MigL

Hold on now... The speed of light is measured to be c in any valid frame. To be able to move at light-speed you and your car need to be massless. There is no valid frame for any massless particle or object. A conundrum ! (always wanted to use that word)

Well since we're already off topic ... If we consider just the Earth-Moon system I would think the gravitational well of the Earth could be considered static, i.e. already existing and not propagating at c, as it is much larger than the moon's. What would be the result of your analisys Enthalpy, if we consider the Earth-Moon system as they orbit about the Sun, such that the Earth's field is constantly moving around the sun ? Maybe I should have been clearer in my thought experiment md65536. I should have stated the two masses have the same velocity, i.e. same speed, same direction, so that they are in effect int he same frame. The 'retarded' potential creates a rearward vector as well as the expected perpendicular. The masses 'drag' each other back ! That is the part I have trouble swallowing.

Had an interesting discussion concerning this effect with someone on another forum. Consider two gravitationally interacting masses moving parallel to each other at, say, 50% light-speed. If they interact instantaneously, there is only the usual force between them orthogonal to their direction of motion, i.e. they will approach each other. If however, we consider the propagation delay ( finite light-speed ), the force is no longer orthogonal to their direction of motion but has a rear-ward component, i.e. they don't only come together, they also slow each other down. This is where my thought experiment ends, as it contradicts what I expect to be true. Perhaps a better mind than mine can shed some insight.

IIRC the negative energy of exotic matter is needed to keep wormholes open and stable.

I'd be very interested in reading a source for the claim that gravitational waves are transverse and quadripolar Enthalpy. I would assume that a gravity wave is simply the communication of a changing or even translating gravitational field. As any mass moves, the space-time curvature is continuously re-estabilished along its line of travel. This information travels outward in all directions at the speed of light. Is this not the wave ?

So a mass wiggling back and forth along a line of sight to me would not produce gravitational waves in my direction ? I beg to differ enthalpy ! Gravitational waves travel at the speed of light, so the wave coming from the front is not nullified by the wave coming from the rear. Especially at the astronomical distances of a red giant about to go supernova, i.e. there is no symmetry.

Virtual particles are the result of the quantum fields which permeate all of space. A simple calculation placing harmonic oscillators at every point in space for energy calculation along with suitable boundary conditions for the cut-off point gives the silly value that Imatfaal alluded to. This vacuum energy ( and false zero states ) have been used to account for inflation and the cosmological constant ( Einstein's biggest blunder ? ). The cosmological constant is one of the leading candidates for universal expansion and acceleration, i.e. dark energy. Just because our calculations are too simplistic and not mature enough to give reasonable results for vacuum energy is no reason to discount the idea that dark energy is related to vacuum energy which may be related to virtual particles.

The term 'flatness' generally refers to an area, volume, etc. where distance in the co-ordinate system is given by the Pythagoras theorem with a unity multiplier. The observable universe seems to be very close to, if not flat. What is amazing is the fact that after 13.7 Byrs of expansion it is STILL very close to flat. That means that it must have started off either flat, or so close to flat as to be indistinguishable from it. Note however that we only have information about the observable universe. And just like the Canadian Prairies seem flat when in actuality the world is definitely spherical, so the universe may approach flat locally or on small scales, but have curvature on extremely large scales.

Much easier to picture in two dimensions using the common elastic sheet with a weight sitting on it. A supernova involves collapsing outer shell and eventual rebound to form the neutron core, while some of the mass is ejected into space along with copious amounts of radiation. Acceleration of this mass, is equivalent to a changing gravitational field, and is represented by the mass on the elastic sheet 'wigglingup and down and making ripples. These ripples are the gravitational waves.

Most modern, highly maneuverable, military jets are stressed for +9g / -3g. Pilots tend to go gray around their visual field ( low blood flow to brain ) at less than this. Probably about +7g sustained, before passing out. I seem to recall several crashes of the F-20 Tigershark due to this.

To be more specific, from one of my previous posts... "In the E8xE8 Heterotic supersymmetric theory, by Gross of Princeton I believe. each closed string has inherent dimensionality of ten in one direction to describe fermionic fields and sixteen more in the opposite direction ( 26 tootal ) to describe bosonic fields. It does not need renormalization and has gravitons as one of the bosonic field excitations. This E8xE8 symmetry breaks into two E8 symmetry groups, which then breaks to an E6 group and again to the familiar SU(3)xSU(2)xU(1) groups of GUT ( SU(3) ) and standard model Electroweak ( SU(2)xU(1) ). The two E8 symmetry groups are in effect two separate universes connected only by gravity since the other forces only arise after the subsequent symmetry breaks. This second universe is invisible to all other forces except gravity, so we have in effect at least doubled the mass of the universe without any visible other matter, and since the second E8 group does not have to break in the same sequence as the first, it could be composed of heavier particles, like say the supersymmetric equivalents of normal particles, explaning why they have never been observed." There would be a kind of 'pinning' together of these separate universes at black holes because ther continues to be gravitational interaction between them. Also note that this idea is a 'flight of fancy' and certainly belongs in the speculation section !!!

E8xE8 Heterotic string theory, Airbrush.

Thanks I.O. I wasn't aware of any of these ongoing developments. You've provided a lot to look into, and think about.

Come on Shneibster, even Lorentz ( and Fitzgerald and Poincare ) were familiar with dimensional analysis. That is, when you write down an equation, you check its validity by making sure the units on one side are equivalent to the units on the other. If they are not, your equation isn't worth a d**m. A transform doesn't change units of distance into units of time. It is used to transform an event from one coordinate system to another.

No, in my opinion and many others, its a cop-out for a wrong or incomplete theory. And again, if there was a baby universe inflating in your pocket, you would definitely know about it as there would be dire consequences. Not just 'echoes' from before or during the inflationary period of the big ang.

Where did you previously discuss LQG, Implicate Order ? I've been away from this rotten weather for a bit amd probably missed it. I wouldn't mind a read as I'm one of those narrow minded people who prefers it over SString or M-theory and really can't see common ground between the two. I prefer LQG's affinity to GR in having no requirement for a background on which it plays out. Incidentally I would have termed that 'background independant', but I'm not very good at keeping terminology straight. And as been prviously discussed, I detest the fact that SString theory has thousands of possible configurations of the compacted 7D Calabi-Yau manifolds with nothing in the equations or the boundary conditions to point to the right configuration. Having to invoke the Anthropic principle is a cop-out. There can be no evidence of 'still-born' universes or multiverses other than this one where the conditions are just right for us to exist and ponder these issues. Other problems include lack of evidence for supersymmetry. Maybe they should call it the God symmetry because it'll probably be harder to find than the God-d**m ( Higg's ) particle. There are also highearchy issues and other problems. As a previous contributor to this forum used to say, string theory is an elegant theory in search of a universe to describe.

I have read Linde and he considered a multitude of universes inflating continuously, not all starting at the same time. In effect he considered the possibility of a universe starting at the Planck scale, and inflating at any point in space-time, such as your pocket. He may have modified his ideas since then, but 'echoes' of other inflations alongside our inflation or 'echoes' of a big crunch or bounce prior to the big bang are new to me. Incidentally, since a bounce would have to reset the entropic 'value' of the universe, how would any kind of information ( echo ) be passed from the previous to the present universe.

In the CMBR? How? The CMBR is very isotropic across the sky ( one part in one thousand or better if I recall ) except for the slight blue shift in the Milky Way's direction of travel and red shift in the opposite, and the best substitute for a universal frame we can ever hope to have. I would think small universes inflating would have a huge effect on the CMBR unless shielded behind an event horizon. The large spherical ( ? ) voids separated by filaments and walls of galaxy clusters are not areas of inflation as they can be explained by quantum fluctuations before the inflation of our universe 13.7 Byrs ago.

Just started working my way through Liddle's book AJB, as time permits. I do tend to believe as Shneibster seems to, that all forms of expansion/inflation are driven by dark energy/cosmological constant-lambda/negative pressure/vacuum energy. Not that I can prove it, just a 'gut feeling'. Not so sure about Linde's eternal inflation. Seems if universes were inflating from Planck scales to macroscopic all around us, there would be some observational consequences.

I don't think so Imatfaal. Even in the very distant future there will be objects transiting out of the observable universe due to expansion. Unless that expansion stops. This means that there will always be objects which aren't gravitationally bound and measurements can be made to determine the rate of expansion. Maybe once we get a grip on vacuum energy, we may even be able to deduce the rate of expansion of flat ( non gravitational ) space without measuring recession rates.

My two cents... Saying 'Time is Change' seems to be circular reasoning, as we define the passage of time by change. It would be akin to saying distance is metres. At a point in time so far in the future that all other galaxies have disappeared from our observable universe, recall that the galaxies aren't moving away, rather spatial separation between them is increasing. This will happen for all other objects in the observable universe ( vast size ), not just galaxies, and I'm sure any surviving intelligent civilization will be able to measure the rate of expansion, and 're-wind' the expansion back to the big bang.

I live 15 min away from the American border at Niagara Falls and have spent many fine nights in the bars and clubs of Western New York over the past 30 yrs. I find no inherent difference in thinking and morals between Americans and Canadians, but, as has been pointed out, countries like Switzerland require adult males to have military weapons in their homes as they may all be called upon to defend their country. Obviously gun ownership is not the problem, and the only possible explanation is that all Americans are nuts. Just kidding, actually the only North American city to have had three school multi-shootings in the last 20 yrs is Canada's own Montreal. But then again, we know that Quebecers are definitely nuts.

The Pauli exclusion principle only comes into play when all lowest orbitals are filled. And this only happens at extremely high densities.

I realise all that John ( and swansont ). The point I was trying to make is that there are no EM emissions from electron level hopping as no electrons are captive in atoms. A plasma is a bunch of free electrons and bare nucleii and of course they will collide and react to external fields and so emit radiation. However, a source of energy had to have been initially applied to strip the electrons from their respective nucleii, and it is greater than any emissions generated by collisions and accelerations. As in the sun !

I believe most of the make-up of the sun is nucleii stripped of all electrons. The early universe before it became transparent was composed of electronless nucleii. I think the critical temp is about 4000 deg. Ok swansont, does a single nucleus of a plasma, if isolated, have a mechanism for emitting EM radiation. And I'm not considering radioactive nucleii, ridiculously high temps or annihilation.