The Origin and Fate of the Universe
It seems reasonable to conclude that if the Universe today is expanding, then
it must have been smaller yesterday. It must have been even smaller last year,
and smaller still a 1000 years ago. Perhaps we can go back far enough along
this line of reasoning until the entire Universe is so very small that it fits
into a tiny dot. What we have learned from the present study of very deep space
objects is shedding light on the potential beginning and fate of the Universe.
The farther out we look into space, the farther back we are looking in time.
We have evidence from deep space surverys that reveal galaxies as they were
beginning to form, when large galaxies had hungry black holes in their cores
that were consuming entire stars and emitting enormous amounts of radiation
(the quasar). What is incredible is that we can "see" beyond the time
when galaxies formed and we observe this faint glow everywhere the telescope
looks. This faint glow is from radiation that has been
stretched so much by its vast distance and velocity of recession that it is
no longer visible light or even infrared light. We are seeing this glow of microwave
and radiowave radiation. What does this tell us?
Above is an image of the sky taken by the COBE
(COsmic Background Observer) spacecraft. Everywhere the spacecraft "looked"
the sky was lit in a faint glow of microwave radiation at the cool temperture
of 3K. Below is the announcement that came with the study from COBE.
1/7/93: BIG BANG THEORY PASSES TOUGHEST TEST
Headquarters, Washington, D.C. January 7, 1993
Goddard Space Flight Center, Greenbelt, Md.
The Big Bang Theory passed its toughest test yet with the latest results reported
from NASA's Cosmic Background Explorer (COBE) team at the American Astronomical
Society meeting in Phoenix, Ariz., today.Precise measurements made by COBE's
FIRAS of the afterglow from the Big Bang -- the primeval explosion that began
the universe approximately 15 billion years ago -- show that 99.97 percent of
the early radiant energy of the universe was released within the first year
after the Big Bang itself."Radiant energy" is energy emitted in any
form of light, from x-rays and gamma rays to visible and infrared light or even
radio waves. COBE's Far Infrared Absolute Spectrophotometer (FIRAS) was designed
to receive the microwave and infrared energy from the Big Bang."The Big
Bang theory comes out a winner," said COBE Project Scientist and FIRAS
Principal Investigator Dr. John C. Mather of NASA's Goddard Space Flight Center,
Greenbelt, Md. "This is the ultimate in tracing one's cosmic roots,"
Mather said.All theories that attempt to explain the origin of large scale structure
seen in the universe today now must conform to the constraints imposed by these
latest measurements.This includes theories that postulate large amounts of energy
released by such things as black holes, exploding supermassive stars or the
decay of unstable elementary particles. In other words, there were not a lot
of "little bangs," as suggested by some theories.The Big Bang Theory
predicts that the spectrum of relic radiation should be that of a perfect "black
body" unless there were major energy releases more than a year after the
explosion. (A black body is a hypothetical cosmic body that absorbs all radiation
falling on it, but reflects none what-so-ever. A black body emits at the same
temperature at every wavelength.) These latest FIRAS results reveal that later
energy releases did not occur.The COBE scientists now can say that the temperature
of the afterglow radiation is 2.726 degrees above absolute zero (273 degrees
below zero on the Celsius scale) with an uncertainty of only 0.01 degrees.Today's
announcement is the result of analyzing data from the FIRAS during its 10 months
of observations. Hundreds of millions of measurements were combined to obtain
these unprecedentedly pre "Making certain that all of the measurements
were combined correctly required exquisitely careful work and lengthy analysis
by a large team of COBE scientists," Mather reported."We are seeing
the cold glow still remaining from the initially very hot Big Bang. These results
now limit the size of any 'after shocks' following the Big Bang. The closer
we examine the Big Bang the simpler the picture gets," said Mather."It
took us 18 years of careful effort to reach this point, but now we can say that
the Big Bang Theory has been tested against observations to a finedegree of
precision," explained Mather."Experimental evidence of the Big Bang
was first found by Edwin Hubblein the 1920's. He found that distant galaxies
in ever direction are going awayfrom us with speeds proportional to their distance.
Therefore, gallaxies thatare farther away are going faster. This is exactly
the pattern that wouldoccur if the entire universe originated in a single explosion,
now called the Big Bang.
Papers on these results and their implications soon will be submitted to the
Astrophysical Journal for publication.
COBE, launched Nov. 18, 1989, is managed by NASA's Goddard Space Flight
Center, for NASA's Office of Space Science and Applications, Astrophysics
Division, Washington, D.C.
Astronomers believe the glow is from a time in the early Universe when things
were so intensely hot that photons created during that time could not penetrate
the cloud of material condensing out of the Big Bang. Only after the first electrons
combined with protons and opened up a pathway for photons to escape was the
Universe transparent. Prior to this time, everything was opaque. On the "other
side" of this opaque background of radiation, the expansion of the Universe
there must be incredibly fast, and thus the early energy levels must have been
incredibly hot. To see what many believe the history of
that early Universe was, go to Inflation
Theory Predicts the History. As we look out into space, and back into time,
we are seeing the glow of the Big Bang when it was too hot for stars or galaxies
to form, and even too hot for photons to escape and be detected. If we could
fly a spacecraft out to this place, we would find the Universe to be expanding
at such great rates and such incredible energies, that we could not possibly
hope to get to an "edge."
The evidence that the Universe is expanding is overwhelming. The question
of its eventual fate and origin is speculative. One has to wonder what will
happen to the Universe in the future. Astronomers believe they have a pretty
good idea of how the Universe may have begun.
Was there anything before the Big Bang?
Will there be a Big Crunch after the Big Bang?
Was the Universe oscillating back and forth before the Big Bang?
Expansion is being Accelerated, but what does this mean?
As astronomers look at the expansion of the Universe, they wonder if it will
expand steadily forever or perhaps gravity will halt its expansion, and like
a giant rubber band, force everything that is out there back inward until it
collapses again into a infinitely small point of energy. This potential collapse
of the Universe is termed the "Big Crunch." Douglas Adams, in his
classic series "Hitchhikers Guide to the Galaxy" described a restraunt
at the end of the Universe. Here, paying customers enjoy a meal while watching
out of their windows as the Universe comes to a complete end. Fortunately, the
engines in the restraunt's rockets are so powerful that they can escape the
immense gravity near the event horizon and repeat the sequence again the next
evening for another crowd of customers.
While I loved his books, his third novel does not really have the answer to
"Life, the Universe, and Everything." In fact, he proposes an answer
of 42, but by the time the seach for the answer is complete, the searchers forgot
the question. Adams is not that far off in his scenario. Indeed, as one falls
inward through the event horizon of a black hole, one sees time accelerating
and space becoming smaller. If we could send a brave astronaut into the event
horizon, perhaps we could discover what awaits our Universe. Since this is presently
impossible, we must conjecture based on the evidence we have from observations
of the Universe.
For gravity to win the ultimate battle, the Universe must consist of enough
mass to halt its own expansion. As astronomers search the Cosmos, they are finding
a smattering of galaxies (over 100 billion at the last estimate and well over
1.5 sectillion stars), a fair amount of dark matter (invisible and as yet undefined
matter whose mass influence is directly responsible for maintaining large spiral
galaxies with their halos of globular clusters without allowing the fast rotation
rate to fling everything haphazardly into space), and a lot of the most exotic
stuff called "dark energy." A piechart of the material comprising
the Cosmos is seen below.
What will happen to the Universe in the Future?
The universe's fate is intimately connected to its shape which,
in turn, depends on a single number, Omega: the ratio of the average mass density
of the universe to the critical value required to just maintain equilibrium.
As seen in the pair ot diagrams above, an open universe, corresponding to
omega less than one, will expand forever. Matter will spread thinner and thinner.
Galaxies will exhaust their gas supply for forming new stars, and old stars
will eventually burn out, leaving only dust and dead stars. The universe will
become quite dark and, as the temperature of the universe will approaches absolute
zero, quite cold. The universe will not end, exactly, just peter out in a Big
The expansion of a closed universe, with an Omega greater than one, will slow
down until it reaches a maximum size, when it begins its inward collapse. Like
a video of the Big Bang and expansion run backward, the universe will become
denser and hotter until it ends in an infinitely hot, infinitely dense Big Crunch--perhaps
providing the seed for another Big Bang.
If Omega equals 1 exactly, then cosmic expansion will coast to a halt infinitely
far into the future. The universe will not end in a Big Crunch nor expand into
an infinite Big Chill, but will remain at equilibrium.
This last case is consistent with the inflation
hypothesis, and also commands the most
observational support. Not to mention the fact that, for most of us, it's
an emotionally appealing scenario. Even though the universe's fate lies billions
of years in the future, it's the only one we have.
Inflation Theory states that the Universe was expanding at super-relativistic
speeds in its earliest moments, and later slowed to its present rate. The discovery
that extreme distant galaxies are moving away faster and faster (accelerating)
indicates that the Universe will never collapse again. It indicates that the
farther away you look in space, the faster and faster things are receeding.
It indicates that the shape of the Universe appears to be "flat" and
prevent the expansion from "circling back upon itself." The flatness
of the Universe puts the age at 11 - 13.5 billion years, and not the 16.5 billion
years proposed by other theories. This ages agrees with much observation about
star clusters, but does not work perfectly for all observations.
What I think is most important to grasp here is that all of the astronomical
observations point to a "beginning," a time when all that is observable
todayt began. It seems to indicate that perhaps oscillation never occurred.
It seems to imply a "one-time" event. I personally find no significance
in a Universe that oscillates between Bang and Crunch, and concludes that my
existence is a blip during, let's say, cycle 10,749 of expansion events. My
mind cannot even fathom the notion that the Universe was oscillating forever
into the past and will continue to do so forever into the future, but there
are plenty of astronomers who contend that is exactly the way it was, and is,
and is to come.
I do find more significance in the notion that my existence happened in a
single cycle of expansion, and perhaps my existence is somewhat important. However,
the single-shot of Big Bang butts up against a perplexing dilemma. If the Universe
began as a single expansion 13.5 billion years ago, then where did the dot of
energy come from? Why did it suddenly begin expanding? Was there anything before
The scientific community becomes divided at this point into two groups. One
group invokes the "Supreme Creator" as being responsible for getting
things started. Some of these theists (those who believe in God, or gods) contend
that the Creator initiated everything and the laws that govern the Universe
and simply sat back to enjoy the show. Others contend that the Creator started
it all off and had "hands" of control on the entire process to direct
things. Still others contend that the Creator made everything in a few words
of command and in a very short period of time. A final group cannot accept the
notion of any "Supreme Being" and proposes alternative explanations
for the origin of everything. These scientists contend that all of the "Universe"
is composed of "multiverses" or "bubble universes" or "sheet
universes" in other dimensions or parallel to our own. Absolutely none
of the groups mentioned above are able to design an experiment to support their
"theory" so these "theories" are not theories at all but
hypotheses. At this point, astronomers move past the realm of science and into
the realm of philosophy and religion.
This course cannot become philosophic (although I push a philosophy throughout
the course that states that you matter and are significant) or religious (and
I have tried hard not to offend anyone's personal faith). This is an astronomy
course and we need to keep the discussion on science. Since plenty of astronomers
wonder about other possibilities that offer an explanation for the Universe,
I now invite you to move to "String Theory and Multiverses."
You could just go back to Inflation Theory,
Expansion, or the Big
Bang. Perhaps your brain is full and you need some time. Maybe you just
want to start over by returning to the Cosmology
Introduction, or go to the Syllabus,
and find something more sane and less stressful to study.
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