My latest for the Wall Street Journal
Spooky Action at a Distance
Albert Einstein used the term “spooky action at a distance” to refer to the way that, according to quantum theory, particles that have once interacted with one another remain in some sense “entangled” even when they are far apart. Poke one particle, in the right quantum-mechanical way, and the other particle jumps, instantly, even if it is on the other side of the Universe. He did not mean the term as a compliment, and did not believe that the effect could be real. Alas for Einstein (but fortunately, perhaps, after his death) experiments based on the theoretical work of the physicist John Bell proved that this entanglement is real. More precisely, they proved that something called “local reality”, which is a feature of everyday commonsense, is not real.
Local reality says that there is a real Universe out there, even when we are not observing it (trees that fall in the woods make a noise even if nobody is there to hear it). The “local” bit of the name says that these real objects can only influence one another by influences that travel at less than or equal to the speed of light. There is no instantaneous linkage. The experiments show that the combination, local reality, does not hold. The simplest explanation is that “locality” is violated – spooky action at a distance. Alternatively, there may not be a real world out there which exists independently of our measurements. In that case, the conceptual problems arise because we are trying to imagine what “particles” are like when they are not being measured; if we discard the idea of such a reality, we can preserve locality. And if you really want a sleepless night, consider that both locality and reality may be violated.
George Musser’s book is likely to invoke such sleepless nights. He starts off with Bell’s work and its implications, building up through a rundown of the history of the development of quantum physics. This, you should be warned, is the easy bit. Having established that local reality is not a valid description of how the Universe works, Musser takes us out into far deeper waters. Quantum field theory is just the beginning, and introduces another form of non-locality. Then the general theory of relativity and black holes offer up another candidate for this entanglement, now see as a universal effect, not something that only particle physicists have to worry about. After all, the general theory allows for the existence of so-called “wormholes”, tunnels through space and time that link different parts of spacetime – distant parts of Universe, or (conceivably, although Musser does not elaborate on this) different universes. A wormhole is intrinsically nonlocal. Some theorists have suggested that mini-wormholes might link entangled particles, and explain their shared properties.
The island of knowledge that we are swimming towards, frantically trying to keep afloat, is that both space and time are illusions. Non-locality is the natural order of things, and space itself is manufactured out of non-local building blocks. “Locality,” says Musser, “becomes the puzzle,” but so is the nature of those building blocks. The analogy he uses to explain this involves water. Individually, the building blocks of water – molecules – are not wet, but collectively they produce the sensation of wetness. Individually, the building blocks of the Universe, yet to be identified, are not spacial, but collectively they produce the sensation of space.
This is tough going, and in spite of the author’s heroic efforts to make difficult concepts comprehensible, he does not always succeed. But the ideas he discusses, such as matrix theory, or the possibility that “our” Universe is a holographic image projected from some higher reality, are at the cutting edge of physics today, and nobody should expect all the loose ends to be neatly tied up.
Indeed, the most powerful message to take from this book is tucked away, almost apologetically, near the end. Science is all about debate, and progress is made by arguing about cherished (but not necessarily correct) ideas, until some consensus emerges. When the consensus is reached, the physicists become bored and move on to something new. The sound of physicists arguing is the sound of science making progress. That is the “sound” of this book. But “yesterday’s drag-out fights are tomorrow’s homework problems”, as Musser succinctly puts it.
As this example illustrates, he has a neat turn of phrase which helps to make the difficult ideas described here slightly less difficult to comprehend. But don’t think “less difficult” means “easy.” Spooky Action at a Distance is an important book which provides insight into key new developments in our understanding of the nature of space, time and the Universe. It will repay careful study, and I am sure it will become a well-thumbed feature of my reference shelf, while the extensive bibliography will help those who want to delve further. But it is not something you can digest in a single reading.