Categories
Physics & Astronomy

How do we know that light is a wave?

We seem to know a lot about waves nowadays.  The language of waves suffuses our vernacular:  “We’re on the same wavelength,” “That speech resonates with me,” “I get weird vibes from him,” all use wave terminology.  We’re intimately familiar with water waves:  we see them in the shower or the sink pretty much every day.  We have a pretty good grasp on sound waves:  we can feel bass vibrations pretty easily and if we play music, we know that we can see vibrating waves in the motions of strings and cymbals, or we can feel vibrations of a saxophone reed or a trumpet mouthpiece.  We tend to accept the existence of things like microwaves and radio waves, which are really just light waves that are outside our range of light perception, much as x-rays and UV light are.  And everyone can recite from their science classes that light is an electromagnetic wave.  But what does that mean?  And how do we know it?

Categories
Chemistry & Biology

How do we know that diamond and graphite are both made of carbon?

Left:  The Hope diamond (Source: David Bjorgen under CC BY-SA)   Right:  Natural graphite (Source: Karel Jakubec--public domain)
Left: The Hope diamond (Source: David Bjorgen under CC BY-SA)
Right: Natural graphite (Source: Karel Jakubec–public domain)

Categories
Physics & Astronomy

How do we know that Voyager 1 has left the Solar System?

This “Family Portrait” of the Solar System was taken on February 14, 1990 by Voyager 1 at a distance of 3.7 billion miles from Earth. Source: NASA/JPL.

Categories
Chemistry & Biology Physics & Astronomy

How do we know that atoms really exist?

Scanning tunneling microscopy image of individual gold atoms. Source: http://en.wikipedia.org/wiki/
File:Atomic_resolution_Au100.JPG (public domain, author: Wikipedia user Erwinrossen)

Categories
Earth Sciences Mathematics

How do we know the Earth is round?

The Blue Marble
The Earth, as seen by astronauts aboard Apollo 17. Source: NASA (public domain).