Everything We Hear, Everything We See

“Everything we hear is an opinion, not a fact. Everything we see is a perspective, not the truth.”  Marcus Aurelius.

Marcus Aurelius was Roman Emperor from 161 to 180 C.E. and is one of the greatest of Stoic philosophers.  Although Stoicism does have a natural philosophy, that is, a physics, this article is not about Stoic science, nor is it a comment on the news media.

I saw this quote and realized how it - unintentionally - emphasizes how little of the universe humans actually experience directly.  We have contact with the universe through our senses.  Historically, the senses consist of sight, hearing, smell, taste, and touch, although we possess many more senses such as balance, temperature, and pain.

The human eye responds to certain frequencies of light. Those frequencies or colors we can see are represented by the rainbow.  How we see other colors like brown, pink, and teal is a cool problem in physics and neurobiology/psychology.  There are other 'colors' though.  Radio waves, microwaves, infrared, ultraviolet, X rays, and gamma rays complete the rainbow (electromagnetic spectrum).

You can visualize (pun intended) an electromagnetic wave as an oscillating electric and magnetic field.  If you've played with a balloon with a static charge, you've played with an electric field.  Same for playing with a magnet.  See Maxwell's Silver Magnet for more on electric and magnetic fields.

Sound on the other hand occurs whenever a substance, usually air, vibrates.  In most science texts, the range of human hearing is given as 20 Hz to 20,000 Hz.  Note that the unit Hz is an abbreviation for Hertz and means the number of vibrations per second.  If you place your hand on a audio speaker you can actually feel these sounds.

However only young 'uns can hear up to 20,000 Hz.  Once people reach the age of 20, their hearing starts to degrade.  I have heard anecdotes that children can be easily annoyed when they hear high frequency sounds that their parents can't hear.  You can purchase ringtones for your phone that only young people can hear.

Are their sounds lower than 20 Hz or higher than 20,000 Hz?  Infrasonic tones are those that are lower than 20 Hz.  Earthquakes are a sound wave (remember sound is a vibration) that have frequencies in the infrasonic region.  The stories of birds and livestock being aware of earthquakes before people are sometimes explained as these creatures being able to detect these low frequencies.  There are studies to suggest that infrasonic sounds can cause people to have feelings of nervousness, fear, and anxiety.

Sounds at the other extreme are called ultrasonic.  Ultrasonic cleansers are a popular and safe way to clean jewelry and golf clubs.  How high can ultrasonic tones go?  There's no theoretical limit.  

In condensed matter physics, the study of nearly everything that's not a gas or plasma, there is a phenomenon called a phonon.  A phonon is a particle of sound the same way a photon is a particle of light.  It's quite common for phonon frequencies to be in the THz region.  That's TeraHertz; 10^15 Hz = 1,000,000,000,000,000 Hz.

What piece of these spectrums to we experience?  A  tiny, tiny, tiny,…, tiny piece.  From the Abstruse Goose comes the graph below.  [WARNING! Notice the axes of the graph.  Each tick mark is a power of 10.  That is, each mark is 10 times bigger than the previous one and 10 times smaller than the next.  I tried to graph this on a regular (linear graph for you math and science folks), but i quickly realized that you wouldn't see anything.]

I feel small.

But on the other hand, everything we know about biology, chemistry, physics, geology, astronomy, and the other fields comes from scientists using their puny senses and rational thought to find ways to not only measure, but to comprehend aspects of nature from the Higgs boson, to my favorite molecule ethanol, to huge molecules like DNA, to cellular structures, to tectonic motion, to extrasolar planets, to galactic motion, and all the way to the Big Bang.

I feel huge.