December 29, 2025 • 29 mins
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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
(00:46):
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 in 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
(02:12):
ancient Greece, where the historian Blutarch 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
(02:33):
Theseus and his crew of Athenians sail back from Crete
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,
(02:56):
the entire ship gets replaced, meaning that not a single
plank 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
(03:16):
half the philosophers in Greece argue the ship is still
the same ship because it retains its identity despite the
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
(03:37):
a thought experiment that surfaces these tough questions about identity
and change. By the way, there are lots of variants
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
(03:58):
been replaced for teen 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 retain its identity if all the parts change? Now,
why would a neuroscience podcast care about the Ship of
Theseus or George Washington's acts. It's because that kind of
(04:22):
wholesale replacement is precisely what's happening to your brain and
your entire body. A big part of the mystery of
selfhood has to 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
(04:43):
this is just cellular stuff. Every bit of the cells
has a lifetime. Most of the cells die or subdivide
at some point. 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,
(05:06):
they're made out of the basic proteins and lipids and
other molecules that make up any cell in the body,
and those things 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,
(05:27):
one molecule at a time. The pieces and parts of
the cell have no meaningful stability, and so a big
part of all 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
(05:48):
the question is how does your self stay intact over
this changing substrate. The answer is it's not clear that
it does. But 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
(06:12):
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 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
(06:35):
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 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.
(06:56):
God resolved at the outset that he wanted every human
to particip paid in the afterlife, but the plans weren't
thought out to completion, and immediately he began to 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
(07:19):
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 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
(07:41):
quickly degenerated into unbounded sexual pursuits, and at middle ages
they talked only about their children and mortgages, making 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
(08:04):
at all possible ages. The you that existed as a
single identity is now all ages at once. These 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
(08:26):
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 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
(08:47):
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 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
(09:09):
surprised to discover that after decomposition into your different ages,
the different us tend to drift apart. You 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
(09:29):
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, the
us have little else in common, but don't lose hope.
The shared resume of life, parents, birthplace, hometown, school, years,
(09:54):
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.
At these reunions, the middle aged will delightedly pinch the
cheeks of the young, and the teenagers will politely listen
(10:15):
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,
the you that moved serially through these different identities, was
(10:36):
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.
You were all these ages, they concede, and you were none.
(11:15):
So we're changing all the time. But why is it
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
(11:36):
growth of our children. You look back at photographs from
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
(11:57):
the correct class because they were divided up by decades,
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
(12:17):
if he still thought of himself as young on the inside.
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.
(12:39):
Memory ties all these versions of you together. Memory serves
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 letter
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.
(15:15):
And there's another quotation that I cite 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
(15:37):
crosses time is our memory. But even 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.
(15:57):
For example, when you look back at a diary entry
that you wrote some years ago, it's 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
(16:18):
always think that there will be little change in the future.
We've changed a lot up until now, 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
(16:40):
we underestimate how much we're going to change in the future.
We acknowledge that we've grown 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
(17:00):
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. 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
(17:23):
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 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.
(17:45):
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, or if I'm in this relationship,
or if I have kids, or if I don't have kids,
this will make me real 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
(18:05):
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 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,
(18:26):
but future changes are hidden in the midst of the future.
We don't know what they are, so let me give
you some concrete examples of this. 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
(18:48):
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 preferences. Are older, you may
recognize that your taste in music has evolved since your
teenage years. Maybe you went from poper rock to maybe
(19:08):
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 instruments that don't even exist yet.
We're thinking about friendships. In your early twenties, you might
(19:29):
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 a totally understandable position, but it underestimates
how friendships shift as you enter different life stages, like
(19:51):
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 fifth these you
notice that you've taken up new hobbies and given up
old ones over the years, 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.
(20:13):
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, 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.
(20:37):
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 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,
(21:02):
we might not be precisely who we are right now. Now,
this whole end of history illusion wouldn't really matter for
(21:26):
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 so your future you will
have a better body. You put your money into retirement
(21:49):
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 fact is that person might
be very different than the current you. So you're donating
(22:12):
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 what you
would never vote for and yet you're slaving away and
handing over all your money to that maniac. And you
also do stuff assuming the best about your future self,
(22:35):
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 the future, but then you don't
really follow through. Your future self isn't as on board
(22:56):
with the plan as your past self believed it. 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 future invitations or obligations like taking on
big new projects or attending multiple social events, And when
(23:19):
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 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.
(23:40):
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 James Murray who in eighteen seventy
eight set out to write the English Dictionary. And the
(24:01):
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. So he worked on this for thirty
six years until he died, and then several editors took
(24:23):
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 were here, I presumably would have done
the same. So as a result of this sort of
(24:43):
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 priorities are go to change over time. Okay,
so let me zoom back out to the big picture.
(25:04):
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 may not be. And by the way, there
are all kinds of complex relationships between your future self
(25:26):
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
some overpriced thing, and then your future self thinks, dang,
(25:46):
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,
But then as retirement approaches, your future self feels mad
(26:07):
at your past self and wishes 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 term outcomes.
In other words, your self in the moment now versus
(26:28):
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 do not change,
learning and growth is impossible. If we do change, does
(26:51):
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 the ship gets replaced
at a time, and we can ask is it still
(27:12):
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 your body, and this
(27:32):
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, we touched on a
(27:52):
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
(28:12):
changing throughout our lives. So you 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
(28:34):
other words, the memories that 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. Go to eagleman dot com slash
(28:59):
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
(00:46):
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 in 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
(02:12):
ancient Greece, where the historian Blutarch 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
(02:33):
Theseus and his crew of Athenians sail back from Crete
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,
(02:56):
the entire ship gets replaced, meaning that not a single
plank 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
(03:16):
half the philosophers in Greece argue the ship is still
the same ship because it retains its identity despite the
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
(03:37):
a thought experiment that surfaces these tough questions about identity
and change. By the way, there are lots of variants
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
(03:58):
been replaced for teen 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 retain its identity if all the parts change? Now,
why would a neuroscience podcast care about the Ship of
Theseus or George Washington's acts. It's because that kind of
(04:22):
wholesale replacement is precisely what's happening to your brain and
your entire body. A big part of the mystery of
selfhood has to 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
(04:43):
this is just cellular stuff. Every bit of the cells
has a lifetime. Most of the cells die or subdivide
at some point. 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,
(05:06):
they're made out of the basic proteins and lipids and
other molecules that make up any cell in the body,
and those things 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,
(05:27):
one molecule at a time. The pieces and parts of
the cell have no meaningful stability, and so a big
part of all 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
(05:48):
the question is how does your self stay intact over
this changing substrate. The answer is it's not clear that
it does. But 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
(06:12):
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 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
(06:35):
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 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.
(06:56):
God resolved at the outset that he wanted every human
to particip paid in the afterlife, but the plans weren't
thought out to completion, and immediately he began to 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
(07:19):
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 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
(07:41):
quickly degenerated into unbounded sexual pursuits, and at middle ages
they talked only about their children and mortgages, making 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
(08:04):
at all possible ages. The you that existed as a
single identity is now all ages at once. These 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
(08:26):
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 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
(08:47):
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 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
(09:09):
surprised to discover that after decomposition into your different ages,
the different us tend to drift apart. You 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
(09:29):
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, the
us have little else in common, but don't lose hope.
The shared resume of life, parents, birthplace, hometown, school, years,
(09:54):
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.
At these reunions, the middle aged will delightedly pinch the
cheeks of the young, and the teenagers will politely listen
(10:15):
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,
the you that moved serially through these different identities, was
(10:36):
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.
You were all these ages, they concede, and you were none.
(11:15):
So we're changing all the time. But why is it
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
(11:36):
growth of our children. You look back at photographs from
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
(11:57):
the correct class because they were divided up by decades,
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
(12:17):
if he still thought of himself as young on the inside.
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.
(12:39):
Memory ties all these versions of you together. Memory serves
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 letter
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.
(15:15):
And there's another quotation that I cite 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
(15:37):
crosses time is our memory. But even 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.
(15:57):
For example, when you look back at a diary entry
that you wrote some years ago, it's 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
(16:18):
always think that there will be little change in the future.
We've changed a lot up until now, 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
(16:40):
we underestimate how much we're going to change in the future.
We acknowledge that we've grown 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
(17:00):
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. 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
(17:23):
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 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.
(17:45):
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, or if I'm in this relationship,
or if I have kids, or if I don't have kids,
this will make me real 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
(18:05):
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 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,
(18:26):
but future changes are hidden in the midst of the future.
We don't know what they are, so let me give
you some concrete examples of this. 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
(18:48):
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 preferences. Are older, you may
recognize that your taste in music has evolved since your
teenage years. Maybe you went from poper rock to maybe
(19:08):
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 instruments that don't even exist yet.
We're thinking about friendships. In your early twenties, you might
(19:29):
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 a totally understandable position, but it underestimates
how friendships shift as you enter different life stages, like
(19:51):
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 fifth these you
notice that you've taken up new hobbies and given up
old ones over the years, 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.
(20:13):
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, 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.
(20:37):
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 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,
(21:02):
we might not be precisely who we are right now. Now,
this whole end of history illusion wouldn't really matter for
(21:26):
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 so your future you will
have a better body. You put your money into retirement
(21:49):
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 fact is that person might
be very different than the current you. So you're donating
(22:12):
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 what you
would never vote for and yet you're slaving away and
handing over all your money to that maniac. And you
also do stuff assuming the best about your future self,
(22:35):
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 the future, but then you don't
really follow through. Your future self isn't as on board
(22:56):
with the plan as your past self believed it. 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 future invitations or obligations like taking on
big new projects or attending multiple social events, And when
(23:19):
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 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.
(23:40):
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 James Murray who in eighteen seventy
eight set out to write the English Dictionary. And the
(24:01):
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. So he worked on this for thirty
six years until he died, and then several editors took
(24:23):
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 were here, I presumably would have done
the same. So as a result of this sort of
(24:43):
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 priorities are go to change over time. Okay,
so let me zoom back out to the big picture.
(25:04):
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 may not be. And by the way, there
are all kinds of complex relationships between your future self
(25:26):
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
some overpriced thing, and then your future self thinks, dang,
(25:46):
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,
But then as retirement approaches, your future self feels mad
(26:07):
at your past self and wishes 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 term outcomes.
In other words, your self in the moment now versus
(26:28):
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 do not change,
learning and growth is impossible. If we do change, does
(26:51):
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 the ship gets replaced
at a time, and we can ask is it still
(27:12):
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 your body, and this
(27:32):
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, we touched on a
(27:52):
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
(28:12):
changing throughout our lives. So you 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
(28:34):
other words, the memories that 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. Go to eagleman dot com slash
(28:59):
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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