How do you know you’re not dreaming? - Daniel Gregory
You’re a butterfly, fluttering around
pursuing a butterfly’s whims.
Then you wake up.
But how do you know
you’re not dreaming now?
The answer might seem obvious,
but it’s actually very difficult
to explain how, definitively,
you know you’re awake.
So difficult, in fact, that it has puzzled
philosophers since ancient times.
In the butterfly scenario,
the ancient Chinese philosopher Zhuangzi
surfaced a mystifying possibility:
if we can dream of being
an entirely different creature,
who's to say we're not actually
a different creature dreaming
of being human?
Bizarre things happen in dreams:
you fly, or conjure an all-you-can-eat
dessert buffet out of thin air,
or get chased by witches through the halls
of your elementary school,
which suddenly looks a lot like Paris.
But the strange things that happen
in dreams don’t seem strange at the time.
So how do you know you’re not
in a dream right now
that will seem very strange
after you wake up?
Well, it is possible to notice
the strangeness of a dream
while you’re dreaming.
Lucid dreamers know they’re dreaming.
By definition, if you were having
a lucid dream, you would know it.
But all that proves is
that you’re not having a lucid dream—
it doesn’t prove you’re awake.
There has to be a surefire test—
something that never— or only—
happens when you’re awake,
something that never— or only—
happens in a dream.
Wake up.
No, that isn’t it—
you can wake up in a dream.
Pinch yourself.
If it hurts, aren’t you really awake?
Try to read or write something.
Run around the room.
Does your pace seem normal
or suspiciously slow?
Suspiciously fast?
Can’t tell? Try to remember
the last time you ran.
Actually, that brings us
to an even better test
from the 17th century French philosopher
René Descartes.
He pointed out that in our memories,
dreams are disconnected—
the events of a dream don’t fit
in to the chain of events
in our waking lives.
This seems rock solid, doesn't it?
You couldn’t possibly have swum
with dolphins in a nameless pink sea
between Christmas
and New Year’s Eve
because you didn’t leave Kansas
and you have the receipts to prove it.
Well, one of Descartes’ contemporaries,
the English philosopher Thomas Hobbes,
had something to say about that:
what if Descartes was performing his test
in a dream?
What if we ask an expert?
A neuroscientist can measure the activity
in different parts of your brain
and tell you whether you’re awake
or sleeping.
But that just brings us back to the idea
that any test you might use
to prove you’re awake
could take place in a dream.
So far, no one has found
a convincing response to this.
But let’s be real: there’s a whole lot
more detail in our waking experience
than in dreams.
We go to sleep and wake up again
day after day for many years,
and each new day is full of countless
people, places, things, experiences.
Even our memories, which capture
just a fraction of this experience,
contain an almost incomprehensibly vast
amount of detail:
we can recall a line from a favorite book
decades later,
remember the musty smell of its pages
and the taste of the lemonade we drank
while reading it,
remember a dream we had
about it and tell someone all this.
Isn't it ridiculous to suggest a dream
could ever simulate this richness?
Well, as the Persian philosopher
al-Ghazali pointed out,
in the same way we think we are now awake
having woken from dreams,
it is possible that we might wake
from our current state
into another state
of even greater wakefulness.
Which would mean we’re really
in a kind of dream-state
when we think we’re awake.
What philosophers really want to know
is what justifies our belief
that we’re awake.
We all want to believe things
because we have reasons for them,
not just because they seem right.
Sometimes, the biggest challenge is
to show why we should believe something
that seems completely obvious to us all.
