Cosmology

From astrophysicist Ethan Siegel at Forbes, t’s one of the most brilliant, controversial and unproven ideas in all of physics: string theory. At the heart of string theory is the thread of an idea that’s run through physics for centuries, that at some fundamental level, all the different forces, particles, interactions and manifestations of reality are tied together as part of the same framework. Instead of four independent fundamental forces — strong, electromagnetic, weak and gravitational — there’s one unified theory that encompasses all of them. Phlogiston and the ether were theories like that too. They explained so much but… Right now, there are only a few sets of dimensions that the string/superstring picture is self-consistent in, and the most Read More ›

From Emily Conover at ScienceNews: The largest particle detector of its kind has failed to turn up any hints of dark matter, despite searching for about a year. Known as XENON1T, the experiment is designed to detect elusive dark matter particles, which are thought to make up most of the matter in the cosmos. Physicists don’t know what dark matter is. One of the most popular explanations is a particle called a WIMP, short for weakly interacting massive particle. More. The researchers saw no collisions with atomic nuclei in 1300 kg of chilled xenon, which is depressing. But at least they are ruling out spaces where dark matter could be. It’s frustrating because, at this point, researchers don’t know whether Read More ›

In Adrian Cho’s interpretation at Science: When Stephen Hawking died on 14 March, the famed theoretical physicist had a few papers still in the works. Today, the Journal of High Energy Physics published his last work in cosmology—the science of how the universe sprang into being and evolved. (Other papers on black holes are still being prepared.) In the new paper, Hawking and Thomas Hertog, a theoretical physicist at the Catholic University of Leuven (KU) in Belgium, attempt to stick a pin in a bizarre concept called eternal inflation, which implies—unavoidably, according to some physicists—that our universe is just one of infinitely many in a multiverse. Borrowing a concept from string theory, Hawking and Hertog argue that there is no Read More ›

A philosophical question to wake you up. A reader directs our attention to a 2015 piece by cosmologist Alexander Vilenkin at Inference Review (2015): THE ANSWER to the question, “Did the universe have a beginning?” is, “It probably did.” We have no viable models of an eternal universe. The BGV theorem gives us reason to believe that such models simply cannot be constructed. More. He offers the Borde-Guth-Vilenkin (BGV) theorem by way of evidence: Loosely speaking, our theorem states that if the universe is, on average, expanding, then its history cannot be indefinitely continued into the past. More precisely, if the average expansion rate is positive along a given world line, or geodesic, then this geodesic must terminate after a Read More ›

From Sophie Hebden at FQXI: A radical theory replaces the cosmic crunchers with fuzzy quantum spheres, potentially solving the black-hole information paradox and explaining away the Big Bang and the origin of time. … If the core of a black hole isn’t confusing enough, things get worse when you consider its surface—or “event horizon”—which marks an imaginary boundary surrounding the black hole. Anything that crosses the event horizon, even light, will be sucked in towards the black hole’s core and crushed into the singularity. At first it was thought that nothing that falls in to a black hole can ever escape. But in 1974, Stephen Hawking calculated that, thanks to quantum effects, black holes can slowly radiate energy from their Read More ›

From Sabine Hossenfelder at her blog BackRe(Action), responding to a physics major who has heard from cosmologist Brian Greene that string theory can be a grand theory of everything: Greene states very carefully that superstring theory “has the capacity to embrace” gravity as well as the other known fundamental forces (electromagnetic, weak, and strong). What he means is that most string theorists currently believe there exists a specific model for superstring theory which gives rise to these four forces. The vague phrase “has the capacity” is an expression of this shared belief; it glosses over the fact that no one has been able to find a model that actually does what Greene says. Superstring theory also comes with many side-effects Read More ›

Dark energy. From Andrew Masterson at Cosmos: The question of dark energy in one universe does not require others to provide an answer. A hypothetical multiverse seems less likely after modelling by researchers in Australia and the UK threw one of its key assumptions into doubt. Dark energy is supposed to be responsible for the accelerating expansion of our universe but current theory suggests that there should be much more than there is, so: The multiverse idea to an extent accounts for and accommodates this oddly small – but life-permitting – dark energy quotient. Essentially it permits a curiously self-serving explanation: there are a vast number of universes all with differing amounts of dark energy. We exist in one that Read More ›

The universe is currently estimated to be about 13.8 billion years old. From Laurel Hamer at ScienceNews: That’s earlier than the 550 million years ago suggested in a previous estimate that also measured starlight from the early universe (SN Online: 2/9/2015). But it’s in the same ballpark as observations reported in March (SN: 3/31/18, p. 6), which suggest star formation began around 180 million years after the Big Bang. That conclusion, however, was drawn from radio signals rather than direct observations of starlight. “If [those] results were true, our results would independently support their claims that star formation activity had already initiated at a very early stage of the universe,” Hashimoto says. More. If it holds up, this finding will Read More ›

From ScienceDaily: Questions about whether other universes might exist as part of a larger Multiverse, and if they could harbour life, are burning issues in modern cosmology. Now new research led by Durham University, UK, and Australia’s University of Sydney, Western Sydney University and the University of Western Australia, has shown that life could potentially be common throughout the Multiverse, if it exists. The key to this, the researchers say, is dark energy, a mysterious “force” that is accelerating the expansion of the Universe. Scientists say that current theories of the origin of the Universe predict much more dark energy in our Universe than is observed. Adding larger amounts would cause such a rapid expansion that it would dilute matter Read More ›

From Katia Moskvitch at Quanta: The neutron-star collision was just the beginning. New data in the months since that discovery have made life increasingly difficult for the proponents of many of the modified-gravity theories that remain. Astronomers have analyzed extreme astronomical systems that contain spinning neutron stars, or pulsars, to look for discrepancies between their motion and the predictions of general relativity — discrepancies that some theories of alternative gravity anticipate. These pulsar systems let astronomers probe gravity on a new scale and with new precision. And with each new observation, these alternative theories of gravity are having an increasingly hard time solving the problems they were invented for. Researchers “have to sweat some more trying to get new physics,” Read More ›

From John Ellis at PJ Media: The belief that inanimate objects, like rocks and tableware, contain consciousness is quickly picking up steam among respected philosophers and scientists. … The problem for these “credible philosophers, neuroscientists, and physicists” who take panpsychist seriously is, as Goldhill points out, “The materialist viewpoint states that consciousness is derived entirely from physical matter. It’s unclear, though, exactly how this could work.” She cites philosophy professor David Chalmers who noted, “It’s very hard to get consciousness out of non-consciousness.” While this is an academic discussion on one level, there is another level that directly affects our ethics. The Judeo-Christian worldview and ethics that undergird Western society have as part of their core anthropology the recognition of Read More ›

And we learn some other things as well. From Suzan Mazur at Oscillations, an interview with Craig James Hogan, affiliated with Fermilab: Suzan Mazur: Thank you. There is criticism that the holographic investigation has been going on for almost 20 years, kicked off by Juan Maldacena and that there’s very little evidence so far, despite the bold headlines. That at some point in scientific investigations if the data doesn’t correlate with the experiment as modeled, it’s time to move on. I gather you don’t share that perspective. You’ve said you’re only at the beginning of the investigation. Do you see this as an emerging field like origin of life, spawning an increasing number of virtual research hubs in various parts Read More ›

From Tyler Krueger at Astronomy: Albert Einstein’s theory of general relativity is just over 100 years old, and so far it has predicted the interaction between celestial objects and the space-time field very well. There are a few troublesome spots, however, in which the theory of general relativity doesn’t agree with quantum mechanics. These gaps have confounded researchers for decades, and have sprouted a handful of hypotheses attempting to explain the dissonance. Dark matter and dark energy are the prevailing stand-in answers for this problem, but they are, as of yet, merely stand-ins. And there are some physicists that do not buy into these explanations. Erik Verlinde, a professor of science mathematics, and informatics at the University of Amsterdam, is Read More ›

From Suzan Mazur at Oscillations, an interview with Iranian-born astrophysicist Niayesh Afshordi: Niayesh Afshordi on Holographic Universe Media Spin & the Iranian Brain Drain Suzan Mazur: How close is the goal of combining Einstein’s theory of relativity and quantum physics? Something Kostas Skenderis at the University of Southampton has described as a new paradigm for physical reality. Niayesh Afshordi: We don’t know. Physicists have been chasing this goal for the past 80 years. We’d like to think that we’re closer than before. There have been new insights, theoretical and observational insights. But whether those are real, it’s difficult to say. Suzan Mazur: Your holographic universe research has been widely touted as “the first observational evidence that our universe could be Read More ›

From Cardiff University at Eurekalert: The birth of stars from dense clouds of gas and dust may be happening in a completely unexpected way in our own galaxy and beyond. This is according to an international team of researchers, including scientists from Cardiff University, who have found that long-held assumptions about the relationship between the mass of star-forming clouds of dust and gas and the eventual mass of the star itself may not be as straightforward as we think. The underlying reasons as to why a star eventually grows to a specific mass has puzzled scientists for some time. It has been assumed that a star’s mass mostly depends on the original structure – known as a star-forming core – Read More ›