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Everything posted by Martin

  1. In June 2009 the IOP (inst. of phys.) published an essay by Smolin in their wide-audience magazine Physics World. The essay called The Unique Universe brings out some new ideas about the universe. It seems to have gotten a good reception. Anyway something has driven the sales of Smolin's book way up. I just checked and the salesrank was 852 compared with Brian Greene's books 2539 and 3817. The five most popular stringy books had average salesrank 6936. So Smolin was doing 8 times better. That was at 11 PM pacific time on 2 July. There haven't been any radio or TV appearances that I know of, all he has done that could possibly boost sales is put this piece in Physics World. (PW readers are all kinds of physicists, students, techies, engineers and kindred sorts. It's for science trained but no one specialty. My guess is that these PW readers got interested in what he has to say and are buying the book. If you know of some other thing that might explain the jump in sales, please mention it.) ===== Anyway, you might like to check the article out. http://physicsworld.com/cws/article/print/39306 It was picked up by a science/technology blog called X-Journals which commented favorably in a post titled "Forget the So-Called Multiverse: One Universe is Enough". http://x-journals.com/2009/lee-smolin-forget-the-so-called-multiverse-one-universe-is-enough/ It could be the string landscape/multiverse idea has gotten into bad odor---enough science people may dislike it that, by coming out against it, Smolin cause a jump in his booksales. I noticed a simultaneous jump in sales of the hardcover edition as well as the paperback.
  2. At the moment all you have is a speculation, Rob. You need several things to make it science. Ultimately you need a system of accounting that says how much matter has to decay to make a certain volume of space. And then you need your system of accounting to match observations. You have to be able to look back and SEE that extra matter in the past that has decayed to produce the extra volume of space. Cosmology is quantitative. So here is a little exercise. The CMB light that we see was emitted around year 380,000 and the redshift it has experienced shows that distances have expanded since then by a factor of about 1000. That means that volume has expanded by a factor of about 1,000,000,000. Now we can look back to that time when the CMB light was emitted and estimate the density of matter in space at that time. The observations seem indicate that there was the same amount of matter as now, just in a smaller volume. As well as we can tell, the density was a billion times higher. But your model would say that there was some extra matter back then, which decayed to form all that extra volume. How much extra matter was there? In conventional cosmo, no force is needed to make the distances between galaxies increase. Space is not a thing (Einst. said it had no objective physical existence) so it doesnt have to be created. If you take the usual cosmo model and zero-out the dark energy you still get an expanding universe. The dark energy is not needed. All it does is accelerate the expansion (make it gradually happen faster.) Important not to imagine space to be a substance, needing to be created. Focus on the geometry---the distances we can actually measure---not on the space (as if it were a substance). Jamey, thanks for helping to get Baroba straightened around. I think what you said was helpful and in the right direction. Dark energy is indeed important (I just had to correct that one detail---you can still have expansion without it, only that the expansion very gradually slows down.)
  3. We got an interesting thread just now, from Mahela, asking what is the most modern definition of the meter. That prompts a question about where the definition of the kilogram is going. Any ideas? Any news about recent developments? Right now I believe the kilogram is defined based on a block of metal kept somewhere in France, sort of like a bank vault. Correct me if I'm wrong about that. Is that situation likely to continue for yet another 10 years?
  4. You need to supply a math model according to which matter flooding into our region of space would cause expansion. According to the theory of gravity (Gen Rel) that we are using nowadays, incoming matter would slow expansion, increase density, and tend to cause collapse---the big crunch scenario. So you need to give us a theory like GR, which explains gravity---how the planets orbit the sun etc---and which explains the geometry we observe (expansion, curvature etc.)---but is different from the theory of gravity/geometry we have now in the sense that matter flooding in would cause expansion. In this kind of discussion you are encouraged to believe whatever you like about the universe, but discussion cannot be based on ignorance of the standard model. You do not have to believe standard physical theory, standard gravity, cosmology etc---but you have to start by being familiar with the commonly accepted ideas as a point of departure. So if you want to challenge and reform cosmology, for example, you must first make yourself familiar with it. That is our common starting point.
  5. http://www.astronomynow.com/090626Cosmicraysefficientlyacceleratedbyexplodedstars.html http://www.sciencedaily.com/releases/2009/06/090625141454.htm Cosmic rays are mostly protons (hydrogen nuclei) which have somehow been accelerated to big energies, some as high as one joule. A joule is the thump released when you drop a (one kilo) textbook ten centimeters onto the table. That is a big thump for such a little particle to deliver. It has been an extreme mystery what has been accelerating all these protons that are constantly arriving to our atmosphere from space with these incredibly high energies. It was thought that there weren't enough supernova explosions in our galaxy often enough to account for this big flux of accelerated particles. Finally a light at the end of the tunnel. These people have got a handle on the problem. They actually observed a supernova remnant expanding shock-wave and were able to determine that the shockwave is more efficent (accelerates more to higher) than the previous mathematical model led us to expect. I think it's an example of good science. They published in Science magazine which is possessive so we only have secondhand. They kept their preprint off the arxiv so we can't get the original article. That's how the prestigeous Science mag makes a buck. OK. So there are the secondhand reports. Eveline Helder is a female, which is always a kick to my atavistic brain. Attractive female scientists who lead world-class research are my pin-ups. So? Here's her picture: http://www.astro.uu.nl/~helder/ Oh oh! She is based at Utrecht. The same place where Gerald 't Hooft got Renate Loll to locate. Loll is a world class quantum gravitist who gets quantum universes to happen in the Utrecht computer. Those dutch! Two reasons to go to Utrecht.
  6. I don't want to get into an argument, but I would like to introduce something to think about. Of course historically it could have gone either way. The original Newton idea of mass was inertia which is how many units of force you have to apply to get a unit of acceleration (like "one meter per second per second") It is very like the idea of resistance in basic electric wiring, how many volt units do you have to apply to get one unit of current ("one coulomb of charge flowing by per second") This idea of inertia is very simple and useful. And then there's Newton G which if you multiply an inertia by it tells the gravitational attractiveness of the thing. Anyway if you study mass in equations you see that the unit is always equivalent to a unit inertia (like "one newton of force per each (meter per second per second) unit of accel") We at SFN have liked to keep it simple and have just one concept of mass, and we go the way the perceived majority physics community goes, which is to keep mass being Newton's idea of inertia. However in the early 20th certain physicists thought would be nice to get rid of that idea and have the mass scale be just a rescale of energy, mass would be E/c^2. But this would no longer correspond to inertia except in certain special cases. Mostly it would just be another way of quantifying the total energy. Which is fine and dandy. It could have gone that way. We could be happy speaking French, or speaking Italian. "Ciao bella! C'est magnifique!" Only some people think they would be more happy to have two separate meanings of mass (and everyday have to explain the difference to some poor soule) or they think they would be happier if everybody meant E/c^2 instead of inertia. The central point, the catch (and I hope Swansont will correct me if I am wrong) is that a moving object does not have a welldefined directionless inertia. If an object is at rest then it does not matter which direction you shove. You always get the same "resistance", the same cost of units of force per unit of acceleration. But if an object is moving then this turns out not to be true. You get more or less acceleration depending on whether you shove along the direction it's going, or you shove crossways. If you shove in exactly the right direction then indeed the inertia will turn out to be E/c^2, which Pete liked to be the mass, and which Proton also liked to be it. If you don't shove in the right direction then it is not E/c^2. In fact, in the majority language, the popularized equation E = mc^2 is only true for objects at rest. There is a slightly more complicated equation for when it's moving. And in the majority language, the mass of an object is defined to be it's inertia at rest. Maybe this could become an informative discussion and not some personal theater hero action movie martyr-for-a-cause episode with hand-to-hand duels and bickering and whining or whatever. I can't remember how it played out when we did this before. But I would like it more impersonal and informative. And if I'm wrong about the directionality of inertia, for moving objects, please correct me. ============================== There's actually some non-trivial content here, I think. Not just controversy soap-opera. It has to do with measurement and standards. there is a branch called metrology. How do you measure voltage? Length? force? time? current? the NIST hires a lot of metrologists It is a very interesting professional line of work. Well a nice thing about inertia is that it is basic and observable. There is a clear operational definition. You shove and you watch and gauge the acceleration. But fundamentally no one knows what energy is. Feynman gave his famous "Dennis the Menace" talk about this. We keep finding new types of energy. So there is no operational definition for that minority mass concept E/c^2. Because at a very primitive basic caveman level you cannot say what E is. But inertia is an operational primitive idea. So if you are going to construct a system of physical quantities this kind of simple defined primitivity might be a consideration. Ugh! Will hit with club! See how fast move!
  7. Proton presented some cogent and well-researched arguments here why we should decide to talk different. Why we should talk like he does, and somebody named Koks does, instead of the way we are used to. Proton and Koks argue that it would be more "convenient." And they cite wellknown precedents such as Rindler. Semantic crusades can be interesting in their own right but they are not physics. Not science of any sort, actually. Since we don't have a special place for preaching by semantic missionaries I think the best venue is Pseudoscience forum. I've moved these arguments to a special Semantic Reform thread in Pseudo. http://www.scienceforums.net/forum/showthread.php?p=500597#post500597 We can discuss the issue there without disrupting regular science forums. We had essentially the same discussion with Pete a while back. He was campaigning for the same mass terminology. Using words different, it is argued, would be more "convenient". Anyone who feels strongly about this kind of convenience please join our discussion down in Pseudo. I'm fine with whatever folks decide as long as any change is coherent consistent and deliberate.
  8. Hi proton. Trying to reform people's language is not science, but it can be very interesting. I like you because you are smart and articulate, but it is inefficient if we start meaning different things by basic words. We have been thru this before and settled on mass = rest mass. We should not change until we have all discussed this and decided. You want us to use "mass" to mean E/c^2. We should not change to that without a vote by the science mods or a decision by people like Swansont and Klaynos etc. Or some kind of deliberate decision process. If we decide not to change our common usage of the word, then you have to abide by that. ================ I noticed in cosmology just now you were talking like an authority but saying something that struck me as nonsense. You are new. Don't assume you know everything and can instruct newcomers. Wait, take it easy. You are bright and articulate and impressive but you also seem to be green, like an undergraduate. That would be my guess. It doesn't matter. 50 years old guys can still be naive and promote non-standard cosmology. ================= From time to time we get these fervent reformers, missionary types. They have a cause they are battling for. The Milne universe, relativistic mass, whatever. It's a cheap way to feel important. Take on a minority cause, like about word usage, and learn all the arguments. And then whereever you go you feel everybody else is wrong and you need to preach the true religion to them. The problem is when you mess with basic language you disrupt other people's communication and confuse newcomers. Here it is important for us to all talk more or less the same, with the same basic dictionary. We can't have two or three kinds of mass, butterscotch mass, chocolate-relativistic mass, transverse mass, longitudinal mass whatever. We have to have one mass concept. Your reform zeal may be right! That guy Koks, who is essentially a nobody with a PhD who has written one book, since he got his PhD in Australia in 1996, that guy Koks might be right. It is not physics. It is just a crusade to make us talk different for our own good. But maybe it is right. Maybe nobody should smoke or drink alcohol and it would be "convenient" for them. You are arguing that it would be more convenient if we said mass to mean E/c^2. OK I grant it. It might be. But before we all change we have to decide we like to talk different, and make the switchover coherently. So I am being as nice about this as I can. Here is a forum where you can argue for relativistic mass. Do not promote semantic reform in the real science forums. Make your case here. We can all discuss it and decide what course we want to take. Any way is fine with me personally. It just means speaking a different language. The issue is not physics, its our choice of words to describe and explain physics. I find the discussion of this more boring each time we go thru, but I think you are a bright young person so please make with the rhetoric about your semantic mission.
  9. Proton you are presenting a view that I haven't heard from any professional cosmologist. Did you make it up? Or have you got an online source we could look at? If there is a professional source it is, I think, likely to be from a small minority who use nonstandard coordinates and concepts. ================= As an afterthought, maybe as a reality check you would work a little problem for us! We see galaxies out to redshift z = 6 and z = 7. So suppose we are observing a galaxy with z = 6. Roughly how fast is the distance to that galaxy increasing? Today. According to the standard cosmo model. And roughly how fast was the distance to that galaxy increasing back then when the light was emitted that is currently reaching us? I am not assuming that the galaxy is moving significantly relative to background, any more than we are. Most galaxies are only going a few hundred km per second relative background which is negligible compared with light speed. But I expect you will find the distance to the galaxy is increasing at a rate which is several times c. So how does that relate to time dilation . Merged post follows: Consecutive posts merged Who says "racing"? Who says "significant fraction"? The current distances to most galaxies are increasing at rates which are several times the speed of light. But this should not be thought of as ordinary motion. It does not get them closer to any destination the way conventional motion does. It is just dynamic changing geometry that you get with Gen Rel. You say you want help. Best help is to first google "wright balloon model" aND watch the galaxies and the photons carefully. Ned Wright teaches cosmo at UCLA and is a world-class top cosmologist. You can trust. The photons are moving at, say 1 mm per second. The galaxies are not moving (stay at same longitude latitude on balloon surface. Distances between many pairs of galaxies are increasing faster than 1 mm per second. That is faster than light. Yet if you watch long enough you will see that photons can make it from one galaxy the next. ============== Once you have internalized the balloon model. Google "cosmos calculator" and see if you can get it to tell you the rate that the distance to a redshift 6 galaxy is increasing. By that I mean a galaxy which is not moving, has no individual motion. (Most galaxies have some individual motion but it doesnt amount to much. Their redshift is not caused by their motion.)
  10. Alien and AlphaBeta, thanks for getting this discussion going. I'm glad you thought I could contribute--actually there are several people around that know something about star and galaxy formation (the general term astronomers use is "structure formation", in this context the word structure covers stars, galaxies, galaxy clusters, filaments, voids etc, the formation of all this structure is a challenge to explain.) The best talk about structure formation that I know is the one given by George Smoot to the TED club, he shows movies and has very good slides. We humans are just at the beginning of understanding structure formation. Evidence is building up that dark matter is real and that it plays an important role in starting the processes of structure formation. It's a good time for scientists to be humble about our understanding, although they can be proud of the progress that has been made (in a modest way) towards comprehending this wonderful process. Clouds of dark matter can actually be "seen" by their optical distortion of more distant objects, even though the clouds themselves are transparent. The way you can tell a curved lens of glass is there even though it is transparent by how it affects the images of what's behind. I'm not exactly sure what Alpha is asking about. Certainly we have seen a lot of pictures of proto stars and proto galaxies, embryonic early stages of these things. And they resemble what they will eventually become, in certain ways. There are star-forming regions even nearby, in Orion, where we can see gas clouds condensing around proto-stars. When gas falls together it has to radiate away extra energy as heat and we can see the heat given off---this is even before any fusion, any ordinary hydrogen burning, has begun. It is not a star yet but it is beginning to look like one. So we have "baby pictures" of young structure. Fuzzy proto galaxies too. But Alpha isn't asking about baby pictures that already RESEMBLE in some way, like being more concentrated blobs. He is asking about how we model the very beginning of concentration and condensation, before you can even see a distinct blob. How does the process proceed before there is any visible resemblance, before any fuzzy blob-ness that you can distinguish with a telescope. This is a very interesting question where some modest progress has been made and which George Smoot talks about. One great tool that is being used to attack this problem is computer modeling. You set up a simplified universe with no ordinary matter in it, only dark matter---because most matter is the transparent kind we call "dark". And you start out with the DM almost perfectly even distributed. Just a few slight ripples caused by quantum fluctuation around the bang time. Just a very very slight "waviness" left over from start of expansion. And you let normal gravity operate, and you see what happens and how long it takes. The falsifiability aspect, at this early stage, is that if doesn't produce structure like what we see, within a reasonable time, then it must be based on wrong premise, and you can rule the model out. This is "seeing" with a computer model. You have to realize that the cosmic structure is more than just individual stars and galaxies. there are huge cobweb wisps comprising clusters of galaxies, and huge voids. It is very beautiful. Delicate and grand. It is not just random speckles splattered about. There are aspects of organic pattern. Have you ever admired cobwebs? Or the way hairy mold grows on bread? Or the wrinkles on someone's face when they are very old? It isn't just random. Or the veins in a piece of rock. Or the smoke rising from a cigarette, from the days when some of us used to smoke them. It's very lovely and not just random. So getting a computer model that just implements the law of gravity to produce something similar is very challenging. The dark matter has to fall together by its own gravity and make just the right pictures. This is something that astronomers are having fun with now. A young grad student or postdoc would quite likely consider getting into structure formation research, as a specialty. And that is what George Smoot was describing in that video lecture to the TED club. Alpha you might enjoy it. Just google "Smoot TED" if you want to watch and listen to the talk.
  11. I would not want to buy anything but the new Steven Weinberg text http://www.amazon.com/Cosmology-Steven-Weinberg/dp/0198526822/ The Amazon page lets you browse inside. It is available for $60 used. I'm just stingy enough that I often use library books instead of buying. I live near a campus. So I don't own this. Are you near to a college or university library?
  12. http://backreaction.blogspot.com/2009/06/shrinking-betelgeuse.html Giant stars have a short lifetime. Consume their fusible elements rapidly. When there is nothing more to fuse, they start cooling and shrinking, then collapse and blow. Interesting to study the shoulder star Betelgeuse (alpha Orionis) with that possibility in mind. It is close enough that instruments can actually resolve it and can measure the diameter by a couple of different methods. Diameter measurements by different teams over the course of fifteen years or so show a downtrend. This could be part of a cycle--and destined to reverse itself. Or it might continue shrinking. At the moment it is just speculation. Some people speculate that the star has already gone supernova and we will find out in 600 years or less (since it is some 600 lightyears away.) Others take a more wait-and-see attitude: "let's watch for another 15 years and see what it does." http://www.berkeley.edu/news/media/releases/2009/06/09_betelim.shtml ========== BTW this is not to worry about. The rotation axis of the star is not pointed in our direction. Here's some additional comment, by John Baez: http://math.ucr.edu/home/baez/week276.html
  13. In general the interval could be several days or weeks, depending on how you picture it. Forgetting about the details of this particular case, suppose the accretion disk is larger than the orbit, and suppose the orbit is circular (for simplicity) and the plane of the orbit is tilted say 30 degrees relative to the plane of the accretion disk. Then in a 12 year orbit, the little one punches thru the disk every 6 years. So we have some leeway, as long as the disk is not a lot smaller than the orbit we can make the interval pretty long duration. The thing we need to do is compare the orbit "R" (semimajor axis) with the estimated size of the disk. I typed this into google "10/52 light years in AU" and it told me something over 12,000 AU. And our figure for the orbit semimajor axis (conventionally written "a" but I was calling it "R") was around 14,000 AU. So the orbit and the disk are roughly the same size. The picture I'm getting in my head is that the two bursts might be a substantial fraction of a year apart. The major party is at the focus of the ellipse. I'm picturing how wide the ellipse is near one of its foci. You know that other Kepler law about equal area swept out in equal time. The whole area of the ellipse is 12 years, equivalent. So on paper you draw the ellipse and you take scissors and cut off one end of the oblong, cutting across the long axis, right at where the focus is. And you judge what fraction of the whole area that nub-end of the oblong is, that you cut off. That fraction of 12 years is how long between bursts. Does this make sense? ================= There are formulas about ellipses we could look up. But suppose we just do this very loosy-goose. The time between bursts is like going on a semicircle with Radius 5000 AU, very fast. Remember we said that the peri-distance was 1/3 of 14,000. And that is about 5000. A semicircle is pi x R and pi is about 3, so the distance traveled is 15,000 AU. And light takes 8 minutes to travel one AU (they told us in 4th grade I think). So let's say the little one is going 1/3 of c for that whole semicircle. (It isn't, and it isn't a semicircle, it is the stub end of an ellipse, but close enough.) So the interval between flashes has to be 8 minutes x 5000 = 40 thousand minutes. I get that it is 28 days. The big error is that it isn't going 1/3 c for most of that time. It is going slower on average, as it rounds the tight end of the ellipse. So the interval is almost certainly more than 28 days. But this is order of magnitude.
  14. Martin

    a postule

    Any proposed law of gravity must pass the Iron Dwarf test. You know those iron Gnomes, little men with beards and pointed hats, that people put in their yards as a garden ornament. Imagine that you drop one off a cliff, and that it takes 4 seconds to hit the bottom of the canyon below. Your proposed formula must say how deep the canyon---how far did it drop? If you are not familiar with iron yard ornaments you can imagine using an old computer monitor or television set.
  15. Airbrush, I have to wimp out on you about OJ287. This is the kind of surprising thing that makes me cautious so I wait until some other team of researchers weighs in on it. As long as it is just one team, the Valtonen et al, I'm scared. Could there be some other explanation of this 12-year cycle of flashes that they have observed? It is a bold interpretation so I need some time to get used to it and decide if I trust it. However let's do the numbers a little bit AS IF we believe their model. Let's just do a classic kepler approximation and not worry about relativistic corrections. And say we call the semimajor axis by the letter R because it is somewhat like a radius. Let R be measured in AU (the earth's orbit semimajor) and let period P be measured in years (the earth's orbit period). And let the combined mass be M measured in solars. Then isn't it true that GM ~ R3/P2 Since it is a proportionality, we can ignore newton's G. So we just have to put P = 12 years and M = 18 billion solar, and we can solve for R. You can do that, just multiply 144 x 18 billion and take cube root. It will give the average distance or semimajor, expressed in astro units (AU). But what we want is the average speed. Then you can adjust later for the ellipticity e = 0.66 which they also tell us. The average or "circularized" speed would be 2 pi R/P This is just back of envelope. I have to go out now but can continue when I get back. OK I'm back at least for the moment. The cube root of 144x18 is 14 and the cube root of billion is thousand. So R must be 14, 000 AU just by kepler law. So a circularized orbit would be taking 12 years to go around 2 pi x 14,000 AU. Now we eat the piece of cake by comparing with earth's orbit speed which is 2 pi x 1 AU every 1 year. This baby is going 14 000/12 = about 1000 times earth speed. You may know that earth speed is about 30 km per second or about 1/10000 speed of light---one ten thousandth, good to remember. So this guy, on a circularized average basis, is going about one tenth of speed of light. More exactly 11 percent, I think. So far the calculation is really back of envelope. You could even do it in your head, without a pencil. Now they say the ellipticity that they estimate (and they still could have the wrong model and be fantasizing) is e = 0.66. So we still have to adjust that ballpark figure of 11 percent or 0.11c to allow for going faster when it is close in and slower when it is farther out. But just using Kepler and some sensible astronomical units we at least have a handle. Maybe that is enough for now. Can continue later. How is this discussion working for you so far? I was in a big hurry earlier and made an arithmetic blunder but I fixed it. Anybody see mistakes? ====================== To continue. We really should call the semimajor by the letter a, instead of R. Intuitively it is an average radius so I'm saying R. The meaning of eccentricity e is that eR is half the difference between the farthest and the nearest (the apo and the peri). So that means that the nearest is 1/3 of 14,000 and the farthest is 5/3 of 14,000 So at closest approach it seems like the speed is about 3 times the average circularized speed I was talking about later. Holy cow. I find that really hard to comprehend, unless I've done something wrong it seems like at least as a rough estimate the thing is going 33 percent of the speed of light. That is, factoring in the ellipticity, 3 times the 11 percent we got earlier. You asked about this. I find this scary and unexpected. Maybe I have made a stupid error. I don't like thinking about an orbital speed like that. There would be some relativistic correction but this is my attempt to get a very simple grip on it using Kepler law, the most classic of the classical.
  16. Great post, thanks for starting such an informative thread. Other posters who haven't tried this may be interested that the JPL catalog you pointed us to has some nice features where you can narrow and manipulate the list just by putting a check in a box. Here it is narrowed to terrestrial exos. http://planetquest.jpl.nasa.gov/atlas/atlas_search.cfm?Planet_Type=Terr&Sort=DiscDate&SortDir=DESC I defer to your knowledge of exoplanets so correct or amend what I say about this---I assume that a pulsar planet wouild be found by wobble, measured very accurately by the doppler of the pulsar signal. Most exoplanets are, I believe, found by wobble detected by the doppler shift of spectral lines in the star's light which I suppose is a lot more difficult than measuring it with a pulsar radio signal. A planet around a white dwarf (re: Widdy's question) would be more difficult to detect by wobble. I did some poking around on the web and could not find any indications that a white dwarf with planet had been found. But I couldn't exclude it, based on what I found. Maybe someone else will find something more conclusive.
  17. Yo' I do think that what I said is right about the Virgo cluster. I wasn't (or didn't mean to be) talking about V. supercluster. A supercluster is more like a "cluster of clusters". Different idea. Higher level collective. Milky belongs to a bunch called the "Local Group", which includes Andromeda and dozen or more others depending on what you decide to count. Maybe 20 if you count more smaller ones. Maybe you could say that the Local Group is one of the clusters belonging to the Virgo Supercluster. But the Virgo cluster (not whatever supercluster, just cluster) is well defined and long established and clearly distinct from the Local bunch. I'm just responding quickly from memory. You can check this with Wiki and perhaps correct me. Anybody else?
  18. Nice web-research and detail. perinigricon for blackholes like perihelion for closest-approach-to-sun and like periastron for other stars
  19. http://video.google.com/videoplay?docid=7136440703094429927 I just watched it---I read the transcript long ago but never watched the video, where he is telling all the stories. I was impressed. Maybe would like to watch more. Is there some other Feynman online video that you think is especially good?
  20. that is interesting, Ophi. In my life i have never suspected there might be life (currently alive life anyway) on Mars. But my past experience of you is knowledgeable and rational, so maybe I will adjust my subjective probabilities by a percentage point or so.
  21. I'm delighted someone else relishes this kind of news. I just learned of a team that last year used an unusual seredipitous method to deduce the mass of another supermassive BH. This time in the quasar galaxy OJ 287. The mass they got was 18 billion solar. They can't actually see the BH but they keep track of the quasar radiation, which fluctuates over time in a curious way. And from the fluctuations they deduced that the galaxy has a small black hole, several hundred or a thousand times less massive, that is in close orbit around the main one. People may have questions about how they came to this conclusion, but the article was published in Nature magazine which usually means it has been thoroughly peer-reviewed. Anyway somehow, by the record of fluctuating luminosity, they deduced the rate of precession of the orbit, and other characteristics, and also got this 18 billion solar figure for the mass. Here is the article by Valtonen et al that reported the OJ 287 bh mass calculation. http://arxiv.org/abs/0809.1280 A massive binary black-hole system in OJ287 and a test of general relativity M. J. Valtonen, H. J. Lehto, K. Nilsson, J. Heidt, L. O. Takalo, A. Sillanpää, C. Villforth, M. Kidger, G. Poyner, T. Pursimo, S. Zola, J.-H. Wu, X. Zhou, K. Sadakane, M. Drozdz, D. Koziel, D. Marchev, W. Ogloza, C. Porowski, M. Siwak, G. Stachowski, M. Winiarski, V.-P. Hentunen, M. Nissinen, A. Liakos, S. Dogru (Submitted on 8 Sep 2008) "Tests of Einstein's general theory of relativity have mostly been carried out in weak gravitational fields where the space-time curvature effects are first-order deviations from Newton's theory. Binary pulsars provide a means of probing the strong gravitational field around a neutron star, but strong-field effects may be best tested in systems containing black holes. Here we report such a test in a close binary system of two candidate black holes in the quasar OJ287. This quasar shows quasi-periodic optical outbursts at 12 yr intervals, with two outburst peaks per interval. The latest outburst occurred in September 2007, within a day of the time predicted by the binary black-hole model and general relativity. The observations confirm the binary nature of the system and also provide evidence for the loss of orbital energy in agreement (within 10 per cent) with the emission of gravitational waves from the system. In the absence of gravitational wave emission the outburst would have happened twenty days later." ==excerpt== It was not until the early 2007 that there were enough data to calculate a definite orbit[11]. The precession rate of the major axis of this orbit is 39.0 degrees per orbit, the eccentricity of the orbit is 0.663, and the mass of the primary black hole is 18.0×10^9 solar masses. These values are reasonable: merging binaries are expected to have eccentricities similar to this at intermediate stages of evolution[20], and the mass of the black hole is at the upper end of the mass range in quasars[21] (which is encouraging, as OJ287 is among the brightest quasars). ==endquote== I havent thought so much about this. And I don't know how far to trust it. But right now I am impressed by the Valtonen et al paper. they seem to have caught a pair of black holes which are spiraling down into each other, on the way to merger, and radiating off the excess energy (which they have to do in order to spiral in closer) by having their orbit generate undulations in the geometry around them---gravity waves carrying off the excess energy
  22. Wait Widdy! Don't you mean 1/2 instead of 1? I'll make the change and see if you like it: At Earth's surface -- 10-9 At Earth's orbit -- 10-8 At Sun's surface -- 10-5 At Neutron Star's surface -- 10-2 At Black Hole Event Horizon -- 1/2 I hope you hear the wise note of caution in DH's post. However people do apply classical and semiclassical analysis to black holes, and it can be interesting to see what you get. In this case if you had a pulley machine and could lower a mass, say like Bernard Madoff, or a broken television set, down to the black hole horizon and have that turn the pulley and generate electricity. Then you would get a large fraction of the energy that you would get by converting Bernard Madoff into pure energy. Say by reacting him with another Madoff made of antimatter. But using the pulley machine I think you wouldn't get the whole energy equivalent, only 50%. Nothing in this world is perfect. This would be another interesting chapter to put in a textbook, or a discussion to have with a class, if you should ever teach a Fun Astrophysics course. The students will be asking questions like "what happens to the mass???!!!" If you measure the mass of a bh, and also a kilogram brick a long ways away. And you drop the brick in. Then the end mass of the bh will be the old mass plus the mass of the brick. But if you lower it down gradually, extracting the energy and using it, say to heat many many cups of coffee. And then you cut the brick loose at the horizon. Then the mass of the bh will only be equal to the old mass plus 1/2 of the mass of the brick. And the students will ask "what happened to the other half kilogram???!!!" and the answer is that all those cups of coffee are now more massive by a total of half a kilogram because of the heat that went into them. Cups of hot coffee weigh more. Is that right? Or did I make a mistake? Notice that the Schw radius is 2GM/c^2, not GM/c^2. You forgot a factor of two in your calculation (something physics teachers habitually do.) If I made an error let me know please. In any case this would make a nice 15 minute class discussion and might lead some of the students to learn a whole lot more about gravity and black holes on their own. "Black holes as an energy source" etc etc.
  23. http://www.astronomy.com/asy/default.aspx?c=a&id=8337 M87 is one of the larger galaxies in the Virgo cluster----the nearest major cluster of galaxies near us. M87 is estimated about three times the mass of Milky. It has been known for a long time to contain a supermassive black hole, but they did not have an accurate estimate of how massive. The black hole at the center of our galaxy is only about 3-4 million solar. So that puts it in perspective. The one in M87 is estimated 6.4 billion solar. Basically they observe the rates that stars are orbiting the center, and estimate the total mass, and the mass of the dark matter halo, in several ways, and then they model the whole galaxy in a supercomputer and find out what choice of parameters makes it act the way it does. So they simultaneously estimate the black hole mass, and the mass of ordinary matter like stars, and the mass of the surrounding dark matter halo. The 6.4 is actually a 68 percent confidence interval 6.4 +/- 0.5. There is a technical paper that goes along with this. I will get the link incase anyone wants to look at the details. I looked up the article by Gebhardt and Thomas on arxiv: http://arxiv.org/abs/0906.1492 The Black Hole Mass, Stellar M/L, and Dark Halo in M87 Karl Gebhardt, Jens Thomas 12 pages, accepted for publication in the Astrophysical Journal (Submitted on 8 Jun 2009) "We model the dynamical structure of M87 (NGC4486) using high spatial resolution long-slit observations of stellar light in the central regions, two-dimensional stellar light kinematics out to half of the effective radius, and globular cluster velocities out to 8 effective radii. We simultaneously fit for four parameters, black hole mass, dark halo core radius, dark halo circular velocity, and stellar mass-to-light ratio. We find a black hole mass of 6.4(+-0.5)x10^9 Msun(the uncertainty is 68% confidence marginalized over the other parameters). ..." The radius of a black hole of that mass would be around 12 billion miles. There was a puzzle about quasars that this helps resolve. In the past when people measured the mass of nearby black holes by directly observing stuff orbiting them, Doppler-gauging the speed of the stars, the most they got was figures like 3 billion solar. But quasars are very distant galaxies with supermassive black holes with stuff spiraling in, and from observing quasars it was estimated that the black holes in some quasars must be at least 10 or more billion solar. So there was this discrepancy. How come some quasars get to have such massive BH if all we can find in our neighborhood are much less massive ones like 3 billion tops. I am just speaking in rough approximation but that was the kind of puzzle it was. Now people are relieved to find that it is more consistent after all. We have a few (or at least one) in our neighborhood that we can actually observe and that is getting up there in the quasar range of mass. The supercomputer they used to model the M87 galaxy has about 5800 central processor units running in parallel. Another nice thing is the M87 black hole has been observed to have that kind of nifty polar jets that you always see pictures of, where stuff spiraling in at the equatorial disk gets ionized and accelerated along magnetic field line out along the spin axis. Virgo cluster is only 59 million lightyears from here, which is pretty close as these things go.
  24. Those were results from 2002. Those are not the farthest redshift quasars. Ones with larger redshifts have been found. The matter should still be there, where it always was*. Why would it have moved? The individual motion of galaxies relative background tend to be fairly trivial, can usually be neglected. As time passes matter takes different form and evolves. A cloud becomes a star, a star maybe explode and become a cloud and a neutronstar etc. Presumably quasars too, have a life cycle. So the matter may look different but that which was a quasar when it sent us the light, however it looks now, must still be there. * in the comoving coordinates that cosmologists most commonly use. The comoving distance is what the calculator normally gives. Comoving distance is a handy way to locate things because it doesn't change as U expands. If you know the balloon model it is like the latitude longitude of a spot on the balloon which doesn't change as the balloon expands. If you want to know the actual distance from us at times in the life of some quasar (say with redshift 6.1) then just use the calculator as I suggested. It will tell you how far from Milky the quasar matter was then when it sent the light we see. And it will tell how far it is now (when for all I know it may have burnt out, or look different due to some kind of aging.)
  25. Well we've gotten to a place of just repeating incomprehension so perhaps I'll say farewell. We all have very limited minds, and scientists have been trying to punch a hole in Gen Rel ever since 1915 when it was published. They like to test and if possible falsify theories, because if you catch a theory out then you get to construct an improved one. And so far Gen Rel has passed all the tests with flying colors (6 decimals precision etc etc.) GR is a theory of geometry---it is also the prevailing picture of how gravity works---but first and foremost it says how geometry changes. And cosmology is about the geometry of the U as a whole, and it derives from GR. So the answer to your question is that YES as far as we can tell, and there are a lot of very skeptical professionals whose job it is to doubt and test theories who would love to poke a hole or catch cosmology out. But they haven't yet. whenever someone thinks he has and goes to a reporter at New Scientist and gets interviewed and makes a big fuss, well 6 months later it is usually found faulty or explained, and it goes away. The only challenge I see making steady progress is Loop-style quantum geometry and the associated quantum cosmology derived from it. That is for now. A new approach could appear next year. But for now that is about it, and Loop has a long way to go. So if you are fated not to personally understand the current work going on in cosmology, don't worry. Nobody can be informed about everything there is to know. The people whose job it is are extremely skeptical and scrutinizing and checking all the time. And the answer is yes, you can rely on the standard cosmo model---the things are currently at about the distances the calculator says. The model fits observational data remarkably well.
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