WEBVTT

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Imagine a brilliant neuroscientist
named Mary.

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Mary lives in a black and white room,

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she only reads black and white books,

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and her screens only display 
black and white.

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But even though she has never seen color,
Mary is an expert in color vision

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and knows everything ever discovered
about its physics and biology.

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She knows how different 
wavelengths of light

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stimulate three types of cone cells
in the retina,

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and she knows how electrical signals

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travel down the optic nerve 
into the brain.

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There, they create patterns 
of neural activity

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that correspond to the millions
of colors most humans can distinguish.

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Now image that one day,

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Mary's black and white screen
malfunctions

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and an apple appears in color.

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For the first time,

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she can experience something
that she's known about for years.

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Does she learn anything new?

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Is there anything about perceiving color
that wasn't captured in all her knowledge?

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Philosopher Frank Jackson proposed
this thought experiment,

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called Mary's room, in 1982.

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He argued that if Mary already knew
all the physical facts about color vision,

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and experiencing color still teaches
her something new,

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then mental states, like color perception,

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can't be completely described 
by physical facts.

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The Mary's room thought experiment

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describes what philosophers call
the knowledge argument,

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that there are non-physical properties
and knowledge

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which can only be discovered
through conscious experience.

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The knowledge argument contradicts
the theory of physicalism,

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which says that everything, 
including mental states,

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has a physical explanation.

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To most people hearing Mary's story,

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it seems intuitively obvious 
that actually seeing color

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will be totally different 
than learning about it.

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Therefore, there must be some quality
of color vision

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that transcends its physical description.

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The knowledge argument isn't just
about color vision.

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Mary's room uses color vision
to represent conscious experience.

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If physical science can't entirely
explain color vision,

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then maybe it can't entirely explain
other conscious experiences either.

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For instance, we could know every
physical detail

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about the structure and function
of someone else's brain,

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but still not understand
what it feels like to be that person.

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These ineffable experiences 
have properties called qualia,

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subjective qualities that you can't 
accurately describe or measure.

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Qualia are unique to the person
experiencing them,

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like having an itch,

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being in love,

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or feeling bored.

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Physical facts can't completely explain
mental states like this.

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Philosophers interested
in artificial intelligence

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have used the knowledge argument

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to theorize that recreating 
a physical state

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won't necessarily recreate
a corresponding mental state.

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In other words,

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building a computer which mimicked 
the function of every single neuron

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of the human brain

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won't necessarily create a conscious
computerized brain.

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Not all philosophers agree that
the Mary's room experiment is useful.

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Some argue that her extensive knowledge
of color vision

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would have allowed her to create
the same mental state

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produced by actually seeing the color.

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The screen malfunction wouldn't
show her anything new.

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Others say that her knowledge
was never complete in the first place

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because it was based only
on those physical facts

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that can be conveyed in words.

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Years after he proposed it,

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Jackson actually reversed his own
stance on his thought experiment.

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He decided that even 
Mary's experience of seeing red

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still does correspond to a measurable
physical event in the brain,

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not unknowable qualia beyond
physical explanation.

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But there still isn't a definitive answer

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to the question of whether Mary would
learn anything new

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when she sees the apple.

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Could it be that there are fundamental
limits to what we can know

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about something we can't experience?

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And would this mean there are certain
aspects of the universe

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that lie permanently beyond
our comprehension?

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Or will science and philosophy allow
us to overcome our mind's limitations?