note the——symbols Δ & γ may cause issues, i re-saved the file as UTF-8——to fix-it, i also changed the font——to math font.

set terminal svg enhanced size 480 480 
set output "Time dilation.svg"
set grid
set xrang※
set yrange※
set xtics 0.1 nomirror
set ytics 1 nomirror
set xzeroaxis -1
set yzeroaxis -1
set xlabel "Speed"
set ylabel "γ=Δt'/Δt"
set border 0
set key off
set samples 3000
plot 1/sqrt(1-x*x) notitle lw 2

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