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abstract: 'We present a discussion of the fundamental loss of unitarity that appears in quantum mechanics due to the use of a physical apparatus to measure time. This induces a decoherence effect that is independent of any interaction with the environment and appears in addition to any usual environmental decoherence. The discussion is framed self consistently and aimed to general physicists. We derive the modified Schrödinger equation that arises in quantum mechanics with real clocks and discuss the theoretical and potential experimental implications of this process of decoherence.'
address:
- 'Instituto de Física, Facultad de Ciencias, Universidad de la República, Iguá 4225, CP 11400 Montevideo, Uruguay'
- 'Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213'
- 'Department of Physics and Astronomy, Louisiana State University, Baton Rouge, LA 70803-4001'
author:
- Rodolfo Gambini
- 'Rafael A. Porto'
- Jorge Pullin
date: March 20th 2006
title: 'Fundamental decoherence from quantum gravity: a pedagogical review'
---

Introduction
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As ordinarily formulated, quantum mechanics involves and idealization. The idealization is the use of a perfect classical clock to measure times. Such a device clearly does not exist in nature, since all measuring devices are subject to some level of quantum fluctuations. Therefore 