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The Big Bang
wasn't really big. Nor was it really a bang. In fact, the
event that created the universe and everything in it was a
very different kind of phenomenon than most people--or, at
least, most nonphysicists--imagine.
Even the name "Big Bang" originally was a put-down
cooked up by a scientist who didn't like the concept when
it was first put forth. He favored the idea that the universe
had always existed in a much more dignified and fundamentally
unchanging, steady state.
But the name
stuck, and with it has come the completely wrong impression
that the event was like an explosion and that the universe
is expanding today because the objects in it are being flung
apart like fragments of a detonated bomb.
Virtually every
basic aspect of this intuitive image for the Big Bang (we
ARE stuck with the name) is incorrect. To understand why,
you need to understand Albert Einstein's general theory of
relativity. Or, at least, you need to have a sense of it.
That may sound daunting, but general relativity is the most
revolutionary scientific advance of the 20th century, and
we all ought to acquire some feeling for it before the century
ends.
After all, it's
been 82 years since Einstein put forth his theory. It's been
tested in scores of experiments and has always passed with
flying colors and is now firmly established as our premier
guide to understanding how gravity operates. Moreover, it
is part of the foundation of Big Bang cosmology. And it is
because of general relativity that we know the Big Bang was
(and is, for the event is still going on) nothing like an
explosion.
Albert Einstein
developed general relativity in order to make his famous theory
of special relativity include the effects of gravity. It is
a better way than Sir Isaac Newton's of understanding how
gravity works. Like a hungry amoeba, general relativity (
or just GR for short) had absorbed both Einstein's newly-minted
special relativity and Newton's physics, giving us the means
to replicate ALL of the predictions from these two great theories,
while extending them into unfamiliar realms of experience.
One of these realms was the Black Hole. The other was the
shape and evolution of the universe itself.
Big Bang cosmology
says that the universe came into existence between 10 to 20
billion years ago, and that from a hot dense state has been
expanding and cooling ever since, remains unassailable. Yet,
Big Bang cosmology is vulnerable. It is based on GR being
accurate over an enormous range of scales in time and space.
Just how good is general relativity? So far, GR has made the
following specific predictions:
1...The entire
orbit of Mercury rotates because of the curved geometry of
space near the sun. The amount of 'perihelion shift' each
century was well known at the time Einstein provided a complete
explanation for it in 1915.
2...Light at
every frequency can be bent in exactly the same way by gravity.
This was confirmed in the 1919 Solar Eclipse for optical light
using stars near the Sun's limb, and in 1969-1975 using radio
emissions from star-like quasars also seen near the limb of
the Sun. The deflection of the light was exactly as predicted
by GR.
3...Clocks run
slower in strong gravitational fields. This was confirmed
by Robert Pound and George Rebka at Harvard University in
1959, and by Robert Vessot in the 1960's and 70's using high-precession
hydrogen maser clocks flown on jet planes and on satellites.
4...Gravitational
mass and inertial mass are identical. Most recently in 1971,
Vladimir Braginsky at Moskow University confirmed GRs prediction
of this to within 1 part in a trillion of the exact equality
required by GR.
5...Black holes
exist. Although these objects have been suspected to exist
since they were first introduced to astronomers in the early
1970's, it is only in 1992 that a critical acceptance threshold
was crossed in the astronomical community. It was then that
Hubble Space Telescope observations revealed monstrous, billion-sun
black holes in the cores of nearby galaxies such as Messier
87, Messier 33 and NGC 4261.
6...Gravity
has its own form of radiation which can carry energy. Russel
Hulse and Joseph Taylor in 1975 discovered two pulsars orbiting
each other, and through careful monitoring of their precise
pulses during the next 20 years, confirmed that the system
is loosing energy at a rate within 1 percent of the prediction
by GR based on the emission of gravitational radiation.
7...A new force
exists called 'gravito-magnetism'. Just as electric and magnetic
fields are linked together, according to GR, a spinning body
produces a magnetism-like force called gravitomagnetism. GR
predicts that rotating bodies not only bend space and time,
but also make empty space spin. A NASA satellite called Gravity
Probe B will be launched in the next few years to see whether
this effect exists. This is a killer. If it is not found,
GR is mortally wounded despite its long string of other successes.
8...Space can
stretch during the expansion of the universe. This was confirmed
by Edwin Hubble's detection of the recession of the galaxies
ca 1929. More recently in 1993, Astronomer Kenneth Kellerman
confirmed that the angular sizes of distant radio sources
shrink to a minimum then increase at greater distances exactly
as expected for a dilating space. This is not predicted by
any other cosmological model that does not also include the
dilation of space as a real, physical phenomenon.
We have now
boxed ourselves into a corner. If we accept the successes
of GR, we are forced to see the world and the cosmos through
its eyes, and its eyes alone, since it is the theory which
satisfies all known tests to date.
So, how should
we think about the Big Bang? Our mental 'fireworks' image
of the Big Bang contains these basic elements: 1) A pre-existing
sky or space into which the fragments from the explosion are
injected; 2) A pre-existing time we can use to mark when the
explosion happened; 3) Individual projectiles moving through
space from a common center; 4) A definite moment when the
explosion occurred; and 5) Something that started the Big
Bang.
All of these
elements to our visualization of the Big Bang are completely
false according to GR!
Preexisting
Space?
There
wasn't any!
The mathematics
of GR state specifically and unambiguously that 3-dimensional
space was created at the Big Bang itself, at 'Time Zero',
along with everything else. It was a 'singular' event in which
the separations between all particles everywhere, vanished.
This is just another way of saying that our familiar 3-dimensional
space vanished. Theorists studying various prototypes for
the Theory of Everything have only modified this statement
somewhat. During its earliest moments, the universe may have
existed in a nearly incomprehensible state which may have
had more than 4 dimensions, or perhaps none at all. Many of
these theories of the earliest moments hypothesize a 'mother
space-time' that begat our own universe, but you cannot at
the same time place your minds eye both inside this Mother
Spacetime to watch the Big Bang happen, and inside our universe
to see the matter flying around. This is exactly what the
fireworks display model demands that you do.
Preexisting
Time?
There
wasn't any of this either!
Again, GR's
mathematics treats both space and time together as one object
called 'space-time' which is indivisible. At Time Zero plus
a moment, you had a well defined quantity called time. At
Time Zero minus a moment, this same quantity changed its character
in the mathematics and became 'imaginary'. This is a mathematical
warning flag that something dreadfully unexpected has happened
to time as we know it. In a famous quote by Einstein, "...time
and space are modes by which we think and not conditions in
which we live". Steven Hawking has looked at the mathematics
of this state using the fledgling physics of Quantum Gravity
Theory, and confirms that at the Big Bang, time was murdered
in the most thorough way imaginable. It may have been converted
into just another 'timeless' dimension of space...or so the
mathematics seems to suggest.
Individual
objects moving out from a common center?
Nope!
GR says specifically
that space is not a passive stage upon which matter plays
out its dance, but is a member of the cast. When you treat
both galaxies and space-time together, you get a very different
answer for what happens than if you treat them separately,
which is what we instinctively always do. Curved space distorts
the paths of particles, sometimes in very dramatic ways. If
you stepped into a space ship and tried to travel to the edge
of the universe and look beyond, it would be impossible. Not
only could you not reach a supposed "edge" of the
universe no matter how long or how fast you traveled, in a
closed universe, you would eventually find yourself arriving
where you departed. The curvature of space would bring you
right back, in something like the way the curvature of Earth
would bring you home if you flew west and never changed course.
In other words, the universe has no edge in space. There is
nothing beyond the farthest star.
As a mental
anchor, many have used the expanding balloon as an analogy
to the expanding universe. As seen from any one spot on the
balloon's surface, all other spots rush away from it as the
balloon is inflated. There is no one center to the expansion
ON THE SURFACE of the balloon that is singled out as the center
of the Big Bang. This is very different than the fireworks
display which does have a dramatic, common center to the expanding
cloud of cinders. The balloon analogy, however, is not perfect,
because as we watch the balloon, our vantage point is still
within a preexisting larger arena which GR says never existed
for the real universe.
The center of
the Big Bang was not a point in space, but a point in time!
It is a center, not in the fabric of the balloon, but outside
it along the 4th dimension...time. We cannot see this point
anywhere we look inside the space of our universe out towards
the distant galaxies. You can't see time afterall! We can
only see it as we look back in time at the ancient images
we get from the most distant objects we can observe. We see
a greatly changed, early history of the universe in these
images but no unique center to them in space.
It is at this
point that common sense must give up its seat on the bus,
and yield to the insights provided by GR. And it is at precisely
this point that so many non-physicists refuse to be so courteous.
And who can blame them? But there's more to come.
Projectiles
moving through space?
Sorry!
GR again has
something very troubling to say about this. For millions of
years we have learned from experience on the savanas of the
African continent and elsewhere, that we can move through
space. As we drive down the highway, we have absolutely no
doubts what is happening as we traverse the distance between
landmarks along the roadside. This knowledge is so primal
that we are incapable of mustering much doubt about it. But
science is not about confirming our prejudices. It's about
revealing how things actually are.
What if I told
you that you could decrease the distance from your house and
the Washington Monument by 'standing still' and just letting
space contract the distance away? GR predicts exactly this
new phenomenon, and the universe seems to be the only arena
we know today in which it naturally occurs. Like spots glued
to the surface of the balloon at eternally fixed latitude
and longitude points, the galaxies remain where they are while
space dilates between them with the passage of time. There
is no reason at all we should find this kind of motion intuitive.
If space is
stretching like this, where do the brand new millions of cubic
light years come from, from one moment to the next? The answer
in GR is that they have always been there. To see how this
could happen, I like to think of the shape of our universe
as a "Cosmic Watermellon". The fact that this is
only the shape for a 'closed' finite universe is only a technicality.
Finite watermellons are also cheaper to buy than infinite
ones.
GR predicts
the entire past, present and future of the universe all at
once, and predicts its entire 4-dimensional shape. As we slice
the 4-dimensional, Cosmic Watermellon at one end of the cosmic
time line, we see 3-dimensional space and its contents soon
after the Big Bang. At the other end of the Cosmic Watermellon
in the far future, we see the collapse of space and matter
just before the Big Crunch. But in between, our slices show
the shape of space (closed, spherical volumes) and the locations
of galaxies ( at fixed locations) as space dilates from one
extreme to the other.
As a particular
slice through an ordinary watermellon, we see that its meat
has always been present in the complete watermellon. The meat
is present as a continuous medium, and we never ask where
the meat in a particular slice came from. Cosmologically,
GR ask us to please think of 3-dimensional space in the same
way. Space, like the meat of the watermellon, has always existed
in the complete shape of the universe in 4-dimensions. But
it is only in 4-dimensions that the full shape of the universe
is revealed. It is a mystery why our consciousness insists
on experiencing the universe one moment at a time, and that
is why we end up with the paradox of where space comes from.
There really is no paradox at all.
Space is not
'nothing' according to Einstein, it is merely another name
for the gravitational field of the universe. Einstein once
said, "Space-time does not claim existence on its own
but only as a structural quality of the [gravitational] field".
If you could experimentally turn-off gravity with a switch,
space-time would vanish. This is the ultimate demolition experiment
known to physics for which an environmental impact statement
would most certainly have to be filed.
The gravitational
field at one instant is wedded to itself in the next instant
by the incessant quantum churnings of the myriad of individual
particles that like bees in a swarm, make up the gravitational
field itself. In this frothing tumult, the gravitational field
is knit together, quantum by quantum, from perhaps even more
elemental building blocks, and it is perhaps here that we
will find the ultimate origin for the expansion of the universe
and the magical stretching of space. We hope the much anticipated
Theory of Everything will have more to say about this, but
to actually test this theory may require technologies and
human resources that we can only dimly dream of.
Was
there a definite moment to the Big Bang?
GR is perfectly
happy to forecast that our universe emerged from an infinite
density, zero-space 'Singularity' at Time Zero, but physicists
now feel very strongly that this instant was smeared out by
any number of quantum mechanical effects, so that we can never
speak of a time before about 10^-43 seconds after the Big
Bang. Just as Gertrude Stein once remarked about my hometown,
Oakland, California that "There is no 'There' there",
at 10^-43 seconds, nature may tell us that before the Big
Bang, "There was no 'When' there" either. The moment
dissolves away into some weird quantum fog, and as Steven
Hawking speculates, time may actually become bent into a new
dimension of space and no longer even definable in this state.
Ordinary GR is unable to describe this condition and only
some future theory combing GR and quantum mechanics will be
able to tell us more. We hope.
Something
started the Big Bang!
At last we come
to the most difficult issue in modern cosmology. In the fireworks
display, we can trace the events leading up to the explosion
all the way back to the chemists that created the gunpowder
and wrapped the explosives. GR, however, can tell us nothing
about the equivalent stages leading up to the Big Bang, and
in fact, among its strongest statements is the one that says
that time itself may not have existed. How, then, do we speak
or think about a condition, or process, that started the whole
shebang if we are not even allowed to frame the event as "This
happened first...then this...then kerpowie!"? This remains
the essential mystery of the Big Bang which seems to doggedly
transcend every mathematical description we can create to
describe it.
All of the logical
frameworks we know about are based on chains of events or
states. All of our experiences of such chains in the physical
world have been ordered in time. Even when the mathematics
and the theory tell us 'What happened before the Big Bang
to start it?' is not a logical or legitimate question, we
insist on viewing this as a proper question to ask of nature,
and we expect a firm answer. But like so many other things
we have learned this century about the physical world, our
gut instincts about which questions ought to have definite
answers is often flawed when we explore the extreme limits
to our physical world.
I wrote this
essay before seeing the new IMAX file at the Air and Space
Museum 'Cosmic Journey", by far one of the nicest and
most heroic movies of its kind I had ever seen. But of course
it showed the Big Bang as a fireworks display. No matter.
It doesn't take a rocket scientist to accept the fact that
the Big Bang was a spectacular moment in history. What is
amazing is that the daring audacity of humans may have demystified
some of it, and revealed a universe far stranger than any
could have imagined.
Still, we are
haunted by our hunches and intuitions gathered over millenia,
and under circumstances far removed from the greater physical
world we are now exploring. No wonder it all seems so alien
and maddeningly complex.
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