Cosmology

A recent piece by Natalie Wolchover in The Atlantic (also in Quanta) tells us: String Theory: The Best Explanation for Everything in the Universe. String theory (or, more technically, M-theory) is often described as the leading candidate for the theory of everything in our universe. But there’s no empirical evidence for it, or for any alternative ideas about how gravity might unify with the rest of the fundamental forces. Why, then, is string/M-theory given the edge over the others? At Not Even Wrong, Peter Woit answers a question with a question: In a time when the credibility of science is under attack, does anyone else see a problem with telling the public that the “Best Explanation for Everything in the Universe” that science Read More ›

That’s the big change that naturalism (nature is all there is and you did not evolve to understand it correctly) has created in science. Evidence isn’t critical any more. From Natalie Wolchover at Quanta: String theory (or, more technically, M-theory) is often described as the leading candidate for the theory of everything in our universe. But there’s no empirical evidence for it, or for any alternative ideas about how gravity might unify with the rest of the fundamental forces. Why, then, is string/M-theory given the edge over the others? … This basic sequence of events has led most experts to consider M-theory the leading TOE candidate, even as its exact definition in a universe like ours remains unknown. Whether the Read More ›

From ScienceDaily: Three mathematicians have a different explanation for the accelerating expansion of the universe that does without theories of “dark energy.” Einstein’s original equations for General Relativity actually predict cosmic acceleration due to an “instability,” they argue in paper published recently in Proceedings of the Royal Society A. Paper. (public access) – Joel Smoller, Blake Temple, Zeke Vogler. An instability of the standard model of cosmology creates the anomalous acceleration without dark energy. Proceedings of the Royal Society A: Mathematical, Physical and Engineering Science, 2017; 473 (2207): 20160887 DOI: 10.1098/rspa.2016.0887 More. Well, if we don’t need dark energy to account for cosmic expansion, isn’t that a bit like not needing Santa Claus to explain the wine, cheese, and chocolates Read More ›

From David N.Schwartz,  author of The Last Man Who Knew Everything: The Life and Times of Enrico Fermi, Father of the Nuclear Age, at NPR: Fermi’s contributions to physics were so broad ranging, his interests so wide, that he made a mark in virtually every area of the field. I find it irresistible to speculate what he would make of physics today or how he would view some of our broader debates on the role of science and society. … What he would make of string theory we will never know, but he was always more comfortable with theories backed by experimental agendas. He would have been amazed at the size of the Large Hadron Collider at CERN, but in fact, Read More ›

From ScienceDaily: Although for five decades, the Big Bang theory has been the best known and most accepted explanation for the beginning and evolution of the Universe, it is hardly a consensus among scientists. Brazilian physicist Juliano Cesar Silva Neves part of a group of researchers who dare to imagine a different origin. In a study recently published in the journal General Relativity and Gravitation, Neves suggests the elimination of a key aspect of the standard cosmological model: the need for a spacetime singularity known as the Big Bang. In raising this possibility, Neves challenges the idea that time had a beginning and reintroduces the possibility that the current expansion was preceded by contraction. “I believe the Big Bang never Read More ›

From theoretical physicist Sabine Hossenfelder at her blog Back(reaction): On the one hand, I understand the concerns about breaking with centuries of tradition. We used to followed up each hypothesis with experimental test, and the longer the delay between hypothesis and test, the easier for pseudoscience to take foothold. On the other hand, I agree that speculation is a necessary part of science and new problems sometimes require new methods. Insisting on ideals of the past might mean getting stuck, maybe forever. Even more important, I think it’s a grave mistake to let anyone define what we mean by doing science. Because who gets to decide what’s the right thing to do? Should we listen to Helge Kragh? Peter Woit? Read More ›

A reluctant physics student wrote to our physics color commentator Rob Sheldon for help recently. What, he asks, is this paper all about: — Journal of High Energy Physics May 2017, 2017:136 Supersymmetric many-body systems from partial symmetries — integrability, localization and scrambling Authors Pramod Padmanabhan, Soo-Jong Rey, Daniel Teixeira, Diego Trancanelli Email author Open AccessRegular Article – Theoretical Physics First Online: 25 May 2017 Abstract Partial symmetries are described by generalized group structures known as symmetric inverse semigroups. We use the algebras arising from these structures to realize supersymmetry in (0+1) dimensions and to build many-body quantum systems on a chain. This construction consists in associating appropriate supercharges to chain sites, in analogy to what is done in spin Read More ›

Via Wuthrich at philosophy of physics blog Taking Up Spacetime, Workshop: “Naturalness, Hierarchy, and Fine-Tuning” Workshop Description: The requirement of naturalness has long served as an influential constraint on model-building in elementary particle physics. Yet there are many ways of understanding what, precisely, this requirement amounts to, from restrictions on the amount of fine-tuning that a model can exhibit, to prohibitions on sensitive dependence between physics at different scales, to the requirement that dimensionless parameters defining the Lagrangian of a theory all be of order one unless protected by a symmetry. This workshop aims to clarify the relationships among these concepts of naturalness and their connection to the hierarchy problem, as well as to assess arguments for and against imposing Read More ›

Astrophysicist Ethan Siegel explains: Our best theories, like the aforementioned theory of evolution, the Big Bang theory, and Einstein’s General Relativity, cover all of these bases. They have an underlying quantitative framework, enabling us to predict what will happen under a variety of situations, and to then go out and test those predictions empirically. So far, these theories have demonstrated themselves to be eminently valid. Where their predictions can be described by mathematical expressions, we can tell not only what should happen, but by how much. For these theories in particular, among many others, measurements and observations that have been performed to test these theories have been supremely successful. More. “Fossils, genetic inheritance, and DNA prove the theory of evolution” Read More ›

From Natalie Wolchover at Quanta: The flurry of findings started last year with a paper that reported the first traversable wormhole that doesn’t require the insertion of exotic material to stay open. Instead, according to Ping Gao and Daniel Jafferis of Harvard University and Aron Wall of Stanford University, the repulsive negative energy in the wormhole’s throat can be generated from the outside by a special quantum connection between the pair of black holes that form the wormhole’s two mouths. When the black holes are connected in the right way, something tossed into one will shimmy along the wormhole and, following certain events in the outside universe, exit the second. Remarkably, Gao, Jafferis and Wall noticed that their scenario is Read More ›

From Sabine Hossenfelder at her blog Backreaction: I was elated when I saw that Gian Francesco Giudice announced the “Dawn of the Post-Naturalness Era,” as the title of his recent paper promises. The craze in particle physics, I thought, might finally come to an end; data brought reason back to Earth after all. … I believe what is needed for progress in the foundations of physics is more mathematical rigor. Obsessing about ill-defined criteria like naturalness that don’t even make good working hypotheses isn’t helpful. And it would serve particle physicists well to identify their previous mistakes in order to avoid repeating them. I dearly hope they will not just replace one beauty-criterion by another. Giudice on the other hand Read More ›

By way of bypassing the Big Bang, from Anu Padmanabhan at Nautilus: The key new ingredient we have introduced, which helps to bypass this technical difficulty, is the concept of cosmic information. The idea that information should play a key role in the description of physics has gained considerable support in recent times. This notion arises in several contexts when one attempts to combine the principles of quantum theory and gravity like, for example, in the study of quantum black holes. There is also the intriguing notion of holography in some of these models, which suggests that the information content in a bulk region can be related to the information content on its boundary. But, unfortunately, the mathematical description of Read More ›

From Emily Thomas at The Conversation: Over the last few decades, a new way of arguing for atheism has emerged. Philosophers of religion such as Michael Martin and Nicholas Everitt have asked us to consider the kind of universe we would expect the Christian God to have created, and compare it with the universe we actually live in. They argue there is a mismatch. Everitt focuses on how big the universe is, and argues this gives us reason to believe the God of classical Christianity doesn’t exist. … The weight of galaxies, and the press of years, seem to sweep us towards atheism. More. The size of the universe would only “sweep us towards atheism” if we wanted to go Read More ›

From a talk advertised at Humane Philosophy: Abstract: This paper examines the effects that a philosophical consideration of nothing has on the debate between theism and atheism. In particular, it argues that surprising conclusions that arise from a close analysis of the concept of nothing result in three claims that have relevance for that debate. Firstly, that on the most plausible demarcation criterion for science, science is constitutionally unable to show theism to be a redundant hypothesis; the debate must take place at the level of metaphysics. Secondly, that on that level, one increasingly popular atheistic response to the question “Why is there something rather than nothing” commits one to rejection of the presumption of atheism. Thirdly, the presumption of Read More ›

From Nancy Atkinson at Seeker: Thomas Kephart from Vanderbilt University and four of his colleagues from around the world wanted to figure out why our universe seemingly has just three dimensions, especially since, as they wrote, “quantum gravity scenarios such as string theory… assume nine or ten space dimensions at the fundamental level.” They combined particles physics with mathematical knot theory to try and work this out, borrowing the concept of “flux tubes,” which are flexible strands of energy that link elementary particles together. … In an environment of extremely high energy, the team said that the quark-gluon plasma would have been an ideal environment for rapid flux tube formation in the very early universe. But, crucially, they noted that Read More ›