Oct 24 2014

The Many Interacting Worlds Hypothesis

Howard Wiseman, a theoretical quantum physicist at Griffith University in Brisbane, Australia, and his colleagues have come up with an entirely new theory to explain the weird behavior of particles at the quantum level. The idea is that quantum effects result from classical universes interacting with each other.

Classical physics is essentially the physics of Newton and describes the macroscopic world. In classical physics particles have a definitive location and momentum. At the scale of fundamental particles, however, the world behaves very differently.

At this so-called quantum level, particles move in waves but then interact as particles. They have only a probabilistic location and cannot be nailed down specifically. There is a minimum amount of uncertainty when trying to measure any linked properties, such as location and momentum. Even more bizarre is quantum entanglement in which particles have linked properties, even when separated across the universe.

The bottom line is that we do not really know why the quantum world behaves as it does. We have experimental data, such as the double-slit experiments, that show consistent results. When light beams shine through two close narrow slits they interfere with each other as if they are moving like waves, even when the beams are so faint that only one photon will be passing through the silts at a time. One photon can apparently cause a wave interference with itself. But when those same photons strike a film plate or detector, they behave like a particle.

The experimental results are fairly clear. What is not clear is how to interpret those results. Quantum mechanics defies all of our evolved intuitions. It seems to reflect an aspect of reality that is completely foreign to us. Our experiments, while important, are not directly accessing the deepest level of reality. We are just probing in ways that we know how to probe and then trying to infer from the results something about reality that goes beyond our current concepts.

Perhaps the most popular interpretation of quantum experiments is the Copenhagen interpretation. This hypothesis states that fundamental particles exist as waves of probability, but when they are forced to interact with their environment the probability waves collapse into a specific value, more like a classic particle. This is a consistent interpretation, but it’s just that – an interpretation.

We cannot conclude that this is likely to be the correct interpretation because we don’t know what all the alternatives are. We don’t know enough about the fundamental nature of reality to have any confidence that we have a complete set of hypotheses.

This new “many interacting worlds” hypothesis is a good example of the fact that physicists can still come up with entirely new interpretations of quantum observations that are no more bizarre than the Copenhagen interpretation. In this hypothesis there are many universes that coexist along with our own, but they are (at least as far as we can say) completely isolated and inaccessible from our own universe. This “many worlds hypothesis” is not new to quantum physics, and has been offered as an interpretation alternative to Copenhagen. In the many worlds view, each collapse of a probability wave actually splits off a separate universe – there is a separate universe in which each quantum possibility becomes reality.

This new twist assumes that universes are classical all the way down. However, these classical universes can bump into each other and interact with each other. They speculate that this interaction might be able to explain some of the quantum experimental observations. For example, two universes bumping into each other might cause one to surge forward while the other bounces back. This behavior could explain the observation of quantum tunneling, where quantum particle will tunnel through a barrier.

It’s actually a little generous to call this a hypothesis. It’s more of a wild speculation, but you have to start somewhere. The next challenge will be to work out some of the math and physics, and to see if this notion could explain other quantum phenomena, like entanglement. Then the real challenge comes – designing an experiment that could distinguish the many interacting worlds hypothesis from the Copenhagen interpretation. It’s possible that the two interpretations will make slightly different predictions about experimental measurements.


It is very uncertain if the many interacting worlds interpretation will turn out to be of any use to theoretical physics and it’s unlikely to transform our understanding of quantum mechanics. It might, but it’s a long shot.

The bigger lesson here, in my opinion, is that it is premature, to say the least, to use any specific interpretation of quantum mechanics as a justification for otherwise fantastical claims.  I find it interesting that most people doing so, for example justifying claims of ESP or astrology, generally don’t really understand quantum theory or the current interpretations, none of which allow for superluminal remote information transfer.

My sense is that we are still a long way away from a meaningful understanding of what our observations of quantum phenomena actually mean in terms of the fundamental nature of reality. There still room for theoretical physicists to say, “hey, what if this completely different interpretation is true.’

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