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.
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.
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.
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.
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.
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.
Galileo Unbound 