If you light a candle in a room lined with perfect mirrors, will the
room stay illuminated even after the flame is extinguished?

Hello cessnavette,

Since this question was asked by an MIT physics graduate student, I
presume that there is no absolutely definitive answer.

"MIT researchers create a 'perfect mirror'" (November 26, 1998)
Massachusetts Institute of Technology
http://web.mit.edu/newsoffice/1998/mirror.html

However, another graduate student has answered essentially the same
question in the affirmative.

"Theoretically would light infinitely bounce, in a room made of
perfect mirrors?" (answered by Andreas Birkedal-Hansen, M.A., Physics
Grad Student, UC Berkeley)
PhysLink.com
http://www.physlink.com/Education/AskExperts/ae164.cfm

Another "yes" answer is found on this page from Cornell University.

"Can a flash of light reflect indefinitely?" (20 December, 2001)
Cornell Center for Materials Research
http://www.ccmr.cornell.edu/education/ask/?quid=417

The subject matter expert (SME) on light mentioned in this article
also gave a "yes" answer to the question (with a light switched on and
off rather than a candle).

"Building Relationships, Engaging Students: A Naturalistic Study of
Classrooms Participating in the Electronic Emissary Project," by K.
Victoria Dimock (1997)
Electronic Emissary [The College of William & Mary]
http://emissary.wm.edu/templates/content/publications/dimock.pdf

In the candle question, I believe that one would have to presume that
the candle, its byproducts (smoke), and anything else in the room have
no effect the light whatsoever, just as the perfect mirrors would not
affect it.  Similar presumptions would be needed for other sources of
the light.

- justaskscott


Search strategy --

Search terms used on Google:

"room * perfect mirrors"
"perfect mirrors" "trap light"
"perfect mirrors" "trapping light"

[I tried a few other searches as well, but the searches I've mentioned
led me to the pages I've cited.]

That's not really a physics question but tautology:

If  walls are perfect mirrors (meaning 100% is reflected)
and space inside is perfectly transparent (meaning 0% absorbtion)

then (by definition) amount of light will remain constant after source
stops producing light.

Let's have a little more fun with this question:

"...will the room remain illuminated even after the flame is
extinguished?"  The room will certainly remain illuminated for a few
nanoseconds, even with imperfect mirrors.

If the question is:  "For what period of time will the room remain
illuminated?", then we'll need to address the nasty question of the
observer.  The wording of the question ("illuminated") implies an
observer.

Also, the fact that the question is listed in the "physics" category
implies an observer.  Physics is by definition an experimental
science.  At what rate must the observer mechanism sample the room to
verify "illumination"?  Does the mechanism absorb at least one photon
each time it samples the space?  If so, the illumination will not
continue indefinitely.

Even with perfect mirrors, no absorbtion, no observers inside the
room, photons can only live for a certain period of live within it (in
average), otherwise you will violate uncertainty principle (you will
know with no error speed of photon (light) and a known error the
position of photon - which can be decreased as room sizes decreases).
That time depends on the size of the room and the energy of the photons

fa_es_11111010-ga 

We always know speed of photons. It is c exactly.
 speed is 299,792,458 meters per second.

Doeas that means all boxes have to be  very large?
 :-)

The room would have to be a vacuum, so no light energy will excite the
oxygen molecules in the air. Moreover, light would be absorbed by the
candle itself. If these two points were neglected, then, yes, the room
would forever be illuminated, for there would be no other chance for
the light energy to escape. Energy cannot be lost or created. It can
merely be transformed. However, you would not be able to observe the
illuminated room. If you were to take a glance at it, your eye would
absorb some of the light energy.

Do a google on "cavity ring-down spectroscopy." It should prove
enlightening as to what happens when people do almost exactly what
you're describing.

Yes quantumdot-ga .

And reffering to eq. in

http://lfw.pennnet.com/Articles/Article_Display.cfm?Section=ARCHI&Subsection=Display&ARTICLE_ID=108788&KEYWORD=saykally&p=12

 and setting A=R=0, we get I = constant, which is still the same statement
made in the first comment;

 If mirrors are 'perfect' (R=0) and there is no absorbtion (A=0), there is
 no damping. 
Another question (this one involving physics)
 is 'is it possible to build perfect mirrors";