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I love a great mystery,
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and I'm fascinated by the greatest
unsolved mystery in science,
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perhaps because it's personal.
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It's about who we are,
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and I can't help but be curious.
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The mystery is this:
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What is the relationship
between your brain
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and your conscious experiences,
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such as your experience
of the taste of chocolate
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or the feeling of velvet?
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Now, this mystery is not new.
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In 1868, Thomas Huxley wrote,
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"How it is that anything so remarkable
as a state of consciousness comes about
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as the result of irritating nervous tissue
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is just as unaccountable
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as the appearance of the genie
when Aladdin rubbed his lamp."
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Now, Huxley knew that brain activity
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and conscious experiences are correlated,
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but he didn't know why.
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To the science of his day,
it was a mystery.
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In the years since Huxley,
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science has learned a lot
about brain activity,
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but the relationship
between brain activity
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and conscious experiences
is still a mystery.
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Why? Why have we made so little progress?
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Well, some experts think
that we can't solve this problem
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because we lack the necessary
concepts and intelligence.
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We don't expect monkeys to solve
problems in quantum mechanics,
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and as it happens, we can't expect
our species to solve this problem either.
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Well, I disagree. I'm more optimistic.
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I think we've simply
made a false assumption.
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Once we fix it, we just
might solve this problem.
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Today, I'd like tell you
what that assumption is,
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why it's false, and how to fix it.
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Let's begin with a question:
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Do we see reality as it is?
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I open my eyes
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and I have an experience that I describe
as a red tomato a meter away.
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As a result, I come to believe
that in reality,
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there's a red tomato a meter away.
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I then close my eyes, and my experience
changes to a gray field,
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but is it still the case that in reality,
there's a red tomato a meter away?
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I think so, but could I be wrong?
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Could I be misinterpreting
the nature of my perceptions?
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We have misinterpreted
our perceptions before.
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We used to think the Earth was flat,
because it looks that way.
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Pythagorus discovered that we were wrong.
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Then we thought that the Earth
is the unmoving center of the Universe,
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again because it looks that way.
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Copernicus and Galileo discovered,
again, that we were wrong.
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Galileo then wondered if we might
be misinterpreting our experiences
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in other ways.
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He wrote: "I think that tastes,
odors, colors, and so on
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reside in consciousness.
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Hence if the living creature were removed,
all these qualities would be annihilated."
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Now, that's a stunning claim.
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Could Galileo be right?
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Could we really be misinterpreting
our experiences that badly?
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What does modern science
have to say about this?
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Well, neuroscientists tell us
that about a third of the brain's cortex
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is engaged in vision.
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When you simply open your eyes
and look about this room,
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billions of neurons
and trillions of synapses are engaged.
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Now, this is a bit surprising,
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because to the extent that
we think about vision at all,
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we think of it as like a camera.
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It just takes a picture
of objective reality as it is.
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Now, there is a part of vision
that's like a camera:
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the eye has a lens that focuses
an image on the back of the eye
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where there are 130 million
photoreceptors,
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so the eye is like a 130-megapixel camera.
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But that doesn't explain
the billions of neurons
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and trillions of synapses
that are engaged in vision.
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What are these neurons up to?
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Well, neuroscientists tell us
that they are creating, in real time,
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all the shapes, objects, colors,
and motions that we see.
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It feels like we're just taking a snapshot
of this room the way it is,
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but in fact, we're constructing
everything that we see.
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We don't construct
the whole world at once.
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We construct what we need in the moment.
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Now, there are many demonstrations
that are quite compelling
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that we construct what we see.
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I'll just show you two.
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In this example, you see some red discs
with bits cut out of them,
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but if I just rotate
the disks a little bit,
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suddenly, you see a 3D cube
pop out of the screen.
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Now, the screen of course is flat,
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so the three-dimensional cube
that you're experiencing
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must be your construction.
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In this next example,
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you see glowing blue bars
with pretty sharp edges
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moving across a field of dots.
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In fact, no dots move.
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All I'm doing from frame to frame
is changing the colors of dots
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from blue to black or black to blue.
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But when I do this quickly,
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your visual system creates
the glowing blue bars
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with the sharp edges and the motion.
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There are many more examples,
but these are just two
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that you construct what you see.
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But neuroscientists go further.
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They say that we reconstruct reality.
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So, when I have an experience
that I describe as a red tomato,
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that experience is actually
an accurate reconstruction
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of the properties of a real red tomato
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that would exist
even if I weren't looking.
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Now, why would neuroscientists
say that we don't just construct,
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we reconstruct?
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Well, the standard argument given
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is usually an evolutionary one.
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Those of our ancestors
who saw more accurately
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had a competitive advantage compared
to those who saw less accurately,
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and therefore they were more likely
to pass on their genes.
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We are the offspring of those
who saw more accurately,
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and so we can be confident that,
in the normal case,
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our perceptions are accurate.
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You see this in the standard textbooks.
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One textbook says, for example,
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"Evolutionarily speaking,
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vision is useful precisely
because it is so accurate."
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So the idea is that accurate perceptions
are fitter perceptions.
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They give you a survival advantage.
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Now, is this correct?
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Is this the right interpretation
of evolutionary theory?
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Well, let's first look at a couple
of examples in nature.
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The Australian jewel beetle
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is dimpled, glossy and brown.
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The female is flightless.
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The male flies, looking,
of course, for a hot female.
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When he finds one, he alights and mates.
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There's another species in the outback,
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Homo sapiens.
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The male of this species
has a massive brain
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that he uses to hunt for cold beer.
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(Laughter)
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And when he finds one, he drains it,
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and sometimes throws the bottle
into the outback.
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Now, as it happens, these bottles
are dimpled, glossy,
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and just the right shade of brown
to tickle the fancy of these beetles.
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The males swarm all over
the bottles trying to mate.
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They lose all interest
in the real females.
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Classic case of the male
leaving the female for the bottle.
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(Laughter) (Applause)
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The species almost went extinct.
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Australia had to change its bottles
to save its beetles.
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(Laughter)
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Now, the males had successfully
found females for thousands,
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perhaps millions of years.
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It looked like they saw reality
as it is, but apparently not.
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Evolution had given them a hack.
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A female is anything dimpled,
glossy and brown,
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the bigger the better.
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(Laughter)
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Even when crawling all over the bottle,
the male couldn't discover his mistake.
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Now, you might say, beetles, sure,
they're very simple creatures,
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but surely not mammals.
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Mammals don't rely on tricks.
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Well, I won't dwell on this,
but you get the idea. (Laughter)
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So this raises an important
technical question:
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Does natural selection really favor
seeing reality as it is?
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Fortunately, we don't have
to wave our hands and guess;
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evolution is a mathematically
precise theory.
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We can use the equations of evolution
to check this out.
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We can have various organisms
in artificial worlds compete
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and see which survive and which thrive,
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which sensory systems are more fit.
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A key notion in those
equations is fitness.
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Consider this steak:
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What does this steak do
for the fitness of an animal?
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Well, for a hungry lion looking to eat,
it enhances fitness.
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For a well-fed lion looking to mate,
it doesn't enhance fitness.
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And for a rabbit in any state,
it doesn't enhance fitness,
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so fitness does depend
on reality as it is, yes,
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but also on the organism,
its state and its action.
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Fitness is not the same thing
as reality as it is,
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and it's fitness,
and not reality as it is,
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that figures centrally
in the equations of evolution.
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So, in my lab,
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we have run hundreds of thousands
of evolutionary game simulations
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with lots of different
randomly chosen worlds
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and organisms that compete
for resources in those worlds.
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Some of the organisms
see all of the reality,
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others see just part of the reality,
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and some see none of the reality,
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only fitness.
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Who wins?
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Well, I hate to break it to you,
but perception of reality goes extinct.
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In almost every simulation,
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organisms that see none of reality
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but are just tuned to fitness
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drive to extinction all the organisms
that perceive reality as it is.
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So the bottom line is, evolution
does not favor vertical,
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or accurate perceptions.
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Those perceptions of reality go extinct.
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Now, this is a bit stunning:
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how can it be that not seeing
the world accurately
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gives us a survival advantage?
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That is a bit counterintuitive.
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But remember the jewel beetle.
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The jewel beetle survived
for thousands, perhaps millions of years,
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using simple tricks and hacks.
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What the equations
of evolution are telling us
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is that all organisms, including us,
are in the same boat as the jewel beetle.
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We do not see reality as it is:
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we're shaped with tricks
and hacks that keep us alive.
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Still,
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we need some help with our intuitions.
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How can not perceiving
reality as it is be useful?
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Well, fortunately, we have
a very helpful metaphor:
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the desktop interface on your computer.
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Consider that blue icon
for a TEDTalk that you're writing.
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Now, the icon is blue and rectangular
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and in the lower right corner
of the desktop.
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Does that mean that the text file itself
in the computer is blue,
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rectangular, and in the lower
right-hand corner of the computer?
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Of course not.
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Anyone who thought that misinterprets
the purpose of the interface.
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It's not there to show you
the reality of the computer.
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In fact, it's there to hide that reality.
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You don't want to know about the diodes
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and resisters and all
the megabytes of software.
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If you had to deal with that,
you could never write your text file
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or edit your photo.
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So the idea is that evolution
has given us an interface
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that hides reality and guides
adaptive behavior.
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Space and time, as you
perceive them right now,
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are your desktop.
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Physical objects are simply icons
in that desktop.
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There's an obvious objection.
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Hoffman, if you think that train
coming down the track at 200 MPH
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is just an icon of your desktop,
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why don't you step in front of it?
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And after you're gone,
and your theory with you,
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we'll know that there's more
to that train than just an icon.
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Well, I wouldn't step
in front of that train
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for the same reason
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that I wouldn't carelessly drag
that icon to the trash can:
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not because I take the icon literally.
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The file is not literally blue
or rectangular.
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But I do take it seriously.
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I could lose weeks of work.
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Similarly, evolution has shaped us
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with perceptual symbols
that are designed to keep us alive.
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We'd better take them seriously.
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If you see a snake, don't pick it up.
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If you see a cliff, don't jump off.
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They're designed to keep us safe,
and we should take them seriously.
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That does not mean that we
should take them literally.
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That's a logical error.
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Another objection: ah, there's
nothing really new here.
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Physicists have told us for a long time
that the metal of the train looks solid
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but really it's mostly empty space
with microscopic particles zipping around.
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There's nothing new here.
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Well, not exactly:
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it's like saying, I know that
that blue icon on the desktop
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is not the reality of the computer,
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but if I pull out my trusty
magnifying glass and look really closely,
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I see little pixels,
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and that's the reality of the computer.
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Well, not really: you're still
on the desktop, and that's the point.
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Those microscopic particles
are still in space and time:
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they're still in the user interface.
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So I'm saying something far more radical
than those physicists.
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Finally, you might object,
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look, we all see the train,
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therefore none of us constructs the train.
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But remember this example.
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In this example, we all see a cube,
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but the screen is flat,
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so the cube that you see
is the cube that you construct.
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We all see a cube
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because we all, each one of us,
constructs the cube that we see.
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The same is true of the train.
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We all see a train because
we each see the train that we construct,
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and the same is true
of all physical objects.
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We're inclined to think that perception
is like a window on reality as it is.
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The theory of evolution is telling us
that this is an incorrect interpretation
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of our perceptions.
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Instead, reality is more like a 3D desktop
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that's designed to hide
the complexity of the real world
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and guide adaptive behavior.
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Space as you perceive it is your desktop.
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Physical objects are just
the icons in that desktop.
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We used to think that the Earth is flat
because it looks that way.
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Then we thought that the Earth
is the unmoving center of reality
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because it looks that way.
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We were wrong.
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We had misinterpreted our perceptions.
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Now we believe that spacetime and objects
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are the nature of reality as it is.
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The theory of evolution is telling us
that once again, we're wrong.
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We're misinterpreting the content
of our perceptual experiences.
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There's something that exists
when you don't look,
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but it's not spacetime
and physical objects.
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It's as hard for us to let go
of spacetime and objects
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as it is for the jewel beetle
to let go of its bottle.
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Why? Because we're blind
to our own blindnesses.
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But we have an advantage
over the jewel beetle:
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our science and technology.
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By peering through the lens of a telescope
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we discovered that the Earth
is not the unmoving center of reality,
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and by peering through the lens
of the theory of evolution
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we discovered that spacetime and objects
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are not the nature of reality.
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When I have a perceptual experience
that I describe as a red tomato,
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I am interacting with reality,
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but that reality is not a red tomato
and is nothing like a red tomato.
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Similarly, when I have an experience
that I describe as a lion or a steak,
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I'm interacting with reality,
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but that reality is not a lion or a steak.
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And here's the kicker:
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when I have a perceptual experience
that I describe as a brain, or neurons,
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I am interacting with reality,
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but that reality is not a brain or neurons
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and is nothing like a brain or neurons.
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And that reality, whatever it is,
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is the real source of cause and effect
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in the world: not brains, not neurons.
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Brains and neurons
have no causal powers.
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They cause none of our
perceptual experiences,
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and none of our behavior.
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Brains and neurons are a species-specific
set of symbols, a hack.
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What does this mean
for the mystery of consciousness?
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Well, it opens up new possibilities.
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For instance,
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perhaps reality is some vast machine
that causes our conscious experiences.
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I doubt this, but it's worth exploring.
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Perhaps reality is some vast,
interacting network of conscious agents,
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simple and complex, that cause
each others' conscious experiences.
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Actually, this isn't as crazy
an ideas as it seems,
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and I'm currently exploring it.
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But here's the point:
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once we let go of our massively intuitive
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but massively false assumption
about the nature of reality,
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it opens up new ways to think
about life's greatest mystery.
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I bet that reality will end up
turning out to be more fascinating
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and unexpected than we've ever imagined.
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The theory of evolution presents us
with the ultimate dare:
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dare to recognize that perception
is not about seeing truth,
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it's about having kids.
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And by the way, even this TED
is just in your head.
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Thank you very much.
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(Applause)
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Chris Anderson: If that's
really you there, thank you.
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So there's so much from this.
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I mean, first of all, some people
may just be profoundly depressed
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at the thought that,
if evolution does not favor reality,
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I mean, doesn't that to some extent
undermine all our endeavors here,
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all our ability to think
that we can think the truth,
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possibly even including
your own theory, if you go there?
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Donald Hoffman: Well, this does not
stop us from a successful science.
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What we have is one theory
that turned out to be false,
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that perception is like reality
and reality is like our perceptions.
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That theory turns out to be false.
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Okay, throw that theory away.
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That doesn't stop us from now postulating
all sorts of other theories
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about the nature of reality,
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so it's actually progress to recognize
that one of our theories was false.
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So science continues as normal.
There's no problem here.
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CA: So you think it's possible
-- (Laughter) --
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This is cool, but what you're saying
I think is it's possible that evolution
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can still get you to reason.
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DH: Yes. Now that's a very,
very good point.
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The evolutionary game simulations that I
showed were specifically about perception,
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and they do show that our perceptions
have been shaped
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not to show us reality as it is,
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but that does not mean the same thing
about our logic or mathematics.
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We haven't done these simulations,
but my bet is that we'll find
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that there are some selection pressures
for our logic and our mathematics
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to be at least in the direction of truth.
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I mean, if you're like me,
math and logic is not easy.
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We don't get it all right, but at least
the selection pressures are not
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uniformly away from true math and logic.
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So I think that we'll find that we have
to look at each cognitive faculty
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one at a time and see
what evolution does to it.
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What's true about perception may not
be true about math and logic.
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CA: I mean, really what you're proposing
is a kind of modern-day Bishop Berkeley
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interpretation of the world:
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consciousness causes matter,
not the other way around.
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DH: Well, it's slightly
different than Berkeley.
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Berkeley thought that, he was a deist,
and he thought that the ultimate
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nature of reality is God
and so forth,
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and I don't need to go
where Berkeley's going,
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so it's quite a bit
different from Berkeley.
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I call this conscious realism.
It's actually a very different approach.
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CA: Don, I could literally talk with you
for hours, and I hope to do that.
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Thanks so much for that.
DH: Thank you. (Applause)
Adrian Dobroiu
2:35 - 2:38 Pythagorus discovered that we were wrong.
It's "Pythagoras".