At the tail end of November, I talked for a bit about the notional decades of physics in the twentieth century, the topics that define particular eras that only roughly approximate calendrical decades. These notional decades parallel what we seen in pop culture: the Beatles define The 1960s in the popular imagination despite not really taking off until the calendrical decade was halfway done.

When I did that post, I stopped with the 1990s, despite the fact that weve had two more calendrical decades since then. I did that because I wanted to leave room to write a post wrapping up the decade thats ending in a few weeks, but the nature of these notional decades means that they spill over a bit. So, you get a two-for-one here: one post, about the physics topics that define two decades. Actually, its more of a three-for-one, because Ill throw out two possibilities for what will come to be seen as The Physics of the 2010s, though in the end I favor one of these.

So, to jump right in, my first definition:

A view of the magnet core of the world's largest superconducting solenoid magnet (CMS, Compact Muon ... [+] Solenoid) at the European Organization for Nuclear Research (CERN)'s Large Hadron Collider (LHC) particle accelerator, which is scheduled to be switched on in November, in Geneva, Switzerland, Thursday, March 22, 2007. Some 2,000 scientists from 155 institutes in 36 countries are working together to build the CMS particle detector. (AP Photo/Keystone, Martial Trezzini)

The 2000s Were the Decade of the Large Hadron Collider.

In very Beatlesesque fashion, the LHC didnt actually turn on until the decade was mostly over, but unlike a pop-cultural phenomenon that can explode out of Liverpudlian obscurity, big physics projects have a long lead time (and a large up-front price tag), so everybody knew this was coming. And this knowledge shaped every discussion about physics for years before the machine actually turned on.

I started blogging in 2002, and by the time I moved to ScienceBlogs in 2006 I was already thoroughly sick of hearing about how awesome the LHC was going to be. And that doesnt even count the many stories about possible disasters Could the LHC Make a Black Hole That Will Destroy the Earth? which culminated in John Olivers 2009 visit to the accelerator for The Daily Show (story about the clip here, video here).

The excitement about the discoveries sure to be made by the LHC had big effects on lots of other experiments, adding an air of desperation to the last runs at Fermilab, as the folks there raced to see if they could detect the Higgs boson before the LHC even turned on. It also penetrated to other subfields I remember listening to talks about searches for an electronic dipole moment of the electron circa 2001 where the speakers guessed they had maybe ten years to do the experiment before the LHC was sure to find whatever beyond-the-Standard-Model particle would turn out to be responsible for the symmetry violation they were hoping to measure.

FILE - In this March 30 2010 file picture s cientist of the European Organization for Nuclear ... [+] Research, CERN, react in the SMS experiment control room at their headquarter outside Geneva, Switzerland. The world's largest and most powerful atom smasher goes into a 2-year hibernation in March 2013 , aiming to reach maximum energy levels that may lead to more stunning discoveries after hunting down the so-called "God particle. But physicists at the European Center for Nuclear Research, known by its French acronym CERN, won't exactly be idle as the US $10 billion proton collider goes on hiatus for maintenance and retooling _ in preparation for unlocking more mysteries. There are still reams more data to sift through since the July discovery of a new subatomic particle called a Higgs boson and promises a new realm of understanding in subatomic science. (AP Photo/Anja Niedringhaus)

The initial turn-on of the LHC in September 2008 was huge news, as was the failure of an electrical connection that shut the whole machine down very shortly thereafter. When it turned on again a bit more than a year later, in November 2009, it was also big news (though slightly more measured), and by 2012 had achieved one of its stated goals, the discovery of the Higgs boson. There were numerous books written anticipating the discovery and about the actual discovery, and eventually the 2013 Nobel Prize in Physics to a subset of the theorists who had a claim on inventing the idea. (As always, the politics of the Nobel are a mess, but that was just more fodder for articles about particle physics...)

So I think its unquestionable that the 2000s were the Decade of the Large Hadron Collider, in the notional decade sense of the 2000s as a period starting in 2005-ish and ending in 2013.

What, then, would that mean for The Physics of the 2010s? I will note up front that this is, to some degree, a fools errand, as you really ought to allow a bit of time to pass before you can truly assess what counts as The physics of a notional decade. Were in an era of instant content generation, though, so we dont have that luxury. In which case, I have two possibilities to offer:

Room with concrete floor and smoke with dark wall background

Possibility 1: The 2010s Were the Decade of Nothing

This is actually a very natural follow-on to the LHC, because in many ways the most notable thing about the Large Hadron Collider is not that it succeeded in detecting the Higgs, but that it hasnt detected anything else. Despite numerous confident predictions that the LHC was going to usher in an era of beyond-the-Standard-Model discoveries, it just hasnt. There dont seem to be any new particles with masses in the energy range where people were expecting new discoveries; it also hasnt obviously made any micro black holes or anything else exotic.

To be fair, the LHC isnt alone in this. Numerous experiments have come online looking for dark matter particles (WIMPs and axions and other such things), and found nothing. Those electric dipole moment searches I mentioned above havent turned up new physics, either. There have been some claims made about detections of weird new phenomena in astrophysical observations, but the splashiest of these was definitively disproven, and others remain controversial.

This has led to endless articles about a Crisis in [Theoretical Particle] Physics. This is in some sense a continuation of a process thats been going on far longer there was the String Theory Backlash back in the mid-2000s but it feels a little different this time. In the past, defenders of particular theories had the LHC and other scheduled experiments to point to, offering hope of a definitive discovery to come. In the present moment, its not clear what the next experiment would even be, let alone whether theres the political will to get a next generation of Big Physics Stuff built.

So, in that bleak atmosphere, its tempting to call the 2010s the Decade of Nothing, in honor of all the new physics that hasnt been discovered. Thats awfully depressing and cynical, though, so Id like to offer a more uplifting possibility:

FILE - In this file photo dated Thursday, Feb. 11, 2016, Laser Interferometer Gravitational-Wave ... [+] Observatory (LIGO) Co-Founder Kip Thorne speaks during a news conference at the National Press Club in Washington, USA, to announce that scientists have finally detected gravitational waves. The Nobel Physics Prize 2017 is announced Monday Oct. 3, 2017, awarded to 3 scientists including Kip Thorne, for discoveries in gravitational waves. (AP Photo/Andrew Harnik, FILE)

Possibility 2: The 2010s Were the Decade of Black Holes

This is really a two-fer in its own right, because it combines two splashy big experiments: the 2015 observation of gravitational waves from two colliding black holes by the Laser Interferometer Gravitational-wave Observatory (LIGO), and the release just this April of an image of the supermassive black hole in the center of the M87 galaxy by the Event Horizon Telescope. The LIGO folks already won the 2017 Nobel Prize in Physics, and Ill be a little surprised if some of the EHT folks dont get a trip to Stockholm sometime in the next several years.

Those two discoveries plus follow-on work fro LIGO and Virgo, and the steady accumulation of observations from people whove been tracking the stars orbiting the black hole Sag A* at the center of the Milky Way have really moved black hole physics into a new era. Of course, the 2010s is also the era of We Cant Have Nice Things, so theres some lingering controversy about the interpretation of LIGOs signals, but on the whole I think these have been the early years of an exciting new era for astrophysics. It also doesnt hurt that black hole physics had a bit of a pop-cultural moment, with Interstellar in 2014.

So, those are the two main possibilities I see for what future physicists will say was The Physics of the 2010s: either black holes, or the failure to find new physics. Given that part of the point of these end-of-decade lists is secretly to look to the future, though, I would tend to give the nod to black holes, as a positive and exciting development that opens up rather than closes off hope for exciting future developments.

IN SPACE - APRIL 10: In this handout photo provided by the National Science Foundation, the Event ... [+] Horizon Telescope captures a black hole at the center of galaxy M87, outlined by emission from hot gas swirling around it under the influence of strong gravity near its event horizon, in an image released on April 10, 2019. A network of eight radio observatories on six mountains and four continents, the EHT observed a black hole in Messier 87, a supergiant elliptical galaxy in the constellation Virgo, on and off for 10 days in April of 2017 to make the image. (Photo by National Science Foundation via Getty Images)

Again, this is a bit of a fools errand, as its difficult to say what will really dominate the perception of physicists of, say, 2050, looking back with a bit more perspective. There might be some development that seems relatively minor now that will come to dominate the future in a way that makes LIGO seem quaint. Theres really no way to say for sure.

I do, however, have a couple of guesses as to some dark-horse candidates for such a discovery. I tend to think, though, that these are things that might be heralding the start of a new decade, though, rather than things that will define the decade just ending. It wouldnt be appropriate to do that much looking to the future, though, so stay tuned for a future post...

Read more:

What Are The Physics Stories That Define The 2000s And 2010s? - Forbes