The cosmological constant is the mathematical description of the energy that drives the ever-accelerating expansion of the cosmos. It’s also the source of one of the most enduring and confounding problems in modern physics.
The constant’s observed value is fundamentally at odds with quantum field theory (QFT), the leading theory describing the elementary particles and forces that make up the universe. QFT predicts that quantum fluctuations in the vacuum of space should make the value of the constant enormous—practically infinite. But its observed value is a tiny fraction of that prediction.
Researchers at Brown University have proposed a provocative new answer for why that is.
A new theoretical study finds shorter laser pulses achieve higher quantum efficiency for photoemission from a solid surface without increasing power or intensity. Using light to knock electrons loose from a surface—known as photoemission—may soon be achievable more easily in smaller labs with smaller lasers. Shortening the length of a laser pulse can increase the emitted electrons by several orders of magnitude without increasing the laser intensity or power, according to a University of Michigan Engineering study.
The study is published in Physical Review Research.
Efficient, low-power photoemission could make particle acceleration and high-resolution imaging techniques to visualize cells and atoms more accessible. It could also help researchers develop lightwave electronics, which use light to move charge carriers, for ultrafast computing.
In the quirky quantum world, particles can be affected by forces that they never directly encounter. A classic example is the Aharonov–Bohm (AB) effect, where electrons are affected by a magnetic field, despite not passing through it. Although predicted in 1959, it took more than two decades to confirm this effect experimentally, as the specific changes to the electrons’ wave properties could only be inferred indirectly, and with great difficulty. Now, physicists from the Okinawa Institute of Science and Technology (OIST), in collaboration with the University of Oslo and Universidad Adolfo Ibáñez, have used a classical fluid analog that mimics and extends the AB effect using a simple platform: a water tank.
In work published in Communications Physics, researchers have revealed that when water waves are sent towards a swirling vortex from opposite directions, it causes a striking pattern, with one or more lines of momentarily still water radiating outward and rotating in an almost hypnotic way.
“This was something new and unexpected,” says Aditya Singh, a Ph.D. student in the Nonlinear and Non-equilibrium Physics Unit and co-first author of the study. “That’s what makes this fluid analog system so valuable. It reveals topological effects—wave behaviors that occur across the whole system—that can’t be seen in quantum experiments.”
The past and future are the same thing | feynman on time symmetry.
Discover one of physics’ most mind-bending secrets: the fundamental laws of nature don’t know which way time flows! In this exploration of Feynman’s ideas on time symmetry, we dive deep into how the equations of physics work equally well forwards and backwards, why positrons are electrons moving backward through time, and how the Wheeler-Feynman absorber theory suggests the future might influence the past.
From billiard balls to quantum mechanics, from Maxwell’s equations to the mystery of why we remember yesterday but not tomorrow, this video unravels the beautiful symmetry hidden beneath our everyday experience of time.
Topics Covered: • Time symmetry in fundamental physics • Positrons as electrons traveling backward in time • Wheeler-Feynman absorber theory • The thermodynamic arrow of time • Path integral formulation and quantum mechanics • Why time appears to flow in one direction • CP violation and the weak nuclear force.
Perfect for physics enthusiasts, students, and anyone curious about the nature of time and reality.
⚠️ DISCLAIMER: This is AI-generated content created in the style of Richard Feynman’s teaching approach. The script synthesizes information from various sources about Feynman’s work and ideas in theoretical physics, including his lectures, published papers, and documented contributions to quantum electrodynamics and time-symmetric theories. While based on authentic concepts from Feynman’s career, this is an educational interpretation and not actual recorded material from Richard Feynman.
Researchers in the UC Santa Barbara Materials Department have uncovered the elusive quantum mechanism by which energetic electrons break chemical bonds inside microelectronic devices—a detrimental process that slowly degrades performance over time. The discovery, published as an Editors’ Suggestion in Physical Review B, explains decades-old experimental puzzles and moves scientists closer to engineering more reliable devices.
Physicists have proposed a new way to make neutrinos at accelerated rates. This method would use a state of matter close to absolute zero called a Bose-Einstein condensate. It would harness quantum effects that can produce neutrinos faster than ordinary radioactive decays. This tool would produce a large and controllable beam of neutrinos. They could have similar properties to photons (particles of light) in an optical laser.
Neutrinos are fundamental particles that interact extremely weakly with matter. It is very difficult to produce and detect neutrinos. It requires large detectors and powerful sources such as nuclear reactors or particle accelerators. A controllable, coherent source of neutrinos on a bench-top scale would have a significant impact on neutrino research. This type of technology would provide new opportunities to understand their interactions and quantum mechanical properties. In addition, the specific radioactive decays that would enable such a controllable, coherent neutrino source on a small scale could lead to new applications. These applications could include production of rare isotopes for medical physics and neutrino-based communication.
Lasers have been revolutionary in enabling the development of many aspects of modern science and technology. They are based on the amplification of light via stimulated emission. This is a quantum mechanical process whereby an excited atom is forced to emit a second photon upon absorption of another with the same wavelength. Due to their tiny masses, neutrinos behave similarly to photons in many situations. However, they cannot be used for lasing because their fermionic nature inhibits stimulated emission. For this reason, it is not possible to develop a neutrino laser using this traditional mechanism.
Physicists explored the concept of negative time, finding it wasn’t just an illusion but potentially described actual physical phenomena. Discover the surprising results of quantum trajectory calculations. #Physics #Science #QuantumMechanics #NegativeTime Full podcast with Prof. Aephraim Steinberg: https://youtu.be/cOZ3Kto6NIc …
