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03/26/2008
Peering into the Past and the Future
Last week I discussed my roots extending back some 50
thousand years to my first male ancestor in Africa, as revealed in
an analysis of my DNA as part of National Geographic’s
Genographic project. That seems like a long period of time but
it’s insignificant compared to the time frames considered in two
articles I read recently. One article asks the question, what
happened before the Big Bang, some 13.7 billion years ago? (I
saw recently that the age of the universe has been pinned down
more precisely recently to within an uncertainty of only plus or
minus some 120 million years.) One obvious answer to that
question is – nothing! However, there are other alternatives, one
of which can actually be tested, at least according to some
theorists.
We’ve talked before about the other end of the scale, namely
what is our fate in the far distant future, not just billions, but
trillions of years hence? The other article looks at the question
from the standpoint of an astronomer of the far distant future and
suggests that we live in a golden age for astronomers. Will
astronomers in the future have no idea of the nature and origin of
our universe? This is the question posed by cosmologists
Lawrence Kraus and Robert Scherrer in their article titled “The
End of Cosmology?” in the March 2008 Scientific American.
They conclude that we may be living in the only epoch in the
history of our universe when we can truly understand the actual
nature of our universe.
It has only been within the past hundred years or so that we
became aware of the billions of stars and galaxies outside our
own Milky Way. It wasn’t until the 1920s that we learned that
the universe is expanding, implying that there might have been a
Big Bang at the beginning of the universe. It was less than 50
years ago that Bell Labs scientists Penzias and Wilson
discovered the cosmic microwave background that helped nail
down the Big Bang. Chemically, the Big Bang after only three
minutes had produced hydrogen and helium, the prime
constituents of the universe even today. And, within the last
decade, astronomers discovered that the rate of expansion of the
universe is actually speeding up, thanks to some mysterious form
of “dark energy”. Now we know that most of the universe is
composed of dark energy and dark matter with only a small
percentage of the stuff we’re made of and understand.
With all this knowledge and fantastic telescopes and other
sensors and brilliant scientists, we know the origin of the
universe in the Big Bang; we know its age and its composition.
We know what powers the nuclear engines in stars and we’re
even finding planets around other stars in our galaxy. It’s a great
time to be an astronomer!
But Kraus and Scherrer are looking into the distant future,
especially into the future when there may be astronomers, if not
on Earth, on other planets. With the rapidly expanding universe,
except for galaxy clusters, the galaxies in the universe are
growing farther and farther apart. In our case, as I’ve noted on
occasion before, we in the Milky Way galaxy are going to collide
with Andromeda a few billion years hence. Five billion years
from now, Andromeda will nearly fill the sky but nobody on
earth will see it. By that time the Sun will have become or will
have been a red giant and Earth will probably be no more.
After we meet Andromeda, the merger will create another
galaxy, probably ball-like in shape and a hundred billion years
from now our galaxy will be floating alone in the sky. With the
expanding universe, all the other galaxies will have faded from
view. There will still be stars and, possibly, planets like our own
with living creatures, possibly even astronomers. This is where
the end of cosmology comes in.
As far as these distant astronomers are concerned, all they see is
their own galaxy with just a bunch of stars. The cosmic
background will have faded to undetectability and, unlike today,
the amounts of helium and hydrogen will be vastly different from
what they are today. These astronomers will have no idea of the
true nature of the universe – unless somehow records of earlier
times such as our own survive and get passed to these new and
different societies, whatever they are. It’s not a likely prospect.
A hundred trillion years from now, all the stars will have burned
out and/or been swallowed up into black holes and the universe
goes black. Eventually the galaxy itself collapses into a
humongous black hole. The End.
In “The Day Before Genesis” in the April 2008 issue of Discover
magazine, Adam Frank discusses three theories dealing with the
question at the other end of the timescale, what caused the Big
Bang? Was there time before the Big Bang? A fellow by the
name of Julian Barbour has an approach that seems really far out.
He suggests essentially that it’s silly to even ask such questions
because time doesn’t exist! Einstein certainly wouldn’t be too
happy with this approach, having made spacetime a concept with
powerful consequences. But Barbour says that each moment is
its own thing that he defines as a “Now”. Put a bunch of Nows
together and you get the illusion of time.
I must admit I have a hard time not accepting time as something
real. Even if there are only a bunch of Nows, inventing
something called time is a great ways to relate one Now to
another and time is certainly a useful concept in predicting in an
infinite number of cases what the next Now will look like!
A second approach to dealing with what happens before the Big
Bang also deals with time. Sean Carroll, a theoretical physicist
at California Institute of Technology, and a graduate student,
Jennifer Chen, also worry about time. They don’t worry about
the beginning of time, but rather about the arrow of time. Why
does time always go forward? Shouldn’t it also be allowed to go
backward or in any direction? Carroll comes up with the concept
of multiverses, not just one universe. With this concept, he says
there can be an infinite amount of space with many “pocket”
universes, some expanding, others condensing into black holes
and evaporating. I don’t pretend to understand it but in this
world, there are an infinite number of universes in infinite space,
much like a foam. As many universes are moving forward in
time as are moving backward.
Finally, the possibility that I find most appealing, if only because
it apparently is a theory that can be tested. This approach
involves string theory, which I make no pretense of
understanding. While the Big Bang itself is very well pinned
down and confirmed, the standard model of the Big Bang
involves an inflationary expansion of space and time, implying
that time didn’t exist before the Big Bang. On the other hand,
string theory itself has yet to be shown to be at all relevant to the
world of relativity and quantum mechanics. The super large
particle smasher, the Large Hadron Collider in Europe, hopefully
comes on board this year and may provide some answers about
string theory.
In the latest elaboration of the theory, branes are the key
ingredients. A brane is short for a membrane, but not your run of
the mill membrane. In this theory our universe is a 3-
dimensional brane moving in a four-dimensional background
called “the bulk”. This “bulk” is full of branes, which very
loosely might be considered analogous to sheets of paper floating
around that can collide. When a brane collides with another
brane, huge amounts of energy are involved and the string
theorists calculate that these energies give rise to just the sort of
explosion as the Big Bang and the results are the same, matter is
formed and stars and galaxies result. As the resulting universe
expands and grows and space is nearly empty, the theory predicts
that the branes would attract each other and collide again,
creating a new universe.
If true, there are cycles and there were and will be lots of Big
Bangs. There was a “before” before our Big Bang! This cyclic
universe theory, if true, apparently predicts that the gravity
waves left over from the Big Bang will have a different shape if
there’s a cyclic universe than if there was just one Bang. The
problem is that we have not yet detected the gravity waves, let
alone their form. Chances are it might be decades before we
finally succeed in detecting and measuring these waves.
Personally, I like the idea of cyclic universes. With an infinite
number of cycles in an infinite amount of space, there might be
another universe where we all will live again. I gather that the
cycles last on the order of a trillion or so years. This seems like a
heck of a long time frame but think of it this way. In my
lifetime, our national budget and/or debt has gone from millions
of dollars to billions of dollars and now to trillions of dollars.
Yet we still remember the saying, “A penny saved is a penny
earned.” What does this have to do with cosmology? Darned if I
know! Down to earth next week.
Allen F. Bortrum
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