Could the accelerated expanding universe be as a result of the decay
of matter into energy, and therefore as matter decays so does Gravity.
As Gravity decays and the universe becomes larger the effect is that
Gravity decays at an accelerated rate. The consequence is an ever
expanding universe at an exceleraterd rate.  At What point will the
univers be expanding at greater than the speed of light? (ie time
line)

Interesting theory...

As for reaching the speed of light, technically, that is impossible. 
In order for something to be accelerated to the speed of light, it
requires infinite energy.  Before that happens, though, all the mass
in the universe will have been converted to energy; meaning there
would be no mass left, meaning there would be nothing left to
accelerate to the speed of light, except for light itself.

A presently accelerating expansion rate is a rather new theory, so it
could fall into disfavor. My guess is only about 1% of the mass of the
universe becomes photons or other energy per billion years, and a tiny
amount of energy is becoming matter, so the matter will not fall to
zero, as new matter will likely continue to form from energy. I
suppose in a trillion years we could have a matter mass reduction of a
trillion times. My guess is a net loss of mass contributes to the
accelleration, but some other cause is dominate.
 It is generally agreed that the outer edge of the visable universe
has been moving away from Earth at the speed of light for billions of
years, and that the portion farther out are moving away faster than
light speed. If so, there is no date. The visable universe will just
shrink very slowly as the acceleration continues. Please refute,
embellish or comment.   Neil

Here is a nice recent article about how the universe is expanding at
an ever greater rate:

http://www.cnn.com/2004/TECH/space/05/18/dark.energy/index.html

As far as your idea goes however, given that the recent evidence shows
that 6 billion years ago there was a shift from decelerating expanding
to accelerating expanding, I would assume there are more forces at
work than we even understand. One of these is dark energy, the force
that pushes galaxies away from each other. Gravity holds them close
together. It seems that dark energy is stronger, since the universe is
expanding, not contracting. We do not understand the nature if dark
energy, but it would seem to me that it would work on a similar
proximity principle. That is, proximity dictates the strength of the
force. If this is the case, then we will accelerate through the cosmos
until the universe is so spread out that dark energy can no longer
push us apart. (nor could gravity pull us back together)

As for celestial bodies reaching the speed of light; unless dark
energy is everywhere, and is infinite (very doubtful), and can
transmit force through enormous distances, it would not be possible.

-Burly

Let me embellish for Neil.  What is your guess based on, when you say
1% of the universe is converted to Photons per Billion years? And what
mechanism is responsible for creating matter?  Remember, that as the
volume of the universe becomes greater, the effect of Gravity becomes
exponentially less.  In effect gravity acceleratorates negatively,
adding to this, the loss of matter, the cumulative effect is clear. 
I?m troubled though by the concept that as the expanding front
approaches the speed of light the mass of the front becomes infinite,
gravity becomes infinite and the dimension becomes ?0? with
singularity as its depth.  As these plains from multiple universes
intersect, at the point of intersection new universe are born and the
process continues.  Last, is this the infamous Neil that I know?
Karl

Karl - seriously - how can anyone , but  Neil himself, say if

 "Last, is this the infamous Neil that I know?" 

But, if you tell us about the Neil you know ...  
      we can make some guesses. 
      

BTW - you do not have to worry about the fronts, .. intersecting ...
sucking in all the energy....

 According to the [search term] cosmological principle
 http://www.astro.ucla.edu/~wright/cosmo_02.htm

 life at the front is same, as life here  'at the center ???'
 (according to folks who have been there :-) 

  The current theory (accelerating ir not) is that anywhere you look
  you see the same thing
namely
  the remote objects moving away
  the remoter, the faster

 but if you would 'go there' - then objects near to your new place,
 would move slowly, and object far from you
 us - would move very fast away from you

In principle:
 Speed is not a property of a given location or object,
  -- object move relative to other objects ---
  universe as a whole, has only  an 'expansion rate' ...
Neil?

relativity tells us that matter and energy are equivalent (recall
E=mc^2), this means that energy also provides a gravitational field.
so even if matter decays into energy there will still be gravitational
fields. additionally, the presence of matter is like a frictional
force in the expansion of the universe, the absence of matter would
not cause the expansion to accelerate just not decelerate. it is true
that the density of matter has to decrease in order for the 'dark
energy' to become the dominant component forcing the expansion to
accelerate, but the fact that the is expanding will already enforce
this, since the density of vacuum energy does not decrease as the
universe expands, but that of matter does.

Pancho 12  No one has measured a gravitatuibak field  associated with
energy.  I have yet to see a tractor beam in real lifr only in Star
Treck
.

Neil, let me elucidate for you.
 At the Wave front all mater has a dimension of singularity in the
direction of travel.  Moments before singularity happens there is a
minor event where mass grows infinite perpendicular to the direction
of flow. This is because the spread of the Wave front travels a
greater distance and reaches the speed of light moments before it does
in the direction of the wave.  Even though the mass of the front is
infinite it has no consequence because its world existed in a
singularity plain and all Gravitation is perpendicular to the
direction of propagation.  The steps repeat themselves over and over
as the matter coming up from behind goes through the same steps...  In
effect at the point of reaching "c"the universe becomes an
electromagnetic waves that now propagated in sheets of singularity
through the rest of the universe.  I repeat as these plains intesect
their hidden dimensions of mass and Gravity are made evident again and
the process continues.

Karl

Present theories concerning the expansion of the universe, are based
on the red shift spectroscopy.  We know through Einstein's theories
and experiments that mass bends light.  Imagine the path that a light
photon must journey to reach the earth so that we can measure it.  It
stands to reason that this photon must be traveling around in circles.
 So the red shift becomes an innappropriate tool for this measurement.
 Yet it is all we really have.  This, if true nullifies both the
boundary of the universe as we theorize and it's expansion rate. 
Maybe even refutes the big bang theory, in favor of the steady state
theory.  Bottom line, our measurement protocols are presently
inadequate to answer this question.  I do not believe the expansion of
the universe is approaching the speed of light.  I do, however believe
that the light of the universe is traveling in circles before it
reaches us.

Not according to General Relativity.

If matter (massive particles) decayed into energy (massless particles)
then they would still have the same 'immediate' contribution to
gravity and gravity would not decay.

General Relativity is a proportionality between a particular
space-time curvature tensor and a tensor comprised of stress, energy,
and momentum. (In this case the tensors are rank 2 and thus very much
like matrices)

The stress-energy-momentum tensor does not care what form the energy
takes persay. Both matter and energy will bend space time. A massless
particle and a massive particle both have energy and momentum. It has
been verified with observational evidence that kinetic energy does
infact bend spacetime. What does change is how fast the stuff can move
around (massless particles must move at the speed of light and massive
particles cannot) and the interrelationship between the stuff and
itself (You wouldn't think of light as having interaction with itself,
but you would for a gas).

So the answer to your question is that matter decaying into energy
will not decay gravity but it will change the cosmology of the
universe.

How about this: If space is curved in however many dimensions, then
picture the Big Bang as occurring at a point on a sphere. As the
universe expands, it gets larger and larger as it covers the surface
of the sphere, and gravity causes the expansion to slow down, as
expected. At some point, the universe would cover half of the sphere.
As it continues to expand, it begins to cover the other half of the
sphere,  and even though it continues to get "larger," the mass in the
universe actually starts to move closer together, eventually coming
together at the opposite pole. During this second half of the
expansion, normal gravity would cause the expansion to accelerate,
which is what we see now.