smeggypants wrote:Take our universe. On the one hand it's almost credible to claim that it 'exploded' from a singularity adn both time and space as we experience it to have started at that point, but logicaly there must have been some event that triggered this.

It's a tricky one, to be sure. There are several issues here, though. The first is that the singularity has never actually been established, and is somewhat problematic. It's a feature of a theorem devised by Hawking and Penrose, yet neither man actually supports the notion any longer, nor have they done for some considerable time. The problem with the theorem is that it relies on a purely relativistic treatment of the the Big Bang theory, but that runs into massive issues as the scale of the cosmos gets to quantum scales. Quantum Mechanics actually has the singularity as asymptotic, which means that it can be approached but never actually reached. Either way, a proper treatment of the cosmos when it reaches the smallest scales, and certainly by the time we get to Planck scales, requires a quantum theory of gravity, and we don't have one of those yet.

There are several extant models dealing with what came before the Big Bang, and not all of them feature a singularity.

Thing is, if you remove the singularity, there's no reason to conclude that time began at the Big Bang. In fact, even with the singularity, there's no reason for such a conclusion, one would only conclude that the singularity didn't experience time. We have entities within our cosmos that don't experience time, namely photons (and any other particles with a zero rest mass, because particles with a zero rest mass

must travel at

c, meaning that all their motion is through space, and none of it through time), yet time still runs in the cosmos.

Even if that event was in a different zone to our spacetime. ( that could be anything from a species in a mother inverse creating a computer simulated universe to a a universal black hole from a previosu universe enduring a critical mass where it's singularity repeats a cycle of expansion/collapse )

The notion of collapse has been pretty much ruled out with the discovery that the expansion is accelerating. The current paradigm is that the universe will continue to expand until all matter is ripped apart and all that's left is a sea of photons. There are models that have another cycle after that, most notably the non-singular 'brane-worlds' hypothesis, which involves the collision of two poly-dimensional membranes as the energy input for the big bang.

Or there might be a mother universe that has a system of spawning many sub-universes, perhaps each resulting in different physical constants, so that only a tiny fraction of those universes becomes one similar to ours.

Well, the currently accepted iteration of Big Bang theory is just such a theory. It's called 'inflationary theory', and it solves some long-standing problems of cosmology, most notably the 'horizon' problem and the 'flatness' problem.

[I could go on infinitely (

) about the various permutations, but the common denominator is an event trigger. The only other alternative is spontaneous 'existence' out of absolutely nothing. Anything else would mean a pre-event.

I cannot get my head around "spontaneous 'existence' out of absolutely nothing" but neither can I can my head around the concept of infinity where there's ALWAYS been a pre-event.

Well, the idea of 'absolutely nothing' is not an idea that's taken seriously by physicists and cosmologists, not least because the persistence of 'nothing' is prohibited by Heisenberg's Uncertainty Principle. That said, Hawking tells us that the net energy of the universe may actually be zero. The positive energy of all the matter and dark matter, balanced against the negative energy of gravity, and the equation runs to zero. The real question here is precisely what do we mean by 'energy'?

In physics, energy is simply defined as 'the ability to perform work'. So what's work? Well, it's essentially the equalisation of differentials. So, in the context of the Big Bang 'coming from nothing', we actually have something that doesn't even require a cause, and experimentally validated, to boot.

Heisenberg's Uncertainty Principle has some interesting consequences, one of which is that particles can spontaneously pop into and out of existence. This is experimentally validated through the Casimir force. So, we have a scenario in which quantum fluctuations can lead to a nugget of mass, which subsequently undergoes expansion through inflation, and gives us the cosmos we see.

Other models also rest on experimentally validated principles, such as a quantum tunnelling event, which rests on exactly the same principle of tunnelling that your computer chips rely on for their operation.

As for an infinity of time, there isn't actually any problem with this, contrary to the wibblings of some religious apologists.