Discoveries in physics in the first quarter of the 21st Century.

May 13, 2026May 13, 2026 by David D. Nolte

The Best Physics of the Century (So Far)

History of Dynamics
Black Hole, Cosmic Microwave Background, Event Horizon Telescope, Exoplanet, Gravitational Wave, Higgs Particle, LIGO, Nuclear Fusion, photon, Quantum computing, Quantum Information, Solar Neutrino Oscillation, Topological physics

Our century is now a quarter complete, from Y2K to today (2000 – 2025). What have been the greatest discoveries in Physics so far? And what do they portend for the rest of the century?

Every century of physics tends to have its own character:

• The 1600’s were the time of Galileo, Descartes, Huygens, Leibniz and Newton who created the science of dynamics out of nothing.

• The 1700’s were the time of du Chatelet, Maupertuis, Euler, Lagrange, and D’Alembert who constructed mathematical physics on the foundation of the calculus.

• The 1800’s were the time of Young, Fresnel, Hamilton, Maxwell, Boltzmann, and Lord Kelvin who completed the program of classical physics.

• The 1900’s were the time of Einstein and Bohr who invented relativistic and quantum physics and launched the grand program of unified forces.

Now we come to the 2000’s. What will this century be known for?

Two topics physicists have at the top of their mind today is Quantum and AI (and there is even quantum AI). But AI is merely a tool (though an important one that is radically changing how physics is done), and quantum is a catch-all (almost everything is quantum at its core).

So, what are the greatest breakthroughs of the 21^st Century so far? And what do they portend for the eventual “character” of 21^st-Century physics when seen in the rear-view mirror of history by the year 2100?

Single-photon Quantum Information (2001)

The century started on July 24, 2000, when a landmark paper was received by Nature magazine submitted by Emanuel Knill and Raymond Laflamme at Los Alamos National Lab in the United States with Gerald Milburn from the University of Queensland, Australia (collectively known as KLM). This little-heralded paper proposed a radical new idea in quantum information, an idea that would have profound effects on the development of quantum science for the coming quarter-century.

The idea was simply that quantum logic could be performed with single photons and linear optics [1]. Up to that point, most research on quantum optical computing was trying to get photons to interact with each other (which they really don’t like to do) in nonlinear media like crystals or trapped atoms. What KLM showed was that quantum information could be manipulated in general ways without interactions. The paper proposed a technique that could perform quantum logic in a universal way using only linear optical elements like single-photon sources, beam splitters, phase shifters, and single-photon detectors, introducing the novel idea of “measurement-based” quantum computing.

Recovery from Z Linear Optical Quantum Computing — Fig. 0. LOQC circuitry from the KLM paper.

In the quarter-century since the publication of the KLM paper, LOQC has steadily progressed via the development of single-photon sources and detectors. Today, numerous start-ups are pursuing LOQC, notably Xanadu in Toronto, Canada, and PsiQuantum in Palo Alto, USA and Brisbane, Australia. By 2100, this century will likely be viewed as the time when applications of quantum information reached their maturity. Where the 20^th century was a century of discovery of quantum phenomena, the 21^st will be the century when it was reduced to practice.

Solar Neutrino Oscillation (2001)

The sun is fueled by the fusion of hydrogen that generates electron neutrinos. The reaction looks like

where p is a proton (hydrogen), ²H is deuterium (a hydrogen nucleus with an extra neutron), e⁺ is a positron (the anti-matter form of an electron) and ν _e is an electron neutrino. This reaction accounts for 99% of the neutrinos generated by the Sun, calculated by the theoretical astrophysicist John Bahcall of the Institute for Advanced Study at Princeton University. Already by the late 1960’s it was suspected that too few of the neutrinos were being detected compared to predictions, so he teamed with Raymond Davis of Brookhaven National Lab to build an experiment to detect the flux of solar neutrinos. To shield the detector from cosmic rays, the experiment was placed at the 4850 level of the Homestake Gold Mine in Lead, South Dakota and operated from 1970 to 1994. The deficit of solar neutrinos was confirmed, and it was huge: Fully two-thirds of expected solar neutrinos were missing!

The simplest solution to the missing solar neutrinos was that they just weren’t there because, on their way to Earth from the Sun, they had converted to something else that was not detectedable. This conversion from one particle to another is possible if neutrinos have a non-zero (but extremely small) mass. If so, then an electron neutrino can convert to a muon neutrino, and if the distance is far enough, they can convert back. In other words, the nature of the neutrino particle is that its identity oscillates. This is called the solar neutrino oscillation, and by the time the neutrinos have arrived at Earth, two-thirds of them have converted to muon neutrinos.

There was a general reluctance to accept neutrino oscillations because it represented a departure from the Standard Model of particle physics and introduced uncomfortably small masses for neutrinos that otherwise behave like massless particles. Two experiments put these qualms to rest: the Super-Kamiokanda expeeriment in Japan and the Sudbury Neutrino Oscillation experiment in Canada. By the early years of the century, neutrino oscillations had been confirmed.

By 2100, the mystery of the ultra-small neutrino masses will likely have been solved. If the answer falls within the Standard Model, then this may be the crowning achievement that “completes” the standard model. If the answer falls outside the Standard Model, then this may be the beginning of a new chapter in high-energy physics.

WMAP and Planck (2003)

The Big Bang may have occurred 13.7 billion years ago, but that Bang echoes to this day across the Universe. At its inception, the reverberations were incredibly hot, but they have cooled now to a mere 3 degrees Kelvin. In 1987, Paul Richards and Andrew Lange at the University of California at Berkeley, recorded the peak of the Planck black body spectrum during a sounding rocket flight that carried a far-infrared spectrometer to the edge of space. (The dichroic bandpass filters in their spectrometer were the first far-infrared metamaterials. I designed and built them as a young grad student at Berkeley! [2]) This experiment was followed by the COBE satellite that measured the presence of minuscule fluctuations in the temperature, representing the original heterogeneity of the universe just after the Big Bang.

COBE flew for a year, followed in 1998 by the BOOMerAng experiment, led by Andrew Lange, that was suspended from a high-altitude balloon circling the South Pole for ten days. This experiment discovered the literal echoes of the Big Bang, acoustic oscillations, in other words, the “sound” of the Bang. It also established that the universe is gravitationally “flat”, which is a direct consequence of cosmic inflation. Once again, these findings were followed by a satellite experiment, the WMAP mission in 2003, that mapped these oscillations over the entire sky. Even finer resolution was obtained by the Planck mission in 2013, measuring higher harmonics of the sound oscillations. These oscillations in the early universe helped seed regions of slightly higher density that condensed into galaxies, leading to the large-scale structure of the universe that we see today.

Anisotropy of the cosmic background radiation — Fig. 2. Successively higher resolution views of the echos of the Big Bang from COBE (1992) to WMAP (2003) to Planck (2013). From Ref.

The 21st Century will likely be known as the time when the physics of the early universe was finally pinned down, and maybe even of what can before. The answers may tell us if there are parallel universes in a much larger metaverse.

Exoplanets (2009)

The Earth is not alone in the Universe. It is not even alone in our little neighborhood of the Milky Way. Within 50 light years it is estimated that there are about 1000 Earth-sized planets in the habitable zone of their respective stars. Why is 50 light years significant? It is because, within this century, the technology to explore those planets is likely to be developed. With the right designs, an unmanned probe could reach 50 light years from Earth within a century, and the time to call back home is only 50 years. So if a probe is launched in the year 2100, we could be receiving transmissions from the new planet by the year 2250.

This estimate of 1000 New Earths is the result of a quiet revolution in planetary science that has been unfolding over the past quarter century. The very first exoplanet was confirmed in 1995 by Michel Mayor and Didier Queloz. Today, as of the writing of this blog, there are 6,278 confirmed exoplanets. Most of these were disovered by the Kepler satellite that was launched in 2009.

Kepler exoplanet discoveries — Fig. 3. An artists rendition of several of the Earth-sized planets discovered by the Kepler satellite. From Ref.

By 2100, we will know where all the exoplanets are that are within 50 light years of Earth, and we will know which ones are potential inhabitable. It may even happen that signs of life on one of these planets will have been discovered. If so, then it is hard to imagine humankind NOT launching probes to visit those planets. If the right propulsion technology is developed, then those probes could be signaling back information from those planets as early as the year 2250…if anyone is still here to listen.

The Higgs (2012)

The crowning achievement of high-energy physics may also have been the last nail in the coffin. Throughout the second half of the 20th century, high-energy physics took the lion’s share of money and attention showered on physics. Beginning in the aftermath of the Manhattan Project, the search for the fundamental constituents of our universe at first found more and more particles, creating a “zoo” that resisted easy classification, until quarks were proposed that simplified the whole thing down into what is now called the Standard Model of Physics.

But one piece of the puzzle was still missing–the explanation of why particles have the masses they do. This missing piece was supplied by the theoretical physicist Peter Higgs in 1964 who proposed that point-like massless particles interacted with a “field” that permeated space. The interaction energy was equivalent to mass through Einstein’s famous E = mc², and the quantization of the field predicted the existence of a “Higgs Boson”. The search for the “Higgs”, as it is called for short, became the Holy Grail of Physics at the end of the last century.

Higgs production, decay and pair processes as Feynman diagrams — Fig. 4. Feynman diagrams that involve the generation of Higgs particles.

The discovery of the Higgs boson was announced on the 4th of July in 2012 [3]. It capped 80 years of progress in high-energy particle physics since the discovery of the positron in 1932. But it may also be the last. Since 2012, over the past 14 years, there have been no new “major” discoveries at the Large Hadron Collider (LHC). Most high-energy talks since then have been about speculative experiments seeking deviations from the Standard Model, but so far there is nothing new.

In the year 2100, looking back, the era of high-energy physics may be relegated to the 20th century, with the Higgs just a finishing touch that tipped over into the new millennium … Or sometime in the next 75 years there will be a discovery that goes beyond standard physics and opens a new chapter in the field. We will have to wait to see.

Gravitational Waves (2015)

Where were you on Nov. 11, 2015 at 10:30 am? Can you remember? I can! I was in a conference room in the Physics Building on the Purdue University Campus waiting with a small crowd of physicists for a news conference to begin. Everyone knew it would be something big. It was. They announced the first detection of a gravitational wave by the LIGO detector (the Laser Interferometric Gravitational Wave Observatory). In a way, it was anti-climactic because we all knew that LIGO would eventually see one. But it was also immensely dramatic, because it was the most sensitive measurement ever made by mankind. The displacement of the mirrors in the interferometer caused by the passing gravitational wave was a tiny fraction of a radius of a proton, yet the signal was as clear as a bell. It came from the merger of two 30 solar-mass black holes in a galaxy far, far away.

First detection of gravitational waves by LIGO — Fig. 5. The two LIGO recordings (at Hanfored and at Livingston) of the first detected gravitaitonal wave. From Ref.

By the year 2100, looking back, multi-messenger astronomy will have been a key part of the physics of the 21st century. Multi-messenger astronomy is when an astronomical event is detected across many detection modes, possibly including light, infrared, ultraviolet, x-ray, neutrino and gravitational wave detection. The field is just beginning and has a long way to go to integrate all these different ways of seeing into a complete picture of what happens out in the universe.

Topological physics (2016)

Of all the topics of this blog, this one is perhaps the most abstract. When we think of geometry, it is natural to think in terms of the symmetries that objects have. The last century was the pinnacle of geometric physics, where Einstein showed that gravity is a geometric property of warped space, where group theory classified all the ways that objects can be constructed and behave, and symmetry breaking was invoked to explain the hierarchy of physical forces.

The new century will be the time of topological physics, where symmetries of matter may not even matter, but the way that properties of matter are connected does. By “property of matter” I mean like the electronic states of a solid state material where the states are excluded from portions of state space, creating topology in abstract spaces. Such topological properties govern how freely currents can flow on surfaces but not in the bulk, or vice versa. In quantum systems, topological properties can protect quantum information from decoherence, which is the bane of most real-world implementations of quantum computers. For instance, by “braiding anyons” it is possible to create qubits that resist dephasing.

Braided anyons at Purdue — Fig. 6. Evidence for the braiding of anyons in the solid state. From Ref.

The importance of topology in physics was recognized with the 2016 Nobel Prize to David J. Thouless, F. Duncan M. Haldane, and J. Michael Kosterlitz for “Theoretical discoveries of topological phase transitions and topological phases of matter.”

Images of Black Holes (2019)

Why hasn’t this gotten a Nobel Prize yet? The imaging of black holes is a tour de force, requiring a telescope with the diameter of a planet, and requiring the collaboration of scientists from across that planet to make it all work.

The physics is straightforward. Everyone knows that bigger telescopes have better resolution, so the logical limit is a telescope the size of the Earth. This is accomplished by using interferometric detection, with data from widely spread millimeter-wave telescopes synchronized by an atomic clock in a network of telescopes known as the Event Horizon Telescope (EHT). The results are constructed numerically, as shown below.

Event Horizon Telescope (EHT) images of a black hole

Fig. 7. The EHT images (left) compared to the model (middle) and the blurred model (right) of the black hole in the M87 galaxy. From Ref.

The next logical step for this kind of imaging is a telescope array that is bigger than the Earth … much bigger! This could be accomplished with an array of Lagrange-point satellites, improving the resolution of the images. By the end of this century, we may be imaging the black holes in all the near-by galaxies.

More to Come?

What are the greatest outstanding problems of physics that may yet yield to solutions within this century? It is impossible to say for certain without a crystal ball, but there are some that are likely to be resolved in the next 75 years:

• Dark Matter: This is the 500 pound gorilla in the room. If most of the tangible universe is made of this stuff, then we had better get around to detecting it!

• Dark Energy: This is the other 500 pound gorilla in the room. If most of the intangible universe is made of this stuff, then we had better get a good understanding of it.

• Quantum Gravity: Of the four forces of physics (gravity, electro-magnetic, weak nuclear and strong nuclear) gravity stands apart in several ways, one of which is that there is no quantum theory for it. We have 75 years to fix this if it is to be a crowning achievement of 21st-Century physics.

• The Evolution of Life: I didn’t include any biophysics in my list of the best physics of the century mainly because I cannot point to a single revolutionary breakthrough of physics in this area. There has been a lot of good progress on the microphysics of biological systems, but nothing like discovering a Higgs boson. This could change if the origins of life turn out to be physics-based rather than just some chemistry.

• The Evolution of Intelligence: I think physics has more to say on the evolution of intelligence than on the evolution of life. Intelligence is the quintessential complex system, and the methods of theoretical physics may yet provide a clear answer to the question of “What is Intelligence?”.

• The Early Universe: This is just starting now with the James Webb Telescope peering into the dark depths of history–nearly to the Big Bang itself.

• Multiple Dimensions: String theory likes to live in 11-dimensional space, so what other parts of our physical universe live there too? Dark Matter? Dark Energy? Do all the extra dimensions need to be compact?

• The Arrow of Time: The physics of time is possibly the greatest unsolved problem in physics. Why does it only go one way?

• Singularity Physics: What happens at the center of a Black Hole? Do wormholes provide hyperspace bypasses? These questions may yet get answers from theoretical physics though likely not from the laboratory unless it is from an AMO analog.

References

[1] E. Knill, R. Laflamme and G. J. Milburn, A Scheme for Efficient Quantum Computation with Linear Optics, Nature 409 (6816), 46–52 (2001).

[2] D. NOLTE, A. LANGE and P. RICHARDS, Far-Infrared Dichroic Bandpass-Filters, Applied Optics 24 (10), 1541–1545 (1985).

[3] CERN. (2012, July 4). CERN experiments observe particle consistent with long-sought Higgs boson [Press release]. https://home.cern/news/press-release/cern/cern-experiments-observe-particle-consistent-long-sought-higgs-boson; ATLAS Collaboration. (2012). Observation of a new particle in the search for the Standard Model Higgs boson with the ATLAS detector at the LHC. Physics Letters B, 716(1), 1–29. https://doi.org/10.1016/j.physletb.2012.08.020 Cited by: 13000+; CMS Collaboration. (2012). Observation of a new boson at a mass of 125 GeV with the CMS experiment at the LHC. Physics Letters B, 716(1), 30–61. https://doi.org/10.1016/j.physletb.2012.08.021

January 24, 2024 by David D. Nolte

Frontiers of Physics: The Year in Review (2023)

These days, the physics breakthroughs in the news that really catch the eye tend to be Astro-centric. Partly, this is due to the new data coming from the James Webb Space Telescope, which is the flashiest and newest toy of the year in physics. But also, this is part of a broader trend in physics that we see in the interest statements of physics students applying to graduate school. With the Higgs business winding down for high energy physics, and solid state physics becoming more engineering, the frontiers of physics have pushed to the skies, where there seem to be endless surprises.

To be sure, quantum information physics (a hot topic) and AMO (atomic and molecular optics) are performing herculean feats in the laboratories. But even there, Bose-Einstein condensates are simulating the early universe, and quantum computers are simulating worm holes—tipping their hat to astrophysics!

So here are my picks for the top physics breakthroughs of 2023.

The Early Universe

The James Webb Space Telescope (JWST) has come through big on all of its promises! They said it would revolutionize the astrophysics of the early universe, and they were right. As of 2023, all astrophysics textbooks describing the early universe and the formation of galaxies are now obsolete, thanks to JWST.

Foremost among the discoveries is how fast the universe took up its current form. Galaxies condensed much earlier than expected, as did supermassive black holes. Everything that we thought took billions of years seem to have happened in only about one-tenth of that time (incredibly fast on cosmic time scales). The new JWST observations blow away the status quo on the early universe, and now the astrophysicists have to go back to the chalk board.

Fig. The JWST artist’s rendering. Image credit.

Gravitational Ripples

If LIGO and the first detection of gravitational waves was the huge breakthrough of 2015, detecting something so faint that it took a century to build an apparatus sensitive enough to detect them, then the newest observations of gravitational waves using galactic ripples presents a whole new level of gravitational wave physics.

*Fig. Ripples in spacetime.* *Image* credit.

By using the exquisitely precise timing of distant pulsars, astrophysicists have been able to detect a din of gravitational waves washing back and forth across the universe. These waves came from supermassive black hole mergers in the early universe. As the waves stretch and compress the space between us and distant pulsars, the arrival times of pulsar pulses detected at the Earth vary a tiny but measurable amount, haralding the passing of a gravitational wave.

This approach is a form of statistical optics in contrast to the original direct detection that was a form of interferometry. These are complimentary techniques in optics research, just as they will be complimentary forms of gravitational wave astronomy. Statistical optics (and fluctuation analysis) provides spectral density functions which can yield ensemble averages in the large N limit. This can answer questions about large ensembles that single interferometric detection cannot contribute to. Conversely, interferometric detection provides the details of individual events in ways that statistical optics cannot do. The two complimentary techniques, moving forward, will provide a much clearer picture of gravitational wave physics and the conditions in the universe that generate them.

Phosphorous on Enceladus

Planetary science is the close cousin to the more distant field of cosmology, but being close to home also makes it more immediate. The search for life outside the Earth stands as one of the greatest scientific quests of our day. We are almost certainly not alone in the universe, and life may be as close as Enceladus, the icy moon of Saturn.

Scientists have been studying data from the Cassini spacecraft that observed Saturn close-up for over a decade from 2004 to 2017. Enceladus has a subsurface liquid ocean that generates plumes of tiny ice crystals that erupt like geysers from fissures in the solid surface. The ocean remains liquid because of internal tidal heating caused by the large gravitational forces of Saturn.

*Fig. The Cassini Spacecraft. Imag*e credit.

The Cassini spacecraft flew through the plumes and analyzed their content using its Cosmic Dust Analyzer. While the ice crystals from Enceladus were already known to contain organic compounds, the science team discovered that they also contain phosphorous. This is the least abundant element within the molecules of life, but it is absolutely essential, providing the backbone chemistry of DNA as well as being a constituent of amino acids.

With this discovery, all the essential building blocks of life are known to exist on Enceladus, along with a liquid ocean that is likely to be in chemical contact with rocky minerals on the ocean floor, possibly providing the kind of environment that could promote the emergence of life on a planet other than Earth.

Simulating the Expanding Universe in a Bose-Einstein Condensate

Putting the universe under a microscope in a laboratory may have seemed a foolish dream, until a group at the University of Heidelberg did just that. It isn’t possible to make a real universe in the laboratory, but by adjusting the properties of an ultra-cold collection of atoms known as a Bose-Einstein condensate, the research group was able to create a type of local space whose internal metric has a curvature, like curved space-time. Furthermore, by controlling the inter-atomic interactions of the condensate with a magnetic field, they could cause the condensate to expand or contract, mimicking different scenarios for the evolution of our own universe. By adjusting the type of expansion that occurs, the scientists could create hypotheses about the geometry of the universe and test them experimentally, something that could never be done in our own universe. This could lead to new insights into the behavior of the early universe and the formation of its large-scale structure.

*Fig. Expansion of the Universe. Image* Credit

Quark Entanglement

This is the only breakthrough I picked that is not related to astrophysics (although even this effect may have played a role in the very early universe).

Entanglement is one of the hottest topics in physics today (although the idea is 89 years old) because of the crucial role it plays in quantum information physics. The topic was awarded the 2022 Nobel Prize in Physics which went to John Clauser, Alain Aspect and Anton Zeilinger.

Direct observations of entanglement have been mostly restricted to optics (where entangled photons are easily created and detected) or molecular and atomic physics as well as in the solid state.

But entanglement eluded high-energy physics (which is quantum matter personified) until 2023 when the Atlas Collaboration at the LHC (Large Hadron Collider) in Geneva posted a manuscript on Arxiv that reported the first observation of entanglement in the decay products of a quark.

*Fig. Thresholds for entanglement detection in decays from top quarks. Image* credit.

Quarks interact so strongly (literally through the strong force), that entangled quarks experience very rapid decoherence, and entanglement effects virtually disappear in their decay products. However, top quarks decay so rapidly, that their entanglement properties can be transferred to their decay products, producing measurable effects in the downstream detection. This is what the Atlas team detected.

While this discovery won’t make quantum computers any better, it does open up a new perspective on high-energy particle interactions, and may even have contributed to the properties of the primordial soup during the Big Bang.

July 26, 2023August 16, 2025 by David D. Nolte

Book Preview: Interference. The History of Optical Interferometry

This history of interferometry has many surprising back stories surrounding the scientists who discovered and explored one of the most important aspects of the physics of light—interference. From Thomas Young who first proposed the law of interference, and Augustin Fresnel and Francois Arago who explored its properties, to Albert Michelson, who went almost mad grappling with literal firestorms surrounding his work, these scientists overcame personal and professional obstacles on their quest to uncover light’s secrets. The book’s stories, told around the topic of optics, tells us something more general about human endeavor as scientists pursue science.

Interference: The History of Optical Interferometry and the Scientists who Tamed Light, was published Ag. 6 and is available at Oxford University Press and Amazon. Here is a brief preview of the frist several chapters:

Chapter 1. Thomas Young Polymath: The Law of Interference

Thomas Young was the ultimate dabbler, his interests and explorations ranged far and wide, from ancient egyptology to naval engineering, from physiology of perception to the physics of sound and light. Yet unlike most dabblers who accomplish little, he made original and seminal contributions to all these fields. Some have called him the “Last Man Who Knew Everything”.

The chapter, Thomas Young Polymath: The Law of Interference, begins with the story of the invasion of Egypt in 1798 by Napoleon Bonaparte as the unlikely link among a set of epic discoveries that launched the modern science of light. The story of interferometry passes from the Egyptian campaign and the discovery of the Rosetta Stone to Thomas Young. Young was a polymath, known for his facility with languages that helped him decipher Egyptian hieroglyphics aided by the Rosetta Stone. He was also a city doctor who advised the admiralty on the construction of ships, and he became England’s premier physicist at the beginning of the nineteenth century, building on the wave theory of Huygens, as he challenged Newton’s particles of light. But his theory of the wave nature of light was controversial, attracting sharp criticism that would pass on the task of refuting Newton to a new generation of French optical physicists.

Chapter 2. The Fresnel Connection: Particles versus Waves

Augustin Fresnel was an intuitive genius whose talents were almost squandered on his job building roads and bridges in the backwaters of France until he was discovered and rescued by Francois Arago.

The Fresnel Connection: Particles versus Waves describes the campaign of Arago and Fresnel to prove the wave nature of light based on Fresnel’s theory of interfering waves in diffraction. Although the discovery of the polarization of light by Etienne Malus posed a stark challenge to the undulationists, the application of wave interference, with the superposition principle of Daniel Bernoulli, provided the theoretical framework for the ultimate success of the wave theory. The final proof came through the dramatic demonstration of the Spot of Arago.

Chapter 3. At Light Speed: The Birth of Interferometry

There is no question that Francois Arago was a swashbuckler. His life’s story reads like an adventure novel as he went from being marooned in hostile lands early in his career to becoming prime minister of France after the 1848 revolutions swept across Europe.

At Light Speed: The Birth of Interferometry tells how Arago attempted to use Snell’s Law to measure the effect of the Earth’s motion through space but found no effect, in contradiction to predictions using Newton’s particle theory of light. Direct measurements of the speed of light were made by Hippolyte Fizeau and Leon Foucault who originally began as collaborators but had an epic falling-out that turned into an intense competition. Fizeau won priority for the first measurement, but Foucault surpassed him by using the Arago interferometer to measure the speed of light in air and water with increasing accuracy. Jules Jamin later invented one of the first interferometric instruments for use as a refractometer.

Chapter 4. After the Gold Rush: The Trials of Albert Michelson

No name is more closely connected to interferometry than that of Albert Michelson. He succeeded, sometimes at great personal cost, in launching interferometric metrology as one of the most important tools used by scientists today.

Albert A. Michelson, 1907 Nobel Prize. Image Credit.

After the Gold Rush: The Trials of Albert Michelson tells the story of Michelson’s youth growing up in the gold fields of California before he was granted an extraordinary appointment to Annapolis by President Grant. Michelson invented his interferometer while visiting Hermann von Helmholtz in Berlin, Germany, as he sought to detect the motion of the Earth through the luminiferous ether, but no motion was detected. After returning to the States and a faculty position at Case University, he met Edward Morley, and the two continued the search for the Earth’s motion, concluding definitively its absence. The Michelson interferometer launched a menagerie of interferometers (including the Fabry-Perot interferometer) that ushered in the golden age of interferometry.

Chapter 5. Stellar Interference: Measuring the Stars

Learning from his attempts to measure the speed of light through the ether, Michelson realized that the partial coherence of light from astronomical sources could be used to measure their sizes. His first measurements using the Michelson Stellar Interferometer launched a major subfield of astronomy that is one of the most active today.

Stellar Interference: Measuring the Stars brings the story of interferometry to the stars as Michelson proposed stellar interferometry, first demonstrated on the Galilean moons of Jupiter, followed by an application developed by Karl Schwarzschild for binary stars, and completed by Michelson with observations encouraged by George Hale on the star Betelgeuse. However, the Michelson stellar interferometry had stability limitations that were overcome by Hanbury Brown and Richard Twiss who developed intensity interferometry based on the effect of photon bunching. The ultimate resolution of telescopes was achieved after the development of adaptive optics that used interferometry to compensate for atmospheric turbulence.

And More

The last 5 chapters bring the story from Michelson’s first stellar interferometer into the present as interferometry is used today to search for exoplanets, to image distant black holes half-way across the universe and to detect gravitational waves using the most sensitive scientific measurement apparatus ever devised.

Chapter 6. Across the Universe: Exoplanets, Black Holes and Gravitational Waves

Moving beyond the measurement of star sizes, interferometry lies at the heart of some of the most dramatic recent advances in astronomy, including the detection of gravitational waves by LIGO, the imaging of distant black holes and the detection of nearby exoplanets that may one day be visited by unmanned probes sent from Earth.

Chapter 7. Two Faces of Microscopy: Diffraction and Interference

The complement of the telescope is the microscope. Interference microscopy allows invisible things to become visible and for fundamental limits on image resolution to be blown past with super-resolution at the nanoscale, revealing the intricate workings of biological systems with unprecedented detail.

Chapter 8. Holographic Dreams of Princess Leia: Crossing Beams

Holography is the direct legacy of Young’s double slit experiment, as coherent sources of light interfere to record, and then reconstruct, the direct scattered fields from illuminated objects. Holographic display technology promises to revolutionize virtual reality.

Chapter 9. Photon Interference: The Foundations of Quantum Communication and Computing

Quantum information science, at the forefront of physics and technology today, owes much of its power to the principle of interference among single photons.

Chapter 10. The Quantum Advantage: Interferometric Computing

Photonic quantum systems have the potential to usher in a new information age using interference in photonic integrated circuits.

A popular account of the trials and toils of the scientists and engineers who tamed light and used it to probe the universe.

Available at Amazon

and at Oxford University Press

and at Barnes & Noble

Galileo Unbound

Blogs inspired by the book Galileo Unbound (Oxford, 2018)

Tag / Gravitational Wave