Is the universe going to die?

Anything that moves faster than light emits radiation. If it's a charged particle, it emits Cherenkov radiation. This is observed, for example, when high-energy particles move through mediums faster than the speed of light in those mediums. If it uncharged, there are other, similar processes (they're slower, but still occur). So not only would anything moving faster than light be very much observable, it would rapidly cease to move faster than light as it loses energy.

That, or it's a tachyon, in which case the extra emission will just cause it to gain speed and emit more radiation, which would cause the universe to explode. As I mentioned.

Hence, it has been observed "when energy particles move through mediums faster that the speed of light", supposes that there is a speed FTL.

the speed of the light beam on the emerging beam would then be slower than light speed due to the lost energy.