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The Big Bang

jorndoe
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Posted 03/08/09 - 03:18 PM: Subject: The Big Bang	#1
This may have been brought up before, in which case I apologize for the repeat. Black holes are fairly well-established, theoretically. I.e. such a monster may come into being, when a star of some specific mass (or larger) collapses "under it's own weight". That is, the localized force of gravity becomes sufficiently high, that escape velocity exceeds that of light (c), essentially meaning that nothing can escape. The Schwarzschild "radius" (or event horizon) of such a gravity well, being defined as the distance where the escape velocity is c. The critical mass of such stars can be calculated using relativity et al, and relativity has been confirmed rather well (at least on larger scales), heck the GPS relies on these theories. To my knowledge there is some (inconclusive) evidence that these exists, but they are thought to exist at the center of galaxies. Alrighty, now my question here, related to the Big Bang. By extrapolating back in time (from the observed universal expansion), entire galaxy clusters must have been much closer in the (distant) past, than they are today. Thus, presumably at some point in the universal past, there must have been a Schwarzschild radius encompassing all (or some) of these galaxy clusters. But does that not mean that massive black holes would exist all over the place? Or perhaps that the entirety of the physical universe would have had a "radius" less than the Schwarzschild radius corresponding to the mass, and thus the known universe is inside a black hole? I don't know enough about such theoreticals as Hawking radiation and the likes, but they theorize that black holes may "evaporate" by emitting radiation (laws of conservation may also play a role here). Would this, then, account for a universe spread out beyond any event horizon that may been prevalent in the earlier universe? I guess my question, in short, is: Why is our universe not (inside) a black hole, given how exceedingly compressed it must have been in the distant past?
People are to themselves what they think; people are to others what they do. ∞ ∑ 1/i² = π²/6 i=1

ManiacJack
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Posted 03/08/09 - 04:11 PM:	#2
I have been pondering this stuff lately, though maybe not too intensively. Anywase, the basic notions of blackholes is that they suck and suck and suck, and eventually the universe will fall in one or be so spread it will fall apart. BS, imo. Now, I'm not a super huge fan of what I am going to suggest here, but I am rather drunk, so I'll say it anywase. What if the big bang were a local occurrence in that this sort of thing happens from time to time... galaxies clump together over large periods of time, of which there is a possible 'breaking point' to ultra-super-massive blackholes in which they explode all their ultra-super-massive amounts of matter across the horizon? That is, why can the universe not have always been and that everything we know about it is cyclic [even blackholes and bigbangs]?
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Kwalish Kid
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1 of 1 people found this post helpful Posted 03/08/09 - 04:22 PM:	#3
Good question. The answer to your final question is, essentially, because space was expanding faster than light. The limits on what speeds an object can reach through amassing kinetic energy do not apply to how fast an object can be carried along by the expansion of space. With the "thinning out" of space, the high temperature of particles kept most of them from clumping together to create large, dense collections that might form black holes. All the particles were bouncing off of each other like pin balls. Even light couldn't travel very far. The resulting pressure kept things from getting to close together. The current theory is that the first regions of density that clumped together were patches of dark matter, since dark matter must have stopped interacting with ordinary matter and photons at some high temperature. The dark matter was free to clump up under gravitational attraction and could also attract other particles through gravity as well. The project of trying to determine the parameters of cosmological theory from the cosmic background radiation is the project of determining just how many clumps formed before the background radiation was released and what kinds and what size of clumps formed.
"Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P Can you pass Religion 101?

wuliheron
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Posted 03/09/09 - 03:54 PM:	#4
Black Holes are extreme even by the standards of cosmology which includes the largest, most violent, and massive events known. They are so extreme that they push the limits of accuracy of the two most accurate theories known, Quantum Mechanics and Relativity. In addition, although the existence of black holes is now considered to be scientific fact, we still don't have a lot of emperical evidence about how they are actually organized and behave. All the known Black holes are shrouded in intense blankets of radiation that make it difficult to see what is going on inside. For cosmology this is all par for the course. As some wit once said, "Each new astronomy headline contradicts the last." It isn't their fault, after all, their field of study is nothing short of life, the universe, and everything that is outside the earth's atmosphere! In recent decades astronomers have finally begun getting the kind of instruments they need to study such extreme events, but without a theory that reconciles QM and Relativity our knowledge of Black Holes may remain largely theoretical for a long time to come.

jorndoe
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Posted 03/11/09 - 02:48 PM:	#5
Thanks for the answers y'all. There are probably vast amounts of calculations involved. Some theoreticals (that I've read) entertain the notion that spacetime itself have a finite "capacity"; that is, only so much stuff+energy+matter can "fit" in so much spacetime. Once this limit is approached, gravity may change from "attracting" (Lorentz) to being "repulsive". And there are various other directions in current theoretical physics. Interesting enough, but far from any kind of consensus on this new research. ManiacJack (#2) wrote: Now, I'm not a super huge fan of what I am going to suggest here, but I am rather drunk, so I'll say it anywase. Yo' party'd out dude! And on a Sunday even.
People are to themselves what they think; people are to others what they do. ∞ ∑ 1/i² = π²/6 i=1

ManiacJack
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Posted 03/11/09 - 03:36 PM:	#6
Hey! It is midterm week. The weekends around midterms and spring break always seem longer. Is 'dark matter' a repulsive gravity, or just a repulsive theory?
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Kwalish Kid
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Posted 03/12/09 - 03:29 AM:	#7
ManiacJack wrote: Hey! It is midterm week. The weekends around midterms and spring break always seem longer. Is 'dark matter' a repulsive gravity, or just a repulsive theory? Dark matter influences spacetime just like ordinary matter, in the sense that it is graviatationally attracted to other matter. Dark energy is a repulsive force, which either exists, or something that mimics it is a part of the underlying equation that governs gravity, or some multiple sets of observations have some weirdly coordinated systematic errors.
"Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P Can you pass Religion 101?

ManiacJack
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Posted 03/12/09 - 07:49 AM:	#8
Has it been supposed that gravity is only partially explained, such that repulsion might be a part of gravity? KK, your post seems to indicate as such. I like: 'gravity is geometry' from Kepler and Einstein among others. But that does not really break down into 'forces' very well. Are our theories simply lacking a holistic view? Well, maybe not 'simply'. Because dark matter is unobserved, correct? And dark energy is the hypothetical force to account for repulsion, correct? Are these two intertwined theories, or is there an important break from one another? Yeah, I got questions...
Space Oil Peaked. Will Smuggle Priceless Astral Goods for Ultimate Price.

Thinking Thing
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Posted 03/12/09 - 12:11 PM:	#9
jorndoe wrote: I guess my question, in short, is: Why is our universe not (inside) a black hole, given how exceedingly compressed it must have been in the distant past? Along lines you've already suggested, the spacetime metric of the big bang is just like that of a black hole, but in reverse. So, to an extent, we were in a kind of black hole, but not any longer.

Kwalish Kid
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Posted 03/12/09 - 12:16 PM:	#10
Repulsion is a part of gravity, at least potentially, because it is possible to include a term in the Einstein Field Equation that can act as a repulsive force depending on its sign (positive or negative). Dark matter and dark energy are intertwined to the extent that all the observations we have that provide a measurement of dark energy also have a measurement of dark matter. However, we also have separate measurements of dark matter. There are hypotheses that dark energy is the produce of a particle, but most of these hypotheses have problems with the available data and none of these hypotheses, as far as I know, propose that dark matter causes dark energy.
"Scientific truth is always paradox, if judged by everyday experience, which catches only the delusive nature of things." - KM, V, P and P Can you pass Religion 101?

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