Consider first the kalam cosmological argument:
1. If the universe began to exist, then there
is a transcendent cause which brought the
universe into existence.
2. The universe began to exist.
3. Therefore, there is a transcendent cause
which brought the universe into existence.
By “the universe,” I mean that reality
which is studied by contemporary cosmology,
that is to say, all of contiguous physical
reality, which currently takes the form of
space-time and its contents.
I take it that (1) is obviously true. Rather
the truly controversial premiss is (2). Traditional
supporters presented philosophical arguments
in support of (2), which, for me, constitute
its primary warrant. But they’re not the
subject of tonight’s debate. Rather what’s
emerged during the 20th century is remarkable
empirical confirmation of the second premiss
from the evidence of astrophysical cosmogony.
Two independent but closely interrelated lines
of physical evidence support premiss (2):
evidence from the expansion of the universe
and evidence from the second law of thermodynamics.
In saying that the cosmogonic evidence confirms
(2), I am not saying that we are certain that
(2) is true. Too many people mistakenly equate
knowledge with certainty. When they say that
we do not know that the universe began to
exist, what they really mean is that we are
not certain that the universe began to exist.
But, of course, certainty is not the relevant
standard here. The question is whether (2)
is more plausible in light of the evidence
than its contradictory. As Professor Carroll
reminds us,
Science isn't in the business of proving things.
Rather, science judges the merits of competing
models in terms of their simplicity, clarity,
comprehensiveness, and fit to the data. Unsuccessful
theories are never disproven, as we can always
concoct elaborate schemes to save the phenomena;
they just fade away as better theories gain
acceptance.
Science cannot force you to accept the beginning
of the universe; you can always concoct elaborate
schemes to explain away the evidence. But
those schemes will not fare well in displaying
the aforementioned scientific virtues.
Even many who have expressed scepticism about
premiss (2) admit that it is more plausibly
true than not. For example, in my recent dialogue
with Lawrence Krauss, he volunteered, “I’d
bet our universe had a beginning, but I am
not certain of it. . . . based on the physics
that I know, I’d say it is a more likely
possibility.” This is to admit precisely
what cosmologists like Alexander Vilenkin
have contended all along: that the evidence
makes it more likely than not that the universe
began to exist.
Consider, first, the evidence from the expansion
of the universe. The standard (Friedman-LeMaître
Robertson-Walker) big bang cosmogonic model
implies that the universe is not infinite
in the past but had an absolute beginning
a finite time ago. Although advances in astrophysical
cosmology have forced various revisions in
the standard model, nothing has called into
question its fundamental prediction of the
finitude of the past and the beginning of
the universe. Indeed, as James Sinclair has
shown, the history of 20th century cosmogony
has seen a parade of failed theories trying
to avert the absolute beginning predicted
by the standard model. Meanwhile, a series
of remarkable singularity theorems has increasingly
tightened the loop around empirically tenable
cosmogonic models by showing that under more
and more generalized conditions, a beginning
is inevitable. In 2003 Arvind Borde, Alan
Guth, and Alexander Vilenkin were able to
show that any universe which is, on average,
in a state of cosmic expansion throughout
its history cannot be infinite in the past
but must have a beginning. In 2012 Vilenkin
showed that cosmogonic models which do not
fall under this condition, including Professor
Carroll’s own model, fail on other grounds
to avert the beginning of the universe. Vilenkin
concluded, “None of these scenarios can
actually be past-eternal.” “All the evidence
we have says that the universe had a beginning.”
The Borde-Guth-Vilenkin theorem proves that
classical space-time, under a single, very
general condition, cannot be extended to past
infinity but must reach a boundary at some
time in the finite past. Now either there
was something on the other side of that boundary
or not. If not, then that boundary is the
beginning of the universe. If there was something
on the other side, then it will be a non-classical
region described by the yet to be discovered
theory of quantum gravity. In that case, Vilenkin
says, it will be the beginning of the universe.
Think about it. If there is such a non-classical
region, then it is not past eternal in the
classical sense. But neither can it exist
literally timelessly, akin to the way in which
philosophers consider abstract objects to
be timeless or theologians take God to be
timeless. For this region is in a state of
constant flux, which, given the Indiscernibility
of Identicals, is sufficient for time. So
even if time as defined in classical physics
does not exist at such an era, some sort of
time would.
But if the quantum gravity era is temporal,
it cannot be extended infinitely in time,
for such a quantum state is not stable and
so would either produce the universe from
eternity past or not at all. As Anthony Aguirre
and John Kehayias argue,
It is very difficult to devise a system – especially
a quantum one – that does nothing ‘forever,’
then evolves. A truly stationary or periodic
quantum state, which would last forever, would
never evolve, whereas one with any instability
will not endure for an indefinite time.
Hence, the quantum gravity era would itself
have to have had a beginning in order to explain
why it transitioned just some 13 billion years
ago into classical time and space. Hence,
whether at the boundary or at the quantum
gravity regime, the universe probably began
to exist.
Consider now the evidence from thermodynamics.
According to the second law of thermodynamics
entropy in a closed system almost never decreases.
Given the naturalistic assumption that the
universe is a closed system, the second law
implies that, given enough time, the universe
will come to a state of thermodynamic heat
death, whether cold or hot. Given that the
universe will expand forever, it may never
reach a state of equilibrium, but it will
grow increasingly cold, dark, dilute, and
dead. But then the obvious question arises:
why, if the universe has existed forever,
is it not now in a cold, dark, dilute, and
lifeless state? P. C. W. Davies gives the
obvious answer: “The universe can’t have
existed forever. We know there must have been
an absolute beginning a finite time ago.”
The universe’s energy, says Davies, was
simply “put in” at the creation as an
initial condition.
By contrast Professor Carroll’s solution
to the problem confronts serious obstacles.
He imagines that the overall condition of
the universe is a state of thermal equilibrium
(a sort of de Sitter space), but that random
fluctuations spawn baby universes, which pinch
off to become wholly independent space-times.
We find ourselves in one such baby universe
in a state of disequilibrium.
Let me raise two concerns about this model.
First, not only are the production mechanisms
of such baby universes admittedly conjectural,
but such a scenario violates the so-called
unitarity of quantum theory by allowing irretrievable
information loss from the mother universe
to the babies. Stephen Hawking, apologizing
to science-fiction fans everywhere, came to
admit, “There is no baby universe branching
off, as I once thought. The information remains
firmly in our universe.”
Second, Professor Carroll’s solution provides
no convincing answer to the Boltzmann Brain
problem. Since the mother universe is a de
Sitter space in which thermal fluctuations
occur and since baby universes grow into de
Sitter spaces themselves, there’s no explanation
in the model why there exists a genuine low
entropy universe around us rather than the
mere appearance of such a world, an illusion
of isolated brains which have fluctuated into
existence out of the quantum vacuum. These
and other problems make Professor Carroll’s
model less plausible than the standard solution
that the universe began to exist with an initial
low entropy condition.
Skeptics might hope that quantum cosmology
might serve to avert the implications of the
second law of thermodynamics. But now a new
singularity theorem formulated by Aron Wall
seems to close the door on that possibility.
Wall shows that, given the validity of the
generalized second law of thermodynamics in
quantum cosmology, the universe must have
begun to exist, unless, as in Professor Carroll’s
model, one postulates a reversal of the arrow
of time at some point in the past, which,
he rightly observes, involves a thermodynamic
beginning in time which “would seem to raise
the same sorts of philosophical questions
that any other sort of beginning in time would.”
Wall reports that his results require only
certain basic concepts, so that “it is reasonable
to believe that the results will hold in a
complete theory of quantum gravity.”
Thus, we have good evidence both from the
expansion of the universe and from the second
law of thermodynamics that the universe is
not past eternal but had a temporal beginning.
So the second premise of the kalam cosmological
argument receives significant confirmation
from the evidence of contemporary cosmology.
We have, then, a good argument for a transcendent
cause of the universe.
So, I think I can make these points basically
by following Dr. Craig’s organization starting
with the kalam cosmological argument, and
unlike what he said I should be doing I want
to challenge the first of the premises: If
the universe began to exist it has a transcendent
cause. The problem with this premise is that
it is false. There’s almost no explanation
or justification given for this premise in
Dr. Craig’s presentation. But there’s
a bigger problem with it, which is that it
is not even false. The real problem is that
these are not the right vocabulary words to
be using when we discuss fundamental physics
and cosmology. This kind of Aristotelian analysis
of causation was cutting edge stuff 2,500
years ago. Today we know better. Our metaphysics
must follow our physics. That’s what the
word metaphysics means. And in modern physics,
you open a quantum field theory textbook or
a general relativity textbook, you will not
find the words “transcendent cause” anywhere.
What you find are differential equations.
This reflects the fact that the way physics
is known to work these days is in terms of
patterns, unbreakable rules, laws of nature.
Given the world at one point in time we will
tell you what happens next. There is no need
for any extra metaphysical baggage, like transcendent
causes, on top of that. It’s precisely the
wrong way to think about how the fundamental
reality works. The question you should be
asking is, “What is the best model of the
universe that science can come up with?”
By a model I mean a formal mathematical system
that purports to match on to what we observe.
So if you want to know whether something is
possible in cosmology or physics you ask,
“Can I build a model?” Can I build a model
where the universe had a beginning but did
not have a cause? The answer is yes. It’s
been done. Thirty years ago, very famously,
Stephen Hawking and Jim Hartle presented the
no-boundary quantum cosmology model. The point
about this model is not that it’s the right
model, I don’t think that we’re anywhere
near the right model yet. The point is that
it’s completely self-contained. It is an
entire history of the universe that does not
rely on anything outside. It just is like
that. The demand for more than a complete
and consistent model that fits the data is
a relic of a pre-scientific view of the world.
My claim is that if you had a perfect cosmological
model that accounted for the data you would
go home and declare yourself having been victorious.
You might also ask, “Could the universe
be eternal?” (since Dr. Craig talked about
this) without having a beginning at all. Again,
the answer is: yes, just build a model. This
is my favorite model. It’s actually not
even a model that I think is right; once again,
it’s a model I helped create. But it’s
about the search for models, not about saying
any one model is the right idea. We hope that
some day we get there but we don’t claim
that we are there yet. So whether or not the
universe can be eternal does not come down
to a conversation about abstract principles.
It comes down to a conversation about building
models and seeing which one provides the best
account for what we see the universe to be
doing.
So I’d like to talk about the Borde-Guth-Vilenkin
theorem since Dr. Craig emphasizes it. The
rough translation is that in some universes,
not all, the space-time description that we
have as a classical space-time breaks down
at some point in the past. Where Dr. Craig
says that the Borde-Guth-Vilenkin theorem
implies the universe had a beginning, that
is false. That is not what it says. What it
says is that our ability to describe the universe
classically, that is to say, not including
the effects of quantum mechanics, gives out.
That may be because there’s a beginning
or it may be because the universe is eternal,
either because the assumptions of the theorem
were violated or because quantum mechanics
becomes important. If you need to invoke a
theorem, because that’s what you like to
do rather than building models, I would suggest
the quantum eternity theorem. If you have
a universe that obeys the conventional rules
of quantum mechanics, has a non-zero energy,
and the individual laws of physics are themselves
not changing with time, that universe is necessarily
eternal. The time parameter in Schrödinger’s
equation, telling you how the universe evolves,
goes from minus infinity to infinity. Now
this might not be the definitive answer to
the real world because you could always violate
the assumptions of the theorem but because
it takes quantum mechanics seriously it’s
a much more likely starting point for analyzing
the history of the universe. But again, I
will keep reiterating that what matters are
the models, not the abstract principles.
Dr. Craig brings up an argument about the
Second Law of Thermodynamics and I’ve written
a whole book, you can buy it on Amazon right
now from your iPhones, about the second law
and its relationship to cosmology. It is certainly
a true issue that we don’t know why the
early universe had a low entropy and entropy
has ever been increasing. That’s a good
challenge for cosmology. To imagine the cosmologist
cannot answer that question without somehow
invoking God is a classic god-of-the-gaps
move. I know that Dr. Craig says that is not
what he’s doing but then he does it. We
don’t know why the early universe had a
low entropy but that is not an argument that
we can’t figure it out. There is more than
one possibility. Maybe there is a principle,
like Stephen Hawking would say, that puts
the early universe in a low entropy state.
Or maybe there is no high entropy state. In
my model of an eternal universe the reason
why our universe is always changing is because
the universe always can change. There is no
equilibrium for it to fall into. Dr. Craig
brings up a quote – he brings up various
things that I think really muddle the cosmological
picture here. He says that my model is not
working very well because it violates unitarity—the
conservation of information—and that is
straightforwardly false. In my model unitarity
is the whole point. There’s a quantum mechanical
wave function that describes the evolution
of the universe from one piece into multiple
pieces and that evolution is perfectly unitarity.
He quotes Stephen Hawking backsliding his
statement about baby universes but that was
in the context of black holes. That had nothing
to do with cosmology. That quote was taken
completely out of context. Finally, he makes
a big deal about Boltzmann Brains. I’m going
to talk about that a little bit later. Most
importantly, he talks about the fact that
if the universe is eternal and you have a
Second Law of Thermodynamics then there must
have been a moment in the middle when the
entropy was lowest, and he calls this a thermodynamic
beginning and he quotes another paper. That’s
fine except it’s an equivocation on the
word beginning. A thermodynamic beginning
is not a beginning—it happens in the middle.
It’s a moment in the history of the universe
from which entropy is higher in one direction
of time and the other direction of time. There
is no room in such a conception for God to
have brought the universe into existence at
any one moment.
If you really believe that the beginning of
the universe is an important piece of evidence
for God, an eternal universe with a low entropy
state in the middle is not helping your case.
What you should be doing is trying to build
models, like I said. So the question is, “Are
there realistic models of eternal cosmologies?”
Well, I spent half an hour on the Internet
and I was able to come up with about seventeen
different plausible looking models of eternal
cosmologies. I do not claim that any of these
are the right answer. We’re nowhere near
the right answer yet but you can come up with
objections to every one of these models. You
cannot say that they are not eternal. There’s
a theorem, Borde-Guth-Vilenkin, that has assumptions
so if you violate those assumptions you can
violate the theorem. Meanwhile, theism, I
would argue, is not a serious cosmological
model. That’s because cosmology is a mature
subject. We care about more things than just
creating the universe. We care about specific
details. At the cosmology conferences we’re
discussing these questions that you see before
you. I’m not going to list all of them but
a real cosmological model wants to predict.
What is the amount of density perturbation
in the universe? And so forth. Theism does
not even try to do this because ultimately
theism is not well defined.
Consider, first, the evidence for the beginning
of the universe from the expansion of the
universe and thermodynamics.
To my surprise, Dr. Carroll challenges the
first premise of this argument by saying it
is based on outmoded Aristotelian concepts
of causality. I protest – not at all! There
is no analysis given of what it means to be
a cause in this first premise. You can adopt
your favorite theory of causation or take
causation to be a conceptual primitive. All
it requires is that the universe did not pop
into being uncaused out of absolutely nothing.
If that is the price of non-theism, then I
think the non-theist is welcome to it. Dr.
Carroll says on the Hartle-Hawking model the
universe is uncaused. Not at all! The universe
comes into being on such a model, and there
is nothing in the theory that
would explain why that universe exists rather
than not. The model may be self-contained;
but that is perfectly consistent with my argument.
I am not arguing for some kind of interventionist
deity, but rather, why does the universe exist?
Why did it come into being at all?
With respect to the second premise, Dr. Carroll
says there are all kinds of beginningless
models of the universe. Well, it certainly
is true that such models exist; but the problem
is that none of them is successful.
As Jim Sinclair has shown in our article in
the Blackwell Companion, all of the models
that Dr. Carroll has mentioned have been shown
to be either untenable or not to avert the
beginning of the universe. Alex Vilenkin says
flatly, “there are no models at this time
that give a satisfactory model for a universe
without a beginning.”
Consider in particular Dr. Carroll’s own
model.
This model presupposes a reductionistic view
of time according to which the direction of
time is defined in terms of entropy increase.
Now, in the model notice there are two arrows
of time for the mother universe pointing in
opposite directions. So on this view of time,
we don’t really have an eternally existing
mother universe here at all. Rather, you have
two universes which share a common origin
in the central surface. So what the model
actually implies, rather than avoids, is a
beginning of time and of the universe. Time
has a beginning on this model, and therefore
it involves all of the problems that are pertinent
to the universe’s coming into being.
Be that as it may, I think it is safe to say
that there is no credible classical model
of a beginningless universe today.
Dr. Carroll does hold out hope that quantum
cosmology might serve to restore the past
eternality of the universe; but I would say
that not only is there no evidence for such
a hope, but I would agree with Vilenkin that
if there is a quantum gravity regime prior
to the Planck Time, then that just is the
beginning of the universe. Dr. Carroll says
you can have quantum descriptions of the universe
that are eternal, and that is certainly true,
but the question is: why would the universe
transition to classical spacetime just 13
billion years ago? It could not have existed
from infinity past in an unstable quantum
state and then just 13 billion years ago transition
to classical spacetime. It would have done
it from eternity past, if at all.
So I think we’ve got good evidence from
the expansion of the universe that the universe
probably began to exist.
What about the evidence from thermodynamics?
First is the problem of information loss to
baby universes on his theory. You will recall
that is why Stephen Hawking rejected the baby
universe hypothesis. Dr. Carroll responds,
“My mechanisms for generating the baby universes
don’t use Hawking’s mechanisms.” All
right; but are they any more successful? I
don’t think so. According to Chris Weaver
in his article on the Carroll-Chen model,
The FGG [Farhi-Guth-Guven] nucleation [that
Dr. Carroll uses] out of a de Sitter space-time
is merely speculative and . . . Carroll’s
discussion of it should be thought of as exploratory.
. . . it is therefore safe to conclude that
a central piece of the model is missing, and
so the CC-M [Carroll-Chen model] is incomplete
in that it does not have a clear recommended
dynamical path from the background [space-time]
to the birth of [universes] like ours.
In fact, Weaver goes on to point out that
for a universe described by the Borde-Guth-Vilenkin
theorem (like ours), the Farhi-Guth-Guven
mechanisms cannot produce such a universe.
Therefore, these mechanisms fail.
I also, secondly, pointed out that there is
a Boltzmann Brain problem with respect to
Dr. Carroll’s model. It seems to me that
he just didn’t respond to the point that
I was making, namely, that since every baby
universe grows into a de Sitter space, there
will be vastly, vastly more of these Boltzmann
Brains in the long run than there will be
ordinary observers. So what Dr. Carroll would
need to do is to justify some non-standard
measure of probability that would make ordinary
observers more probable than Boltzmann Brains.
But he admits that he cannot do it.
We also then saw that quantum gravity will
not avert this conclusion because of the Wall
theorem, which should be valid for the quantum
gravity era and requires a beginning of the
universe.
So it seems to me we’ve got good evidence
from the expansion of the universe and from
thermodynamics that the universe is probably
not past eternal but began to exist.
So let’s go to the kalam cosmological argument.
There’s a deep philosophical difference
between us. I claim that a consistent, complete
model that fits the data accounts for what
we see in the world is a success. There’s
no right that we have to demand more than
that, and I believe that Dr. Craig’s response
was, “Yes there is.” I don’t think this
counts as a very good response. It’s a very
difficult thing because the universe is different
than our everyday experience. That doesn’t
sound like a surprising statement but we really
need to take it to heart. To look at a modern
cosmological model and say, “Yes, but what
was the cause?” is like looking at someone
taking pictures with an iPhone and saying,
“But where does the film go?” It’s not
that the answer is difficult or inscrutable;
it’s completely the wrong question to be
asking. In fact it’s a little technical,
most of my second talk here, but I think it’s
worth getting it right. Why should we expect
that there are causes or explanations or a
reason why in the universe in which we live?
It’s because the physical world inside of
which we’re embedded has two important features.
There are unbreakable patterns, laws of physics—things
don’t just happen, they obey the laws—and
there is an arrow of time stretching from
the past to the future. The entropy was lower
in the past and increases towards the future.
Therefore, when you find some event or state
of affairs B today, we can very often trace
it back in time to one or a couple of possible
predecessor events that we therefore call
the cause of that, which leads to B according
to the laws of physics. But crucially, both
of these features of the universe that allow
us to speak the language of causes and effects
are completely absent when we talk about the
universe as a whole. We don’t think that
our universe is part of a bigger ensemble
that obeys laws. Even if it’s part of the
multiverse, the multiverse is not part of
a bigger ensemble that obeys laws. Therefore,
nothing gives us the right to demand some
kind of external cause.
The idea that our intuitions about cause and
effect that we get from the everyday experience
of the world in this room should somehow be
extended without modification to the fundamental
nature of reality is fairly absurd. On a more
specific level we talked about my model. Again,
I’m not trying to defend my model; I’m
the first one to say that it has problems.
None of the problems that it has are the ones
that Dr. Craig raised. He says that it’s
not really eternal, which it is hard to express
the extent to which I think this is grasping
at straws. The axis for time goes from the
top to the bottom and it goes forever. The
only sense in which this universe is not eternal
is that there is a moment in the middle where
the entropy is lowest. I made the point in
my opening speech that that has nothing to
do with the kind of beginning you would need
to give God room to work and as far I can
recall Dr. Craig didn’t address that argument.
He does say that it is speculative, the idea
of baby universes coming into existence. I’m
the first to agree. It’s completely speculative.
He quotes a paper that says the mechanism
by which baby universe are created is speculative,
it might not be right. Again, it’s completely
true. He claims to use it to say that unitarity
is violated even though the quote he read
didn’t even mention unitarity and wasn’t
about unitarity. That is not a sensible objection.
I will repeat – the quantum eternity theorem,
a sensible analysis of the history of the
universe, might be with the rules of quantum
mechanics. He claims that someone else said
there might be a singularity in quantum gravity
but he gives us no understanding, he simply
repeats his previous analysis. So, I want
to draw attention not to my model but to the
model of Anthony Aguirre and Steven Gratton
because this is perfectly well defined. This
is a bouncing cosmology that is infinite in
time, it goes from minus infinity to infinity,
it has classical description everywhere. There
is no possible sense in which this universe
comes into existence at some moment in time.
I would really like Dr. Craig to explain to
us why this universe is not okay.
Now there’s a theorem by Alan Guth, Arvind
Borde, and Alex Vilenkin that says the universe
had a beginning. I’ve explained to you why
that’s not true but in case you do not trust
me I happen to have Alan Guth right here.
One of the authors of the Borde-Guth-Vilenkin
Theorem, Alan what do you say? He says, “I
don’t know whether the universe had a beginning.
I suspect the universe didn’t have a beginning.
It’s very likely eternal but nobody knows.”
Now how in the world can the author of the
Borde-Guth-Vilenkin theorem say the universe
is probably eternal? For the reasons I’ve
already told you. The theorem is only about
classical descriptions of the universe not
about the universe itself.
Let’s look again at those arguments that
I defended.
First, the kalam cosmological argument. Dr.
Carroll challenges the first premise, that
if the universe came into existence, there
is a transcendent cause that brought the universe
into being. Honestly, I am quite astonished
that he would think that the universe can
literally pop into being out of nothing. Let
me just give three arguments for why there
must be a cause.
First of all, it seems to me a metaphysical
first principle that being doesn’t come
from non-being. Things don’t just pop into
existence from literally nothing. Nothingness
has no properties, no potentialities. It is
not anything. So it seems to me inconceivable
metaphysically to think the universe can come
into being from nothing.
Secondly, if the universe could come into
being from nothing, then why is it that only
universes can pop into being out of nothing?
Why not bicycles and Beethoven and root beer?
What makes nothingness so discriminatory?
If universes could pop into being out of nothing,
then anything and everything should pop into
being out of nothing. Since it doesn’t,
that suggests that things that come into being
have causes.
Finally, all the empirical evidence we have
supports the truth of the causal principle.
When Dr. Carroll says, “The universe is
different than our experience,” this is
really committing what Alexander Pruss calls
the taxi-cab fallacy, that is to say, you
go with the causal principle until you reach
your desired goal and then you think you can
just dismiss it like a hack because you don’t
want there to be a cause of your entity – the
universe. But if the universe came into existence,
if the universe is not eternal, then surely
it would need to have a cause. In fact, to
deny this is unscientific because the whole
project of contemporary cosmogony is to try
to find what is the cause of the universe!
So on his principle, it would be a science-stopper
and would destroy his very field of expertise.
With respect to the second premise that the
universe did begin to exist, he denies that
he actually has an origin of time going in
two opposite directions.
But this is a different diagram of his model.
Notice that on this diagram, you have a non-reductionistic
arrow of time that goes from past to future.
This is not an arrow of time that is determined
by entropy increase, as he had in the other
diagram. This is a non-reductionistic view
of time, that Professor Maudlin and I accept,
where the direction of entropy increase doesn’t
define the direction of time. On this model,
the universe contracts down from eternity
past from infinity to a relatively low entropy
point and then begins to expand again. That
kind of model is physically impossible. It
contradicts the second law of thermodynamics.
That is why you have got to have the arrows
pointing in both directions, if you want to
hope for this model to be realistic. But if
you have a double-headed arrow of time in
both directions, then you have a beginning
of time and of the universe. So I want to
co-opt Dr. Carroll’s model for myself! On
his model of the universe, the universe began
to exist, along with time.
I also pointed out that on the Borde-Guth-Vilenkin
theorem, there are no classical models that
succeed in showing the universe to be beginningless.
He rightly points out this is just classical
space-time. But then I never heard a response
to my claim that if there is a quantum gravity
era prior to the Planck time, then it would
have to be itself finite because otherwise
it becomes inexplicable why classical spacetime
only came into being 13 billion years ago
rather than from eternity past.
So I think we have got good evidence for the
beginning of the universe from the expansion
of the universe.
As for thermodynamics, here I argued that
in order to explain why we are in a low entropy
state, the standard answer is that the universe
began relatively recently with its low entropy
condition at the beginning. By contrast, his
model, I charged, violates the unitarity of
quantum physics. He says, “No, because I
am not using the same mechanisms as Hawking.”
But then I pointed out that the mechanisms
that he appeals to are both conjectural and
actually incompatible with a universe described
by the Borde-Guth-Vilenkin theorem, as Christopher
Weaver points out in his critique of the model.
Secondly, the Boltzmann Brain problem. I don’t
think that Dr. Carroll has really come to
grips with this, quite honestly. There are
at least two reasons why Boltzmann Brains
would dominate. First, because on his multiverse
model, in the long run every baby universe
becomes a de Sitter space and will become
dominated with Boltzmann Brains. Secondly,
in all of the other worlds that are not fine-tuned,
there just aren’t any ordinary observers;
but there will be thermal fluctuations that
will produce Boltzmann Brains. So he is the
one who has to justify some non-standard measure
of probability in order to explain why ordinary
observers like us should exist rather than
Boltzmann Brains.
Then I appealed to the Wall theorem to show
that even on a quantum gravity theory you
are not going to avoid the beginning of the
universe. Dr. Carroll may have responded to
this, but if he did, it went by so quick I
didn’t hear it. So it seems to me we’ve
still got the Wall theorem showing that even
with a quantum gravity era there has to be
a beginning.
First, I want to notice some of the things
he did say. He said he was astonished that
I refused to accept the fact that things need
causes to happen. To which I could only quote
David Lewis, “I do not know how to refute
an incredulous stare.” I tried to give the
reason why the causation analysis that we
use for objects within the universe does not
apply to the universe but that more or less
whizzed on by. Dr. Craig gets a lot of mileage
out of the presumed nuttiness of things just
popping into existence. “Why don’t bicycles
just pop into existence?” Again, I tried
to explain what makes the universe different
but more importantly the phrase “popping
into existence” is not the right one to
use when you’re talking about the universe.
It sounds as if it’s something that happens
in time but that’s not the right way to
do it because there’s no before the beginning,
if there’s a beginning. The correct thing
to say is there was a first moment of time.
When you say it that way it doesn’t’ sound
so implausible. The question is, is there
a model in which that’s true? Do the equations
of the model hang together? Does the model
fit the data? And we have plausibly positive
answers to all of those.
He spends a lot of time on my own model, more
time than I would have spent on it. He is
upset that I did not include an arrow at the
bottom in my axis when I drew the graph previously.
I don’t care about that to be very honest.
The double arrows here are just to express
the fact that there’s no intrinsic arrow
of time. The arrow of time that we experience
is because of the behavior of matter in the
universe—the entropy increasing. And he
says that’s in violation of the Second Law
of Thermodynamics. Yes, it is an explanation
of the Second Law of Thermodynamics. This
is the reason why we in our little part of
the universe observe the second law. He mentions
once again Boltzmann Brains and he says that
there should be more Boltzmann Brains than
ordinary observers. I again explain why that’s
not true because it’s a model dependent
statement. In this particular model it turns
out to be easier to make a universe than to
make a brain. That’s a selling point of
the model.
