Condensed matter lessons about the origin of time

TL;DR

This paper explores how condensed matter physics can provide insights into the origin of time in quantum gravity, highlighting multiple characteristic scales and questioning traditional hierarchies in physics.

Contribution

It introduces the perspective that condensed matter physics offers valuable lessons on the nature of time and quantum gravity, emphasizing multiple scales and challenging conventional hierarchies.

Findings

Multiple characteristic scales in quantum gravity effects.

Quantum gravity effects may be undetectable at Planck scale.

Hierarchy between relativity theories may need reinterpretation.

Abstract

It is widely hoped that quantum gravity will shed light on the question of the origin of time in physics. The currently dominant approaches to a candidate quantum theory of gravity have naturally evolved from general relativity, on the one hand, and from particle physics, on the other hand. A third important branch of 20th century `fundamental' physics, condensed-matter physics, also offers an interesting perspective on quantum gravity, and thereby on the problem of time. The bottomline might sound disappointing: to understand the origin of time, much more experimental input is needed than what is available today. Moreover it is far from obvious that we will ever find out the true origin of physical time, even if we become able to directly probe physics at the Planck scale. But we might learn some interesting lessons about time and the structure of our universe in the process. A first lesson is that there are probably several characteristic scales associated with "quantum gravity" effects, rather than the single Planck scale usually considered. These can differ by several orders of magnitude, and thereby conspire to hide certain effects expected from quantum gravity, rendering them undetectable even with Planck-scale experiments. A more tentative conclusion is that the hierarchy between general relativity, special relativity and Newtonian physics, usually taken for granted, might have to be interpreted with caution.