12
way, any worries about fine- tuning and the existence of life evaporate. Find-
13
ing ourselves in a universe that is hospitable to life is no stranger, nor any
14
more informative, than finding ourselves living on Earth: there are many
15
different regions, and this is the one in which we can live.
16
What should be our credence that there is such a multiverse? It’s diffi-
17
cult to say with our current level of understanding of fundamental physics
18
and cosmology. Some physicists would put the chances at nearly certain,
19
others at practically zero. Perhaps it’s fifty- fifty. For our present discussion,
20
what matters is that there is a simple, robust mechanism under which natu-
21
ralism can be perfectly compatible with the existence of life, even if the life
22
turns out to be extremely sensitive to the precise values of the physical pa-
23
rameters characterizing our environment.
24
25
•
26
So what about the likelihood of a universe like ours appearing under the-
27
ism? Here we are faced with a similar problem: the word “theism” doesn’t
28
refer to a unique, predictive theory of the world. People will interpret it in
29
different ways, leading to different estimates of the likelihoods of various
30
observable features. We have little choice but to proceed, keeping in mind
31
the inherent uncertainties of the question.
32
It’s reasonable to accept that theism predicts the existence of life with
33
high probability. At least, most theists do not advocate a conception of God
34
under which he is completely indifferent to the existence of human beings.
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We could imagine such a conception; a noninterventionist God who
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created or sustained the universe but had no special regard for what you and
02
I would call “life.” But we can afford to err on the side of generosity, and
03
assume that the probability of life existing under theism is appreciable;
04
larger, indeed, than it would be under naturalism.
05
That is far from the end of the story, however. There is an important
06
distinction between “life” and “the numbers describing a universe consis-
07
tent with the existence of the kinds of complex chemical reactions we iden-
08
tify with biological organisms.” God might care about the former, but it’s
09
far less clear that he would care about the latter.
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The physical parameters of our universe govern what can happen accord-
11
ing to the laws of physics. But under theism, “life” is generally something
12
other than a simple manifestation of the laws of physics. Theists tend to be
13
non- physicalists; they believe that living organisms are more than simply the
14
collective behavior of their physical parts. There is a spirit, soul, or life- force
15
that is the most important part of what life really is. The physical aspects
16
may be important, but they are not at the heart of what we mean by “life.”
17
And if that’s true, it’s unclear why we should care about fine- tuning of
18
physical features of the universe at all. The physical world could behave in
19
any way it pleases; God could still create “life,” and associate it with differ-
20
ent collections of matter in whatever way he might choose. The require-
21
ment that our physical situation be compatible with complex networks of
22
chemical reactions that perpetuate themselves and feed off of free energy in
23
the way we usually associate with living organisms is only relevant if natu-
24
ralism is true. If anything, the fact that our universe does allow for these
25
physical configurations should be taken to increase our credence for natu-
26
ralism at the expense of theism.
27
Any theist worth their salt could, admittedly, come up with a number
28
of reasons why God would choose to associate immaterial souls with com-
29
plex self- sustaining chemical reactions, at least for a time. Likewise, if we
30
lived in a universe where life was not associated with matter in such a way,
31
it wouldn’t be hard to come up with justifications for that. This is the prob-
32
lem with theories that are not well defined.
33
•
34
35S
There is another substantial difficulty for the idea that fine- tuning provides
36N
evidence for theism. Namely, there is more to the laws of nature and the
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configuration of our universe than simply whether or not life can exist. If
01
one wants to claim that theism explains certain features of our universe
02
because we predict that God would want life to exist, we must then ask
03
what other features of the universe we would predict under theism. It is
04
here that theism doesn’t fare so well.
05
Predicting what the universe should look like under theism is difficult,
06
for two reasons. There are many different conceptions of God, all of which
07
are somewhat vague on the specifics of God’s intentions about the con-
08
stants of nature. Furthermore, the fact that we know a lot about what the
09
actual universe does look like tends to color our predictions. It’s an inherent
10
problem with any theory that is formulated using words. Equations provide
11
less freedom to shape predictions in order to match known results.
12
Nevertheless, let’s give it a shot. There are a number of features of the
13
universe that we would probably expect to see if the existence of life (or hu-
14
man beings) was a primary consideration in its design. Let’s highlight three:
15
16
• degree of fine- tuning. If the reason why certain character-
17
istics of the universe seem fine- tuned is because life needs to
18
exist, we would expect them to be sufficiently tuned to allow
19
for life, but there’s no reason for them to be much more tuned
> 20
than that. Vacuum energy actually has this property; it is less
21
than it could be, but big enough to be observable. But other
22
numbers— the entropy of the early universe, for example—
23
seem much more tuned than is necessary for life to exist. Life
24
requires an arrow of time, so there must be some sort of low-
25
entropy early state. But in our universe, the entropy is far
26
lower than it needs to be just to allow for life. From purely
27
anthropic considerations, there is no reason at all for God to
28
have made it that small. We therefore think there is some
29
dynamic, physics- based reason why the entropy started off
30
with the fine- tuned value it did. And once we allow for that
31
possibility, other purported fine- tunings may have similar
32
physical explanations.
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• Messiness of observed physics. If the laws of physics were
S35
chosen so that life could exist, we would expect that each of
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the various features of those laws would play some important
02
role in the unfolding of life. What we see, on the contrary, is
03
something of a mess. All living beings are made out of the
04
lightest generation of fermions— the electron and the up and
05
down quarks, with occasional appearances from electron
06
neutrinos. But there are two heavier families of particles,
07
which don’t play any part in life. Why did God make the top
08
and bottom quarks, for example, and why do they have the
09
masses they do? Under naturalism we would expect a variety
10
of particles, some of which are important to life and some of
11
which are not. That’s exactly what we do observe.
12
13
• Centrality of life. If the eventual appearance of life were an
14
important consideration for God when he was designing the
15
universe, it is hard to understand why life seems so unim-
16
portant in the final product. We live in a galaxy with more
17
than 100 billion stars, in a universe with more than 100 bil-
18
lion galaxies. All of this splendor is completely superfluous,
19
as far as life is concerned. Nothing about biology here on
20
Earth would be noticeably different if we lived in a universe
21
with just our solar system and maybe a few thousand sur-
22
rounding planets. Perhaps we could throw in the rest of our
23
galaxy just to be generous. But the billions of galaxies that we
24
can barely detect in our most powerful telescopes play no
25
part in our existence. As far as physics and biology are con-
26
cerned, the universe could easily have consisted of a relatively
27
small number of particles that came together to make a few
28
stars, and that would be enough to provide a comfortable en-
29
vironment for human life. Theism predicts that most other
30
stars and galaxies shouldn’t be there at all.
31
32
If life were important to God, our existence here on Earth would seem
33
like a bigger deal, cosmically speaking. One possible response is to say, “God
34
is inscrutable; we have no idea what kind of universe he would design.”
35S
That’s a plausible position, but it’s not quite fair in this context. The essence
36N
of the fine- tuning argument is that we do know something about the
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universe God would design: one with physical laws that allow for the emer-
01
gence of the complex chemical reactions we know as living organisms. It’s
02
illegitimate to claim that we know that, but nothing further about what
03
God would do. A theory gets credit for explaining features of the world
04
only to the extent that it goes out on a limb and makes predictions for what
05
the world should be like.
06
A somewhat better response is to put forward some positive theory for
07
why God would want the universe to look the way it does, in particular why
08
it seems so wildly extravagant, with all of those stars and galaxies and what-
09
not. Typically such theories end up positing some physical reason for why
10
it is simpler or easier for God to make many galaxies rather than just one.
11
Maybe God likes inflation and the multiverse.
12
There are a few problems here. First, it’s not true; there’s nothing in the
13
laws of physics that gets in the way of a more compact and focused universe
14
than the one we see around us. Second, one would have to invent a reason
15
why God prefers to make easy universes rather than to exert himself a bit.
16
And third, you can see the road this takes us down: in the course of explain-
17
ing why God would want to make a universe like the one we see, we end up
18
removing his special influence from it, and falling back on purely physical
19
mechanisms. If it’s so easy to make a universe like the one we see, why rely
20
on God at all?
21
Our theories are inevitably influenced by what we already know about
22
the world. To get a more fair view of what theism would naturally predict,
23
we can simply look at what it did predict, before we made modern astro-
24
nomical observations. The answer is: nothing like what we actually observe.
25
Prescientific cosmologies tended to resemble the Hebrew conception illus-
26
trated in chapter 6, with Earth and humanity sitting at a special place in the
27
cosmos. Nobody was able to use the idea of God to predict a vast space with
28
hundreds of billions of stars and galaxies, scattered almost uniformly
29
through the observable universe. Perhaps the closest was Giordano Bruno,
30
who talked about an infinite cosmos among his many other heresies. He
31
was burned at the stake.
32
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P A R t F I v E
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t hI n K I ng
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Crawling into Consciousness
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A
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lmost 400 million years ago, a plucky little fish climbed onto land
12
and decided to hang out rather than returning to the sea. Its
13
descendants evolved into the species Tiktaalik roseae, fossils of
14
which were first discovered in 2004 in the Canadian Arctic. If you were
15
ever looking for a missing link between two major evolutionary stages, Tik-
16
taalik is it; these adorable creatures represent a transitional form between
17
water- based and land- based animal life.
18
One can’t help but wonder— what were they thinking about, those first
19
land- dwelling animals?
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A reconstruction of Tiktaalik roseae, crawling onto land. (Illustration by Zina Deretsky, S35
courtesy of the National Science Foundation)
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We don’t know, but we can make some reasonable guesses. As far as
02
stimulating new avenues of thought is concerned, the most important fea-
03
ture of their new environment was simply the ability to see a lot farther. If
04
you’ve spent much time swimming or diving, you know that you can’t see
05
as far underwater as you can in air. The attenuation length— the distance
The Big Picture Page 53