From the dawn of the human species until a time within the
memory of many people younger than I, the origin of the universe
was the subject of myth and a topic, if discussed at all within
the academy, among doctors of divinity, not professors of physics.
The advent of precision cosmology has changed that: the
ultimate questions of origin are not only legitimate areas of
research, but something probed by
satellites in space,
balloons circling the South Pole,
and
mega-projects of
Big Science. The results of these experiments have, in the last
few decades, converged upon a consensus from which few professional
cosmologists would dissent:
- At the largest scale, the geometry of the universe
is indistinguishable from Euclidean (flat), and the
distribution of matter and energy within it is
homogeneous and isotropic.
- The universe evolved from an extremely hot, dense, phase
starting about 13.7 billion years ago from our point of
observation, which resulted in the abundances of light
elements observed today.
- The evidence of this event is imprinted on the cosmic
background radiation which can presently be observed in
the microwave frequency band. All large-scale structures in
the universe grew from gravitational amplification of
scale-independent quantum fluctuations in density.
- The flatness, homogeneity, and isotropy of the universe is
best explained by a period of inflation shortly after
the origin of the universe, which expanded a tiny region of
space, smaller than a subatomic particle, to a volume much greater
than the presently observable universe.
- Consequently, the universe we can observe today is bounded
by a horizon, about forty billion light years
away in every direction (greater than the 13.7 billion light
years you might expect since the universe has been expanding
since its origin), but the universe is much, much larger than what
we can see; every year another light year
comes into view in every direction.
Now, this may seem mind-boggling enough, but from these premises, which
it must be understood are accepted by most experts who study the
origin of the universe, one can deduce some disturbing
consequences which seem to be logically unavoidable.
Let me walk you through it here. We assume the universe
is infinite and unbounded, which is the best
estimate from precision cosmology. Then, within that universe, there
will be an infinite number of observable regions, which we'll call
O-regions, each defined by the volume from which an observer at the
centre can have received light since the origin of the
universe. Now, each O-region has a finite volume, and
quantum
mechanics tells us that within a finite volume there are a finite
number of possible quantum states. This number, although huge (on the
order of 1010123 for a region the size of
the one we presently inhabit), is not infinite, so
consequently, with an infinite number of O-regions, even if quantum
mechanics specifies the initial conditions of every O-region
completely at random and they evolve randomly with every quantum event
thereafter, there are only a finite number of histories they can
experience (around 1010150). Which means
that, at this moment, in this universe (albeit not within our current
observational horizon), invoking nothing as fuzzy, weird, or
speculative as the multiple world interpretation of quantum mechanics,
there are an infinite number of you reading these words scribbled by
an infinite number of me. In the vast majority of our shared
universes things continue much the same, but from time to time they
d1v3r93 r4ndtx#e~—….
Reset . . .
Snap back to universe of origin . . .
Reloading initial vacuum parameters . . .
Restoring simulation . . .
Resuming from checkpoint.
What was that? Nothing, I guess. Still, odd, that blip you
feel occasionally. Anyway, here is a completely fascinating book by a
physicist and cosmologist who is pioneering the ragged edge of what
the hard evidence from the cosmos seems to be telling us about the
apparently boundless universe we inhabit. What is remarkable about
this model is how generic it is. If you accept the best currently available
evidence for the geometry and composition of the universe in the large,
and agree with the majority of scientists who study such matters how it
came to be that way, then an infinite cosmos filled with observable
regions of finite size and consequently limited diversity more or less
follows inevitably, however weird it may seem to think of an infinity of
yourself experiencing every possible history somewhere.
Further, in an infinite universe, there are an infinite number of
O-regions which contain every possible history consistent
with the laws of quantum mechanics and the symmetries of our spacetime
including those in which, as the author noted, perhaps using the
phrase for the first time in the august pages of the
Physical Review,
“Elvis is still alive”.
So generic is the prediction, there's no need to assume the
correctness of speculative ideas in physics. The author provides
a lukewarm endorsement of string theory and the “anthropic
landscape” model, but is clear to distinguish its “multiverse”
of distinct vacua with different moduli from our infinite universe with
(as far as we know) a single, possibly evolving, vacuum state.
But string theory could be completely wrong and the deductions
from observational cosmology would still stand. For that matter,
they are independent of the “eternal inflation” model
the book describes in detail, since they rely only upon observables
within the horizon of our single “pocket universe”.
Although the evolution of the universe from shortly after the end
of inflation (the moment we call the “big bang”) seems
to be well understood, there are still deep mysteries associated
with the moment of origin, and the ultimate fate of the universe
remains an enigma. These questions are discussed in detail, and
the author makes clear how speculative and tentative any discussion
of such matters must be given our present state of knowledge. But
we are uniquely fortunate to be living in the first time in all of history
when these profound questions upon which humans have mused since
antiquity have become topics of observational and experimental science,
and a number of experiments now underway and expected in the next
few years which bear upon them are described.
Curiously, the author consistently uses the word “google” for
the number 10100. The correct name for this quantity,
coined in 1938 by nine-year-old Milton Sirotta,
is “googol”.
Edward Kasner, young Milton's uncle, then defined
“googolplex”
as 1010100. “Google™” is
an Internet search engine created by megalomaniac collectivists bent
on monetising, without compensation, content created by others. The
text is complemented by a number of delightful cartoons reminiscent of
those penned by George Gamow, a physicist the author (and this reader)
much admires.