The Quantum Structure of Space and Time (293 pages)

Cosmology 241

remind, as Galison very nicely talked about in the first talk in this conference,

and Polchinski was mentioning as well, that the issue of how much we get to

predict is really not up to us. The angst over not having one world or maybe
worlds pales in comparison to the angst that the Laplacian determinists
must have felt when they were told that they could not predict the position and
velocity of every particle deep into the future from measuring the positions and
velocities of every particle now. We are talking about a far less drastic reduc-
tion in the degree of predictivity than was already suffered in this transition
from classical to quantum mechanics.
Finally I just want to make a concrete point when we talk about the cosmological

constant as the “central engine” that is motivating us to think about all of

these issues. It is really true that throughout particle physics, and other parts

of cosmology, there are, at a much smaller and less dramatic level, but certainly

present, many little tunings like this on which the existence of interesting atoms,

more complex structures, stars etc., really critically depend. And if you really

believe that there is a unique theory, and a unique vacuum, then you really

believe that there is a formula involving pure numbers that sets each and every

one of those constants. And in such a situation it would really be shocking that

so many of them ended up having just the right values that they had to have

in order to allow us to exist.

I can just make one last comment. The situation is a lot like in biology. Not

everything is selected for. Some things are the way they are because they

are selected for, some things are the way they are because they cannot be

any other way. It is the analog of environmental selection versus symmetries

and dynamics, and one of the characteristics of biological creatures is that

somethings are exquisitely designed, and other things are just sort of random,

and the standard model looks a lot like that. There are some things that are

exquisitely adjusted like the vacuum energy, there are all these irrelevant things

like the third generation, Vcb, and the bottom quark mass which may just be

incidental things that came along for the ride, correlated with other things that

happened to be selected for. I think we would all agree that if this was not the

picture of the world, we would have an easier job. But it does not strike me

as a particularly awkward thing, and certainly not worse than the classical to

quantum transition, at least as the issue of predictivity is concerned.