Quantum strings and black holes

TL;DR

This paper explores how increasing string coupling causes quantum string states to transition into Schwarzschild black holes, supporting the idea that black hole entropy can be explained by string state counting.

Contribution

It demonstrates the transition mechanism from string states to black holes and confirms the string theory explanation for black hole entropy at a critical coupling.

Findings

String states shrink and match black hole properties at critical coupling.

Black hole entropy can be derived from string state counting.

Quantum black hole states have extremely small level spacing.

Abstract

The transition between (non supersymmetric) quantum string states and Schwarzschild black holes is discussed. This transition occurs when the string coupling $g^2$ (which determines Newton's constant) increases beyond a certain critical value $g_c^2$. We review a calculation showing that self-gravity causes a typical string state of mass $M$ to shrink, as the string coupling $g^2$ increases, down to a compact string state whose mass, size, entropy and luminosity match (for the critical value $g_c^2 \sim (M \sqrt{\alpha'})^{-1}$) those of a Schwarzschild black hole. This confirms the idea (proposed by several authors) that the entropy of black holes can be accounted for by counting string states. The level spacing of the quantum states of Schwarzschild black holes is expected to be exponentially smaller than their radiative width. This makes it very difficult to conceive (even Gedanken) experiments probing the discreteness of the quantum energy levels of black holes.