stephon_h_alexander's picture
Professor of Physics at Brown University; Author, The Jazz of Physics
The Light Side of Locality

Before I entered the intellectual funnel of graduate school, I used to cook up thought experiments to explain coincidences, such as  running into a person immediately after a random thought of them. This secretive thinking was good mental entertainment, but the demand of forging a serious career in physics research forced me to make peace with such wild speculations.  In my theory of coincidences, non-local interactions as well as a dark form of energy was necessary; absolute science fiction!  Fifteen years later, we now have overwhelming evidence of a 'fifth-force' mediating an invisible substance that the community has dubbed 'dark energy'.   In hindsight, it is of no coincidence that I have changed my mind that nature is non-local. 

Non-local correlations are not common experience to us, thus it is both difficult to imagine and accept.  Often, research in theoretical physics encourages me to keep an open mind; or to not get too attached to ideas that I am deluded into thinking should be correct.   While this has been a constant struggle for me in my scientific career thus far, I have experienced the value of this theoretical ideology weaning process.  After years of wrestling with some of the outstanding problems in the field of elementary particle physics and cosmology, I have been forced to change my mind on this predisposition that has been silently passed on to me by my physics predecessors, that the laws physics are, for the most part, local.

During my first year in graduate school, I came across the famous Einstein, Podosky and Rosen (EPR) thought experiment, which succinctly argue for the inevitable 'spooky action at a distance' in quantum mechanics.   Then came the Aspect experiment that measured the non-local entanglement of photon polarization confirming EPRs expectation that there exist non-local correlations in nature enabled by quantum mechanics (with a caveat of course).   This piece of knowledge had a short life in my education and research career.

Non-locality exited the door of my brain once and for all, after I approached one of my professors, an accomplished quantum field theorist.  He convinced me that non-locality goes away once quantum mechanics properly incorporates causality, through a unification with special relativity; i.e. a theory known as quantum field theory.   With the promise of a sounder career path I invited these, then comforting words, and attempted to master quantum field theory.   Plus, even if non-locality happens, these processes are exceptional events created under special conditions, while most physics is completely local.  Quantum field theory works and it became my new religion.  I have since remained on this comfortable path.

Now that I specialize in the physics of the early universe, I have first hand witnessed the great predictive and precise explanatory powers of Einstein's general relativity, married with quantum field theory to both explain the complete history and physical mechanism for the origin of structures in the universe, all in a seemingly local and causative fashion.  We call this paradigm cosmic inflation and it is deceptively simple.  The universe started out immediately after the big bang from a microscopically tiny piece of space then inflated 'faster than the speed of light'.   Inflation is able to explain our entire complexity of observed universe with the economy of a few equations that involve general relativity and quantum field theory.

Despite its great success inflation has been plagued with conceptual and technical problems.  These problems created thesis projects and inevitably, jobs for a number of young theorists like myself.  Time after time, publication after publication, like a rat on his wheel, we are running out of steam, as the problems of inflation just reappear in some other form.  I have now convinced myself that the problems associated with inflation won't go away unless we somehow include non-locality. 

Ironically, inflation gets ignited by the same form of dark energy that we see permeating the fabric of the cosmos today, except in much greater abundance fourteen billion years ago.  Where did most of the dark energy go after inflation ended?  Why is some of it still around?  Is this omniscient dark energy the culprit behind non-local activity in physical processes?  I don't know exactly how non-locality in cosmology will play itself out, but by its very nature, the physics underlying it will affect 'local' processes.  I still haven't changed my mind on coincidences though.