Light as Form of Matter
Kate wants to know what form of matter is light? or is it?
Usually, the term "matter" implies a substance/material that has mass, so
by that criterion light would not be a form of matter. However, it is a
definition, so if you want to change the definition to say a substance
that has momentum, then light would be a form of "matter" so defined.
There are also some ambiguous categories such as liquid crystals,
quasi-crystals, plasmas that stretch the usual categories of solid,
liquid, and gas.
Scientists who study physics thought the whole word was made of
three kinds of things:
1) space and time (the place everything lives in)
2) matter (all the objects made of particles with weight)
3) forces and energy (which tell all the matter where to go in space and
Light is a little wave of force and energy.
Just a little wiggle in the carpet of space, that flies by very fast,
like a fast little earthquake under your feet.
If it is not moving, it does not exist!
Matter can exist standing still. It has mass.
And it has a location, a particular place in space where it is.
Waves like light are kind of spread-out instead.
(Fuzzy, fluffy, cloudy, we need a good word for this.)
Make a little wave in a bowl of water. Look for the edges of that wave.
There are no sharp edges, and it is pretty hard to decide
where the wave begins or ends.
Light waves are like that too.
That is what I mean by fuzziness.
In the last century scientists figured out that
matter can be turned into energy and back.
We cannot quite build matter-things out of energy;
so far it is too messy and we cannot control it.
But it still means that matter and light-waves are sort of the same stuff,
even though they move differently.
Scientists call that stuff "Mass-Energy".
And guess what:
Really small pieces of matter are spread-out and fuzzy too,
just like light.
As pieces of matter get bigger, the fuzziness gets smaller.
Big pieces of matter are all the normal objects we are used to handling.
They seem almost perfectly sharp, not fuzzy at all.
But scientists now have a few kinds of instruments that can measure
some of the tiny, atom-sized fuzziness around their edges.
This is another way in which Light and Matter seem almost the same.
There is still one big difference.
Light is the kind of Mass-Energy that only moves fast or it does not exist.
Matter is the kind of Mass-Energy that can exist standing still,
and cannot ever go as fast as light.
Hope that is not too confusing.
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Update: June 2012