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FW: Simple Question
[[Mod. note -- ... [snip] ...
If the universe is not expanding (point 2), then the CMBR temperature should have been the same in the past. -- jt]] In article , Richard S. Sternberg writes: I hope I won't lose in accuracy what I gain in easy comprehension for lay consumption, but isn't this more easily stated as Ober's Paradox, also called the Bright Sky Paradox: [[Mod. note -- It's _Olber_'s Paradox. Olbers', please. Or I suppose Olbers's if you are a hypermodernist. [[Mod. note -- ((cringing)) Oops, mea culpa! -- jt]] However, I don't see Olbers' paradox being the same as the Moderator's initial point. Seeing the CMBR temperature higher in the past says the Universe is evolving, but it isn't the same observation as noting the night sky is dark. We can imagine a dark night sky in an unevolving Universe (one finite either in age or in space) or a bright night sky in an evolving Universe (one densely packed with stars). As it happens, the explanations for the two observations are closely related. We appear to live in a Universe of finite age (explaining the dark night sky) that is expanding (explaining the hotter microwave background in the past). -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
#2
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FW: Simple Question
[[Mod. note -- ... [snip] ...
If the universe is not expanding (point 2), then the CMBR temperature should have been the same in the past. -- jt]] In article , Richard S. Sternberg writes: I hope I won't lose in accuracy what I gain in easy comprehension for lay consumption, but isn't this more easily stated as Ober's Paradox, also called the Bright Sky Paradox: [[Mod. note -- It's _Olber_'s Paradox. Olbers', please. Or I suppose Olbers's if you are a hypermodernist. [[Mod. note -- ((cringing)) Oops, mea culpa! -- jt]] However, I don't see Olbers' paradox being the same as the Moderator's initial point. Seeing the CMBR temperature higher in the past says the Universe is evolving, but it isn't the same observation as noting the night sky is dark. We can imagine a dark night sky in an unevolving Universe (one finite either in age or in space) or a bright night sky in an evolving Universe (one densely packed with stars). As it happens, the explanations for the two observations are closely related. We appear to live in a Universe of finite age (explaining the dark night sky) that is expanding (explaining the hotter microwave background in the past). -- Steve Willner Phone 617-495-7123 Cambridge, MA 02138 USA (Please email your reply if you want to be sure I see it; include a valid Reply-To address to receive an acknowledgement. Commercial email may be sent to your ISP.) |
#3
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FW: Simple Question
Richard S. Sternberg wrote:
If the Universe is infinite and uniform (Condition #1) and not expanding (Condition #2, which is somewhat duplicative of Condition #1), then the sky should be infinitely bright at night. No matter how small of a percentage of the sky is generating the light, if it has been generating that light for an infinite time from infinite points in space, then the resulting light must be infinite. Since the sky is dark at night, the Universe cannot be infinite and uniform unless the proponent offers a different solution to the Paradox. OTOH, if an infinite non-expanding universe had a roughly uniform finite energy density at one point in time, it would be rather surprising if it came to have an infinite energy density at some future time. Therefore Olbers Paradox tells us next to nothing about the real universe except that somewhere in it someone did the sums wrong. :-) If such a universe existed over vast eons of time then clearly there would need to be a balance between dust and other absorption and stellar processes emissions and a means to recycle energy between these. The fact that we don't know about any physics for such processes might have more to do with the fact that they are inherently less likely to be observed (and therefore lead to them becoming known physics) than with them not existing. Ray Tomes |
#4
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FW: Simple Question
Richard S. Sternberg wrote:
If the Universe is infinite and uniform (Condition #1) and not expanding (Condition #2, which is somewhat duplicative of Condition #1), then the sky should be infinitely bright at night. No matter how small of a percentage of the sky is generating the light, if it has been generating that light for an infinite time from infinite points in space, then the resulting light must be infinite. Since the sky is dark at night, the Universe cannot be infinite and uniform unless the proponent offers a different solution to the Paradox. OTOH, if an infinite non-expanding universe had a roughly uniform finite energy density at one point in time, it would be rather surprising if it came to have an infinite energy density at some future time. Therefore Olbers Paradox tells us next to nothing about the real universe except that somewhere in it someone did the sums wrong. :-) If such a universe existed over vast eons of time then clearly there would need to be a balance between dust and other absorption and stellar processes emissions and a means to recycle energy between these. The fact that we don't know about any physics for such processes might have more to do with the fact that they are inherently less likely to be observed (and therefore lead to them becoming known physics) than with them not existing. Ray Tomes |
#5
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FW: Simple Question
In message , Ray Tomes
writes Richard S. Sternberg wrote: If the Universe is infinite and uniform (Condition #1) and not expanding (Condition #2, which is somewhat duplicative of Condition #1), then the sky should be infinitely bright at night. No matter how small of a percentage of the sky is generating the light, if it has been generating that light for an infinite time from infinite points in space, then the resulting light must be infinite. Since the sky is dark at night, the Universe cannot be infinite and uniform unless the proponent offers a different solution to the Paradox. OTOH, if an infinite non-expanding universe had a roughly uniform finite energy density at one point in time, it would be rather surprising if it came to have an infinite energy density at some future time. Therefore Olbers Paradox tells us next to nothing about the real universe except that somewhere in it someone did the sums wrong. :-) Talking about infinities is a sure way to lead to mistakes, and I'm probably going to make one, but why should the light be infinite? Won't it be the same as the surface of a star over the whole sky? BTW, Charlier's cosmology apparently leads to an infinite static universe which does not suffer Olber's paradox. -- "Roads in space for rockets to travel....four-dimensional roads, curving with relativity" Mail to jsilverlight AT merseia.fsnet.co.uk is welcome. Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk |
#6
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FW: Simple Question
In message , Ray Tomes
writes Richard S. Sternberg wrote: If the Universe is infinite and uniform (Condition #1) and not expanding (Condition #2, which is somewhat duplicative of Condition #1), then the sky should be infinitely bright at night. No matter how small of a percentage of the sky is generating the light, if it has been generating that light for an infinite time from infinite points in space, then the resulting light must be infinite. Since the sky is dark at night, the Universe cannot be infinite and uniform unless the proponent offers a different solution to the Paradox. OTOH, if an infinite non-expanding universe had a roughly uniform finite energy density at one point in time, it would be rather surprising if it came to have an infinite energy density at some future time. Therefore Olbers Paradox tells us next to nothing about the real universe except that somewhere in it someone did the sums wrong. :-) Talking about infinities is a sure way to lead to mistakes, and I'm probably going to make one, but why should the light be infinite? Won't it be the same as the surface of a star over the whole sky? BTW, Charlier's cosmology apparently leads to an infinite static universe which does not suffer Olber's paradox. -- "Roads in space for rockets to travel....four-dimensional roads, curving with relativity" Mail to jsilverlight AT merseia.fsnet.co.uk is welcome. Or visit Jonathan's Space Site http://www.merseia.fsnet.co.uk |
#7
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FW: Simple Question
In article , Jonathan
Silverlight writes: Talking about infinities is a sure way to lead to mistakes, and I'm probably going to make one, but why should the light be infinite? Won't it be the same as the surface of a star over the whole sky? BTW, Charlier's cosmology apparently leads to an infinite static universe which does not suffer Olber's paradox. I REALLY recommend the corresponding chapter in Edward Harrison's COSMOLOGY textbook to all interested in Olbers's paradox. @BOOK {EHarrison81a, AUTHOR = "E. R. Harrison", TITLE = "Cosmology, the science of the universe", PUBLISHER = "Cambridge University Press", YEAR = "1981", ADDRESS = "Cambridge" } |
#8
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FW: Simple Question
In article , Jonathan
Silverlight writes: Talking about infinities is a sure way to lead to mistakes, and I'm probably going to make one, but why should the light be infinite? Won't it be the same as the surface of a star over the whole sky? BTW, Charlier's cosmology apparently leads to an infinite static universe which does not suffer Olber's paradox. I REALLY recommend the corresponding chapter in Edward Harrison's COSMOLOGY textbook to all interested in Olbers's paradox. @BOOK {EHarrison81a, AUTHOR = "E. R. Harrison", TITLE = "Cosmology, the science of the universe", PUBLISHER = "Cambridge University Press", YEAR = "1981", ADDRESS = "Cambridge" } |
#9
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FW: Simple Question
In article , "Richard S.
Sternberg" writes: BTW, Charlier's cosmology apparently leads to an infinite static universe which does not suffer Olber's paradox. I haven't heard of that, and I'm quite interested. Could you either provide a brief synopsis of Charlier's cosmology or provide a current hyperlink. Thx. Basically, this is a hierarchical model. Galaxies are grouped into supergalaxies which in turn are grouped into hypergalaxies etc. This occurs in such a way that the average density decreases the larger the volume. It's not viable as a realistic cosmological model, but is an interesting test case for testing assumptions etc, the exception that proves the rule. I believe Harrison discusses it in the book I mentioned previously in this thread. (Note: The word "prove" in this old adage means "test", as in the German "pruefen" (to test) "Pruefung" (test, examination) etc and in the English "proving ground" (e.g. for testing rockets). I never cease to be amazed to what extent this is mis-interpreted; some people really think that exceptions PROVE rules in the more usual sense of the term. There isn't a German adage "Die Ausnahme prueft die Regel", but there IS "Die Ausnahme bestaetigt die Regel", which is obviously a translation of the mis-interpretation of the English adage. [Mod. note: accented characters, mangled in transmission, turned into 7-bit ASCII digraphs. In general, please try to post in plain ASCII -- Usenet and e-mail are often not 8-bit clean.] [Mod. note #2: An alternative, and in my view correct, point of view about this expression is that it means that the fact that an exception is documented proves *that the rule exists*; for example, in legal contexts. The German version of the expression seems consistent with this. See also http://alt-usage-english.org/excerpts/fxtheexc.html. But we wander away from astrophysics -- mjh] |
#10
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FW: Simple Question
In article , "Richard S.
Sternberg" writes: BTW, Charlier's cosmology apparently leads to an infinite static universe which does not suffer Olber's paradox. I haven't heard of that, and I'm quite interested. Could you either provide a brief synopsis of Charlier's cosmology or provide a current hyperlink. Thx. Basically, this is a hierarchical model. Galaxies are grouped into supergalaxies which in turn are grouped into hypergalaxies etc. This occurs in such a way that the average density decreases the larger the volume. It's not viable as a realistic cosmological model, but is an interesting test case for testing assumptions etc, the exception that proves the rule. I believe Harrison discusses it in the book I mentioned previously in this thread. (Note: The word "prove" in this old adage means "test", as in the German "pruefen" (to test) "Pruefung" (test, examination) etc and in the English "proving ground" (e.g. for testing rockets). I never cease to be amazed to what extent this is mis-interpreted; some people really think that exceptions PROVE rules in the more usual sense of the term. There isn't a German adage "Die Ausnahme prueft die Regel", but there IS "Die Ausnahme bestaetigt die Regel", which is obviously a translation of the mis-interpretation of the English adage. [Mod. note: accented characters, mangled in transmission, turned into 7-bit ASCII digraphs. In general, please try to post in plain ASCII -- Usenet and e-mail are often not 8-bit clean.] [Mod. note #2: An alternative, and in my view correct, point of view about this expression is that it means that the fact that an exception is documented proves *that the rule exists*; for example, in legal contexts. The German version of the expression seems consistent with this. See also http://alt-usage-english.org/excerpts/fxtheexc.html. But we wander away from astrophysics -- mjh] |
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