A Space Whale has been traveling from point A (let it be Sirius) to point B (let it be Vega) faster than light (FTL). Did it emit Cherenkov radiation while traveling?

Cherenkov radiation is radiation emitted when some particles travel faster than the speed of light of the medium in which they travel. It can be seen sometimes at submerged nuclear reactors and has a beautiful blue color.

Cherenkov Radiation in a submerged nuclear reactor

Before you say it I ALREADY KNOW that currently we think (from what empiric results tell us) that nothing can go faster than the speed of light in a vacuum, just answer the question and don't come at me with the 'nothing can go faster than light'.

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    $\begingroup$ So you mean actual, legit FTL. Not spatial warping or any tricks like that? $\endgroup$ May 23, 2021 at 21:37
  • $\begingroup$ @Xavon_Wrentaile Yup, that would be it. No wormholes, no warp drives, maybe using space curvature, but I prefer to use the question of the whale, thus obscuring how a spaceship attained such speed. Maybe they used a space whale as a horse. $\endgroup$ May 23, 2021 at 21:40
  • $\begingroup$ It depends on how the physics works in your version of the universe. $\endgroup$
    – Slarty
    May 23, 2021 at 22:38
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    $\begingroup$ It would, if it could, but it can't, so it wont. $\endgroup$
    – PcMan
    May 23, 2021 at 23:09

2 Answers 2


If it has a net electric charge, then yes. If a charge source is moving faster than changes in the field can propagate, you get shockwaves--which in the case of the electromagnetic field, manifest as Cherenkov radiation.

This is why charged tachyons can't exist (at least, not in the modern universe); if they did, they would constantly accelerate while emitting photons, making the vacuum unstable.

If it's electrically neutral, you won't get Cherenkov radiation, but you will get gravitational wave shockwaves--the gravitational equivalent of Cherenkov radiation. That's far less noticeable, though.


Nope. Vacuum is not a polarizable medium because nothing is there.


Cherenkov radiation results when a charged particle, most commonly an electron, travels through a dielectric (can be polarized electrically) medium with a speed greater than light's speed in that medium... When any charged particle passes through a medium, the particles of the medium will polarize around it in response. The charged particle excites the molecules in the polarizable medium and on returning to their ground state, the molecules re-emit the energy given to them to achieve excitation as photons.

With no molecules of medium to excite there is nothing to re-emit the energy.

  • $\begingroup$ So Cherenkov radiation would only be emited when the space whale crossed a nebula? $\endgroup$ May 23, 2021 at 21:52
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    $\begingroup$ False. en.wikipedia.org/wiki/Vacuum_polarization $\endgroup$ May 23, 2021 at 22:02
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    $\begingroup$ @LoganR.Kearsley - I thought those virtual particles in the void were too transient to do such matter-like work as radiating energy. Do virtual particles emit electromagnetic radiation, under any circumstances, ever? $\endgroup$
    – Willk
    May 23, 2021 at 22:09
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    $\begingroup$ @Willk A "virtual particle" is just a particle that only appears on the interior of a Feynman diagram and does not escape. So yes, they can emit photons. But you don't really need to go down to that level: the vacuum has measurable permeability and permittivity, which is why light can travel at all, and that's all you need. $\endgroup$ May 23, 2021 at 23:02

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