andrew s

This is a simple derivation which makes an approximation I used in my physics exam 50 odd yrs ago. https://sites.pitt.edu/~jdnorton/teaching/HPS_0410/chapters/E=mcsquared/proof.html#:~:text=We want to show that,outcomes returns E%3Dmc2. Regards Andrew

Not withstanding the news resolution on no new kit, what are you going to use it for? Regards Andrew

Sorry too much wine on the last day of my holiday! Oh yes and a total inability to spell. 😊. Your no sloth! Regards Andrew

Having given a talk at a joint BAA/AAVSO meeting I often get invited to publish in such journals. I am sure I could concoct some plausible theory for the fun if it. However I am sure super sleuth @vlaiv would call me out. Regards Andrew

I doubt anyone on here would put in the effort to know one way or another. One simple question would be why a proton? Such particles only form late in the process as the temperature of the Universe cools so given they did not exist initially why should they be singled out for this miracle. Regards Andrew

It's certainly not main stream as the link @vlaiv shows. The key is he has no publications in serious peer reviewed journals. Regards Andrew

@saac this Wiki page is quite good. https://en.m.wikipedia.org/wiki/Birefringence Yes stress can cause these effects as @Ouroboros pointed out. Regards Andrew

Yes biefringent crystals like calcite . Different polarisation of light have different refractive indices. It is due to their anisotropic crystal structure. Regards Andrew

Then Barclay James Harvest offered us superluminal velocity with "Didn't anybody see his hand move faster Than the lightning in his eyes" Regards Andrew

And my favourite Jethro Tull quote of all time will be or was "Your wise men don't know how it feels To be thick as a brick." Regards Andrew

True but we have some very accurate models that can predict outcomes with exquisite precision. Regards Andrew

I think Einstein had it about right when he said time is what a clock measures and space is what a stick measures (or words to that effect ). In GR energy density, including mass, bends spacetime not space or time individually . In some fundamental sense we don't understand anything totally. We just get used to using the concept. They are just terms in "models" we used to make sense of the world. Regards Andrew

Me too.

This was published to day "Using sedimentary and eclipse-based measurements of the lunar recession velocity, we derive a new local-Universe measurement of the Hubble constant (H0) from the recession rate of Earth's Moon. Taking into account the effects of tides, we find a value of H0 = 63.01 ± 1.79 km s−1 Mpc−1, which is in approximate agreement with the Planck space mission's measurement using the cosmic microwave background (CMB) and base ΛCDM. Our new measurement represents the first ever model-independent, single-step measurement of the Universe's current expansion rate. This is also the first major local Universe measurement of H0 which is below the measurement from Planck. Importantly, it is robust to the systematic errors that may be present in other H0 measurements using other cosmological probes such as type Ia supernovae, baryon acoustic oscillations, or lensed quasars. Our work provides key evidence towards the notion that the existing Hubble tension may indeed be a result systematic uncertainties in the local distance ladder." Full paper here Regards Andrew

Well the CMB light started of as peaking in the UV and is now down to microwave frequencies. So the have lost energy. The accepted explanation is due to the expansion of the Universe. Other theories, such as tired light, don't match all the observations. As I posted before take a look at this An unrelated effect, as @vlaiv mentioned, is interstellar reddening where objects appear redder due to scattering much as why the sky is blue and the sun redish (especially noticeable when its low on the horizon) and not white. Regards Andrew

The effective "stretching" force due to the expansion is orders of magnitude smaller than the electromatic or nuclear forces so has no effect on normal objects. For gravitationally bound object you have to go to scales larger than galaxies or close cluster for it to have a noticible effect. For example galaxies in our local cluster have a mix of red and blue shifts but as you go further away they all go red. This has been seriously studied but predictions based on it don't match the observations. Regards Andrew This gives a good readable overview on the problems with tired light theories.

Indeed and science fiction! 😊

The radius of the EV horizon is proportional to the mass while the tidal forces are proportional to the qube root of the mass. For small black holes there are significant tidal forces outside the EV but for very large ones you can get well inside before you would feel them. Regards Andrew

The accretion disks around black holes, powered by gravitational potential energy, emit jets not the black holes themselves. Regards Andrew

As I just posted for a large black hole you may not notice you have crossed the event horizon but sure as eggs us eggs you will get spaghettified. Regards Andrew R

This is covered in the paper I linked to. For a large black hole you might not even notice you have passed the event horizon. Objects that are in free fall do reach the singularity in finite "time". The link I am looking for is dead unfortunately. All that light is mainly the CMB on the area of the event horizon so yes over time it will add mass. The reality is we don't know as we belive GR breaks down at the singularity. Regards Andrew

No it takes a finite "time" for the in falling person (or what's left of them) to reach the singularity. There is a calculation on Physicsform some where which gives the numbers but I need to try harder to find it. I put "time" as once inside the event horizon the coordinates become more and more space like and in effect measure the radial distance from the singularity. Not sure about the big rip in this context. Currently the scale factor goes to infinity as time does given the current cosmological parameters. The big rip, as currently defined, requires the scale parameter to go to infinity in a finite time. Not good on wild speculation I find the real science confusing and fascinating enough! 😊 Regards Andrew

This gives a good description of falling into a black hole. Here is the relevant section on what you see as you fall in. "Will you see the universe end? If an external observer sees me slow down asymptotically as I fall, it might seem reasonable that I'd see the universe speed up asymptotically—that I'd see the universe end in a spectacular flash as I went through the horizon. This isn't the case, though. What an external observer sees depends on what light does after I emit it. What I see, however, depends on what light does before it gets to me. And there's no way that light from future events far away can get to me. Faraway events in the arbitrarily distant future never end up on my "past light-cone," the surface made of light rays that get to me at a given time." The whole is well worth a read and gives a full context for the quote. Regards Andrew

I think the issue here is not differentiating between coordinate time and Proper time. In our frame of reference we set up a Minkowski coordinate system based on SR (neglecting gravity for now). We use this to calculate speeds and in SR the speed of light is fixed and is the same in all inertial frames. So yes in this frame a light pulse takes time to get from there to here. It is in essence a coordinate time as to do the measurement you need a coordinate system and to synchronise clocks using Einstein's synchronisation convention (which makes the speed of light the same in both directions - not the only option but the one physics chooses). In doing this we use a clock and ruler. As Einstein said a good local clock measures Proper time and a good local measuring stick measures proper distance. As @vlaiv said before your local clock always measures one second per second by definition. So what about proper time for the light pulse well no material clock can travel at the seed of light so Proper time is formally undefined. If you apply the normal SR transformations you get a proper time of zero. However, this is wrong as a light pulse is not in an inertial frame which is what the equations relate. You can't ride along on a light beam. On time travel if you add in gravity for separated (I.e. non local) events you can't consistently say if two events happen at the same time so all bets are off. Personally time travel happens to me all the time - one second per second but seems to get faster as I get older 😊 Regards Andrew

Well within Quantum field theory (QFT), the best theory we have, the field is king. Particles are localised excitations of the field. In most cases there is not a number operator so asking how many particles (e.g. photons) is meaningless. The idea of photon traveling from a star to your eye while appealing is mistaken. In a very real sense (the maths) photons only exist when created, at the star, and destroyed, by your eye. The rest of the time you just have an energised quantum field with little or no localisation in to particles. Regards Andrew