We Just Discovered the Sounds of Spacetime. Let’s Keep Listening
Less than a decade since the first detection of gravitational waves—ripples in spacetime itself—proposed budget cuts threaten to silence this groundbreaking science
Illustration of two black holes orbiting each other.
Mark Garlick/Science Photo Library/Getty Images
Long ago, in a galaxy far away, two black holes danced around each other, drawing ever closer until they ended in a cosmic collision that sent ripples through the fabric of spacetime. These gravitational waves traveled for over a billion years before reaching Earth. On September 14, 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) heard their chirping signal, marking the first-ever detection of such a cosmic collision.
Initially, scientists expected LIGO might detect just a few of these collisions. But now, nearing the first detection’s 10th anniversary, we have already observed more than 300 gravitational-wave events, uncovering entirely unexpected populations of black holes. Just lately, on July 14, LIGO scientists announced the discovery of the most massive merger of two black holes ever seen.
Gravitational-wave astronomy has become a global enterprise. Spearheaded by LIGO’s two cutting-edge detectors in the U.S. and strengthened through collaboration with detectors in Italy (Virgo) and Japan (KAGRA), the field has become one of the most data-rich and exciting frontiers in astrophysics. It tests fundamental aspects of general relativity, measures the expansion of the universe and challenges our models of how stars live and die.
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LIGO has also spurred the design and development of technologies beyond astronomy. For example advances in quantum technologies, which reduce the noise and thereby improve LIGO’s detector sensitivity, have promising applications to both microelectronics and quantum computing.
Given all this, it comes as no surprise that the Nobel Prize in Physics was awarded to LIGO’s founders in 2017.
Yet despite this extraordinary success story, the field now faces an existential threat. The Trump administration has proposed slashing the total National Science Foundation (NSF) budget by more than half: a move so severe that one of the two LIGO detectors would be forced to shut down. Constructing and upgrading the two LIGO detectors required a public investment of approximately $1.4 billion as of 2022, so abandoning half this project now would constitute a gigantic waste. A U.S. Senate committee in mid-July pushed back against hobbling LIGO, but Congress has lately folded against administration budget cut demands, leaving it still on the table.
The proposed $19 million cut to the LIGO operations budget (a reduction from 2024 of some 40 percent) would be an act of stunning shortsightedness. With only one LIGO detector running, we will detect just 10 to 20 percent of the events we would have seen with both detectors operating. As a result, the U.S. will rapidly lose its leadership position in one of the most groundbreaking areas of modern science. Gravitational-wave astronomy, apart from being a technical success, is a fundamental shift in how we observe the universe. Walking away now would be like inventing the microscope, then tossing it aside before we had a good chance to look through the lens.
Here’s why losing one detector has such a devastating impact: The number of gravitational-wave events we expect to detect depends on how far our detectors can “see.” Currently, they can spot a binary black hole merger (like the one detected in 2015) out to a distance of seven billion light-years! With just one of the two LIGO detectors operating, the volume we can probe is reduced to just 35 percent of its original size, slashing the expected detection rate by the same fraction.
Moreover, distinguishing real gravitational-wave signals from noise is extremely challenging. Only when the same signal is observed in multiple detectors can we confidently identify it as a true gravitational-wave event, rather than, say, the vibrations of a passing truck. As a result, with just one detector operating, we can confirm only the most vanilla, unambiguous signals. This means we will miss extraordinary events like the one announced in mid-July.
Accounting for both the reduced detection volume and the fact that we can only confirm the vanilla events, we get to the dreaded 10 to 20 percent of the expected gravitational wave detections.
Lastly, we will also lose the ability to follow up on gravitational-wave events with traditional telescopes. Multiple detectors are necessary to triangulate an event’s position in the sky. This triangulation was essential for the follow-up of the first detection of a binary neutron star merger. By pinpointing the merger’s location in the sky, telescopes around the world could be called into action to capture an image of the explosion that accompanied the gravitational waves. This led to a cascade of new discoveries, including the realization in 2017 that such mergers comprise one of the main sources of gold in the universe.
Beyond LIGO, the proposed budget also terminates U.S. support for the European-led space-based gravitational-wave mission LISA and all but guarantees the cancellation of the next-generation gravitational wave detector Cosmic Explorer. The U.S. is thus poised to lose its global leadership position. As Europe and China move forward with ambitious projects like the Einstein Telescope, LISA and TianQin, this could result not only in missing the next wave of breakthroughs but also in a significant brain drain.
We cannot predict what discoveries still lie ahead. After all, when Heinrich Hertz first confirmed the existence of radio waves in 1887, no one could have imagined they would one day carry the Internet signal you used to load this article. This underscores a vital point: while cuts to science may appear to have only minor effects in the short term, systematic defunding of the fundamental sciences undermines the foundation of innovation and discovery that has long driven progress in the modern world and fueled our economies.
The detection of gravitational waves is a breakthrough on par with the first detections of x-rays or radio waves, but even more profound. Unlike those forms of light, which are part of the electromagnetic spectrum, gravitational waves arise from an entirely different force of nature. In a way, we have unlocked a new sense for observing the cosmos. It is as if before, we could only see the universe. With gravitational waves, we can hear all the sounds that come with it.
Choosing to stop listening now would be foolish.
This is an opinion and analysis article, and the views expressed by the author or authors are solely their own and not those of any organization they are affiliated with or necessarily those of Scientific American.