I am not an astrophysicist or even a physicist, so bear with me. What happens in the far future really depends on what theory you look at. Is dark energy accelerating the expansion of the universe? If so, there will be a point where all we can see is our own galaxy. Proton decay? Experimental evidence says that protons are stable, or the half-life is much longer than 10^38 years.<p>Shock waves from supernovae trigger star formation by compressing the intragalactic hydrogen, but they dont provide the material for fusion. (Lots of other effects though.) So when the hydrogen is too dilute, star formation stops. There are old galaxies wher star formation has essentially stopped.<p>Edit: I meant this as a reply to gpmedia, but pushed the wrong link, giving a real astrophysicist the chance to reply.