Talk:Big Bang/Archive 5

message: I'm taking another guess.  Current version (without links, sorry):
"The details of the distribution of galaxies and quasars both constrain and confirm current theory. The finite age of the universe at earlier times means that galaxy evolution is closely tied to cosmology. The types and distribution of galaxies appear to change markedly over time, evolving by means of the Boltzmann Equation. Observations reveal a time-dependent relationship of the galaxy and quasar distributions, star formation histories, and the type and size of the largest-scale structures in the universe (superclusters). These observations are in statistical agreement with simulations. They are well explained by the Big Bang theory and help constrain model parameters."
My suggestion:
"The details of the distribution of galaxies and quasars both constrain and confirm current theory. The changing conditions in the Big Bang universe mean that galaxy evolution is different at different epochs. (In contrast, the growth and death of organisms in a stable ecology are overall the same in different years.) In fact, the types and the distribution of galaxies appear to change markedly over time, evolving by means of the Boltzmann Equation. Observations reveal a time-dependent relationship among the galaxy and quasar distributions, star formation histories, and the type and size of the largest-scale structures in the universe (superclusters). These observations are in statistical agreement with Big Bang simulations and help constrain model parameters."  —JerryFriedman 16:08, 27 Apr 2005 (UTC)
replies: text: The details of the distribution of galaxies and quasars provides strong evidence for the Big Bang. A combination of observations and theory suggest that the first quasars and galaxies formed about a billion years after the big bang, and larger structures have been forming since then, such as galaxy clusters and superclusters. Galaxy populations have been aging and evolving, so that distant galaxies observed in the early universe appear very different from nearby galaxies. Moreover, galaxies that formed relatively recently apear markedly different from galaxies formed shortly after the big bang. These observations are strong arguments against the steady-state model.  Observations of star formation, galaxy and quasar distributions, and larger structures are helping to complete details of the big bang theory, and are in good agreement with simulations of the formation of structure in the universe. --Joke137 19:12, 27 Apr 2005 (UTC)
replies: text: I understand it and I'm about to add it, with a minor change or two.  —JerryFriedman 16:28, 29 Apr 2005 (UTC)
thread_title:  Confused about galaxy formation 

message: While I'm at it, does anyone understand the time mentioned in this sentence?  "There is no compelling physical model for the first 10-33 seconds of the universe."  What happened at 10-33 seconds?  Is there any chance that's a typo for 10-43 seconds, roughly the Planck time?  —JerryFriedman 16:11, 27 Apr 2005 (UTC)
replies: text: It's the GUT time, which corresponds to an energy scale of around 1014 GeV (actually, the GUT scale is more like 1016 GeV, but who's counting?), roughly the scale of inflation and perhaps baryogenesis, when our understanding of the particle physics gets hazy. You could probably push things back to 10-37 seconds, but I think it would be wrong to choose the Planck time. --Joke137 18:45, 27 Apr 2005 (UTC)
thread_title:  Confused about 10<sup>-33</sup> s. 

message: Why is Vesto Slipher not mentioned in this article?  --Mmcarvalho  18:18, 28 Apr 2005 (UTC)
replies: text: He should be -- in the history section. Why don't you try to work him in? Joshuaschroeder 16:04, 29 Apr 2005 (UTC)
replies: text: Okay, I did instead.  From what I found on the Web, I'm assuming that the statement that Hubble found the recession speeds of "spiral nebulae" in 1913 was simply wrong.  —JerryFriedman 19:27, 4 May 2005 (UTC)
thread_title:  Vesto Slipher 

message: Current version:
"In the 1990s, detailed measurements of the mass density of the universe revealed a value that was 30% that of the critical density. For the universe to be flat, as is indicated by measurements of the cosmic microwave background, this would have meant that fully 70% of the energy density of the universe was left unaccounted for. Measurements of Type Ia supernovae reveal that the universe is undergoing a non-linear acceleration of the Hubble Law expansion of the universe. General relativity requires that this additional 70% be made up by an energy component with large negative pressure."
My suggestion:
In the 1990s, detailed measurements of the mass density of the universe revealed a value that was 30% that of the critical density. Since the universe is flat, as is indicated by measurements of the cosmic microwave background, fully 70% of the energy density of the universe was left unaccounted for. The mystery was parametrized further by independent measurements of Type Ia supernovae which revealed that the universe is undergoing a non-linear acceleration of the Hubble Law expansion of the universe. To explain this acceleration, general relativity requires that much of the universe consist of an energy component with large negative pressure. This "dark energy" is now thought to make up the missing 70%."
—JerryFriedman 18:15, 2 May 2005 (UTC)
replies: text: Not bad. I tweaked it slightly to avoid the "From another quarter" awkward wording. Joshuaschroeder 19:42, 2 May 2005 (UTC)
replies: text: Hm, I can't understand "The mystery was parametrized further".  Since I gather my version didn't introduce any mistakes, I'm going to put it into the article with yet another beginning of that sentence, and you (or anyone) can improve that if necessary.  —JerryFriedman 22:01, 2 May 2005 (UTC)
thread_title:  Slightly confused about dark energy (but who isn't?) 

message: It would be totally cool to have some more, within reason.  Just a thought.  —JerryFriedman 17:05, 4 May 2005 (UTC)
thread_title:  Philosophical and religious references 

message: I moved the "Dark Energy" subsection after "Globular Cluster Age" because it led so nicely into the next section, but now I see that it also followed "Dark Matter" nicely.  So I'll let others decide whether to move it back.
Also, each "standard problem" is bolded (horizon problem, flatness problem, etc.  I don't think this adds anything to most of the subsections—but it would make me smile to see dark matter and dark energy in dark type.  Too frivolous?  —JerryFriedman 19:37, 4 May 2005 (UTC)
thread_title:  Dark matter and energy 

message: I really don't understand the reference to symmetry breaking in the CMB section. The radiation was in equilibrium from the end of baryogenesis to photon decoupling, wasn't it? --Joke137 01:58, 16 May 2005 (UTC)
replies: text: It is in the sense of symmetry breaking being a feature of traveling out of thermal equilibrium... but I can see that it isn't the most standard use of the term. Rewording it is fine. Joshuaschroeder 04:02, 16 May 2005 (UTC)
thread_title:  CMB 

message: The big bang was not an explosion as we are used to think of it. It was not a normal explosion in space, it was an explosion of space. When the universe inflated, new space was created (see image. []. That's the way it was according to general relativity. See also the balloon analogy and dark energy. 
Take note that the big-bang model is based on two assumptions. The first is that Albert Einstein's general theory of relativity correctly describes the gravitational interaction of all matter. The second assumption, called the cosmological principle, states that an observer's view of the universe depends neither on the direction in which he looks nor on his location. This principle applies only to the large-scale properties of the universe, but it does imply that the universe has no edge, so that the big-bang origin occurred not at a particular point in space but rather throughout space at the same time. These two assumptions make it possible to calculate the history of the cosmos after a certain epoch called the Planck time. Scientists have yet to determine what prevailed before Planck time. Joshuaschroeder 16:02, 23 Mar 2005 (UTC)
thread_title:  Correction 

message: I would like to change the name of this section. Does anyone have any ideas?
It's confusing: why are the problems "standard"? I have a suspicion that it refers to the standard problems resolved by cosmic inflation, but that only applies to the first three. –Joke137 15:56, 2 Jun 2005 (UTC)
thread_title:  Standard Problems 

message: Is there some reason we're being so careful not to commit ourselves to the concept of a gravitational singularity?  Does anyone have a reference that indicates that some scientists consider the singularity to be in doubt?  --Doradus 12:48, Jun 9, 2005 (UTC)
Yes. I think most theories of quantum gravity attempt to eliminate the singularity. As it exists in general relativity, the singularity is a bad thing because it is not predictive. In no particular order, a list of attempts to resolve the singularity:
* Loop quantum gravity uses some technology to show that the superspace volume operator is bounded below (so that there is a minimum volume of space that can exist).
*String theory has some other ideas, some of which have to do with making singularities more fuzzy and some of which have to do with "resolving" the singularity by various mathematical tricks. 
*The Hartle-Hawking state try to show that there is a unique, non-singular initial condition for the universe determined by some criteria or other.
*Brane cosmology may resolve the singularity by saying that, while it looks catastrophic in four dimensions, in a higher dimensional theory it is a less singular event, like the collision of two membranes.
*People used to think cosmic inflation resolved the singularity problem, but it turns out that inflation cannot go on eternally to the past, because de Sitter space is unstable.
*People used to believe that the singularity predicted by general relativity was a mere accident due to the high degree of symmetry of the Friedmann-Lemaître-Robertson-Walker universe, and that the universe would actually contract to a very dense state and start expanding again: the oscillatory universe. This idea was disproved by Steven Hawking in 1967, and it was shown that you would need to resort to quantum mechanics or exotic forms of matter to make the universe bounce in that way.
I could dig up references for any of these things, but it is hard to see where to start.–Joke137 18:40, 9 Jun 2005 (UTC)
thread_title:  Singularity or not singularity? 

message: I was looking for information on the origin of the universe and studied the big bang theory for a few years but i kept coming back to what came before the primeval atom? what caused or "created it?" how did it come into exsistence?
:those questions are referenced in the second-to-last question in the article. Joshuaschroeder 12:56, 19 Jun 2005 (UTC)
thread_title:  What About before the primeval atom? 

message: Does anyone have any additional information regarding apparent expansion? It seems plausible, but would require some more details.
:The "apparent expansion" that was included in the article did not belong here and was removed. Joshuaschroeder 13:42, 22 Jun 2005 (UTC)
thread_title:  Apparent Expansion