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SUNDAY SCIENCE: HAPPY BIRTHDAY, LIGO. NOW DROP DEAD.  
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Dennis Overbye
September 10, 2025
The New York Times
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_ Ten years ago, astronomers made an epic discovery with the Laser
Interferometer Gravitational-Wave Observatory. Cosmology hasn’t been
the same since, and it might not stay that way much longer. _

An artist’s rendering of two black holes spiraling around each
other, a phenomenon scientists believe produced the gravitational
waves of the GW170104 signal detection of Jan. 4, 2017,
LIGO/Caltech/MIT/Sonoma State (Aurore Simonnet), via Science Source

 

It’s been 10 years since astronomers first felt the universe
tremble.

At 4 a.m. on Sept. 14, 2015, in both the desert of eastern Washington
State and the backwoods of Louisiana, two beams of light began
quivering in distant synchrony as the space through which they were
traveling stretched and shrank at a rate of 250 times a second.

These were the twin antennas of the Laser Interferometry
Gravitational-wave Observatory, or LIGO. Far out there in time and
space a pair of black holes, gargantuan pits of eternally dark
nothingness, had collided and merged, sending gravitational waves
rippling through the universe and across the paths of the two
antennas.

The whole encounter lasted one-fifth of a second. But that instant
changed astrophysics, opening a window onto previously inaccessible
realms of nature in which space could rip, bend, puff up, crumple and
even vanish.

It was the first direct proof that ripples in space-time, predicted by
Albert Einstein a century earlier, actually existed. In the decade
since, LIGO and other experiments have logged more than 300 of these
violent collisions, providing astronomers with clues regarding the
evolution of black holes across cosmic history.

That black holes are ubiquitous in the universe is now beyond doubt.
The LIGO antennas have justified their once contentious title as
observatories, and similar observatories — VIRGO in Italy, KAGRA in
Japan — have been started; some 1,600 astronomers and physicists
worldwide are doing business as the LIGO/VIRGO/KAGRA, or LVK,
collaboration. LIGO’s founders, Rainer Weiss of M.I.T. and Kip
Thorne and Barry Barish of the California Institute of Technology,
were awarded the Nobel Prize in Physics in 2017.

The anniversary festivities commence on Sept. 13 with parties and open
houses at the LIGO observatories in Hanford, Wash., and Livingston,
La., A symposium follows on Oct. 10 at Caltech, with speeches by Nobel
laureates.

As an opening drumroll, on Sept. 10, a team of more than 1,000
astrophysicists led by Katerina Chatziioannou of Caltech announced
that LIGO had confirmed a groundbreaking conjecture, first enunciated
more than 50 years ago by Stephen Hawking, that black holes could only
grow, a notion that has revolutionized theoretical physics.

But the celebrations have fallen under a shadow. In late August, Dr.
Weiss, a garrulous lab rat and tinkerer, died at age 92, less than a
month before the anniversary of his greatest achievement. Without him,
scientists say, there would have been no gravitational wave
observatory.

“I don’t know anybody who had any substantial interactions with
Rai that didn’t come away from them a better person in some way,”
said David Reitze, a physicist at Caltech and director of the LIGO
Laboratory, which runs the two antennas.

Rainer Weiss inside the Laser Interferometer Gravitational-Wave
Observatory Lab at M.I.T. in 2018.Credit...Kayana Szymczak for The New
York Times

More ominously, President Trump has proposed slashing LIGO’s
operating budget in 2026 by 40 percent, to $29 million from $48
million, and eliminating one of the antennas. That could spell
disaster, as it takes two antennas to triangulate the origins of
gravitational waves.

Dr. Reitze, who spent an agonizing summer studying budget scenarios,
said he thought the observatory could be run on the budget suggested,
but barely. “It’s going to be ugly,” he said. Most immediately
affected would be the 200 or so scientists and technicians at the LIGO
Laboratory who run and maintain the antennas on behalf of the larger
LVK community. Dr. Reitze described them as “very special scientists
and engineers with very specialized skills who have mortgages to pay
and kids to put through college.”

The impact on performance and future upgrades would be devastating, he
added: “It would be nearly impossible for LIGO to recover from a cut
of this magnitude.”

A gadget with gravity

Dr. Weiss liked to say that he learned the most by building a gadget
and then trying to get it to work. That’s the story of LIGO, in a
nutshell.

In the 1970s, in a ramshackle M.I.T. building where radar had been
invented three decades earlier, Dr. Weiss began assembling a device to
detect the subtle squeezing and stretching of space-time thought to be
produced by gravitational waves, still hypothetical at the time. Only
the densest, most extreme objects in the universe — black holes and
neutron stars — were expected to be able to produce faint waves of
this sort. Many astronomers, especially at M.I.T., doubted that black
holes even existed.

In time, the National Science Foundation merged Dr. Weiss’s efforts
with a similar project at Caltech, where black holes were more in
fashion. The result was a pair of L-shaped buildings in Hanford and
Livingston; each housed laser beams that bounced back and forth
between mirrors and would reveal any incoming fluctuations.

For years the scientists heard nothing, even as they and increased
their analytical and computational powers and improved the sensitivity
of the antennas. Then, in September 2015, they turned on their latest
version of the device, called Advanced LIGO. The detection bells
sounded.

“It was waving hello,” Dr. Weiss later said. “It was amazing.
The signal was so big, I didn’t believe it.”

In the void 1.3 billion light-years away, two black holes, 29 and 36
times as massive as the sun, had collided and merged to become a black
hole with the mass of 62 suns. Three suns worth of mass and energy,
equivalent to the light from a billion trillion stars, had disappeared
into the rippling of space-time.

A comparison of a newly detected gravitational-wave signal called
GW250114 with the first gravitational-wave signal ever detected,
GW150914, in 2015. Both signals came from colliding black holes, each
between 30 to 40 times the mass of the Sun.CreditCredit...LIGO/Derek
Davis (URI)

That was enough energy to budge LIGO’s mirrors and stretched the
distance that the laser beams traveled by four one-thousandths the
diameter of the nucleus of a hydrogen atom.

As it happens, the ringing of space-time caused by the collision of
these particular black holes produced waves at the same frequencies
that humans hear. Translated into acoustical waves, those first
gravitational waves were a brief chirp, ending in a middle C.

Such chirps are now a regular feature of the science; if you have the
Gravitational Waves Events app on your smartphone, you hear them every
three days or so. The most recent compilation of gravitational wave
events, released this week, included at least one object not massive
enough to be a black hole, and a couple that were too massive,
according to standard astrophysical lore.

One disappointment has been the lack of opportunity to engage in what
the community calls multi-messenger astronomy, combining
gravitational-wave studies with traditional telescopic observations.
Black holes being invisible, there is nothing to see.

Multi-messenger astronomy reached its full potential in 2017, when a
pair of neutron stars — the dense remnants of collapsed stars —
collided, producing a new kind of explosion called a kilonova. Neutron
stars are full of stuff that generates both light and noise, and the
collision rang the antennas with a chirp that drew more than 4,000
astronomers who would later sign on to one of the many scientific
papers on the event. Astronomers calculated
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the blast generated 40 to 100 Earth masses worth of gold in a fraction
of a second — future cosmic bling.

Sadly, nothing similar has happened since. “It appears that we just
got REALLY lucky with GW170817,” Daniel Holz, an astrophysicist at
the University of Chicago, wrote in an email. “And that set up
completely unrealistic expectations for the rate of these systems.”

But hope springs eternal out there, and strange, novel events could
occur any time. “The excitement in this field is that we may be
discovering new things,” Dr. Reitze said. “We may be pointing
ourselves, telling our astronomer friends to point their telescopes,
in places where they even discover new things that aren’t associated
with gravitational waves. So we’ll have to see how this plays out
over probably the next weeks or months.”

How black holes grow

David Reitze, executive director of the LIGO Laboratory, right,
speaking at a news conference to discuss developments in
gravitational-wave astronomy at the National Press Club in Washington
in 2016.Credit...Alex Wroblewski for The New York Times

At the same time, there is the fulfillment of a longstanding promise
made to Stephen Hawking, the celebrated English cosmologist and black
hole expert.

 

In 1970, Dr. Hawking made a bold conjecture after studying the
equations that describe black holes: The area of a black hole’s
event horizon — the invisible bubble in space that defines its point
of no return — must always increase. Nature didn’t have to work
that way. Why couldn’t black holes split in two, or splatter off
each other and disappear like soap bubbles? According to Hawking,
these bubbles of nothingness could only grow.

Dr. Hawking’s insight became a keystone of a 1973 paper, “The Four
Laws of Black Hole Mechanics,
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wrote with James Bardeen, a physicist at the University of Washington,
and Brandon Carter, now at the French National Center for Scientific
Research. They compared the idea to a famous law in thermodynamics,
which stated that entropy — the amount of wasted heat or energy in a
system — always increased. (Entropy is why you can never build a
perpetual motion machine.)

This idea implied that black holes had entropy — as Jacob
Bekenstein
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then a graduate student at Princeton, first argued — and heat, which
suggested that they were not so black after all. They could be hot and
even explode, as Hawking predicted a few years later. Among other
things it suggested that the growth of black holes is as ineluctable
as rust, and that the entropy and disorder in the universe will
continue to grow.

A half-century later, some of the best minds in the world are still
arguing
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how that would work, and what it might mean. At stake is the question
of whether Einsteinian gravity, which shapes the larger universe,
plays by the same rules as quantum mechanics, the paradoxical laws
that prevail inside the atom.

In 2003, Dr. Thorne predicted that LIGO would be able to test
Hawking’s theory by actually measuring the sizes and other
properties of black holes. That would be his present to his friend
Hawking on his 70th birthday in 2012, Dr. Thorne told him.

But the data from the first recorded black hole collision, in 2015,
was too noisy and uncertain to draw any immediate conclusions, and Dr.
Hawking died three years later. In 2021, after years of computer
simulations and data wrangling, a team led by Maximiliano Isi, a
physicist at now at Columbia University, announced
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there was a 97 percent chance
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Dr. Hawking had been right: The total area of the black holes had
increased during the merger, at least for this particular black hole
collision.

Stephen Hawking in his office at the Center for Mathematical Sciences
in Cambridge, England, in 2007.Credit...Leon-Neal/Agence France-Presse
— Getty Images

Now the team led by Dr. Chatziioannou, which includes Dr. Isi, has
surpassed the first result, providing what they say is the best and
clearest evidence yet, at a more than 99 percent level of confidence,
that Dr. Hawking was right.

The evidence emerged in January, when LIGO recorded the collision of
two evenly matched black holes, 33.6 and 32.2 times as massive as the
sun.

“It was twice as loud as the next loudest thing we have seen,” Dr.
Chatziioannou said in a telephone interview. This was mainly because
the LIGO detectors had been improved greatly since the first collision
in 2015. “We immediately understood that you could do interesting
things with it,” she said.

The merged black hole was 62.7 times as massive as the sun, which
meant that three suns worth of mass had disappeared into gravitational
waves.

Teasing out these details of the collision required a deep dive into
the last few moments of black-hole annihilation and creation. When a
newly merged black hole forms, it vibrates like a drum or a bell,
generating a fundamental tone and a raft of overtones and undertones.
As a result, Dr. Chatziioannou said, “Space-time, the gravity around
it, is a mess.”

Because the chirp was so loud, Dr. Chatziioannou and her team were
able to neglect the messiness and identify the final reverberations
produced as the new black hole settled down. These revealed that the
two black holes had begun with a combined area of 240,000 square
kilometers, but merged into one with an area of 400,000 — a
resounding growth.

“Our results suggest that astrophysical black holes are indeed
extremely simple objects that follow general relativity,” Dr.
Chatziioannou and her colleagues concluded. And with that, Dr.
Hawking’s mortal remains can continue to rest quietly among those of
Britain’s other scientific heroes in London’s Westminster Abbey.

_DENNIS OVERBYE [[link removed]] is the
cosmic affairs correspondent for The Times, covering physics and
astronomy._

_Subscribe to the NEW YORK TIMES
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Scientists Take on Trump: These Researchers Are Fighting Back
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By Dan Garisto, Max Kozlov & Heidi Ledford
Nature
Through lawsuits, grant tracking, whistle-blowing and more, resistance
to the US war on science is growing.
September 10,  2025

* Science
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* Donald Trump
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