Two mirrors facing each other in a vacuum.

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What happens when you put two mirrors next to each other?Is it possible to have a lot of reflections?

In classical physics the waves that create the reflections are uniform and the energy loss due to the reflection is what will make them faint and fainter, but the process is continuous and there is a limit in luminosity.As time goes on, a totally reflecting material will go to infinite reflections.The wavefronts are instantaneous according to the original statement.The light's speed is finite.

It will take a long time to reach the next reflection, even for a total reflector, since there will be an enormous number of reflections.

There can't be a completely reflecting mirror in a thought problem.When the wavefront is terminated, the images will get less and less defined until they are absorbed.

An optical cavity is an arrangement of mirrors that form a standing wave resonator for light waves.A major component of lasers are optical cavities.https://en.m.wikipedia.org/title/Optical-cavity