A thought experiment with clocks in static gravity

Time measured by an ideal clock crucially depends on the gravitational potential and velocity of the clock according to general relativity. Technological advances in manufacturing high-precision atomic clocks have rapidly improved their accuracy and stability over the last decade that approached the level of 10$^{-18}$. Based on a fully relativistic description of the background gravitational physics, we discuss the impact of those highly-precise clocks on the realization of ...

When addressing the notion of proper time in the theory of relativity, it is usually taken for granted that the time read by an accelerated clock is given by the Minkowski proper time. However, there are authors like Harvey Brown that consider necessary an extra assumption to arrive at this result, the so-called clock hypothesis. In opposition to Brown, Richard T. W. Arthur takes the clock hypothesis to be already implicit in the theory. In this paper I will present a view di...

The Equivalence Principle (EP) is at the heart of General Relativity (GR), tested in many aspects. It is often used to discuss qualitatively the influence of gravity on physical phenomena. But can this be made more precise? We compare clock rates, frequency shifts, light deflection and time delay in simple static spacetimes to the analogous phenomena seen by accelerated observers in Minkowski space. In contrast to previous studies, we do not assume that the gravitational fiel...

While Einstein clocks synchronization process is performed, one has a well defined region in which the clocks are synchronized and another one in which the clocks are not yet synchronized. The frontier between them evolves differently from the perspective of observers in relative motion. A discussion is conducted upon direct observation of the phenomenon and Minkowski diagrams.

Simple physical models of a measuring rod and of a clock are used to demonstrate the contraction of objects and clock retardation in special relativity. It is argued that the models could help in promoting student understanding of special relativity and in distinguishing between dynamical and purely perspectival effects.

We critically discuss the measure of very short time intervals. By means of a Gedankenexperiment, we describe an ideal clock based on the occurrence of completely random events. Many previous thought experiments have suggested fundamental Planck-scale limits on measurements of distance and time. Here we present a new type of thought experiment, based on a different type of clock, that provide further support for the existence of such limits. We show that the minimum time inte...

We solve the linearized Einstein equations for a specific oscillating mass distribution and discuss the usual counterarguments against the existence of observable gravitational retardations in the "near zone", where d/r << 1 (d = oscillation amplitude of the source, r = distance from the source). We show that they do not apply in the region d/r \approx 1, and prove that gravitational forces are retarded in the immediate vicinity of the source. An experiment to measure this re...

Several physical concepts, including the concept of time, are clarified herein by taking into account existing experimental data. In addition, the missing links among these physical concepts are established. This allows us to take another step towards understanding the physical nature of time.

This tutorial, addressing physics teachers and undergraduate students, aims at clarifying some aspects of time in special relativity. In particular, time dilation is usually presented only as the well-known ratio of lab time over proper time, $R$. Above ratio is useful, e.g. for describing the decay length of an unstable particle in the lab. But essential characteristics of time dilation, missed out in many textbooks, are manifest in the differences (quadratic, absolute and r...

An elementary account of special relativity for school-children.