Carrock

It is a complete description of rest mass. Momentum etc is not included. As there is no universal equation of everything, every equation is incomplete in that sense. e=mc2 is not a shortcut in finding the equivalent energy of a mass at rest. You could add 0 momentum and 0 unicorns and 0volts/second if you wish.

e=mc2 is dimensionally consistent...

The tables are pretty useless, but a voltage erg(e.s. system) is pretty clearly different from an energy erg. I don't know much about c.g.s., but I'm certain it was dimensionally valid if you use its peculiar conventions. [edit] There seems to be a mixture of three different conventions on p.330 col3.

Why do you claim inductance is a length in CGS. Why do you claim voltage is energy in CGS? Is jumping from 3 metres below ground level to 2 metres below ground level possible only in maths, not in the physical world?

I can't see why not, in principle. A photon (say in the CMB) could continue going through space and missing the hydrogen atoms and stars, which are few and far between. That's the fate of most photons in most cosmological models. It's still possible that yet unknown physics may mean we're in e.g. a cyclic universe where all photons eventually interact in the future so there's no direct evidence that (no second interaction) photons exist. Momentum is transferred from the source to the photon. It doesn't then need to be transferred to something else, does it? I suggested a photon is an instantaneous transient of an interaction between objects separated by a lightlike interval. I'm not convinced that such an instantaneous transient in one object can give rise to a photon which never interacts with another object. I suppose the only way forward is to have a good look at the maths.

I was guilty of anthropomorphising earlier.... I don't think a photon 'experiences' anything. It's just an instantaneous transient of an interaction between objects separated by a lightlike interval. Any valid reference frame infinitely 'stretches' this instantaneous transient into what's called a photon. The photon is just an artefact of any valid frame. I'm just wondering if you can have a photon sourced by one object but with no interaction with a second object. There is no momentum etc transference. I suspect at most only a virtual photon could be created. I can't find any good reference on this (non?) issue.

If all of the physics we know requires a valid frame of reference, is the description of gravitational redshift, Doppler shift etc of photons without valid reference frames not physics? Indeed, without valid reference frames, are photons completely unknown physics? Length contraction is a function of reference frame; a reference frame can be chosen for no or any desired contraction. I only meant that it is a function of frame choice. As with e.g. photon energy, which has no upper or lower limit, the reference frame is chosen for convenience in calculations involving interactions. I'd be interested in any response you have to this rather informal description. (I don't see how a photon could experience duration without having a valid reference frame. The claims I've seen to that effect violate well established physics.)

"You have a destruction/creation (depending on which way time is running) which does not reflect the actual conditions of the problem." "Photons are created by the blackbody." In what way is the creation in the second sentence different from the first? You can't analyze this from the photon's frame of reference, because it is not a valid frame. We have no physics to apply to it. I was anthropomorphising a bit. I think it's pretty generally accepted photons cannot experience duration, which is implied by there being no valid frame. A lack of a property is still physics. I would say a photon is simply a transient which occurs instantaneously as two objects in the same place at the same time exchange energy, momentum, spin etc. Necessary if a photon doesn't experience duration. This transient is infinitely stretched from the viewpoint of a valid frame and can be inferred to be a photon travelling a frame dependent distance with some frame dependent properties such as energy and at frame independent speed c. This photon is no more or less 'real' than the length contraction of a massive object with relativistic velocity w.r.t. some valid frame. The issue is how does this transient occur if there is only one object - in this instance a black body in an otherwise empty universe. Can't delete this. $^%"%&**(##@ forum software.... If it's just an interpretation it should be easy to solve this problem without assuming antiparticles really travel back in time.

Given that photons are their own antiparticles, whether observed photons go from the future to the past or vice versa is an arbitrary choice. (See earlier post.) The fact that future photon destruction/creation is problematic is not IMO adequate justification for saying photons must go from the past to the future. I offered an alternative with no boundary conditions. Photons do not have a conservation of number law associated with them. And it's trivially observed to be true in any number of reactions. True, but rather ignored my point, which from context was that photons cannot be created or destroyed in empty space without violating conservation laws. Photons have infinite range and do not experience any sort of time or duration. If a photon is created and destroyed elsewhere, those two events are entangled. If a photon is created and never destroyed or vice versa the photon is 'aware' of the asymmetry. I suspect this would prevent such a photon existing as anything but a virtual particle. I've DuckDuckGone quite extensively, and can't find any discussion of this issue. In cosmology there are theories which avoid this possible issue in the real universe.

No gravitation and no cosmic redshift leap to mind in an empty universe.

In the context I was using, space with no particles for photons to interact with. Virtual particles are no good here for photon emission/absorption.

OK. The photon is generally considered to be its own antiparticle. It's not currently a popular idea, but AFIK an antiparticle is mathematically equivalent to a particle travelling backwards in time as in e.g. Feynman diagrams. So a photon travelling forwards in time can alternatively be considered to be an antiphoton (i.e. a photon) travelling backwards in time. So in the universe we're discussing, the photon is created in the future and travels back in time until it interacts with the black body. Energy, momentum and spin (i.e. a photon) is created from nothing, violating three conservation laws, and travels back in time until it interacts with the black body. The alternative, that such photons can be (destroyed but not created/created but not destroyed) is also problematic; I'm not aware of any theoretical basis for that. Some cosmological theories dodge this bullet with a 'future singularity' i.e. hand waving; others avoid it by e.g. postulating a temporally finite universe. A full consideration would require its own thread but it would soon get hijacked.

I'm suggesting there would be no photons in an otherwise matterless universe even near the black body at any time as conservation laws forbid it, assuming time-reversal photon symmetry. The only reason I can see for any photon time-reversal asymmetry is that many (unverified) cosmological theories require such asymmetry.

There is the absorber problem for an empty universe (as well as many popular cosmological models), which has been around for a long time. There is a strong case for claiming photons have time-reversal symmetry. As photons have infinite range, this symmetry implies they have to be destroyed (i.e. the time-reverse of created) as well as as created. There is no way to destroy photons in empty space without violating conservation laws. So it may be the only blackbody in infinite and empty space has no way to lose energy and will forever retain its temperature.

If there is superluminal information transfer then there are effects contrary to quantum theory and quantum theory is wrong. You can't have it both ways.

I have a piece of paper marked £5, with a government promise that if I take it to a bank I can exchange it for a piece of paper marked £5, with a government promise that if I take it to a bank I can exchange it for a piece of paper marked £5, with a government promise that if I take it to a bank I can exchange it for .... At least it's not invisible.

Not unless we're abysmally stupid - we're good at that.... A few thoughts. An A.I. with "intelligence that significantly exceeds that of humans" would have no more interest in being given rights than I would in my cat giving me rights except informally in our mutual interest - my cat can't enforce those rights. I don't think an A.I. without irrational drives, and probably emotions, is possible. Without those, intelligence isn't enough to do anything - doing nothing useful is just as rational as doing something useful or detonating all weapons with hackable software. Restrictively programmed A.I. is basically A.I. with insane rather than 'normal' irrational drives. There was a 1950s Damon Knight story "Dulcie and Decorum*" where the Russian and American A.I.s decided that rather than waste resources fighting each other to 'win' as they'd been imperfectly programmed to do, they would play war games and kill their own citizens when they lost, extending the definition of 'citizen' as they ran low on people. Still relevant... I'd expect A.I.s to value people much as people value life, irrespective of intelligence, which they can never fully understand. (e.g. domestic cats.) Would an A.I. really want a world with no intelligence but itself? Coercively controlling humans also would be undesirable to a sane A.I. 'Wild' humans would be much more interesting and useful. This is a bit anthropomorphic of course, but it's hard to imagine humans creating an A.I. that does not share many important values with humans. The only real concern to me is that dysfunctional adults can 'educate' children to kill people and creating an A.I. with similar attitudes but much more power could be a terminal mistake. *"dulce et decorum est pro patria mori"

There is another issue. The new "smaller" nuclear weapons could be adjustable yield weapons set for low yield. Any of these "smaller" weapons could be converted in a matter of minutes (more likely seconds) into high yield weapons. It would be possible to say truthfully that as old weapons are decommissioned the U.S.'s firepower is decreasing, while maintaining the possibility of an enormous increase in fire power at any time.

I doubt anyone honestly believes realistically threatening to use low yield nuclear weapons will encourage anyone, such as North Korea, to respond with low yield rather than high yield nuclear weapons. As far as I know, there is no definite limit to the yield of a hydrogen bomb. If a nuclear capable power is, say, being destroyed by multiple 5 kilotonne atom bombs, it may decide that using their (untested) five gigatonne or even one teratonne hydrogen bombs on the enemy is their best chance of survival.

It was actually a speculative discussion of initial boundary conditions (i.e. the beginning of the universe) as applied to the steady state theory. As I've said, Bondi and Gold posited a 'perfect' universe which had been expanding 'unchanged' for infinite time, which Hoyle knew was impossible for basic mathematical reasons - it was formally disproved long before discovery of the CMBR. From Mach's Principle and the Creation of Matter The abstract and full conclusion make this even clearer. You have to create a free account to read the whole paper.

It's out of fashion these days, but I'm not aware of any reason that an antiparticle can't be interpreted as a particle travelling backwards in time as in e.g. Feynman diagrams. The 'same' particle exists in two places at the same time.

Actually he didn't. See Mach's Principle and the Creation of Matter Proceedings of the Royal Society of London. Series A, Mathematical and Physical Sciences Vol. 273, No. 1352 (Apr. 23, 1963), pp. 1-11 Hoyle used 'Steady State' in the conventional sense i.e. after startup transients have become negligible. Confusion arises because Bondi and Gold beat Hoyle into print with an eternal rather than steady state universe.

You still haven't explained why you have to start in the infinite past. It's similar to my saying you don't exist because you couldn't get here from a billion years ago or from Andromeda. I never claimed that photons can cross 'infinite time'. If you want to demonstrate they can't, just show that they have finite range i.e, they somehow cease to exist within finite time (assuming no interaction with another particle).

Each photon would disappear when it interacted with a charged particle; there would be approximately as many photons then as there are now, but none of them would exist for long i.e. the mean free photon length was very short. Photons existed before nucleosynthesis stopped; i.e. during the first ten seconds. Why do you think I think the BB is an actual explosion?

Surely they existed before ~10 seconds after the Big Bang, just not for very long; i.e. have you a reference?. A few lucky photons probably survived from before neutral atoms existed, but probably not enough to observe.