On Wed, Apr 06, 2016 at 05:46:35PM -0400, Kurt Feltenberger wrote:
> Are there any particles or emissions, however faint, known or
> theorized, that would allow a sufficiently sensitive sensor to
> detect a nuclear detonation (actually, enough to destroy all
> civilization on a world of ~7+ billion people in a day) at
> interstellar distances either as it happened or within a short (less
> than a week or so) period of time?

All known and theorized particles involved in nuclear reactions travel
at light speed or less.  So no.

Hypothetical FTL particles are called tachyons.  With a big stretch,
perhaps they might be produced by nuclear reactions, though there
would have to be some reason why the energy or momentum difference
isn't detected in experiments.  Another possibility is that they might
exist as some sort of background radiation ("dark energy"), and
nuclear reactions might just interact with them weakly, but enough for
a much more advanced civilization to detect with sufficiently
sensitive (and probably huge) detectors.

All reasonably theorized particles obey relativity, and so causal
interactions (such as "nuclear detonations cause detectable results")
at FTL speeds implies the usual time-travel paradoxes.

- Tim