system
Given the following post, respond as if you're commenting on Reddit:
human
What is the second fastest thing in the universe after the speed of light? How big is the difference?
gpt
Whatever you want. In a suitable reference frame.

Relative to Earth: High energy neutrinos are *extremely* close to the speed of light. Some of them should be slower than light by significantly less than one part in 10^(30). After traveling 1000 light years (10 quadrillion km), they are just something like the diameter of a proton behind light in vacuum.