Recently finished John Scalzi’s fine Old Man’s War. One plot point is that tachyons come to betray attacking ships emerging from wormholes. Tachyons have never been detected nor is their place in reality even theoretically firm. But considering the compelling hypothesis that there is an observer duality between reference frames outside a black hole, and the frame of reference of an observer falling into a black hole (laid out in Leonard Susskind’s excellent The Black Hole War), combined with the ever more salient model of a multiverse (if you haven’t read it already, see Max Tegmark’s Our Mathematical Universe), it may be inevitable that tachyons are all around us.
First, presume Tegmark’s “level-one” multiverse exists. If I remember his levels correctly, this is the simplest multiverse model that simply states that our observable universe is not special, that the Big Bang – whatever it was that started an Inflationary expansion – occurs from time to time within a larger space, like inflationary bubbles. Assume this has been going on for long time frames, such that many bubbles have expanded, like stars in our own reality – generations of universes that have come and gone. From time to time (possibly often, depending on how rare Inflationary expansions are), the 3- (or 11- or 12-) dimensional “domain” of one universe expands into another adjacent universe. We’re not talking about universes with differing “constants” – this multiverse is the model where the same laws of physics apply across the entire multiverse. We already pretty much know that there is an (inverted) event horizon at the edge of the observable universe, where the expansion of spacetime apprears to us to be faster than light. So what would it look like if another Inflationary universe was already expanding into our own observable universe?
For each of the reference frames in both intersecting universes to be consistent, it seems pretty necessary that either the particles of one universe will pass thru the other as high energy photons, with relativistic time dilation resolving the excess energy implied by the faster-than-light collision; or, if we suppose that time dilation is inconsistent or not in play between the intersecting universes, the particles of one universe will appear as tachyons to the other universe.
If it ends up as tachyons, what happens when these tachyons occasionally impact a particle in our universe? Perhaps tachyons decay into normal-looking matter in our own universe? Maybe they do this via neutrino creation. Maybe this constant influx of matter everywhere within the intersection domain (which might easily be as large as our entire universe – imagine the generations of intersecting universes in the same way that myriad dust clouds from generations of dead stars now intersect and overlap in our own universe as a tangled mess), is playing a part in what we currently call Dark Energy – a mysterious, unresolved acceleration in the expansion of our observable universe. Do tachyons, or at least the particles of intersecting universes, play a role in Dark Matter? Do they play a role in the statistical nature of Quantum Mechanics? Is the apparent randomness of QM transitions actually being influenced by unseen other particles? Could we test this intersecting-universes model by analyzing the cosmic microwave background – or maybe it is only visible by looking at the cosmic background in much lower or higher energies? On the other hand, maybe such a survey would see nothing but a random tangle of exotic decays, because that’s the only pattern…?
The thing I find most compelling is simply the near necessity that this is what is occurring. To say that this is not what the larger level-1 multiverse looks like requires invoking a special place for we humans – or our universe. This view seems to be the natural extrapolation of assuming that not even our position in time, within the lifespan of the multiverse, is special.