One of the great intellectual achievements of the twentieth century was the theory of quantum mechanics, according to which observational results can only be predicted probabilistically rather than with certainty. Yet, after decades in which the theory has been successfully used on an everyday basis, most physicists would agree that we still don’t truly understand what it means. Sean Carroll will discuss the source of this puzzlement, and explain why an increasing number of physicists are led to an apparently astonishing conclusion: that the world we experience is constantly branching into different versions, representing the different possible outcomes of quantum measurements. This could have important consequences for quantum gravity and the emergence of spacetime.
Sean Carroll is a research professor at CalTech, Homewood Professor of Natural Philosophy at John’s Hopkins University, and Fractal Faculty at SFI. His research focuses on fundamental physics and cosmology, quantum gravity and spacetime, philosophy of science, and the evolution of entropy and complexity. He’s authored “Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime;” “The Big Picture;” “The Particle at the End of the Universe;” “From Eternity to Here;” and the textbook “Spacetime and Geometry.”
An update to an experiment run by Henry Cavendish in 1773 could be a cheaper and faster way to spot a potential dark matter particle – and may be 10,000 times more sensitive
In a striking glimpse into extreme physics, scientists have captured the split-second chaos that unfolds when powerful laser flashes blast matter into a superheated plasma. By combining two cutting-edge lasers, researchers were able to track how copper atoms lose and regain electrons in trillionths of a second, creating and dissolving highly charged ions in a rapid, almost cinematic sequence.
Symmetry is one of the most fundamental principles in nature. It describes the rules that make an object look unchanged after a rotation, reflection, or other transformations. In materials, symmetry governs how atoms and electrons are arranged, and how they move together. Crucially, symmetry can even prevent certain collective atomic motions (vibrations) from interacting at all: some are simply forbidden to talk to each other. But what if those symmetry restrictions are not as rigid as they seem?
A new study in Nature Physics shows that these constraints can be partially lifted. Researchers at the University of Texas at Austin and the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) in Hamburg found that electronic fluctuations can dynamically bridge vibrations that symmetry would normally keep separate. Led by Edoardo Baldini’s group at UT Austin, the study reveals how light, vibrations, and electrons become intertwined in a special type of crystal known as ferroaxial, opening new opportunities for controlling quantum states with light.
The researchers focused on a layered material that at room temperature develops an exotic quantum state. Ions and electrons rearrange together into a static, wave-like pattern known as a charge-density wave (CDW), which manifests as a tiling of star-of-David clusters.
Magnons are tiny waves in magnetization that travel through solid magnetic materials, much like the ripples that spread across a pond when a stone is thrown into it. Unlike photons, which travel through empty space or optical fibers, magnons propagate within a magnetic solid. Their wavelengths can be reduced to the nanometer range, meaning that magnonic circuits could, in principle, fit onto a chip no larger than those found in today’s smartphones. Furthermore, as an excitation of a solid, a magnon naturally couples to numerous other fundamental quasi-particles—phonons, photons and others—making it an ideal building block for hybrid quantum systems and quantum metrology.
Until now, there has been one major obstacle: magnons have had a very short lifetime. This lifetime—the period during which they can reliably carry quantum information—was limited to a few hundred nanoseconds at best. Far too short for any practical quantum computation. The team led by Wiener has now achieved a breakthrough: the physicists were able to measure magnon lifetimes of up to 18 microseconds—almost a hundred times longer than any value observed to date.
In this state, magnons are no longer fleeting signals, but become long-lived, reliable carriers of quantum information, comparable to the superconducting qubits used in today’s leading quantum processors. The study has recently been published in the journal Science Advances.
Quantum technology has promising potential to revolutionize how large and complex amounts of information are processed. While already in use primarily in laboratory and research settings globally, quantum technologies are in a transition phase for broader industry applications across many economic sectors.
In researching fundamental aspects of quantum physics, or the behavior of nature at the smallest scales—involving atoms, electrons and photons—a study led by Cal Poly Physics Department Lecturer Ian Powell analyzed how a changing magnetic field can make matter behave in unusual ways.
Powell and student researcher Louis Buchalter, who graduated with a Cal Poly bachelor’s degree in physics in 2025, published the article “Flux-Switching Floquet Engineering” in the journal Physical Review B, highlighting how changing magnetic fields over time can create quantum states that do not exist in any stationary material (remaining in the same state as time elapses).
A long-standing cosmic mystery is beginning to yield new clues as researchers uncover a strikingly consistent pattern in the behavior of high-energy particles traveling across the universe.
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CHAPTERS 0:00 Why Universe is inside an Atom 1:29 What is an atom? 4:44 Louis de Broglie finds waves! 6:28 Electromagnetic force explained 7:24-Sponsor InVideo 8:35 Strong Force explained, color charges! 12:33 Weak Force explained 14:58 Why is Weak Force called a \.
The Delayed Choice Quantum Eraser explained simply provides a shocking answer to whether the future affects the past. Could it be possible that that the future can influence the present? An enhanced version of the famous double slit experiment, called the delayed choice quantum eraser implies exactly that mind blowing scenario – that future events can influence past results.
What exactly is a delayed choice quantum eraser, and how can it possibly show that the future is affecting the past? In 1978, a physicist by the name of John Archibald Wheeler proposed a thought experiment, called delayed choice. Wheeler’s idea was to imagine light from a distant quasar being gravitationally lensed by a closer galaxy. Wheeler noted that this light could be observed on earth in two different ways. This is called a delayed choice because the observer’s choice of selecting how to measure the particle is being done billions of years from the time that the particle left the quasar.
But how could this be?…the light began its journey billions of years ago, long before we decided on which experiment to perform. It would seem as if the quasar light “knew” whether it would be seen as a particle or wave billions of years before the experiment was even devised on earth. Does this prove that somehow the particle’s measurement of its current state has influenced its state in the past? The act of measurement gives reality to the quantum particle. So in the delayed-choice experiment, this means the quantum doesn’t become “real” until you measure it. So this experiment does not prove that the present has influenced the past because the light could have been a wave and particle at the same time, and only become real when it was measured.
However, another more recent experiment set up used a more complicated method to determine this idea of the future influencing a past. It introduced something called the quantum eraser to the delayed choice. So it is called the Delayed Choice Quantum Eraser designed by Kim, Kulik, Shih and Scully in 1999.
It is a complicated construction that introduced entangled pairs of photons to Wheeler’s delayed choice experiment.
I am going to show you a much simpler set up that will illustrate this concept in easier-to-understand terms. The results of this experiment are pretty amazing — because Here’s what happens. It tells us that when the which way information is known, that is, when the detector can ascertain which slit the photon came from, it always presents as a particle. But when the detector cannot ascertain which slit the photon came from, that is, when the which way information is erased, then the photon acts like a wave.
