(Music)
(Thud.. rattle)
[WILLIAM IRVINE] The main result of our 
paper is that we’re reporting the creation,
to the best of our knowledge, for the first time,
a vortex, but not a trivial vortex in a loop,
but tied into a knot.
Knotted vortices, and knotted 
configurations inflows have been
conjectured for almost a century.
They are thought to occur in many differences systems.
Starting from turbulent plasmas,
like the sun, turbulent flows
in regular fluids. They’ve been conjectured
to exist in the course of neutron stars
We got the first glimpse into their
evolution in a real system.
So far there’s been theories for how they
should have evolved, how long they should live
and what their dynamic should be.
Pretty much there were predictions for all 
ends of the spectrum of what they should do.
Across different knot types and
different link configurations,
we've seen that they evolved to 
self interact and at some point,
apparently, un-tie themselves.
Although there's some subtleties in the way that
they do that, but we think that
but we think that not untying themselves, 
but just hiding the way they’re knotted
into finer details of the structure.
[DUSTIN KLECKNER] The first thing we do
is we take one of these hydrofoils
and we attach it to the frame.
And then what we do is lower this thing into the
water and then we coat the hydrofoil with bubbles.
There’s just a little gird, underneath,
on the bottom of the tank and
basically you run current through this grid
and this makes micro bubbles of
hydrogin and oxygen.
These actually get caught on the hydrofoil itself.
Basically what they get attracted to the
closest vortex around.
So this is what you’re actually seeing,
is the cores of these vortices
basically low pressure centers
due to the centrifugal acceleration 
of the vortex itself.
So this really lets you see where 
the center of the vortex is.
The reason that we wanted to use water
instead of using air, for example,
is that actually there is some sense in 
which the viscosity of water is
actually less than of air.
So if you just make a ring,
a normal vortex ring in water,
you actually expect it to last longer
than the same vortex ring would last in air.
The other reason we really wanted to water
is that the is this beautiful technique
for visualizing the vortices using bubbles.
But if you have something that's lighter
than the fluid which its embedded it'll 
actually get attracted to the core of vortex.
This becomes very important if you
want to understand both fine structure and
you want to be able to see more
complicated shapes.
So hydrofoil is basically a wing 
that’s designed for use in water.
And the reason that we use hydrofoils is
because when you accelerate them
they produce a vortex ring.
The shape of which traces the 
trailing edge of the wing
And this lets us make vortices,
and vortices shapes that are very
difficult to make by using conventional
methods said by just pushing some water
out of a hole.
Which is the way actually you make a
smoke ring with your mouth, for example.
This let's let us make topologies, if you like,
of knotted shapes that are not
possible to make with conventional methods.
Now that we’ve sort of established the
basics of what a knotted vortex does
we want to understand them in more detail.
So there's a lot of open questions.
For example, after one of these things
unties itself it creates what’s known as
kelvin waves on the resulting vortices.
And we want to understand how these things
evolve.  Ok, so this is an open question
which actually ties into a bunch
of other fields.
[IRVINE] Since nobody had ever managed to 
create a vortex knot in a laboratory
where you could study it,
a lot of theoretical work
remained without its experimental twin.
Being able to create it allows 
you to look and experiment
at what has been so far conjecture.
One of the wonderful things about 
working at the JFI is that we
have a a tremendously collaborative atmosphere.
Without this sort of atmosphere
and without using the the printer,
which was in fact in Heinrich Jaeger’s lab
we probably wouldn't have been able to
do this research.
