sol: Speed of light and Minkowski metric
In lorentz: The Lorentz Transform in Relativistic Physics

Description Usage Arguments Details Note Author(s) Examples

Getting and setting the speed of light

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sol(c)
eta(downstairs=TRUE)
ptm(to_natural=TRUE, change_time=TRUE)

`c`	Scalar, speed of light. If missing, return the speed of light
`downstairs`	Boolean, with default `TRUE` meaning to return the covariant metric tensor g_ij with two downstairs indices, and `FALSE` meaning to return the contravariant version g^ij with two upstairs indices
`to_natural,change_time`	Boolean, specifying the nature of the passive transform matrix

In the context of an R package, the symbol “c” presents particular problems. In the lorentz package, the speed of light is denoted “sol”, for ‘speed of light’. You can set the speed of light with sol(x), and query it with sol(); see the examples. An infinite speed of light is sometimes useful for Galilean transforms.

The speed of light is a global variable, governed by options("c"). If NULL, define c=1. Setting showSOL to TRUE makes sol() change the prompt to display the speed of light which might be useful.

Function eta() returns the Minkowski flat-space metric

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Note that the top-left element of eta() is -c^2, not -1.

Function ptm() returns a passive transformation matrix that converts displacement vectors to natural units (to_natural=TRUE) or from natural units (to_natural=FALSE). Argument change_time specifies whether to change the unit of time (if TRUE) or the unit of length (if FALSE).

Typing “sol(299792458)” is a lot easier than typing “options("c"=299792458)”, which is why the package uses the idiom that it does.

Robin K. S. Hankin

sol()                          # returns current speed of light
sol(299792458)                 # use SI units
sol()                          # speed of light now SI value

eta()                          # note [t,t] term
u <- as.3vel(c(100,200,300))   # fast terrestrial speed, but not relativistic
boost(u)                       # boost matrix practically Galilean
is.consistent.boost(boost(u))  # should be TRUE
sol(1)                         # revert to relativisitic units