# Can cherenkov effect be used for telling how fast FTL spaceship moves?

Imagine an alternate universe where FTL do happens, let's just say the inhabitants discovered a hypothetical particles that allows ordinary matter to temporarily be in superposition of any amount of mass including negative value... [I'm drunk don't mind me]

Okay straight to the point, there should be luminous boom, a flash when the spaceship goes faster than light so I'm wondering if we can measure the blue shift or any properties of this cherenkov effect to determine how much faster than the speed of light the spaceship moved? Please show your working and round off to the third sig fig.

• lets rethink this, first we need to know the starting frequency Apr 4, 2020 at 1:56
• also you mean redshift because when it moves away it stretches the light Apr 4, 2020 at 1:59
• and cherenkov radiation is already blue talking about reactors at least Apr 4, 2020 at 2:03
• but since we are talking about a spaceship i assume it would have different effects Apr 4, 2020 at 2:05
• being drunk doesn't justify lack of research
– L.Dutch
Apr 4, 2020 at 3:04

$$d^2E \over dxd\omega=q^2 \over 4\pi\mu(\omega)\omega(1-{c^2 \over v^2n^2(\omega)})$$
The Frank–Tamm formula describes the amount of energy E emitted from Cherenkov radiation, per unit length traveled x and per frequency $$\mu$$. $$\mu(\omega)$$ is the permeability and $$n(\omega)$$ is the index of refraction of the material the charge particle moves through. q is the electric charge of the particle, v is the speed of the particle, and c is the speed of light in vacuum.