according to which God always acts in the best possible way, including
02
in the creation of the world. This is only a persuasive argument if we ac-
03
cept the new principle as truly inescapable, which is rarely the case for
04
people who were skeptical of the Principle of Sufficient Reason in the first
05
place.
06
The other possible angle is to claim that something like the Principle of
07
Sufficient Reason is inherent in the very act of logical thinking itself, that
08
rationality is implicitly committed to it. Imagine, for example, that you
09
went to take a shower one day, only to find that there was an accordion sit-
10
ting in your bathtub. It would be hard for you not to think that there must
11
be some reason why the accordion was there. It probably didn’t just happen.
12
Similarly, so this line of thought goes, for every fact we notice about the
13
universe: as soon as we apprehend it, we think there must be a reason be-
14
hind it.
15
This isn’t an argument that the Principle of Sufficient Reason is logically
16
incontrovertible; it only implies that we often act as if something like it
17
were true. If we’re honest, it’s an empirical, evidence- based argument, not
18
an a priori one. We’re not used to seeing accordions appear without good
19
reason, as a matter of empirical fact; but we could certainly imagine a world
20
in which they did so.
21
Metaphysical principles are tempting shortcuts but not reliable guides.
22
There are good reasons why things often seem to happen for reasons— and
23
also reasons why that’s not a bedrock principle.
24
•
25
26
It may seem strange to suggest, on the one hand, that we live in a Laplacian
27
universe where one moment follows directly from the next in accordance
28
with unbreakable laws of physics, and on the other hand that there are facts
29
that don’t have any reasons to explain them. Can’t we always give a reason
30
for what happens, namely “the laws of physics and the prior configuration
31
of the universe”?
32
That depends on what we mean by a “reason.” It’s important to first
33
distinguish between two kinds of “facts” we might want to explain. There
34
are things that happen— that is, states of the universe (or parts thereof) at 35S
specific moments in time. And then there are features of the universe, such
36N
42
Big Picture - UK final proofs.indd 42
20/07/2016 10:02:39
R E A S O n S W h y
as the laws of physics themselves. The kinds of reasons that would suffice to
01
explain one have a different character from the other.
02
When it comes to “things that happen,” what we mean by a “reason” is
03
essentially the same as what we mean when we refer to the “cause” of an
04
event. And yes, we are free to say that events are explained or caused by “the
05
laws of physics and the prior configuration of the universe.” That’s true even
06
in quantum mechanics, which is itself sometimes erroneously offered up as
07
an example of things (like the decay of an atomic nucleus) happening with-
08
out reasons. If that’s what one is looking for in a reason, the laws of physics
09
do indeed provide it. Not as some metaphysical principle but as an ob-
10
served pattern in our universe.
11
However, that isn’t really what people have in mind when they’re search-
12
ing for reasons. If someone asks “Why did that tragic shooting occur?” or
13
“Why is the average temperature of the Earth’s atmosphere rising so rap-
14
idly?” answering with “Because of the laws of physics and the prior configu-
15
ration of the universe” isn’t going to be satisfying. What we are really after
16
is some identifiable aspect of the configuration of the universe without
17
which the event in question would not have occurred.
18
The laws themselves, as we’ve discussed, make no reference to “reasons”
19
or “causes.” They are simply patterns that connect what happens at different
20
places and times. Nevertheless, the concept of a “reason why” something is
21
true is a very useful one in our daily lives. Any sensible poetic naturalist
22
would judge it to be a helpful part of an accurate way of talking about a
23
certain part of the universe. Indeed, we talked that way in the very first
24
paragraph of this chapter.
25
What we might want to ask is: “What is the reason why it makes sense
26
to talk about ‘reasons why’?” And there’s a good answer, namely: because of
27
the arrow of time.
28
The observable universe around us isn’t just an arbitrary collection of
29
stuff obeying the laws of physics— it’s stuff that starts out in a very particu-
30
lar kind of arrangement, and obeys the laws of physics thereafter. By “starts
31
out” we are referring to conditions near the Big Bang, a moment about 14
32
billion years ago. We don’t know whether the Big Bang was the actual be-
33
ginning of time, but it was a moment in time beyond which we can’t see any
34
further into the past, so it’s the beginning of our observable part of the
S35
N36
43
Big Picture - UK final proofs.indd 43
20/07/2016 10:02:39
T H E B IG PIC T U R E
01
cosmos. The particular kind of arrangement the universe was in at that time
02
is one with a very low entropy— the scientific way of measuring disorderli-
03
ness or randomness of a system. Entropy used to be very low, and has been
04
growing ever since— which is to say our observable universe used to be in a
05
specific, orderly arrangement, and has been becoming more disorderly for
06
14 billion years.
07
It’s that tendency for entropy to increase that is responsible for the exis-
08
tence of time’s arrow. It’s easy to break eggs, and hard to unbreak them;
09
cream and coffee mix together, but don’t unmix; we were all born young,
10
and gradually grow older; we reme
mber what happened yesterday, but we
11
don’t remember what will happen tomorrow. Most of all, what causes an
12
event must precede the event, not come afterward.
13
Just as there is no reference to “causes” in the fundamental laws of phys-
14
ics, there isn’t an arrow of time, either. The laws treat the past and future on
15
an equal footing. But the usefulness of our everyday language of explana-
16
tion and causation is intimately tied to time’s arrow. Without it, those
17
terms wouldn’t be a useful way of talking about the universe at all.
18
We’ll see how our convictions that things happen for reasons, and ef-
19
fects follow causes, are not bedrock principles. They arise because of a con-
20
tingent feature of how matter is evolving in our local universe. There is a
21
close connection between cosmology, on the one hand, and knowledge, on 22
the other. Understanding our universe helps us perceive why we are so con-
23
vinced that things happen for reasons.
24
The “reasons” and “causes” why things happen, in other words, aren’t
25
fundamental; they are emergent. We need to dig in to the actual history of
26
the universe to see why these concepts have emerged.
27
•
28
29
An obvious place where it’s tempting to look for reasons why is the question
30
of why various features of the universe take the form that they do. Why was
31
the entropy low near the Big Bang? Why are there three dimensions of
32
space? Why is the proton almost 2,000 times heavier than the electron?
33
Why does the universe exist at all?
34
These are very different questions from “Why is there an accordion in
35S
my bathtub?” We’re no longer asking about occurrences, so “Because of the
36N
laws of physics and the prior configuration of the universe” isn’t a good
4 4
Big Picture - UK final proofs.indd 44
20/07/2016 10:02:39
R E A S O n S W h y
answer. Now we’re trying to figure out why the fundamental fabric of real-
01
ity is one way rather than some other way.
02
The secret here is to accept that such questions may or may not have
03
answers. We have every right to ask them, but we have no right at all to
04
demand an answer that will satisfy us. We have to be open to the possibility
05
that they are brute facts, and that’s just how things are.
06
These kinds of “Why?” questions don’t exist in a vacuum. They make
07
sense in some particular kind of context. If we ask “Why is there an accor-
08
dion in my bathtub?” and someone answers “Because space is three-
09
dimensional,” we aren’t going to be happy— even if it’s arguably true that
10
the accordion wouldn’t have been in there if space were only two-
11
dimensional. We ask the question in the context of a world where there are
12
things called accordions, which tend to appear in some places and not oth-
13
ers, and that there is something called your bathtub, in which certain things
14
regularly appear and others do not. Part of that context might be that you
15
have a roommate who had some friends over last night, and they had too
16
much to drink, and one of them brought along an accordion, and she
17
wouldn’t stop playing it, and ultimately the decision was made to hide it
18
from her. It’s only within that kind of context that we can hope for answers
19
to such “Why?” questions.
20
But the universe, and the laws of physics, aren’t embedded in any bigger
21
context, as far as we know. They might be— we should be open- minded
22
about the possibility of something outside our physical universe, whether
23
it’s a nonphysical reality or something more mundane, like an ensemble of
24
universes that make up a multiverse. In that context we could start asking
25
questions about what kinds of universes are “natural” or easy to create, and
26
possibly discover an explanation for the particular features we observe. Al-
27
ternatively, we could discover reasons why the laws of physics themselves
28
necessitate that something we thought was arbitrary (like the masses of the
29
proton and the electron) can actually be derived from a deeper principle.
30
Then, in a different way, we would be able to pat ourselves on the back for
31
having explained something.
32
What we can’t do is demand that the universe scratch our explanatory
33
itches. Curiosity is a virtue, and it’s good to look for answers to “Why?”
34
questions whenever we might be able to find them, or when we think that
S35
asking such questions might help us to understand things better. But we
N36
45
Big Picture - UK final proofs.indd 45
20/07/2016 10:02:39
T H E B IG PIC T U R E
01
should be at peace with the possibility that, for some questions, the answer
02
doesn’t go any deeper than “That’s what it is.” We’re not used to that— our
03
intuition assures us that every event can be explained in terms of some rea-
04
son why. To understand why we have that impression, we need to dig more
05
deeply into how our actual universe has evolved.
06
07
08
09
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35S
36N
46
Big Picture - UK final proofs.indd 46
20/07/2016 10:02:39
01
02
6
03
04
Our Universe
05
06
07
08
09
10
11
12
13
14
n
15
othing puts human existence into context quite like contemplat-
16
i
ng the cosmos. What you might not guess, sitting comfortably in
17
your living room with a glass of wine and a good book, is that
18
what’s happening in your immediate neighborhood is dramatically affected
19
by the evolution of the whole universe. Many of the most important fea-
20
tures of our lives here on Earth— our notion of the passage of time, the
21
existence of causes and effects, our memories of the past, and freedom to
22
make choices about the future— are ultimately consequences of conditions
23
near the Big Bang. To get ahold of the big picture, we need to put ourselves
24
in cosmological context.
25
It’s hard not to be moved when looking at the night sky. In true darkness,
26
far away from the all- pervasive lights of human civilization, the inky- black
27
background comes alive with thousands of stars, a handful of planets, and
28
the majestic sweep of the Milky Way galaxy stretching from one horizon to
29
the other. It’s also hard to grasp the true extent of the universe on the basis
30
of what we see when we look at the sky. There is no sense of scale, no famil-
31
iar landmarks by which to judge size and separation. The stars bear a close
32
resemblance to the planets, even though we now know they are quite dif-
33
ferent; they look nothing like the sun, although we now know they are very
34
similar.
S35
N36
47
Big Picture - UK final proofs.indd 47
20/07/2016 10:02:39
T H E B IG PIC T U R E
01
02
03
04
05
06
07
08
09
10
11
12
13
14
15
16
An ancient Hebrew cosmology.
17
(Illustration by George L. Robinson)
18
19
20
It’s not surprising that ancient cosmologists, when theorizing about the
21
universe, took as its fulcrum the thing they understood the best: them-
22
selves. Cultures scattered throughout history have devised a number of
23
imaginative cosmological scenarios, and they tended to share a common
24
conviction that our home, the Earth, was somehow special. Sometimes
25
Earth was at the center of it all, sometimes it was at the bottom, very often
26
it held particular significance for whatever force or god was responsible for
27
creation. One way or another, there was a shared belief that we mattered in
28
the greater scheme of things.
The Big Picture Page 8