Wednesday, November 19, 2008

Lawrence Krauss on why there's something rather than nothing

In 1973, Ed Tryon proposed that the total energy of our universe might be zero, and that our universe might be a fluctuation of the quantum vacuum. This idea was adopted within inflationary cosmology by luminaries such as Alan Guth, who claim that the flat universe predicted by inflation is just such a universe of zero total energy. Today in New Scientist, a full 35 years after Tryon's proposal, Lawrence Krauss attempts to use this idea to explain why there is something rather than nothing:

"The key point...is that with zero total energy, Aquinas's puzzle is resolvable. And once the energy fluctuations of quantum mechanics are thrown into the mix, the idea of something arising from nothing can become not just possible, but necessary."

Tryon conjectured that all conserved quantities have a net value of zero for the universe as a whole, and, noting that in Newtonian theory the gravitational potential energy is negative, he proposed that there might be a sense in which the negative gravitational energy of the universe cancels the positive mass-energy.

Unfortunately, as I have pointed out in the past, Tryon’s idea runs aground on a fact that Guth himself mentions:

"In general relativity there is no coordinate-invariant way of expressing the [gravitational] energy in a space that is not asymptotically flat, so many experts prefer to say that the total energy is undefined," (footnote, p6). As Robert Wald also points out, "it has long been recognized that there is no meaningful local notion of gravitational energy density in general relativity," (p20).

Let us suppose, however, that this is merely a technical issue, which might ultimately be resolvable, and that there might be a well-defined sense in which the total energy of a flat universe is, indeed, zero. Even then, the notion that the universe was created by a fluctuation of the quantum vacuum, cannot explain why there is something rather than nothing, for the existence of the quantum vacuum pre-supposes the existence of a background space-time equipped with quantum fields in their vacuum states, and this is clearly far from being nothing.

Krauss anticipates that "Purists will argue that this begs the question of how the physical laws that make it all possible arose," but the immediate problem is more that the quantum vacuum, and the pre-existing space-time required by the quantum vacuum, are very much something.

1 comment:

Doug Hudson said...

As King Lear said, "Nothing? Nothing comes from nothing."