The Quantum Theory Of Gravitation, Effective Field Theories, and Strings: Yesterday And Today (2403.14008v1)

Abstract: This paper analyzes the effective field theory perspective on modern physics through the lens of the quantum theory of gravitational interaction. The historical part argues that the search for a theory of quantum gravity stimulated the change in outlook that characterizes the modern approach to the Standard Model of particle physics and General Relativity. We present some landmarks covering a long period, i.e., from the beginning of the 1930s until 1994, when, according to Steven Weinberg, the modern bottom-up approach to General Relativity began. Starting from the first attempt to apply the quantum field theory techniques to perturbatively quantize Einstein's theory, we explore its developments and interaction with the top-down approach encoded by String Theory. In the last part of the paper, we focus on this last approach to describe the relationship between our modern understanding of String Theory and Effective Field Theory in today's panorama. To this end, the non-historical part briefly explains the modern concepts of moduli stabilization and Swampland to understand another change in focus that explains the present framework where some string theorists move.

• The paper details the evolution of quantum gravity, highlighting key shifts from perturbative GR to effective field theories and string theory.
• It outlines seminal contributions from pioneers like Feynman, Weinberg, and Donoghue, emphasizing the role of non-renormalizable interactions in finite predictions.
• The work connects historical insights with modern frameworks, elucidating the impact of the Swampland program on redefining viable quantum gravity models.

The Quantum Theory of Gravitation, Effective Field Theories, and Strings: An Analytical Discourse

The paper by Rocci and Van Riet offers a comprehensive analysis of the evolution of thought regarding quantum theories of gravity, effective field theories (EFT), and string theory, tracing a trajectory from the early 1930s to the contemporary landscape. This disquisition provides an extensive historical and modern perspective on how these concepts have interplayed to shape the current understanding of fundamental physics.

Historical Context and Theoretical Development

The evolution of effective field theory in the context of gravitational interactions unfolds from the initial application of quantum field theory (QFT) techniques to general relativity (GR). Starting with Rosenfeld's pioneering work in the 1930s, the paper delineates the trajectory through mid-20th-century developments, acknowledging contributions from figures like Feynman and DeWitt, whose insights on perturbative approaches and higher derivative theories were seminal in addressing infinities in gravitational interactions. These foundational concepts paved the way for the modern understanding of GR as an effective field theory.

The emphasis on perturbative quantization of GR served as a precursor to recognizing the potential of string theory as a unifying framework, addressing quantum gravity's non-renormalizability issues highlighted by the work of 't Hooft and Veltman. The culmination of these efforts bore fruit in the utilization of effective theories as strategic tools rather than fundamental representations of physical reality, leading to a departure from reductionist perspectives.

The Ascendancy of Effective Field Theories

Weinberg's seminal contributions in the late 20th century are portrayed as a paradigm shift towards the acceptance of non-renormalizable theories within particle physics and beyond. His insights posited GR and the Standard Model (SM) not as fundamental theories but effective ones, applicable over specific energy scales. This notion was instrumental in fostering the modern conception of EFT as a pragmatic framework for yielding finite predictions in quantum gravity, divorced from the need for ultraviolet completion.

Donoghue's work in the 1990s is cited as pivotal, employing EFT methods to extract quantum corrections to Newtonian gravity, highlighting practical methodologies for coping with gravitational divergences. These techniques underscore the relevance of non-renormalizable interactions in low-energy effective actions, marrying the conceptual frameworks of chiral perturbation theories with gravitational forces.

String Theory: From Landscape to Swampland

In re-evaluating string theory, the narrative transitions into the contemporary discourse on moduli stabilization and the Swampland program, contrasting with the erstwhile Landscape paradigm. The authors elucidate the paradigm shift instigated by the Swampland conjectures, such as the Weak Gravity Conjecture, proposing rigorous criteria for demarcating viable EFTs in the landscape of string-theoretic vacua. This delineation invokes broader questions about the feasibility of various EFT frameworks within consistent quantum gravity theories, emphasizing the critical role of global consistency conditions in string compactifications.

Implications and Future Trajectories

Rocci and Van Riet offer an astute synthesis of the historical and philosophical evolution leading to present-day quantum gravitational theories. The practical implications reside in refining our understanding of GR and SM as effective theories, providing both clarity and precision to experimental physics' role in testing quantum gravity frameworks. Theoretical implications abound, particularly in augmenting the coherence of gravitational and particle physics under the unifying auspices of a complete quantum framework.

The prospects for future research extend into attaining precise and experimentally verifiable predictions from the Swampland and reflections on the interplay of top-down and bottom-up approaches. These endeavours hold promise for deeper insights into the fabric of spacetime and the formulation of a more profound theory encompassing all known forces of nature.

The paper asserts that the concerted exploration of quantum gravity through theoretical innovation and empirical rigor will continue to shape and redefine the contours of modern physics, invigorated by advances in both effective field theory and string theory landscapes.