I recently got an interesting e-mail about the Big Bang. The writer said she didn’t see how you could make something out of nothing. She collects creation myths and thought that, no matter how you sliced it, it’s always “turtles all the way down.” This is a reference to creation myths where the world is poised on top of a turtle, which is itself poised on top of something else, but raises the issue: Is there any firm ground?
This is worth addressing because it illustrates the gulf between the understandings in people’s minds about the Big Bang on one hand, and how physicists deal with it on the other. To be clear – we have a wealth of observations that support the Big Bang, but you have to be careful. We can only look back into the universe to a moment 300,000 years after the ‘start,’ as best we can discern it. At this early moment, the universe went from being opaque to transparent. Before this moment, ionized gas kept light from traveling any distance, but once protons and electrons cooled enough to form neutral hydrogen, light (photons) could travel long distances. The remnant photons from this time are seen as the so-called cosmic microwave radiation. These photons were first observed by Arno Penzias and Robert Wilson in the 1960’s and continues to be a rich source of information about the early universe.
What do we see? We see galaxies moving away from each other. The further away we look, the faster they appear to recede. Einstein’s gravity has a number of solutions for possible universe structures. One of these solutions describes the expanding universe very well, and, if taken at face value, would extrapolate back in time to an initial state when all matter in the universe existed as a single point of infinite density. But, does a point of infinite density make sense? The author of the e-mail question thinks not, that it’s like pulling a rabbit out of the hat. You can’t make something from nothing, and this apparent absurdity invalidates the Big Bang model.
The main issue is that, although our observations are very consistent with this model of a Big Bang universe, we cannot actually see the initial moment. It’s hidden from view. We strongly suspect that the laws of physics might change dramatically when distances scales and energy densities approach the conditions very close to initial moment. We know that when the classical laws of physics are combined with quantum mechanics, new phenomena emerge. This was the case of our theory of electromagnetism. When we incorporated quantum mechanics with electromagnetism, the phenomenon of anti-matter became apparent. We have yet to find a satisfactory theory of gravity that combines quantum mechanics. The manifestations of quantum mechanics in gravity will only emerge at extremely high energy densities, such as those in the very early universe, near the time of this infinite density, and will likely modify our current models. For all we know, space-time might resemble some Escher print, eluding the concept of an infinite density starting point through a twisted configuration that folds in on itself.
Rather than dealing with a concept that seems almost theological in nature, physicists try to reconcile models against data. We fully realize that our models will extrapolate to conditions that raise difficult issues, like infinite densities. More often than not, the difficult conditions are something we avoid talking about, because, largely, we cannot really test or measure these. If it is inaccessible, it is inaccessible. The work can be perhaps more likened to the work of explorers. Our job is to map new territories, and, if anything, we can only report on territories we’ve explored. What lies beyond the horizon is a matter of speculation.
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