Hi, Dan (jetdog-ga):
The short answer to your question is that the expansion of the
universe is not restricted by a "speed of light" consideration.
Einstein's special theory of relativity says that an observer will
always perceive/measure the motions of objects relative to his/her
frame of observation as being less than the speed of light (or equal,
perhaps, in the case of light itself or possibly other massless
particles).
This doesn't constrain the overall expansion of the universe. When
Einstein first formulated his general theory of relativity, it was
widely thought that the universe existed in an essentially stable
configuration. Einstein found that his equations of general
relativity would have models in which the gravitational force was most
likely either so strong as to cause a rapid collapse of the universe,
or so weak as to cause the universe to expand indefinitely, creating a
pretty barren existence.
In order to provide for the possibility of a universe with long term
stability, Einstein made an ad hoc introduction of a repulsive force,
counter to gravitation, in his equations. This term, called the
"cosmological force", was later consider by Einstein to be his
"greatest blunder".
The cause of this regret was Edwin Hubble's astronomical observations
of red-shifts in the spectra of remote stars and galaxies, which was
interpreted as a velocity of recession. In other words the general
movement of distant objects in the universe appears to be away from
us, a phenomenon which most physicists now agree to be strong evidence
that the universe is expanding.
For a good summary of the history and conclusions circa 1995, see this
site:
[Expanding Universe]
http://archive.ncsa.uiuc.edu/Cyberia/Cosmos/ExpandUni.html
and its related pages of explanation.
Hubble's observations suggested but by no means proved a linear
relationship between distance and velocity of recession. The ratio of
these two quantities (at sufficient distance to diminish the effects
of "local motion") then came to be known as the Hubble constant.
However the simple assumption, that the "rate of expansion" given by
this ratio is constant over all times and all places in the universe,
has not stood up to later observations.
The simplest approach, assuming a constant rate of expansion based on
the best "standard candle" observations, leads by backward
extrapolation to a "Big Bang" at some time between 10 and 20 billion
years ago. The reader may consider this to be a larger range of ages
for the universe than one might expect of modern physics, but in one
of the central paradoxes of physics during the 1990's, a conflict
developed between the measurement of the ages of the universe (based
on rate of expansion, corresponding to the measured Hubble "constant")
and the ages of the oldest stars in the Milky Way (based on models of
nuclear chemistry).
The best Hubble constant evidence provided an age for the universe of
between 10 and 12 billion years, while the models of nuclear reactions
in stars plainly assigned ages of as much as 14 billion years to the
oldest stars on the "main sequence" of stellar evolution in our own
galaxy. The tension between these two points of view is obvious.
Writing in the "revised and updated edition" of The Big Bang (1989),
Joseph Silk could state that the largest red-shifts then observed
corresponded to approximately one-third of the speed of light for the
most distant galaxies, which were accordingly considered to lie at a
distance of 5 billion light years.
Today, with the advantage of the Hubble Space Telescope, astronomers
have sampled red-shifts up to 80% of the speed of light, albeit not
for galaxies per se but for quasars (quasi-stellar objects),
mysterious "star-like" objects that appear to produce prodigious
amounts of energy from very small volumes of space.
[Sea and Sky: Quasars]
http://www.seasky.org/cosmic/sky7a09.html
I mention these objects because it is possible for astronomers to
observe such very distant objects moving away from us in opposing
directions. If an object in the direction of our North Pole appears
to have a recessional velocity of 0.75c, while one in the direction of
our South Pole appears to have a recessional velocity of 0.75c in the
opposite direction, then the distance between them appears to us to be
increasing at a rate of 1.5c (greater than the speed of light).
The implication here is that light from one of these objects has not
yet had time to reach the other object, and also that if the
recessional velocities were not to slow, then light will _never_ reach
from one to the other.
Recently scientists have concluded that the expansion of the universe
is actually accelerating:
[Dark Energy in the Accelerating Universe]
http://snap.lbl.gov/brochure/foreword.html
[Accelerating Universe Theory Dispels Dark Energy]
http://www.nature.com/nsu/030630/030630-7.html
Dating back to the late 1970's it was theorized by Alan Guth that
during a very brief period in the universe, there was hyper-expansion
known as "inflation" that produced exponential doubling of the
universe's size through a "false vacuum" state that made gravitation a
repulsive force:
[An Eternity of Bubbles by Alan Guth]
http://www.pbs.org/wnet/hawking/mysteries/html/uns_guth_1.html
[The Inflationary Universe: The Quest for a New Theory of Cosmic
Origins]
http://www.amazon.com/exec/obidos/tg/detail/-/0201328402/002-1050136-3460825?vi=reviews
"According to Guth (physics, Massachusetts Institute of Technology),
before the big bang the universe began in an area smaller than an
atom<-->a "false vacuum" filled with negative gravity<-->and in the
first fraction of a second before the bang, the negative gravity
produced a "hyper-inflation" causing the universe to expand at rate
faster than the speed of light i.e. the [bang] of the big bang."
(Copyright 1999, Book News, Inc., Portland, OR)
However, regardless of whether or not the rate of expansion of the
universe is constant, the existence of locations arbitrarily remote
from us now is not ruled out Einstein's theory of special relativity.
regards,
mathtalk-ga |
