Ralph M. Deal of Kalamazoo, MI, asks:

I'm a physical chemist, quite naive on astronomic topics, who found your statement that "the Big Bang really is not an explosion in the normal sense....The Big Bang created time and space itself" fascinating and quite mysterious. Does it make sense to talk about the duration or size of "the Big Bang" at all? If not, why not? If this is just an extrapolation of motions and distances to a single point in "time" and "space", do we know anything about the bag bang at all otherwise? It is quite strange for me to think about an origin of time. Do you have some references you can suggest for me to clarify my confusion? Thanks.

Dr. David Helfand of Columbia University responds:

It is, indeed, strange to think of what the "origin of time" means, because the first question one asks is "when" did it occur; of course, if there is no time, there is no "when" (just as if there is no space, there is no "where" for it to happen).

All we can observe today is a fossil record of what the earliest moments of the universe were like, and we attempt to construct a model for the Big Bang based on that record. For example, we see that at a wavelength of radiation a million times longer than our eyes can detect, the sky is ablaze in all directions. This light is the afterglow of the Big Bang itself, and has been coming toward us (indeed, filling all of space) since only 300,000 years after the Big Bang when the Universe had cooled to a temperature of about 3000 degrees so that atoms could form. This is the most distant point to which we can, even in principle, "see" directly. But the slight ripples in the intensity of this radiation bear the imprint of events that went before.

Furthermore, the amount of helium in the oldest stars gives us a glimpse of conditions in the first three minutes of the universe's life, since it is then that this helium was synthesized. And, in turn, the number of neutrons available during this period provides a clue to what happened even earlier (in the period from 1 million to one tenth thousandth of a second). So, as you can see, we can run this model back very close to the beginning using the physics we have verified in the laboratory. However, we do reach a limit at the absurdly small value of .000000000000000000000000000000000000000000001 seconds after the beginning. Here, space and time are scrambled in such a way that there is no backwards or forwards, here or there. And until we have a theory which unites our currently disparate concepts of gravity and the behavior of matter at the smallest scale (quantum mechanics), we are stuck at that point.

By far the best book I know of on these subjects is E.R. Harrison's "Cosmology: The Science of the Universe" which was published by Cambridge University Press. Unfortunately, it is out of print now, but might stilll be available from some bookstores or the publisher.