If you are sealed into a sphere with a highly mirrored interior and you turn on a flashlight and then turn it off will the interior stay lit up?

No. I think there is a certain amount of electron displacement that occurs with each reflection, which absorbs some of the light energy so that the reflection would eventually stop. However, if the mirrors were completely reflective (which I don’t think is possible with current technology) then yes the interior would stay lit up.

In a short time (100 or so “bounces” of light), the mirrors will absorb most of the photons as mainly heat energy.

Kindof like this?

No.

you would need something more reflective than a mirror… so no… not yet

Interesting question. The least reflective thing in the sphere would be you and your flashlight. Your own body and clothing would absorb any photon reflecting off a mirror and hitting it. Add that light absorption to the absorption of the mirrors, even if they were high-quality first-surface mirrors, and photons would get trapped here and there quite quickly. Because light travels at such an incredible speed, it would look to you like the light went entirely out almost immediately after you turned the flashlight off.

@ETpro , What if the person is wearing reflective clothes or is inside a mirrored room inside the sphere? Now it is just the flashlight that absorbs light, and that can be kept to minimal size. I wonder if the light would persist for a noticeable amount of time. Would the effect be enhanced if a laser were used instead of a flashlight?

@LostInParadise I don’t really know in that case, but my guess remains that the tiny losses in reflectivity would pile up very rapidly owning to the almost incomprehensible speed of light, and things would quickly slide back to darkness.

According the ever-loving wiki on mirrors

For technical applications such as laser mirrors, ... [] ... and achieve reflectivities of 90–95% when new. ... [] ... Applications requiring higher reflectivity or greater durability where wide bandwidth is not essential use dielectric coatings, which can achieve reflectivities as high as 99.999% over a narrow range of wavelengths.

So we need a laser, some dielectric coatings (whatever that means), and a perfect sealed sphere…

Then we’re making the first Fluther science fair project in your back yard. Go team.

I did a quick calculation. Suppose the sphere is a mile wide, to make calculations simple. At 186,500 miles per second for the speed of light, that would mean something on the order of 186,500 reflections. Assuming 99.999% reflectivity, I used my calculator to raise .99999 to the 186,500 power and got about .15. So after a second the laser beam would have about 15% of its original strength. That means for a sufficiently powerful laser, there should be a noticeable effect.

@LostInParadise That is correct, assuming the experiment is enclosed in a perfect vacuum. The effect could only be observed if after 1 second, 0.15 of the light ends its journey on a sensor. The familiar straight beam of laser light is an effect of dust in the air diffusing part of the beam. In reality, the light will last 5 – 20 miles or 5 – 20 reflections when the beam is seen.

If the mirrors are less than 100% relective, and/or there is air in the room, the light will eventually fade away.

But if you intersperse photo cells amongst the mirror than you could extend the life of the light transmission. I’m not an engineer….someone else needs to figure out how long the light could be extended.

You could just turn on a lamp and make the light last as long as you want.

In theory what you’re asking for is impossible. Light is energy, and entropy demands that energy dissipates. Even with perfect technology you would need to input energy faster than it dissipates to keep it (light) present.

A more interesting question to me is, how much, how long, and how well can you light up a single space?