From: Eric Flesch (eric@flesch.org) Message 1 in thread Subject: Quasars understood! Big-Bang gets the boot! Newsgroups: sci.physics, sci.astro Date: 1998/01/10 In his paper 1997 ApJ...480...568S Charles Steidel used the HST to follow up his 1992 observations of QSO 3C336. What he found left him more mystified than ever. The QSO, with z=0.927, has a collection of small foreground galaxies (0.8 What does General Relativity have to say about such a > gravitational mountain? Well, light will be reflected off the sides > of this gravitational rise on the 4-D manifold, opposite to the > effects of a gravitational depression. This reflection off the side > of the shiny volcano will mean that shrunken images of more-distant > galaxies will be seen to be adhering to the slopes of the quasar. > Thus the quasar is seen to be a relatively nearby object, bearing the > shrunken images of optically nearby galaxies on its flanks. This is not true; you have quite misunderstood the nature of light bending in gtr. You appear to refer to the "rubber sheet" analogy, which is quite misleading and which has mislead you. In fact, if you did the math you'd find that even in the rubber sheet analogy, "hills" and "pits" have the exactly the same effect; the variations in intrinsic curvature a hill and an identically shaped (but inverted) pit cause are identical. But more importantly, the rubber sheet model only takes account of one additional dimension in the embedding space; most models in gtr require two. Without two you can have stretching OR compression but not BOTH, and most tidal force fields cause BOTH stretching and compression (in different directions, at any given event). Chris Hillman Followups should go to sci.physics.relativity to reduce bandwidth on sci.physics and sci.astro From: Eric Flesch (eric@flesch.org) Message 3 in thread Subject: Re: Quasars understood! Big-Bang gets the boot! Newsgroups: sci.physics, sci.astro Date: 1998/01/10 On Fri, 9 Jan 1998 16:47:31 -0800, Chris Hillman wrote: >You appear to refer to the "rubber sheet" analogy, which is quite >misleading and which has mislead you. In fact, if you did the math you'd >find that even in the rubber sheet analogy, "hills" and "pits" have the >exactly the same effect; the variations in intrinsic curvature a hill and >an identically shaped (but inverted) pit cause are identical. Yes, but the signs are opposite, which is the whole point. In the rubber sheet analogy (which you first denounce and then endorse?) the photon rolls inwards into a gravitational depression, then emerges with a new trajectory shifted in the direction of the gravitating body. Thus the distant observer sees the light source shifted away from the intervening body. For a gravitational swelling, the photon climbs the swelling then falls away from the gravitational slope, thus the distant observer sees the object as being close to the intervening body. This is immediate, Chris. You have mis-interpreted GR. But it's more dramatic than that. The gravitational column of the quasar, being pushed up by the hypersphere, is a steeper slope than the gentle gradations of gravitational valleys. We will see *two* images of the optically-nearby galaxy, the regular one and a separate copy, shrunken and mirrored on the quasar slope. And the cosmos immediately behind the quasar will be blocked out, replaced by these shiny highlights. Theory must ever be confirmed by observation. Up to now, we've had no confirmation of the behavior of a gravitational column. Now we do. If there is found to be a discrepancy between observation (and I believe GR perfectly describes the situation at hand), then theory must change to accomodate the observations. The shrunken miniature galaxy images on the flanks of the quasars (linkable to larger galaxy images nearby) are clear hallmarks of the quasars' gravitational towers, and the ensuing bending of the background galaxies' light. cheers, Eric Flesch From: Chris Hillman (hillman@math.washington.edu) Message 4 in thread Subject: Re: Quasars understood! Big-Bang gets the boot! Newsgroups: sci.physics Date: 1998/01/10 On Sat, 10 Jan 1998, Eric Flesch wrote: > On Fri, 9 Jan 1998 16:47:31 -0800, Chris Hillman wrote: > >You appear to refer to the "rubber sheet" analogy, which is quite > >misleading and which has misled you. In fact, if you did the math you'd > >find that even in the rubber sheet analogy, "hills" and "pits" have the > >exactly the same effect; the variations in intrinsic curvature a hill and > >an identically shaped (but inverted) pit cause are identical. > > Yes, but the signs are opposite, which is the whole point. Signs of what? My point is that the intrinsic geometry of pits and identical but inverted hills are identical. > In the rubber sheet analogy (which you first denounce and then endorse?) I denounced it as misleading; I did not endorse it. > the photon rolls inwards into a gravitational depression, then emerges > with a new trajectory shifted in the direction of the gravitating body. > Thus the distant observer sees the light source shifted away from the > intervening body. For a gravitational swelling, the photon climbs the > swelling then falls away from the gravitational slope, thus the distant > observer sees the object as being close to the intervening body. This > is immediate, Chris. You have mis-interpreted GR. Not I. In fact, -you- are wrong, on at least three fundamental points. First, in gtr, nothing rolls along a path; rather, the entire kinematical (motion) history of each body is represented by a curve, the "world line" of the body, in spacetime. If the body is falling freely, its world line is a geodesic (timelike, if it is a body with positive mass; null or lightlike if it is a photon). If it is accellerating, the path curvature is proportional to the accelleration, at each point along the world line. Proper time of a clock carried with a positive mass body is simply the length along the world line. This means that, in the Schwarzschild geometry for instance, if you try to compute the way light is bent near the sun, if you take a constant time slice through the spacetime geometry and look at geodesic curves, you will find these bend, but unfortunately they are NOT the "projections" to the constant slice surface of the actual null geodesics in spacetime, which bend more than this naive method would predict. For all of the above, see any textbook on gtr, such as MTW, Gravitation, Freeman, 1970. (130 more lines) From: Eric Flesch (eric@flesch.org) Message 5 in thread Subject: Re: Quasars understood! Big-Bang gets the boot! Newsgroups: sci.physics, sci.physics.relativity, sci.astro Date: 1998/01/11 On Sat, 10 Jan 1998 17:29:57 -0800, Chris Hillman wrote: >Sigh... you are in error, not I. See my reply to your earlier post, in >which I have done the math for you. Yes, it looks impressive, and I'll read through it tonight. Looks like textbook (MTW?) excerpts though. And it treats the rubber sheet aspect only, so it's an incomplete description. See below... > As you can see, I was correct in >stating that "pits" and identically shaped but inverted "hills" are >indistinguishable in terms of their intrinsic geometry. Well of course they are! Just turn the one upside-down to get the other. Obviously the photon moves the same way. But that wasn't the point. The point is that the "rubber sheet" analogy tells only half of the GR story; the other half is the slowing of time, as is dealt with next... > Eric Flesch wrote: >> think of how time >> depends on gravity. If the photon traverses a gravitational well then >> time slows at the midpoint where gravity is at a maximum. In >> contrast, when the photon traverses a gravitational tower, time flows >> fastest at the midpoint where gravity is least. No thanks necessary. > >I have no idea what you are talking about here... "time" does not "flow" >in gtr. But this is the whole point of why the "hills" and "valleys" behave differently. GR (and SR) are ultimately about the flexibility of time. I think I see what the problem here is, and part of it is that we've been at cross purposes. You've thought that I used the rubber sheet analogy to *formulate* my thoughts. Not at all! I interpret GR (and SR) wholly in terms of flexible time. OK, GR models the lengthening of the path entering and leaving the gravitating body, but this is equivalent to Newtonian gravity and is the same for gravitational valleys or hills (which you correctly point out). However, where the photon drops toward a gravitational depression, time slows and so the photon slows. The gravitating body thus has more time to swing the photon's path along, in the gravitating body's direction. When, instead, the photon climbs a gravitational column, time *speeds up*. The photon moves faster and so escapes the column quickly. This is why the behavior is opposite. >> One, two, or n, it makes no difference. > >Perhaps you misunderstood my point. I was saying that if you embedd a >surface in E^3, you can only increase distances beyond what you would >expect in E^2. For instance, in a radially symmetric "pit" (OR "hill"; it >makes no difference), the distance between concentric circles will be >greater than expected in E^2. ... It looks to me like you are thinking of GR in terms of distances only. Until you add the time equations, you'll have only half the picture. The full picture of GR correctly models the galactic highlights on the flanks of the quasar's gravitational tower. Best wishes, Eric Flesch ©2002 Google