andrew s

You could imagine stimulating an environment with no limitations of any of the requirements for life. Energy in a low entropy state, materials etc. and a set of mutating reproducing organisms. They would just grow exponentially with no evolutionary pressure so predation would not have any obvious advantage. Not very interesting, so say one or more constraints were added then a limit would be reached. However, now any organisms that evolved a way of extracting the limiting resources from another organisms would be at an advantage . Predation would be an advantage. Regards Andrew

An entropy gradient is what's needed. You need a source of low entropy to drive the creation of order and a sink for high entropy. For, example the Sun provides UV and visible light as a low entropy source and IR light is radiated into the sink of empty space. Give or take global warming the earth us in thermal equilibrium. What makes predation advantageous is that it provides a concentrated source of low entropy. Regards Andrew

Exactly. Regards Andrew PS It might be worth recalling spacetime has properties and in GR they are dynamic.

Very interesting as always @ollypenrice. What our singular example has shown is that our evolution of "thinking ability" and the development of "technology" has enabled us to out compete those species that don't have these abilities. Evolution is blind to good or bad as shown by the first oxygenators killing off all the organisms that exploited the reducing atmosphere but could not adapt to it becoming oxidising. How extraterrestrial organisms evolve will depend on what evolutionary pressure they are presented with. For good or ill we are what we have evolved to be. Regards Andrew

What I was saying the isotropy is built into the assumtions in the current SI system and via the Einstein clock synchronisation protocol into relativity and QED. You can perfectly well have an anisotropic speed of light but all the equations are much more complex. Experimentally you can't tell them apart. Photons etc don't need to know what to do. If you pass light through an anisotropic crystal like calcite you naturally get the splitting into the ordinary and extraordinary rays due to the interaction of the EM field of the crystal to the of the light. If space were anisotropic the different speeds would just happen due to the anisotropy. I am very happy to go with it being isotropic as there is no indication it's not. Regards Andrew

Wedge is when the surfaces of the corrector plate are not parallel and resemble a weak prism. As they are thin with near zero power, as said above, they cause little chromatic aberration. In larger sizes it can be an issue and the UK Schmidt camera has an achromatic doublet corrector. Regards Andrew

Yes your right about energy eigen states. The remeasurement holds for discrete eigen states. As to your question I better understand it now. I have never read any proposal to this effect. I would assume 1) from all I have read. 2) would require something like the Block Universe where spacetime is a static 4d cube where we just experience dynamics. Bell's inequallity excudes any classical determinism of the kind you propose. Regards Andrew

@vlaiv not as I understand it. Firstly, if a system is in an eigen state it will remain in it as it evolves in time. If it is not it will evolve as per the time dependant Schrodinger equation. Both these assume no interaction with the environment. If you make a measurement on an otherwise isolated system you will always get an eigen state as the answer. If you remeasure it in the same way you get the same answer. If you don't know the state (say electrons from a heated fillament) your results will be truly random on the first measurement. A measurement entangles, say the electron, with the instrument. You only get a non random result on remeasuring an eigen state again in the same way otherwise it is always random. Decoherence is in effect a series of weak measurements on the system. It entangles the system with the environment and in so doing it removes any superposition and pushes the system into the classical states. You can do the double slit experiment with electrons in a vacuum and gradually raise the air pressure as you do the interference pattern weakens and finally goes with the classical trajectories taking over. Regards Andrew

I agree the state is as you say but the measurement will give spin up a^2 of the time and b^2 there rest of the time. Any given result is random. If you changed your mind and did it at a different angle you would get different results depending on the a and b. There is no determined answer to be revealed on a measurement by measurement basis. What Bell's inequality says is that there can be no classical local variable that could code the outcome of a given measurement (e.g. no hidden gloves) or give rise to the probabilities of multiple measurements on repeated experiments. Regards Andrew PS also the states are not fixed in a single basis. Say you have |up> in the z direction you could express this as a|+45> + a|-45> in a basis at 45° to the z axis. Where the "a" are such to normalise the state. This can be easily shown with 3 linear polarising sheets. Take a randomly polarised light source and pass it through the first vertical polariser and 50% gets through . Add one at 90° and none gets through. Place the third at 45° in the middle and 25% gets through.

This is not true in QM. The outcome of some measurements on a given prepared state can only be given as probabilities. Any one measurement is indeterminate in principle given the no local hidden variables consequence of the violation of the Bell inequality. You have to do many identical experiments on identically prepared states to get the results to match the predicted probabilities. Regards Andrew

Classical physics follows both classical logic and the simplest probability rule. For probability it means if the are n exclusive options the sum of the probabilities of each n individually sum to one. This is the simplest probability theory but not the only possible one. Quantum theory does not follow classical logic nor classical probability. The failure to follow classical logic is exemplified by the violation if the Bell inequality. Quantum probabilities follows the second simplest probability theory which is that the sum of squares of the "n options" adds to one. Both are related to the quantum state being a vector (strictly a ray) in a suitable complex space and not a real number space as in classical physics. The violation of Bells inequality also shows there can be no local classical theory underlying QM (no hidden variables). Regards Andrew PS Schrodinger's cat is never in a superposition of dead and alive it is in an entangled state with the trigger/poison being either trigger fire and dead or trigger not fired and alive. All entangled means is that measuring (e.g. looking at) one element gives information about the other.

Maybe our and their technology is not up to it yet. Strength of signal and sensitivity of detectors. Regards Andrew

A whole new game for you imagers Singing images . Will PI be Philharmonic images? Regards Andrew

Loss of entanglement is due to decoherence. Evidence points against a universal reference frame difficult to know what it could be in curved spacetime with no universal coordinates possible. The closest you can get to predetermined is the Block Universe where all spacetime exists all at once and is unchanging. It is just that we are embedded in it and perceive it as dynamic. Tought stuff. Regards Andrew

You can measure the state when you open the box and from that in some circumstances (measured orientation v the entangle state orientation) deduce what the other state would be exactly. So if you measured "up"" the other would be "down". You can't choose which of up or down you will get. This is as close as you get to classical correlation where a red sock is put in one box and blue in the other. Open one and you instantly know what the other one is however far apart they are. More generally you would only know the probability of what would be measured at the other end. Neither amounts to communication as you say, just correlation. To me the mind boggling fact is that the two measurements can be space like separated (I.e. you can't even say which took place first) and at any chosen measurenent angles, decided just before the measurements are made, the correlations will still persist. Regards Andrew

Entanglement requires a local interaction to entangle the particles and they would then need to be separated. In addition you would have to stop them interacting with anything else on route to prevent destroying the entanglement. The CMB is very efficient in this regard. Regards Andrew

I always struggle with the Null hypothesis but I think 5 sigma amounts to a 1 in 3.5 million of the result being due to chance alone. Something has to be wrong with the standard model as we are here (excess in matter over antimatter) and it is symmetric in this regard. Maybe this will point the way. Now back to Stoppards play Rosencrantz and Gildenstern are dead. Heads, heads, heads.... Regards Andrew

Coin tossing is very similar to the LHC experiment as the standard model predicts equal numbers of muons and electrons from the decay! However, tossing coins is a lot cheaper but less fundamental. Regards Andrew

That is exactly how we "observe" it. That is we deduce the existance of dark matter from it's effect on light. For example we don't see enough normal matter to explain some gravitational lensing. Regards Andrew

The resolution of 35nm at 750 nm is about 20 so very low. I am not clear what you want to measure the spectra of. Is it sky brightness, how a stars spectra changes with altitude etc. Can you explain what you will be measuring. If its star then a Star Analyser in slitless mode would do R ~100 but if is the sky the you will need a slit spectrograph. These links might help ROBIN'S ASTRONOMY PAGE SPECTROSCOPY (threehillsobservatory.co.uk) & Photometric slit (astrosurf.com) Regards Andrew

What resolution are you looking for? If you want to do diffuse object you will need a slit or fiber spectrograph. How bright are the objects, size if telescope? Regards Andrew

Have a look here https://www.shelyak.com/produits/?lang=en. Some of them are available in the UK via @FLO . Regards Andrew

You want the size of the end of the sight tube to match the diameter of the secondary as closely as possible when viewed via the peep hole. This would lead me to conclude longer is better. The eye is not good at matching concentric circles so you want them as close as possible. Regards Andrew

But I study flares!

@JeremyS looks like it's time to clear out your gutters. Regards Andrew PS feel free to come round and do mine as well.