MigL

+ or - indicating direction.

Maybe I'm being too simplistic, But a single photon will, under the right circumstances, create an electron- positron pair, ie matter and antimatter. Now, the original photon has the same gravitational force and sign as an equivalent amount of mass, the electron has the same sign and gravitational force for its mass, so why would the gravitational field change polarity for the positron ? And why would it flip back again when the electron-positron pair annihilate ? Obviously it doesn't. The gravitational field is related to the mass and energy of the particle ( more or less ) and this relationship works the same for matter and antimatter. As to rigorous proof and papers which can be quoted, I don't know of any either.

What would it be rotating relative to ?? See Newton's and Mach's 'bucket of water' thought experiment. And, does rotation not imply a centre to the universe ? Or, at the very least, does rotation of the universe imply a 'preferred' direction, thereby undermining symmetry and momentum conservation laws ??

If you think about causal disconnection, you realise that as you 'wind the film backwards' in time the disconnection becomes larger, not smaller. So without inflation, there would never have been a time where causal connectivity ensured isotropy. But maybe what DrR means is that all parts and times of the universe are causally connected to the Big Bang event, although all parts and times of the universe are no longer ( post inflation ) causally connected to each other.

Well I hate to disagree with the good Doctor, but its my understanding that the post-inflation universe has causally disconnected observable universes, which, because of the finite speed of light, cannot freely pass information to each other. Guth's inflation then, adds a pre-inflation period where the distances between regions were small enough for light to reach all parts and therefore insure isotropy.

Wow. That is so far off the mark, I don't know where to start. I guess i should recommend you read agood book explaning the BB theory.

I assume Khaled means binding energy since he has mentioned the 'forces in the space between quarks' in other threads. He mistakenly assumes the force to be gravitational.

From your answer to the OP, swansont, I would guess that you've taught in the past, or even currently. Have you ??

Macroscopic waves can occupy a single position. Take the shock wave where air is decelerated from supersonic to subsonic at a projection ( or air intake lip ), admittedly not a point but a surface, nonetheless it can be located to a very high accuracy by computational methods, and exactly by solving the fluid flow equations. Quantum mechanical equations have the HUP, and the resulting uncertainty or 'smearing out', built into the equations themselves, by definition, making improved accuracy, beyond that allowed by the HUP, impossible. Unless someone comes up with a different theory than Quantum Mechanics for atomic processes, or some hidden variables are identified, we are stuck with the limits imposed by the HUP.

So time varying fields are not allowed while static fields can be considered to 'pass through' the event horizon. Or would it better to consider the field as originating at the event horizon since the horizon preserves pre-collapse static field information. In effect, what is the difference and consequence of considering the mass and charge of a black hole to be localised either at the 'centre' of the event horizon, or the 'surface' of the event horizon ?

No. HUP has nothing to do with wave-particle duality which has been around since the time of Newton and Hyugens ( spelling ?? ). A macroscopic wave has no uncertanty, but on the quantum level everything ( time , energy, momentum, position ) is 'smeared out' by the HUP such that nothing is deterministic, but probabilistic.

Its very hard explaining the Heisenbrg Uncertainty Principle to someone who keeps trying to put it into common sensical, everyday perspective. I know, I spent years trying to make sense of it. Its not a case of not being able to make accurate enough measurements or knowing the actual mechanism, but the physics will not allow you to measure accurately enough or know exactly. It is actually not allowed and therefore impossible.

What is missing from the standard model of gravity, GR, is a description of processes at very small distances and other special circumstances. What is needed is a quantum field description of gravity along the same lines as QED and QCD. Any quantum field theory predicts the existence of force carrying bosons to propagate the field. The Higg's mechanism is a theory which models the spontaneous symmetry breaking leading to the separation of the weak and electromagnetic forces at 250 GeV. A scalar field, the Higg's field then permeates all of space, causing a drag on accelerated particles which we associate with inertial mass ( gross oversimplification ). The Higg's field is also a quantum field and has associated force carrying bosons. For the gravity field that predicted boson is the massless, spin 2 graviton. For the scalar Higg's field, it is the massive ( >250 GeV ) Higg's particle.

And further to Chris's reply, yes Electrons can settle into the nucleus. The uncertainty principle doesn't say you cannot fix the location of an electron to an arbitrarily small space, rather location and momentum cannot be fixed to arbitrarily small values. In other words if you fix the location of an electron to the nucleus or smaller, its momentum ( energy ) can assume wild and large excursions. The upper limit for the momentum, and I believe the method Subrahim Chandrashekar ( spelling ?? ) used in his calculation on his way to London to see Eddington, is then the speed of light. That gives values for electron degeneracy pressure to counteract gravity. Note that I'm not asking wether gravitational collapse of an extremely strong gravitational field is probable, it most likely isn't, notice the scenario needed to make 'favourable' conditions for it. I'm asking wether GR allows it or it is possible.

No, i thought I was being rather clear. Can you have a gravitational FIELD which has enough energy density to collapse and form an event horizon without any matter mass actually being involved in the collapse. This would depend on the way gravitational energy ( potential ) is handled by GR, as opposed to mass/energy.

Again I need to preface this with the comment that I'm not very familiar with M-theory. I'm only just dipping my toes in it. If we were 'stuck' on a 3-brane, everything i've read or heard implies that force carrier bosons are all open ended 'attached' strings, ie. their ends are attached to the brane and so are also stuck in it, they cannot pass to the other dimensions, wether compact or large. The only force carrier boson that is different is the graviton, which is not attached and can pass through all dimensions. This implies that at smallish distances, much smaller than the three large observed dimensions. the strength of gravity does not fall off with the square of the distance, but falls off with (n-1) of the distance, where n is the total number of spatial dimensions. This also implies that at progressively smaller distances, the force of gravity becomes progressively larger with respect to the other forces, ie we don't need to go to the Planck scale to see equivalent strengths of the forces, rather gravity would get to equivalence much quicker. The LHC gets nowhere near Planck scale energy, but it does place sufficient energy in a small enough space that, if gravity was stronger than expected at small scales, microscopic black holes should have been formed. Since none were, does this mean gravity is not 'free' to pass through all the dimensions, and so the m-theory string model of the bosons is not valid. Another wrench in the works, if you will.

The CMB is not visible light. It was 300000 yrs after the Big Bang, but it has since lost most of its energy because its wavelength has increased to the microwave range. Prior to 300000 yrsABB the universe was filled with a plasma, much like the Sun, where the temperature or particle energy is high enoigh ( approx 4000 deg ) that electrons cannot stick to Hydrogen and Helium nuclei ( as soon as they do, they are bounced free by energetic photons ). This plasma is by definition , opaque, ie the whole universe would have been filled with glowing plasma like the surface of the sun. After 300000 yrs ABB, the temperature dropped enough that electrons were no longer kicked free ( ionized ) by the radiation ( photons )and could form stable atoms of Hydrogen and Helium ( and miniscule quantities of deuterium and lithiun. nothing else I think, but not sure ). It was at this point that the universe became transparent, and is the earliest point we will be able to see. I hope this explanation is a little simpler to follow.

If I remember correctly, the idea of strings was introduced to get rid of the quantum effects that make a point-particle quantum gravity theory untractable, ie not renormalisable. And the string vibrational harmonics account for different elementary particles' masses ( almost, to a general approximation where very little=0 ). But, why strings ?? At the Planck scale where string dimensions lie, we start losing distinction between spatial dimensions and time, so that ascribing a structure to strings is probably absurd and certainly unverifiable. Why not simple harmonic oscillators, or pulsing spheres or even something ( ?? ) which exsists in multiple or all times. All we really require is that a certain size ( Planck scale ) of space/time be allowed to vibrate/oscillate/pulse with differing harmonics. Or is the particular structure needed to account for certain properties ??

Black holes and the ultimate fate of massive stars is predicted by GR,is backed up by indirect observation and is more-or-less generally accepted fact. I have always wondered about other effects and their plausability, and maybe some of the members ( DrR where are you ? ) who are better versed in GR than I am can provide some guidance. Consider an arrangement of massive stars all going supernova at the exact same time, and collapsing to black holes at the same time ( I know, not possible, but humour me ). At the moment the Swartzchild radius is reached, a massive gravity wave leaves each collapsing star. Now imagine that the arrangement of the original stars is such that these resultant gravitational waves interfere constructively, leading to a massive gravitational energy density at a specific point. If this gravitatinal energy is dense enough, can it collapse to form a black hole even though no actual matter mass has collapsed ? I know J.A. Wheeler did some work on stable energy orbits in the 50s and found that the energy density of these 'geons' was enough to keep the enrgy itself in a very unstable circular orbit ( donut shape ) and the slightest deviation led to dissipation or gravitational collapse. And it makes sense since energy and mass are equivalent. But this was trictly EM energy. Has anyone investigated the gravitational collapse of gravitational energy of sufficient density ?

Not very well informed on M-theory, but... I was of the impression that, to account for the 'handedness' of the weak force, only an odd number of spatial dimensions will do. The max number of dimensions then becomes 9 spatial and one of time, for ten alltogether. Eleven total dimensions implies ten spatial dimensions ( plus time ), and that throws a wrench into the weak force machinery. Or am I wrong about the weak force.

We can't escape the moon because its gravity well is located inside the gravity well of the earth, which is located inside the gravity well of the sun,which is located inside the gravity well of the galaxy, etc. In effect if the earth were to escape the sun's gravity well, it would take the moon with it. Just semantics, I know, but sometimes you need to be anal about word meanings on these forums.

You are right the event horizon is defined in terms of mass and radius. However a non radiating collection of critical mass, has no counter to gravitational force, such as a 3-4 solar mass object compose of iron. It doesn't matter what its radius is, it will collapse to form a black hole if its mass is above the critical limit ( it'll just take a little longer to form a horizon ). The radius of its eventual event horizon will be given by the mentioned formula.

Unlike the mid-last cntury quest to find how and why civilizations rose and fell which failed miserably, quantum theories such as QED and QCD make unbelievably accurate real-world predictions even though the theory is probabilistic in nature. Most people accept the theory as' that's the way nature behaves' and use it for very accurate science. Some however see some results ( double slit as an example ) that cannot be adequately explained and argue that there are 'hidden variables' that haven't been accounted for ( see Bohm and Bell along with deBroglie and even Einstein ).

Sorry got a little confused there and posted too quickly. You are both right, it is white dwarfs that keep assimilating mass and upon reaching a specific limit ( Chandrachekar or about 1.4 sol mass ) collapse to become neutron stars. The gravitational collapse, subsequent heating and bounce leads to a 'standard' supernova.

Look up Kerr ( rotating ) black hole. They still form black holes but have many interesting proprties. The ambiguity as to the number of solar masses required for gravitational collapse to a black hole, is because stellar evolution is not completely understood. Before the collapse, to either neutron star or black hole, significant amounts of stellar material is blown off in the supernova explosion. If enough mass is blown off a 10 solar mass star it may only have enough remaining to form a neutron star. If not enough is blown off it may become a black hole. But the mass needed to form an event horizon is known exactly. Incidentally, neutron stars continue to assimilate mass due to their gravitational force, especially if they are located in a gas or dust cloud. Eventually they reach the critical mass at which an event horizon is formed, but on the way there, they go supernova, Type Ia supernova, because conditions are pretty well identical for all type Ia supernova and their luminosity is a fixed figure. These are used as standard candels to determine intergalactic distances. They were recently used in the determination ( at the end of the last century ) that universal expansion is accelerating.