is about there being episodes of approximate > thermal equilibrium of particles, such as during the quark-gluon plasma > phase, electroweak period, the QED equilibrium of electrons and photon or > the plasma phase that ended by producing the CMB. > > To think about physics one has to do a sort of Buddhist middle way. It is > not good to either be too liberal or given to extreme speculations, but it > is also not good to be overly conservative. > > LC >
The new tech way: deep nets for deep space. https://bids.berkeley.edu/events/physics-machine-learning-workshop This workshop focused on substantive connections between machine learning (including but not limited to deep learning) and physics (including astrophysics). Namely, we are interested in topics like imbuing physical laws into training (e.g., physics regularization of layers), learning new physical phenomena from learned models, physics-constrained reinforcement learning, prediction outside training parameters, causal inference, and the (physical) interpretability of models. @philipthrift -- 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 view this discussion on the web visit https://groups.google.com/d/msgid/everything-list/fc391760-6bc7-42ea-843c-2f96ff5bf950%40googlegroups.com.
