Barish, Barry

experimental physicist, Caltech; Nobel laureate for contributions to LIGO and the detection of gravitational waves

Barry Barish: Gravitational Waves and the Most Precise Device Ever Built

Lex Fridman Podcast · Aug 23, 2021

• Barry Barish
• LIGO
• gravitational waves
• general relativity
• Einstein and gravitational wave history
• interferometer engineering
• seismic isolation
• black hole formation
• Nobel Prize reflections
• Fermi paradox
• dark matter and dark energy
• unification of physics
• Russian literature

Core ideas

Barish traces his scientific temperament to childhood curiosity (an early unanswered question about why ice floats) and laments that formal education tends to suppress rather than nurture this trait in most people. He singles out Enrico Fermi as a formative influence for being the last major physicist to excel simultaneously as theorist and experimentalist — describing how Fermi, within months in 1933-34, both wrote a lasting theory of beta decay (initially rejected by Nature as "too speculative") and had the experimental insight to bombard nuclei with newly discovered, uncharged neutrons rather than charged particles, laying groundwork for fission. Barish uses Fermi's legacy — including his later documented unease about the hydrogen bomb and the "ratchet of curiosity" (a one-way process by which acquired scientific knowledge cannot be un-learned or fully controlled) — to draw an explicit parallel to present-day risks in AI and bioengineering, where exciting near-term applications may obscure long-term, hard-to-reverse dangers.

He gives a detailed account of general relativity's prediction of gravitational waves: Einstein's 1915 theory of gravity left Newton's force unexplained mechanistically, and in a 1916 paper Einstein noticed that his field equations resembled those of electromagnetism (which had waves), leading him to intuit — before any rigorous derivation, and despite an initial factor-of-two error he silently corrected — that gravity should also propagate as waves, sourced by a "quadrupole" (not dipole) moment such as two massive objects orbiting each other. Barish narrates a colorful episode in which Einstein and collaborator Nathan Rosen submitted a 1936 paper (titled "Do Gravitational Waves Exist?") to Physical Review after encountering mathematical infinities; peer reviewer Howard Percy Robertson identified the fix, but Einstein — evidently unfamiliar with anonymous peer review — angrily withdrew the paper and never published in that journal again, printing a corrected version elsewhere instead. Barish also credits Richard Feynman's 1957 "sticky bead" thought experiment (showing gravitational waves could do mechanical work, and thus carry real energy) as pivotal in convincing the physics community the phenomenon was real and, in principle, detectable, even though the effect size — a distortion of one part in 10^21 — remained absurdly small.

Barish explains LIGO's core method (a laser interferometer splitting a beam down two perpendicular kilometers-long arms, detecting the relative stretching and squeezing of space predicted by a passing gravitational wave) and dwells at length on the engineering challenges required to reach that sensitivity: isolating the instrument from the Earth's constant ambient motion using multi-stage, springier-than-automotive "shock absorbers," compounded by an active noise-cancellation system (analogous to noise-cancelling headphones) using seismometers and actuators to sense and counteract residual motion in real time, achieving a further reduction of one part in 10^12. He also describes the challenge of building and maintaining the world's largest high-vacuum system (rolled and spiral-welded from stainless steel over kilometers) without any way to leak-test it using conventional helium methods. He recounts the extended, decade-long iterative process from the initial 1999 LIGO build (lacking active seismic isolation) through repeated cycles of running, diagnosing limitations, and upgrading, culminating in a roughly $100 million active-isolation upgrade that led to the first detection in 2015 — a signal from two colliding black holes that matched Einstein's predicted waveform so cleanly it appeared almost immediately in the raw data, though the team still spent about a month privately verifying the instrument hadn't malfunctioned or been "hacked" before going public.

On leading the roughly-thousand-person LIGO collaboration, Barish frames the core managerial challenge as achieving genuine synergy rather than mere aggregation of individual contributions — attracting the world's best specialists (citing competing laser-physics groups who were persuaded to collaborate rather than compete) by offering them a scientifically compelling shared goal that no individual team could achieve alone. He reflects candidly on the Nobel Prize: while structurally arbitrary (singling out a few individuals from a massive collaborative effort) and not something one can meaningfully aim for, he considers it valuable for publicizing science broadly and, more specifically, for giving scientists outsized influence with policymakers who otherwise rarely defer to scientific expertise.

Looking ahead, Barish describes near-term plans for an instrument roughly ten times more sensitive (enabling detection out to a thousand times greater volume of the universe, effectively shifting gravitational-wave research from astronomy toward cosmology by probing further back in time) and space-based efforts like LISA (three satellites separated by hundreds of thousands of kilometers, exchanging laser beams to detect lower-frequency waves inaccessible from Earth) as complementary rather than competing approaches. He is candid about deep unresolved puzzles gravitational-wave astronomy might eventually illuminate: the unexplained matter-antimatter asymmetry of the early universe, the physical origin of unexpectedly massive black holes (some possibly "primordial," dating to the Big Bang itself, and potentially linked to dark matter), and — most ambitiously — whether extreme environments like the interior of black holes, where both general relativity and quantum field theory apply simultaneously, might supply the experimental clues currently missing for unifying physics's two incompatible foundational theories. He is skeptical of string theory's practical value despite its mathematical elegance, citing its lack of unique, falsifiable predictions in our four-dimensional world as "a killer."

On broader existential questions, Barish revisits the Fermi paradox, suggesting the missing variable may be how long technologically capable civilizations typically survive, and voices measured, uncertain optimism about humanity's own longevity given self-inflicted risks like engineered pandemics or nuclear war; he favors a modest, Antarctic-research-station model of possible Mars settlement (rather than full "colonization") explicitly framed as an off-site backup for civilization. He discusses his early ambition to be a novelist, his formative and lasting attachment to Russian literature (particularly Dostoevsky, whom he credits with originating both polyphonic narration and existentialist literature, and with whose humble, self-doubting character Prince Myshkin from The Idiot he personally identifies), and his recent rereading of Camus's The Plague during pandemic isolation as a meditation on human solidarity and love. He closes by defining a meaningful life as one that positively affects something or someone beyond oneself, expresses sadness rather than fear at mortality (a feeling he says extends to a general "terror" at the deep mystery of consciousness itself), and states he hopes to be remembered less for personal achievement than as part of a collaborative human effort — the LIGO instrument itself — that represents "humanity at its best."

Excerpts