The Why and How of It All
Nothing is a tricky concept. Consider this peculiar argument by
Descartes against the possibility of a vacuum: “If someone asks what
would happen if God were to take away every single body contained in a
vessel, without allowing any other body to take the place of what had
been removed, the answer must be that the sides of the vessel would, in
that case, have to be in contact. For when there is nothing between two
bodies, they must necessarily touch each other”. Descartes has confused
the concept of a vacuum with that of nothing: a vacuum is empty space,
and the empty space in the bell jar is something. It has properties such
as size and shape even if it fails to contain matter.
The distinction between a vacuum and nothing plays a central role
in both Jim Holt’s Why Does the World Exist? and Lawrence Krauss’s A
Universe form Nothing: Why there is Something Rather than Nothing. By
their titles, one might expect Krauss’s book to answer Holt’s question.
But both authors tend to run together two distinct questions. One—
Holt’s main quarry—is “Why is there something rather than nothing?”.
The other, which predominates in Krauss’s book, is “How can something
come from nothing?”. The predilection to regard these as equivalent is
puzzling. No one would confuse the question “Why is the universe
matter rather than anti-matter?” with the question “How can matter
come from anti-matter?”. The muddle becomes more severe since
“nothing” means different things in the two questions.
The “nothing” in Holt’s question is a state of universal and total
absence: no matter, no fields, no laws, no space, no time, ever. If this is a
possibility, it is a possibility that does not actually obtain. And if it might
have obtained but doesn’t, then it seems legitimate to seek an
explanation of why it doesn’t obtain. But on reflection, the quest for an
explanation here appears doomed to failure. If one tries to explain why
there is something rather than nothing by invoking some item, or cause,
or principle, then we can equally wonder why it exists.
The “nothing” in Krauss’s question is a different beast. For most of
his book, “nothing” means a vacuum state in some physical theory.
Krauss’s “nothing” is certainly not universal: a universal vacuum,
through all space and time, is incompatible with the existence of us now.
We can’t have come from Holt’s “nothing”, by its very definition.
Holt’s question is philosophical, so he consults philosophers.
Adolph Grunbaum argues that there is no problem: the felt need for an
explanation arises from an unjustifiable conviction that nothingness is
somehow more probable or expectable than the existence of something.
Absent any principle for preferring nothing over something, no
explanation is required. Holt finds no flaw in Grunbaum’s argument but
it still does not feel right to him, so he presses on with other
philosophers, physicists, theologians and even the novelist John Updike.
It makes for an amusing and stimulating, if somewhat picaresque, tale.
(One recurring motif is that Holt imbibes significant quantities of
alcohol while his interlocutors prefer caffeinated beverages.)
The theologian Richard Swinburne opines that the physical world
exists because God made it and punts on the question of why God exists.
Speculative cosmologist John Leslie suggests that the universe exists
because it is good, and hence ought to exist. Philosopher Derek Parfit
focuses on the form that an explanation might take, considering how
some property the universe has might account for its existence. Parfit
calls such a property a selector. Leslie’s view is that goodness is the
selector, but one might also imagine other properties playing the
explanatory role: simplicity, variety, etc. Parfit’s idea is that if there is a
selector, we can get evidence for what it is by seeing which property (if
any) the universe maximally exemplifies. Holt, by a somewhat
convoluted argument, considers the possibility that the relevant
property might be mediocrity.
The physicists that Holt consults tend to be more on Grunbaum’s
side. Steven Weinberg and David Deutsch both recognize the hopeless of
the explanatory regress: anything one invokes to explain the totality of
existence must itself be something that exists. One can react to this by
saying that we are always stuck with a mystery or, as Grunbaum would
prefer, by saying that there is nothing mysterious since no answerable
question is left unanswered.
Physicists do investigate Krauss’s question. Suppose there is a
certain physcial state, not of the whole of existence but rather of just a
part, that deserves the name “vacuum state”. The present universe, filled
with stars and dark matter and radiation, is certainly not in that state.
But the laws of physics might allow the present universe to evolve from
the vacuum state. If that happened, and if we call the vacuum state
“nothing”, then one can say that physics explains how something came
from nothing.
Despite it’s title, the majority of Krauss’s book does not discuss
this possibility. Rather, it summarizes our present cosmological picture
of the history and fate of the observable part of the universe. We have
strong evidence, for example, that the visible part of the universe
presently consists of about 70% dark energy, 25% unknown dark
matter, 4% invisible known matter and only 1% visible known matter.
Krauss presents the case for an early period of hyperinflation, which left
marks on the cosmological background radiation. Observations indicate
that the dark energy is causing the universe to expand at a quickening
pace, and we can speculate where that will lead. Krauss explains the
evidence clearly and accessibly.
This is the important story of the triumphs of modern cosmology.
But by itself, it does nothing to address either of our two questions.
Krauss does not really confront Holt’s question. He does devote some
effort arguing that the vacuum state can properly called “nothing”, so
that the present universe arising from a vacuum would be an instance of
“something from nothing”.
Let’s break down the issue into three parts. First, what can we
reasonably surmise about the state from which the present universe
arose? Second, by what right (if any) should such a state be called a
vacuum state? Third, even if the present state arose from a vacuum
state, why think that that would end our explanatory regress?
Unlike the detailed claims of modern cosmology mentioned above,
the nature of the pre-inflationary state of the universe is a matter of
conjecture. Was there any state that preceded our “Big Bang”, and if so
was there anything before that? Does the very temporal notion of
“before” break down, and if so why say that the present state “came
from” some other one? Does the regress in time go on forever or come
to an end with an initial state? We have no clear answers to any of these
questions, although various inflationary scenarios and hints from string
theory provide fodder for speculation.
Krauss’s main argument for denominating the initial state
“nothing” arises from considerations of energy. He argues that
according to a certain way of quantifying the total energy content of the
universe, including the gravitational energy, the entire present universe
might have zero energy. Wouldn’t that mean that we could get the
universe “for free”: something from nothing?
Well, no. As Krauss acknowledges, the calculation of total energy
in Newtonian gravitational theory uses an arbitrary choice of gauge for
the gravitational potential energy. The amount of potential energy can
be changed at will without affecting the physics, and can in particular
take negative values by choosing one particular state as the “zero
potential energy” state. Given this freedom, one can make a choice that
sets the total energy to zero, but one can also just as legitimately set it to
any value one wishes.
Shouldn’t we be using the General Theory of Relativity rather than
Newtonian gravity in any case? But, as Krauss also admits, there is no
accepted method for ascribing a gravitational potential energy in the
General Theory, much less a precise value of negative energy. Krauss
does argue that we have good reason to think that the present universe
is (nearly) flat, but this is not the same as “zero energy”.
Suppose all this could work out, and we came to see our universe
as arising from some sort of quantum vacuum. Still we would have the
same question: why did things start out that way? Physicists invoke
their own selector here, and it is neither goodness nor zero energy: it is
symmetry. The “false vacuum” of inflationary theory (which Krauss
mentions but does not explain) is not special because of its moral or its
energetic properties: it is special because of its symmetries. Physicists
apparently regard these symmetries as making the state “to be
expected” or “not in need of further explanation”. Why this should be so
is a question that neither of our authors manages to confront.
Tim Maudlin haunts the Philosophy Department at New York
University. His most recent book is Introduction to the Philosophy of
Physics: Space and Time, e-mail twm3@NYU.edu.