The short answer
- Big Bang theory does not say that the universe came from nothing.
- For all anyone can tell, it is possible for something to come from nothing.
The long answer
I. Does Big Bang theory say that the universe came from nothing?
Big Bang theory uses Einstein’s general theory of relativity (just a theory?) to trace the history of the universe back to a moment in time when the entire universe was concentrated in a point of infinite density called a singularity. This account of the history of the universe is simplified because it ignores quantum mechanics. About 13.8 billion years ago, at a point in time called the Planck time, the universe was small enough to experience quantum mechanical effects. To know exactly what these quantum mechanical effects mean for the pre-Planck-time universe would require a theory of quantum gravity—a theory which combines general relativity and quantum mechanics.
There are thus two standpoints from which we can consider the question of whether Big Bang theory says the universe came from nothing: from (a) the simplified standpoint that uses general relativity alone, and from (b) the more complete—but murkier—standpoint that uses quantum gravity.
(a) General relativity alone. One consequence of relativistic physics is that space and time (which relativity unifies as spacetime) are themselves inseparable aspects of the universe. Therefore, if we go by general relativity alone the origin of the universe was the origin of space and time themselves. This would mean there could not have been any time prior to the initial singularity: the very idea of prior to the singularity would make no sense. Hence, the vision of the universe somehow “coming from” a primordial nothingness, far from being a stipulation of Big Bang theory (without quantum mechanics), is inconsistent with it.
For the universe literally to have come from nothing, it would at least have to be the case that at some point in the past there was nothing, and then at some later point in time the universe suddenly existed. However, as we have seen, Big Bang theory without quantum mechanics entails that the universe existed at every moment of time there has ever been. One cannot in one breath talk about the universe existing at the first moment of time, and then, in the next breath, imply that there was a time before this first moment of time in which nothing existed.
Stephen Hawking sums all up all of this nicely when he points out that “to talk about causation or creation implicitly assumes there was a time before the big bang singularity. We have known for twenty-five years that Einstein’s general theory of relativity predicts that time must have had a beginning in a singularity fifteen billion years ago” (Hawking 1993:46).
(b) Quantum gravity. What happens when one takes quantum mechanics into account? Right now it is difficult to say, because there still is no scientific consensus on a theory of quantum gravity. However, according to physicist Lee Smolin, there are only three possible consequences any theory of quantum gravity could have:
[A] There is still a first moment in time, even when quantum mechanics is taken into consideration.
[B] The singularity is eliminated by some quantum mechanical effect. As a result, when we run the clock back, the universe does not reach a state of infinite density. Something else happens when the universe reaches some very high density that allows time to continue indefinitely into the past.
[C] Something new and strange and quantum mechanical happens to time, which is neither possibility A or B. For example, perhaps we reach a state where it is no longer appropriate to think that reality is composed of a series of moments that follow each other in a progression, one after another. In this case, there is perhaps no singularity, but it may also not make sense to ask what happened before the universe was extremely dense. (Reformatted from Smolin 1997:82)
Possibility A gives us the same situation as that described by standard (no quantum mechanics) Big Bang theory: a universe which exists at every instant of time and hence does not come from a prior state of nothingness. Possibility B gives us a universe extending back infinitely in time. Possibility C (of which the quantum cosmological speculations of Hawking 1988 are one example) once again gives us a universe which cannot be described as coming from a prior state of nothingness, since the very notion of time-ordering ceases to have meaning in the early universe.
Apparently, then, under every possible option for a Big Bang supplemented with quantum gravity, it still would be incorrect to describe Big Bang theory as saying that the universe came from nothing. None of the options allows for a moment of time at which the universe did not exist.
II. Can something come from nothing?
Even were we to assume, against physics, that there was some time prior to the origin of the universe when there was nothing except time, it is unclear what problem this supposedly would raise. There certainly is no logical contradiction in imagining there being nothing at one point in time and there being something at a later point in time. It is not as though we are talking about nothingness somehow metamorphosing into an existent something. Although the notion that something cannot come from nothing seems to some people to be a matter of common sense, this notion—like so many of our common sense intuitions—lacks any rigorous logical support.
(a) Do we ever observe something coming from nothing? One argument against the idea of something coming from nothing—and the probable source of our flawed common sense intutions about it—is that we never see this happen. However, if we are referring to empty space when we talk about nothing, then physicists actually do observe things coming from nothing. The quantum mechanical uncertainty principle allows for particle-antiparticle pairs to appear spontaneously out of empty space for very brief periods of time. These so-called virtual particles (or quantum vacuum fluctuations) are ubiquitous, and create measurable effects such as the Casimir-Polder force and the Lamb shift. Some physicists (most famously, Tryon 1973) even appeal to the same kind of mechanism to explain the origin of the entire universe from a background of empty spacetime.
One can, of course respond that virtual particles do not in fact appear out of literally nothing, because they occur in a background of spacetime in which quantum mechanics operates. While true, this response undermines the claim that we know from observation that nothing can come into existence out of nothing, since the closest thing to nothing that we have ever observed is empty spacetime.
One could also assert that perhaps, for all we know, virtual particles are created by God who chooses for unknown reasons to create them in a lawlike fashion but through a process invisible to scientists, so that quantum vacuum fluctuations only appear to be spontaneous. This is possible. It is also possible that bullets never kill anyone: it is possible that every time a bullet appears to kill someone, the killing is actually caused for unknown reasons by a hyperdimensional space spider in a way that is invisible to scientists. The price of taking seriously the possibility of mysterious, invisible causes at the level of a God responsible for virtual particles is agnosticism about all cause and effect claims. It should be easy to understand why such possibilities have no place in rational discussion.
(b) Would something coming from nothing require self-creation? Another argument against the idea of something coming from nothing is that this supposedly would require self-creation, and that self-creation is impossible since nothing can have causal power before it exists. For instance, creationists often assert that to say that the universe came from nothing is to say that it created itself. But this is not the case. The idea of the universe coming from nothing commits one only to the view that at one time there was nothing, and then at a later time the universe existed. Talk of causation, much less self-causation, does not need to enter the picture at all.
(c) Would something coming from nothing violate the principle of sufficient reason? Some philosophers believe in a proposition called the principle of sufficient reason, according to which every event must have a cause. If at one time there was nothing at all, and then at a later time the universe existed, then this would seem to violate the principle of sufficient reason. However, the principle of sufficient reason is dubious as a universal proposition—it is not a truth of logic, no consensus has formed around any philosophical argument for it, and there is no empirical evidence for it at scales where quantum mechanical effects become noticeable.
III. Also worth noting
Vilenkin (1982), in an extension of Tryon (1973), has proposed that quantum mechanics alone could allow for the transition of a universe with no geometry (no points) to a universe with a geometry. I do not know what to make of this proposal because I do not understand how one is supposed to parse the idea of a transition without time; however, I mention it as something for others to be aware of.
Readers are directed to Guth (1997:271-276) for a brief discussion of proposals by Tryon, Vilenkin, and Hawking.
References
Guth AH. 1997. The Inflationary Universe. Reading, MA: Helix Books.
Hawking SW. 1988. A Brief History of Time. Toronto: Bantam.
Hawking SW. 1993. Black Holes and Baby Universes. New York: Bantam.
Leslie J (ed). 1998. Modern Cosmology and Philosophy. Amherst, NY: Prometheus.
Smolin L. 1997. The Life of the Cosmos. Oxford: Oxford University Press.
Tryon EP. 1973. Is the universe a vacuum fluctuation? pp. 222-225 in Leslie 1998.
Vilenkin A. 1982. Creation of universes from nothing. Physics Letters 117B:25-28.