Expert: Philip Stahl - 3/8/2009

Question
I was hoping you could answer these questions as soon as possible.
1. What are your thoughts on the Big Bang theory?
2. If we were to take a peek at the galaxies right now, would they be isolated or merging?
3. How do you think that will effect the end of the universe considering these 4 assumptions:Big Bounce, Big Freeze, Big Rip, or the Big Crunch?

Answer
Hello,

I believe I have given my thoughts on the Big Bang before, but in any case will summarize again:

1) I will accept the Big Bang (perhaps better known as the "expanding universe" theory since no literal "bang" need have occurred) until such time any counter-theory is proposed that can also account for the 2.73K microwave background radiation. Up to now, I have seen none.

2) Your question here is somewhat unclear. Do you mean galaxy clusters isolated or merging, or individual galaxies themselves? In terms of the expanding universe, the focus is on galaxy clusters.

However, the Sloan Digital Sky Survey has produced a map of the distribution of galaxies which you can find here:

http://www.sdss.org/includes/sideimages/sdss_pie2.html

3) The data so far, from Type II supernova data, indicate a "Big Rip" in the far distant future- no big crunch, or bounce. Simply the contents of the cosmos spreading out forever in essentially flat Euclidean 4-space.

Let's examine this in more detail. Geometries of the cosmos are predicated mainly on Friedmann-Robertson- Walker or F-R-W based cosmologies (which you can also google).

Using a particular F-R-W template, one can have:

k = +1 (positive curvature - spherical geometry)

k = -1 (negative curvature - hyperbolic or horse saddle type geometry)

k = 0 (flat or Euclidean universe)

Universes that re-collapse (decelerate), expand forever with zero limiting velocity (e.g. v uniform) or expand forever with positive limiting velocity (accelerate) are called in turn: 'closed' (can have curvature k = +1); 'critical' (k=0)or 'open' (can be k = -1), respectively

Now, to determine whether any F-R-W cosmological template leads to deceleration or not, we need to find the cosmic density parameter:

Omega = rho / rho_c

where the denominator refers to the critical density. Thus if:

rho (greater than) rho_c

(c = critical)

then the cosmic density is able to reverse the expansion (e.g. decelerate it) and conceivably usher in a new cycle. (New Big bang etc.) The observations that help determine how large rho is, come mainly from observing galaxy clusters in different directions in space and obtaining a density estimate from them.

Current data, e.g. from Boomerang and other satellite detectors shows that  Omega ~ 0.3 or that:


rho = 0.3 (rho_C)

I.e. that  rho <  rho_c so there is no danger of the cosmos decelerating.

Precision measurements of the cosmic microwave background (CMB), including data from the Wilkinson Microwave Anisotropy Probe (WMAP), have recently provided further evidence for dark energy. The same is true of data from two extensive projects charting the large-scale distribution of galaxies - the Two-Degree Field (2DF) and Sloan Digital Sky Survey (SDSS).

Adding to this, Dark energy has been further corroborated from plots of Type Ia Supernovae data. (See, e.g. 'Supernovae, Dark Energy and the Accelerating Universe', by Saul Perlmutter, in Physics Today, April, 2003, p. 53.) This leads directly to the inference of an equation of state:

w = (Pressure/ energy density) = -1

And here is where dark energy enters – not by choice- but by the data and observations being forced on us to accept it!

This is consistent with Einstein's general theory of relativity - which one could say approaches the status of a 'basic law of physics'. In this case, the existence of a negative pressure is consistent with general relativity's allowance for a "repulsive gravity" - since any negative pressure has associated with it gravity that repels rather than attracts.

Specifically the term (rho + 3 p) acts as a source of gravity in general relativity, (where rho = energy density).

If we set: 0 = (rho + 3p) then:

p = - rho /3

and if: p < (-  rho /3) we have gravity that repels

Looking back to the earlier equation for w, one finds:

p = - rho   (e.g. pressure = - energy density)

and -  < (- p /3)

Ancillary with this is the plot of Type 1a supernovae (as used in the supernova Cosmology Project) according to:


Corrected Apparent magnitude
^
!
!
!  
!
!
!
_14
!------------------!---Redshift Z
0……………………….1.0

where you may visualize four distinct plots all originating near the 14 notch on the vertical scale and extending toward the upper right – diverging in a mild ‘spread’ on reaching redshift z= 1.0

The curves from other data with corrected apparent magnitude v. redshift (z) give different combinations of  Omega_dark to Omega_matter over the range. However, only one of the graph combinations bests fits the data:

OMEGA_dark = 0.65 and  OMEGA_matter = 0.35

Corresponding to an expansion accelerating for the last 6 million years- with much more dark energy involved (0.65) than ordinary matter.

When the predictions of the different theoretical models are combined with the best measurements of the cosmic microwave background, galaxy clustering and supernova distances, we find that 0.62 < OMEGA_dark < 0.76, where OMEGA_dark = rho_dark/ rho_critical, and -1.3 < w < -0.9

In tandem, the numbers show unequivocally that dark energy is the acceleration agent, and in addition – dark energy comprises the lion’s share of what constitutes the cosmos.


In addition, all of this data is firmly backed up by earlier Boomerang (balloon) data that – when plotted on a power spectrum- discloses two adjacent ‘humps’ one a bit higher than the other. The “first acoustic peak” and the “second acoustic peak” fit uncannily to the sort of spherical harmonic function that describes a particular plasma condition. In this case, one that conforms to the supernova-derived values of OMEGA (d, m).

So, the 1st and 2nd acoustic peaks (defined for a cosmological plasma) in tandem with the Type II supernova data, pretty well show indefinite and accelerated expansion leading ultimately to the "big Rip".