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All physics is fields. I wouldn't even
know how to do any calculation without
fields. I mean essentially everything
everything in modern physics relies
on fields and they're extremely
powerful exactly because you can
describe a lot with just one field.
In physics a field is something very real.
In fact for modern physicists fields are
currently the correct point of view from
which to understand the real world.
Fields are quantities distributed
through space and space-time where every
point has a distinct value. For instance
the temperature in this landscape is a
field where every point in space has a
temperature value. This is a scalar field
because temperature is fully described
by a single quantity. On the other hand
wind is a vector field where every point
has two values the wind speed and the
wind direction. Because fields are
represented mathematically they can be
added or averaged together to give
general views of the field like in this
global temperature map or this one that
shows wind velocities.
Yet as useful as fields are they are far
more than practical tools. The first time
I actually managed to get a clear
description of a field in my own mind is
when I did an experiment of putting two
magnets and all iron filings around
it. So you can clearly see the lines of
force because the iron filings are like
test particles here which are following
the field lines or the force lines in
the field. So they orient themselves in
these kind of patterns and you can see
in the direction of their orientation
the direction of how a test particle
would move in the field. Even though we
often represent fields as being flat
objects spread out in space a field like
the magnetic field created by this
magnet occupies the space all around it
as we can see if we pause this splash of
iron filings midair. Or even more vividly
in a spectacle of the Northern Lights.
But what do modern field theories tell
us about reality that older theories do
not?
In high school you don't see the reason
the fields are useful and the reason
they're useful is when you look at
things that are moving - we're always
talking with static things when you're in high school
and so that the useful
difference is that if you move a
charge and you ask - how do things
respond to that motion that's where the
field comes in. Now when we're figuring out
what the fundamental forces are we are
doing fields and nobody tries not to do
fields. Fields are it. And so
we talk about fundamental forces but
what we really mean are fundamental
fields. Fields occupy space
store and transfer energy and momentum
and even curve space-time. Einstein's
theory of general relativity is a type
of field theory of gravity where the
field is the degree of curvature in
space-time created by the presence of
energy or mass. It is a field theory of
gravity that reflects reality in every
way we've been able to test including
the nature of black holes and how light
bends around stars and galaxies. All of
the different forces all the different
interactions including electromagnetism
and gravity and the weak and strong forces
are mediated by fields which basically
means that something happens here and
then there is kind of a disturbance in
the field that propagates at this speed
of the field usually it's the speed of
light. Quantum field theory uses fields
to describe not only fundamental forces
but it tells us that fundamental
particles are oscillations of particular
fields. So we can understand a field as a
collection of vector points in
space-time and then this collection of
vector points of space-time will have
collective excitations and then
this collective excitations will have a
particular energy and will have a
particular momentum and as we know from
our wave-particle duality we can
describe a excitation which has a
particular energy and a momentum as a
particle. The field is really the
fundamental concept and then the
particle is one way of looking at the
field - a force is another way of
looking at fields there's not an dichotomy
between forces and particles any more.
And in fact quantum field theory is
literally the most well-tested theory in
all of science and all of its
predictions have been shown to be true.
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