ch15 - light history

A Brief

History of

Light

Since the dawn of time…

Up until Sir Isaac Newton, two theories existed as to the nature of light.

1. Objects emitted “corpuscles” of light that entered the eye.

2. The eye emitted rays that reflected off of objects and allowed us to see.

Sir Isaac Newton (1666)Newton systematically studied light.

Passed sunlight through a prism and observed the band of colors that emerged.

Concluded that light was made of small particles traveling at enormous speeds. (This explains why light travels in straight lines and cast such sharp shadows.)

But why don’t the particles collide and interact when two beams of light crossed each other?

And, why would one color particle be bent more than another?

Christian Huygens (1678)Suggests that light is actually small waves.

This answers the previous questions, but begs more…

• Why can’t light go around obstacles then?

• And how can it travel in a vacuum?

Thomas Young, 1801Passed a beam of light through two closely spaced holes. The light diffracted demonstrating light is more wavelike.

Newton vs. Huygens

For 100 Years the argument went on…

Particle vs. Wave

So they had to come up with some explanations!

Since space is “empty”, there had to be something else called “ether”.

Properties of ether:– Has to be everywhere

– More dense than steel

– Anything can move through it with great ease.

• Ether– If Earth has ether around it, then Earth would

cause “ether waves” as it travels through it. (Like a beach ball in a tub.)

– Light going with the ether waves would be faster. Light going across the waves would have the same velocity.

– Michelson and Morley, 1887• Developed interferometer:

– Measures wave speeds.

• What did it show?!?!?!?!• The speed of light is unchanging!• Does ether exist then?

Electromagnetic RadiationCurrent theory says that light is caused by

Electricity and Magnetism combined. Because of this, it can travel through a vacuum.

Wave - Particle Duality

Light exists as both a wave and a particle at the same time. It shows itself however you are looking for it.

If your experiment looks at it like a particle, it behaves like a particle… and vice versa.