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John Clauser
John Clauser
John Clauser
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John Francis Clauser (/ˈklaʊzər/; born December 1, 1942) is an American theoretical and experimental physicist known for contributions to the foundations of quantum mechanics, in particular the Clauser–Horne–Shimony–Holt inequality.[1] Clauser was awarded the 2022 Nobel Prize in Physics, jointly with Alain Aspect and Anton Zeilinger "for experiments with entangled photons, establishing the violation of Bell inequalities and pioneering quantum information science".[2] In 2023, he declared himself as a climate change denier.

Key Information

Early life

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Clauser was born in Pasadena, California. His father, Francis H. Clauser, was a professor of aeronautical engineering who founded and chaired the aeronautics department at Johns Hopkins University. He later served as the Clark Blanchard Millikan Professor of Engineering at the California Institute of Technology (Caltech).[3] His mother, Catharine McMillan, was the humanities librarian at Caltech and sister of 1951 Nobel Prize in Chemistry laureate Edwin McMillan.[4]

He received a Bachelor of Science in physics from Caltech in 1964, where he was a member of Dabney House.[5] He received a Master of Arts in physics in 1966 and a Doctor of Philosophy in physics in 1969 from Columbia University[1] under the direction of Patrick Thaddeus.[6][7]

Career

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From 1969 to 1975, he worked as a postdoctoral researcher at the University of California, Berkeley and Lawrence Berkeley National Laboratory. In 1972, working with Berkeley graduate student Stuart Freedman, he carried out the first experimental test of the CHSH-Bell's theorem predictions. This was the first experimental observation of a violation of a Bell inequality.[1][8] In 1974, working with Michael Horne, he first showed that a generalization of Bell's Theorem provides severe constraints for all local realistic theories of nature (a.k.a. objective local theories). That work introduced the Clauser–Horne (CH) inequality as the first fully general experimental requirement set by local realism. It also introduced the "CH no-enhancement assumption", whereupon the CH inequality reduces to the CHSH inequality, and whereupon associated experimental tests also constrain local realism. Also in 1974 he made the first observation of sub-Poissonian statistics for light (via a violation of the Cauchy–Schwarz inequality for classical electromagnetic fields), and thereby, for the first time, demonstrated an unambiguous particle-like character for photons.[citation needed]

Starting in 1973, Clauser published the newsletter Epistemological Letters, which was created because mainstream academic journals were relunctant to publish articles about the philosophy of quantum mechanics.[citation needed] Clauser worked as a research physicist mainly at Lawrence Livermore and Berkeley from 1975 to 1997. In 1976 he carried out the world's second experimental test of the CHSH-Bell's Theorem predictions.[9]

Clauser was awarded the Wolf Prize in Physics in 2010 together with Alain Aspect and Anton Zeilinger. The three were also jointly awarded the 2022 Nobel Prize in Physics.[10]

Climate change denial

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In May 2023, Clauser joined the board of the CO2 Coalition, a climate change denial organization.[11] Later that year, Clauser called himself a "climate denier" and claimed "there is no climate crisis".[12] Clauser's views on climate change have been described as "pseudoscience".[12] His belief that cloud cover has more of an impact on Earth's temperature than carbon dioxide emissions is contradicted by the overwhelming scientific consensus on climate change.[12][13][14][15] Observational evidence shows the overall current cloud feedback amplifies global warming and does not have a cooling effect.[16]

Personal life

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Clauser is an atheist. He has emphysema due to smoking cigarettes in his youth.[12]

References

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John Clauser

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John Francis Clauser (born 1942) is an American experimental physicist renowned for his pioneering work in quantum foundations, particularly for conducting the first tests of Bell inequalities that confirmed the predictions of quantum mechanics regarding entanglement and non-locality.
He received a B.S. in physics from the California Institute of Technology in 1964 and a Ph.D. in physics from Columbia University in 1969. In 1972, Clauser and Stuart Freedman performed the inaugural experiment demonstrating violation of the Clauser-Horne-Shimony-Holt (CHSH) inequality using entangled photons, providing empirical evidence against local hidden variable theories and supporting quantum superposition. For these contributions to establishing the reality of quantum entanglement, Clauser shared the 2022 Nobel Prize in Physics with Alain Aspect and Anton Zeilinger.
Clauser's career also includes advancements in atom interferometry and X-ray imaging techniques. More recently, he has critiqued the prevailing assertions of an anthropogenic climate crisis, signing the Clintel World Climate Declaration—which states "there is no climate emergency" and emphasizes that natural factors and observational data do not support catastrophic predictions—and joining the board of the CO2 Coalition to advocate that elevated atmospheric CO2 functions primarily as beneficial plant food rather than a pollutant.

Early Life and Education

Family Background and Childhood

John Clauser was born on December 1, 1942, in . His father, Francis H. Clauser, was an and Caltech alumnus (BS 1934, MS 1935, PhD 1937) who held academic positions in aeronautics, including chairing the department at after the family's relocation to . In , Clauser attended , completing an advanced college preparatory curriculum focused on technical subjects. He excelled in and , earning recognition as the most proficient student in that field upon graduation around 1960. Clauser displayed an early aptitude for practical experimentation by designing and building rudimentary computer-driven video games during high school, which he entered in the and won awards for in 1959 and 1960. These projects involved interfacing early computing elements with display technology, reflecting a hands-on engagement with emerging scientific tools rather than purely theoretical pursuits.

Undergraduate and Graduate Studies

John Clauser received a degree in physics from the in 1964. He then attended for graduate studies, earning a Master of Arts in physics in 1966 and a in physics in 1969. His was Patrick Thaddeus. Clauser's PhD thesis examined molecular , providing foundational experience in precise spectroscopic measurements.

Scientific Career

Early Research and Academic Positions

Following his Ph.D. from in 1969, John Clauser accepted a joint postdoctoral research associate position at the , and the , roles he held until 1975. Concurrently, he served on the faculty of the UC Berkeley Physics Department during this period. In these capacities, Clauser pursued initial experimental investigations into detection and polarization, developing improved polarizers and detectors essential for precise optical measurements. By 1975, Clauser transitioned from his Berkeley affiliations to a research physicist position primarily at the , where he continued work while maintaining some Berkeley ties until 1996. This shift marked his departure from full-time academic teaching and post-doctoral research, amid challenges in securing sustained university funding for independent quantum foundation studies.

Quantum Entanglement Experiments

In 1969, Clauser co-authored the , providing a mathematically rigorous, experimentally testable formulation to distinguish predictions of non-locality from those of local hidden-variable theories. This inequality bounds the correlation between measurements on two separated particles under local realism to |S| ≤ 2, whereas allows violations up to |S| = 2√2 ≈ 2.828. Clauser's first major experiment, conducted with Stuart Freedman in 1972, tested these predictions using entangled photon pairs produced via an atomic cascade decay in calcium atoms excited by a laser. The photons, emitted in opposite directions, were directed toward linear polarizers and photomultiplier detectors to measure polarization correlations at various angles. Over 400,000 coincidence counts were recorded, yielding correlations that violated the CHSH bound with a result of S ≈ 2.45 ± 0.18, aligning with quantum expectations and contradicting local hidden variables. The experiment faced significant technical hurdles, including photodetector efficiencies below 1%, which limited coincidence detection rates and introduced potential biases from undetected events. Clauser and addressed this by employing a no-enhancement assumption—ensuring detectors did not artificially boost signals—and conducting measurements under controlled conditions to minimize systematic errors like and polarizer misalignment. These efforts demonstrated correlations inconsistent with classical locality, supporting quantum entanglement's prediction of instantaneous, distance-independent influences dubbed "spooky ."

Later Professional Engagements

In the mid-1970s to , Clauser served as an experimental plasma physicist at , where he led efforts in high-precision diagnostics for fusion research. He designed and implemented ruby-laser systems to measure plasma density and temperature with sub-millimeter resolution, alongside Langmuir probe arrays for real-time data acquisition in the 2XIIB experiment. These contributions advanced applied techniques for controlled fusion, emphasizing empirical validation over theoretical modeling. After concluding formal research physicist positions at the in 1997, Clauser established J.F. Clauser & Associates as a self-employed focused on physics and advisory services. The firm applied his foundational expertise in and precision measurement to practical problems, including interferometric methods for high-resolution imaging. In this capacity, Clauser developed and patented ultrahigh-resolution interferometric X-ray imaging technology in 1998, utilizing Talbot-Lau interferometry to enable phase-contrast visualization of soft tissues without contrast agents, with potential extensions to defense and applications. During semi-retirement, he sustained engagements in through technical writings and specialized lectures on entanglement experiments and local realism critiques, extending into the while prioritizing verifiable experimental data over interpretive consensus.

Key Contributions to Physics

Development of Bell Test Experiments

In 1969, Clauser proposed an experimental scheme to test John Bell's theorem by generating pairs of entangled photons through atomic cascades, such as in calcium atoms, rather than using massive particles like electrons, which posed challenges for achieving sufficient spatial separation to enforce locality conditions without superluminal influences. This approach leveraged photons' propagation at light speed to naturally satisfy the no-signaling constraint while enabling polarization measurements via polarizers and detectors. Collaborating with Michael Horne, Abner Shimony, and Richard Holt, Clauser developed the in 1969, formulating it as ∣E(a,b)−E(a,b′)+E(a′,b)+E(a′,b′)∣≤2|E(\mathbf{a},\mathbf{b}) - E(\mathbf{a},\mathbf{b}') + E(\mathbf{a}',\mathbf{b}) + E(\mathbf{a}',\mathbf{b}')| \leq 2, where EE denotes the expectation value of the between measurement outcomes for polarization settings a,b\mathbf{a}, \mathbf{b}, etc., under the assumption of local realism and perfect detection. This inequality provided a falsifiable distinct from ' maximum violation of 22≈2.8282\sqrt{2} \approx 2.828
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