Kind: captions
Language: en
check this out I'm using this speaker to
vibrate a petri dish containing silicon
oil now if I take this toothpick and I
make a little droplet on the surface the
droplet will stay there hovering above
the
surface the droplet is actually bouncing
and it'll keep bouncing for a very long
time now the reason for this is there's
a little layer of air between the
droplet and the surface and the
droplet's bouncing so rapidly that that
layer never shrinks to about 100 NM
which is what it would take for the drop
droplet to recombine with the oil now
every time the droplet lands on the
surface it creates a wave but this is a
special type of wave driven by the
vibration of the oil bath it is a
standing wave meaning that it's not
traveling out it's just oscillating up
and down so the droplet makes the wave
and then it interacts with that wave on
its next bounce if the drop lands on one
side of the wave it is pushed forwards
and as long as the bounce of the droplet
remains synchronized with the wave it'll
keep landing on the front side of the
wave and getting pushed farther forwards
droplets like these are known as Walkers
The Bouncing oil drops have been known
about since the 1970s but only recently
has it been discovered that you can use
these little droplets to replicate many
of the strange phenomena of quantum
mechanics now obviously this is not a
Quantum system the droplets are about a
millimeter in diameter but you can think
of the droplets like uh Quantum
particles say electrons one experiment
that captures the key features of
quantum mechanics is the double slit
experiment if you send a beam of
electrons at two narrow slits well the
electrons rather than behaving like
particles and ending up in two clumps
behind the slits they produce an
interference pattern even when you send
each electron through one at a
time with walking droplets the pilot
wave goes through both slits interfering
with itself while the droplet only goes
through one slit the droplet doesn't
move in a straight line though it's
deflected by its interaction with the
wave the resulting distribution of where
the droplets end up looks very similar
to Quantum double slip interference
patterns or take tunneling in quantum
mechanics it's possible for a particle
to get through a barrier that it
wouldn't classically have enough energy
to get over this has been demonstrated
with Walkers by creating a shallow
barrier under the surface of the oil
usually the barrier reflects the pilot
wave and its bouncing droplet but in
rare cases the droplet does cross the
boundary and the probability of the
droplet crossing the barrier decreases
exponentially with the increasing width
of the barrier just as in Quantum
tunneling perhaps the most surprising
thing about these Walkers is they
exhibit quantization just like electrons
bound to atoms here the Walker is
confined to a circular Corral the
droplet seems to move around randomly as
it interacts with its pilot wave the
complex interaction between the droplet
in the wave leads to chaotic motion of
the droplet but over time a pattern
builds up
this is the probability density of
finding the droplet at any point within
the Corral and it looks very similar to
the probability density of electrons
confined in a Quantum Corral all of
these similarities are no coincidence
the walking droplets actually create a
remarkable physical realization of a
theory proposed by De broi nearly a
hundred years ago in the early days of
quantum mechanics he postulated that all
particles have a wave that accompanies
them and guides their motion and that
wave is actually created by tiny
oscillations of the particle now this
pilot wave theory was marginalized when
the standard Copenhagen interpretation
became widely adopted the Copenhagen
interpretation excludes anything that
cannot be directly observed and it says
everything that can be known about a
particle is contained in its so-called
wave function but adopting this view
forces you to give up on some common
sense Notions like the idea that
particles have a definite position and
momentum even when they're not being
measured and it also meant that the
Universe was no longer deterministic
Randomness is built into standard
Quantum Mechanics for example take the
double slit experiment according to
Quantum Mechanics the wave function of
the electron is a superposition of the
electron going through one slit and the
other slit simultaneously using this
wave function you can calculate the
probability of where the electron is
likely to be and then when you detect it
at the screen the electron pops up at
one point at random that was in that
distribution we say that its wave
function collapses instantaneously at
the moment of measurement you can't say
that the electron was there before you
measured it and you can't even say that
the electron must have gone through one
slit or the other compare that with a
picture provided by The Bouncing
droplets in this case the pilot wave
goes through both slits but the droplet
only goes through one the droplet is
pushed around by its interaction with
the wave so that the resulting
statistical distribution is the same the
droplet never exists in two places at
once and there's no Randomness if there
is any uncertainty it's just due to our
ignorance of what's going on it's not
that it doesn't exist so pilot wave
Dynamics can produce many of the same
results as quantum mechanics does this
mean that this is really what Quantum
particles are doing no but I think it'll
at least suggest that this is possible
these are possible dynamics that could
lead to the statistics which are
captured in the quantum mechanical
Theory and what's appealing about this
is it gives you a clear idea of what's
going on you don't have to abandon the
idea that the universe is deterministic
and you get particles with definite
position and momenta I think it's great
that we have two competing theories for
the same experiments and they both ask
you to accept odd things just different
odd things and it comes down to what
you're comfortable with really whether
you prefer the Copenhagen interpretation
standard quantum mechanics or a pilot
wave theory
let me know what you think in the
comments do you like the pilot waves I
mean it's definitely a very appealing
picture whether or not it corresponds to
reality that remains to be
seen hey this episode of veritasium was
supported in part by viewers Like You on
patreon and by Google's making and
science initiative which seeks to
inspire people to learn more about
science and pursue their science goals
now I know someone else who is pursuing
their science goals this weekend that
it's destined over at smarter every day
he and I were looking at basically the
same phenomenon but he was looking at
water droplets and why they don't coales
so if you want to see how that works and
how it works in space go check it out on
his channel over at smarter everyday and
as always thanks for
watching looking at only one frame per
bounce you can see how the droplet's
motion is Guided by The Wave It's
effectively surfing on and the wave
remains even if the droplet disappears
as happens sometimes if it encounters a
little bit of dirt what's really cool
about this is the wave actually stores
information about where the droplet has
been this is because every time the
droplet bounces it creates a new
circular wave centered on its present
location and that wave adds to the
existing wave field on the surface so as
the droplet moves the waves it makes
keep adding up storing the information
of where it's been in fact you can
actually get the droplet to land on the
back side of the wave so now it's pushed
backward Wards and it retraces its steps
erasing each wave it made previously one
at a time