The Spontaneous Beginning of Spacetime

[Alex K]

There are lots of possibilities (which really means that we don't know).  Think about the future of the universe.  The last I read on the subject, the universe was believed to be presently expanding (for the latest, you might want to ask Alex K, the rocket scientist who we are depending on to solve our mineshaft-gap problem).

The fuck is a mineshaft-gap problem?

 It could conceivably continue expanding forever.  Or another possibility is that gravity will slow everything down, and eventually pull everything back toward each other, which would result in a rather large bang when everything crashes into everything else.  If that is what will happen, perhaps that is what the "Big Bang" was all those years ago, and maybe this has been going on over and over forever.

The simplest way to have Dark Energy is by simply adjusting the cosmological constant to an appropriate value. From a modern perspective that is a very conservative assumption since the cosmological constant basically has to be there as a free parameter anyway. In that case, the main mystery about dark energy is why the value of the cosmo constant is so tiny compared to the Planck scale.

So far, the fit of astrophysics observations to the so-called lambda-CDM model, where there's cold dark matter and a simple cosmological constant, looks good enough that there's not really a good reason to think that dark energy is more complicated than that.

If dark energy indeed has this simple form, which currently is the most parsimonious explanation, the universe will likely keep expanding forever since matter and radiation keep getting diluted but the dark energy doesn't, until one ends up with basically a universe that only contains dark energy. In such a universe, the expansion is exponential with a factor a = e^Ht, where H is a Hubble constant which is actually constant and proportional to the square root of the cosmological constant, and t is the time.

There are however alternative proposals of a dynamic dark energy where it comes from the cosmological constant as well as something similar to the Higgs field, and can thus vary with time. In such models, the universe could re-collapse if dark energy is reduced in value over time. One other crazy thing that could change this fate is if the Higgs field turns out to be unstable, for which there are speculative indications. If the Higgs field tunnels to a different value, the value of dark energy will change drastically and strange things will happen, first and foremost the violent destruction of everything.

Of course, we don't know if that is what is going on or not, or, at least, the last time I bothered reading anything on this, we did not know. Certainly, you are right that not knowing the answer to something does not justify the claim that God did it.

Some things, you just don't know, and pretending to know does not alter that fact.

If you invoke God, you're doing it the hard way...