Something Deeply Hidden by Sean Carroll

Lately I have been reading several books on the subject of quantum physics. I had previously posted commentary on Kenneth W. Ford’s The Quantum World here. Unlike that general work, Something Deeply Hidden by Sean Carroll tries to make the case for a particular interpretation of quantum mechanics known as the many worlds or Everett theory. I found this book to be interesting and worthwhile. The information here is fresh as this was first published in 2019. It is essentially for laypeople and Carroll is a good writer and a good explainer. However, like all the books that I read on this subject, I found some of the science here difficult to understand. 

When approaching this book, it makes sense to start with what many call quantum weirdness. That term refers to the fact that what is observed on the subatomic level, seems to defy what we think of as everyday reason. Basically, subatomic particles often show wavelike characteristics, that is, they seem to be in multiple places at one time, just like a water wave in the ocean. Despite this, at other times these subatomic phenomena do not act like waves but act and appear as particles that can be pinned down as existing at a particular place. When scientists do pin down these particles as being in a particular place, the wave “collapses” and stops existing in multiple places at the same time.  There are many other strange aspects to quantum mechanics. Sometimes a pair of subatomic particles are tied in an odd way. For instance, changing the direction of spin of one particle changes the spin of the particle that it is paired with even if the particles are at great distance from one another. Another odd phenomenon is known as the Heisenberg Uncertainty Principle. This means that two properties of a particle can never both be known.  If one of the properties becomes know through observation the other property then becomes impossible to determine. For instance, if a position of a particle is found, its velocity becomes undefined, if its velocity is measured then the opposite happens, its position becomes undefined and undetectable. Carroll does a good job at explaining this mind - bending stuff. It is important to understand that even though some observations seem bizarre, there is a mathematical basis to quantum mechanics and these strange observations are supported by the math.

As per Carroll, many physicists just accept what is going on without digging too deeply. Instead, they just use these quantum rules as something of cookbook as to how the universe works. However, some physicists try to dig deeper and try to figure out if there is a more logical explanation or more concrete meaning behind this strange stuff. Carroll writes,

We have a recipe that we can safely apply in certain prescribed situations, and which returns mind-bogglingly precise predictions that have been triumphantly vindicated by the data. But if you want to dig deeper and ask what is really going on, we simply don’t know. Physicists tend to treat quantum mechanics like a mindless robot they rely on to perform certain tasks, not as a beloved friend they care about on a personal level.

I think that the above quotation illustrates that Carroll is a very eloquent science writer. 

The Many Worlds approach is not the theory that the majority of scientists believe. Currently a majority of experts in the field favor something called the Copenhagen Interpretation. My understanding of the Copenhagen Interpretation is that subatomic particles do not have defined properties. The oddness that is observed in then subatomic world is just a reflection of reality. Things work differently in the subatomic world. 

Another, somewhat less popular interpretation of known as hidden variables. There are various subsets to this theory but it basically says that there are all sorts of hidden phenomena going on that connects particles and waves under the surface. These unseen phenomena would provide a logical explanation as to why all these odd things are happening if we could only observe them. 

The many worlds interpretation is different. At times, when a subatomic particle acts in a wavelike manor it shows signs of being in many places at once. But when scientists try to pin it down the particle it sometimes appears in a particular place. It then stops being a wave or it stops being in multiple places at one time. Many worlds advocates argue that at the moment that the location of the particle becomes defined, the universe divides in to multiple universes, each universe containing the particle in a different place. Theorists believe that an astronomically high number of universes have been created this way. 

To a person unfamiliar with all this, many worlds may seem far - fetched. Indeed, based upon this book and my other readings on the subject, most physicists do not concur with this interpretation. However, some very prominent scientists think that it is the most likely explanation of all this. It is also not a theory attributed to cranks. Even the majority of scientists who disagree with it seem to take it seriously. Furthermore, it seems supported by the math, is considered elegant and relatively simple comparted to other interpretations, which, when one digs into them, seem to twist logic. Many scientists find the other interpretations incomplete.

Many world theory has been around for a long time. It has become a popular subject for science fiction writers. Roger Zelazny's Chronicles of Amber series and Robert Heinlein's Number of the Beast are just a couple of examples are books that have been influenced by these ideas. The various Star Trek series are filled with stories based on this theory. Carrol's work is very science orientated and does not explore these cultural aspects however.

My take is that Many Worlds is probably not what is really going on. As Carl Sagan once commented “extraordinary claims require extraordinary evidence". The extraordinary evidence has not yet been produced by the many worlds advocates. However, based upon everything that I have learned from my readings, I believe that this is all possible. As a good scientist will do, Carroll acknowledges that this interpretation has not been proven and may not be the true.

Though this book focused upon one particular theory, it helped me to understand the subject in general. Ford is a good writer and explains things well. He goes beyond the theory that he is advocating and explains the basics of quantum physics here too. Furthermore, he does a good job of laying out multiple competing interpretations, he explains both their strengths and weaknesses. Despite all that, quantum physics can be a very difficult subject. Like other books on this subject, there were parts of this that I did not understand.

This is the third book on the subject of quantum physics that I have recently read. Since this book deviates from an introductory work, I would not recommend that someone not familiar with the subject start here. In Search of Schrödinger’s Cat by John Gribbin may be the best introductory book that I have read. I think that someone who is already familiar with a little bit of this subject will find this an educational and a worthwhile read. Quantum physics is a subject that digs into the nature of reality itself. It is worth trying to understand. This book helps one to understand while exploring  some intriguing possibilities.