| MadSci Network: Astronomy |
Let me address your questions and summarize the inflationary big bang theory.
First, the initial singularity is predicted by general relativity; whether or not this represents physical reality is currently unknown. Our present theories only take us back to the Planck time, 10^(-43) seconds after the beginning; before that, a quantum theory of gravity is needed (or at least something that contains both general relativity and quantum mechanics), and we don’t have one. However, assuming that whatever theory does in fact turn out to describe this era is consistent with quantum mechanics, the uncertainties inherent in position and momentum determination prevent anything from ever being localized to a single point; the uncertainties for the early universe are expected to be of the order of the Planck length and time. For more details, see this Ask an Astronomer question.
The temperature is indeed defined in terms of the kinetic energy (this is
true even classically); E = kT, where E is the kinetic
energy, T is the
temperature, and k is Boltzmann
’s constant. In general relativity, this
can also be related to the age of the universe; the temperature at a time
t is proportional to the inverse of the square root of the time.
For more
details, see Lecture 20
in the Elementary Particle Physics lecture series.
As there is no limit on kinetic energy (although there is a limit on speed), there is no limit on temperature. However, at the relevant energies, one needs a relativistic description of kinetic energy.
At around 10^(-37) seconds, the universe enters an inflationary period, in which it expands by about 25 orders of magnitude. This period lasts until about 10^(-34) seconds. It is true that this represents an expansion which exceeds the speed of light, but it is spacetime itself that is expanding, not any material substance. Indeed, the particles created in the pre- inflationary period probably do not survive inflation; for an explanation, see the inflationary epoch.
This inflation is not driven by gravity (or antigravity, as far as that goes), but rather by pressure; the universe gets into a false vacuum state, which causes a large negative pressure (that can be thought of as a large repulsive gravitational force).
What happens to the temperature of the universe after inflation, as well as during the linear expansion that follows, is well described by the theory, and is consistent with recent observations of the remnant blackbody radiation. Ned Wright has put together a brief timeline giving the times and temperatures, along with key events in the expansion.
There is a new theory about the origin of the big bang which may interest you; it is derived from string theory rather than from quantum mechanics, and says that the big bang starts with the collision of two three- dimensional universes along an extra, hidden dimension. It is called the ekpyrotic universe and is extremely speculative at the moment.
The 2002 April issue of Discover magazine has a good, not too technical, article on the big bang theory, including inflation. Here are some more references you may find useful:
[Moderator: For even more details, Peebles' book, Principles of Physical Cosmology offers an excellent, though technical, summary of the observational evidence and theoretical basis for the Big Bang model.]
Try the links in the MadSci Library for more information on Astronomy.