This raises the question: Will it be small again someday? Is the present trajectory of matter in the Universe an ``escape trajectory'' so that the Universe will keep on expanding indefinitely, or is there enough mass present to bind the Universe - slowing down the ``shrapnel'' by gravitational attraction until it stops and begins to fall inexorably inwards
To the best of my knowledge (which isn't all that impressive), opinion is divided. No one has been able to account for enough mass to keep the Universe ``closed'' (bound), so that it looks like a `` Big Crunch'' is not in store for us. On the other hand, a careful analysis of the present distribution of matter in the Universe suggests (or so I am told) that a ``wide open'' Universe (forever expanding) is not compatible with its present homogeneity. In fact, the theorists would be happiest with a perfect balance so that the Universe can't quite make up its mind whether it is bound or not! [This would appeal to anyone, but I think they actually have arguments why it must be so.] If this is the case, we must be missing two things: (1) a lot of mass that doesn't interact much and hence is known as dark matter composed of Weakly Interacting Massive Particles or wimps; (2) any idea of the mechanism that ensures such incredibly ``fine tuning'' of the so-called cosmological constant - if it were infinitesimally larger, the Universe would have collapsed back upon itself in a matter of seconds, while a slightly smaller value would have us lost in empty space by now.
Am I out of my depth here, or what?