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State of the Big Bang Theory - part 3

05/19/2007 6:03 PM

My own comments are in [square brackets].

Part 3

In 1998, two groups of astronomers obtained startling new evidence from supernovae seen in far-distant galaxies that the expansion of the universe is accelerating. This resurrected a long discarded term in Einstein's equations that he had put in when he thought the universe was static. It was to keep the matter out in space from collapsing together from its gravitational attraction. When Einstein found out that the universe was expanding, he called it his "greatest blunder" (because without the term, his equations predicted expansion). This additional term was quickly named the cosmological constant. The justification of the cosmological constant is explained as follows: Every newly created cubic centimeter of space has the same energy as all the cubic centimeters that already exist. A universe with a cosmological constant has the ability to create new energy continuously, literally from nothing. [Why does it have to be energy? Why can't it be that each cubic centimeter of ordinary vacuum has a repulsion force to the matter outside of it (force is not energy)? Vacuum has always contained the laws of the universe.]

The value of the cosmological constant is different than Einstein proposed; it is set to match the observations of the recent data. The statements in part 1 about the universe being open or closed only hold true when the cosmological constant is zero. The average density of matter in the universe (ratio of actual density to critical density) is now called Ωm, and the effect of a cosmological constant is called Ωλ. For a flat universe Ωm + Ωλ must equal 1. Inflationary theories say that they do. One theory proposes that during the inflationary era, the universe acquired an enormous cosmological constant, which faded to zero as the universe became 10-30 seconds old.

Astronomers first detected dark matter by observing the motions of stars in galaxies and of galaxies in galaxy clusters by the Doppler effect. Astronomers can attempt to "weigh" a galaxy by measuring the speeds at which stars move in orbit around its center. They now believe that dark matter is about 75% of the total, and that Ωm has a value of 0.2 to 0.4.

Supernovae Type Ia are used as "Standard Candles" to determine the distances to faraway galaxies. They are believed to all have very close to the same peak luminosity. During in the mid 1990s, the High-Z Supernova Search Team and the Supernova Cosmology Project have established better values. Supernova observations give us the measurement that Ωm - Ωλ = -0.4. Observation of redshifts and apparent brightness of Type Ia supernovae reject the possibility of a flat universe with a zero cosmological constant. A flat universe with an average density much less than the critical density is suggested. It is also based on the assumption from Inflation that Ωm + Ωλ = 1. This would mean that we will never have the "Big Crunch."

Supernova data with red-shift more than about 0.2 have to be adjusted for the slowing down of time due to Einstein's special theory of relativity. The rise-time and fall-time of the apparent brightness are greater from the observer's point of view than a supernova with no red-shift. Since supernovae are never seen at the start of their cycle, this is important to calculate their start time and to determine what type of supernovae they are. When this is done, data for distant supernovae appear closer to the mean in a velocity versus distance graph (Hubble diagram).

Astronomers have admittedly incomplete theories about supernova explosions. If closer supernovae luminosity turns out to be 25% more than high redshift ones, the cosmological constant will revert back to zero. Dust in a galaxy causes reddening by absorbing more shorter wavelength light than red light. Dust is hard to estimate in far away galaxies. Interstellar dust is at such low levels it is neglected. This reddening is recognized in the spectral analysis, and can be compensated. Hypothetical "gray" dust could absorb all light colors equally. There has been discussion between cosmologists on this issue.

The cosmic background radiation can tell us the sum of Ωm + Ωλ if low angular measurements (lower than COBE made) are made with sufficient accuracy. Our best measurements [2000] now imply that the sum is between 0.4 and 1.5. Generations of astronomers have employed generations of improved computers to model the universe's evolution of galaxy formation. The best that modelers can say now is that Ωm lies somewhere between 0.1 and 0.5. Counting and modeling large clusters of galaxies like the Virgo cluster in a fixed volume of space over a large time period yields a value for Ωm of about 0.2.

A superb verification of Einstein's General Theory of Relativity is the "Einstein Ring" or arc. A galaxy between us and another galaxy bends the light of the distant one around the in-between one. The result appears as a ring of light. This allows us to calculate Ωλ, [and the mass of the in-between galaxy. See Jorrie's blog on Relativity and Cosmology]. The current results from observations of gravitational lensing show that if the sum of Ωm and Ωλ equals 1, then the value of Ωλ almost certainly lies below 0.75, and likely lies below 0.5. [If we take this value to be 0.4, then the supernova data gives us zero for the mass of the universe, which is clearly nonsense. The point here is that there is too much uncertainty in these measurements to prove the existence of the cosmological constant.]

(Adapted from the runaway universe by Donald Goldsmith, copyright 2000)

[Part 4 will be a summary of recent data. Let's discuss the "gray" dust, which according to Anthony Aguirre could be rapidly rotating, elongated, roughly cylindrical graphite fibers. What about magnetic monopoles?]

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#1

Re: State of the Big Bang Theory - part 3

05/20/2007 11:36 PM

Hi S, again, a nicely done summary, although I have not read The Goldsmith book that you referenced.

I'm a bit sceptical of some of the values he proposed, when read together with the modern papers. I have the feeling that Goldsmith rushed out this book very shortly after the discovery of the accelerated cosmic expansion, when there was a mild "bewilderment" in the cosmology camp! I will comment on this a bit fuller after your next part, on some more recent data...

On your comment: "[Why does it have to be energy? Why can't it be that each cubic centimeter of ordinary vacuum has a repulsion force to the matter outside of it (force is not energy)? Vacuum has always contained the laws of the universe.]"

My view is that it must be energy because it works both ways: it "forces" space to expand more rapidly and at the same time adds to the gravitational pull to balance the "books".[1] When the supernova data sets are read together with the WMAP CMB data (plus some other, less important sets), that's what come out.

On the "gray dust" effect:

I recall that it was almost, but not quite, ruled out by 2001 as a cause for the dimmer-than-expected SNe1A findings by Berkeley Lab scientists: http://www.lbl.gov/Science-Articles/Research-Review/Magazine/2001/Fall/departments/frontline/supernova.html. Quote:

"But SN 1997ff dates from a time before acceleration, so early that the expansion of the universe was still slowing under the influence of gravity. Instead of being dimmer than expected, it is brighter, an effect that rules out both gray dust filters and the inherent dimness of the most ancient supernovae."

I haven't heard much about it lately, so there may be more recent analyses.

-J

[1] I wrote a bit about this in my mini-series on Cosmology: http://cr4.globalspec.com/blogentry/456/Cosmology-Equations-Part-4

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#2
In reply to #1

Re: State of the Big Bang Theory - part 3

05/21/2007 11:08 AM

It's very interesting that the accelerating expansion of the universe happens due to the "quantic fluctuations" of the vacuum (dark energy) which causes a kind of "inside pressure" to the content of the universe... The density of the total "mass+energy" of the universe (which produces the gravity force that slows down the expansion) is reduced while the density of the vacuum (dark) energy (which causes the accelaration of the expansion) remains the same during the expansion of the universe... So, in the long past, the gravity surpassed the repulsion of the vacuum energy and the expansion of the universe was retarding... But there was a time that this two opposite forces became equal and, after that, the vacuum repulsion started to exceed the gravity so the expansion of the universe became accelerating (since today)... What is your opinion???...

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#3
In reply to #2

Re: State of the Big Bang Theory - part 3

05/21/2007 12:17 PM

Hi George, you wrote: "But there was a time that this two opposite forces became equal and, after that, the vacuum repulsion started to exceed the gravity so the expansion of the universe became accelerating (since today)... What is your opinion???... "

Yes, this is basically what the standard Lambda-CDM model says. I have stated it more or less this way in my CR4 Blog posts on cosmology equations. There was a time in the very early post-inflation universe where radiation energy density dominated and caused the highest value of deceleration so far.

-J

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#7
In reply to #2

Re: State of the Big Bang Theory - part 3

05/22/2007 3:52 AM

Ok, so we are given two forces (events regarding vacuum repulsion and gravity at 10-30 or so, and effects of the density of the universe) that have been utilized in thoughts concerning expansion of the universe since the Big Bang. At the time of the Bang, however, some very basic equal and opposite force to the intitial impetus that still pertains must have also been created, and seems to be missing from the equation. Also missing is any mention of resistance to the expansion from either expanding space or the existence of "dark matter" which, if credence is to be given to 'inside pressure' and the extremely minute forces of expansion slowdown due to gravitational forces, might well be an additional frictional component of expansion retardation. Please help out a non-cosmologist on these points.

Mark

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#4
In reply to #1

Re: State of the Big Bang Theory - part 3

05/21/2007 9:59 PM

Hi Jorrie,

Thanks again and for the link. Goldsmith hinted that the gray dust issue might be solved in a year or two. I don't really believe it's the issue, but brought it up for discussion anyway. The link talks about the supernova being brighter than expected, so I think that needs to be explained, and 1 sample is not really enough. It also mentioned that the infrared was missing initially. There is a possibility that it was a different type of supernova, so I think they are a bit hasty to 'put a nail in a coffin'. I didn't see anything in your equations sections about gray dust, or did you mean something else?

S

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#5
In reply to #4

Re: State of the Big Bang Theory - part 3

05/22/2007 12:48 AM

Hi S.

On the distant supernova interpretations: The CMB, supernova and galaxy structure observations have a very compelling overlap area that suggest that all three of them may be essentially reliable, within observational limits of course. However, there are more than one cosmic model that fits the data! My next CR4 Blog post will discuss one such alternative.

"I didn't see anything in your equations sections about gray dust, or did you mean something else?"

Those posts were all about the "balancing of the energy books", so I did not cover the observational issues. Maybe the topic of a future post, or, perhaps we can collaborate?

-J

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#6
In reply to #5

Re: State of the Big Bang Theory - part 3

05/22/2007 3:25 AM

We could say that the evolution of the universe has followed 4 phases:

1) The "birth" which lasted from t=0 to t=10-45sec (this period is being studied by the quantum cosmology... it's under investigation...)

2) The cosmic inflation which lasted from t=10-45 to t=10-33sec (exponential expansion of the universe... during cosmic inflation, its size had increased from 10-28 cm to, almost, 1m...)

3) The decelerating expansion (due to the domination of the gravity)

4) The accelerating expansion (due to the domination of the "dark (vacuum) energy) (I don't remember when this "change" happened... help me...)

[What I mentioned in the previous text (about the evolution of the gravity and dark energy during the expansion e.t.c.) has to do, of course, with the 3rd and 4th phase.]

(Sorry if I made any mistake about the numbers that I mentioned above... It is what I can remember... Make a correction if it's necessary)

I would like to have some more infos about the cosmic inflation (Alan Guth's theory)... Maybe you could make a new topic about this issue... I haven't understand how this happened (I mean what caused the inflation)... It's mentioned as a kind of a "change of the phase" but I can't understand what this means exactly...

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#8
In reply to #6

Re: State of the Big Bang Theory - part 3

05/23/2007 8:41 PM

Hi G.K..

You said: "Sorry if I made any mistake about the numbers that I mentioned above... It is what I can remember... Make a correction if it's necessary"

Guth only said in his book that inflation lasted for maybe 10-30 seconds. In the book Wrinkles in Time by George Smoot and Keay Davidson, inflation started at maybe 10-43 seconds and ended at 10-34 seconds. I don't know where they get these numbers from. I think it might be from the Grand Unified Theories, which I have no knowledge of.

"It's mentioned as a kind of a "change of the phase" but I can't understand what this means exactly..."

A phase transition is a sudden change in the behavior of a material as the temperature is varied. Examples are boiling and freezing of water. According to Guth, GUTs predict that the hot matter of the early universe would have undergone a phase transition at about 10-37 seconds after the BB. The matter would have been supercooled by the expansion.

Regards,

S

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#9
In reply to #5

Re: State of the Big Bang Theory - part 3

05/23/2007 9:19 PM

Hi Jorrie,

Lets talk about the issue you brought up in part 1: "It is today accepted that the universe at large could be "flat", meaning it could have started out infinitely large, with infinite density."

This is the most incomprehensible thing I have ever heard, not to mention that it is in complete disagreement with the BB theory. The whole point of the BB theory is to explain how it grew from a size of a billionth of a proton to its present size. We now have 2-8 atoms per cubic meter. Infinite density would be much more than 1080 grams per cubic centimeter, which is the 'seed' density of inflation, and it would exist for trillions of miles in every direction to infinity! I would have to ask where all that matter went. I forsee that you would say "It expanded outward." I would have to ask "How can an infinite universe expand?" There is nothing to expand into. What would cause an expansion in an infinite universe?

This is the 2nd time I have heard you say this. The 1st time nobody questioned it, but now I must ask you for your references. Who has accepted this? Has it been peer reviewed?

Regards,

S

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#10
In reply to #9

Re: State of the Big Bang Theory - part 3

05/24/2007 3:26 AM

Hi S, you wrote: "This is the most incomprehensible thing I have ever heard, not to mention that it is in complete disagreement with the BB theory. The whole point of the BB theory is to explain how it grew from a size of a billionth of a proton to its present size."

I think the confusion comes from the different meanings of "universe". What you described here, I refer to as the "observable universe". I usually, but not always, use "universe" for the "universe at large".

Now back to the issue, if it is still an issue: if the "universe at large" is spatially flat, then according to standard BB cosmology, it must be infinite in size. Why - because it must be isotropic and cannot have a center. (Not to say that the BB cosmology is correct, though!)

I first read this in Prof. P.J. Peebles' "Principles of Physical Cosmology" (1993). The exact reference I will look up and let you know. Prof. Peebles were however quick to add that, apart form the fact that the universe appears to be spatially flat and theory predicts it to be infinite, we simply don't know if this is true or not. This is why I qualified those statements that you referred to with "may be".

Now comes the most incomprehensible part: if the universe at large is infinite, it must have started out infinite, whatever that may mean. A finite thing cannot become infinite later!

-J

P.S., an infinite thing can expand: 2 times infinity = infinity!

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#11
In reply to #10

Re: State of the Big Bang Theory - part 3

05/24/2007 7:17 AM

Hi S, further to my: "Now comes the most incomprehensible part: if the universe at large is infinite, it must have started out infinite, whatever that may mean. A finite thing cannot become infinite later! "

Don't take this as me advocating an infinite or even a spatially flat universe - I sincerely hope that the "slight statistical bias towards a closed universe" in the WMAP data proves to be correct, thereby avoiding such thorny issues as "infinitely large".

-J

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#13
In reply to #11

Re: State of the Big Bang Theory - part 3

05/24/2007 5:21 PM

Hi Jorrie,

In your E-book in the chapter for Friedman equations you implied that a closed universe has positive curvature. The WMAP paper that I summarized in State of the Big Bang Theory - part 4 has a "table"* with curvature measurements (Ωk). All but one are zero within the uncertainty, but all have a negative sign. This would seem to indicate a bias away from a closed universe - or what am I missing?

* The CR4 editor would not accept a table from MS Word, and would not even let me put in 2 spaces between sections, so I underlined the pieces to show separation.

Regards,

S

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#16
In reply to #13

Re: State of the Big Bang Theory - part 3

05/25/2007 1:52 AM

Hi S, you asked: "...with curvature measurements (Ωk). All but one are zero within the uncertainty, but all have a negative sign. This would seem to indicate a bias away from a closed universe - or what am I missing?"`

I think Ωk is referring to "curvature density" where Ωk = 1 - Ωtot, meaning Ωk is negative for Ωtot > 1 (closed universe, positive curvature). Utterly confusing, but it comes out of this Friedmann equation version:

where Ωk = 1 - Ω, used to balance the expansion "books". Think about it this way: for a given expansion rate and Hubble constant, the more (positive) density there is in the form of mass, radiation and vacuum, the more negative the first term under the root must be.

-J

PS: My eBook is also confusing, following the Peebles definition, that calls it the "curvature parameter" and labels it ΩR = 1 - Ωtot. The common definition of curvature parameter is k, where k = -1 for negative curvature and +1 for positive curvature. "Curvature density parameter" would have been a better choice for ΩR or Ωk.

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#19
In reply to #16

Re: State of the Big Bang Theory - part 3

05/25/2007 5:40 AM

I wrote: "PS: My eBook is also confusing, following the Peebles definition, that calls it the "curvature parameter" and labels it ΩR = 1 - Ωtot. The common definition of curvature parameter is k, where k = -1 for negative curvature and +1 for positive curvature. "Curvature density parameter" would have been a better choice for ΩR or Ωk."

Close inspection has shown that my eBook's paragraph on this (middle of page 185) is very confusing indeed! It reads:

Better wording would have been: The quantity 1 - Ω is sometimes called the "curvature density parameter", i.e., ΩR = 1 - Ω. (See e.g., [Peebles]). When ΩR = 0 there is no curvature (flat geometry); when ΩR < 0 then there is positive curvature (closed geometry) and when ΩR > 0 then there is negative curvature (open geometry). Note that this has the opposite sign to the "curvature parameter" k.

I will post an erratum on my website.

-J

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#12
In reply to #10

Re: State of the Big Bang Theory - part 3

05/24/2007 3:09 PM

Hi Jorrie,

I'm confused or you're confused or both.

"I think the confusion comes from the different meanings of "universe". What you described here, I refer to as the "observable universe". I usually, but not always, use "universe" for the "universe at large"

It makes little difference which one. My original reply was an extreme understatement. It is 6 trillion miles to the nearest star. The observable universe it 13+ billion light years across. I can't conceive of infinite density in all of that, or anywhere for that matter. What about the text by Dr. Peacock, did he say the same thing?

I buy this:

"...if the universe at large is infinite, it must have started out infinite, whatever that may mean. A finite thing cannot become infinite later!"

but not this:

"an infinite thing can expand: 2 times infinity = infinity!"

A math book may say this, but I don't buy it. To me it is as incomprehensible as dividing by zero. Now, you bring up another curiosity:

"...if the "universe at large" is spatially flat, then according to standard BB cosmology, it must be infinite in size. Why - because it must be isotropic and cannot have a center"

The closed universe that has been described is a 4-dimension hypersphere which has a center in the 4th? dimension. Do the flat and open universes have 4 dimensions too, or only 3? This is a little off the subject, but I have wanted to ask it. Einstein said that time is the 4th dimension. Is it the one with a center?

Regards,

S

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#14
In reply to #12

Re: State of the Big Bang Theory - part 3

05/25/2007 12:36 AM

Hi S, you wrote: "The observable universe it 13+ billion light years across. I can't conceive of infinite density in all of that, or anywhere for that matter."

If we apply the Friedmann equation (i.e. before inflation was brought in), our observable universe did indeed start out at infinite energy density. How else if all the mass-energy we can see were located at a single point? This is standard BB cosmology, as you probably know.

Inflation came to the rescue by having a low (unknown AFAIK, because quantum gravity may have ruled) density before the exponential phase and a very high, but not infinite, energy density directly after inflation.

You also wrote that you don't buy this: "an infinite thing can expand: 2 times infinity = infinity!"

Say the universe is infinite (which is still a possibility) - Do you then reckon that the expansion is a fallacy? Consider the "infinite lattice of my last Blog post. What would prevent individual rods to extend if there is nothing that absolutely constrains the ends? (Ends? What ends? It's infinite!!)

You asked: "Do the flat and open universes have 4 dimensions too, or only 3?"

The standard BB always has 4 dimensions: 3 space and 1 time - there is no 4th space dimension in the standard BB. This is a crutch that humans use to visualize curvature of space, but it is purely fictitious. A flat (Ω=1, identically) universe do not need this crutch. Any other value needs it, but its still a crutch!

"Einstein said that time is the 4th dimension. Is it the one with a center?"

Nope. It is tempting to view it like that, but it is false. The spherical cosmic model is a mathematical construct with 4 space and 1 time dimensions. There is a center in the 4th space dimension, but like the dimension itself, it's imaginary (in the literal, not the mathematical sense!).

Hope these ramblings of mine help! -J

PS: I still hope it is closed and not infinite!

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#15
In reply to #14

Re: State of the Big Bang Theory - part 3

05/25/2007 1:41 AM

Jorrie:

Was the BB accompanied by the Big Implosion; and if so, where is the BI now; and what affect might the BI have on the BC (Big Crunch) ?

Is the expansion of observable space hindered, even in the smallest measure, by either 'expansion' (as in extending its area of influence) or 'space' (as in frictional resistance by dark matter) as it is by 'density' or 'gravity'?

Mark

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#17
In reply to #15

Re: State of the Big Bang Theory - part 3

05/25/2007 2:03 AM

Hi Mark, you asked: "Was the BB accompanied by the Big Implosion; and if so, where is the BI now; and what affect might the BI have on the BC (Big Crunch) ?"

What BI are you referring to? I don't think standard cosmology talks about a BI! It is hypothesized that it all started from a quantum fluctuation in the vacuum.

-J

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#18
In reply to #17

Re: State of the Big Bang Theory - part 3

05/25/2007 2:31 AM

Jorrie

Just a little Newtonian notion about reactions. Do cosmologists think/believe that the BB occurred in isolation to physics? A firecracker can 'start' from a small fluctuation on the wick called heat. But there is a dent in the ground (a footstep of reaction) left after its BB.

Regardless of how quantum the fluctuation was, the BB is still quite B . And in space, where can any reaction to a BB hide? What affect might it produce? I only posited the notion that it might be a BI. Hasn't anyone been looking for the BR ?

But seriously, Jorrie, how can the BB have occurred without some R?

Mark

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#20
In reply to #18

Re: State of the Big Bang Theory - part 3

05/25/2007 5:47 AM

Hi Mark, you asked: "... how can the BB have occurred without some R[eaction]?"

I think the "Big R" (the reaction to the action) of the BB is gravity. The positive energy of the expansion (kinetic) is balanced by the negative gravitational (potential) energy, for a total energy of zero!

-J

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#21
In reply to #20

Re: State of the Big Bang Theory - part 3

05/25/2007 12:23 PM

I really like your idea that gravity is the footprint or BR of the BB. That's wonderful creative thought. Is it yours?

A total "balance" energy of zero, though, would seem to beg the question of expansion. Whee-oooo!!

This is a real koan. Perhaps we should all become Buddhists and just accept the whole thing. (Unless the "amount" of gravity increases as expansion "continues" to maintain the zero balance.) Is the entire universe, then, interconnected simultaneously by gravity? Being constant and therefore instantaneous, are gravity interconnections faster than the speed of light?

"What expands and yet does not expand because it has zero energy?" Ooooooohhmmm.

Mark

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#22
In reply to #21

Re: State of the Big Bang Theory - part 3

05/25/2007 2:42 PM

Hi Mark, you asked: "I really like your idea that gravity is the footprint or BR of the BB. That's wonderful creative thought. Is it yours?"

Nope, this is an old idea; someone (can't remember who) wrote something like: "the BB may be the ultimate free lunch". To comprehend this, remember that a cannon ball shot into space at escape velocity also has zero total energy in Newton's mechanics. As it travels away, its positive kinetic energy always equals its negative potential energy, or: ½mv2 + GmM/r = 0, where m is the mass of the cannon ball, M the mass of Earth, v the speed and r the distance from Earth.

A flat, Ω=1 universe works on a similar principle. The amount of gravitational potential energy of the expanding universe equals the kinetic energy of the expansion. The equation that I gave in reply #16 above essentially tells us this. Square both sides and you have (expansion rate)2, which is equivalent to kinetic energy, on the left and energy density (potential energy) on the right. For Ω=1, this can be written as kinetic energy + potential energy = 0.

If this energy book does not balance (doesn't add up to zero), then the nett energy goes into curvature, either positive (closed geometry) or negative (open geometry).

-J

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#23
In reply to #5

Re: State of the Big Bang Theory - part 3

05/28/2007 10:38 PM

Hi Jorrie,

I was reading this article on Space.com http://www.space.com/scienceastronomy/070528_nearby_universe.html about a dwarf galaxy they have named "Andromeda XII" that has moved into the vicinity of the Milky Way. I am very perplexed about some of the things they bring up in the article. I was hoping maybe you could shed some light on it for me.

First of all the Title of the article itself: Dwarf Neighbor Moves in Next to Milky Way.

I was under the impression that all galaxies were always moving away from all other galaxies like, as someone said, painted spots on an expanding balloon. The article says: "The traveling galaxy is the fastest known galaxy in this region and could sweep through the Local Group without so much as a "rub" with the natives, hurling back out into empty space. "

This implies that the galaxy is in an orbit, as they go on to say: "From their observations, they estimated the galaxy's orbit, speed and dark-matter content. They found the galaxy has a highly eccentric orbit and is moving at a swift pace through the Local Group."

How can a galaxy orbit and what is it orbiting around?

I'd appreciate your insights on this.

John

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#24
In reply to #23

Re: State of the Big Bang Theory - part 3

05/29/2007 1:26 AM

Hi John, you asked: "How can a galaxy orbit and what is it orbiting around? "

The cosmic expansion rate is overwhelmed by gravitational binding at short ranges.(1) The galaxies in our local group all orbit their common center of mass, sometimes in very elliptical orbits. This is thought to be part of a fairly chaotic formation process from one or more concentrations of dust/gas. In fact the Andromeda galaxy and our Milky Way are in such a highly elliptical orbit that it appears as if they are coming right at each other!

Our local group (which is a small cluster of galaxies) is also thought to orbit the center of our super-cluster (Virgo). On larger scales, there is no evidence of things orbiting, but there is the peculiar movement of the whole super-cluster towards a presumably huge concentration of mass, called the "Great Attractor".(2)

-J

(1) The cosmic expansion rate at the 2 million ly distance of Andromeda and in the absence of gravitational binding, is around 140 km/s, which is super-fast! However, Andromeda is approaching us at around 300 km/s, so if the expansion worked in gravitationally bound systems, it would be overwhelmed by this peculiar movement.

(2) My eBook chapter, freely available from here: Introduction to Cosmology, has a bit more on this.

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#25
In reply to #24

Erratum on #43

05/29/2007 1:57 AM

I wrote: "(1) The cosmic expansion rate at the 2 million ly distance of Andromeda and in the absence of gravitational binding, is around 140 km/s, which is super-fast! However, Andromeda is approaching us at around 300 km/s, so if the expansion worked in gravitationally bound systems, it would be overwhelmed by this peculiar movement."

I slipped up by 100 km/s: The cosmic expansion rate at 2 million ly is about 40 km/s, not 140!

-J

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#26
In reply to #25

Re: Erratum on #43

05/29/2007 5:19 AM

Some thoughts:

For years I was thinking of the the Universe as an expanded "hypersphere" with a curvature that, gradually, was reduced (the curvature now is so reduced that the Universe seems to be flat)... I tended to suppose that there was a 4th (space) dimension out there where this "hypersphere" exists in... After all, we had to consider the curvature of the Universe in relation with something (a 4th dimension of course... and this 4th has nothing to do with "time"... it's a "space" dimension... ) But noone was talking about such a thing... After a long time, I understood that there is no need of a 4th dimension that "physically" exists out there... Maybe it's convenient to think of a 4th dimension "geometrically" but the curvature doesn't need the actual existence of this "extra" dimension... So, we can think of the Universe as a "hyper-surface": a "hypersphere" (closed Universe), a "hyperplane" (flat Universe) or a "hypersaddle" (open Universe)...

It's easy to imagine a "hypersphere" that is expanded (as Universe does) but not a "hypersaddle" that is expanded... And something else: It's probable that the Universe is "open" (the fact of the accelerating expansion, as discovered lately, shows that, probably, the Universe is "open")... I have a question though: Does this mean that the Universe began its existence in an "hypersaddle" form?????... or its geometry changed during the expansion (starting as an "hypersphere" then changed to "hyperplane" and then to "hypersaddle"?????... It's a little confused thing...

The more disturbing thing is that, in the past, that the expansion was retarding (due to the dominance of the gravity) the Universe seemed to be closed (with a geometry of a "hypersphere") but, later, the expansion became accelerating so the Universe seemed to be open (with the geometry of a "hypersaddle")... Has the Universe changed it's shape or the shape was predeterminated (from it's birth) as a "hypersaddle"?????... Please, help me to clear up things...

Another question: What is the "great attractor"???... Is it a giant cluster of galaxies???... Can we see something there???... or we don't know yet???...

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#27
In reply to #26

Re: Erratum on #43

05/29/2007 8:10 AM

Hi G.K, you asked:

"... Does this mean that the Universe began its existence in an "hypersaddle" form?????... or its geometry changed during the expansion (starting as an "hypersphere" then changed to "hyperplane" and then to "hypersaddle"?????..."

The best indication from the data today is that the universe started out spatially "flat" and remained so until now - it may remains so forever.

There is however this slight statistical bias in the data towards being just closed (Ω ~ 1% above unity). This may mean that it started out closed and will remain so forever.

The accelerated expansion (from dark energy) does not mean the universe becomes open. This misconception came from the "old days" of cosmology, when a universe that would expand forever was considered "open". Not anymore. Dark energy changed all that. Now we can have a closed universe that expand forever!

Closed, open or flat states are defined by Ω and it includes all forms of energy and mass, including the dark ones...

-J

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#28
In reply to #27

Re: Erratum on #43

05/29/2007 9:55 AM

Hi, Jorrie... You say that the universe begun its existence spatially "flat"... Flat means infinite... (you have, already, mentioned above that the universe could be infinite from its start)... I also can't understand this (although I tried )...

What if we could suppose that the universe started its existence as an expanded "hypersphere"???... As it is expanded its curvature is reduced... In the present, its curvature may be so little hence "localy" it looks like almost "flat"... But we could still consider it as a "huge hypersphere"...?????... ( or, maybe, it has another "closed" shape like a "hyper-doughtnut"...???...)

From your previous answer, we could suppose that the universe can be "geometrically closed" although it can be expand forever (i.e. accelerating expansion due to the dark energy)... Hence the "shape" of the universe has nothing to do with its future fate (e.g. endless expansion or contraction and "big crunch")... Am I right?????...

I, also, asked you if the universe could change its "shape" during its expansion... Is there any such possibility???... I mean that the "shape" must be, necessarily, the same during its whole evolution???...

What about the "great attractor"...???... (I would like to have some more infos)...

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#29
In reply to #28

Re: Erratum on #43

05/29/2007 2:39 PM

Hi George, you wrote: "As it is expanded its curvature is reduced... In the present, its curvature may be so little hence "locally" it looks like almost "flat"... But we could still consider it as a "huge hypersphere"...?????"

Yes, that is possible, given that the curvature is positive and not zero!

Take into account that the "shape of the universe" is a slippery concept! One has to consider both curvature and topology to get a reasonable answer to that "shape". So in a sense, you are right when saying: "Hence the "shape" of the universe has nothing to do with its future fate (e.g. endless expansion or contraction and "big crunch" "

Depending of the definition of "shape", the universe can have the same shape forever, but that is not an absolute requirement. Who knows?

About the Great Attractor: hmmm... don't know too much about it! Apparently (according to Wikipedia), it's some 250 million light years from the Milky Way, in the direction of the Hydra and Centaurus constellations. One of the problems in observing it is that the Milky Way's disc obscures it a bit.

-J

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#30
In reply to #29

Re: Erratum on #43

05/29/2007 4:33 PM

Perhaps this GA might be the BR, occurring at the same time as the BB, kind of like the cinder left over!

This is marvellous stuff. I can't believe the information I'm learning. When I win the big one, I'm going to open a new college of marine engineering, and cosmology and theoretical physics will be a definite part of the curriculum! How else are we going to get the Scottys and Jordies, Alcubierres and Ericksons into space and whistling between the planets exploring the universe?

Mark

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#31
In reply to #28

Re: Erratum on #43

05/29/2007 5:01 PM

Hi GK,

You wrote "What about the "great attractor"...???... (I would like to have some more infos)..."

The great attractor is probably a supercluster with Abell 3627 near its center according to info from NASA's Goddard Space Flight Center. Here's a link to the article which also contains a link to an optical image:

http://imagine.gsfc.nasa.gov/docs/ask_astro/answers/990924a2.html

Regards,

John

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#32
In reply to #31

Re: Erratum on #43

05/30/2007 2:44 AM

Thank you Jorrie (and JohnJohn)... You were very helpfull...

(Oh, I love these conversations)

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