--------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00005 Date: 12/25/97 From: JOAN KELLY Time: 08:25am \/To: ALL (Read 4 times) Subj: Another Astronomy Echo Hello! I found this in ELIST and thought folks might be interested. While now it must be polled directly from the originating board, if enough interest is shown it will qualify for the backbone. Please note that I have nothing whatsoever to do with this echo other than reading this entry in the ELIST. Cheers! * Moved (from: echolist) by Joan Kelly using timEd/386 1.10. In Email dated 23 Dec 97 the Elist entry for the SOLAR_SYSTEM echo was updated, and the following information was recorded: SOLAR_SYSTEM Comets Asteroids Planets and Moons Discussion This conference is for the discussion of the human and robotic exploration of the Solar System and the utilization of any materials found there. Discussion of visual, telescopic and space probe sensing of solar system objects is permitted as well as discussion of colonization and terraforming by human and robotic means. Discussion of Lunar and Mars bases and mining of Solar System resources is encouraged. Discussion of UFO's and speculative alien life forms is off topic and will not be permitted. Origin: 1:116/35 Distribution: By request from 1:116/35 # Nodes: N/A Volume: 25/Week Rules: Flags: Moderators: John Graves, 1:116/35 Last changed: 24 Dec 97 by john.graves@nashville.com The above data will be added to the Echolist file ELIST801.TXT which will be distributed on 01 Jan 98. Keeper, Echolist Robot --- timEd/386 1.10 * Origin: TNC - (860) 963-1187 - 2.4kbps-33.6kbps! (1:320/2112) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00006 Date: 12/25/97 From: ROY MCNEILL Time: 11:22pm \/To: MARK KAYE (Read 4 times) Subj: Skyline for 1997-12-12 On (18 Dec 97) Mark Kaye wrote to Mark Kaye... MK> Nearly all North Americans have a fine view of the star Aldebaran MK> being occulted by the nearly full Moon Friday night, December 12/13. MK> Except, of course, for the thick bank of clouds that seems to be almost MK> everywhere! MK> MK Christmas night here, and the first clear night for almost a month (fluke - forecast is showers). LMC and SMC naked eye after 20 seconds dark adaptation, 47 Tuc after 1 minute. Big dob in the garage screaming "Take me out! Please!" M42 trumpeting "I'm gorgeous!" Horsehead whispering "I'm here! Truly! I'm not fibbing this time!" Fornax galaxies yelling in the far distance "Look at us! Look at us!" Eta Carinae snickering "How big am I tonight?" That 8th mag deep red star right next to Beta Crucis just smoulders away. And me? Too damned tired. --- PPoint 1.88 * Origin: Silicon Heaven (3:712/610.16) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00007 Date: 12/25/97 From: W BOSON Time: 11:27pm \/To: LANCE REYNOLDS (Read 4 times) Subj: Palomar Obs LR> Hyya W! WB> Only been to Palomar once - it was interesting, though. LR> How long ago was that? Its still in operation, isn't it? Seems like > I remember it was the reason the city tried to switch over to those > yellow lights a few years ago. It was a while ago - 7 years, perhaps? I don't know their current status or hours, you ought to call them up if you need to know. -- SPEED 1.40 [NR]: It's more than a reader. It's a message base manager! --- WtrGate+ v0.93.p4 sn 146 * Origin: Midnight Express * San Marcos, CA * 760-598-9650 (1:202/1205) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00008 Date: 12/25/97 From: W BOSON Time: 11:27pm \/To: LANCE REYNOLDS (Read 4 times) Subj: Charged Black Holes LR> Oh dear. Whats the concept of the geometric point of view? The concept is simplest for GR, where one treats space-time as being curved, and the apparent "force" of gravity is really due to the curvature of space-time. Other theories add more dimensions to the picture, and can replace other "forces" with curvature in these other dimensions. It sounds abstract, and it is, but it's a good candidate AFAIK for future unified field theories. WB> (one integrates the component of the electric field passing WB> through a sphere around the black hole to get the value for WB> charge.) LR> Wha....? _Well_ over my head. Sorry. Algebra 101 was as high as I > got in math. Looks like I'm going to need a _lot_ more to understand > whats going on in this conf. Hmmm - guess it was college physics where I first heard about Gauss's law, but it now seems like really basic stuff to me. The concept isn't that difficult, really, but it's hard to explain unless you have the vocabulary. Especially without diagrams. Gauss's law explains my remark about the relation of charge conservation and electric fields leaving a black hole. Basically, we know that charges must have electric fields associated with them, and if a black hole has charge, it must also have an electric field. If we wish to conserve charge, we can't have the black hole swallow charge without becoming charged itself, and since charges must have an electric field, a BH must have an electric field. WB> From the particle point of view, this involves the exchange of WB> virtual photons (I'm not real fond of that view personally, as I WB> mentioned before, however.) LR> I'm not fond of anything that has to have a virtual reality to work. > If the theory needs virtual anything to explain what happens, then the > theory needs help. IMHO, of course. Virtual particles can be useful, but it's a mistake to ascribe all the properties of reality to them. But it also appears to be a mistake to ascribe all the properties of reality to any quantum particle or system. Which makes one wonder about what reality is. Which makes one's head hurt . So the bottom line is, have a happy holiday, and if your head hurts from thinking too much about philosophy, reality, ontology, quantum mechanics, general relativity, cosmlology, astophsics, life, the universe, and everything - have another beer! -- SPEED 1.40 [NR]: Gee officer, I just wondered how fast SPEED READ was. --- WtrGate+ v0.93.p4 sn 146 * Origin: Midnight Express * San Marcos, CA * 760-598-9650 (1:202/1205) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00009 Date: 12/25/97 From: W BOSON Time: 11:27pm \/To: BOB KING (Read 4 times) Subj: Galaxy Missing Mass 1/2 > We are talking about thermal Hawking radiation > here, which is essentially undetectable in most cases. > Black holes will, however, emit copious amounts of > X-ray radiation due to the very hot accretion disk > sitting outside the event horizon. BK> Hang on a minute! > If the Hawking radiation comes only from the accretion disk which is > 'outside' the Bh then it can have nothing to do with the Bh losing ythin You are missing what Andrew was saying here - if you read it again you should see that the accretion disk radiation is NOT hawking radiation. BK> I have read his stuff, probably why I am asking all these questions, a > it went over my head. Well, if you think that's bad - consider the following from the www. Before it gets too deep, parts of it may be of some use to you. (I start to get lost about the point where Bogoliubov transforms are mentioned.) This is from the sci.physics FAQ on hawking radiation, by the way. ========================================= Original by John Baez Hawking Radiation In 1975 Hawking published a shocking result: if one takes quantum theory into account, it seems that black holes are not quite black! Instead, they should glow slightly with "Hawking radiation", consisting of photons, neutrinos, and to a lesser extent all sorts of massive particles. This has never been observed, since the only black holes we have evidence for are those with lots of hot gas falling into them, whose radiation would completely swamp this tiny effect. Indeed, if the mass of a black hole is M solar masses, Hawking predicted it should glow like a blackbody of temperature (6 x 10^{-8}/M) kelvin, so only for very small black holes would this radiation be significant. Still, the effect is theoretically very interesting, and folks working on understanding how quantum theory and gravity fit together have spent a lot of energy trying to understand it and its consequences. The most drastic consequence is that a black hole, left alone and unfed, should radiate away its mass, slowly at first but then faster and faster as it shrinks, finally dying in a blaze of glory like a hydrogen bomb. However, the total lifetime of a black hole of M solar masses works out to be 10^{71} M^3 seconds so don't wait around for a big one to give up the ghost. (People have looked for the death of small ones that could have formed in the big bang, but they haven't seen any.) How does this work? Well, you'll find Hawking radiation explained this way in a lot of "pop-science" treatments: Virtual particle pairs are constantly being created near the horizon of the black hole, as they are everywhere. Normally, they are created as a particle-antiparticle pair and they quickly annihilate each other. But near the horizon of a black hole, it's possible for one to fall in before the annihilation can happen, in which case the other one escapes as Hawking radiation. In fact this argument also does not correspond in any clear way to the actual computation. Or at least I've never seen how the standard computation can be transmuted into one involving virtual particles sneaking over the horizon, and in the last talk I was at on this it was emphasized that nobody has ever worked out a "local" description of Hawking radiation in terms of stuff like this happening at the horizon. I'd gladly be corrected by any experts out there... Note: I wouldn't be surprised if this heuristic picture turned out to be accurate, but I don't see how you get that picture from the usual computation. The usual computation involves Bogoliubov transformations. The idea is that when you quantize (say) the electromagnetic field you take solutions of the classical equations (Maxwell's equations) and write them as a linear combination of positive-frequency and negative-frequency parts. Roughly speaking, one gives you particles and the other gives you antiparticles. More subtly, this splitting is implicit in the very definition of the vacuum of the quantum version of the theory! In other words, if you do the splitting one way, and I do the splitting another way, our notion of which state is the vacuum may disagree! This should not be utterly shocking, just pretty darn shocking. The vacuum, after all, can be thought of as the state of least energy. If we are using really different coordinate systems, we'll have really different notions of time, hence really different notions of energy - since energy is defined in quantum theory to be the operator H such that time evolution is given by exp(-itH). So on the one hand, it's quite conceivable that we'll have different notions of positive and negative frequency solutions in classical field [ Continued In Next Message... ] --- SPEED 1.40 [NR] SPEED READ does everything but think up new taglines! --- WtrGate+ v0.93.p4 sn 146 * Origin: Midnight Express * San Marcos, CA * 760-598-9650 (1:202/1205) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00010 Date: 12/25/97 From: W BOSON Time: 11:27pm \/To: BOB KING (Read 4 times) Subj: Galaxy Missing Mass 2/2 [ ...Continued From Previous Message ] theory -- a solution that's a linear combination of those with time dependence exp(-i omega t) is called positive or negative frequency depending on the sign of omega -- but of course this depends on a choice of time coordinate t. And on the other hand, it's quite conceivable that we'll have different notions of the lowest-energy state. Now when we are in good old flat Minkowski spacetime, a la special relativity, there are a bunch of "inertial frames" differing by Lorentz transformations. These give different time coordinates, but one can check that the difference is never so bad that different coordinates give different notions of positive or negative frequency solutions of Maxwell's equations. Nor will different people using these coordinate systems ever disagree about what's the lowest-energy state. So all inertial observers agree about what's a particle, what's an antiparticle, and what's the vacuum. But in curved spacetime there aren't these "best" coordinate systems, the inertial ones. So even very reasonable different choices of coordinates can give disagreements about particles vs antiparticles, or what's the vacuum. These disagreements don't mean that "everything is relative", because there are nice formulas for how to translate between the descriptions in different coordinate systems. These are Bogoliubov transformations. So if there is a black hole around... on the one hand we can split solutions of Maxwell's equations into positive frequency in the most blitheringly obvious way that someone far from the black hole and far in the future would do it... and on the other hand we can split solutions of Maxwell's equations into positive frequency in the most blitheringly obvious way that someone far from the black hole and far in the past would do it. and we find that if the guy far in the past says there are no particles, i.e., it's just vacuum, the guy far in the future says there ARE particles and antiparticles. That'd be the heuristic explanation I'd give that most closely corresponds to the usual computation. There are additional things to say about the fact that the guy far in the future and far away from the black hole can't see what's in the hole, so he has incomplete information about the state, so he sees a state with entropy, in fact a thermal state. (Here I'm assuming the black hole was NOT eternal, so the guy way back in the past didn't have the black hole to contend with. Apparently Hawking's original computation dealt with this case, but people subsequently watered down his explanation by assuming the black hole was there eternally, to simplify the math. This is what the guy at the talk said... I'd only seen the watered-down version!) Now in fact when you do a Bogoliubov transformation to the vacuum you get a state in which there are pairs of particles and antiparticles, so this is possibly the link between the math and the heuristic explanation. Hopefully whoever made up the usual heuristic explanation understood the link better than I do! References Robert M. Wald, General Relativity, Sections 14.2-14.4, University of Chicago Press, Chicago, 1984. (A good precise introduction to the subject.) Stephen W. Hawking, Particle creation by black holes, Commun. Math. Phys. 43 (1975), 199-220. (The original paper.) --- SPEED 1.40 [NR] SPEED READ does everything but think up new taglines! --- WtrGate+ v0.93.p4 sn 146 * Origin: Midnight Express * San Marcos, CA * 760-598-9650 (1:202/1205) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00011 Date: 12/26/97 From: BARTON PAUL LEVENSON Time: 10:51am \/To: ADAM MAJER (Read 4 times) Subj: Gravitons AM> There's no second question. It's an idea. If gravity was travelling AM> through space time and not on spacetime (2D universe view) then it would AM> never be affected by the curvature of spacetime. According to General Relativity, gravity _is_ the curvature of space-time! --- Maximus 3.01 * Origin: SoundingBoard, Pittsburgh PA (1:129/26) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00012 Date: 12/26/97 From: BARTON PAUL LEVENSON Time: 10:51am \/To: ADAM MAJER (Read 4 times) Subj: Infinity BPL>The Universe may be infinite. BPL>And the expansion at c does not rule out the Universe being infinite. AM> Doesn't it? No. Mathematically, you can have an infinite space expanding at any arbitrarily low speed. --- Maximus 3.01 * Origin: SoundingBoard, Pittsburgh PA (1:129/26) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00013 Date: 12/26/97 From: BARTON PAUL LEVENSON Time: 10:53am \/To: ROY MCNEILL (Read 4 times) Subj: Privileged position RM> I was trying to imply that my statement was so improbable, that RM> some other explanation was required. Is between-the-lines reading RM> no longer a kindy course in USA? I saw nothing in your post to say that you weren't advancing the idea seriously. --- Maximus 3.01 * Origin: SoundingBoard, Pittsburgh PA (1:129/26) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: EGW00014 Date: 12/26/97 From: BARTON PAUL LEVENSON Time: 10:56am \/To: BOB KING (Read 4 times) Subj: Galaxy Missing Mass > [. . .] BK> Thanks for posting that. BK> It appears to me that if the above is true then we are BK> back to accepting the theory (which I like) of a BH BK> being connected to a Quasar by a wormhole, the BH being BK> the entrance and the Quasar being the exit. BK> I thought the scientists had thrown this idea away. They have. Quasars appear to be black holes at the centers of early galaxies, with massive infall due to thick nearby interstellar medium. The gas falling into the black hole in an "accretion ring" gives off the radiation. White holes are not needed and there's nothing to indicate that they are, in fact, present in or near quasars. --- Maximus 3.01 * Origin: SoundingBoard, Pittsburgh PA (1:129/26)