The most incomprehensible
thing about this world is that it is comprehensible.
— Albert Einstein
three wishes from Aladdin's lamp or some other magical device,
the hero always makes a disappointing choice: a pile of gold, a castle,
a princess. How selfish! Why not wish for universal health care (or universal
good health)? Or material prosperity for all? Or that everyone could lead
a full and rich life of the mind and the spirit? It may be overstepping
the bounds of politeness to ask so much of the genie of the lamp.
My curiosity is such that, given three lamp-wishes,
I'd be tempted to spend at least one of them on a physics experiment.
What would our world be like if the gravitational constant, which specifies
how strongly each bit of matter is attracted to each other, were ten percent
less? Apparently, in this case, our universe would be destined for infinite
expansion. Would life exist? Would it be very much different? There are
a number of physical constants that seem fine-tuned for life: if they
were changed a little either way, life (at least on earth) wouldn't have
In my Aladdin's-lamp physics experiments,
I wouldn't limit myself to changing constants in existing physical laws.
I could enact new laws of physics and repeal old ones. What would it be
like if I repealed relativity and quantum mechanics and returned to a
universe governed by Newton's laws? Would the people be friendlier? Are
there rules for universe design? Is it difficult to invent a consistent
set of laws of physics? It certainly is difficult to envision the effect
a change in physics would have on the world around us. What we need is
a way to simulate the universe, another sort of Aladdin's lamp.
There is a game called Life, which has simple
rules and yet produces complex and life-like phenomena. A flat playing
surface is divided by a grid into small squares, each of which may contain
a cell or be empty. The player selects an initial pattern of cells, the
first generation, and the rules take over from there, deriving the second-generation
pattern from the first generation. If a square has empty spaces all around,
or just one neighbor cell, it will be empty in the new generation. If
it has 2 neighbors, it stays as it is. If it has 3 neighbors, it will
contain a cell, even if it was empty in the first generation. If a square
has cells in 4 or more neighboring squares, it will be empty. These rules
may be interpreted in a life-like way: cells die from isolation or overcrowding,
cells are born and flourish with moderate population density. Applying
these rules to every square of the first generation gives the second generation.
Applying them to the second gives the third generation, and so on. Generations
are usually calculated by computer, with the playing surface displayed
on the computer screen, several generations per second. The game produces
amazingly complex and lifelike phenomena, starting from very simple initial
I picture our universe as like this game.
The laws of physics are the rules of the game. There was an initial state
at the moment of creation of the universe, 10 to 20 billion years ago.
It's open to conjecture whether there is an interpretive mechanism for
the universe, analogous to the computer and the game-of-life program.
Maybe so, or maybe the universe simply is, a direct implementation of
those physical laws.
There is no way we can ever know the answer
to this question. Imagine that we are playing a game like the game of
Life on a very large playing surface with a very fast computer, and that
we selected just the right rules and initial condition so that, after
the game had been running a long time, a set of sentient beings arose
in the changing patterns of the cells. Imagine that these beings conducted
scientific research and figured out the rules of their game, the size
of the playing surface, and the initial configuration that gave rise to
their universe. As part of their research, they might have constructed
their own games of life, running at a slower speed, with smaller playing
surfaces, simulating their own universe and its “physical”
laws. They would know essentially everything there is to know about themselves
in low-level physical terms; they would have the recipe for their own
creation. They might ask the question that we just asked: is there an
interpretive mechanism that is the substratum for their “physical”
universe? The answer, of course, would be “yes,” and there
is no way they could ever know it.
(If this analogy seems impossibly far-fetched
to you, it may be that you're not a materialist, as I am. I don't believe
in Gods or spirits or life forces or ghosts or anything else that doesn't
follow the laws of physics, whatever they are. I believe that human beings
are complicated mechanisms that have developed out of billions of years
of evolution. I am a materialist because it is the simplest plausible
explanation of the observed facts.)
Could we, in principle, simulate our own
universe on some future souped-up computer? The simulation would start
with the universe's initial condition, and follow every subatomic particle,
every ray of light, every stray electromagnetic field in minute detail,
instant by instant, in all their interactions with one another. It would
require a tremendous amount of computation, many orders of magnitude more
than we get from our present-day machines.
If the universe is deterministic, and if
the initial condition was simple and well enough defined, a complete and
perfect universe simulator running faster than real-time would be like
a time machine, with all its paradoxes. It would allow us to simulate
the past and the future, to make changes and see the consequences —
how the French Revolution would have sorted itself out without Napoleon,
or what life would be like now if Germany had beat us to the finish line
in the race to develop the atomic bomb. This simulator would be an Aladdin's
lamp, allowing us to alter our universe at will and see the results.
The operators of the game, running the simulations
of our universe, would be Gods in their own right. They would be omnipotent,
able to change anything in their universes, even the rules of the game,
at any time. They could create and destroy, punish and reward the beings
in their simulations. They would be omniscient in the sense that the whole
simulated universe, with all its space and time, matter and energy, would
be open for their inspection. They would be omniscient in this sense,
though they wouldn't know any more than you or I. Humans or other beings
in these simulated universes would believe in God if the operators were
constantly and heavy-handedly interfering. Rational beings in universes
without interference would not. There would be no way they could detect
us or our world.
These simulated beings would be as real
as we are. Their world would look the same to them as our does to us.
They would behave as we do, feel as we do, live, die, learn, love, go
to war. The only difference would be that their physical world would be
simulated in our simulation machine, at another level of existence. How
far can this go on? Our physical reality could be, in turn, simulated
by a still higher-level interpretative machine, and so on.
A simulation of our universe, running at
real-time speed or faster would be impossible since the simulation would
have to include the computer running the simulation, since it's part of
the universe. It would take all of the computer's power (and probably
more) just to simulate itself, with none left over for simulating the
rest of the universe. This problem would be avoided if the simulation
ran slower than real-time; this also avoids the paradoxes of time travel
into the future. With our present technology, we are nowhere near this
massive scale of simulation — our fastest computers are inadequate
to simulate the weather on a small part of our little planet.
Another prerequisite for exactly simulating
the universe is perfect knowledge of the laws of physics. Will we ever
know, perfectly and completely, the rules that determine how the material
objects in our universe behave? It seems quite possible. I can imagine
that, with a few key insights and breakthroughs, we come up with a final,
complete, self-consistent theory that explains all the low-level physical
phenomena that we can observe, and that we can reconcile it with cosmology
so that the theory explains how the universe got to be as it is, starting
from a simple initial condition. I can imagine this theory withstanding
the test of time, so that it remains unchanged for a few centuries, and
we come to realize that this is it, we've really learned the rules of
the game, there's no need to do more physics research. I can imagine that
the final and true laws of physics can be written as equations on ten
sheets of paper. There is something paradoxical about the recipe for creating
the universe being so simple when the universe contains such complication.
It would not mean that we understand everything
about everything; we would understand just the physical level of our universe.
We would understand the low-level interactions between the matter and
energy that make up our brain, but wouldn't necessarily know the brain's
chemicals, or how cells are constructed from them, how the cells are organized
into larger structures such as nerves, how these integrate as a thinking
machine, or what makes us conscious.
We may never know all there is to know about
physics. Toward the start of the twentieth century, prominent physicists
were saying that 90% of the work of physics was done, and the other 10%
would involve just cleaning up certain nagging details. This was in the
days when electrons, protons and neutrons were the smallest known particles
(it having been realized that the “atoms” they make up were
not the primitive, indivisible components of matter that the name implies).
This view seems ludicrous now that we've gone on to discover relativity
and quantum mechanics and another level of subatomic particles. It's possible
that this will continue, so that every time we break through to another
level of understanding, we come to realize that there's more, and we still
have only an approximation. Maybe there are an infinite number of rules
in our game. And maybe not.
It would make a big difference for us to
completely understand the physical laws of the universe. Our science has
made us bigger than the earth upon which we grew up, something that was
inconceivable just a thousand years ago. We can now contemplate building
ourselves new places to live, away from the earth. In the same way, knowledge
of physical laws would give us mental mastery over the universe. We would
know the recipe for constructing the universe and our selves, even if
we didn't have the physical means to realize it.
On the other hand, it would increase our
sense of a frustrating circumscription in the universe, a feeling I have
now when I read about cosmology; our universe is made cramped by our dawning
understanding of its limits since our minds can surpass these limits to
imagine something greater, or at least something else. Why is the gravitational
constant not ten percent less? Why do we have this set of physical laws
rather than another? It seems so arbitrary that this can't be all there
is. What is there at a higher level that we can probably never know?