Expert: Philip Stahl - 9/16/2009

Question
Hi I have read that stars either die  as black holes or supernova explosion ..

so based on that learning how do scientist predict that big bang is the beginning of the universe  and not a explosion of a star from which other galaxies and stars or other space objects are born...

how can astro-scientist say that looking back in time based that big bang was the only one big bang explosion..?  

Answer
Hello,

Basically, the answer to the first question is a matter of degrees....in temperature! While the exploding cores of massive stars may reach temperatures of billions of Kelvin, the Big bang initial temperatures were in the trillions of K!  Indeed, for a very long time only radiation could exist, no subatomic particles.

Then, there is the mass differential.  No single "star" (or even supermassive black hole, such as at the center of our galaxy) could spawn all the derivative mass, objects that were spawned from the Big bang. (This was after the matter-radiation decoupling, some 300,000 years after the initial event).

Thus, a single star - irrespective of how massive- can't give rise to a cosmos. However, an *earlier* collapsed universe (Big crunch) could. The problem here is that the data do not show or indicate that successive big bangs occur.

That brings us to your second question. The original data supporting a single big bang (which is equivalent to there being a 'flat cosmos') appeared in the Search & Discovery Section of Physics Today in July 2000('Balloon Measurements of the Cosmic Microwave Background Strongly Favor a
Flat Cosmos', p. 17)


You may still be able to get hold of it. Basically here's the deal:

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 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 >   rho_ c

and the mass-energy density is higher than the theoretical critical value, 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.

Data, e.g. from Boomerang and other satellite detectors (see the earlier referenced article)shows that  rho ~ 0.3 or that:

rho = 0.3 (rho_c)

i.e. that  rho <  rho_ c,   so there is no chance of the cosmos decelerating. Hence, only one Big bang. No more.