# How a moving passive observer can perceive its environment ? The Unruh effect revisited

## TL;DR

This paper demonstrates how a moving observer in a noisy medium can perceive its environment and detect obstacles by analyzing the autocorrelation of recorded signals, revisiting the Unruh effect in a new context.

## Contribution

It shows that an accelerating observer can perceive environmental features through signal correlation, extending the Unruh effect to noisy media with practical obstacle detection.

## Key findings

- The autocorrelation function reveals environmental information.
- The Rindler trajectory uniquely maintains a constant local spectrum.
- Obstacles perturb the signal spectrum, enabling localization.

## Abstract

We consider a point-like observer that moves in a medium illuminated by noise sources with Lorentz-invariant spectrum. We show that the autocorrelation function of the signal recorded by the observer allows it to perceive its environment. More precisely, we consider an observer with constant acceleration (along a Rindler trajectory) and we exploit the recent work on the emergence of the Green's function from the cross correlation of signals transmitted by noise sources. First we recover the result that the signal recorded by the observer has a constant Wigner transform, i.e. a constant local spectrum, when the medium is homogeneous (this is the classical analogue of the Unruh effect). We complete that result by showing that the Rindler trajectory is the only straight-line trajectory that satisfies this property. We also show that, in the presence of an obstacle in the form of an infinite perfect mirror, the Wigner transform is perturbed when the observer comes into the neighborhood of the obstacle. The perturbation makes it possible for the observer to determine its position relative to the obstacle once the entire trajectory has been traversed.