Physlib

Physlib.SpaceAndTime.SpaceTime.Boosts

Boosts of space time

i. Overview

In this module we consider boosts acting on points in space time,and recover simple formulae for such applications.

Note that the material here currently assumes that the speed of light `c = 1`.

ii. Key results

  • `boost_x_smul` : The action of a boost in the x-direction on a point in space time.

iii. Table of contents

  • A. The action of a boost in the x-direction

iv. References

See e.g. - https://en.wikipedia.org/wiki/Lorentz_transformation

A. The action of a boost in the x-direction

We show that boosting in the `x`-direction takes `(t, x, y, z)` to `(γ (t - β x), γ (x - β t), y, z)`.

2 declarations

theorem

Lorentz boost in the xx-direction transforms (t,x,y,z)(t, x, y, z) into (γ(tβx),γ(xβt),y,z)(\gamma(t - \beta x), \gamma(x - \beta t), y, z)

Let xx be a point in spacetime with coordinates (t,x,y,z)(t, x, y, z), where tt is the temporal component and x,y,zx, y, z are the spatial components. For a velocity parameter βR\beta \in \mathbb{R} such that β<1|\beta| < 1 and the Lorentz factor γ(β)=11β2\gamma(\beta) = \frac{1}{\sqrt{1 - \beta^2}}, the action of a Lorentz boost in the xx-direction on xx transforms the coordinates according to: - t=γ(β)(tβx)t' = \gamma(\beta)(t - \beta x) - x=γ(β)(xβt)x' = \gamma(\beta)(x - \beta t) - y=yy' = y - z=zz' = z

theorem

Action of the Inverse Lorentz Boost in the First Direction on Spacetime Coordinates (t,x)(t, \mathbf{x})

In a spacetime with d+1d+1 spatial dimensions, consider a point with temporal component tt and spatial vector x=(x0,x1,,xd)Rd+1\mathbf{x} = (x_0, x_1, \dots, x_d) \in \mathbb{R}^{d+1}. Given a speed of light cc and a velocity parameter βR\beta \in \mathbb{R} such that β<1|\beta| < 1, the action of the inverse Lorentz boost B1B^{-1} in the first spatial direction (the direction corresponding to index 00) on the spacetime point (t,x)(t, \mathbf{x}) results in a transformed point (t,x)(t', \mathbf{x}') defined by: - t=γ(β)(t+βcx0)t' = \gamma(\beta) \left( t + \frac{\beta}{c} x_0 \right) - x0=γ(β)(x0+cβt)x'_0 = \gamma(\beta) (x_0 + c \beta t) - xj=xjx'_j = x_j for all j{1,,d}j \in \{1, \dots, d\} where γ(β)=11β2\gamma(\beta) = \frac{1}{\sqrt{1 - \beta^2}} is the Lorentz factor.