It is a story in three acts, ending with many bangs and much whimpering.
Act I: In the early 20th century, a small cadre of physicists laid the groundwork for quantum physics and Albert Einstein theorized general relativity.
Act II: In the mid 20th century, physicists united quantum physics with electrodynamics to create quantum electrodynamics and created the Standard Model of Particle Physics which now stands at 6 leptons, 6 quarks, 12 gauge bosons (including the photon and 8 types of gluons), and the recently detected Higgs boson.
Act III: In the late 20th century particle physics, heady with a solid century of mathematically driven success, hypothesized supersymmetry, string theory, dark matter, dark energy, and multiverse theory, all of which predicted a host of new particles that were just awaiting the right experiments to push humanity to new and strange vistas of understanding. Within the last decade, we’ve detected gravitational waves (2017) and discovered the Higgs boson (2012), which is great-n-all, but so far, in spite of ever more refined experimental methods and three decades of trying, none of the particles predicted by physicists’ more recent theories have been found.
None of them.
It’s a problem that the physics community understandably is reluctant to talk publicly about – how will people support the building of newer and larger colliders if the ones we now possess manifestly haven’t found any of the things we were assured they would find? And while many physicists seem to continue to believe that success is just around the corner, a younger generation is rising and asking the tough question – Are we on the right track?
The key popular text for that movement might well come to be Lost in Math: How Beauty Leads Physics Astray (2018) by Sabine Hossenfelder (b. 1977), a particle physicist out of Germany who has publicly wondered for some time just where physics is going, and why it can’t seem to shake itself from its most seductive past theoretical visions. In this book, Hossenfelder lays out the last century of physical research as a case of once-useful assumptions and practices run amok.
During its long Golden Age physics developed theories to account for data using the reality conquering might of mathematics. In this, it was uproariously successful, but the road was strewn with Messiness – aesthetically ugly quantities and constants that needed to be “fine-tuned” in order to keep the models approximating observed reality. Somewhere along the way, it was decided that Nature surely couldn’t allow such messiness in her ledger, and new physical theories were proposed that got rid of the fine-tuned quantities and their attendant absurdly low or high values, but at a cost.
The cost for these new theories with their more natural numbers and higher physical unifications was an explosion of new particles and dimensions that had not yet been observed but that, given the more powerful super colliders being proposed in the 1990s, surely would be soon. For science nerds growing up in the 80s and 90s, those visions, as explained by physicists turned popular communicators like Steven Weinberg, Stephen Hawking, and Roger Penrose, were absolutely intoxicating and lured a fresh crop of new talent into the physics fold. Is reality based on multi-dimensional vibrating strings? Is most of the universe composed of a dark matter that we can’t observe but that is changing the course of galaxies? Will dark energy one day consume us all? Does each physical event branch into an Everything That Can Happen Does plethora of multiverse chains of which we are just one?
Full of excitement about finding at last the One Rule to Ring Them All, a generation rushed into string theory and supersymmetry and dutifully pushed their shoulders to the stuck wheel of their educational mentors. Hossenfelder too, after receiving her undergraduate degree in 1997 from the Johann Wolfang Goethe-Universitat, hopped into Kaluza-Klein theory, a five-dimensional theory dating from the 1920s that hoped to merge the field equations of Einstein, the equations of Maxwell, and the findings of quantum mechanics. Klein had taken Kaluza’s 5 dimensional theory and interpreted his 5th dimension as an ultra-miniscule (on the order of 10-30 cm) curled dimension.
This notion of using small scale curled extra dimensions to explain and unify our known four-dimensional theories was a predecessor of modern string theory, but after two years Hossenfelder, like so many before and since, hadn’t been able to make it quite come out as hoped, and so she switched her doctoral thesis to “Black Holes in Large Extra Dimensions” (2003) and headed out into the scientific wilderness to strike her own path as a quantum gravity physicist.
It has been a path encompassing multiple media – in 2006 she launched a science blog, BackReaction, still in existence, as a means of communicating new developments in physics to a world intensely interested in new physical theories, but lacking access to the specialty journals where the latest debates are being fought or a ready familiarity with the deep math at the heart of those academic tussles. Her online voice is that of a fearless, irreverent revolutionary speaking up for unfashionable disciplines. While thousands of researchers throw billions of dollars at increasingly elaborate plans to discover dark matter particles with increasingly discouraging results, Hossenfelder has advocated for a modified Newtonian gravity approach which is as plausible but has garnered a fraction of the public attention. She sticks up for messy constants and grotesque theorems as against the self-feeding tidal wave of academic pressure that Truth is (Mathematical) Beauty and (Mathematical) Beauty Truth.
In 2016, Hossenfelder set out on a world tour to speak with physicists about the aesthetic biases of new physics and to gauge their feelings about where physics is now that decades of expensive testing have failed to yield the desired results. The outcome of those interviews is this year’s Lost in Math, a sobering tromp through broken careers and the musings of confused and depressed mathematical titans. One by one, they each express optimism about what the future holds only to admit that the criteria by which new theories are chosen for testing are less than rigorous, and the cavalcade of negative results markedly less than encouraging. Reading the book is like visiting a cemetery where none of the bodies have quite realized that they’re dead, but deep in the sadness of lost illusions there is at the same time a great exhilaration. Supersymmetry may be dead, but that means there is still Work To Do. We have not yet reached the stage so feared by the late 19th century, where physics is merely a matter of mopping up a few loose details, and everywhere you turn, if you have eyes to see them, there are people working on the fringes at beautifully ugly theories that might, after decades of neglect, turn out to be the Stuff of Truth after all.
This is where Hossenfelder does her work in quantum gravity, sending reports back to the normal world of the pock-marked battlefield she surveys before her, inspiring a generation of quirky non-conformists to try something new. In speeches and research, through blogging and song, Hossenfelder is knocking the rust out of our scientific joints. The question of course remains, will we use this gift? Will we remain where we are or will we run?
Lead image by Jörg Steinmetz, published on Women You Should Know with express permission of the photographer.
FURTHER READING: Lost in Math is a great book wherein Hossenfelder leads you, Virgil-like, through the labyrinth of modern physics research, past physics colossi wallowing in disillusion and into the lairs of rogue physicists crafting new approaches to old problems. You can find her blog here, and on her YouTube channel you can see not only neat explanatory videos about modern physics but also some music videos of songs Hossenfelder wrote.