Today, Schrödinger's Cat changes our view of
science. The University of Houston's College of
Engineering presents this series about the machines
that make our civilization run, and the people
whose ingenuity created them.
Philosopher Abner Shimony
makes a puzzling remark. He says:
Physical systems cannot be said to have definite
properties independent of our observations.
Does he mean we give our world existence
by looking at it? That sounds like a paranoid
delusion, but Shimony is quite sane. He's explaining
Shrödinger's Cat, a creature born in the
strange new thinking of quantum mechanics.
The riddle of the cat begins with Heisenberg's
Uncertainty idea: the most precise measurement we
could ever make would be to shoot one photon of
light at a moving object. But even so delicate a
peek will change the position and motion we're
trying to measure. At best, you always measure with
That's easy enough to understand. But an awesome
subtlety turns it into a new tenet of scientific
faith. It makes precise measurement unthinkable.
And that means we no longer have reason for
thinking the world has any ultimate precision to
So we take the last terrible step. We admit the
world is indeterminate. We admit that electrons
have fuzzy edges. When one collides, it may bounce
one way. It may bounce the other.
Schrödinger said that if that's the case,
let's seal a cat, a geiger counter, a fragment of
radioactive material, and a bottle of poison gas
into a box for one hour. There's a 50-50 chance
that radioactive decay will trigger the geiger
counter, activate a mechanism that breaks the
bottle, and poison the cat. He asks if we'll find a
live cat or a dead one when we open the box.
That sounds like the "Lady or the Tiger," but it's
much worse. The man who has to open either of two
doors knows a lady is behind one and a killer tiger
behind the other. He doesn't know which door leads
to the tiger, but the answer is knowable.
Radioactive decay occurs on the level of
indeterminancy. No knowledge of the system inside
the box will ever let you predict the fate of
Schrödinger's Cat. Whether it lives or dies is
absolutely unknowable -- until you open the box.
Physicists agonize while that Cheshire cat sits and
smiles. They try to write wave functions for cats
and gamma radiation. They conclude goofy things:
maybe the cat in the unopened box is both alive and
dead at the same time. Steven Hawking, the
physicist who writes about black holes from his
wheelchair, throws up his hands and cries: "When I
hear of Schrödinger's cat, I reach for my
But in the end we have to look inside the box to
learn whether the cat is alive or dead. So it is
that the observer determines the the truth. This
makes an odd commentary on objective science. We're
left to wonder if scientists aren't far more deeply
interwoven with the world they observe than they
would like to be.
I'm John Lienhard, at the University of Houston,
where we're interested in the way inventive minds