Imagine a film of the galaxies all racing away from each other. Now play the film backwards. It's easy to imagine that they all used to be really close together and that something violently blasted them apart. All of the galaxies exert a gravitational pull on each other, dragging against the expansion of space, and there is much debate on whether the expansion and contraction balance each other out or not. Some mysterious form
of energy, the "dark energy" on the diagram, is thought to be gently
accelerating the expansion of space.
So what were things like right after the bang? All the matter in the universe crowded
tightly together, extremely hot and furiously energetic. At
the very first instant of time, everything explodes with unbelievable
force, rapidly flinging everything away from everything else. This isn't an explosion
of something in space out into a wider area of space; it's
an explosion of space itself, happening everywhere at once. The name 'big bang' starts to
sound like ironic understatement, and in fact it was
coined derisively by astronomer Fred Hoyle, an early and vocal
intellectual opponent of the idea.
At the moment of the Bang, we know that space was extremely
tiny. Put another way, everything was extremely close together,
and there was nowhere you could really go before winding up
immediately back where you started. Imagine if the earth was
twenty feet across - its surface would be unbounded, you'd
never come to the end of it, but if you walked in in any direction,
you'd soon be back where you began. If space is closed, then
it behaves like a wraparound video game screen, like in Asteroids
or Pac-Man. If you get to the edge, you instantly disappear, and reappear on the far side of the screen. At
the first instant after the Big Bang, the universe's 'screen'
was only one 'pixel' wide, with all the matter and energy
there is crammed into it.
How the universe got to be like this in the first place is
an open question.
Timothy
Ferris does the best job of telling the Big Bang story
verbally. He asks you to imagine a staircase going exponentially
backwards in time. Step one is a billion years after the beginning
of time. Step two is a hundred million years after the beginning
of time, step three is ten million, step four is a million,
and so on. With me so far? Okay, here's where the fun begins.
I summarize and quote from Ferris:
step one | a billion years after the beginning of time
Everything in space is younger, hotter and closer together
than in the present universe.
step two | one hundred million years after the beginning
of time
The universe is mostly dark. The few stars are in a "dark
soup of hydrogen and helium gas, whirlpooling here and
there into protogalaxies."
step three | ten million years after the beginning
of time
All of space is at room temperature.
step four | one million years after the beginning of
time
There are so many electrically charged particles rubbing
against each other that the entire universe erupts with
blinding white light.
step six | ten thousand years after the beginning of
time
The entire universe is the same temperature as the surface
of our sun, and totally dark - there isn't enough space
between particles for the photons to get anywhere before
whacking into something and being reabsorbed.
step eleven | one month after the beginning of time
The entire universe is hotter than the center of the
sun.
step fifteen | five minutes after the beginning of
time
The entire universe is at a temperature of a billion
degrees Kelvin, or around 1.8 billion degrees Fahrenheit.
between steps seventeen and eighteen | one second after
the beginning of time
The entire universe is "denser than rock and as
hot as the explosion of a hydrogen bomb."
step twenty-two | 0.000001 seconds after the beginning
of time
The entire universe is an ocean
of free quarks and other elementary particles. For
every billion antiquarks, there are a billion and one
quarks. Why this particular ratio, no one knows, but if
there weren't that slight imbalance, there wouldn't be
any matter in the universe at all.
Further into the past, no one's sure what was going on. We'll
need to build some bigger
underground particle accelerators to find out. Neato,
right?
The initial condition of the universe is presumed to have
been a highly symmetric, ordered, low-entropy state. The entropy
of the universe has been steadily increasing since then, as
lower-probability symmetries and order give way steadily to
higher-probability asymmetries and disorder. Some physicists
conceptualize the earliest moments of the universe as a series
of phase transitions, like steam to water to ice.
At extremely high energy levels, the weak nuclear force and
electromagnetism merge into a single force, the evocatively
named electroweak force. There's reason to believe that at
even higher energy levels, the electroweak force merges with
the strong nuclear force, and at higher temperatures still,
that all of them merge with gravity into The Force. There's
also reason to believe that the universe may have split off
early on into the four-dimensional spacetime we inhabit and
a crumpled,
six-dimensional space existing invisibly at every point in
our world. The idea is that as the universe cools off,
it's hardening into an asymmetrical arrangement, like more-symmetric
steam hardens into less-symmetric ice as it cools.
In the staircase thing I blithely kept talking about the
beginning of time, but what does it even mean for time to
have a beginning? Stephen Hawking has a great metaphor. Imagine
that time is shaped like the earth. The big bang is the North
Pole, and as time passes it moves south into the future. Just
as it's meaningless to talk about the point a hundred miles
north of the North Pole, it's meaningless to talk about a
time before the Big Bang. We'll need some new linguistic and
mathematical equipment before we're ready to see past that
boundary.
© ethan hein 2007 | back
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