Jesse Mazer <laserma...@gmail.com> Wrote: > > > you made a sweeping statement that "If there are 2 different states of > the universe that could have produced things as they are now then the laws > of physics are not reversible." >
Yes I said that and is one of the most non-controversial things I ever said. > > This would be true if [...] > There is no "if" about it! What I said was a tautology and like all tautologies it has the virtue of always being true. > > "things as they are now" referred exclusively to the MICROstate, but if > it referred to the MACROstate it would be wrong, since classical > statistical mechanics is definitely a reversible theory, > Chaos theory tells us that even in classical physics a change in a micro state can soon lead to a change in the macro state. And if it's a reversible theory then there are NOT 2 different states of the universe that could have produced things as they are now. > >> I am saying that Kip Thorn, one of the world's best physicists, wrote >> on page 446 of his book "A Black Hole's entropy is the logarithm of the >> number of ways that the hole could have been made". >> > > > He didn't say that was a new DEFINITION of entropy though > Who gives a damn if it's a definition or a popsicle? And what's with the all capital letters? It's almost as if you think the word is especially relevant to the question at hand. The fact remains that if Entropy is proportional to the logarithm of the number of microstates something can be in and still have the same macrostate then it's also proportional to the logarithm of the number of ways the thing could have been produced and still have the same macrostate. > > I already linked in my last post to another book by Kip Thorne where he > [...] > In one of your typical posts you provide about 6.02 * 10^23 links, but you never give any indication that you understand one word in them. As a example see below: > > the "entropy of a black hole", which had already been DEFINED to be the > surface area times a specific constant factor based on arguments from black > hole thermodynamics > MEGA-BULLSHIT!!! Bekenstein DERIVED that the entropy of a Black Hole was proportional to it's 2D surface area, to just define it that way without any arguments showing how it was consistent with physics previous use of the word "entropy" would have been imbecilic, and Jacob Bekenstein is not an imbecile. > > If physicists were actually proposing a change in the basic statistical > mechanics definition of entropy as a result of the theoretical study of > black holes then one would expect modern statistical mechanics textbooks > would reflect this re-definition, > WHY?? How would it change anything about how we imagine the world works? Regardless of what English word you call it if X is proportional to the logarithm of the number of microstates something can be in and still have the same macrostate then X is also proportional to the logarithm of the number of ways the thing could have been produced and still have the same macrostate. AND if X is proportional to the logarithm of the number of ways the thing could have been produced and still have the same macrostate then X is also proportional to the logarithm of the number of microstates something can be in and still have the same macrostate. > >> And I'm saying that in classical physics a state can produce only one >> future state, but any given state can have been produced in more than one >> way >> > > > Many models in classical physics are reversible, > Some deterministic laws are reversible and some, like the deterministic laws of the Game of Life, are not reversible. But even if the laws of physics were 100% reversible that wouldn't necessarily mean that a given system was symmetrical with regard to time; even the second law of thermodynamics by itself is not enough to explain the arrow of time. It's true that there are vastly more high entropy states than low ones so it's overwhelmingly likely that tomorrow entropy will be higher than it was today, but by using the very same reversible logic and reversible physical laws we could also conclude that entropy was almost certainly higher yesterday than it was today, but that is clearly not the case. So if time's preferred direction doesn't come from physical law it must come from the initial conditions, and we need to add a past hypothesis, namely that in the distant past for some reason entropy was much lower than it is today. We call that distant past event "The Big Bang". > >> why in hell do you say Entropy is proportional to the logarithm of the >> number of microstates something can be in and still have the same >> macrostate, but it is not proportional to the logarithm of the number of >> ways the thing could have been produced? >> > > > Because it's logically possible to have laws where, unlike in unitary > QM, it's NOT true that two notions are equivalent--this would be true if > information is genuinely lost when a black hole swallows up matter and > later evaporates. > If Physics is not unitary then the old definition of Entropy becomes meaningless with regard to Black Holes because it would contain no microstates you could take a logarithm of, but it would still be true that the Entropy of a Black Hole is proportional to the logarithm of the ways it could have been formed. And for everything else except for a Black Hole the old understanding would still work. Entropy would still be proportional to the logarithm of the number of microstates something can be in and still have the same macrostate, and it would still be proportional to the logarithm of the number of ways the thing could have been produced and still have the same macrostate. And the leader of the small minority of physicists who thought that things were not unitary, Stephen Hawking, now says he was wrong and things are unitary after all. >> As far back as 1963 it was noticed that clocks tick slower on the first >> floor of the physics building at MIT than they do on the second floor, >> Special Relativity had no explanation for this but General Relativity did >> >> > > That is not "in an elevator in free fall in deep space", > If gravity is not involved General Relativity is not needed, Special Relativity works just fine. > >> Yes something under pressure (or tension) does contain more energy than >> something not being compressed and that does bend spacetime, but in >> addition to that there is a additional contribution made by pressure >> itself. >> >> > > I wasn't saying that pressure and tension didn't have to be accounted > for separately from energy density when calculating the spacetime > curvature, I was just saying I thought that pressure and tension could > probably be derived from a sufficiently detailed accounting of the > different types of potential energy at each point in spacetime (whereas I > think the energy density that appears in the equations just lumps together > all forms of potential as well as kinetic into one term). I could be wrong > of course, it's just a hunch. > But that wouldn't explain the fact that something under tension also has more energy than something not being pulled apart and this does indeed mean the increase in mass\energy causes more gravitational attraction BUT there is another component to consider. According to General Relativity another result of this tension is a gravitational REPULSION not attraction. This effect isn't talked about as much as the component made by pressure because we've seen objects under astronomical amounts of pressure such as a Neutron Star, and if you want to understand the geology of a Neutron Star the additional gravitational attraction caused by the pressure becomes important, but up to now we've never seen a object undergoing comparable amounts of tension. Or at least we've never seen something like that before yesterday, after looking at the polarization patterns of the Cosmic Microwave Radiation it now looks like the cosmic inflation theory may be correct, and it hypothesized a substances under enormous tension that produced a huge repulsive effect. > >> Special Relativity says nothing about gravity curving something and >> Einstein never even mentioned spacetime. >> > > > But later when general relativity was developed, it was shown that > general relativity reduces to special relativity in the limit as > mass/energy/pressure/tension go to zero, > As I said Special relativity works just fine if gravity is not involved, > > it remains a useful theory rather than having been made completely > irrelevant by general relativity. > Obviously, and the same could be said of Newton's theory. > >The above quote never actually says that the lasers are being used to > measure spacetime curvature rather than spatial curvature > Please show me a place where 3D space is curved but 4D space-time is not and explain how such a thing could come to be. As Herman Minkowski, Einstein's old mathematics teacher and the man who invented the very concept of spacetime said in the last sentence of his famous paper, the one Einstein at first didn't like and then became its greatest champion: "Henceforth space by itself and time by itself are doomed to fade away into mere shadows and only a kind of union of the two will preserve a independent reality". > > The line OP is the SPATIAL PART OF THE GEODESIC OF THE LIGHT RAY > [emphasis mine] that travels from source to observer." > And my emphasis is that the geodesic of ANY curved space is the path that a ray of light takes. > > Also, if you look at diagrams showing how the angles of a triangle would > differ depending on curvature, you can see many many examples where they > draw the triangles on curved surfaces > They're doing the best they can to get your head around a difficult concept but those are just analogies! Every such example shows a triangle on a curved 2D surface because nobody knows how to imagine curved 3D space or knows how to draw such a thing on a piece of paper, much less knows how to draw curved 4D spacetime. > > Also see the diagram at the bottom of the right-hand column at tp:// > www.lightandmatter.com/html_books/lm/ch27/ch27.html which shows a > triangle on a saddle-shaped surface of negative curvature, > And the reason drawing a triangle with a crayon on a horse's saddle tells you nothing of any profundity about the nature of 4D spacetime even though the triangle does contain less than 180 degrees is because all you've done is drawn it on a curved 2D surface and all you've proven is that surface (the horse's saddle) is not flat. If you drew it with light beams in a volume not a surface and the triangle still had less than 180 degrees then you'd know that higher dimensional things are curved, but nobody knows how to print a illustration of something like that in a book so they resort to lower dimensional analogies. > > the text explicitly says that the three cases are "space is open and > negatively curved like the shape of a saddle", "space is flat like a sheet > of paper", and "space is closed and positively curved like the surface of a > sphere", > And they explicitly say "like" not "is" because it's yet more analogies. And they're right, curved 3D space is "LIKE" a curved sheet of paper, even curved 4D spacetime is "LIKE" it, that is to say it's analogous to it and such analogies are valuable because it's as close as we can get to visualizing such things, but we shouldn't forget it's not really very close and nobody can visualize curved 3D space, much less curved 4D. To work out the details about the consequences of higher dimensional curvature forget about trying to figure out what it would look like and just accept what the mathematics say. > > obviously they think that light paths tell us something about the > curvature of 3D spacelike surfaces in the 4D spacetime, > And obviously the number of degrees a triangle formed by those light paths tells us something about the curvature of 4D spacetime. You're so confused you've forgotten what side you're arguing on. > > http://books.google.com/books?id=fzZMuP2sF9sC&lpg=PP1&pg=PA108 > > "Suppose we construct a surveying apparatus, using lasers and instruments > capable of precisely measuring distances and angles ... There must be three > such stations, creating a huge triangle in space. According to the laws of > Euclidean geometry, we are taught that the sum of the measures of the three > interior angles of any triangle is 180 degrees. But, this hold true only if > the SPACE under consideration, containing the triangle, is Euclidean. ... > Figure 6-21 shows to possible instances where this law of Euclidean > geometry is violated. At A, we have a continuum with spherical or > 'positive' curvature, where the sum of measures of the angles will be more > than 180 degrees. At B, the continuum has 'negative' or saddle-shaped > curvature, and this kind of non-Euclidean space will result in a total > interior angle measure of less than 180 degrees. The drawings in Fig. 6-21 > apply just as well to THREE-SPACE as to two-space" > Correct. And the reason the drawings were of curved two-space rather than curved three-space is because nobody knows how to draw or imagine curved three-space, so we do the best we can and make analogies. > > http://books.google.com/books?id=kgsBbv3-9xwC&lpg=PP1&pg=PA275 > > Describing a universe with positive curvature, the author writes "This > means that the triangle contains three right angles and so has an angular > sum of 270. In principle this could be checked in our universe using a > large enough 'triangle'--perhaps by shining laser beams between space > probes." Then after describing other possible geometries, the author writes > "In summary then, the intrinsic 'geometry' of a universe can be appreciated > by any beings that happen to live inside the universe. One does not need to > have access to any 'higher' dimensions within which the curvature of the > space is clear to see. Simple geometrical experiments (testing the angles > of a suitably large triangle) will show the inhabitants what sort of > universe they live in. Visualizing the curvature of a two-dimensional > universe would be as impossible for the flat ants living in it as > comprehending that our THREE-DIMENSIONAL universe [making clear that he's > talking about curvature of 3D space, not 4D spacetime] has curvature is to > us." > OK fine, no argument, "Simple geometrical experiments (testing the angles of a suitably large triangle) will show the inhabitants what sort of universe they live in". Ah..., do you actually think this passage supports your position and not mine?? If I'd found this quote first it would have been me who was quoting it to you not the other way around. Read it again. Slowly, carefully. > > If you go to http://www.amazon.com/gp/product/0521857147 and click the > cover to "look inside the book", then search for the phrase "initially > parallel laser beams", you find a page where he talks about the current > hypothesis that "the universe is flat, but accelerating" and says that this > means "when averaged over large volumes containing huge numbers of stars > and galaxies, the average curvature is flat IN THREE DIMENSIONS [clearly > indicating he's talking about a flat 3-curvature, not 4-curvature]; > Show me a place in the universe where 3D space is flat but 4D spacetime is not. Or if you don't want to do that just show me one of Einstein's field equations where time is equated to X where X is a quantity that has no spacial component or things like speed, mass, monentum or energy that have no meaning without space. Do either of those things and you've won the argument. > the analogy of a flat plane, a space in which, on average, two initially > parallel laser beams will always remain parallel and, if we could do the > measurement, all very large triangles would always have their interior > angles sum to 180 degrees." > OK fine. Ah..., do you actually think this passage supports your position and not mine?? He even uses the word "analogy". A curved sheet of paper is analogous to curved 4D spacetime, but a curved sheet of paper is NOT curved 4D spacetime. > >>> The curvature of spacetime as a whole is defined by a metric which >>> tells you the proper time along any arbitrary timelike path and the proper >>> distance along any arbitrary spacelike path. >>> >> >> >>That's nice but I didn't ask for a definition, I asked for a >> technique. I repeat, If you don't like light beams and triangles for some >> reason then how do you determine if spacetime is curved or not? Please be >> as clear and specific as I have been. >> > > > You obviously aren't reading very carefully, I already linked to where > to go to find info on the procedure for measuring local spacetime curvature > You've provided wall to wall links and tons of quoted verbiage, but I don't think you understand any of it. Prove me wrong, not with yet another link (I know how to use Google too), but with an explanation in your own words on how you would perform a experiment to determine if your local spacetime is curved. I have given a clear explanation on how I would do it, but you don't like how I did it so I want to know how you would. > >>> Long story short, if you have lasers attached the the wall of an >>> accelerating elevator, this particular setup of lasers might count as a >>> valid way of measuring spatial curvature in *some* coordinate system, but >>> [...] >>> >> >> >>There are no "buts" about it, if one observer says there are not 180 >> degrees in a triangle then all of them do. >> > > > Only if you ignore my point about angles being different for observers > at different velocities that pass through the point in spacetime where two > lines meet. > Different observers might disagree about the distance between 2 events in space or the distance between them in time but they will always agree on the distance between them in spacetime. So different observers might disagree about the size of any of the individual 3 angles of the light triangle, but when the 3 numbers were added up all observers would get the same number > > How would you define the angle at a single EVENT of two lasers meeting? > An event is a point is spacetime, so mount 3 lasers that fire in 2 directions 180 degrees apart at any 3 points, the point in spacetime where the photons from the lasers intersect forms the vertices of the triangle you're measuring. > > could you please also address the question I asked about whether you > understand that an observer could be within the volume of an accelerating > observer yet himself qualify as an inertial observer, > I already did, everybody agrees on how many degrees the triangle has so everybody agrees if the space the triangle is drawn in is curved or not. John K Clark -- You received this message because you are subscribed to the Google Groups "Everything List" group. 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