Are cats liquid? | Marc-Antoine Fardin | TEDxTours

Marc-Antoine Fardin sheds light on a discipline that is little known among the general public: rheology, the study of the resistance of material to stress and distortion such as the flowing of substances, be they cells, tissues, polymers or ... cats. Cats? Can these little felines be liquid?

Marc-Antoine Fardin is a physicist and researcher at the French National Center for Scientific Research (CNRS) at the Jacques Monod Institute of the University of Paris Diderot. He was awarded the Ig Nobel Prize that recognizes quirky and even farcical scientific research that nevertheless provokes thought.

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I'd like to tell you
something about physics.

So, it's not exactly the physics
we'd usually see in textbooks.

Physics is a bit megalomaniac,
it tends to want to govern everything

from the infinitely small
to the infinitely large.

So to cover such a broad spectrum,

plenty of imagination
is needed, of course,

because what is happening in an atom,

in a grain of sand,
a petanque ball, or a planet,

isn't necessarily the same thing,

so you have to be ready
to invent new laws.

But in parallel to this approach,

knowing how to use some form
of laziness is also necessary

because what is actually
happening in an atom,

a grain of sand,
a petanque ball, or a planet,

can be similar in many ways.

And to be able to identify
theses similarities

between objects that are
at first glance totally different,

you have to know how to ask
questions that are a bit weird,

and I have put together a few for you.

So what is the commonality between
the break of an uncooked spaghetto

and the fracture of a metal beam?

Or between the vortex that I generate
with my spoon in a cup of coffee

and hurricanes in the atmosphere?

Another one is what is the connection

between the physics of accretion
disks around forming stars -

which is very serious -
and the physics of cake dough?

Or between mayonnaise on one hand,

and nuclear fusion
by confinement on the other?

Now I'm going to talk about
one of these weird questions tonight,

that is "What does a liquid ...

and a cat have in common?"

(Laughter)

Obviously behind this question
lies another more serious question that is

"What is a liquid?"

Well, a liquid is a material
that takes the shape of its container

while maintaining a constant volume.

This is the official
definition of a liquid.

And we see in numerous cases,

(Laughter)

that cats seem to fit
this definition pretty well.

They adapt their shape to their container.

Maybe you've already seen
pictures like these.

Quite a lot of these have been circulating
on the internet for many years.

And, well, I spend a bit
of my time on the internet,

as a researcher, I mean!

(Laughter)

And I didn't miss
the appearance of this meme,

plenty of pictures related
to the question "Are cats liquid?"

Now several years ago,

on a spring afternoon

that wasn't motivating me
to do what I was supposed to do,

I decided to write a scientific
article with the title:

"On the rheology of cats"
in order to take this question seriously.

This procrastination actually
led to a bit of success

since a few years later,
it won me the Ig Nobel prize of physics

which rewards research that makes
people both laugh and ponder.

I said that this scientific article
was called "On the rheology of cats,"

but what does "rheology" mean?

Rheology comes from the greek
"rheo" which means to flow.

This same root is found in other words
such as "rhythm" for example,

or more pompous words
such as "logorrhea" -

I'm going to try not to do that myself -

and some slightly less
pompous words such as"diarrhea,"

everyone knows that one! (Laughter)

So the idea was to take
the question "Are cats liquid?"

and use it to illustrate several issues
that are quite serious this time,

that rheologists face
and try to solve every day.

But anyway, are cats liquid or not?

In fact, the key is
that the answer to this question

depends on the span of time
we're ready to allow it.

Because if we look carefully
at the definition of a liquid,

"adapting one's shape" is an action
that isn't going to happen instantly.

Behind this adaptation,
there's a characteristic time,

and this characteristic time

(Laughter)

is called the "relaxation time".

In many cases - the cases
that are easiest to deal with -

the relaxation time is something
intrinsic to the material.

So in the case of a cat,
it will depend on its age or its breed.

Here we see that number 107
looks more liquid

and thus has a shorter relaxation time.

Because this is precisely the key
behind the concept of relaxation time,

it's that in reply to the question

"Is a cat liquid?" or "Is such
and such material liquid?",

you must answer another question that is
"What is this material's relaxation time?"

So for a cat, same thing,
we will ask this question,

"what is the relaxation time of a cat,
what does it depend on?"

Here I've chosen a case,
the easiest to deal with,

when the time of relaxation
only depends on the material itself.

But it can also depend on the container

since we can easily imagine
that a cat relaxes more easily,

liquefies more easily on the lap
of its owner than in a cage.

Now, let me give you another
example, that of a drop of water.

Water is the liquid par excellence.

We tend to expect it to spread
on any kind of surface,

but in some contexts,
we see that water forms droplets.

Now trying to better understand
why in some cases

the material flows whereas in others
it doesn't depending on the container,

relates to questions that imply
research on what we call "wetting".

And research on wetting

includes everything from the development
of super water-resistant windshields

which circumvent the need
for windshield wipers,

to research that attempt to understand
the development of cancerous tumors

because actually, the way
cancerous cells and tissues spread

can also be understood in this manner.

In fact, trying to estimate,

to measure, calculate, maybe even modify

the one or several relaxation times
of the most diverse and varied materials

is kind of what is at the heart
of rheologists' research.

And what you need
to try to keep in mind

is that these relaxation times

can last from one millisecond
to millions of years.

That doesn't take anything
away from the fact

that if we observe these materials
long enough, we will see them flow.

One example over a period
of several decades or years,

you may have notice
that down a sloping road

the asphalt sometimes forms like bumps.

That's because over a period of years,
the asphalt flows down the slope.

And the same thing can happen

with all sorts of construction
materials from concrete to steel,

and that's why the industries
that manufacture those materials

spend a lot of money
to better understand their rheology.

Sometimes, it is microscopic details
that have an enormous impact.

The collapse of a building
sometimes depends

on the precise physics
of the grains of sand that make it up.

And a good example
of this potentially significant impact

of the microscopic on the macroscopic
is found among firefighters

who often like to add
tiny filamentary molecules

in small quantities, to their water tanks,

and these filamentary molecules help
reduce turbulence inside the fire hoses,

thereby allowing them to spray
the water farther with the same power.

Now the solutions that rheologists
create for various problems

are sometimes rather odd.

You may have seen in public buildings -

not here I think
but in recent public buildings -

big columns situated
in front of the emergency exits.

Well, we may think it's a little weird,

but actually rheologists have shown
that when a crowd moves,

these columns tend to reduce
congestion and jams at the exit.

So in reality,

if we wait long enough

everything flows.

That's the motto of rheology.

Even the materials that we walk on
and we usually consider to be solid,

even those materials flows.

So if we take a glacier, for example,
over several decades -

and that's what
some scientists are doing

by observing glaciers
with timelapse cameras -

we can see the ice flowing
into the valley.

And if we had the chance
to wait millions of years,

we would see the same thing
happening to mountains,

and we would see
that peaks and valleys

are like the crests and troughs
of an ever-moving ocean.

Alright!

Now you may ask again
"But are cats liquid or not?"

So, my advice is just wait a little bit

before giving your final answer.
(Laughter)

Thank you.

(Applause)