String Theory and Quantum Gravity Conjectures

String theory offers a unified framework in which the fundamental constituents of nature are one-dimensional objects whose vibrational modes give rise to particles and forces. By embedding gravity within a quantum mechanical setting, it seeks to reconcile general relativity with the principles of quantum field theory. Central to this endeavour are a series of conjectures that aim to delineate which low-energy effective theories can emerge from a consistent quantum theory of gravity. These include the Weak Gravity Conjecture, which posits that gravity must be the weakest force; the Swampland Distance Conjecture, which relates large excursions in scalar field space to the appearance of an infinite tower of light states; and the de Sitter Conjecture, which constrains the form of scalar potentials to rule out stable accelerated expansion in a pure quantum gravity context. Together these conjectures chart the boundary between the so-called Landscape of viable theories and the Swampland of inconsistent ones. Developments in this area have profound implications for early-universe cosmology, the nature of dark energy, and the search for unified models that respect both observational data and fundamental consistency requirements.

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String Theory and Quantum Gravity Conjectures publication trend

The graph below shows the total number of articles in string theory and quantum gravity conjectures across all publications each year (not limited to Nature Index journals).

Technical terms

String theory: A framework in which particles are one-dimensional strings whose vibrational modes define mass and charge.

Weak Gravity Conjecture: The hypothesis that gravity must be the feeblest force, ensuring the existence of superextremal charged states.

Swampland Distance Conjecture: A proposal linking large field-space excursions to the emergence of an infinite tower of light states.

de Sitter Conjecture: A criterion forbidding stable or metastable de Sitter vacua in a consistent quantum gravity theory.

Moduli space: The geometric parameter space of scalar fields arising from extra-dimensional compactification.

Calabi–Yau manifold: A special class of compact, Ricci-flat spaces used to preserve supersymmetry in string compactifications.

References

1. Cosmic acceleration and turns in the Swampland. Journal of Cosmology and Astroparticle Physics (2023).
2. The dark dimension and the Swampland. Journal of High Energy Physics (2023).
3. Aspects of the dark dimension in cosmology. Physical Review D (2023).
4. Infinite distances in field space and massless towers of states. Journal of High Energy Physics (2018).