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What is driving the mulitverse theory? Are the multiverse stories only a sticky-plaster solution to the Big Bang theory problem? Leading thinkers Sabine Hossenfelder, Roger Penrose and Michio Kaku debate.

00:00 Introduction.
02:22 Michio Kaku | Multiverse theory has now dominating cosmology; it is unavoidable.
06:03 Sabine Hossenfelder | Believing in the multiverse is the logical equivalent to believing in God.
07:57 Roger Penrose | Universes are sequential and so are not independent worlds.
16:36 Theme 1 | Do scientifc theories need to be testable?
28:45 Theme 2 | Are tales of the multiverse solutions to the Big Bang theory in trouble?
42:49 Theme 3 | Will theories of the universe always be bound by untestable elements?

Multiverses are everywhere. Or at least the theory is. Everyone from physicists Stephen Hawking and Brian Greene to Marvel superheroes have shown their support for the idea. But critics argue that not only is the multiverse improbable, it is also fantasy and fundamentally unscientific as the theory can never be tested — a requirement that has defined science from its outset.

Should we reject the grand claims and leave multiverse theories to the pages of comic books? Are tales of the multiverse really sticking-plaster solutions for Big Bang theory in trouble? Or should we take multiverse theory as seriously as its proponents, and accept that modern science has moved beyond the bounds of experiment and into that of imagination?

Sean Carroll: We might solve free will one day. But here’s why I doubt it.

Up next, The great free will debate ► https://youtu.be/3O61I0pNPg8

Debates about the existence of free will have traditionally been fought by two competing camps: those who believe in free will and those who don’t because they believe the Universe is deterministic.

Determinism is the thesis that every event — from when a volcano erupts to what cereal you buy at the supermarket — is a theoretically predictable result of the long chain of events that came before it. Free will, it was long thought, cannot exist in a world where all events are already causally determined.

Sometimes astrophysics gets super weird.


A recent study of the star’s surface, published in the journal Nature Astronomy, says that we’re seeing Gamma Columbae in a short, deeply weird phase of a very eventful stellar life, one that lets astronomers look directly into the star’s exposed heart.

What’s New – The mix of chemical elements on the surface of Gamma Columbae look like the byproducts of nuclear reactions that should be buried in the depths of a massive star, not bubbling on its surface.

The observations could not be explained by Newton’s law of universal gravitation. An alternative theory of gravity might provide the answer. Astrophysicists observed mysterious behavior in star clusters that could lead to a rewrite of fundamental principles of the theory of gravity and even disprove the existence of dark matter, a press release explains.

The new findings challenge existing preconceptions based on widely-accepted principles from Newton’s law of universal gravitation, which explain the large-scale structure and movements of the universe.

An analysis of more than two decades’ worth of supernova explosions convincingly boosts modern cosmological theories and reinvigorates efforts to answer fundamental questions.

A powerful new analysis has been performed by astrophysicists that places the most precise limits ever on the composition and evolution of the universe. With this analysis, dubbed Pantheon+, cosmologists find themselves at a crossroads.

Pantheon+ convincingly finds that the cosmos is made up of about two-thirds dark energy and one-third matter — predominantly in the form of dark matter — and is expanding at an accelerating pace over the last several billion years. However, Pantheon+ also cements a major disagreement over the pace of that expansion that has yet to be solved.

A team of astrophysicists has revealed an unusual discovery they say appears to challenge our current understanding of gravity based on Newton’s law of universal gravitation, according to a newly published paper.

The controversial claim, published in the Monthly Notices of the Royal Astronomical Society, appears to be consistent with alternative interpretations about one of physics’ most mysterious fundamental interactions.

In their new study, an international team of astrophysicists says that they came upon the discovery while investigating open star clusters. These formations are created as a gas cloud emerges following the birth of thousands of stars within a relatively short time, the remnants of which are ejected as these clusters of stars ignite and begin to expand, which can result in the formation of anywhere from several dozen, to several thousands of new stars.

A ring-shaped waveguide with a particular pattern of notches can force a light wave to make two round trips before completing an integer number of wave cycles.

Light can travel along a closed path inside a ring of glass or similar material, reflecting repeatedly from the interior surface. Although such closed-loop waves generally have integer values of angular momentum, researchers using a small gear-shaped ring have now demonstrated an ability to generate similar waves with unusual fractional values of angular momentum [1]. As in a Möbius strip, the waves must make two round trips to return to their initial configuration. The ability to tune the angular momentum in this way could give researchers more precise control of light in advanced devices such as single-photon emitters.

Physicists refer to the closed-loop waves as whispering gallery modes, named after an acoustic effect in round rooms, where sounds reflect multiple times off the walls. Ordinarily, a wave of this kind moves around a single closed loop before retracing its earlier path. The phase of the electric field associated with the wave front must go through an integer number M of cycles in making one loop. Technically, this condition also implies that the photons associated with the wave will carry an integer number M units of angular momentum.

An international team of astrophysicists has made a puzzling discovery while analyzing certain star clusters. The finding challenges Newton’s laws of gravity, the researchers write in their publication. Instead, the observations are consistent with the predictions of an alternative theory of gravity. However, this is controversial among experts. The results have now been published in the Monthly Notices of the Royal Astronomical Society.

In their work, the researchers investigated open star clusters. These are formed when thousands of stars are born within a short time in a huge gas cloud. As they “ignite,” the galactic newcomers blow away the remnants of the gas cloud. In the process, the cluster expands considerably. This creates a loose formation of several dozen to several thousand stars. The weak gravitational forces acting between them hold the cluster together.

“In most cases, open star clusters survive only a few hundred million years before they dissolve,” explains Prof. Dr. Pavel Kroupa of the Helmholtz Institute of Radiation and Nuclear Physics at the University of Bonn. In the process, they regularly lose stars, which accumulate in two so-called “tidal tails.” One of these tails is pulled behind the cluster as it travels through space. The other, in contrast, takes the lead like a spearhead.