Re: Can the energy of the universe change in the near future say within 1 GYR?

Within a few years of the publication of the General Theory of Relativity various scientists 
(Einstein, de Sitter, Friedmann and Lemaitre, in particular) investigated its application to the 
Universe as a whole.  They produced theoretical "models" which have turned out to be very 
successful in describing the evolution of the expanding Universe from the Big Bang to the 
present day.  Several constants in these theoretical models are now fairly well measured 
observationally (the Hubble constant, the energy density and the so-called "cosmological 
constant"), and so we can predict the behaviour of the Universe with some confidence into 
the far future.  Certainly on the time-scale of a mere(!) billion years we can calculate that the 
temperature will just continue to cool a little (about 0.2 degrees) from its present value.

On a much longer timescale, our confidence in the theoretical models and observational 
constraints becomes much less.  For example, we currently have very little understanding of why 
the cosmological constant has the value it seems to, and even whether it is a constant.  With 
those kinds of uncertainties, it is plausible (although not favoured by our present knowledge) 
that the Universe may at some point begin to contract which would indeed lead to a heating of 
the background radiation, and ultimately have an impact on life, in whatever form it might take 
at that time.

However, as scientists we need always to be aware of the possibility of something much more 
unexpected.  For example, we believe that very early in the Big Bang the Universe went through a 
number of "phase transitions", where the character of the fundamental fources changed along 
with the nature of empty space (the vacuum) itself.  If this were to happen again, and we have no 
compelling reason to assume it won't, then we (and the whole physical Universe as we know it) 
would indeed cease to exist in an instant.  There would be no warning of such an event, so our 
hope must be that an improved understanding of fundamental physics in the future will allow us 
to say with more confidence whether such an event is possible, or at all likely to happen.  

However, we shouldn't let this thought spoil our day!  The Universe has existed now for nearly 
14 billion years without such a catastrophe, so there's certainly no reason to expect it to happen 
soon!