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Everything posted by Martin

  1. Simon, welcome. Sisyphus and Mr.Skeptic are explaining things in words but you might also need to get some mental imagery. So I suggest you google "wright balloon analogy" and watch it for 3 or 4 minutes as the two 2D universe expands Then type a number 2 into the URL and get the second version "Balloon2", that has light in it. Little wigglers representing photons, that move across the 2D surface while it is expanding. Also you mentioned the special relativity (1905) speed limit. That does not govern the rate that distances can expand in the improved (1915) theory called genera
  2. Sometimes a user will refuse to admit they made an error and continue arguing. Not listen to what they are told. Misinterpret what is being said, take issue with strawmen, and so on. It gets to seem like they are arguing just for argument's sake. We need a place for posts that might arise this way, so we can move them here and take some time to think about it---see if the post might have merit, or arises from honest misunderstanding, or is just arguing for its own sake. So here's a thread for that kind of thing, so we can move posts here and check them out. And in some cases move them
  3. These links are old. The thread is dated. I will move it to the speculations trash and think what new resource links for QC and QG to post.
  4. As DH said, stop putting words in our mouths. Nothing wrong with isotopes being formed in iron core supernova. Didn't say there was. You seem more interested in arguing than in learning. DH already called troll. I have to reluctantly go along.
  5. ===quote DH== ... In fact, they produce quite a bit of iron. The iron is produced by the supernova event in the case of a pair instability supernova or a Type 1a supernova. ... ==endquote== I have been reading the first of those two references in post #25---the one about SN 2007bi. An important PISN (pair instab. SN) signature was the large amount of Nickel-56. Predicted by the PISN model. 56 is divisible by 4. 14 helium nuclei come together. Energetically favored. Ni-56 is made at the time of the explosion and decays over a few days to iron. I gather the PISN mode
  6. Steevey, you aren't listening. Please read post #17 again. When a high enough temperature is reached the gamma radiation is no longer efficient at supporting outer layers. And the hotter it gets the less effective fusion becomes at supporting outer layers. That is why your reasoning just now is bad. Your reasoning in this post is bad. A typical "non-metallic" core in this case might be primarily oxygen and around 100 solar masses. (star more massive, core say 100 solar). All that oxygen is potential fusion fuel. But the fusion energy is now being bled off into the pair creation
  7. I should have spoken more precisely. As I understand it they found that amount of patterning can occur randomly. As one paper said, to the extent that Penrose found concentric circles you could just as well find triangles or squares. There will always be randomly occurring patterns but it does not mean anything. So the papers contested the claim that the findings were significant. ==================================================================== I may be mistaken. PENROSE AND GURZADYAN posted a second paper today, answering their critics and maitaining that the observed pattern
  8. http://arxiv.org/abs/1012.1268 A search for concentric circles in the 7-year WMAP temperature sky maps I. K. Wehus, H. K. Eriksen http://arxiv.org/abs/1012.1305 No evidence for anomalously low variance circles on the sky Adam Moss, Douglas Scott, James P. Zibin Sean Carroll pointed these out. Looks like Penrose circles not confirmed. http://blogs.discovermagazine.com/cosmicvariance/2010/12/07/penroses-cyclic-cosmology/
  9. Thanks for the correction. Should have said wavelength. Since neutrinos are massive particles I'll just think of them as slowing down as they lose momentum, in contrast to light.
  10. Short answer is YES neutrinos lose momentum--from the standpoint of observers at rest relative to primordial light (CMB). Since neutrinos have mass, losing momentum means losing speed. An article I read a couple of years ago said that STEVEN WEINBERG in his textbook COSMOLOGY goes through the math for a general particle with mass, traveling over long period of time in expanding space and shows how it loses momentum (so speed) due to expansion. The author provided what he said was a more concise proof. It is not too surprising. People use this fact when they run simulations of
  11. In part your questions show me my understanding is inadequate. So I looked around and didn't find much. I did find this: http://www.scholarpedia.org/article/Accretion_discs I may find more later. You sound like you have it pictured in mind at least as well as I do, or did until reading the Scholarpedia on Accretion discs. My intuitive picture is based on the ideas of conservation of energy and of angular momentum. I know that around a BH there is a minimum circular orbit size, where stuff is circling at near the speed of light. I haven't done a back-of-envelope calculation to es
  12. Be careful about dismissing people if you don't always know what you are talking about, Steevey. Nobody knows it all (not me anyway.) Arch gave a fairly clear (if very brief) mention of the pair-instability hypernova mechanism. Indeed it is believed to proceed by a kind of chain reaction which in effect traps increasing numbers of gamma photons once they reach a certain threshhold energy---so they no longer help to support the outer layers by radiation pressure. The gamma photon reacts with an atomic nucleus to produce an electron positron pair. The particles and antiparticles in the
  13. You know an asteroid falling towards some other body when it hits can release enough heat to melt rock. It can melt part of the asteroid and part of the crater---even vaporize. That is just a small conversion of gravitational energy. How much energy depends (among other things) on the square of the escape velocity at the surface of the target body. The grav. energy in this context is what does the heating. It isn't just a "fancy talk" equivalence---it is a meaningful straight-talk equivalence. Nuclear fusion only gets you on the order of 1% of the mass converted to energy (gamma radiati
  14. Nice! Did you do the labeling on that diagram? Ned Wright's cosmology tutorial had some basic diagrams like that, but last time I looked it did not have the labeling with words like "distant galaxy" and "Milkyway". Ned Wright's diagrams had the teardrop shape lightcones, and the worldlines with little local forward lightcones along them. A light ray worldline passing one of those has to be running parallel to one side or the other of the small local triangle. The plot is with proper time and proper distance. It's a really good tutorial and the diagrams are a great help. But I haven't
  15. I defer to Spyman and only comment in support of his explanation, but yes and you can figure for yourself that since the redshift z = 8.6 the surrounding galaxies were about 10 times closer than today on average. The relevant ratio is z+1 = 9.6 or about 10. You are talking about the universe at redshift 8.6 when it was already about 600 million years into its expansion history (correct me if you mean something else.) So the CMB radiation would have a temperature 10 times hotter. Today it is about 2.75 Kelvin. So back then the microwave soup around you would be 27.5 Kelvin. Still
  16. Then hopefully that part of the discussion is over. In case anyone else might be interested in the galaxy that was the main thread topic, you might want to check its recession rates (both then, when it emitted the light, and also now) or its distances from us then, and now. I suspect that many here (several, anyway) have used the "cosmo calculator" at Wright's website, but in case you haven't and want to, google "cosmo calculator". Then type in 8.6 for the redshift, over on the left. When the calculator comes up it has a "3" in the redshift box, as an example. You need to replace that
  17. I don't think your terminology problem is that you have the same ideas as the others but merely call them by different names. I think your underlying set of ideas is different. When there is a long argument that doesn't get anywhere, it often arises from some language problem---mismatched terminology, incongruent concepts. How about this? You totally stop arguing and make a determined effort to understand what I'm trying to communicate. The CMB is not something in the past, or something somewhere else, it is a soup of photons all around us that we swim through. CMB photons, on a pe
  18. In normal cosmology talk, the CMBR is not a horizon. It is the background radiation filling the whole universe (approximately uniformly) that arose from a definite event that occurred some 380,000 years after the start of expansion, universe time---the measure of time built into the standard model used by cosmologists. This diagram looks OK to me except that the usual term for the red circle is "surface of last scattering". The CMBR is radiation. It is not a place. It is not an event. It arose from an event, which we can date reasonable confidence---we can say when (in standard model
  19. Nice closeup shot of comet: http://blogs.discovermagazine.com/badastronomy/2010/11/04/amazing-close-ups-of-comet-hartley-2/
  20. Yes, you are quite possibly right. I don't know enough to guess as to the scientific interest---it will say a lot about the chemical composition of the very early solar system. Surely one of the most interesting things inside the orbit of Jupiter (as you say, the inner solar system.) I keep returning to the thought that it might also turn out to be the most USEFUL new object in the inner system. It's water is at a HIGHER GRAVITATIONAL POTENTIAL than elsewhere. It is easier to get stuff off the surface of Ceres, than, for example off the surface of the Moon or Mars. Stuff incoming
  21. I am intrigued by the Dawn mission to Vesta and Ceres---the two largest in the asteroid belt. Ceres is now rated "dwarf planet", diameter ~1000 km, estimated large amount of underground water. Dawn uses solar-powered Xenon ion drive. Dawn and Vesta are now both roughly the same distance from the sun (about 2 AU) and "running neck and neck" at roughly the same speed around 20 km/second. Vesta is slowly overtaking and Dawn is thrusting to speed up, so that it can exactly match speeds. It is now about 0.1 AU from Vesta. Ion propulsion is very gradual. It will take 9 to 10 months
  22. http://arxiv.org/abs/1010.4312 Look at the attached PDF. It has the pictures they took of the galaxy. Galaxy is now 13.1 billion years old. The baby picture that European Southern Observatory (ESO) took of it is when the universe had been expanding for only 600 million years. ESO is great. Somewhere down in Chile. They have done some terrific things. Like make a timestop movie of stars orbiting the black hole at the center of our galaxy. Like over 10 to 20 years. They see in the infrared, need to because for z=8.6 the wavelengths have been stretched out by a factor of 9.6.
  23. No, time would not reverse. Your first description was accurate enough. Gravity slows expansion down and gradually halts it. Then stuff falls back together. Nothing said about time reversing. No reason it should.
  24. That's a point. There's apt to be a lot of available energy, if there were complex life-forms able to utilize it. But those same conditions (as I imagine it) might make it hard for complex organisms to evolve in the first place! I suppose there are always caves, and cracks in the rock, and craters---providing shelter where primitive single-cell goo can develop. Microbes have colonized all sorts of niches on earth from hot to cold and wet to dry. But if there are these strong winds always blowing across the borderland from cold to hot, transporting water, as vapor, hotwards away from the
  25. I suppose the prevailing surface winds at the border would be hotwards (toward the hot spot). I'm just thinking along similar lines to you. It makes sense. And highaltitude winds would blow coldwards, towards the cold spot. By analogy to what I guess the windpattern would be like on Earth if it were not for the Coroloris effect of Earth's rotation. The surface winds would blow towards equator (hotwards) and then heated air would rise and return to polar regions (coldwards). I don't know how powerful the winds would be at the border. As I imagine it, with a dense atmosphere (given pla
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