# relativity

Relativity posts

## Lorentz velocity addition

This post follows on the Gamma factor post here. The form of velocity addition based on the Lorentz transformation is related to a combination of additive and harmonic addition. Galilei velocity addition is Lorentz velocity addition is which equals In this way the Lorentz transformation attempts to combine arithmetic and harmonic addition.

## Michelson Morley Experiment Re-examined

The Michelson-Morley experiment, compared the longitudinal and transverse cases of reflected light, expecting to detect an ether wind (Figure 1). Figure 1. Michelson-Morley apparatus They explain: “Let sa … be a ray of light which is partly reflected in ab, and partly transmitted in ac, being returned by the mirrors b and c, along ba

## Gamma factor between means

Consider the mean between two quantities: The arithmetic mean is The harmonic mean is where which equals the gamma factor of the Lorentz transformation. The geometric mean is Then the factor γ2 transforms a harmonic mean into an arithmetic mean: The inverse γ factor transforms an arithmetic mean into a geometric mean: so that The

## Light clock in motion

This post builds on the post about the Michelson-Morley experiment here. Compare the light clock in the “Derivation of time dilation” (e.g., here). Linear Light Clock A linear light clock is a thought experiment in which a light beam reflects back and forth between two parallel mirrors that are a distance D apart (see figure

## Dilation of time or distance

The common justification for time dilation in the special theory of relativity goes like this: (Sacamol, CC BY-SA 4.0) From Wikipedia: In the frame in which the clock is at rest (see left part of the diagram), the light pulse traces out a path of length 2L and the period of the clock is 2L divided by

## Invariance of round-trip speed

The mean round-trip speed, as in simple harmonic motion, is Galilean invariant. There are two senses in which this is the case: (1) the time is the same in both directions, and (2) the distance covered is the same in both directions. In the first case, the mean round-trip speed equals the arithmetic mean of

## Dual Euclidean transformations

Dual Euclidean transformations are required to transform six dimensions of length and duration: one Euclidean transformation for length space with time and one Euclidean transformation for duration space with distance. The two Euclidean transformations are: x′ = x − vt and z′ = z − ws where x and x′ are length space vectors, t

## Lorentz transformation derivation fails

Attempted derivations of the Lorentz transformation in the previous post here, which is similar to the light wavefronts approach here, do not work. The reason is that independent and dependent variables are treated alike, but they are not. I suspect this applies to all derivations of the Lorentz transformation. Let us look at the first

## General Galilean invariance

The following is generalized from the explanation of Galilean invariance here. Chorocosm (inertial frames) Among the axioms from Newton’s theory are: (1) There exists an original inertial frame in which Newton’s laws are true. An inertial frame is a reference frame in uniform motion relative to the original inertial frame. (2) All inertial frames share

## Time transformation

The length part of the Galilean transformation is: with the relative velocity v. The time part of the Galilean transformation is: so that time is the same for all observers. Einstein made time relative and symmetric with length (at least in one dimension) by assuming an absolute speed of light, c. With β = v/c