Theory Q: "Persistence of Light Inside an Impenetrable Sphere?

  • Context: Graduate 
  • Thread starter Thread starter shoook
  • Start date Start date
  • Tags Tags
    Light
Click For Summary

Discussion Overview

The discussion revolves around the theoretical implications of light persistence within a perfectly reflective and impenetrable sphere. Participants explore the nature of light behavior in such a scenario, including the properties of materials that could achieve high reflectivity and impenetrability. The conversation touches on both conceptual and technical aspects of light reflection and absorption.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification, Debate/contested

Main Points Raised

  • One participant suggests that if the sphere is perfectly reflective, the interior would remain lit indefinitely.
  • Another counters that perfect reflection does not exist, noting that even highly reflective surfaces would allow light to escape after a very short time due to absorption and the speed of light.
  • A question is raised about the existence of materials that are the most reflective or impenetrable to light, prompting further exploration of specific materials and their properties.
  • It is mentioned that mirrors can be designed for specific wavelengths, achieving high reflectivity but potentially being absorptive at others.
  • One participant cites a claim of mirrors with over 99.999% reflectivity at a specific wavelength, discussing the implications for light persistence in a vacuum and calculating the time it would take for light intensity to reduce significantly.

Areas of Agreement / Disagreement

Participants express differing views on the feasibility of perfect reflection and the persistence of light within the sphere. There is no consensus on whether the interior would remain lit indefinitely, as opinions vary on the nature of reflection and absorption in materials.

Contextual Notes

Limitations include the dependence on specific wavelengths for reflectivity and impenetrability, as well as the assumption of ideal conditions that may not be achievable in practice.

Who May Find This Useful

This discussion may be of interest to those exploring optics, material science, and theoretical physics, particularly in relation to light behavior in confined spaces.

shoook
Messages
23
Reaction score
0
Hey guys, I have a theory question for you that may have been posed before but I can't find an answer to (not a school question):

There is a sphere with a completely impenetrable and reflective interior surface. A light in the visible spectrum is emitted from within this sphere. Because no light can escape from the spherical container, does the interior of this sphere stay lit forever?

Thanks for any help.
 
Last edited:
Science news on Phys.org
Yup.
 
Perfectly reflective and within the visible region I would say sure.
 
Except there is no such thing as perfect reflection. And even if it is 99.99%, light only stays there for nanoseconds because of its great speed, if it's a human-scale sphere.
 
Thanks for the input guys! Is there a known material that is "most reflective" to light? Is there a known material that is "most impenetrable" by light? Thanks again.
 
mirror.
 
shoook said:
Thanks for the input guys! Is there a known material that is "most reflective" to light? Is there a known material that is "most impenetrable" by light? Thanks again.

It depends on the wavelength. If you choose a specific wavelength, a mirror can be designed to be as reflective as one can afford, for that wavelength, but it may be absorptive or transmissive to other wavelengths.

On the other hand, if you want a mirror that can reflect many wavelengths, metals are usually best for the visible range, but they all have some level of absorption, and reflection is not equal for all wavelengths.

As for most "impenetrable", again, this fundamentally depends on wavelength. See http://en.wikipedia.org/wiki/Attenuation_coefficient
 
One online company claims to produce mirrors with better than 99.999% reflectivity in the 800 nm region of the spectrum. Going with the 99.999% number, it will take about 100,000 reflections for the energy to be reduced to 37%.

Put the mirrors in vacuum making a cavity 15 cm long having a round-trip time of one nanosecond, the storage time to 37% is 50 milliseconds. –that's longer than I expected.
 

Similar threads

  • · Replies 9 ·
Replies
9
Views
2K
  • · Replies 20 ·
Replies
20
Views
3K
  • · Replies 21 ·
Replies
21
Views
4K
  • · Replies 8 ·
Replies
8
Views
2K
  • · Replies 29 ·
Replies
29
Views
2K
  • · Replies 3 ·
Replies
3
Views
2K
  • · Replies 23 ·
Replies
23
Views
4K
  • · Replies 16 ·
Replies
16
Views
2K
  • · Replies 6 ·
Replies
6
Views
2K
  • · Replies 5 ·
Replies
5
Views
2K