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Everything posted by Tiki

  1. Thanks Stu, that sounds like some good practical advice. I just have to summon the necessary courage!
  2. I need to remove the rear lens cell on my TV 101 in order to give it a clean. There are appears to be a couple of spots of mould/ fungus on the rear element. It looks as though everything should simply unscrew once I have removed the grub screws (see photos). Is this indeed the case?
  3. I am looking for a 2" Lumicon OIII filter. Must be in excellent condition. Cash waiting. I also have some premium eyepieces that I would consider trading with possible cash adjustment either way. Paul
  4. Hi iPeace, If you are still looking for a 15mm Panoptic then I can possibly help. Mine has not been used for a couple of years and needs a new home. I have the box, paper (signed by Al Nagler) etc. Paul
  5. I like his enthusiasm, his originality, his intellectual integrity and his big red books. I also like the very notion of a Nobel Laureate with a 'gangster accent'.
  6. Thanks Fozzie, what a beautiful image. These images showing myriad galaxies have a special feel; they give a hint at the enormity of The Universe. An Einstein ring is a visual artefact of gravitational lensing. Just out of interest, are there any galaxy clusters that are close enough and dense enough to be in range of amateur astro-photographers to give a similar effect to Hubble images like the one above (minus lensing)?
  7. Or rather sadly we might surmise that the Renaissance was fifteen hundred years behind its time.....
  8. Yes. The lunar distance tables were published up until about 1906, being made redundant I suppose by reliable chronometers. Slocum rather famously circumnavigated the world in the 1890's with an 'old tin clock with only one hand' which had to be boiled whenever it stuck!! A competent navigator with a sextant and chronometer is reckoned to be able to fix his position within about a mile. Lunar distance methods are much more sensitive to error and yield fixes to within about 15ish miles.
  9. From the horses mouth: JA Wheeler in his nineties . Video no.59 is the one about the positron.
  10. Apparently not. It was all JA Wheeler's idea. The idea is based on the world lines traced out across spacetime by every electron. Rather than have myriad such lines, Wheeler suggested that they could all be parts of one single line like a huge tangled knot, traced out by the one electron. Any given moment in time is represented by a slice across spacetime, and would meet the knotted line a great many times. Each such meeting point represents a real electron at that moment. At those points, half the lines will be directed forward in time and half will have looped round and be directed backwards. Wheeler suggested that these backwards sections appeared as the antiparticle to the electron, the positron. Many more electrons have been observed than positrons, and electrons are thought to comfortably outnumber them. According to Feynman he raised this issue with Wheeler, who speculated that the missing positrons might be hidden within protons.[1] Feynman was struck by Wheeler's insight that antiparticles could be represented by reversed world lines, and credits this to Wheeler, saying in his Nobel speech: “ I did not take the idea that all the electrons were the same one from [Wheeler] as seriously as I took the observation that positrons could simply be represented as electrons going from the future to the past in a back section of their world lines. That, I stole![1] ” Feynman later proposed this interpretation of the positron as an electron moving backward in time in his 1949 paper "The Theory of Positrons".[2] Yoichiro Nambu later applied it to all production and annihilation of particle-antiparticle pairs, stating that "the eventual creation and annihilation of pairs that may occur now and then is no creation or annihilation, but only a change of direction of moving particles, from past to future, or from future to past. Cut and pasted from here: https://en.wikipedia.org/wiki/One-electron_universe
  11. Perhaps this is something for string theorists to ponder..... Arghhh!
  12. No-one really knows what light is. It is defined as a disturbance in space that carries information about charges and their motion (or acceleration). If 'everything happened at once', then the wave equation would lose it's time dependence. 'Space-time' would become 'space'.
  13. Maxwell's equations and the Lorenz force law describe classical electromagnetism. If the speed of light were infinite then time would collapse and classical electromagnetism would essentially be Coulombs Law. Vacuum permeability would be a meaningless concept and vacuum permittivity would survive insofar as force would need to be redefined. A slight shift in vacuum permittivity would lead to massive consequences for the periodic table as it is closely related to the fine structure constant and stellar nuclear processes. As for E=mc^2, Special Relativity collapses as the speed of light has no meaning and the theory is lacking a postulate. There is an excellent book called 'Just Six Numbers', by Sir Martin Rees. An easy and fascinating read that marvels at the fortuitous values of certain constants of nature. It certainly wouldn't.
  14. Good call. The Wikipedia page has a lot of content on this very event. There is thought to have been something like 10 earth masses of gold created in the merger! https://en.wikipedia.org/wiki/GW170817
  15. Whilst I agree that a spherically symmetric stellar core collapse would not produce any gravitational waves, real-world stellar cores are axisymmetric objects and are expected to produce gravitational waves. There has been a fair amount of research into predicting the precise nature of these emitted waves. "Stellar core collapse events are expected to produce gravitational waves via several mechanisms, most of which are not yet fully understood due to the current limitations in the numerical simulations of these events." From the abstract of https://arxiv.org/abs/1701.02638
  16. The only gravitational effects of the formation of a new and relatively nearby black-hole would would be a barely perceptible ripple in space-time. Hopefully our gravitational wave detectors would be able to detect it . Tidal forces are at the heart of Einstein's gravitational theory and they fall off according to an inverse cube law. This means that all the gnarling of space-time that occurs in the vicinity of compact objects fall off even more quickly than might be at first suspected.
  17. According to quantum mechanics, there is a natural limit to how accurately one is able to specify the position and energy of an object. This means that it is very unlikely that any two objects will have the same temperature let alone a 'gazillion' objects such as in the early universe. Whilst the temperature of the early universe might very nearly be the same everywhere it won't be exactly the same. These 'quantum fluctuations' are expected to have evolved into relatively large differences (about 10% according to mid-1970's calculations) by the present day. There is a natural limit to how well we can predict the interactions of snooker balls on a snooker table. If we specify the position of the balls and the initial velocity of the cue-ball as accurately as possible in accord with quantum mechanics then it is found that we are unable to predict what happens after a dozen or so cue-ball interactions. The equations governing snooker-ball paths are well known and are presumably more simple than the equations governing the evolution of the universe. By analogy, doesn't it make sense that the Universe should appear less isotropic than it actually does? Although the horizon problem originates from the 1950's, it became much more of a problem once the CMB was detected and the scientific importance of Big Bang cosmologies became to be more widely realized. I hope this helps.
  18. Interesting and long. Not read myself yet either. Interesting and short: https://www.smbc-comics.com/comic/the-talk-3 .
  19. I have no idea what Shapley actually did. Do you know which underlying assumptions he made about the likely distribution of globular clusters?
  20. Strong gravity => slow clocks High constant velocity => slow clocks These two effects are unrelated. If you consider how the Laws of Physics might appear in a freely falling elevator and are as smart as Einstein then you would be able to deduce the Principles Of General Relativity. One of these principles being the similarity between accelerated frames of reference and gravity. An accelerated frame of reference is of course one which has a non-constant velocity. I hope this helps.
  21. I feel that the video is slightly confusing. In the video, 'optics' is defined as the study of how light interacts with matter. This interaction is then explained as 'scattering'. 'Scattering' is a huge subject of which there are a great many different cases to consider, this is all glossed over in the video. To make sense of 'optics' when defined like this is difficult. 'Geometric optics' on the other hand has some simplifying assumptions which although fall short of the complete picture of light, do in fact provide a useful approximation of what happens with lenses, mirrors etc. It is assumed that light propagates as a ray and that the size of any mirrors/lenses are large when compared to the wavelength of light. With these simplifying assumptions, Fermat's Principle of Least Time describes geometric optics perfectly. This one principle describes everything. Geometric optics in a sense is in fact simple.... https://en.wikipedia.org/wiki/Fermat's_principle
  22. Feynman's lectures I and II are excellent and relatively inexpensive. You get an insight into a great mind with a lot of interpretation of equations. Much maths is also covered in detail. You could also use these books to chart your way across physics buying various other maths books as required. Volumes I and II are a great reference. Volume II is worth buying just for the short section where Feynman explains his own way of linking special relativity with Maxwell's equations. Pure gold. Schaum's outline series is excellent for both pure and applied maths. I just checked on abebooks . com and the excellent 'Vector Analysis' by Murray Spiegel can be had for less than a three quid as can 'Linear Algebra' by Seymour Lipschutz. Schaum's series has a great number of worked examples and might therefore be useful for home-study. Good luck.
  23. Thanks for pointing this out, I'd never really thought this through before and had just assumed that it was the intensity that mattered. It makes me feel good to know that as our gravitational wave detectors improve, then the volume of Universe where we may directly detect 'gravitational wave producing events' increases rapidly. I am not sure of your question regarding bias. For example, if we are able to double the efficiency of our GW detectors then we will be able to detect GW events in a volume 8 (2^3) times as great as we could before. This is a sevenfold increase in volume meaning that newly detected GW events would be approx. 7 times (actually slightly more than 7) more likely to be more distant than previous detections. All detections are good news to me. Only a few years ago I used to wonder if we would ever be able to directy detect any GW's at all, it seems now that such detectable events might even become commonplace. I can't wait.....
  24. I wasn't referring to the arbitrary choice for zero potential energy in a system as this would not contribute to the active gravitational mass. I was referring to short-lived negative energy virtual particles (important in Hawking radiation), negative energy densities in the Casimir effect etc.
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