[♪ INTRO]
We’ve all seen people act in ways that seem
totally irrational
—and for most of us, unpredictability is
just part of human nature.
But for scientists, when something is unpredictable,
that’s usually
a sign that they don’t fully understand
what’s going on.
Which isn’t really shocking when it comes
to people.
Our brains are just vastly more complex than
we have the tools
to understand right now.
But even if we can’t understand the brain
down to the deepest level,
some psychologists think that a set of ideas
borrowed from
quantum physics could help us make sense of
human behavior.
The notion is called quantum cognition—and
it isn’t suggesting
that our brains actually function at the quantum
level, just that
the mathematical tools of quantum mechanics
could help
make human behavior more predictable.
Now, the idea that this bizarre branch of
physics could be useful
for understanding the brain might seem like
a stretch—but the reason
it’s useful is because quantum mechanics
is all about statistics.
For instance, it’s impossible to know where
an electron is
at any given time; you can only know how likely
it is that,
when you measure it, you will find it in a
given place.
And that’s not because we’re bad at measuring—that’s
just how
the universe works on a fundamental level.
Statistics are also useful in other branches
of science, though,
for different reasons: They can help us understand
the big picture
even when we don’t know all the lower-level
details.
Like, you can use statistics to predict how
a group of people will vote
even if you don’t know what every individual
person will do.
And when it comes to the brain, there are
a bunch of low-level details
that we don’t understand.
For example, while neuroscientists have figured
out
where our short-term and long-term memories
are stored,
it’s still not clear how your brain selects
certain details
to remember and others to forget.
But in some cases, we can use statistics to
make decent predictions
about how people will behave even if we’re
not really sure why.
Traditionally, these cognitive models have
relied
on classical probability, which can be pretty
black or white.
Like, you either have three aces in your poker
hand or you don’t.
You either blew off that important project
or you didn't.
…or did you just kind of drag your feet
until it was too late?
See, human cognition is full of ambiguities,
and classical probability
just isn’t well-suited to handling them.
That’s where quantum mechanics might be
useful.
The quantum world is anything but black and
white,
but we’ve developed really powerful tools
to deal with that ambiguity.
And recently, psychologists have been exploring
whether or not
those tools could be reused to help understand
the brain.
In fact, quantum cognition models are already
performing as well
or better than classical models at predicting
some kinds of human behavior.
For example, it’s really tricky to predict
how humans
will make decisions.
Like, no matter how well you know someone,
the things they decide just don’t always
seem logical.
In the early 1990s, psychologists showed this
with a simple experiment.
In it, they asked 98 subjects to guess the
result of a coin flip.
If they were right, they’d win 200 dollars,
and if they were wrong,
they would owe 100.
After the first flip, everyone was asked if
they wanted to play again.
In general, both winners and losers wanted
to flip again,
which is reasonable since you’re more likely
to win money
after multiple rounds than lose it.
But that was not true for everyone.
Specifically, subjects who weren’t told
whether they’d won or lost
the first coin flip mostly decided not to
play again.
Even though the odds were in their favor.
From the perspective of classical cognition
models,
this doesn’t make any sense.
After all, if subjects were told whether they’d
won or lost,
neither result affected their decision—in
general,
they all wanted to play again.
This is called the sure thing principle because
all the options
seem to lead to the same result.
But somehow, not knowing made it not a sure
thing.
And while classical models of cognition struggle
to explain
how that could be, one principle from quantum
physics does
offer a way to understand it.
See, in the quantum world, just the fact that
something is unknown
can change the outcome of an event.
That’s the premise of the famous double-slit
experiment:
In one version of the experiment, physicists
fire a beam
of electrons at a detector.
In front of the detector there’s a barrier
with two slits in it.
When the beam is turned on, the electrons
strike the detector
in a pattern that looks a lot like the pattern
you get
when two sets of ripples interfere with each
other.
The weird thing is, even if you release the
electrons one by one,
you still get this interference pattern.
In other words, the electron is interfering
with itself.
That’s because it doesn’t exist in a single,
precise location,
so there’s some ambiguity about which slit
it passes through.
But, if you set up a sensor to measure which
gap each electron
travels through, this diffraction pattern
disappears.
So, the instant the electron’s position
is known,
the ambiguity is gone, and the interference
is, too.
So, broadly speaking, this shows that in quantum
mechanics,
simply not knowing can produce a totally unexpected
result.
Similarly, in the coin-flip experiment, just
the existence of doubt
changed the likelihood that someone would
play another round.
As illogical as these scenarios sound, though,
neither one
is unpredictable.
In physics, scientists use quantum probability
theory,
which is a model that accounts for the fact
that knowledge of something can affect the result.
And weirdly enough, you can apply the same
theory
to human decision-making to predict how people
will make decisions,
even if we don’t understand precisely why.
Psychologists were able to use this quantum
model to correctly predict
people’s decisions in the coin-flip experiment,
even when the classical model failed.
And they also applied it to the famous prisoner’s
dilemma.
The prisoner’s dilemma is a scenario in
which you imagine
that you and a friend are both arrested for
committing a crime.
If you both say nothing, you’ll each get,
say, a year in jail.
If you rat out your friend, you might get
off scot-free
while your friend gets a maximum sentence.
And if you both rat each other out, you’ll
both get a few years.
So, if your friend doesn’t say anything,
selfishly speaking,
it’s in your best interest to rat them out.
And if your friend does say something,
it is also in your best interest to rat them
out.
It’s another case of the sure thing principle.
And yet, many versions of this experiment
have shown that if someone
doesn’t know what the other is doing, they’re
less likely to snitch.
Even though it’s better for them to snitch
either way!
Just like with the coin flipping, this seems
to defy logic—
but quantum probability theory can accurately
predict that result.
In general, though, the way someone answers
a question
can be unpredictable for a lot of reasons.
In fact, just the order of questions you ask
someone
has a big effect on the answers they give.
For example, imagine that I ask you, “How
was your vacation?”
And after you answer, I might follow that
up with,
“How did you get along with your sister?”
But if I asked those questions in the opposite
order—
and if you’d gotten in a fight with your
sister, you might say that
you liked your vacation less than you would
have otherwise.
Which, from a purely logical standpoint, is
kind of weird.
Like, if you think of your brain as a computer,
it already has
all the information it needs to answer both
questions,
and the order of the questions doesn’t change
that…
but somehow the order can still change your
answer.
And classical models have trouble explaining
that,
but quantum mechanics might be able to help
here, too.
See, in quantum mechanics, things that seem
like basic math—
like multiplication—aren’t so straightforward.
For instance, A times B will often give you
a different answer
than B times A.
So quantum models have to account for those
weird rules
to make accurate predictions.
And oddly enough, psychologists have managed
to do a similar thing.
By using quantum-inspired math, they built
rules that account
for order into their models.
And because of that, they were able to do
something really unusual:
In 2014, they made a specific, numeric prediction
about how
an experiment would turn out before it even
happened.
That’s a run-of-the-mill step in lots of
kinds of science,
but it’s really rare in psychology.
Psychologists often don’t know enough about
the underlying causes
of a person’s behavior to make specific
predictions.
But in this experiment, a team of researchers
analyzed
70 national surveys conducted by Pew and Gallup
that
randomly ordered pairs of questions.
They made a specific prediction about how
the order of the questions
would affect the answers, and the results
proved they were right!
Which suggests there are ways to predict human
behavior,
even when it doesn’t seem to make logical
sense.
Human behavior isn’t the only element of
our cognition that can
be unpredictable, though.
Even the things we perceive can sometimes
seem inexplicable.
Think about one of those optical illusions
where the same image
can take on two different forms.
This is called bistable perception, and it’s
been baffling scientists
for hundreds of years.
For instance, this Necker cube was introduced
in 1832.
Now, you might perceive it as either jutting
out of the screen
or coming into it—and if you stare long
enough,
your perception will randomly switch back
and forth.
But why?
You’d think that one set of input information,
like the lines of the cube, should only be
able to create one image
in the brain.
Again, the tools of quantum mechanics can
give us a way to understand it.
In quantum mechanics, something like an electron
exists
in multiple positions at once—until you
observe it,
when those multiple possibilities instantaneously
collapse down to one.
This is called superposition, and similarly,
when you perceive
an optical illusion, it’s kind of like you’re
seeing it
in multiple states at once.
It’s just when you focus on observing the
object
that those multiple states collapse down to
one.
And there’s more: Different people see different
versions
of optica l illusions, but each person tends
to see one version
over the other.
That suggests that the illusion has a certain
probability
of being viewed in a certain state.
And that fits the analogy, because in quantum
superposition,
an electron has a certain probability of being
observed
in any given location.
So by using this same statistical approach,
we can at least
characterize the way our brains process optical
illusions,
even if we don’t fundamentally understand
why.
For example, in 2007 a team of scientists
modeled the brain’s response
to the Necker cube as a simple, two-state
quantum system.
That system modeled how often a person’s
view of the cube flipped
from one version to the other.
Then the scientists compared the frequency
of those flips
to two biological timescales: the amount of
time it takes the brain
to process new sensory input, and the amount
of time it takes us
to react to that new information.
When they compared this quantum-inspired model
to the real results
of past experiments, they found that it generally
predicted
the way people’s brains responded to this
illusion.
Now quantum mechanics and cognition might
seem about as far apart
as two scientific disciplines can get, but
this shows us why
it can be useful to look for answers in non-obvious
places.
Because in all of these situations, our friends
in physics
can make unpredictable humans a little easier
to understand.
Thanks for watching this episode of SciShow
Psych!
And if you’re interested in learning more
about the quantum world,
you can head over to our main SciShow channel
for more videos on that.
[♪ OUTRO]
