MadSci Network: Physics
Query:

Re: Accurate measurement in Mickelson-Morley Experiment?

Date: Thu Jul 19 05:53:23 2001
Posted By: Nial Tanvir, Faculty, Astrophysics, University of Hertfordshire
Area of science: Physics
ID: 995313298.Ph
Message:

The basic idea of the Michelson-Morley experiment was to measure differences in the velocity of light rays moving on paths perpendicular to each other. If the Earth was moving through an "ether" then the velocity perpendicular to the direction of flow should be different from that parallel. Although the difference is small, it should be possible to measure with interferometry, since that allows you to measure differences on scales smaller than the wavelength of the light itself.

The actual apparatus was a little more sophisticated - the rays were bounced back and forth several times to magnify the effect, and the whole optical setup was mounted on a large slab of marble which rotated on a mercury bearing. The importance of the mounting was (a) that the marble was very stable and rigid, and (b) by rotating the apparatus it was possible to look for variations at any angle. So, even if the initial path lengths of the arms differed, some movement of the fringes would be expected as the table was rotated.

In fact no movement was seen within the errors - the experiment being repeated at different times of the year and in different geographical locations. (See description at the American Institute of Physics site.) This was the first direct experimental evidence that the speed of light is a constant of nature.


Current Queue | Current Queue for Physics | Physics archives

Try the links in the MadSci Library for more information on Physics.



MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci


MadSci Network, webadmin@www.madsci.org
© 1995-2001. All rights reserved.