One thing that is, on the face of it at least, attractive about the Mirror Universe made of anti-matter on the "other-side" of the Big Bang is the fact that when dealing with quantum mechanics and particle physics, anti-matter can be thought of in terms of "time-reversed normal matter". What is meant by this is that a positron travelling forward in time is mathematically, and to a certain extent, physically identical to a positron (the anti-particle to the electron) travelling backwards in time (but see note below). John Wheeler once explored the idea that there was only one single electron made in the Big Bang, that moved forward in time before reaching the temporal and spacial end of the universe (whatever that was as he was not concerned with what it was), before traveling backwards in time (and thus appearing as an positron to us folk made out of normal matter and whose arrows of time are fixed) to the moment of the Big Bang, at which point it would travel forwards in time again looking like an electron...ad infinitum. The upshot would also be the same for all other types of particle within the particle zoo,

There were of course flaws with this idea, such as one would expect to see at any one moment in time, a roughly equal number of particles and anti-particles within this universe, which is not what we see. Indeed, it appears that the universe is made up almost entirely of matter rather than anti-matter. We do not yet know why this asymmetry occurs, especially since most models suggest that the bog bang should produce matter and anti-matter in equal numbers, so this is an ongoing research question.

But to bring it back to Turok's idea, then the Big Bang could have produced two universes, one of matter and one of anti-matter heading in different directions of time (which might explain the matter/anti-matter asymmetry we observe in our universe). So the universe on either side of the big bang would appear to be expanding under their own times-arrow direction. However, from the view point of our universe, one could could consider the mirror universe either as an expanding universe of anti-matter, or, as a collapsing universe of normal matter. In other words, it could look like the big crunch of a previous universe to our own, when viewed from the perspective of a direction of the arrow of time.

While I like Turoks idea, I wouldnt bet on it being correct, but it is fun on speculating upon it, and who knows it might lead to some insights into some of the unsolved cosmological mysteries.


*Note, I said that an anti-particle is identical to a time reversed normal particle, but that it can also be thought of as being identical both mathematically and to a certain extent physically. this is because some particles do not conserve what is known as CPT symmetry (or CP-symmetry as it is also sometimes known). This symmetry states that if you reverse the Charge (i.e exhange a particle for its anti-particle), Parity (mirror the spacial coordinates), and the direction of Time (time reversal), then the physical evolution of a system or interaction will remain unchanged. However, it was found that some particles undergoing decay (such as Kaons) violate CP symmetry, and it is these violations that could be the cause of the observed matter/anti-matter asymmetry that we observe today. So in some cases it may be the case that a particle travelling forwards in time is identical to an antiparticle travelling backwards in time.

Jonny

The path to good scholarship is paved with imagined patterns. - David M Raup