Last week I was supposed to be in England for HowThe LightGetsIn, an amazing science and arts festival in Hay.  I was going to give a talk on our book The Blind Spot. How Science Cannot Ignore Human Experience and be part of many really cool panels.  Then I got sick and had cancel.  It was very disappointing and a reminder of the brute reality of living in a human body. 

One of the panels I was looking forward to included me, physicist Chiara Marletto and physicist/science popularizer Brian Green.  Its title was “The Unintelligible Universe”.  Even though I could not participate then, I want to explore a little bit of the ground we were to cover today . 

Here is the way the question was posed.

“Look deep into nature, and you will understand everything better,” claimed Albert Einstein. And we naturally expect scientific investigation into nature to reveal a comprehensible universe. Yet the more modern physics develops, the less it seems to make sense. Relativity tells us that the passing of time is an illusion; quantum mechanics implies observation creates reality; string theorists claim we inhabit a universe of 26 hidden dimensions.

Physicists admit they can ''calculate but not visualize'' with little agreement on what their own theories mean. Is our inability to make our physical theories intelligible a challenge to our everyday understanding of the world, or a challenge to contemporary physics? Should we treat the theories as mathematical models and give up on them as descriptions of reality? Or could it be that theoretical physics can capture in mathematics a truth about the universe that is beyond our understanding?

So how would I have addressed this question?

To begin with I would have pushed a little on the formulation.  Something strange has happened over the last 50 years in the domain sometimes called “foundations of physics” (we’ll call it Foundations).  In the past, there was always a tight coupling between our most advanced theories of nature and our ability to test those theories in the lab.  But sometime around 1970 a gradual divergence between theory and experiment occurred.  Theorists began exploring ever more speculative extensions of our best tested models (what's called the Standard Model of Particle Physics).  These works often outpaced our ability to test their consequences via experiments.  The result became a kind of Alice-in-Wonderland proliferation of physical theories with ever wilder expansions of the meaning of reality.

String Theory is the poster child for this untethering.  Introduced in the 1980s, String Theory proposed that the world is not made of little bits of matter i.e. particles.  Instead, it was composed of tiny vibrating strings.  It was a cool idea and, initially, seemed to hold a lot of promise for unifying the two great edifices of 20^th century physics: Einstein’s Relativity Theory which describes Space and Time, and Quantum Mechanics which describes the nature of matter. 

But there was a price.  To make String Theory work theorists needed reality to have many “hidden dimensions” of space beyond the three we experience (up-down, left-right, forward-backward). It was heady stuff.

In the 1990’s and early 2000s’ String Theory was an exciting idea for both physicists and the general public.  Lots of popular books were written about those amazing hidden dimensions and how profoundly they change our ideas about what’s real.

Except they didn’t.

By the mid 2000’s it became clear that String Theory was running out of steam.  It simply was not delivering on its promise of being a “Theory of Everything”.  Even worse, by the late 2010’s the Large Hadron Collider kicked a leg from the chair String Theory was standing on.  Originally, String Theory was really Supersymmetric String Theory.  That’s because it depended on another unproven theory called Supersymmetry (or SUSY) which was supposed to take us to the next level beyond the Standard Model (see the image below).

In spite of Supersymmetry’s popularity, the giant particle accelerator called The Large Hadron Collider found no evidence for it (at least its most favored version).  While String Theorists have looked for work-arounds, by 2020 if you asked an average physicist if String Theory was still exciting, the answer would be a definitive “No”. 

Yet, somehow, in the popular imagination String Theory - with all its heady talk of extra-dimensional Space-Time membranes - lives on.  Just as dangerous, with the demise of String Theory, the disconnect between theory and experiment in Foundations has continued with new hyper-speculative untestable proposals being put forward every week. 

This, to me, is a lot of what’s happening with the idea that physics is full of “unintelligible” ideas.  It feels a lot like physicists in this one domain are, as we used to say in Jersey, “smoking their own stash”.

Now don’t get me wrong, Relativity and Quantum Mechanics have some amazing things to teach us showing us a world far richer than we might naively imagine. But I think they are intelligible, especially once we understand how they are both deeply grounded in our experience as agents in the world. That’s a subject I promise to come back to in future posts.

What is important to understand today, however, is that despite of what’s happened in the subfield of Foundations, physics is doing just fine.  Because of what’s happened with String Theory and its ilk, some people say “progress in physics has stalled”.  This is crazy talk.  From Quantum Information Theory to Complex Systems to Exoplanet science, physics is exploding with new ideas and new, experimentally verified discoveries. 

It’s an amazing time to be alive.

What this does mean, however, is 21^st century physics may look very different from 20^th century physics.  Different kinds of foundational questions – answerable questions - are coming to the fore.  There are new frontiers and new fundamentals being explored.  This includes my favorite mystery “What is Life”.

 So… stay tuned.

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PS If you have specific questions or issues you want me to address leave a comment on the website or email me at [email protected]

— Adam Frank 🚀