The probability wavefunction; a creature whose characteristics propose the existence of simultaneously dead and alive cats, observational dependent existence, and other hard to swallow quantum truths, may have collapsed- indefinitely.

As a reminder, the probability wave function is the way of describing the state of a quantum mechanical system. For such a system, the most that can be known before measurement is the probability of it being in a certain state. There may be it a high probability it is in state X and a low probability it is in state Y and all this information is mapped out with the wavefunction. Then when a measurement is made, to assume a value of the state, the probability wavefunction collapses to one single point.

Now, quantum mechanics has often been characterized as the quasi-sci-fi realm of physics and when one enters this rabbit hole to the quantum world they are confronted by a vast array of weirdness. See ‘The Nature of Reality‘ for some examples. However, Professor Howard Wiseman, physicist at Griffith University in Brisbane Australia, along with Dr. Michael Hall and Dr. Dirk-Andre Deckert of University of California, Davis have come up with a new ‘Many Interacting Worlds’ (MIW) theory which seeks to present Quantum 2.0 – without the weirdness (well not as much).

Firstly a little bit of history – a theory of many worlds* has been around for quite some time. The ‘many-worlds interpretation’ (MWI – an annoyingly very similar acronym) of quantum mechanics was introduced in 1957 by Hugh Everett. Everett suggested that instead of a simple collapse of the probability wavefunction every time a quantum measurement was made, resulting in one distinct outcome – all possible outcomes happen, each occurring in its own separate universe. The probability predicting a particle may be here or there actually reflects that in one universe it is here and in another universe it is there. As an illustration if a coin is flipped, the probability of it landing heads or tails is 50:50, however instead of one outcome occurring, both occur, both heads and tails but in different parallel universes. As the coin is flipped, crudely speaking in this example, the universe “splits” in two, in each with a future occurring heads or tails, and you in each of these universes looking at the outcome thinking your reality is the only reality. The MWI claims to reconcile how we can perceive non-deterministic events, such as the random decay of a radioactive atom, with the deterministic equations of quantum physics.

Throughout the life of quantum mechanics, the probability wavefunction has been a core entity providing the understanding for fundamental quantum properties such as wave –particle duality. Wiseman however interjects stating ‘You can’t think of the wave function as a real thing.’ The MIW  does away with the wavefunction entirely and the complexity of Schrodinger’s equations that come along for the ride. Instead, it postulates that the parallel universes have always existed, they are not a by-product of quantum measurement and conversely the quantum effects we detect arise from the interactions between these worlds themselves. Wiseman and colleagues claim that the quantum weirdness is the resulting effect of the particles in these worlds interacting with each other via repulsive forces between corresponding particles as soon as they diverge a tiny bit. The interaction only occurs under very specific conditions and the particle twins need to be on roughly a nanoscopic distance scale. However it is believed the resulting minute interactions under these strict conditions are enough to explain quantum behavior.

Wiseman uses the famous double-slit experiment to support his case that particles in or universe feel the presence of their corresponding particles living alongside in the ‘ghost universes’. In this experiment, a beam of photons is fired at a barrier in which two slits have been cut. The light that passes through the barrier in then recorded on a photographic plate. Even when firing single photons, which if in accordance with Newtonian mechanics should act as bullets, going through one slit or another, a wave interference pattern still occurs, commonly only produced by interfering particles on a wave front. The MIW theory proposes it is the interaction with these phantom photons residing in the parallel universes that causes the interference pattern to arise. In fact Wiseman showed that taking a framework where only 41 worlds exist, the same interference pattern as observed would arise.

The beauty of this theory resides in the satisfying ‘visual’ picture it paints. If there was only our world the mechanics would reduce to the familiar Newtonian workings. However if the number of worlds is colossal, or perhaps infinite, quantum mechanics becomes the natural fall out due to Many World Interaction. The apparent weirdness is only construed as weird from our perspective because we are unable to see outside of our own universe, we are unable to see the full stage of actors in play. The ghost universes and phantom particles remain in their very nature hidden from our analysis and according to Wiseman leave traces of their presence in the form of quantum quirks.

* Here, a “world” means an entire universe with well-defined properties, determined by the classical configuration of its particles and fields.