Since ancient times, we've looked into the
night skies and wondered:
How far do the stars stretch out into space?
And what's beyond them?
In modern times, we built giant telescopes
that have allowed us to cast our gaze deep
into the universe.
Astronomers have been able to look back to
near the time of its birth.
They've reconstructed the course of cosmic
history in astonishing detail.
From intensive computer modeling, and myriad
close observations, they've uncovered important
clues to its ongoing evolution.
Many now conclude that what we can see, the
stars and galaxies that stretch out to the
limits of our vision, represent only a small
fraction of all there is.
Does the universe go on forever? Where do
we fit within it?
And how would the great thinkers have wrapped
their brains around the far-out ideas on today's
cutting edge?
To begin to get a handle on infinity, we're
going to need some perspective on the numbers
and scales that define our universe.
One place to start is a narrow side street
in Charles Dickens' London.
A Curiosity Shop, fictional to be sure.
Here you can find an unparalleled collection
of stuff.
Old shrunken heads, manuscripts, newspapers,
books, and rare examples of impressively large
numbers.
From Zimbabwe comes a 100 trillion dollar
note. In late 2008, with that nation battered
by hyperinflation, it was worth about a dollar
fifty US.
Go up two orders of magnitude to something
decidedly more useful. The fastest supercomputer
in history will soon hum along at 20 thousand
trillion calculations per second, a twenty
followed by 15 zeroes.
You'll have to run it about a day and a half
for your calculations to equal the number
of grains of sand on all the world's beaches.
That's around a sextillion, a ten followed
by 22 zeroes.
That's roughly the number of stars in the
visible universe.
Atoms in the visible universe? That's upwards
of 10 to the 78th power, a 10 with 78 zeroes.
Cubic centimeters? A mere ten to the 84th,
a septvigintillion.
To go up from there, we turn to no less a
source than the Guinness Book of World Records.
The largest named number in regular decimal
notation: the Buddhist time period Asamkhyeya
is ten to the 140th years, or 100 quinto-quadragintillions.
Then there's the largest number ever used.
Graham's number is a calculation of angles
in a type of hypercube.
If you divided the visible universe into the
smallest units known, called Planck volumes,
the total of those units wouldn't get you
anywhere close to Graham's number.
But it's still nowhere close to the ultimate
ceiling: infinity.
For those who find infinity hard to grasp,
even troubling, you're not alone. It's a concept
that has long tormented even the best minds.
Over two thousand years ago, the Greek mathematician
Pythagoras and his followers saw numerical
relationships as the key to understanding
the world around them.
But in their investigation of geometric shapes,
they discovered that some important ratios
could not be expressed in simple numbers.
Take the circumference of a circle to its
diameter, called Pi.
Computer scientists recently calculated Pi
to 5 trillion digits, confirming what the
Greeks learned: there are no repeating patterns
and no ending in sight.
The discovery of the so-called irrational
numbers like Pi was so disturbing, legend
has it, that one member of the Pythagorian
cult, Hippassus, was drowned at sea for divulging
their existence.
A century later, the philosopher Zeno brought
infinity into the open with a series of paradoxes:
situations that are true, but strongly counter-intuitive.
In this modern update of one of Zeno's paradoxes,
say you have arrived at an intersection. But
you are only allowed to cross the street in
increments of half the distance to the other
side. So to cross this finite distance, you
must take an infinite number of steps.
In math today, it's a given that you can subdivide
any length an infinite number of times, or
find an infinity of points along a line.
What made the idea of infinity so troubling
to the Greeks is that it clashed with their
goal of using numbers to explain the workings
of the real world.
To the philosopher Aristotle, a century after
Zeno, infinity evoked the formless chaos from
which the world was thought to have emerged:
a primordial state with no natural laws or
limits, devoid of all form and content.
But if the universe is finite, what would
happen if a warrior traveled to the edge and
tossed a spear? Where would it go?
It would not fly off on an infinite journey,
Aristotle said. Rather, it would join the
motion of the stars in a crystalline sphere
that encircled the Earth.
To preserve the idea of a limited universe,
Aristotle would craft an historic distinction.
On the one hand, Aristotle pointed to the
irrational numbers such as Pi. Each new calculation
results in an additional digit, but the final,
final number in the string can never be specified.
So Aristotle called it "potentially" infinite.
Then there's the "actually infinite," like
the total number of points or subdivisions
along a line. It's literally uncountable.
Aristotle reserved the status of "actually
infinite" for the so-called "prime mover"
that created the world and is beyond our capacity
to understand.
This became the basis for what's called the
Cosmological, or First Cause, argument for
the existence of God.
Another century later, Archimedes incorporated
"actual infinity" into measurements of curved
lines and volumes.
His method boils down to a process of summation.
Place a triangle inside a circle. Turn it
into a square, then a pentagon, and so on.
As the number of sides increases, to infinity,
their combined lengths equal the circumference
of the circle.
By slicing and dicing curves into an infinite
number of straight lines, he was able to compare
a variety of curves, areas, and volumes.
Archimedes anticipated techniques developed
two thousand years later.
And yet, his ideas on infinity did not carry
forward, due to what the author David Foster
Wallace described as a mathematical allergy
to the concept that developed in response
to Aristotle's "potential infinity."
It was Aristotle's ideas that passed into
the Christian era along with his cosmology,
with Earth seated firmly at the center.
That view was not universal. Islamic, Hindu,
and even some western thinkers posed alternate
views that included infinite space.
In European circles, the issue of infinity
resurfaced during the Renaissance.
In 1543, the Polish astronomer Nikolas Copernicus
argued that Earth orbits the Sun, not the
other way around.
The old Greek spheres began to fall by the
wayside when a distant supernova, then a comet,
were spotted by the astronomer Tycho Brahe.
These objects seemed to behave independently
of the other stars.
A monk named Giordanno Bruno inflamed the
issue by traveling Europe at the height of
the Inquisition to proclaim an infinite universe.
In the year 1600, he was burned at the stake
for this and other heresies.
Just nine years later, in 1609, Galileo Galilee
used the first astronomical telescope to show
that the universe is much larger than we thought.
In later writings, he even sought to discredit
the distinction between potential and actual
infinity.
Galileo was forced to recant his views, and
the old Aristotelian view held sway. Any attempt
to assign a value to infinity, in numbers
or in nature, was doomed, for that was the
unique province of God.
Finally, at the end of the 19th century, the
mathematician Georg Cantor sought once and
for all to divorce metaphysics from the abstract
pursuit of math.
Infinity, he wrote, had to be studied without
"arbitrariness and prejudice."
He became known for folding finite and infinite
numbers into a unified theory of number sets,
considered a foundation of modern math.
One of his defenders used a paradox to show
how infinite sets are subject to concrete
comparisons.
Say you've come to stay at this grand hotel.
You're in luck, because here there is an infinite
number of rooms.
Oddly enough, you learn there are "No Vacancies."
Fortunately, the manager says: I can still
check you in. He assigns you to room #1 and
directs you down the corridor. Then, he goes
to work, shifting the guest in room 1 to room
2 -- room 2 to 3 -- 3 to 4 -- and so on.
So in this hotel, there's a number set that
includes an infinite number of guests and
rooms. Then there's that same set plus you...
two infinite sets, yet one is a subset of
the other.
Being able to use infinite sets of different
sizes allowed mathematicians to design equations
describing continuous motion and change over
time.
Echoing Aristotle, a critic of the new set
theory suggested that the end of the corridor
is still only a potential infinity, with God
representing the only actual infinity.
For those who pine for humble accommodations,
we'll recommend an alternative later on.
Even as mathematicians embraced infinity,
astronomers in the early 20th century still
saw a limited universe... centered on the
galaxy, a flat disk of stars.
Did the limits of our vision, like the horizon
at sea, conceal an infinite universe beyond?
Albert Einstein, for one, believed that if
that were true, then the night sky would be
filled with dense starlight shining from every
direction. We'd reel from the effects of infinite
gravity.
Arguing for a finite universe, he described
a people living on the 2D surface of a sphere.
To them, a beam of light moving through space
would appear to go straight, on an infinite
journey. In fact, it follows a path determined
by the overall gravity of the universe, and
curves back around.
Like the old Greek spheres, this view of a
static and limited universe began to fall
by the wayside in the 1920s.
Edwin Hubble and Milt Humason used the new
100" telescope on Mt. Wilson in California
to look at mysterious fuzzy patches of sky
called "nebulae." They found that these patches
were galaxies like our own, and that some
were very far away.
What's more, they found that most are moving
away from us. In fact, the farther out they
looked, the faster the galaxies are moving.
This fact, known as Hubble's law, led to an
inescapable conclusion: that the universe
is expanding. Furthermore, if you run the
clock back on this expansion, it appears that
it all began in one singular moment.
That moment has traditionally been described
as an explosion... a "Big Bang."
How large the universe has gotten since then
depends on how long it's been growing, and
how quickly.
Using an array of modern telescopes, astronomers
have recently narrowed the beginning to 13.7
billion years ago. Taking into account the
expansion of space ever since, the radius
of the visible universe, the part we can see,
has expanded out to 46 billion light years.
These measurements have raised anew the ancient
questions: What's beyond our cosmic horizons?
Is there an edge? Or does it somehow go on
forever?
A new set of answers has emerged from a theory
designed to address questions that arose from
the original model of the Big Bang.
For one, how did the universe get so large?
The Hubble Deep Field contains images of infant
galaxies at less than 10% of the age of the
universe, near the edge of our cosmic horizons.
By the time one of those galaxies reached
maturity, it would have moved far, far beyond
our horizon.
And what of all the galaxies visible at its
horizons?
For another, how did the universe get so smooth?
In every direction you look, the density of
galaxies is the same on large scales.
Astronomers believe that whatever process
flung the universe outward, must have also
blended it in its earliest moments.
The theory that addresses these questions
was based on the discovery that energy is
constantly welling up from the vacuum of space
in the form of particles of opposite charge,
matter and anti-matter.
The idea is that in primordial times, an energy
field embedded in this so-called quantum vacuum
suddenly moved into a higher energy state,
causing space and time to literally inflate,
and our universe to burst forth.
If this theory is right, then our universe
is incomprehensibly large. Its author, the
scientist Alan Guth, wrote that the universe
as a whole would have grown to at least ten
billion trillion times the size of our visible
patch. That's a ten followed by 23 zeroes.
If you think that's big.
A variation on the theory describes the origin
of our universe as a physical process that
exists far beyond it, out into the seemingly
infinite void that had confounded Aristotle
and other Greek thinkers.
In that case, our universe would have inflated
like a bubble, and joined a stream of other
bubble universes frothing up and expanding
across an endless ocean of time and space.
A related idea theorizes a cosmic landscape
unfolding in vast fractal patterns.
These new, more expansive, visions of the
cosmos are not without their paradoxes.
Logically speaking, with infinite stars, infinite
planets, infinite universes, you will also
have infinite possibilities.
The so-called infinite monkey theorum has
its roots in Aristotle's attempts to illustrate
the perils of thinking about infinity.
Ask a monkey to type, or ask an infinite number
of monkeys to type, for an infinite amount
of time. You're sure to get a lot of random
letters.
But there is a chance, however small, that
somewhere, some how, you'll get the full text
of Shakespeare's Hamlet.
It's clearly absurd.
Then again, consider the increasingly strange
nature of our universe, as suggested by some
new observations.
This is where we draw your attention from
the famous Hotel Infinity -- to a less well-appointed
alternative.
You're sure to get a big welcome at the old
Hall of Mirrors.
This ramshackle place would have thrown even
the great thinkers for a loop.
It represents a kind of optical illusion that
may be present in our view of deep space,
according to a new interpretation of data
from one of the most important space satellites
ever launched.
WMAP was sent out to make precision measurements
of radiation left over from a period about
300,000 years after the Big Bang.
It revealed an intricate pattern of hot and
cold spots, now thought to represent the seeds
of galaxy filaments and walls seen on large
scales.
The pattern was laid down by pressure waves
that ricocheted through the expanding gas
of the early universe.
One group of scientists, looking at the sizes
of these waves, suggested that some are actually
mirror images of themselves. From this, they
argue that the universe could be much smaller
than we think.
That's not the only strange new line of evidence.
Tracking the movement of distant galaxies,
astronomers found huge clusters moving at
about two million miles per hour in the direction
of the Constellation Centaurus.
With the results published in a top scientific
journal, the astronomers describe an immense
gravitational presence that may loom beyond
our visible horizon, perhaps another universe
that inflated near our own.
Ideas like these may well have led to imprisonment
or death in centuries past. Now, they are
part of a field of study that is bursting
with data and ideas.
Cosmology, the study of the universe as a
whole, has long been infused with metaphysics
and philosophy. Today, it's steadily merging
into the physical sciences.
So is the universe infinite?
Scientists will continue to look for evidence
of what lies beyond our horizons and test
theories on the nature of time and space.
But like the room at the end of an endless
corridor, the final final answer will always
elude us.
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