Do we see reality as it is?

I love a great mystery,

and I'm fascinated by the greatest
unsolved mystery in science,

perhaps because it's personal.

It's about who we are,

and I can't help but be curious.

The mystery is this:

what is the relationship
between your brain

and your conscious experiences,

such as your experience
of the taste of chocolate

or the feeling of velvet?

Now, this mystery is not new.

In 1868, Thomas Huxley wrote,

"How it is that anything so remarkable
as a state of consciousness comes about

as the result of irritating nervous tissue

is just as unaccountable

as the appearance of the Genie
when Aladdin rubbed his lamp.

Now, Huxley knew that brain activity

and conscious experiences are correlated,

but he didn't know why.

To the science of his day,
it was a mystery.

In the years since Huxley,

science has learned a lot
about brain activity,

but the relationship
between brain activity

and conscious experiences
is still a mystery.

Why? Why have we made so little progress?

Well, some experts think
that we can't solve this problem

because we lack the necessary concepts

and intelligence.

We don't expect monkeys to solve
problems in quantum mechanics,

and as it happens, we can't expect
our species to solve this problem either.

Well, I disagree. I'm more optimistic.

I think we've simply
made a false assumption.

Once we fix it, we just
might solve this problem.

Today, I'd like tell you
what that assumption is,

why it's false, and how to fix it.

Let's begin with a question:

do we see reality as it is?

I open my eyes

and I have an experience that I describe

as a red tomato a meter away.

As a result, I come to believe
that in reality,

there's a red tomato a meter away.

I then close my eyes, and my experience
changes to a grey field,

but is it still the case that in reality,
there's a red tomato a meter away?

I think so, but could I be wrong?

Could I be misinterpreting
the nature of my perceptions?

We have misinterpreted
our perceptions before.

We used to think the Earth is flat,

because it looks that way.

Pythagorus discovered that we were wrong.

Then we thought that the Earth

is the unmoving center of the Universe,

again because it looks that way.

Copernicus and Galileo discovered,
again, that we were wrong.

Galileo then wondered if we might
be misinterpreting our experiences

in other ways.

He wrote: "I think that tastes,
odors, colors, and so on

reside in consciousness.

Hence if the living creature were removed,

all these qualities would be annihilated.

Now, that's a stunning claim.

Could Galileo be right?

Could we really be misinterpreting
our experiences that badly?

What does modern science
have to say about this?

Well, neuroscientists tell us
that about a third of the brain's cortex

is engaged in vision.

When you simply open your eyes
and look about this room,

billions of neurons
and trillions of synapses are engaged.

Now, this is a bit surprising,

because to the extent
we think about vision at all,

we think of it as like a camera.

It just takes a picture
of objective reality as it is.

Now, there is a part of vision
that works like a camera:

the eye has a lens that focuses an image
on the back of the eye

where there are 130 million
photoreceptors,

so the eye is like a 130 megapixel camera.

But that doesn't explain
the billions of neurons

and trillions of synapses
that are engaged in vision.

What are these neurons up to?

Well, neuroscientists tell us
that they are creating, in real time,

all the shapes, objects, colors,
and motions that we see.

It feels like we're just taking a snapshot
of this room the way it is,

but in fact, we're constructing
everything that we see.

We don't construct
the whole world at once.

We construct what we need in the moment.

Now, there are many demonstrations
that are quite compelling

that we construct what we see.

I'll just show you two.

In this example, you see some red discs

with bits cut out of them,

but if I just rotate
the disks a little bit,

suddenly, you see a 3D cube
pop out of the screen.

Now, the screen of course is flat,

so the three dimensional cube
that you're experiencing

must be your construction.

In this next example,

you see glowing blue bars

with pretty sharp edges

moving across a field of dots.

In fact, no dots move.

All I'm doing from frame to frame

is changing the colors of dots

from blue to black or black to blue.

But when I do this quickly,

your visual system creates
the glowing blue bars

with the sharp edges and the motion.

There are many more examples,
but these are just two

that you construct what you see.

But neuroscientists go further.

They say that we reconstruct reality.

So, when I have an experience
that I describe as a red tomato,

that experience is actually
an accurate reconstruction

of the properties of a real red tomato

that would exist
even if I weren't looking.

Now, why would neuroscientists
say that we don't just construct,

we reconstruct?

Well, the standard argument given

is usually an evolutionary one.

Those of our ancestors
who saw more accurately

had a competitive advantage compared
to those who saw less accurately,

and therefore they were more likely
to pass on their genes.

We are the offspring of those
who saw more accurately,

and so we can be confident that,
in the normal case,

our perceptions are accurate.

You see this in the standard textbooks.

One textbook says, for example:

"Evolutionarily speaking,

vision is useful precisely
because it is so accurate."

So the idea is that accurate perceptions

are fitter perceptions.

They give you a survival advantage.

Now, is this correct?

Is this the right interpretation
of evolutionary theory?

Well, let's first look at a couple
of examples in nature.

The Australian jewel beetle

is dimpled, glossy, and brown.

The female is flightless.

The male flies, looking, of course,
for a hot female.

When he finds one, he alights, and mates.

There's another species in the outback,

homo sapiens.

The male of this species
has a massive brain

that it uses to hunt for cold beer.

(Laughter)

And when he finds one, he drains it,

and sometimes throws the bottle
into the outback.

Now, as it happens, these bottles
are dimpled, glossy,

and just the right shade of brown

to tickle the fancy of these beetles.

The males swarm all over the bottles

trying to mate.

They lose all interest
in the real females.

Classic case of the male
leaving the female for the bottle.

(Laughter) (Applause)

The species almost went extinct.

Australia had to change its bottles

to save its beetles.

Now, the males had successfully
found females for thousands,

perhaps millions of years.

It look like they saw reality as it is,

but apparently not: evolution
had given them a hack.

A female is anything dimpled,
glossy, and brown,

the bigger the better.

(Laughter)

Even while crawling all over the bottle,
the male couldn't discover his mistake.

Now, you might say, beetles, sure,
they're very simple creatures,

but surely not mammals.

Mammals don't rely on tricks.

Well, I won't dwell on this,
but you get the idea. (Laughter)

So this raises an important
technical question:

does natural selection really favor
seeing reality as it is?

Fortunately, we don't have
to wave our hands and guess:

evolution is a mathematically
precise theory.

We can use the equations of evolution
to check this out.

We can have various organisms
in artificial worlds compete

and see which survive and which thrive,

which sensory systems are more fit.

A key notion in those
equations is fitness.

Consider this steak:

what does this steak do
for the fitness of an animal?

Well, for a hungry lion looking to eat,

it enhances fitness.

For a well-fed lion looking to mate,
it doesn't enhance fitness.

And for a rabbit in any state,
it doesn't enhance fitness,

so fitness does depend
on reality as it is, yes,

but also the organism,
its state, and its action.

Fitness is not the same thing
as reality as it is,

and it's fitness,
and not reality as it is,

that figures centrally
in the equations of evolution.

So, in my lab,

we have run hundreds of thousands
of evolutionary game simulations

with lots of different
randomly chosen worlds

and organisms that compete
for resources in those worlds.

Some of the organisms
see all of the reality,

others see just part of the reality,

and some see none of the reality,

only fitness.

Who wins?

Well, I hate to break it to you,

but perception of reality goes extinct.

In almost every simulation,

organisms that see none of reality

but are just tuned to fitness

drive to extinction all the organisms
that perceive reality as it is.

So the bottom line is, evolution
does not favor vertical,

or accurate perceptions.

Those perceptions of reality go extinct.

Now, this is a bit stunning:

how can it be that not seeing
the world accurately

gives us a survival advantage?

That is a bit counterintuitive.

But remember the jewel beetle.

The jewel beetle survived
for thousands, perhaps millions of years,

using simple tricks and hacks.

What the equations
of evolution are telling us

is that all organisms, including us,
are in the same boat as the jewel beetle.

We do not see reality as it is:

we're shaped with tricks
and hacks that keep us alive.

Still,

we need some help with our intuitions.

How can not perceiving
reality as it is be useful?

Well, fortunately, we have
a very helpful metaphor:

the desktop interface on your computer.

Consider that blue icon
for a TEDTalk that you're writing.

Now, the icon is blue and rectangular

and in the lower right corner
of the desktop.

Does that mean that the text file itself

in the computer is blue,

rectangular, and in the lower
right-hand corner of the computer?

Of course not.

Anyone who thought that misinterprets

the purpose of the interface.

It's not there to show you
the reality of the computer.

In fact, it's there to hide that reality.

You don't want to know about the diodes

and resisters and all
the megabytes of software.

If you had to deal with that,
you could never write your text file

or edit your photo.

So the idea is that evolution
has given us an interface

that hides reality and guides
adaptive behavior.

Space and time, as you
perceive them right now,

are your desktop.

Physical objects are simply icons
in that desktop.

There's an obvious objection.

Hoffman, if you think that train
coming down the track at 200 MPH

is just an icon of your desktop,

why don't you step in front of it?

And after you're gone,
and your theory with you,

we'll know that there's more
to that train than just an icon.

Well, I wouldn't step
in front of that train

for the same reason

that I wouldn't carelessly drag
that icon to the trash can:

not because I take the icon literally.

The file is not literally blue
or rectangular.

But I do take it seriously.

I could lose weeks of work.

Similarly, evolution has shaped us

with perceptual symbols
that are designed to keep us alive.

We'd better take them seriously.

If you see a snake, don't pick it up.

If you see a cliff, don't jump off.

They're designed to keep us safe,
and we should take them seriously.

That does not mean that we
should take them literally.

That's a logical error.

Another objection: ah, there's
nothing really new here.

Physicists have told us for a long time
that the metal of the train looks solid

but really it's mostly empty space
with microscopic particles zipping around.

There's nothing new here.

Well, not exactly:

it's like saying, I know that
that blue icon on the desktop

is not the reality of the computer,

but if I pull out my trusty
magnifying glass and look really closely,

I see little pixels,

and that's the reality of the computer.

Well, not really: you're still
on the desktop, and that's the point.

Those microscopic particles
are still in space and time:

they're still in the user interface.

So I'm saying something far more radical
than those physicists.

Finally, you might object,

look, we all see the train,

therefore none of us constructs the train.

But remember this example.

In this example, we all see a cube,

but the screen is flat,

so the cube that you see

is the cube that you construct.

We all see a cube

because we all, each one of us,
constructs the cube that we see.

The same is true of the train.

We all see a train because
we each see the train that we construct,

and the same is true
of all physical objects.

We're inclined to think that perception
is like a window on reality as it is.

The theory of evolution is telling us
that this is an incorrect interpretation

of our perceptions.

Instead, reality is more like a 3D desktop

that's designed to hide
the complexity of the real world

and guide adaptive behavior.

Space as you perceive it is your desktop.

Physical objects are just
the icons in that desktop.

We used to think that the Earth is flat

because it looks that way.

Then we thought that the Earth
is the unmoving center of reality

because it looks that way.

We were wrong.

We had misinterpreted our perceptions.

Now we believe that spacetime and objects

are the nature of reality as it is.

The theory of evolution is telling us
that once again, we're wrong.

We're misinterpreting the content
of our perceptual experiences.

There's something that exists
when you don't look,

but it's not spacetime
and physical objects.

It's as hard for us to let go
of spacetime and objects

as it is for the jewel beetle
to let go of its bottle.

Why? Because we're blind
to our own blindnesses.

But we have an advantage
over the jewel beetle:

our science and technology.

By peering through the lens of a telescope

we discovered that the Earth

is not the unmoving center of reality,

and by peering through the lens
of the theory of evolution

we discovered that spacetime and objects

are not the nature of reality.

When I have a perceptual experience
that I describe as a red tomato,

I am interacting with reality,

but that reality is not a red tomato

and is nothing like a red tomato.

Similarly, when I have an experience
that I describe as a lion or a steak,

I'm interacting with reality,

but that reality is not a lion or a steak.

And here's the kicker:

when I have a perceptual experience
that I describe as a brain, or neurons,

I am interacting with reality,

but that reality is not a brain or neurons

and is nothing like a brain or neurons.

And that reality, whatever it is,

is the real source of cause and effect

in the world: not brains, not neurons.

Brains and neurons have no causal power.

They cause none of our
perceptual experiences,

and none of our behavior.

Brains and neurons are a species-specific
set of symbols, a hack.

What does this mean
for the mystery of consciousness?

Well, it opens up new possibilities.

For instance,

perhaps reality is some vast machine

that causes our conscious experiences.

I doubt this, but it's worth exploring.

Perhaps reality is some vast,
interacting network of conscious agents,

simple and complex, that cause
each others' conscious experiences.

Actually, this isn't as crazy
an ideas as it seems,

and I'm currently exploring it.

But here's the point:

once we let go of our massively intuitive

but massively false assumption
about the nature of reality,

it opens up new ways to think
about life's greatest mystery.

I bet that reality will end up
turning out to be more fascinating

and unexpected than we've ever imagined.

The theory of evolution presents us
with the ultimate dare:

dare to recognize that perception
is not about seeing truth,

it's about having kids.

And by the way, even this TED
is just in your head.

Thank you very much.

(Applause)

Chris Anderson: If that's
really you there, thank you.

So there's so much from this.

I mean, first of all, some people
may just be profoundly depressed

at the thought that,
if evolution does not favor reality,

I mean, doesn't that to some extent
undermine all our endeavors here,

all our ability to think
that we can think the truth,

possibly even including
your own theory, if you go there?

Donald Hoffman: Well, this does not
stop us from a successful science.

What we have is one theory
that turned out to be false,

that perception is like reality
and reality is like our perceptions.

That theory turns out to be false.

Okay, throw that theory away.

That doesn't stop us from now postulating
all sorts of other theories

about the nature of reality,

so it's actually progress to recognize
that one of our theories was false.

So science continues as normal.
There's no problem there.

CA: So you think it's possible
-- (Laughter) --

This is cool, but what you're saying
I think is that evolution

can still get you to reason.

DH: Yes. Now that's a very,
very good point.

The evolutionary game simulations that I
showed were specifically about perception,

and they do show that our perceptions
have been shaped

not to show us reality as it is,

but that does not mean the same thing
about our logic or mathematics.

We haven't done these simulations,
but my bet is that we'll find

that there are some selection pressures
for our logic and our mathematics

to be at least in the direction of truth.

I mean, if you're like me,
math and logic is not easy.

We don't get it all right, but at least
the selection pressures are not

uniformly away from true math and logic.

So I think that we'll find that we have
to look at each cognitive faculty

one at a time and see
what evolution does to it.

What's true about perception may not
be true about math and logic.

CA: I mean, really what you're proposing
is a kind of modern-day Bishop Berkeley

interpretation of the world:

consciousness causes matter,
not the other way around.

DH: Well, it's slightly
different than Berkeley.

Berkeley thought that, he was a deist,
and he thought that the ultimate

nature of reality was his God
and so forth,

and I don't need to go
where Berkeley's going,

so it's quite a bit
different from Berkeley.

I call this conscious realism.
It's actually a very different approach.

CA: Don, I could literally talk with you
for hours, and I hope to do that.

DH: Thanks so much for that.
(Applause)