--------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00117 Date: 04/14/98 From: ARNOLD G. GILL Time: 10:23am \/To: PAUL M. DAVIS (Read 1 times) Subj: A 5th force? [2/2] Hello Paul! On 11 Apr 98, Paul M. Davis wrote to Barton Paul Levenson: BPL>> Sure it can. Depends on what value you give it. Positive BPL>> lambda increases the acceleration of the Universe, negative BPL>> lambda retards it, zero lambda has no effect. I'd recommend BPL>> looking up some books on cosmology to go into the details. PD> Aha! Just what I said. Care to recommend a cosmology book? It depends on your mathematical skills. I would suggest you read some Steven Weinberg, either "The First Three Minutes" (for a layman overview) or "Gravitation and Cosmology: Principles and Applications of the General Theory of Relativity" (tensor heavy). Another suggestion is Jim Peebles' "Principles of Physical Cosmology" - much less math and good observational reasoning of various results and alternatives. Arnold G. Gill - astrophysician at play --- GoldED 2.41 * Origin: Got a sick star? Call the Astrophysician! (FidoNet 1:153/6.5) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00118 Date: 04/14/98 From: ARNOLD G. GILL Time: 10:27am \/To: CURTIS JOHNSON (Read 1 times) Subj: White dwarfs Hello Curtis! On 11 Apr 98, Curtis Johnson wrote to Barton Paul Levenson: CJ>> New stars are also being created. And the greatest number CJ>> of stars are white dwarfs, which have a lifetime greater than CJ>> the age of the universe. BPL>> You were doing okay until you came to this point. According to BPL>> HR diagrams of the 10,000 or so closest stars, about 90% of BPL>> stars are on the main sequence, 9% are white dwarfs and 1% are BPL>> red giants. This doesn't count invisible stars, e.g. neutron BPL>> stars and black holes. CJ> I just flipped through three astronomy textbooks, without CJ> finding any answer. Barton is correct with his statistics. This has a lot to do with the finite age of the universe, the initial mass function, and the main sequence lifetime. By far the vast majority of stars (like 96% or so) on the Main Sequence (MS) are stars less massive than the Sun. However, these stars also have lifetimes on the Main Sequence of 10+ billion years - most have MS lifetimes longer than the age of the universe. Thus, by far the vast majority of stars are stars that have not yet evolved off of the Main Sequence, and so are not even close to becoming white dwarfs yet. In fact, if one can get a complete survey of the population of white dwarfs vs nearby stars, modeling should allow one to come up with an age for the Milky Way, and thus a minimum age for the universe. It will involve a number of parameters (read, assumptions), but it would be doable. Arnold G. Gill - astrophysician at play --- GoldED 2.41 * Origin: Got a sick star? Call the Astrophysician! (FidoNet 1:153/6.5) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00119 Date: 04/14/98 From: ARNOLD G. GILL Time: 11:59am \/To: MIKE ROSS (Read 1 times) Subj: Big Bang Hello MIKE! On 13 Apr 98, MIKE ROSS wrote to Barton Paul Levenson: BPL>> Aren't you assuming that physical compression is equivalent to BPL>> data compression? I don't know that that follows. MR> A neutron star is an example of physical compression. In it the MR> redundant space between the electrons and all the nuclei is MR> eliminated. It becomes a giant neutron when all the electrons are MR> absorbed. When it decays the original varieties of atoms are restored. Two points. One: How does a neutron star "decay"? As far as I know, there is no mechanism for such an occurrence. Two: Even if it could decay, what is restored is _not_ what went in. No memory remains of the infalling matter. It is a similar situation with a black hole. Hawking radiation will, given enough time and appropriate conditions, spew all of the matter that fell into the black hole out again, but it won't be the same matter, and it won't be the same mix of matter. MR> Perhaps the singularity is simply a point where mass/energy becomes MR> separated from the causality environment of spacetime among other MR> effects. The information about our spacetime environment, which is MR> present in the mass/energy before falling in, is removed from it. MR> Absolute information compression! That is _not_ information compression, that is information _loss_!! Ask a programmer about the difference between loss of information/data and compression of that information/data. Arnold G. Gill - astrophysician at play --- GoldED 2.41 * Origin: Got a sick star? Call the Astrophysician! (FidoNet 1:153/6.5) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00120 Date: 04/14/98 From: ARNOLD G. GILL Time: 12:08pm \/To: JONATAN T. ALLIK (Read 1 times) Subj: A 5th force? [1/2] Hello Jonatan! On 06 Apr 98, Jonatan T. Allik wrote to Barton Paul Levenson: JTA>> It's that for sure? So, the big bang point is known? BPL>> Yes, and it's all points. There is no "center." The whole BPL>> Universe was at one point when the Big Bang began. It's an BPL>> expansion _of_ space, not _into_ previously existing space. JA> I read about it. But even with that, a center must exist. I'm sure that many will respond to this, but a center does not have to exist. In particular, an identifiable center in our dimension need not exist, though it may exist in a higher dimension. If, following Stephen Hawking, one looks at the 4-D spacetime, then a center does exist, at the coordinates t = 0. :-) Arnold G. Gill - astrophysician at play --- GoldED 2.41 * Origin: Got a sick star? Call the Astrophysician! (FidoNet 1:153/6.5) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00121 Date: 04/14/98 From: ARNOLD G. GILL Time: 12:14pm \/To: BOB KING (Read 1 times) Subj: light Hello Bob! On 11 Apr 98, Bob King wrote to MIKE ROSS: >> A simple example of when the speed of light clearly >> changes was recently discussed here. For example when light crosses into >> transparent medium such as glass or water, the speed of light changes >> which has effects such as an index of refraction and Cherenkov radiation >> among others. BK> I may well have misunderstood what Arnold and others have said,(I BK> cannot help being a bit thick), but my understanding from what they BK> said was that light entering another medium did not slow down but BK> simply travelled further to get through that medium (whatever it may BK> be). Are you now saying this is wrong? It all depends on the interpretation of it - if you wish, the model used to place a quantum phenomena into the macroscopic universe. There are two main choices of models, depending on whether you view light as a particle or as a wave. As with all quantum objects, you _CANNOT_ do both at the same time. If a particle, then photons always travel at the speed of light. Interactions between photons and atoms in some medium cause collisions, with scattering or absorption. If absorbed, then for some small finite time, the photon does not exist except as an excited state in the atom. Once re-emitted, it continues on its way - again, at the speed of light. If a wave, then one needs to look at the electromagnetic properties of the medium. In effect, the changing EM properties have the effect of changing the local geometry of the spacetime (changes to the stress-energy tensor). Measured in local coordinates, the light wave still travels at the speed of light. However, for a distant observer, the changes in the local curvature of spacetime will give the appearance of a change in direction and/or speed. But that arises because the curvature of the spacetime of the distant observer is different from that where the photon is, or where it has traveled through. The net result, though, is unchanged. The photon travels at the speed of light, using the proper coordinates. Arnold G. Gill - astrophysician at play --- GoldED 2.41 * Origin: Got a sick star? Call the Astrophysician! (FidoNet 1:153/6.5) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00122 Date: 04/14/98 From: ARNOLD G. GILL Time: 12:28pm \/To: MIKE ROSS (Read 1 times) Subj: Are atoms expanding? Hello MIKE! On 13 Apr 98, MIKE ROSS wrote to Barton Paul Levenson: MR> However, don't forget that in the MR> measurements we make locally the ruler itself changes by the same MR> ratio. This is a point that I have always had trouble with when it comes to measuring the effects of gravitational waves (say from a supernova). You have some large massive object, which stretches (distorts) when a gravitational wave passes through. My ruler also distorts by the same amount. Then how can I measure the effects of the gravitational wave? The answer I get back seems to be that after the passage of the wave, the massive object "rings" like a bell, and the amplitude and orientation of the standing wave allows one to infer approximate magnitudes and directions of the gravitational wave. Personally, I'm not sure I understand this idea yet - after all, if all of the rulers are distorted by the same amount, why would it ring? Unless it arises due to differential distortion due to the non-linear shape of the wave? I just don't know. Nevertheless, the experts believe they understand this well, and the designs for gravitational wave satellite systems are on the drawing boards. All they need are detectors with a sensitivity increase of a factor of 10 or 100. Arnold G. Gill - astrophysician at play --- GoldED 2.41 * Origin: Got a sick star? Call the Astrophysician! (FidoNet 1:153/6.5) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00123 Date: 04/14/98 From: MIKE ROSS Time: 07:49am \/To: ALL (Read 1 times) Subj: Sunspots Just had a look at the Sun. Saw a large group of spots in the south. Looks like things are picking up for the next cycle's peak indeed! --- Blue Wave/DOS v2.30 * Origin: Juxtaposition BBS. Lasalle, Quebec, Canada (1:167/133) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00124 Date: 04/12/98 From: TONY DUNLAP Time: 10:05pm \/To: MIKE ROSS (Read 1 times) Subj: Are atoms expanding? ...and thus spake MIKE ROSS unto Bob King: MR> A simple example of when the speed of light clearly changes MR> was recently discussed here. For example when light crosses MR> into a transparent medium such as glass or water, the speed MR> of light changes which has effects such as an index of MR> refraction and Cherenkov radiation among others. But is it actually the speed of light changing or is it the distance the photons must travel through the medium greater? Later Tony Dunlap, (tdunlap@odot.dot.ohio.gov) ...Well, it USUALLY works... --- * Origin: Discover! (1:2220/30.1) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00125 Date: 04/15/98 From: MIKE ROSS Time: 07:48pm \/To: SID LEE (Read 1 times) Subj: Re: Asteroid passing close to Sid Lee said the following to MIKE ROSS on the subject of Re: Asteroid passing close to (14 Apr 98 14:52:18) -=> Quoting MIKE ROSS to Sid Lee <=- SL> All true of course but electromagnetic disturbances are not SL> generally regarded as "radiation" in the nuclear or "atomic" SL> sense. X-Rays are part of the electromagnetic spectrum but since SL> they arise from energetic transitions of electrons rather than SL> the fission or fusion of nucleii they "don't count" either SL> though of course they are dangerous/lethal in sufficient SL> strengths ;-) Oh, you nitpicker you! It's still all just Cajun Chicken in the end. ... Anyone not wearing 2,000,000 sunblock is gonna have a REAL_ BAD_ DAY_ --- Blue Wave/DOS v2.30 * Origin: Juxtaposition BBS. Lasalle, Quebec, Canada (1:167/133) --------------- FIDO MESSAGE AREA==> TOPIC: 180 ASTRONOMY Ref: F5G00126 Date: 04/15/98 From: MIKE ROSS Time: 08:31pm \/To: MARTYN HARRISON (Read 1 times) Subj: Re: Are atoms expanding? Martyn Harrison said the following to Paul M. Davis on the subject of Are atoms expanding? (09 Apr 98 10:35:00) MH> The expansion "force" of the universe between two linked atoms Yes, it is negligible at atomic distances in our lifetimes. MH> However, by comparison the magnetic and atomic MH> bond forces are very large, taking microseconds to restore MH> deviations due to chance or universal expansion or whatever. MH> As such, the atoms will remain at the same distance from one another MH> providing the much larger atomic forces are superior in magnitude to MH> the much smaller forces of universal expansion. The islands of matter in the universe affect their local spacetime by their gravitation. The individual atoms behave according to the local conditions established by the whole clump. The greater the matter density the greater the effects will be. This is what is being observed near black holes where the spacetime is more distorted. The one thing we know for sure of the BB is that the matter density of the universe went from a very high value to what we see today. Even that at some point in the past the energy density may have dominated. So in 12 billion years of evolving is it so unreasonable to see a difference? MH> If the magneto-atomic MH> forces vary with time, this will be very noticeable because being MH> strong forces the dynamics of atomic relationships will vary strongly MH> and the perculiarily fortunate values these constants have to have for MH> life to exist would not have been the case. We'd notice. Or perhaps we wouldn't notice anything out of sorts. I'm starting to think this idea of a special set of physics is a creationist idea. PMD> MR> so sure the meter stick is not connected to the cosmological? PMD>I've been having a similar discussion to this in the SCIENCE echo. My PMD>conclusion about the meter stick not expanding with the cosmological expans PMD>is that, if it were, then we would not observe any expansion in the Univers PMD>ie. there would be no redshift due to Hubble expansion and we would not see PMD>objects /receding/ from us at greater speeds the more distant they are. MH> Er, yes we would. MH> Even if the yardstick varies with time, it can still be used by me to MH> show that these wavelengths are shorter than these other wavelengths. MH> I can put one set beside the other set and discover that red shifting MH> is variable with distance, if I have a good estimate for distance. My MH> estimate for distance might make me find a faulty one due to my dodgy MH> yardstick, in which case I find red shift is proportional to distance MH> cubed or sommat, but vary it certainly does. Maybe the plot would show a slight deviation from that expected by theory. On the first hand it would seem to be difficult to pin down some absolute reference. After all we do have a strong belief and need for absolutes on which to anchor our perception of the universe. The truth is even our perceptions are malleable to the environment but that is a problem for the psychology forum. ... Fifth Rule of Creationism: Lying for the Lord is okay. --- Blue Wave/DOS v2.30 * Origin: Juxtaposition BBS. Lasalle, Quebec, Canada (1:167/133)