[MUSIC PLAYING]
What is this material?
How do I even start?
It's all around us.
And yet unlike so many
of the common materials
that we get to play
with every day,
the understanding of how
sand moves is just so poor.
It's one of the biggest
open questions in science.
[WAVES CRASHING]
[THUNDER]
[THUD]
Is it a solid?
Is it a liquid?
Or is it a gas?
I think the truth of the
matter is it's really just all
of the above.
[MUSIC PLAYING]
When I was a student,
I would take classes
where I would learn some
kind of a general governing
equation that explains
how a material behaves
in a general circumstance.
This is true in fluids.
This is true in solids--
even quantum mechanics.
And I was just
astounded when I learned
that there wasn't a similar set
of equations that worked just
as well for sand.
I became enamored with
this idea that maybe we
could come up with the answer.
[MUSIC PLAYING]
One of the things that we knew
was what a granular material
does when it's put into simple
shear and run to steady state.
But what was weird was
we also had some data,
in other cases,
other geometry, which
seemed to violate the rules
that we saw in simple shearing.
And I became very
intimately engaged
with all of those
little violations.
And in my heart, I
knew that there just
had to be a simple way to
insert one extra non-local term.
And if we got it
right, I had a feeling
that it could solve everything.
I was inspired when I came
across an approach that
had been used previously
for emulsions.
And when I looked at that
form, the light bulb went off.
And I said, something
like that has
to be behind granular materials.
So I adopted the framework and
changed all of the ingredients
so that it might reflect sand.
And we took this model
that we had written,
we tried it in every data set
we could find in the literature.
And we were just
astounded when we
saw that the model had
predicted all of them.
[MUSIC PLAYING]
Just think about all
the places that we
deal with grains, and all
the ways that you could now
design for those applications--
pills, powders, you know,
food, raw materials.
Think about all the
factories and plants
that have to manipulate this
material around, and just
imagine that you can now design
the equipment, optimally.
We have this tool.
We can actually, hopefully,
quantitatively predict.
[MUSIC PLAYING]
