MadSci Network: Physics

Re: Is there any form of matter that 'light' can not travel through?

Date: Fri May 6 04:16:38 2005
Posted By: Douglas Eaton, Staff, Engineering, Varian Medical Systems
Area of science: Physics
ID: 1113961800.Ph

Hello Justin,

Indeed, your teacher was correct.  There really is no "known" form of 
matter that will block all "light".

The ability of materials to block (absorb) photons of light is mostly a 
function of the density of the material.  As the wavelength of photons 
decrease ( the frequency increases ), their ability to pass through 
materials increases, but, with thick enough material, all of the photons 
will eventually be absorbed.  This process is known as the 'photoelectric 

You can see this effect with a flashlight and some paper ( your physics 
textbook would even work).  In a dark room, put the flashlight up against a 
few pages of paper.  You can see the some of the light coming through the 
pages.  Add more pages and you see less light.  Find a brighter source of 
light and more photons will pass through a given number of pages.  Even 
with very dense material like lead or tungsten, higher energy forms of 
electromagnetic energy ( like X-rays ) will pass through some thickness of 
the material.  If you make the material thick enough, it will block all of 
the X-Rays.

Check out this web link for a more in-depth description.

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