Should we abandon the multiverse theory? | Sabine Hossenfelder, Roger Penrose, Michio Kaku

The panel discussion begins with an introduction to the concept of the multiverse, highlighting its popularity in both scientific and fictional realms. The participants include notable physicists and theorists who will debate whether the multiverse exists or if it remains in the realm of science fiction. The panelists are set to address the central question of the multiverse's existence within a three-minute time frame each.

The conversation shifts to the discussion of quantum theory's success and its implications on the concept of a multiverse. The speaker explains the quantum principle of superposition, where electrons can exist in multiple states until measured, and extends this idea to the universe itself, suggesting the possibility of multiple universes or a 'bubble bath' of universes. The discussion touches on the inflationary theory and its relation to string theory, proposing that universes are constantly being born, with supporting data leaning towards this idea.

A panelist argues that multiverse theories emerging from the foundations of physics stem from a misunderstanding, where physicists attribute reality to the mathematics they work with. The critique points out that just because certain predictions align with observations, it doesn't mean the entire mathematical framework is a true representation of reality. The discussion also explores the potential value of these theories as philosophical speculations and their inspirational impact on artists and writers, while acknowledging the possibility of future testability.

Nobel laureate Roger Penrose shares his concerns about the inconsistencies in quantum mechanics, particularly the measurement problem. He highlights the theory's success but points out its 'blemish', exemplified by Schrödinger's cat paradox. Penrose suggests that the foundational principles of quantum mechanics and general relativity are in conflict, and that a successful theory should resolve this, eliminating the need for superpositions in macroscopic bodies. He emphasizes the need for a theory that is consistent and rids quantum mechanics of its measurement problem.

Penrose introduces the concept of a cyclical multiverse, where our universe is part of a continuous sequence of expansions and contractions. He differentiates this from the idea of a multiverse with infinite universes, stating that his model involves only one universe going through various stages. The discussion touches on the implications of these phases being observationally testable and how they have been supported by some tested conclusions.

The panel delves into the necessity of testability in scientific theories and whether the multiverse theory threatens this principle. A participant argues that theories may not be testable yet, could be switched to avoid falsification, or may have parts that are testable. The conversation emphasizes the indirect evidence supporting the multiverse theory, comparing it to the indirect methods used to confirm the existence of atoms and other physical phenomena not directly observed.

The discussion continues with a challenge to the audience to propose a theory that unifies general relativity with quantum mechanics, satisfying specific criteria. The speaker emphasizes the importance of testability and mathematical consistency in the pursuit of a 'Theory of Everything'. The conversation also touches on the Fermi laboratory's discovery of an anomalous behavior in a muon's magnetic moment, suggesting a new force outside the standard model and indicating a potential revolution in quantum physics.

The panelists debate the existence of scientific evidence for the multiverse theory. One participant argues that indirect evidence and parallel developments in physics support the multiverse concept, while another asserts that these do not constitute evidence for string theory or the multiverse. The discussion highlights the challenges in inferring theoretical conclusions from observations and the potential for future discoveries that could provide more clarity on these issues.

The conversation turns to the public's fascination with the multiverse concept. Panelists discuss the psychological appeal of the idea of infinite versions of oneself and the potential for good fiction and science storytelling. The discussion also touches on the historical context of parallel universes and the role of physical theories in entertaining and exploring these concepts.

The panel concludes with a reflection on the potential for untestable elements in scientific theories and the nature of the scientific method itself. The participants consider whether there will always be aspects of our understanding of the universe that remain untestable, and whether this should lead us to consider theories like the multiverse. The conversation acknowledges the limitations of human observation and the potential for theories that simplify our understanding, even if they are not directly testable.