Why Gravitational Wave Science Is The Future Of Astronomy

By John Oncea, Editor

LIGO’s 2025 detection confirmed Hawking’s black hole area theorem, proving black holes only grow post-merger and highlighting gravitational wave astronomy’s future.

A couple of years ago, our sister site, RF Globalnet, invited readers to jump into Mr. Peabody’s WABAC Machine and journey to 1977. There (or should we say “then”), we witnessed the reception of a 72-second radio signal at the Big Ear that may have been a communication from an extraterrestrial civilization.

It was a wild ride, so much so that I’m inviting Photonics Online readers to do the same, setting the date to 1971 and the location to Oxford, England. More specifically, to Stephen Hawking’s workplace at the University of Cambridge, where, at the time, he held a fellowship at Gonville and Caius College and was a Research Fellow, working in the Department of Applied Mathematics and Theoretical Physics, which housed many theoretical cosmologists, and where he was a leading figure in black hole research.

It was during this time that Hawking derived the black hole area theorem, which states that the total surface area of a black hole’s event horizon can never decrease over time. It is considered the second law of black hole mechanics and is analogous to the second law of thermodynamics. This means that when two black holes merge, the resulting black hole’s event horizon area must be greater than or equal to the combined area of the original two black holes.

Hop back into your WABAC machine and go forward a year to witness Jacob Bekenstein conjecture that black holes have entropy proportional to their event horizon area. Another short, two-year jump to hear Hawking provide us with a physical basis for Bekenstein’s conjecture by showing that black holes emit Hawking radiation, a thermal radiation that causes them to lose energy, while simultaneously showing that their area must increase.

Next, set your dial for September 14, 2015, and your destination to the Laser Interferometer Gravitational-wave Observatory (LIGO), where researchers, according to NPR, detected the first gravitational waves from a black hole merger, event GW150914. The event involved two black holes merging to form a new, larger black hole, with the final area being greater than the combined areas of the initial black holes, consistent with Hawking’s area theorem.

One more jump, this one to 2021 and Cornell University (or Massachusetts Institute of Technology, if you prefer), where physicists confirm Hawking’s area theorem for the first time using the 2015 LIGO data. They analyzed the gravitational wave signal to compare the black holes' areas before and after the merger.

This brings us back to 2025 and the announcement by LIGO that Hawking’s 50-year-old theorem on how black holes merge together has been proven. According to Northwestern, “By analyzing the frequencies of gravitational waves from a merger between two black holes, the team verified … Hawking’s 1971 black-hole area theorem, which states the total surface area of black holes cannot decrease.

“The signal is the clearest to date detected by … LIGO, Virgo, and KAGRA (LVK) collaboration. The finding sheds further light on the mysterious nature of black holes, one of the most extreme objects in the universe.”

Playing a large part in this recent discovery were advances in gravitational wave astronomy, which helped astronomers catch the waves caused by an unusually powerful collision as they passed Earth at the speed of light.

While gravitational waves aren’t a recent discovery, the use of them by researchers at facilities such as LIGO to help measure the minute ripples in space-time caused by passing gravitational waves from cataclysmic cosmic events, such as the collision of neutron stars or black holes, or supernova, is.

So, go ahead and park your WABAC machine, and let’s dig into what gravitational waves are, how they’re being used, and what role photonic technology is playing in enabling their ability to improve the future of astronomy.

What Is Gravitational Wave Science?

Gravitational wave science is the study and detection of ripples in spacetime generated by massive accelerating objects such as merging black holes and neutron stars. These waves were predicted by Albert Einstein in 1916 as a consequence of general relativity, according to Caltech.

In simple terms, when extremely massive bodies move rapidly in curved spacetime, they disturb that curvature, sending propagating distortions outward at the speed of light. Unlike electromagnetic radiation, gravitational waves interact only very weakly with matter, meaning they carry nearly pristine information about processes that are otherwise hidden or invisible. This feature is what has made gravitational wave astronomy one of the most rapidly expanding frontiers of astrophysics.

Gravitational wave science is particularly notable because the primary tool for detecting these waves is laser interferometry, implemented at extraordinary length scales, stability requirements, and noise suppression levels. Instruments such as LIGO operate by measuring differential length changes on the order of 10⁻¹⁹ meters, or about one-thousandth the diameter of a proton.

Achieving this sensitivity requires extremely stable laser systems, kilometer-scale Fabry-Perot cavities, suspended optics, advanced vibration isolation, and quantum noise reduction techniques such as squeezed-light injection. For engineers accustomed to integrated photonics, fiber-optic metrology, or ultrastable laser systems, gravitational wave observatories are effectively interferometers pushed to the edge of physical possibility.

History and Theoretical Foundations

Einstein first proposed gravitational waves in 1916, but their status remained unclear for decades; at one point, he briefly argued that they might not exist, before the issue was resolved mathematically, according to Princeton.

The first strong indirect evidence came in 1974, when Russell Hulse and Joseph Taylor observed a binary neutron star system whose orbital decay precisely matched the rate predicted if the system were radiating energy as gravitational waves, according to The Nobel Prize Foundation. This confirmed the phenomenon, but it did not provide direct detection.

During the mid-20th century, multiple experimental approaches were proposed. In 1962, M. E. Gertsenshtein and V. I. Pustovoit outlined how optical interferometers could detect gravitational waves, though their proposal initially drew little attention. In the late 1960s, Joseph Weber attempted detection using resonant aluminum bars, but his signals could not be replicated, according to NIST.

The decisive conceptual advance came from Rainer Weiss, who independently developed the idea of a kilometer-scale Michelson interferometer with suspended mirrors to detect differential strain, according to LIGO. By 1979, the U.S. National Science Foundation began supporting interferometer design studies. In 1990, funding was approved for the full construction of LIGO. After decades of engineering development, LIGO and its European partner Virgo reached operational sensitivity in the 2010s.

On September 14, 2015, LIGO detected gravitational waves from the merger of two black holes roughly 1.3 billion light-years away. The signal, named GW150914, was announced publicly in 2016 and confirmed Einstein’s prediction with direct observation, a moment marking the birth of gravitational wave astronomy.

Current Scientific Uses and Instrumentation Significance

Today’s gravitational wave science focuses on using interferometers to observe astrophysical events that would otherwise be invisible. Black holes, for example, do not emit light. Before gravitational wave detection, evidence for black holes came from indirect effects, such as gravitational lensing or accretion disk emissions.

Gravitational waves allow us to detect black hole mergers directly and reconstruct properties such as mass, spin, and orbital dynamics. Because gravitational waves are not absorbed or scattered by dust or matter, they serve as probes of regions inaccessible to traditional electromagnetic telescopes.

Interferometric gravitational wave detectors operate by measuring tiny changes in the effective optical path length between two perpendicular arms. Laser beams are split, bounced off suspended mirrors at the ends of each arm, and recombined at a photodetector. When a gravitational wave passes, spacetime itself stretches one arm while compressing the other. Even for large astrophysical events, these strains are incredibly small, requiring photonic systems with unprecedented isolation from thermal noise, seismic vibration, optical scatter, and quantum uncertainty.

The refinement of quantum noise suppression has become critical as instruments reach fundamental sensitivity limits. The injection of frequency-dependent squeezed states of light reduces shot noise at high frequencies while not worsening radiation pressure noise at low frequencies, a technique now standard in LIGO and Virgo operations, according to arXiv. Optical coatings, mirror mass, suspension geometry, beam size, and laser stability all represent ongoing photonic and precision-fabrication research frontiers.

The Current Landscape and Collaborative Global Network

LIGO in the United States, Virgo in Italy (European Gravitational Observatory), and KAGRA in Japan (Institute for Cosmic Ray Research, University of Tokyo) form the baseline global detection network. A coordinated network allows triangulation of event locations, improving sky localization and enabling electromagnetic follow-up observations.

In August 2017, LIGO and Virgo observed the merger of two neutron stars (GW170817), and telescopes across the electromagnetic spectrum confirmed the event, linking gravitational wave sources to heavy-element production in kilonova explosions. This was the first instance of multi-messenger astronomy, demonstrating how gravitational waves complement traditional telescopes.

Looking Ahead: Future Directions

The future of gravitational wave astronomy involves improved sensitivity, broader frequency coverage, and space-based detection. On Earth, upgrades such as LIGO A+ aim to enhance mirror coatings, squeezed-light injection, and suspensions. Larger next-generation ground detectors such as the proposed Einstein Telescope in Europe and Cosmic Explorer in the United States would use longer arms and quieter environments to detect fainter and more distant events, according to the Einstein Telescope project.

Space-based detection will open an entirely different frequency band. The Laser Interferometer Space Antenna (LISA), scheduled for launch in the 2030s by the European Space Agency in partnership with NASA, will place three spacecraft in a triangular formation millions of kilometers apart. This architecture will detect gravitational waves from supermassive black hole mergers and galactic binaries, complementing the higher-frequency ground-based observatories.

For photonics engineers, LISA represents one of the most ambitious interferometric systems ever conceived, demanding long-distance laser phase stability, autonomous formation flying, and new drag-free inertial reference systems.

Gravitational wave astronomy transforms how we study the universe. By detecting tiny distortions in spacetime using sophisticated laser interferometry, scientists can now observe events that produce little or no electromagnetic radiation. Each advance in interferometric sensitivity expands the volume of the observable universe and the range of astrophysical processes accessible to science. F

This field is not only a scientific revolution but also an ongoing engineering challenge: pushing lasers, mirrors, coatings, suspensions, and quantum optical techniques to new limits. Gravitational waves are to astronomy what sound is to sight. Now that we can hear the universe, the symphony is only beginning.