Will a Spark of Light,for a very small time, at the centre of a Opaque Hollow Sphere make it glow eternally?

No. The light will be very quickly absorbed by the sphere just like it always it. Light does not go away because it slips through cracks or escapes through windows. Most the light is absorbed. When you turn off your light at night, your room gets dark because the light is very quickly absorbed and turned to heat by the atoms of the objects it hits. Even an excellent mirror is partially absorptive and will absorb all of the light in a few microseconds after several bounces. The best way to get long-lived light is to shoot in through outer space so that it does not hit anything that will absorb it. Some of the starlight coming to us has been traveling for billions of years.

Opps- excellent imagination ! Theoretically it's going to appear that he sphere will glow for ever (or eternally ! ) however virtually no longer ! The source and the detector will bog down the reflection ! There has to be ideal zero air / vacuum inside the Sphere, the skin of the Sphere has to be particularly skinny so that no aberration is crated, The reflections from quite a lot of aspects will interfere with every other. Lastly nothing is eternal on this Universe ! !

Only if the light is reflected with 100% efficiency, and there is nothing in the sphere to absorb the light.

If reflection is not 100% efficient, and some energy is absorbed, either by the sphere walls, or by anything in the sphere, then over time, the amount of light will diminish. But if this does not happen, then yes, the light should reflect eternally.

To sustain the light for ever, reflection must be 100%.Which is not possible even at 100% opaqueness sphere.

Energy always transfer into other beings, not constant. Light to heat and sphere cools, so no more light.

i used to fantasize these kind of stuff in physics class!! :D

i thought that it can glow eternally..but then i got confused with losses due to interference and absorption!

but till now i don't know the exact reason..! ipoo puriyudhu :D

Thanks for reminding that and thanks for clearing my old doubt.. :)

welcome arun!