Like many others, I listened to yesterday's (10/16/17) press release at the NSF without a special prior insight in the physics of neutron star mergers, or in the details of the measurements we can extract from the many observations that the detected event made possible. My knowledge of astrophysics is quite incomplete and piecemeal, so in some respects I could be considered a "layman" listening to a science outreach seminar.

Yet, of course, as a physicist I have a good basic understanding of the processes at the heart of the radiation emissions that took place two hundred million years ago in that faint, otherwise unconspicuous galaxy in Hydra. 

Such a superposition of states - half layman, half professional - prevents me from stepping up and giving some critical insights in the science of what was observed. For that, I believe there are dozens of very reliable and readable sources you can peruse, a click or two away. On the other hand, maybe in my position I can still be useful, by making some personal observation on the matter.

Let me be clear about one thing. The last two years of gravitational waves astronomy have brought us an immense wealth: the dream of being able of studying the universe with a battery of simultaneous probes (the so-called "multi-messenger astrophysics") has become true. Whoever says this is not a scientific revolution has not grasped the implications, or is just envious for not being involved. 

It is funny from my viewpoint, as for decades I have observed my colleagues working on gravitational wave antennas wondering how they felt, as they were always left out of the big hype banquet set and consumed when large particle physics experiments came online and made discoveries, or when large neutrino facilities found neutrino oscillations, or when space observatories produced groundbreaking new results on the cosmos. They worked in the dark, carefully tuning their interferometers, studying for years how to dampen the noise and increase their sensitivity. They deserve the spotlights now. 

Physicists, astrophysicists, and astronomers deal with different physics processes with different instruments, but we are really one big community which attacks the few big questions from different sides. One example will suffice to explain what I mean: we all look for dark matter (DM), which most of us believe is made up by weakly-interacting particles that were produced in the big bang and still hang around today. But while collider physicists seek in their detectors for DM in processes where two ordinary particles hit each other and produce a pair of DM particles (so you have zero DM particles to start with, and end up with two), astrophysicists look up in the sky for a signal of DM particles annihilating and producing two ordinary particles (processes where there are two DM particles at the beginning, and zero at the end). And then there are those underground detectors, operated by physicists who have the strong background in nuclear physics necessary to understand down to the excruciating detail the background from common sources; they search for the scattering of a DM particle off an ordinary one, when you have one DM particle in the initial state and one in the final state. 

As you see, different kinds of physics backgrounds are required for very different tasks: studying subnuclear physics collisions, studying flashes of light from the sky, or studying recoil of nuclei in underground detectors; but the goal is the same. Now, what happens with these new gravitational waves signal we have started to detect from far-away locations in the universe is that they allow for a big part of the community of researchers in fundamental physics and astrophysics to join forces, and make their instruments a better bang for the buck. The single neutron-star merger discussed in yesterday's press release has allowed over 70 different collaborations of scientists to combine their data, and obtain astounding amounts of information. 

And this is just the beginning, as after the Ligo and Virgo detectors will finish their upgrade (scheduled for the next 12 months), they will be able to extend the volume of space where they can detect similar events by a factor of eight. This will further multiply the information we can collect on the evolution of the universe. Furthermore, some more good things await us: we have not yet seen a coincident signal of gravitational waves and neutrinos, something that is expected at least in the case of (relatively close) supernova explosions, if we increase our sensitivity and wait for enough time. We have tens of neutrino detectors in operation nowadays, so a further increase in the pool of involved physicists is expected then. 

As a particle physicist who has steadily remained in the field of hadronic collisions for almost three full decades, I cannot help realizing, finally, that I now know how my gravitational wave colleagues must have felt when the top quark was found, when neutrinos were shown to oscillate, when the LHC became operational, or when the Higgs boson was discovered. Not jealous at all, but eager to know more about what is going on in my colleagues' field. 

Do I feel the urge to move to astrophysics today? Well, no, although I would be happy to participate - I am too overcommitted to take on something so different from scratch. On the other hand, my knowledge is best spent where I currently am, and I believe the same holds for many of my colleagues. If as I hope gravitational wave detectors will increase in number and attract more physicists, these should be young new forces. And I do hope that in some way collider physics will soon come to connect more closely to astrophysics and cosmology, by e.g. discovering dark matter particles. Don't be mistaken: at the LHC we do perform a lot of measurements that increase our knowledge of the early universe; but these are small, incremental steps, which fail to excite laypersons or call for press releases. So, dear colleagues, here's my suggestion: stand your ground. We need you where you are.


Tommaso Dorigo is an experimental particle physicist, who works for the INFN at the University of Padova, and collaborates with the CMS experiment at the CERN LHC. He coordinates the European network AMVA4NewPhysics as well as research in accelerator-based physics for INFN-Padova, and is an editor of the journal Reviews in Physics. In 2016 Dorigo published the book “Anomaly! Collider physics and the quest for new phenomena at Fermilab”. You can purchase a copy of the book by clicking on the book cover below.