On the left side, we have a scattering process involving two gluons (green/yellow and blue/cyan) interacting to produce a gluon (red/magenta) and a Higgs particle (white). The more complex scattering process to the right is mirrored by the simpler one on the left, but here we have a scattering process of two gluons (green/yellow and blue/cyan) interacting to produce four gluons (red/magenta, red/yellow, blue/magenta and green/cyan). The black color symbolizes the fact that in the collision itself, many different elementary interactions can occur, and we have to sum over all possibilities. According to the Heisenberg uncertainty principle, we cannot know what possibility exactly occurred – so it’s a “black box”. Drawing: Søren J. Granat

Read more at https://nbi.ku.dk/english/news/news22/new-and-surprising-duality-found-in-theoretical–particle-physics/

]]>Exactly one hundred years ago, Alexander Friedmann discovered that General Relativity (GR) predicts non-stationary Universe. His equation describing the evolution of the Universe is now named after him. In this paper we briefly recall the human and scientific aspects of this revolutionary change in our picture of the world. We also recall that immediately after finishing his seminal paper Friedmann wrote a book on GR for a wide audience. In that book he presented an impressive picture of the expanding Universe created from nothing…

Read more at https://arxiv.org/pdf/2204.10650.pdf

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In this episode of “What We’ve Learned from NKS”, Stephen Wolfram is counting down to the 20th anniversary of A New Kind of Science with [another] chapter retrospective. Read all of NKS here: https://www.wolframscience.com/nks/

00:00 Stream Begins 2:28 Stephen begins talking 6:16 Section 1: The Problems of Physics 8:18 Section 2: The Notion of Reversibility 14:58 Section 3: Irreversibility and the Second Law of Thermodynamics 30:15 Notes 42:33 Section 4: Conserved Quantities and Continuum Phenomena 50:09 Section 5: Ultimate Models for the Universe 53:15 Section 6: The Nature of Space 54:00 Section 7: Space as a Network 57:54 Section 8: The Relationship of Space and Time 1:01:40 Section 9: Time and Causal Networks 1:06:08 Section 10: The Sequencing of Events in the Universe 1:09:00 Section 11: Uniqueness and Branching in Time 1:12:50 Section 12: Evolution of Networks 1:17:47 Section 13: Space, Time and Relativity 1:20:54 Section 14: Elementary Particles 1:22:16 Notes 1:34:06 Section 15: The Phenomenon of Gravity 1:43:22 Section 16: Quantum Phenomena 1:50:54 Wrap up of Chapter 9 1:56:30 Is measurement a time irreversible process? Is it the case that in order to gain information about a system the system must have an arrow of time? Or is the flow of time itself the generation of information? 1:57:12 Does this mean the universe is perhaps on a trajectory to reverse to it’s initial state or will the rule expand randomly forever. if the former will time run backwards or will everything that “exists” be organically destroyed in the reversal? 1:57:45 Is there a network defined by a few simple rules, implying that the monster group and the 6 pariah groups give rise to the Standard Model with 6 basic quarks? 1:58:30 Has anyone ever run two rules in a combined computational space, could the rules “procreate” in this instance at connecting points to combine and create new rules? 1:58:46 Is there any evidence of higher complexity classes of connections in regions of branchial space that are contained in finite spaces of physical space? E.g, planets 1:59:33 It seems like half integer spin particles are only observed because the universe is 3 dimensional. If your model implies that the universe is not exactly 3 dimensional, does this mean that we can observe fractional spin particles? 2:01:30 Farewell Remarks

]]>**Masayuki Nakahata**

The first solar neutrino experiment led by Raymond Davis Jr. showed a deficit of neutrinos relative to the solar model prediction, referred to as the “solar neutrino problem” since the 1970s. The Kamiokande experiment led by Masatoshi Koshiba successfully observed solar neutrinos, as first reported in 1989. The observed flux of solar neutrinos was almost half the prediction and confirmed the solar neutrino problem. This problem was not resolved for some time due to possible uncertainties in the solar model. In 2001, it was discovered that the solar neutrino problem is due to neutrino oscillations by comparing the Super-Kamiokande and Sudbury Neutrino Observatory results, which was the first model-independent comparison. Detailed studies of solar neutrino oscillations have since been performed, and the results of solar neutrino experiments are consistent with solar model predictions when the effect of neutrino oscillations are taken into account. In this article, the history of solar neutrino observations is reviewed with the contributions of Kamiokande and Super-Kamiokande detailed…. read more at

**James Hartle**

Brief recollections by the author about how he and Stephen Hawking arrived at the theory of the No Boundary Quantum State of the Universe. Read more at

String theory has dominated discussions at the frontiers of physics for decades, especially in the attempts to build a quantum theory of gravity. But does it deserve its exalted status? Nobel Prize winner and String Theory pioneer David Gross debates Carlo Rovelli, one of the founding fathers of Loop Quantum Gravity. The discussion is lively; full of insights, insults, backhanded compliments and even some common ground as to the nature of physics.

Timecodes 0:00 Introduction 3:00 David Gross early years, 4:00 Carlo Rovelli early years 5:22 David on string theory 20:22 Carlo on string theory 31:08 David&Carlo on string theory 53:20 Loop Quantum Gravity 1:00 David&Carlo on LQG 1:21 Black Holes 1:30 Predictions and the Scientific Method

]]>**Frank Wilczek**

Handedness, or chirality, has been a continuing source of inspiration across a wide range of scientific problems. After a quick review of some important, instructive historical examples, I present three contemporary case studies involving sophisticated applications of chirality at the frontier of present-day science in the measurement of the muon magnetic moment, in topological physics, and in exploring the “chirality” of time. Finally, I briefly discuss chirality as a source of fertile questions.

Read more at https://arxiv.org/abs/2112.06927

]]>Colm Bracken, Jonte R. Hance, Sabine Hossenfelder

The Delayed-Choice Quantum Eraser experiment is commonly interpreted as implying that in quantum mechanics a choice made at one time can influence an earlier event. We here suggest an extension of the experiment that results in a paradox when interpreted using a local realist interpretation combined with backward causation (“retrocausality”). We argue that resolving the paradox requires giving up the idea that, in quantum mechanics, a choice can influence the past, and that it instead requires a violation of Statistical Independence without retrocausality. We speculate what the outcome of the experiment would be.

read more at https://arxiv.org/abs/2111.09347

read also: …a comment… and the Reply…

]]>Our ability to explore the cosmos by direct contact has been limited to a small number of lunar and interplanetary missions. However, the NASA Starlight program points a path forward to send small, relativistic spacecraft far outside our solar system via standoff directed-energy propulsion. These miniaturized spacecraft are capable of robotic exploration but can also transport seeds and organisms, marking a profound change in our ability to both characterize and expand the reach of known life. Here we explore the biological and technological challenges of interstellar space biology, focusing on radiation-tolerant microorganisms capable of cryptobiosis. Additionally, we discuss planetary protection concerns and other ethical considerations of sending life to the stars….

Read more at *Lantin et al https://arxiv.org/abs/2110.13080*