Wave propagation

WAVES

This is the simplest answer I can muster to the question: "Why does light but not sound travel through space?"

Bullets can travel through the air. A bullet can travel through water. A bullet can travel through the vacuum of outer space. A bullet is a mechanical object (an actual thing) that you can shoot anywhere.

Waves of sound can only travel through air or solid matter (a non-vacuum). Just like waves of water can only travel through water. Sound is a mechanical wave. It moves through the air like waves move through water. Take away the air or water and you get no more waves in them.  Sound actually travels more than four times faster through water than air, because the water molecules that get banged into (vibrate) to propagate the waves are packed more closely together. For this reason sound travels faster in hot (vibrating) air more quickly than in cold air with its more slowly vibrating molecules. Simple.

Light is made of photons that can travel through a vacuum, air, water because photons are like little bullets of light that travel in waves…so they are particles and waves together. Not so simple.

Electrons can travel through the air and the vacuum of outer space. Electrons travel in waves called electromagnetic waves…so they are particles and waves together…Light is considered and electromagnetic wave, as are radio waves, ultraviolet, infrared, microwaves, x-rays, gamma-rays, etc. 

Since when acting as a mechanical object (a light photon smacking into atmosphere) an electromagnetic wave starts vibrating atoms (just like waves in water) these electromagnetic waves travel slower when they're not in a vacuum! In a vacuum they travel at the speed of light...because it is light. Light travels at the speed of light...in a vacuum...duh!

Light moves through a vacuum at 186,282 miles per second; through Earth's atmosphere it moves at 186,227 miles per second.

You'd think that since soundwaves travel faster in water, that electromagnetic waves would travel faster in air (than in a vacuum). You'd be wrong, as we've just read. 

Mechanical waves (water, sound, bullets) are like clunking people's head's together. If the Three Stooges are standing close to each other and you slap Curly all three heads clunk together quickly, the farther apart the Stooges are standing the slower each clunk is. Water is closer together than air.

Electromagnetic waves behave more like waves when they hit solid things, the waves distort and slow down. Yep, it's weird.

Anyway, most stuff moves in waves. Most particles show a dual wave/particle nature: electrons, photons and even some (by comparison) HUGE molecules will flow through a Young's Double Slit Experiment will show light going through two slits in a metal plate: it will come out as a wave on the other side...but if it's a photon particle how is it a wave? Even a single electron fired through one of the slits will go through and impact a screen behind the plate...if you fire electrons (or just about anything else) through the slit one after the other they make a wave-shaped pattern on the screen! Single particles move with the probability of a wave.

Single food particles ended up on MY side of the screen. Yum!