November 25, 2024 • 29 mins
Every cell in your body changes, so why do you have a sense of continuity of the self – as though you're the same person you were a month ago? What does this have to do with the watercraft of the Greek demigod Theseus, or the End-of-History illusion, or why you go through so much trouble to make things comfortable for your future self, even though you don't know that person? And if there really were an afterlife, what age would your deity make everyone for living out their eternities? Join this week for a two-parter about the mysteries of selfhood.
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Speaker 1 (00:05):
Although every cell in your body changes such that you
are never again the same person physically, and your neural
networks change every hour of your life as you absorb
new experiences. Why do you have an illusion of consistency,
as though you're the same person you were a week
(00:26):
ago or a year ago. What does this have to
do with the mythical watercraft of the Greek demigod Theseus?
What is the end of history illusion? And why do
you go through so much trouble to make things comfortable
for your future self even though you don't know that
(00:47):
person and you can be guaranteed that that person is
not going to feel the same way you do now.
And if there were an afterlife, what age would your
deity dial you to for living out eternity? Welcome to
Inner Cosmos with me David Eagleman. I'm a neuroscientist and
(01:08):
an author at Stanford and in these episodes we dive
deeply into our three pound universe to uncover some of
the most surprising aspects of our lives. Today, we're going
(01:30):
to talk about the notion of having a self and
what that has to do with our memory. And this
is a big topic, so we're going to do this
in two parts. Today, we're going to talk about how
and why we think of ourselves as lasting through time
and what that has to do with our memories. And
in next week's episode, part two, I'm going to talk
(01:51):
with my colleague, neuroscientist Michael Levin, one of the most
energized and original thinkers in the field, and I'm going
to talk with him about the way which memories can
be thought of like little creatures of their own that
carry messages in a bottle from one version of you
to the next. So for today, let's start in ancient Greece,
(02:13):
where the historian Bluetarch wrote about a tough puzzle that
had been floating around in the Greek philosopher circles, and
they were all arguing about it. The puzzle was this,
imagine the ship of Theseus. Theseus was the hero in
Greek mythology who slayed the minotaur. The idea is that
Theseus and his crew of Athenians sail back from Crete
(02:37):
and dock his wonderful ship. But then the ship sits
in harbor for a long time and one of the
planks starts to rot, so it gets replaced with new
and stronger timber, and then that happens with another plank
on the ship, and another, and eventually, with enough time,
the entire ship gets replaced, meaning that a single plank
(03:01):
is the same as what it was when the ship
first docked. And the question is is it the same
ship of Theseus or is it not his ship anymore?
Because every single part has been replaced. Plutarch suggested that
half the philosophers in Greece argue the ship is still
the same ship because it retains its identity despite the
(03:23):
changes to its parts, and the other half of philosophers,
he suggested, argued that the ship is not the same
ship because no part of it is the same. So
for thousands of years, the Ship of Theseus has been
a thought experiment that surfaces these tough questions about identity
and change. By the way, there are lots of variants
(03:46):
on this. My father had an axe in the garage,
and he would always hold it up and tell me
this was actually George Washington's axe. Oh, but the handle
has been replaced twelve times and the axe head has
been replaced for times. It was obviously a joke, but
it got me thinking from a young age about the
nature of identity in the face of change. Does something
(04:09):
retain its identity if all departs change? Now, why would
a neuroscience podcast care about the Ship of Theseus or
George Washington's acts. It's because that kind of wholesale replacement
is precisely what's happening to your brain and your entire body.
A big part of the mystery of selfhood has to
(04:32):
do with the fact that all the pieces and parts
that make up you are constantly turning over. Your body
is built out of thirty trillion cells, and this is
just cellular stuff. Every bit of the cells has a lifetime.
Most of the cells die or subdivide at some point.
(04:52):
But even those cells that stick around your whole life
and don't divide, like your neurons, they're totally different every
few years. Why because brain cells aren't made out of
something stable like metal or cement. Instead, they're made out
of the basic proteins and lipids and other molecules that
make up any cell in the body, and those things
(05:13):
aren't particularly stable. So every single neuron and every cell
in your body is like the Ship of Theseus. Every
part of it is getting rebuilt all the time, one
planket a time, or in this case one molecule at
a time. The pieces and parts of the cell have
no meaningful stability, and so a big part of all
(05:36):
that cellular machinery is simply building and rebuilding and rebuilding,
and in this way everything gets replaced. So who you
are physically changes all the time, and the question is
how does your self stay intact over this changing substrate.
The answer is it's not clear that it does. But
(06:00):
cognitively you have this illusion of stability. You are one being.
You've spent your whole life with a fixed history, as in,
I grew up here, here's my name, this was my hometown,
these are my parents. This is how my trajectory in
life has unfolded, leading me from here to there to there.
And so we tend to hold the impression that our
(06:23):
identities are something very stable, but in fact who you
are drifts in this light. It's always struck me as
funny to think about the notion of an afterlife, because
what age would you be Depending on when you get there,
you might be a very different person than you were
even five years before that. And so all this inspired
(06:44):
me to write a short story that's published in my
book Some sum and I'm going to read that story
to illustrate the questions of this episode. The story is
called Prism. God resolved at the outset that he wanted
every human to partippaid in the afterlife, but the plans
weren't thought out to completion, and immediately he began to
(07:07):
run up against some confusion about age. How old should
each person be in the afterlife. Should this grandmother exist
here at her age of death, or should she be
allowed to live as a young woman, recognizable to her
first lover but not to her granddaughter. He decided it
was unfair to keep people the age they were at
(07:29):
the end of their lives, when much of their beauty
and alacrity had been worn down. Allowing everyone to live
as a young adult proved an unviable solution, because the
afterlife quickly degenerated into unbounded sexual pursuits, and at middle
ages they talked only about their children and mortgages, making
(07:50):
conversations in the afterlife. Tedious God finally landed on an
ingenious solution while watching light diffract through a prism. So
when you arrive here, you are split into your multiple
selves at all possible ages. The you that existed as
a single identity is now all ages at once. These
(08:13):
pieces of you no longer get old, but remain ageless
into perpetuity. The ewes have transcended time. This takes them
getting used to The different beams of you might run
into each other at the grocery store, like separate people
do in earth life. Your seventy six year old self
may revisit his favorite creek and run into your eleven
(08:36):
year old self. Your twenty eight year old self may
break up with a lover and a diner and notice
your thirty five year old self visiting that spot, lingering
on the air of regret hanging over the empty seat. Typically,
the different youws are happy to see each other because
they possess the same name in a shared history. But
(08:57):
the ewes are more critical of yourselves than they are
of others, and so each you quickly identifies habits that
get under your skin. It's a fact of the afterlife.
Don't be surprised to discover that after decomposition into your
different ages, the different us tend to drift apart. You
(09:19):
discover that the you of eight years old has less
than common than expected with the U of thirty two
and the U of sixty four. The eighteen year old
you finds more in common with other eighteen year olds
than with your seventy three year old you. The seventy
three year old you doesn't mind a bit seeking out
meaningful conversations with others of the same generation. Beyond the name,
(09:44):
the us have little else in common, but don't lose hope.
The shared resume of life, parents, birthplace, hometown, school, years,
first kiss has a magnetic nostalgic pull. So once in
a while, the different yous organize a gathering like a
family reunion, bringing together all your ages into a single room.
(10:08):
At these reunions, the middle aged will delightedly pinch the
cheeks of the young, and the teenagers will politely listen
to the stories and advice of the elderly. These reunions
reveal a group of individuals touchingly searching for a common theme.
They appeal to your name as a unifying structure, but
they come to realize that the name that existed on earth,
(10:31):
the you that moved serially through these different identities, was
like a bundle of sticks from different trees. They come
to understand with awe the complexity of the compound identity
that existed on the earth. They conclude with a shudder,
that the earthly you is utterly lost, unpreserved in the afterlife.
(10:55):
You were all these ages, they concede, and you were none.
So we're changing all the time. But why is it
(11:18):
hard to keep track of these changes. Obviously it's because
everything in our lives and our biology changes so slowly.
It's like the hour hand of a clock. You can
see that it's moved, but you can't see it move.
In general, we can see change most readily in the
growth of our children. You look back at photographs from
(11:39):
a year ago on your phone and you can't believe
how much things have changed. But it's hard to keep
track of the changes in yourself. A friend of my
parents went to his high school reunion, which was taking
place at a hotel, and he went around looking at
the different conference rooms to figure out which one was
the correct class, because they were divided up by decades,
(12:00):
And he thought he found the right room, but he
popped his head in and he realized that's completely not
the right room. All of those are very old people.
And then he stepped back and looked at the sign
and realized that indeed this was the correct room, and
he too must presumably look that old to others, even
if he still thought of himself as young on the inside.
(12:21):
So it's hard to keep track of our own changes
because they happen slowly. But maybe the thing that binds
your self together across the ever changing physical substrate is
the one thing you have that remains constant, your memory.
Memory ties all these versions of you together. Memory serves
(12:43):
as the thread that weaves through all these transformations, anchoring
a sense of self. So that sounds very nice, but
there's a fundamental problem with this, which is that memory
itself is not stable. It drifts, and I've talked about
this in several episodes. Memory is not a faithful, unchanging
(13:03):
record of the past. It's instead a fragile brain state,
and it needs to be reactivated and reconstructed each time
you recall it. And in this process, memories morph, So
we can't really think of them as an archive. They're
more of a story which we continually rewrite. And that
(13:24):
would be fine to keep rewriting a story, except that
we assume at all times that our memories form the
core of a stable identity. So let me give an
example of how memories change Imagine that you and two
friends were at some rooftop party and you were best
friends since college, and the night was full of jokes
and old stories, and you remember feeling grateful for this
(13:47):
bond that you shared, and you can still picture the
three of you by the fireplace, vowing to never let
life pull you apart. But now, a year later, everything
has changed. Those two guys are now enemies. It all
fell apart because one of them had an affair with
the other's girlfriend. So now when you think back on
that rooftop party, you wonder was there something in the
(14:09):
way he and the other guy's girlfriend exchanged glances across
the room? You now think you sort of remember there
were little stolen looks, there was some subtle tension in
the air. Did your other friends sense that something was funny?
Even then, the memory that once felt warm and comforting
now feels different, like a scene in a movie that
(14:31):
you're watching for the second time but noticing new things now.
The past hasn't changed, but your present knowledge of what
came after that party colors the memory and reshapes it,
and it makes you question what was really there and
what you've unconsciously added. Memory is slippery, like that, the
more you revisit it, the more it shifts and blurs,
(14:53):
which reminds me of a great quotation from Sigmund Freud
on this topic. In eighteen ninety six, he wrote a
letter to to a colleague about quote, the material present
in the form of memory traces being subjected from time
to time to a rearrangement in accordance with fresh circumstances,
to a retranscription. And there's another quotation that I cite
(15:17):
often from a writer named John Dufresny, who once wrote
that quote, Memory is a myth making machine. What we
do is keep revising our past to keep it consistent
with who we think we are. So here's where we
are so far. Our biology is always changing, and so
the thing that crosses time is our memory. But even
(15:39):
that changes all the time, drifting or warping or disintegrating altogether.
And as a result, who you are is always on
the move. Now, I've been speaking as though we're not
always aware of so much change happening over time, But
of course we can come to be aware of this
in some circumstances. For example, when you look back at
a diary entry that you wrote some years ago, it's
(16:02):
often surprising how much you've changed, how much the person
who held that pen is a bit different than who
you are now. So we do confront this sometimes. But
what's weird is despite the massive changes that happen in
our past, we always think that there will be little
change in the future. We've changed a lot up until now,
(16:24):
but now we've settled into place and there won't be
much change from here. And this is a cognitive illusion
known as the end of history illusion. In other words,
we can recognize significant changes in ourselves when we think
about our past, but we underestimate how much we're going
to change in the future. We acknowledge that we've grown
(16:46):
or evolved, but we incorrectly assume that who we are
right now is pretty close to our final or mature
version of ourselves. This end of history illusion was first
studied by psychology just like Daniel Gilbert and his colleagues,
and they surveyed people on their values and their preferences,
their personality traits, their life goals, and across the board.
(17:09):
They found that people consistently believe that they've undergone more
change in the past than they will in the future.
But of course it's an illusion because change is a
continuous process. In other words, if I ask you now
if you've essentially finished changing in life, if you're likes
and personality have settled, you'll say yeah. But if I
(17:30):
track you down and ask you again in five years,
you'll say, actually, the past five years did hold a
lot of change for me, but now I've finally arrived
at my stable self. And it's the same story if
I survey you five years after that. And this is
problematic because, for example, we're always trying to predict our
future emotions. You think, oh, if I get that job promotion,
(17:54):
or if I'm in this relationship, or if I have kids,
or if I don't have kids, this will make me happy.
Or if I lose this job and I have to
find a new one, that's going to make me miserable.
This is what psychologists call affective forecasting, where we project
how we think we're going to feel, but it's based
on your current limited knowledge about the world, and that
(18:15):
might change. So why do we have an end of
history illusion. Well, presumably it's because it's easier for us
to see the past changes because we have memories and
experiences to draw from, but future changes are hidden in
the mists of the future. We don't know what they are,
so let me give you some concrete examples of this.
(18:36):
Think about the way we have our career goals. As
a thirty year old, you might look back and realize
your career aspirations have changed, maybe significantly, from the time
you were twenty, but you might assume that your current
career goals are unlikely to change much in the next
ten years, even though lots of people shift career paths
or professional interests throughout life. Or think about your music
(18:58):
preferences you are older. You may recognize that your taste
in music has evolved since your teenage years. Maybe you
went from popper rock to maybe jazz or classical. But
despite that, you're likely to believe that your current musical
preferences are going to remain stable for the rest of
your life, even though your musical tastes are going to
keep evolving with exposure to new genres and bands and
(19:23):
instruments that don't even exist yet. We're thinking about friendships.
In your early twenties, you might reflect on how your
circle of friends has changed from high school to college.
There's a big shift in relationships there, but you might
simultaneously feel certain that the college friends you have now
are going to be your closest companions for life. That's
(19:43):
a totally understandable position, but it underestimates how friendships shift
as you enter different life stages, like when you start
a family or you move to a new city. The
same reasoning applies to everything, So take hobbies and interest
When you're in your fish, you notice that you've taken
up new hobbies and given up old ones over the years,
(20:04):
but you'll generally believe that your current interests will remain
consistent for the coming decades, when in fact, new hobbies
and interests will still emerge. You just can't see that
because they're ensconced in the dark forest of the future.
Possibly there's some new technology that you're going to be
obsessed with that hasn't even been invented or named yet. Okay,
(20:26):
And the one that's really hard for us to admit
to is future changes in our political values and social beliefs,
and possibly religious beliefs. When you look back on any
of your beliefs from a decade ago, you can sometimes
see there have been some changes. But again, we tend
to assume that our current values are now locked into
(20:46):
place for the rest of our lives. We all fail
to anticipate that our worldview is going to continue to
get reshaped by life experiences, by new information, by changing
social contexts. In a decade, we might not be precisely
who we are right now. Now, this whole end of
(21:23):
history illusion wouldn't really matter for our lives, except that
it affects how we make decisions. Because so much of
what you do is in service to the assumed future you.
You suffer through courses and trainings now to make things
better for your future you. You sweat through a workout
(21:44):
so your future you will have a better body. You
put your money into retirement plans to make sure that
the future you has the resources that you predict that
stranger will need. The difficulty simply is that we're not
good predictors. You don't really know who that person is.
That person shares your name and your history, but the
(22:06):
fact is that person might be very different than the
current you. So you're donating your retirement money for this
future person that you can essentially guarantee will be not
who you currently believe. That person might vote for the
other political party, the what you would never vote for
and yet you're slaving away and handing over all your
(22:29):
money to that maniac. And you also do stuff assuming
the best about your future self, but sometimes that's not
useful either. We tend to assume that our future self
will be more motivated or disciplined than we are today.
So because of that, you might sign up for an
expensive gym membership believing that you'll be more committed in
(22:51):
the future, but then you don't really follow through. Your
future self isn't as on board with the plan as
your past self believed it would be. As a related example,
I'm chronically over committed because at every moment I assume
that my future self is going to be less busy
than I am now, and so I say yes to
(23:11):
future invitations or obligations like taking on big new projects
or attending multiple social events, And when the time arrives,
my future me wishes that my past me hadn't over committed.
And more generally, we fall victim to lots of planning fallacies.
We underestimate how long it's going to take to complete
(23:34):
some task. You might think cool, I can knock that
thing out in a week, and then you find that
it takes twice as long now. That happens because we
typically fail to correctly predict all the possible setbacks and
complexities that will run into in the future. My favorite
example of a planning fallacy is with a gentleman named
(23:55):
James Murray who in eighteen seventy eight set out to
write the for the English Dictionary, and the idea was
to capture all the words in the English speaking world
and give definitions for all of their various shades of meaning.
And this seemed like a big undertaking, but not big
enough that he couldn't complete it in a few years.
(24:16):
So he worked on this for thirty six years until
he died, and then several editors took up the mantle
after him, and the first edition of the Oxford English
Dictionary was finally completed seventy years after he began. He
totally misapprehended the size of the project, and if I
(24:38):
were here, I presumably would have done the same. So
as a result of this sort of planning fallacy, we're
constantly making decisions that our future selves are going to
regret or disagree with. Why. It's not because we're idiots now,
but instead because our circumstances and our preferences and our
(24:58):
priorities are to change over time. Okay, so let me
zoom back out to the big picture. We are creatures
who live and change through time, but we're yoked with
this illusion that we are unchanging, and so we misremember
our past and we work hard for future versions of
ourselves who we assume will be like us, but they
(25:20):
may not be. And by the way, there are all
kinds of complex relationships between your future self and your
past self through time, so it gets pretty crowded. Your
past self says, oh, I'm not gonna worry about my
future self, and your future self looks back and says,
what a jerk like. When people make the decision in
the short term to postpone their education or splurge on
(25:42):
some overpriced thing, and then your future self thinks, dang,
I wish I'd gone to that class or spent my
money on something more meaningful or necessary. This comes up
for many people. In terms of retirement savings. People will
make the decision to spend now rather than save for
their future self. They keep thinking, oh, I'll start saving later,
(26:03):
But then as retirement approaches, your future self feels mad
at your past self and wished as you had started
saving earlier, and I suspect this is true. Anytime we
choose instant gratification over long term goals, our future selves
look back and they're mad about it. And all this
highlights the challenge of balancing short term desires with long
(26:24):
term outcomes. In other words, your self in the moment
now versus yourself in the future. So let's wrap up.
In the next episode, Part two, we're going to dive
deeper into all these paradoxes of the self by talking
with my colleague neuroscientist Mike Levin, who wrote a recent
paper in which he pointed out that quote if we
(26:45):
do not change, learning and growth is impossible. If we
do change, does not the current self cease to exist
in an important sense end quote. So let's summarize where
we got in this episode. We began by looking at
the illusion of continuity, and we use the ancient thought
experiment of the ship of Theseus, where one plank of
(27:08):
the ship gets replaced at a time, and we can
ask is it still the ship of theseus after every
plank has been replaced. We looked at this question because
we are always surfing on top of constant physical changes,
and yet we perceive ourselves as consistent over time. The
planks and theseus's ship are the cells and molecules in
(27:30):
your body, and this foregrounds the question about what makes
you the same person over time. We asked the question
of whether we can really say that memory is the
thread holding identity together, because the truth is that memory
is far from reliable. It's constantly being rewritten. And finally,
(27:51):
we touched on a cognitive bias known as the end
of history illusion, which is where we massively underestimate how
much we're going to change in the future, even though
we're aware that we've changed in the past. We tend
to believe that our current tastes and values and personalities
are going to remain consistent from here on out, even
though we keep on changing throughout our lives. So you
(28:16):
can't actually be your past self. But as we'll see
in part two next week, we constantly try to reconstruct
that person. We constantly try to revivify that past self
based on the evidence provided by reinterpreting the clues that
are left by them. In other words, the memories that
(28:36):
are buried in the neural network. In this view, memories
are like a message in a bottle thrown from your
present self into the ocean for someone to find, and
that someone is a future you who you don't necessarily know.
(28:57):
Go to Eagleman dot com slash podcast for more information
and to find further reading. Send me an email at
podcasts at eagleman dot com with questions or discussion and
check out Subscribe to Inner Cosmos on YouTube for videos
of each episode and to leave comments until next time.
I'm David Eagleman and this is Inner at Cosmos.
Although every cell in your body changes such that you
are never again the same person physically, and your neural
networks change every hour of your life as you absorb
new experiences. Why do you have an illusion of consistency,
as though you're the same person you were a week
(00:26):
ago or a year ago. What does this have to
do with the mythical watercraft of the Greek demigod Theseus?
What is the end of history illusion? And why do
you go through so much trouble to make things comfortable
for your future self even though you don't know that
(00:47):
person and you can be guaranteed that that person is
not going to feel the same way you do now.
And if there were an afterlife, what age would your
deity dial you to for living out eternity? Welcome to
Inner Cosmos with me David Eagleman. I'm a neuroscientist and
(01:08):
an author at Stanford and in these episodes we dive
deeply into our three pound universe to uncover some of
the most surprising aspects of our lives. Today, we're going
(01:30):
to talk about the notion of having a self and
what that has to do with our memory. And this
is a big topic, so we're going to do this
in two parts. Today, we're going to talk about how
and why we think of ourselves as lasting through time
and what that has to do with our memories. And
in next week's episode, part two, I'm going to talk
(01:51):
with my colleague, neuroscientist Michael Levin, one of the most
energized and original thinkers in the field, and I'm going
to talk with him about the way which memories can
be thought of like little creatures of their own that
carry messages in a bottle from one version of you
to the next. So for today, let's start in ancient Greece,
(02:13):
where the historian Bluetarch wrote about a tough puzzle that
had been floating around in the Greek philosopher circles, and
they were all arguing about it. The puzzle was this,
imagine the ship of Theseus. Theseus was the hero in
Greek mythology who slayed the minotaur. The idea is that
Theseus and his crew of Athenians sail back from Crete
(02:37):
and dock his wonderful ship. But then the ship sits
in harbor for a long time and one of the
planks starts to rot, so it gets replaced with new
and stronger timber, and then that happens with another plank
on the ship, and another, and eventually, with enough time,
the entire ship gets replaced, meaning that a single plank
(03:01):
is the same as what it was when the ship
first docked. And the question is is it the same
ship of Theseus or is it not his ship anymore?
Because every single part has been replaced. Plutarch suggested that
half the philosophers in Greece argue the ship is still
the same ship because it retains its identity despite the
(03:23):
changes to its parts, and the other half of philosophers,
he suggested, argued that the ship is not the same
ship because no part of it is the same. So
for thousands of years, the Ship of Theseus has been
a thought experiment that surfaces these tough questions about identity
and change. By the way, there are lots of variants
(03:46):
on this. My father had an axe in the garage,
and he would always hold it up and tell me
this was actually George Washington's axe. Oh, but the handle
has been replaced twelve times and the axe head has
been replaced for times. It was obviously a joke, but
it got me thinking from a young age about the
nature of identity in the face of change. Does something
(04:09):
retain its identity if all departs change? Now, why would
a neuroscience podcast care about the Ship of Theseus or
George Washington's acts. It's because that kind of wholesale replacement
is precisely what's happening to your brain and your entire body.
A big part of the mystery of selfhood has to
(04:32):
do with the fact that all the pieces and parts
that make up you are constantly turning over. Your body
is built out of thirty trillion cells, and this is
just cellular stuff. Every bit of the cells has a lifetime.
Most of the cells die or subdivide at some point.
(04:52):
But even those cells that stick around your whole life
and don't divide, like your neurons, they're totally different every
few years. Why because brain cells aren't made out of
something stable like metal or cement. Instead, they're made out
of the basic proteins and lipids and other molecules that
make up any cell in the body, and those things
(05:13):
aren't particularly stable. So every single neuron and every cell
in your body is like the Ship of Theseus. Every
part of it is getting rebuilt all the time, one
planket a time, or in this case one molecule at
a time. The pieces and parts of the cell have
no meaningful stability, and so a big part of all
(05:36):
that cellular machinery is simply building and rebuilding and rebuilding,
and in this way everything gets replaced. So who you
are physically changes all the time, and the question is
how does your self stay intact over this changing substrate.
The answer is it's not clear that it does. But
(06:00):
cognitively you have this illusion of stability. You are one being.
You've spent your whole life with a fixed history, as in,
I grew up here, here's my name, this was my hometown,
these are my parents. This is how my trajectory in
life has unfolded, leading me from here to there to there.
And so we tend to hold the impression that our
(06:23):
identities are something very stable, but in fact who you
are drifts in this light. It's always struck me as
funny to think about the notion of an afterlife, because
what age would you be Depending on when you get there,
you might be a very different person than you were
even five years before that. And so all this inspired
(06:44):
me to write a short story that's published in my
book Some sum and I'm going to read that story
to illustrate the questions of this episode. The story is
called Prism. God resolved at the outset that he wanted
every human to partippaid in the afterlife, but the plans
weren't thought out to completion, and immediately he began to
(07:07):
run up against some confusion about age. How old should
each person be in the afterlife. Should this grandmother exist
here at her age of death, or should she be
allowed to live as a young woman, recognizable to her
first lover but not to her granddaughter. He decided it
was unfair to keep people the age they were at
(07:29):
the end of their lives, when much of their beauty
and alacrity had been worn down. Allowing everyone to live
as a young adult proved an unviable solution, because the
afterlife quickly degenerated into unbounded sexual pursuits, and at middle
ages they talked only about their children and mortgages, making
(07:50):
conversations in the afterlife. Tedious God finally landed on an
ingenious solution while watching light diffract through a prism. So
when you arrive here, you are split into your multiple
selves at all possible ages. The you that existed as
a single identity is now all ages at once. These
(08:13):
pieces of you no longer get old, but remain ageless
into perpetuity. The ewes have transcended time. This takes them
getting used to The different beams of you might run
into each other at the grocery store, like separate people
do in earth life. Your seventy six year old self
may revisit his favorite creek and run into your eleven
(08:36):
year old self. Your twenty eight year old self may
break up with a lover and a diner and notice
your thirty five year old self visiting that spot, lingering
on the air of regret hanging over the empty seat. Typically,
the different youws are happy to see each other because
they possess the same name in a shared history. But
(08:57):
the ewes are more critical of yourselves than they are
of others, and so each you quickly identifies habits that
get under your skin. It's a fact of the afterlife.
Don't be surprised to discover that after decomposition into your
different ages, the different us tend to drift apart. You
(09:19):
discover that the you of eight years old has less
than common than expected with the U of thirty two
and the U of sixty four. The eighteen year old
you finds more in common with other eighteen year olds
than with your seventy three year old you. The seventy
three year old you doesn't mind a bit seeking out
meaningful conversations with others of the same generation. Beyond the name,
(09:44):
the us have little else in common, but don't lose hope.
The shared resume of life, parents, birthplace, hometown, school, years,
first kiss has a magnetic nostalgic pull. So once in
a while, the different yous organize a gathering like a
family reunion, bringing together all your ages into a single room.
(10:08):
At these reunions, the middle aged will delightedly pinch the
cheeks of the young, and the teenagers will politely listen
to the stories and advice of the elderly. These reunions
reveal a group of individuals touchingly searching for a common theme.
They appeal to your name as a unifying structure, but
they come to realize that the name that existed on earth,
(10:31):
the you that moved serially through these different identities, was
like a bundle of sticks from different trees. They come
to understand with awe the complexity of the compound identity
that existed on the earth. They conclude with a shudder,
that the earthly you is utterly lost, unpreserved in the afterlife.
(10:55):
You were all these ages, they concede, and you were none.
So we're changing all the time. But why is it
(11:18):
hard to keep track of these changes. Obviously it's because
everything in our lives and our biology changes so slowly.
It's like the hour hand of a clock. You can
see that it's moved, but you can't see it move.
In general, we can see change most readily in the
growth of our children. You look back at photographs from
(11:39):
a year ago on your phone and you can't believe
how much things have changed. But it's hard to keep
track of the changes in yourself. A friend of my
parents went to his high school reunion, which was taking
place at a hotel, and he went around looking at
the different conference rooms to figure out which one was
the correct class, because they were divided up by decades,
(12:00):
And he thought he found the right room, but he
popped his head in and he realized that's completely not
the right room. All of those are very old people.
And then he stepped back and looked at the sign
and realized that indeed this was the correct room, and
he too must presumably look that old to others, even
if he still thought of himself as young on the inside.
(12:21):
So it's hard to keep track of our own changes
because they happen slowly. But maybe the thing that binds
your self together across the ever changing physical substrate is
the one thing you have that remains constant, your memory.
Memory ties all these versions of you together. Memory serves
(12:43):
as the thread that weaves through all these transformations, anchoring
a sense of self. So that sounds very nice, but
there's a fundamental problem with this, which is that memory
itself is not stable. It drifts, and I've talked about
this in several episodes. Memory is not a faithful, unchanging
(13:03):
record of the past. It's instead a fragile brain state,
and it needs to be reactivated and reconstructed each time
you recall it. And in this process, memories morph, So
we can't really think of them as an archive. They're
more of a story which we continually rewrite. And that
(13:24):
would be fine to keep rewriting a story, except that
we assume at all times that our memories form the
core of a stable identity. So let me give an
example of how memories change Imagine that you and two
friends were at some rooftop party and you were best
friends since college, and the night was full of jokes
and old stories, and you remember feeling grateful for this
(13:47):
bond that you shared, and you can still picture the
three of you by the fireplace, vowing to never let
life pull you apart. But now, a year later, everything
has changed. Those two guys are now enemies. It all
fell apart because one of them had an affair with
the other's girlfriend. So now when you think back on
that rooftop party, you wonder was there something in the
(14:09):
way he and the other guy's girlfriend exchanged glances across
the room? You now think you sort of remember there
were little stolen looks, there was some subtle tension in
the air. Did your other friends sense that something was funny?
Even then, the memory that once felt warm and comforting
now feels different, like a scene in a movie that
(14:31):
you're watching for the second time but noticing new things now.
The past hasn't changed, but your present knowledge of what
came after that party colors the memory and reshapes it,
and it makes you question what was really there and
what you've unconsciously added. Memory is slippery, like that, the
more you revisit it, the more it shifts and blurs,
(14:53):
which reminds me of a great quotation from Sigmund Freud
on this topic. In eighteen ninety six, he wrote a
letter to to a colleague about quote, the material present
in the form of memory traces being subjected from time
to time to a rearrangement in accordance with fresh circumstances,
to a retranscription. And there's another quotation that I cite
(15:17):
often from a writer named John Dufresny, who once wrote
that quote, Memory is a myth making machine. What we
do is keep revising our past to keep it consistent
with who we think we are. So here's where we
are so far. Our biology is always changing, and so
the thing that crosses time is our memory. But even
(15:39):
that changes all the time, drifting or warping or disintegrating altogether.
And as a result, who you are is always on
the move. Now, I've been speaking as though we're not
always aware of so much change happening over time, But
of course we can come to be aware of this
in some circumstances. For example, when you look back at
a diary entry that you wrote some years ago, it's
(16:02):
often surprising how much you've changed, how much the person
who held that pen is a bit different than who
you are now. So we do confront this sometimes. But
what's weird is despite the massive changes that happen in
our past, we always think that there will be little
change in the future. We've changed a lot up until now,
(16:24):
but now we've settled into place and there won't be
much change from here. And this is a cognitive illusion
known as the end of history illusion. In other words,
we can recognize significant changes in ourselves when we think
about our past, but we underestimate how much we're going
to change in the future. We acknowledge that we've grown
(16:46):
or evolved, but we incorrectly assume that who we are
right now is pretty close to our final or mature
version of ourselves. This end of history illusion was first
studied by psychology just like Daniel Gilbert and his colleagues,
and they surveyed people on their values and their preferences,
their personality traits, their life goals, and across the board.
(17:09):
They found that people consistently believe that they've undergone more
change in the past than they will in the future.
But of course it's an illusion because change is a
continuous process. In other words, if I ask you now
if you've essentially finished changing in life, if you're likes
and personality have settled, you'll say yeah. But if I
(17:30):
track you down and ask you again in five years,
you'll say, actually, the past five years did hold a
lot of change for me, but now I've finally arrived
at my stable self. And it's the same story if
I survey you five years after that. And this is
problematic because, for example, we're always trying to predict our
future emotions. You think, oh, if I get that job promotion,
(17:54):
or if I'm in this relationship, or if I have kids,
or if I don't have kids, this will make me happy.
Or if I lose this job and I have to
find a new one, that's going to make me miserable.
This is what psychologists call affective forecasting, where we project
how we think we're going to feel, but it's based
on your current limited knowledge about the world, and that
(18:15):
might change. So why do we have an end of
history illusion. Well, presumably it's because it's easier for us
to see the past changes because we have memories and
experiences to draw from, but future changes are hidden in
the mists of the future. We don't know what they are,
so let me give you some concrete examples of this.
(18:36):
Think about the way we have our career goals. As
a thirty year old, you might look back and realize
your career aspirations have changed, maybe significantly, from the time
you were twenty, but you might assume that your current
career goals are unlikely to change much in the next
ten years, even though lots of people shift career paths
or professional interests throughout life. Or think about your music
(18:58):
preferences you are older. You may recognize that your taste
in music has evolved since your teenage years. Maybe you
went from popper rock to maybe jazz or classical. But
despite that, you're likely to believe that your current musical
preferences are going to remain stable for the rest of
your life, even though your musical tastes are going to
keep evolving with exposure to new genres and bands and
(19:23):
instruments that don't even exist yet. We're thinking about friendships.
In your early twenties, you might reflect on how your
circle of friends has changed from high school to college.
There's a big shift in relationships there, but you might
simultaneously feel certain that the college friends you have now
are going to be your closest companions for life. That's
(19:43):
a totally understandable position, but it underestimates how friendships shift
as you enter different life stages, like when you start
a family or you move to a new city. The
same reasoning applies to everything, So take hobbies and interest
When you're in your fish, you notice that you've taken
up new hobbies and given up old ones over the years,
(20:04):
but you'll generally believe that your current interests will remain
consistent for the coming decades, when in fact, new hobbies
and interests will still emerge. You just can't see that
because they're ensconced in the dark forest of the future.
Possibly there's some new technology that you're going to be
obsessed with that hasn't even been invented or named yet. Okay,
(20:26):
And the one that's really hard for us to admit
to is future changes in our political values and social beliefs,
and possibly religious beliefs. When you look back on any
of your beliefs from a decade ago, you can sometimes
see there have been some changes. But again, we tend
to assume that our current values are now locked into
(20:46):
place for the rest of our lives. We all fail
to anticipate that our worldview is going to continue to
get reshaped by life experiences, by new information, by changing
social contexts. In a decade, we might not be precisely
who we are right now. Now, this whole end of
(21:23):
history illusion wouldn't really matter for our lives, except that
it affects how we make decisions. Because so much of
what you do is in service to the assumed future you.
You suffer through courses and trainings now to make things
better for your future you. You sweat through a workout
(21:44):
so your future you will have a better body. You
put your money into retirement plans to make sure that
the future you has the resources that you predict that
stranger will need. The difficulty simply is that we're not
good predictors. You don't really know who that person is.
That person shares your name and your history, but the
(22:06):
fact is that person might be very different than the
current you. So you're donating your retirement money for this
future person that you can essentially guarantee will be not
who you currently believe. That person might vote for the
other political party, the what you would never vote for
and yet you're slaving away and handing over all your
(22:29):
money to that maniac. And you also do stuff assuming
the best about your future self, but sometimes that's not
useful either. We tend to assume that our future self
will be more motivated or disciplined than we are today.
So because of that, you might sign up for an
expensive gym membership believing that you'll be more committed in
(22:51):
the future, but then you don't really follow through. Your
future self isn't as on board with the plan as
your past self believed it would be. As a related example,
I'm chronically over committed because at every moment I assume
that my future self is going to be less busy
than I am now, and so I say yes to
(23:11):
future invitations or obligations like taking on big new projects
or attending multiple social events, And when the time arrives,
my future me wishes that my past me hadn't over committed.
And more generally, we fall victim to lots of planning fallacies.
We underestimate how long it's going to take to complete
(23:34):
some task. You might think cool, I can knock that
thing out in a week, and then you find that
it takes twice as long now. That happens because we
typically fail to correctly predict all the possible setbacks and
complexities that will run into in the future. My favorite
example of a planning fallacy is with a gentleman named
(23:55):
James Murray who in eighteen seventy eight set out to
write the for the English Dictionary, and the idea was
to capture all the words in the English speaking world
and give definitions for all of their various shades of meaning.
And this seemed like a big undertaking, but not big
enough that he couldn't complete it in a few years.
(24:16):
So he worked on this for thirty six years until
he died, and then several editors took up the mantle
after him, and the first edition of the Oxford English
Dictionary was finally completed seventy years after he began. He
totally misapprehended the size of the project, and if I
(24:38):
were here, I presumably would have done the same. So
as a result of this sort of planning fallacy, we're
constantly making decisions that our future selves are going to
regret or disagree with. Why. It's not because we're idiots now,
but instead because our circumstances and our preferences and our
(24:58):
priorities are to change over time. Okay, so let me
zoom back out to the big picture. We are creatures
who live and change through time, but we're yoked with
this illusion that we are unchanging, and so we misremember
our past and we work hard for future versions of
ourselves who we assume will be like us, but they
(25:20):
may not be. And by the way, there are all
kinds of complex relationships between your future self and your
past self through time, so it gets pretty crowded. Your
past self says, oh, I'm not gonna worry about my
future self, and your future self looks back and says,
what a jerk like. When people make the decision in
the short term to postpone their education or splurge on
(25:42):
some overpriced thing, and then your future self thinks, dang,
I wish I'd gone to that class or spent my
money on something more meaningful or necessary. This comes up
for many people. In terms of retirement savings. People will
make the decision to spend now rather than save for
their future self. They keep thinking, oh, I'll start saving later,
(26:03):
But then as retirement approaches, your future self feels mad
at your past self and wished as you had started
saving earlier, and I suspect this is true. Anytime we
choose instant gratification over long term goals, our future selves
look back and they're mad about it. And all this
highlights the challenge of balancing short term desires with long
(26:24):
term outcomes. In other words, your self in the moment
now versus yourself in the future. So let's wrap up.
In the next episode, Part two, we're going to dive
deeper into all these paradoxes of the self by talking
with my colleague neuroscientist Mike Levin, who wrote a recent
paper in which he pointed out that quote if we
(26:45):
do not change, learning and growth is impossible. If we
do change, does not the current self cease to exist
in an important sense end quote. So let's summarize where
we got in this episode. We began by looking at
the illusion of continuity, and we use the ancient thought
experiment of the ship of Theseus, where one plank of
(27:08):
the ship gets replaced at a time, and we can
ask is it still the ship of theseus after every
plank has been replaced. We looked at this question because
we are always surfing on top of constant physical changes,
and yet we perceive ourselves as consistent over time. The
planks and theseus's ship are the cells and molecules in
(27:30):
your body, and this foregrounds the question about what makes
you the same person over time. We asked the question
of whether we can really say that memory is the
thread holding identity together, because the truth is that memory
is far from reliable. It's constantly being rewritten. And finally,
(27:51):
we touched on a cognitive bias known as the end
of history illusion, which is where we massively underestimate how
much we're going to change in the future, even though
we're aware that we've changed in the past. We tend
to believe that our current tastes and values and personalities
are going to remain consistent from here on out, even
though we keep on changing throughout our lives. So you
(28:16):
can't actually be your past self. But as we'll see
in part two next week, we constantly try to reconstruct
that person. We constantly try to revivify that past self
based on the evidence provided by reinterpreting the clues that
are left by them. In other words, the memories that
(28:36):
are buried in the neural network. In this view, memories
are like a message in a bottle thrown from your
present self into the ocean for someone to find, and
that someone is a future you who you don't necessarily know.
(28:57):
Go to Eagleman dot com slash podcast for more information
and to find further reading. Send me an email at
podcasts at eagleman dot com with questions or discussion and
check out Subscribe to Inner Cosmos on YouTube for videos
of each episode and to leave comments until next time.
I'm David Eagleman and this is Inner at Cosmos.
Host
David Eagleman
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