in the last episode we saw how matter
feels mass because of the energy of its
internal moving parts you might want to
watch that episode now because today
we're going to go even deeper and
explore the connection between matter
motion and the nature of time the
watched pot never boils a boring college
lecture lasts forever while weekends and
summer break seemed to finish even
before they starts our perception of
time depends on how much attention we
pay to it we have internal clocks neural
processes dedicated to the counting of
seconds and hours while our memories
layer over the course of our lives and
in their ordering we see the flow of
years our often flawed perception of
time comes from watching patterns in our
brains evolve but that's just perception
writes a second is a second a decade is
a decade and a perfectly engineered
clock will always tick at the same rate
actually no any clock is just an
arrangement of matter every tick is the
result of countless interactions between
the tiniest subatomic elements the
rotating gears are comprised of atoms
vibrating in metal lattices bound by
electrons flickering in their orbits
themselves held in place by protons that
are comprised of quarks in constant
motion
the sum total of this motion results in
a smooth consistent evolution of time
but do the individual components of the
clock feel the same flow of time down to
the atoms and nuclei yes the most
accurate clocks in the world are atomic
clocks which can drift by less than a
billionth of a second each day all of
the atoms in such a clock feel the same
length of a second but what about the
quarks the electrons this is where our
conception of time starts to break down
why because of motion see the flow of
time depends fundamentally on motion the
faster an object moves relative to you
the slower its clock appears to tick a
particle moving at the speed of light
experiences know time is clock is frozen
those electrons and quarks bounce
at such high speeds inside the atom that
they experience time very differently to
the atom itself and in a sense the most
elementary particles are intrinsically
timeless the familiar smooth flow of
time only emerges as these particles are
bundled into what we think of this
matter time happens for the atom in a
way that it doesn't for the atoms parts
today I want to show you why time
depends on motion which in turn will
show us why Lightspeed particles are
timeless and why having mass and
experiencing time are fundamentally
connected in the last episode we
compared the nucleons of atoms protons
and neutrons to the imaginary photon box
a massless mirrored box filled with
lights which despite being composed only
of massless things itself does have mass
we're going to use a very close cousin
to the photon box to explore time a
thought experiment of Einsteins the
we'll call the photon clock imagine a
clock made from two mirrors and a photon
bouncing between them every
back-and-forth bounce of the photon
results in a tick of the clock the tick
rate depends on the speed of light and
on the distance that the photon has to
travel between the mirrors the rate of
ticks is consistent time flows smoothly
until the clock starts moving relative
to me now imagine moving the mirrors
sideways from my perspective light now
takes a longer diagonal path but here's
the weird thing as we saw in a previous
episode the speed of light is what we
call invariance all observers regardless
of their own speed will report seeing
the same speed for any particle of light
any Photon this fact isn't intuitive but
it's extremely well tested okay so from
my point of view the photon takes longer
to make the up-down journey it appears
to travel more distance but at the same
old speed to me it appears as though the
ticks take longer in the moving clock
compared to an identical photon clock
standing still right next to me
which ticks up the normal rate some
other guy who is riding along with the
moving clock would see it ticking at the
normal rate and quite bizarrely will see
my clock ticking slower after all my
clock is moving relative to them this
effect is the time dilation of
Einstein's special relativity and again
it's very well tested now what if the
clock is traveling at the speed of light
the apparent distance of the photo needs
to travel to reach that top mirror
becomes larger and larger as the clock
speed increases and that distance is
infinite when the clock reaches the
speed of light from our point of view
the photon clock could never complete a
tick because the photon can never reach
that mirror time is frozen by the way
similar arguments will show us that a
photon clock in an accelerating
reference frame say on a rocketship in
empty space will also tick slower
compared to a non accelerating clock the
overall distance that the photon has to
travel is larger in an accelerating
frame because that top mirror is running
away from the rising photon faster than
the bottom mirror catches up to the
falling photon ticks take longer but
Einsteins equivalence principle tells us
that a frame suspended in a
gravitational field is indistinguishable
from an accelerating frame and so clocks
must also tick slower the deeper they
are in that gravitational field this is
the gravitational time dilation of
general relativity so what does this odd
example of the photon clock have to do
with real time and real matter well if
our photon clock behaves this way then
so does the photon box they're really
the same thing in a fast-moving photon
box we perceive that its internal
particles have further to travel to
bounce off the walls compared to an
identical stationary photon box know
that this is not the same thing as
accelerating the photon box which gives
it the feeling of mass here we're
talking about something moving at a high
but constant speed and from the last two
episodes we know that atoms and their
nucleons are all kind of like photon
boxes they're made up of things that
would move at the speed of light except
that they're confined quarks and
electrons confined first by their
coupling with the
Kingsfield and then by the forces
binding them into atoms
so as an atom races pass through at high
speed you would see all its internal
bits ticking slower just like the photon
clock see in an atom that ticking
corresponds to interactions between its
component particles and fields in which
the internal parts exchange energy
momentum and other properties
interactions which hold the atom
together the rate of these interactions
this ticking represents the rate at
which the atom will change from one
arrangement one state to the next the
rate at which anatomy evolves in a fast
moving object the interactions driving
this evolution appear to happen more
slowly time passes more slowly move fast
enough and time barely passes at all so
the confinement of Lightspeed particles
gives matter mass in fact this
confinement this bundling of energetic
moving parts is what makes it matter but
now it looks like this same bundling of
Lightspeed particles can also give
matter time atoms feel time in their
internal evolution similar to our own
perception of the change in patterns in
our brains but what is it about not
traveling at the speed of light that
allows matter to have structure
interchange what prohibits matter from
reaching the speed of light is time even
a real dimension and what defines its
direction will have time for all of this
on a future episode of space time in the
last episode we talked about the true
nature of matter and mass and you guys
asked the hard questions parentage
seeing and a few others questioned the
plausibility of massless walls in our
photon box thought experiment and yes
massless walls are impossible however
the thought experiment still works if
you say that the walls do have some mass
in that case the boxes mess increases by
the amount equal to the energy of the
contained photons divided by the speed
of light squared Bernardo Souza and a
number of others want to know whether a
compressed spring really is
actually heavier than our lack of spring
and whether that's measurable and yes it
really is more massive but not by much
compressor car suspension spring
completely and its weight would increase
by maybe a treatment of a gram not
measurable on your bathroom scales but
it would be measurable on very precise
laboratory scales joshua hilary raises a
great point sure the resistance to
acceleration produced by a compressed
spring only take effect along the length
of the spring as opposed to the side
actually no in the compressed spring
there's increased pressure throughout
the material that pressure increases the
resistance to further compression in all
directions so it feels massive
regardless of the direction in which you
push it