25 October 2019

Making real sense of quantum mechanics: “Something deeply hidden”

The new book by Sean Carroll, Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime, is probably the single best argument for the Everett understanding of quantum mechanics.

That’s the approach named after physicist Hugh Everett III and which is often also called (although slightly misleadingly) the “Many Worlds Interpretation”.

In his book, Carroll makes clear the powerful attractions of the Everett understanding, and persuasively counters the objections that are commonly raised against it. He highlights how this approach is the natural, straightforward response to the extraordinary success of the quantum formalism. Despite its apparent profligacy of multiple worlds (multiple diverging branches of reality), it’s actually a lean and austere interpretation of quantum mechanics. Unique among interpretations of quantum mechanics, it adds in nothing beyond the wave equation itself.

Back in the 1980s I spent four years mulling the philosophical implications of quantum mechanics. Over time, against my initial inclinations (and hopes), I came to have an increasing respect for the Everett understanding – an outcome I wrote about here. Alongside my grudging respect for that interpretation, I retained the view that it still faced many hard questions. However, Carroll’s book has convinced me that these questions aren’t particularly daunting. In other words, the book has strengthened my conviction that these “Many Worlds” do come into being whenever quantum transactions are macroscopically magnified.

In terms of the history of the topics covered, and the pros and cons of the different interpretations reviewed, I see Carroll as being overwhelmingly correct. I particularly liked his demolition of the idea that there’s such a thing as a coherent “Copenhagen interpretation” of quantum mechanics. The only area where I wanted to see the argument extended was that more could have been said about how all the non-Everett interpretations of quantum mechanics have to accept one or other kind of radical non-locality (despite the attempts of various writers to “have their cake and eat it”).

The final third of the book may be the most important. It reviews the possibility for progress in an area of physics that has long experienced troubles: quantum gravity. Carroll argues that the best hopes for us obtaining a correct quantum theory of gravity (that works at all energy scales) is to take quantum mechanics itself more seriously. This part of the book is more speculative than the earlier parts, but it has raised my interest in delving more into these topics.

This final part of the book also underlines the difficulties faced by the non-Everett interpretations of quantum mechanics in dealing, not with particles, but with the relativistic fields which modern physics views as being more fundamental than particles. This part also reviews how space and time should emerge from the theory of quantum gravity, rather than being presupposed as the canvas upon which the theory would operate. Some of the potential implications for black holes (and maybe even the Big Bang) are mind-stretching.

It’s a shocking possibility that each of us exist alongside numerous different versions of ourselves, in the overall multiverse – versions that have increasingly divergent experiences. I see this possibility as one of the most remarkable insights to have arisen from humanity’s millennia-long exploration into science. It’s an insight that takes time to sink in. It’s a good question how much this insight should change our day-to-day behaviour. Carroll has an answer to that too: not as much as we might first think. Personally I find it a humbling realisation.

PS For another book that addresses some of the same topics – inside an even larger set of profound ideas – I recommend Our Mathematical Universe by Max Tegmark.

30 January 2014

A brilliant example of communication about science and humanity

Mathematical Universe

Do you enjoy great detective puzzles? Do you like noticing small anomalies, and turning them into clues to an unexpected explanation? Do you like watching world-class scientists at work, piecing together insights to create new theories, and coping with disappointments when their theories appear to be disproved?

In the book “Our mathematical universe”, the mysteries being addressed are some of the very biggest imaginable:

  • What is everything made out of?
  • Where does the universe come from? For example, what made the Big Bang go “bang”?
  • What gives science its authority to speak with so much confidence about matters such as the age and size of the universe?
  • Is it true that the constants of nature appear remarkably “fine-tuned” so as to allow the emergence of life – in a way suggesting a miracle?
  • What does modern physics (including quantum mechanics) have to teach us about mind and consciousness?
  • What are the chances of other intelligent life existing in our galaxy (or even elsewhere in our universe)?
  • What lies in the future of the human race?

The author, Max Tegmark, is a Swedish-born professor of physics at MIT. He’s made a host of significant contributions to the development of cosmology – some of which you can read about in the book. But in his book, he also shows himself in my view to be a first class philosopher and a first class communicator.

Indeed, this may be the best book on the philosophy of physics that I have ever read. It also has important implications for the future of humanity.

There are some very big ideas in the book. It gives reasons for believing that our universe exists alongside no fewer than four different types of parallel universes. The “level 4 multiverse” is probably one of the grandest conceptions in all of philosophy. (What’s more, I’m inclined to think it’s the correct description of reality. At its heart, despite its grandness, it’s actually a very simple theory, which is a big plus in its favour.)

Much of the time, the writing in the book is accessible to people with pre-university level knowledge of science. On occasion, the going gets harder, but readers should be able to skip over these sections. I recommend reading the book all the way through, since the last chapter contains many profound ideas.

I think you’ll like this book if:

  • You have a fondness for pure mathematics
  • You recognise that the scientific explanation of phenomenon can be every bit as uplifting as pre-scientific supernatural explanations
  • You are ready to marvel at the ingenuity of scientific investigators going all the way back to the ancient Greeks (including those who first measured the distance from the Earth to the Sun)
  • You are critical of “quantum woo woo” hand-waving that says that quantum mechanics proves that consciousness is somehow a non-local agent (and that minds will survive bodily death)
  • You want to find more about Hugh Everett, the physicist who first proposed that “the quantum wave function never collapses”
  • You have a hunch that there’s a good answer to the question “why is there something rather than nothing?”
  • You want to see scientists in action, when they are confronted by evidence that their favoured theories are disproved by experiment
  • You’re ready to laugh at the misadventures that a modern cosmologist experiences (including eminent professors falling asleep in the audience of his lectures)
  • You’re interested in the considered viewpoint of a leading scientist about matters of human existential risk, including nuclear wars and the technological singularity.

Even more than all these good reasons, I highlight this book as an example of what the world badly needs: clear, engaging advocacy of the methods of science and reason, as opposed to mysticism and obscurantism.

Footnote: For my own views about the meaning of quantum mechanics, see my earlier blogpost “Schrödinger’s Rabbits”.

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