Multiverse

To hear the multiverse enthusiasts tell it, many worlds theory offers no problems. But you probably sensed that that wasn’t very likely: It says that our unique experience as individuals is not simply a bit imperfect, a bit unreliable and fuzzy, but is a complete illusion. If we really pursue that idea, rather than pretending that it gives us quantum siblings, we find ourselves unable to say anything about anything that can be considered a meaningful truth. We are not just suspended in language; we have denied language any agency. The MWI — if taken seriously — is unthinkable. Its implications undermine a scientific description of the world far more seriously than do those of any of its rivals. The Read More ›

We are told: “Wherever you look in the cosmos, things don’t seem to add up.” And now physicists like Sabine Hossenfelder are accused of cheating: Ethan Siegel, astrophysicist-blogger behind Forbes’ Starts With a Bang! blog, responded with a post titled “There’s A Debate Raging Over Whether Dark Matter Is Real, But One Side Is Cheating.” He wrote that, in order to win favor from the public, Hossenfelder and McGaugh were setting up a false narrative by treating the fight as an even one, even though the support for a dark matter particle far outweighs the opposing side. Naturally, McGaugh and Hossenfelder were not happy to be called cheaters. McGaugh argued that he’s published far more scientific papers than Siegel has. Read More ›

From Ethan Siegel at Forbes: So why do so many theoretical physicists write papers about the multiverse? About parallel Universes and their connection to our own through this multiverse? Why do they claim that the multiverse is connected to the string landscape, the cosmological constant, and even to the fact that our Universe is finely-tuned for life? Because even though it’s obviously a bad idea, they don’t have any better ones. … As I’ve explained before, the Multiverse is not a scientific theory on its own. Rather, it’s a theoretical consequence of the laws of physics as they’re best understood today. It’s perhaps even an inevitable consequence of those laws: if you have an inflationary Universe governed by quantum physics, Read More ›

From Jim Baggott at Prospect: Over the last few decades “multiverse theories” have become increasingly fashionable within a relatively small—but publicly vocal—group of theoretical physicists. This group specialises in foundational problems in cosmology, particle physics, and quantum mechanics. These theories are advertised as science’s answer to much that we can’t otherwise explain about the universe we inhabit, the elementary particles we have discovered in it, and the reasons for our own existence. … The first victim is context. For example, in a recent post to this blog, Philip Ball reports on a paper published by a team of astrophysicists in the “Monthly Notices of the Royal Astronomical Society.” Ball reports on this paper with an accuracy entirely consistent with his Read More ›

From Columbia mathematician Peter Woit at Not Even Wrong: New Scientist today has a feature article headlined How to think about… The multiverse The idea of an infinite multitude of universes is forced on us by physics. It starts off quoting Sean Carroll: “One of the most common misconceptions is that the multiverse is a hypothesis,” says Sean Carroll at the California Institute of Technology in Pasadena. In fact, it is forced upon us.”It is a prediction of theories we have good reason to think are correct.” The problem with this claim is that it’s simply not true. There is no model that “we have good reason to think [is] correct” that predicts a multiverse of universes with different physics Read More ›

  From astrophysicist Ethan Siegel, reviewing Sabine Hossenfelder’s new book, Lost in Math: How Beauty Leads Physics Astray, at Forbes: The history of physics is filled with great ideas that you’ve heard of, like the Standard Model, the Big Bang, General Relativity, and so on. But it’s also filled with brilliant ideas that you probably haven’t heard of, like the Sakata Model, Technicolor theory, the Steady State Model, and Plasma Cosmology. Today, we have theories that are highly fashionable, but without any evidence for them: supersymmetry, grand unification, string theory, and the multiverse. … Yet unlike in the past, these dead-ends continue to represent the fields in which the leading theorists and experimentalists cluster to investigate. These blind alleys, which have 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 ›

In his final paper, with Hertog, scaling back the multiverse? From Philip Goff at the Guardian: But if all of the universes have exactly the same laws – as in Hawking and Hertog’s proposal – the problem returns, as we now need an explanation of why the single set of laws that govern the entire multiverse is fine-tuned. Hertog seems not to agree, arguing that the paper does make progress on fine-tuning: “This paper takes one step towards explaining that mysterious fine-tuning … It reduces the multiverse down to a more manageable set of universes which all look alike.” However, this merely puts off the explanation of fine-tuning, for the result is that the laws underlying the generation of the 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 ›

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 ›

Asks Columbia mathematician Peter Woit at Not Even Wrong: University press offices and grant agencies put out irresponsible hype about the work of one their faculty or grantees. In this case, it’s Taming the multiverse: Stephen Hawking’s final theory about the big bang from Cambridge, and Stephen Hawking’s last paper, co-authored with ERC grantee Thomas Hertog, proposes a new cosmological theory, in which universe is less complex and finite from the European Research Council. And, of course, pop science media run with it, even if it’s old and debunked news. Woit laments, This is rather depressing, making one feel that there’s no way to fight this kind of bad science, in the face of determined efforts to promote fake physics Read More ›

From ScienceDaily: The theory of eternal inflation that Hawking and Hertog put forward is based on string theory: a branch of theoretical physics that attempts to reconcile gravity and general relativity with quantum physics, in part by describing the fundamental constituents of the universe as tiny vibrating strings. Their approach uses the string theory concept of holography, which postulates that the universe is a large and complex hologram: physical reality in certain 3D spaces can be mathematically reduced to 2D projections on a surface. … Hertog and Hawking used their new theory to derive more reliable predictions about the global structure of the universe. They predicted the universe that emerges from eternal inflation on the past boundary is finite and Read More ›

Astronomer Brian Keating has a new book out, Losing the Nobel Prize, detailing the rise and fall of an apparent confirmation of cosmic inflation in 2014. From the publisher: In 2014, astronomers wielding BICEP2, the most powerful cosmology telescope ever made, revealed that they’d glimpsed the spark that ignited the Big Bang. Millions around the world tuned in to the announcement broadcast live from Harvard University, immediately igniting rumors of an imminent Nobel Prize. But had these cosmologists truly read the cosmic prologue or, swept up in Nobel dreams, had they been deceived by a galactic mirage? The latter, it would seem. A free excerpt is available at Nautilus: The broadcast from Harvard’s Center for Astrophysics captivated media around the Read More ›