Question

Is it possible for a patch of light (or a shadow to travel faster than the speed of light? i.e. if a searchlight were swung around very fast, would the patch of light on the clouds be able to move at ANY speed, depending how far away the clouds are?

Asked by: Mark Griffiths

 Answer

Yes, a PATCH of light can appear to travel at any speed. The Special Theory of Relativity sets c (the speed of light in a vacuum) as the speed limit for any physical object or packet of energy.

Your examples do not violate Relativity principles because any single photon does not exceed c. Imagine throwing tennis balls along a wall, with each ball hitting some distance to the right of the previous one. The apparent path of each hit against the wall moves at a rate that depends only on the distance between them and how frequently the balls are thrown. The speed of the balls is not important. The 'patch of light' example just replaces tennis balls with photons.

Note from the editor: However, even with your clever scheme, Mark, you can NOT transfer useful information faster than speed of light. Just think about it. Try to devise any scheme to transfer information by swinging a search light - it is impossible!

Answered by: Paul Walorski, B.A. Physics, Part-time Physics Instructor

Search

Loading



Sponsors

USC University of Southern California Dornsife College Physics and Astronomy Department McMaster University Physics and Astronomy Department

Science Quote

'We should take care not to make intellect our god; it has powerful muscles but no personality.'

Albert Einstein
(1879-1955)

Deal of the Day

Image of Shark Tooth Fossil in Matrix. Click on this image for more info. Shark Tooth Fossil in Matrix
Regular Price: $39.95
Today's Price: $15.00
Superb shark fossil specimen for the science classroom! Buy it now! Deal ends at midnight!

Top Selling

Here are our physics & astronomy bestsellers:
Mini Plasma Ball
Slide Making Kit
Top Secret - Spinning Top
Wood Grain Newtons Cradle
Deluxe 3D Mirascope
Solar Radiometer
Periscope
Solar Science 4M Kit
Ultimate Chemistry Set CHEM C3000
3D Magnetic Field Tube