According to one version of the Big Bang theory of cosmology, in the beginning the universe had infinite density. Such a description seems to be at odds with everything else in physics, and especially quantum mechanics and its uncertainty principle. It is not surprising, therefore, that quantum mechanics has given rise to an alternative version of the Big Bang theory.

According to some quantum loop gravity theorists, the Big Bang was merely the beginning of a period of expansion that followed a period of contraction. In this view, one could talk of a Big Crunch followed by a Big Bang, or more simply, a Big Bounce.

The main idea behind the quantum theory of a Big Bounce is that, as density approaches infinity, so the behavior of the quantum foam changes.

Perhaps all the so-called fundamental physical constants, including the speed of light in a vaccuum, were not so constant during the Big Crunch, especially in the interval stretching 10**-43 seconds before and after the point of inflection. (One unit of Planck time is about 10**-43 seconds.)

If the fundamental physical constants were determined in a quantum-mechanical manner during the Big Crunch, then their apparently inexplicable values in this universe would not be so surprising, it being understood here that a universe is that which exists between a Big Bang and its Big Crunch. The problem of failed universes (those that fail to produce carbon-based life forms) is also resolved.

Table of contents
1 Objections
2 See also
3 Reference


One of the main objections to the Big Bounce view is the evidence that has been accumulating that our universe is destined for a Big Freeze rather than a Big Crunch (see Accelerating universe). However, this evidence does not exclude the possibility that our Big Bang was preceded by the very last Big Crunch, at least the very last one in our vicinity.

Furthermore, it remains a possibility that a better understanding of quantum foam may result in a re-interpretation of the evidence regarding the fate of our universe.

See also

Anthropic principle
John Wheeler


Joao Magueijo. Faster than the Speed of Light: the Story of a Scientific Speculation. Perseus Publishing, 2003.