Chirps of exultation, triggered by a press conference held yesterday in Washington, D.C., are rippling through the noosphere.
Scientists overseeing LIGO, the Laser Interferometer Gravitational-Wave Observatory, announced that they had detected gravitational waves, first predicted by Einstein’s theory of general relativity a century ago. “This was truly a scientific moonshot, and we did it, we landed on the moon,” LIGO executive director David Reitze declared, according to Scientific American’s Clara Moskowitz.
On September 14, LIGO observed a “chirp” lasting about a fifth of a second. Analyses of the signal suggest that it was produced by the cataclysmic collision of two black holes a billion light years away.
To get a sense of the excitement over LIGO, see this Scientific American “Special Report” as well as stories by Moskowitz, Davide Castelvecchi, Lee Billings, Roger Blandford or Dennis Overbye of The New York Times (whose front-page story was headlined, "Gravitational Waves Detected, Confirming Einstein's Theory"). In part because this coverage is so enthusiastic, I feel obliged to raise two curmudgeonly questions. Here’s the first:
Is it true?
Media coverage of LIGO is remarkably similar to that generated by a previous gravitational-wave announcement. In March 2014, a team overseeing the Background Imaging of Cosmic Extragalactic Polarization observatory, or BICEP2, claimed to have detected gravitational waves produced by inflation, an extremely rapid--and hypothetical—cosmic growth spurt.
The lead BICEP2 researcher, John Kovac, assured The New York Times that “the chance that the results were a fluke was only one in 10 million.” I expressed doubts, saying I wanted “an explanation of why only inflation, and not other more conventional physical phenomena, can account for the gravity-wave findings.” Early in 2015, the BICEP2 researchers withdrew their claim, acknowledging that their observations had been distorted by dust in the Milky Way.
I doubt the LIGO team will meet a similar fate, for several reasons. First, LIGO consists of two separate observatories, in Louisiana and Washington State, each of which recorded the chirp on September 14. Second, precisely because of the BICEP2 debacle, the LIGO team has no doubt extra-obsessively rechecked its observations. Third, the theoretical basis for black holes is more sound than that for inflation.
But I still wonder about the specificity of the colliding-black-holes explanation. Here is how the Times put it: “One of [the black holes] was 36 times as massive as the sun, the other 29. As they approached the end, at half the speed of light, they were circling each other 250 times a second. And then the ringing stopped as the two holes coalesced into a single black hole, a trapdoor in space with the equivalent mass of 62 suns.”
Non-LIGO theorists are undoubtedly now seeking alternative explanations. Ultimately, as the LIGO team itself acknowledges, its findings will need to be buttressed by other gravitational-wave observatories, including, possibly, space-based ones. Even given confirmation, the LIGO result raises another question:
Was it worth it?
LIGO has cost American taxpayers about $1.1 billion. That is how much the National Science Foundation has spent on the project over the past 40 years, according to the Times. Unfortunately, federally-funded science is a zero-sum game. More spending on one project means less spending on others.
Chemist Ashutosh Jogalekar, who blogs as Curious Wavefunction, notes that while “the detection of gravitational waves will be a fitting testament to both experimental and theoretical science and the dedication of countless scientists over the years, in one sense it would be utterly unsurprising. That's because it is the logical prediction of a theory that has been around for a hundred years.”
Jogalekar adds that “some sources are already calling the putative finding one of the most important discoveries in physics of the last few decades. Let me not mince words here: if that is indeed the case, then physics is in bad shape.”
In an email to me, a historian of technology was more blunt: “So a 100 year old theory has been confirmed experimentally--big whup. Did anyone think Einstein was wrong? There wasn't any controversy, was there? Was anyone credible claiming that spacetime isn't curved, or that black holes don't exist? I can get that this was quite an experimental trick and technological feat… But this isn't doing anything to convince me that public funds spent on this stuff wouldn't be better spent on medical research. Or clean fuels, or any number of things that would apply scientific expertise toward justice or the alleviation of human suffering."
I share these concerns. On the other hand, $1.1 billion spent over decades isn’t exorbitant, especially considering that the U.S. spends almost a thousand times that much on “defense” every year.
I also find LIGO thrilling in part because it has no practical benefits. It is a manifestation of one of our most admirable attributes, the desire for knowledge not as a means to an end—like power, prosperity or health--but simply for its own sake. No science is “pure,” but LIGO comes close.
In a recent post, I said that “physics desperately needs not new ideas but new facts. Discoveries, not inventions. Ideally, physicists will stumble on something so startling that they abandon their pursuit of multiverses, strings and other fantasies and return to reality.”
Gravitational-wave astronomy could be exactly what physics needs. I hope the LIGO claim is confirmed, and that it helps propel physics into a new era of discovery.