Katie Mack Lifealtering questions about the end of the universe TED
Lily James Olds: Hi, Katie, welcome.
Katie Mack: Thank you.
Thanks for having me.
LJO: So happy to have you.
I would love if, for those of us
who are not astrophysicists,
you could return and help us
give a little refresher
on how the universe did begin
and how we know that.
KM: Right, right, yeah.
So we know actually quite a lot
about the early universe,
about the beginning of the universe,
because we can actually see it.
And this is the wildest part of astronomy,
that we can see
the beginning of the universe.
So the universe is
about 13.8 billion years old,
and when we look out into the cosmos,
we see distant galaxies.
And when we look at the distant ones,
they’re all moving away from us.
And so for a long time,
there’s been this idea that, well,
if the galaxies are moving
away from us now,
they must have been closer
in the past.
The universe in the past
must have been smaller in some sense,
hotter and denser,
everything packed into less space.
And that’s the Big Bang theory,
the idea that the universe was smaller
and denser and hotter in the past.
And we got really direct
evidence of that in the 1960s
when we’re able to actually see the light
from the very early universe.
So let me take one more step back.
When we look at a distant galaxy,
the light from that galaxy
takes some time to reach us.
So we see, you know,
we see a galaxy shining.
That light might have taken
a billion years to cross the space
between there and here.
We can see galaxies that are so distant
that the light took 10 billion years,
even 13 billion years to reach us,
and the universe is only
13.8 billion years old.
So what happens if you look
at something so far away
that the light has taken
more than, you know,
more than 13 billion years to reach us?
What happens when you try
and look at something even farther?
Well, there’s a limit
to how far you can look,
the observable universe,
and that limit is defined
by how long it takes light to travel.
So if something is so far away
that the light would take
15 billion years to reach us,
we can’t see it because the light
hasn’t gotten here yet.
But if we look at something
that’s, you know, so far away,
the light’s taken 13.8
billion years to reach us,
then what we’re looking at is a time
when the universe was just beginning.
We’re looking at the light
from the very beginning of the universe
and what we should see,
if we look at something that far away,
is fire, right?
So we take this idea
that the early universe was hot and dense,
everywhere in the cosmos was, like,
filled with this sort of roiling plasma.
And so if we look far enough away,
we should see it,
because we’re looking so far back in time
that we’re looking at the time
when the whole universe was on fire.
And we do see that shockingly,
we actually do see that.
When we use microwave telescopes,
we see this background light
every direction we look.
You know, at the edges
of our vision, is this heat, this fire,
and we know that it’s heat,
we can analyze the spectrum of the light
and we can see that this microwave light,
this radiation,
is the kind of light you get
when something is just glowing
because it’s hot.
And so we can see
that every direction we look,
if we look far enough away,
we’re looking so far back in time
that we’re seeing a universe
that is still on fire.
So that’s the Big Bang.
Exactly what happened,
you know, around that time,
how that fire got started,
that’s a whole other very complicated
story that we’re still figuring out.
So we think that, you know,
before the fiery part there was
this inflation, this rapid expansion.
Before that, maybe
there was a singularity,
maybe not, we don’t know.
We don’t know what started
that rapid expansion.
But we do know that for the first
380,000 years of the cosmos,
it was this sort of,
all of space was filled with this fire.
And we know that because we can see it.
LJO: It’s amazing.
Well, let’s get into some
of the juicy specifics
of how exactly the universe might end.
I know that you’ve talked to many
other cosmologists yourself
and there are a lot
of different theories on this.
Where do you think we should begin?
Dealer’s choice.
What’s in store for us?
KM: Well, so the one that is,
as far as we know, the most likely,
the one that we talk about the most
in cosmology, is the heat death.
So this is what I discussed
in my TED Talk,
and the idea there is that, you know,
the universe is currently expanding.
Galaxies are getting farther
and farther apart from each other.
When we measured the expansion,
it turned out that it was not
slowing down at all,
it was actually speeding up.
And that was like if you throw
a ball up into the air,
it slows down for a little while
and then just shoots off into space.
It’s very similar physics,
and we didn’t have any idea
why that should happen.
So we still don’t know
why that’s happening.
We attribute it to something
we call “dark energy.”
We don’t know what dark energy is.
It’s just something that seems
to be pushing things apart,
making the universe expand faster.
And because of that,
it looks like we will end up
with everything, really –
you know, all the galaxies
really isolated,
the stars will die away.
The universe will get
very dark, very cold.
And you know, we’ll end up
with this basically empty,
cold, dark, lonely universe.
And that’s called the heat death.
The reason it’s called the heat death
is because, like …
Everything’s decaying into,
like, the waste heat of creation.
So, you know, just as you can’t have
a machine that’s perfectly efficient,
it’ll always lose a little bit
of energy through friction.
That’s a property of physics in general,
it’s called the second law
of thermodynamics.
Everything sort of decays
into entropy, into disorder,
and that is called heat
from a physics perspective.
So the heat death is when nothing is left
but the waste heat of the universe.
Which is part of why it’s fun
to talk about the alternatives,
because we don’t know for sure
that the heat death will happen.
Partially because we don’t know
what dark energy is.
We don’t understand this stuff
that’s making the universe expand faster.
Maybe it’s just a property
of space where, you know,
space just has this sort of,
expansion built in,
and it’ll keep going the way it’s going.
But maybe it’s something
that changes over time.
Maybe it’ll turn around
and we’ll get a big crunch
and everything will come back together.
Or maybe it’ll become more powerful.
And then you end up with something
called a “Big Rip,”
where if the dark energy
becomes more powerful,
it starts to not just move galaxies
apart from each other,
but actually expand the space in galaxies
and move stars away from galaxies
and then pull apart planets and stars
and eventually destroy
the entire universe.
So those are other possibilities
that I talk about in the book.
Because we don’t know what dark energy is,
and we don’t know for sure
what it’ll do in the future.
LJO: I want to open up to some
of the questions from the audience.
Vasily asks,
“Have you ever asked the question
‘If there were no universe,
what would there be?’
This leads to the question
of what will be after the universe ends?”
KM: So I think that gets
into tricky questions
of how do you define universe, right?
So you can define universe
as being everything,
and then it becomes
a less clear question.
What does it mean for something
other than everything?
Then, you know, if there is anything else,
it’s by definition part of the universe.
But one of the ways we often talk
about the universe in cosmology,
is we talk about the observable universe,
where the observable universe
is the part of the cosmos we can see,
where the light has had time
to reach us since the Big Bang.
So I talked about that before.
The edge of the observable universe
is where we see that Big Bang light.
The actual universe,
we think extends far beyond
the edge of the observable universe.
The observable universe is just
a perspective thing.
It’s like a horizon when you’re on Earth,
you can only see so far
because of where you’re standing,
but the Earth keeps going
beyond the horizon.
And similarly, with the universe,
we’re pretty sure that it extends
much, much farther than what we can see,
what we can observe.
But we can see the observable
universe and we can study,
we can learn about
the observable universe,
and we can’t get any information
about what’s beyond it.
So, you know, that brings up things
like a multiverse,
where you can have regions of space
that are so far away from us
that they’re effectively another universe,
and those regions can have
a totally different history,
a totally different future,
different laws of physics even.
So, there are possibilities
for things that carry on
long after our observable universe
is decayed into entropy
or maybe meets another fate.
And there are even possibilities
where there could be higher
dimensions of space,
like directions that we can’t conceive,
you know, space that’s separated from us
by some other dimension of space,
some other direction
that we don’t, you know,
perpendicular to all of our
spatial directions,
which I can’t sort of envision.
But mathematically,
that makes sense in some ways.
So there are those kinds of possibilities.
And you know, you can get
into really weird stuff
about the nature of space and time
with you if you really dig into it.
But in the book,
I really just talk about our observable
universe in terms of the fate of that,
because that’s all we can really study.
I do talk a little bit
about the multiverse
and the possibilities
of other parts of space.
But in terms of what happens
when our universe is destroyed,
I mean, it depends on how it’s destroyed,
whether there’s, you know,
the observable universe is over
but there’s more space beyond it or not.
And that’s all the realm
of speculation at the moment.
LJO: So I want to switch
gears a little bit,
because one of the articles
that you wrote fairly recently
talked about how time and space
might not be real,
and how there might be a deeper,
more abstract mathematical
reality to the universe,
and that time and space
might just be what we perceive.
Can you tell us more about this?
How is this possible?
Talk about your mind doing backflips.
KM: Yeah, yeah, this is really wild.
So I first heard about this
a couple of years ago
where somebody was talking about how,
if you do calculations of particles
interacting with other particles,
like the kind of stuff relevant
to particle collider experiments
where you’re slamming protons
into each other
and measuring what happens
to the particles that come out,
there are ways to do those calculations
where you can kind of put them
into an abstract mathematical format
and do the calculation.
And then you get the same answer
as if you do the calculation
the usual way,
assuming, you know, it’s actually
particles moving through space
and interacting with each other
in space and time.
And since there are ways
to do some of these calculations
without making use
of the ideas of space or time,
you just have this sort of abstract
mathematical space,
it sort of suggests that maybe space
and time are not helping you
and not necessary for understanding
how these processes work.
And there is actually a lot
that you can calculate in physics
at the sort of, subatomic scale,
where space and time
are not salient variables.
They’re not part of the calculation.
And you get the right answer
when you do that.
And that sort of hints at this idea
that maybe space and time
are not the fundamental things
that govern how the universe works,
that you don’t have to assume
that, you know,
everything happens in a background
of a space measured by time.
If you talk to the theoretical physicists
who are working in these areas
and are actually doing these calculations,
doing these equations,
they will say things like,
“Oh yeah, we’ve known for years
that space and time are not fundamental.”
And you’re like, “Wait, what?”
LJO: I missed that memo.
KM: Yeah, no, totally.
And you dig down into it and they say,
“Well, you know, maybe they’re emergent.”
Maybe it’s like, you know,
they’re sort of real.
Like, we live in space,
we experience time.
But the actual, sort of,
fabric of the universe
is some other mathematical space
that just doesn’t map well
to space and time.
That’s not the same kind of thing,
doesn’t follow the same kind of rules.
But in some sense, you know,
maybe we are mathematical,
you know, some kind
of instantiation of mathematics
rather than objects in space
existing in time.
And that’s the more fundamental thing.
And it’s just that because of our
perspective, because of our experience,
we think we see objects in space and time.
In fact, that is not what
the universe is really made of.
LJO: I love that.
You know, it turns out
you are also a poet.
I don’t want to put you on the spot,
but I’m wondering,
I really love your poem “Disorientation,”
and I feel like it states
this really beautifully, actually.
I was wondering if you’d be willing
to read the last few stanzas?
KM: Sure, yeah, I can do that.
Yes, this was a poem I wrote
a few years ago,
and I wrote it
as a Twitter thread actually,
just because I thought
it would be kind of fun.
So each stanza is a tweet.
But it sort of encapsulates
how I think about the universe.
So, yeah, this is the last bit.
I want you to believe that the universe
is a vast, random, uncaring place
in which our species, our world,
has absolutely no significance
And I want you to believe
that the only response
is to make our own beauty
and meaning and to share it while we can
I want to make you wonder
what is out there.
What dreams may come in waves of radiation
across the breadth of an endless expanse.
What we may know, given time,
and what splendors
may never, ever reach us
I want to make it mean something to you.
That you are in the cosmos.
That you are of the cosmos.
That you were born from stardust
and to stardust you will return.
That you are a way for the universe
to be in awe of itself.
LJO: I love that.
Thank you so much, Katie.
Thank you for such a thoughtful
and engaging conversation.
It’s really been such a pleasure.