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Tracking gravitational waves—invisible ripples in space-time from intense astronomical events—pushes the limits of what astronomers must do to reduce unwanted noise. Scientists have been getting increasingly better at doing just that, but new research warns that something rather unexpected might be getting in the way: daylight savings time.
In a preprint titled “Can LIGO Detect Daylight Savings Time?,” Reed Essick, former LIGO member and now a physicist at the University of Toronto, gives a simple answer to the paper’s title: “Yes, it can.” The paper, which has yet to be peer-reviewed, was recently uploaded to arXiv.
That might seem like an odd connection. It’s true that observational astronomy must contend with noise from light pollution, satellites, and communication signals. But these are tangible sources of noise that scientists can sink their teeth into, whereas daylight savings time is considerably more nebulous and abstract as a potential problem.
To be clear, and as the paper points out, daylight savings time does not influence actual signals from merging black holes billions of light-years away—which, as far as we know, don’t operate on daylight savings time. The “detection” here refers to the “non-trivial” changes in human activity having to do with the researchers involved in this kind of work, among other work- and process-related factors tied to the sudden shift in time.
The presence of individuals—whether through operational workflows or even their physical activity at the observatories—has a measurable impact on the data collected by LIGO and its sister institutions, Virgo in Italy and KAGRA in Japan, the new paper argues.
We ripple in space
To see why this might be the case, consider again the definition of gravitational waves: ripples in space-time. A very broad interpretation of this definition implies that any object in space-time affected by gravity can cause ripples, like a researcher opening a door or the rumble of a car moving across the LIGO parking lot.
Of course, these ripples are so tiny and insignificant that LIGO doesn’t register them as gravitational waves. But continued exposure to various seismic and human vibrations does have some effect on the detector—which, again, engineers and physicists have attempted to account for.
What they forgot to consider, however, were the irregular shifts in daily activity as researchers moved back and forth from daylight savings time. The bi-annual time adjustment shifted LIGO’s expected sensitivity pattern by roughly 75 minutes, the paper noted. Weekends, and even the time of day, also influenced the integrity of the collected data, but these factors had been raised by the community in the past.
“[Gravitational wave] interferometers are not uniformly sensitive to signals coming from different relative directions and orientations,” Essick wrote in the paper. This inconsistency, in tandem with changes in Earth’s rotations and known noise factors, could “easily create non-trivial selections” and a “systemic bias” in gravitational wave astronomy, he added.
No clear path forward
A solution to this problem won’t come easily. What’s more, the new research suggests “other hidden selections might be present within gravitational wave observations,” Essick remarked.
That said, the analysis is more of a reminder that our data could be biased in unexpected ways, he added. Gravitational wave astronomy is a growing field, and as we collect more data, the influence of these subtle effects will grow in scale.
Multi-messenger astronomy—using different techniques to cross-check the same phenomenon—could help verify results. Space-based observatories with zero human presence could eliminate this problem altogether. The lesson is to just “retain healthy skepticism,” Essick wrote.
And really, that’s a prudent stance to have for scientific pursuits in general.
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Gayoung Lee
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