Barry Barish: Gravitational Waves and the Most Precise Device Ever Built | Lex Fridman Podcast #213

Barry Barish walks Lex Fridman through the century-long arc of gravitational waves, from Einstein's 1916 prediction and the early controversy over whether they exist, to the engineering feats that made LIGO work. He explains how LIGO uses kilometers-long laser interferometers, multi-layer shock absorbers, and active seismic cancellation to measure distortions one-thousandth the width of a proton. The conversation covers black holes, the matter-antimatter asymmetry, dark matter, string theory's lack of predictive power, and the dream of a unified theory. It closes on Fermi's paradox, Mars as an off-site backup for humanity, Russian literature, and Barish's reflections on mortality and legacy.

• Einstein himself doubted gravitational waves existed and submitted a 1936 paper titled 'Do Gravitational Waves Exist?' that he withdrew in anger after a critical peer review.
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• Einstein never published in Physical Review again after the editor sent his paper to a referee who found his math error.
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• LIGO measures distortions of 10 to the minus 18 meters, one-thousandth the size of a proton, the smallest measurement ever attempted.
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• Beyond the world's fanciest four-layer shock absorbers, LIGO adds active noise cancellation using seismometers and actuators inside the isolation system.
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• The black hole collision LIGO detected happened 1.3 billion years ago, when life on Earth was just transitioning from single-cell to multicellular.
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• After a 100-million-dollar rebuild adding active seismic isolation, LIGO turned on in 2015 and almost instantly saw its first black hole collision.
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• The team verified they had not been hacked, even though LIGO is not on the internet, before announcing the discovery.
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• Barish says reading Moby Dick at 15 'cured' him of wanting to be a novelist and pushed him toward physics.
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• LIGO's two detectors sit 3,000 kilometers apart with four-kilometer vacuum arms, operating in unison.
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• Enrico Fermi was the last physicist of note to be both a great experimentalist and theorist, writing his beta-decay theory in 1933.
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• GPS would put you off the road within minutes if it did not correct for Einstein's general relativity.
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• Human ears evolved to hear in the audio band precisely because that is the frequency range where the Earth is quietest.
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• LIGO is the world's biggest high-vacuum system, built from stainless steel spiral-welded into four-kilometer tubes.
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• Before the pandemic LIGO was detecting a gravitational wave event roughly once a week.
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• LIGO has observed a black hole system 140 times the mass of the Sun, which standard star collapse should not be able to produce.
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• Barish compares a future Mars settlement to the self-sustaining South Pole station, which he visited at minus 51 degrees.
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• We detect only about four percent of what is out there using electromagnetic waves.
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