How Large is the Universe?

October 19, 2019 0 By Stanley Isaacs


The universe has long captivated us with its
immense scales of distance and time. How far out does it stretch? Where does it
end, and what lies beyond the star fields and the streams of galaxies that extend as
far as telescopes can see? These questions are beginning to yield to
a series of extraordinary new lines of investigation, and to technologies that are letting us peer
not only into the most distant realms of the cosmos but at the behavior of matter and energy
on the smallest of scales. Remarkably, our growing understanding of this
kingdom of the ultra-tiny, inside the nuclei of atoms, is now enabling us to glimpse the
answer to the ancient question: How large is the universe? In ancient times, most observers saw the stars
as a sphere surrounding the earth and as the home of deities. The Greeks were the first to see celestial
events as phenomena, subject to human investigation rather than the fickle whims of the Gods. One philosopher and sky-watcher named Anaxagorus
suggested that meteors are made of materials found on Earth and therefore, might have even
come from the Earth. Those early astronomers built the foundations
of modern science. But they would be shocked to see the discoveries being made by their
counterparts today. The stars and planets that once harbored the
gods are now seen as infinitesimal parts of a vast scaffolding of matter and energy that
extends far out into space. Just how far began to emerge in the 1920s.
Working at the huge new 100-inch Hooker Telescope on California’s Mt. Wilson, astronomer Edwin
Hubble, along with an assistant named Milt Humason, analyzed the light of fuzzy patches
of sky known then as nebulae. They showed that these were actually distant
galaxies located far beyond our own. Hubble and Humason discovered that most of
them are moving away from us. The farther out they looked, the faster these objects
are receding. This fact, now known as Hubble’s law, suggests
that there must have been a time when the matter in all these galaxies was together
in one place. Everything that astronomers saw in their increasingly
large telescopes would have dated back to a singular beginning, now called the Big Bang. That the universe could expand had been predicted
back in 1917 by Albert Einstein, except that Einstein himself didn’t believe it until
he saw Hubble and Humason’s evidence. Einstein’s general theory of relativity
suggested that galaxies could be moving apart because space itself is expanding. So when
a photon gets blasted out from a distant star, it moves through a cosmic landscape that is
getting larger and larger, increasing the distance it must travel to reach us. So, how large the cosmos has gotten since
the big bang depends on how long its been growing, in addition to its expansion rate. Recent precision measurements gathered by
the Hubble space telescope and other instruments have brought a consensus, that the universe
dates back 13.7 billion years. In that time a beam of light would have traveled
13.7 billion light years, or about 1.3 quadrillion kilometers. But taking into account the expansion of the
universe, the most distant galaxies discovered by the Hubble space telescope are actually
46 billion light years away from us in each direction and almost 92 billion light years
from each other. So is that the size of the universe? It’s not, according to a dramatic new theory
that describes the origins of the cosmos. It holds that our 92 billion light-year patch
is a mere speck within the universe as a whole. The theory is 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. Back in the 1980s, the physicist Alan Guth
proposed that energy fields embedded in the vacuum of space had suddenly tipped into a
higher energy state, causing space and time to literally “inflate.” The universe went from atomic size to cosmological
size within an infinitesimally short time. As a result, according to Guth’s calculation,
the universe as a whole would have grown to some ten billion trillion times the size of
the observable universe. That’s a ten followed by 24 zeroes. Put another way, the whole universe is to
the observable universe – as the observable universe is – to an atom. The incredible fury of cosmic inflation helps
explain the immense size and smoothness of the universe. But to succeed, the theory must also account
for how the universe produced what we see around us, all those stars and galaxies and
clusters of galaxies, and ultimately us. Scientists are now attempting to piece together
the chain of events that launched our universe in its earliest moments by generating what
you might call a “little bang.” At the Brookhaven National Lab in New York
State, they are blasting gold atoms in opposite directions down tunnels almost two and a half
miles long. When these atoms reach velocities just short
of the speed of light, they are sent into a violent collision. A fireball erupts, reaching a temperature
exceeding two trillion degrees Centigrade. As far as we know, the last time anything
in our universe was that hot was about a millionth of a second after its birth. What interests the scientists is the splatter
of subatomic particles, a super-hot soup of quarks and gluons that theory says gave rise
to matter as we know it. In initial tests, this quark-gluon plasma
has shown a crucial property: extremely low viscosity or resistance to flow. Scientists
call it a perfect liquid. To grasp its importance, we go back to those
primordial energy fields that the theory says spawned the big bang. The thinking is that
those fields contained tiny fluctuations that were blown up to huge size during inflation. In the ultra-dense quark-gluon mix, these
fluctuations generated pressure waves, or ripples. As the universe evolved, these ripples
gave rise to variations in the density of matter. Amazingly, the imprint of those primordial
ripples is out there today in a faint signal discovered accidentally back in the 1960s. Working for the Bell Telephone Company, physicists
Arno Penzias and Robert Wilson had built a giant horn-shaped antenna. But wherever they
pointed, the contraption picked up excessive noise in the microwave portion of the electromagnetic
spectrum. That noise turned out to match a prediction
made years earlier: that in the wake of the big bang, the universe was filled with a cloud
of extremely hot gas that scattered all light. As the universe cooled, the cloud dissipated.
Light then shone through Over time the spectral signature of this light
would have shifted, as the universe expanded and cooled, to what Penzias and Wilson detected.
What they’d heard was the echo of the Big Bang. This image shows the smooth contours of the
light recorded by the Bell team. Scientists would have to look closer to find the imprint
of cosmic inflation. The Space Shuttle Discovery lifted the Hubble
Space Telescope into orbit on April 24, 1990, in one of the most important scientific milestones
of our time. Another launch, arguably just as important,
took place five months earlier. The Cosmic Observation Background Explorer,
COBE for short, was sent up to take a harder look at the microwave radiation discovered
by Penzias and Wilson. The results came out two and a half years
later. The light of the early universe contained a pattern of hot and cold spots. In this image was nothing less than the origin
of all we see around us today, smooth on a large scale, but with significant clumps from
which gravity would form gas clouds, then stars, and galaxies. With this cosmic template in hand, astronomers
set out to discover how the patterns and the dimensions of the universe evolved over time. In an age of computer controlled telescopes
and automated observing, astronomers could now launch huge international collaborations
with the goal of mapping a large fraction of the universe in three dimensions. At Apache Point in New Mexico, the Sloan Digital
Sky Survey set the standard for mass production astronomy. A series of steel plates are drilled with
holes that exactly match the location of galaxies in the night sky. After plugging fiber optic sensors into the
holes, the plates capture the light of hundreds of galaxies per night. From that light the
astronomers calculate their distances from Earth. Another survey is named the 2 Micron All Sky
Survey, or 2Mass, after the frequency of infrared light its detectors are tuned to capture. In this image, the 2Mass data covers a region
60 million light years across. The local group of galaxies, including the Milky Way, are
in the center. This is our intergalactic neighborhood. Jump further out to a region about 200 million
light years across. Our location is linked to the densely packed Virgo Supercluster,
the nearest intergalactic city. Stepping out to a region over 320 million
light years across, you can see the full breadth of our local region of the universe. Galaxies
line up in walls and arcs. Beyond them are sparsely-populated voids, the rural cosmic
countryside. Moving out with the data, this region is over
650 million light years across. Then almost two billion. 3.2 billion. And finally out to a region 6.5 billion light
years from end to end: the cosmic continent. In the middle of it all, our galaxy, so immense
from our Earthly perspective, is less than a speck. The 2mass study, the Sloan Digital Sky Survey,
and the 2 Degree Field in Australia have extended our maps to a quarter of the way back to the
beginning of the universe. They have laid out a grand cosmic roadmap. COBE’s successor, the Wilkinson Microwave
Anisotropy Probe, or “WMAP”, was launched to scan the early universe for the fine-scale
origins of this cosmic atlas. WMAP traveled beyond any interference from
Earth, to a position balanced between the Earth and the Sun. There, for two years, its detectors took in
the pristine light of deep space. This is what WMAP saw: a pattern consistent
with the filaments and voids that had evolved in the universe at large. Scientists are poring over the WMAP data for
clues to the true dimensions of the universe. One group, for example, looked for repeating
patterns that could be evidence of pressure waves that ricocheted through the hot gas
of early times. They saw none, which implies that the universe
had grown so large during inflation that such waves could not cross it. Then they did the math and reported that the
entire universe must have a minimum diameter of 78 billion light years. So what is its maximum size, and what’s
beyond that? We will never know for sure what lies beyond
our visual horizon, but astronomers are turning up some surprising hints in the universe they
can see. To ancient observers, the universe was made
of five classical elements: Earth, Water, Air, Fire, and a fifth, Quintessence, or space. Aristotle believed the stars, unchanging and
incorruptible, were made of this fifth element. Today, we are finding that space, in fact,
has a character of its own. Astronomers have calculated the gravitational
pull needed to bind stars as they orbit a galaxy or galaxies as they orbit a cluster
of galaxies. They have found that there is simply nowhere
near enough visible matter there to hold these structures together. The missing ingredient, its identity still
unknown, they call: Dark Matter. In supercomputer simulations of cosmic evolution,
dark matter is added in to supply the gravitational tug needed to form the web pattern of filaments
and walls; voids and dense clusters we see in the universe at large. But something else appears to be happening
on these large scales. Astronomers have been making refined measurements
of the cosmic expansion rate with a new type of distance marker. They wanted to know if gravity was slowing
down the pace at which the universe is growing. The markers they used, type 1A supernovae,
are thought to burn at uniform intensities throughout the universe. By measuring changes in the brightness of
these so-called standard candles at various distances, the researchers can spot changes
in the cosmic expansion rate. To their surprise, the data showed that the
universe as a whole is not only expanding, it’s actually accelerating outward! The culprit is thought to be energy welling
up from the vacuum of space, similar to what occurred in the early moments of the Big Bang,
causing cosmic inflation. By emerging in minute quantities everywhere,
it is pushing space outward across the whole universe. Over time, this so-called “Dark Energy”
has grown to an astonishing three-fourths of all the matter and energy in the universe. With data like this pointing to an underlying
dynamic within our universe, some scientists are thinking of the cosmos in far broader
terms than ever before. There is a version of inflationary theory,
for example, that suggests we live in one of many universes, that may co-exist side
by side but do not touch one another. Like bubbles, they are continually rising
up and expanding across the oceans of infinity. Just 500 years ago, in Galileo’s time, many
people looked out into space and saw a universe of lights centered on the Earth. The invention of the telescope revealed stars
far from our planet, then galaxies, clusters of galaxies, and beyond them, vast walls and
filaments of matter. Newer ideas about the size of the universe
amount to a quantum leap in our sense of scale, by extending these structures far, far beyond
our horizon. Do these discoveries push us, on our tiny
out-of-the-way planet, into a smaller and smaller corner of Creation? Or does our ability to comprehend and imagine
the far limits of time and space somehow expand our importance in the grand scheme of things?