February 28, 2019 • 37 mins
How long has the Universe been cooking, and how do we know?
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Episode Transcript
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Speaker 1 (00:07):
Hey, Jorge, I've been meaning to ask you a really
important question. Yeah, go ahead, How old are you? How
old am I? That? Isn't that a rude question? It's
a little bit rude, but I want to mask it
by saying that I'm interested scientifically. I just want to know, like,
how did the Jorge begin? Did you start with a
big bang? Well, I'm not sure how my mom would
describe it. Am I getting better with age? Is that
(00:30):
kind of why you're asking? Yeah, it's Orge like a
fine wine that just gets better and better and more valuable,
or sort of like yesterday's banana. I have been working
on my earthly bouquet and under tones of cherry and oak.
I'll give you ninety points on the wine scale. Don't
you think we should focus on bigger topics? Perhaps? Yeah?
(00:51):
I think asking the age of stuff is a really
good way to figure out like where it came from
and why it's important and uh, and you know where
it's going to go and the whole context of every thing.
So yeah, I'm interested in how old you are, But
I'm also interested in how old the Earth is, or
how old the Solar system is, or how old the
galaxy is or even how old is like everything? You
(01:11):
want to be rude to everything. Yeah, I want to
ask your mom if she was around during the Big
Bang and so she can tell us all about it.
Your mom is so old she witnessed the Big Bang. Hey, look,
you're the one who brought your mom into this. Hi'm
(01:42):
Borning and I'm Daniel, and I'm about forty two years old.
Forty two years is the perfect age, actually, since that's
the answer to life, the universe and everything. Yeah, that's
why I brought it up, because you know, I'm the
answer to everything. They didn't notice you highly avoided staying
in your age. I thought I was doing. Did you
(02:03):
think that was sly? I just kind of avoid that,
didn't Yeah, and now that's double stubble sly. Oh my goodness,
can you can you go for a triple sly? Well,
let me tell you from the advanced age of forty
three that forty two is a good year. You should
enjoy yourself while you're young. You should go out there
and you know, enjoy your fitness and your your flexibility,
(02:25):
because when forty three comes around, everything changes, really peak life,
no jokes aside. For me, every year has been better
than the last so so far, forty three is the
best year I've ever had. Awesome? Oh what are we
talking about? This is our podcast Daniel and Jrnean explained
the universe. This is not just us chatting about random stuff.
(02:46):
This is our podcast where we try to explain the
whole universe to you, from front to back, from start
to finish. Today's topic how old is the universe? How
long has all of creation been around this amazing, beautiful, crazy,
chaotic mess that we find ourselves in. How long has
(03:07):
this party been going on? Are we at the beginning
of the party? Is a party ending? We're the best
moments of the party in the very early evening and
we've missed it already. Is the universe equivalent of forty two?
Or is it all downhill from here? That's right. Let's
hope that, like my life, every year in the universe
just gets better than the last. Right, that would be
pretty nice. Um, But I think it's a it's a
(03:29):
really important question. It's interesting not just from a you know,
academic physics point of view, like can we figure this out?
But I think it's one of these great questions that
touches on something. I think everybody wants to know the
answer to right, like how did it all start? And
where is it? Where is it going to go? Yeah,
it's pretty amazing to imagine not knowing how old you are.
Can you can you imagine not knowing how old you are?
(03:51):
That is kind of hard to imagine. I think actually
a lot of people in the world used to not
know like when they were born or how old they were,
and their parents were to tell them, oh, you were
born in the summer, it was several years ago. And
you know, I think a lot of people don't keep
track of their age. But you're right. For most modern people,
we know exactly how old we are, and that is
a big part of our identity. Yeah, I wonder if
you could figure it out, Like if you if I
(04:11):
went into your brain and erased that little bit of
neurons that store how old you are, if you could
piece it together just from your memories. I think if
you slice my brain open, yeah, you would find rings
and probably be able to count them and figure out
how old that was. Don't recommend doing that at home.
By the way, people said, where your old book comes from? Them? Yeah,
(04:32):
if I was a fine one, I think I would
be I would taste them sassy but unpretentious. Yeah, and
I'm a little nerdy, just a little bit of nerty,
just a little PhD in physics, nerdy but not not overpowering,
just enough in its undertones. Yeah, but yeah, I imagine
how disorienting it would be not to know how old
you are. Absolutely, I guess I'm trying to say. It's
(04:53):
that it's important to our identity to know how old
we are. Yeah, it is. And it's important identity to
know how old human civilization is, Like what is our history?
How long have people have been crawling along this planet?
How long have people been people? Right? That tells you, um,
you know of something about the context and of your
own life. And I think even more interesting is how
(05:13):
long our lives are compared to how long the world
has been around? You know, like we live a hundred years?
Is that long compared to the lifespan of the Earth
or in the universe? Is the universe two hundred years
old and I'm gonna live a hundred or is it
a tiny flicker in this vast, incredibly old universe? Right?
I think that helps us understand like whether we mean
(05:34):
anything spoiler, we don't yeah, kind of like where does
it Where do our lives fit in the history of
everything else? Yeah? And uh, even more interesting, I think
the unanswerable is not just a question of how long
are our lives compared to the history of the universe
so far, but how much history is left in the universe? Right?
Are we in the very, very beginning stages of the universe?
(05:56):
Is the universe of baby or is it middle age? Right?
We have a whole other podcast about that. So these
questions are important, I think. Yeah, I feel like we're
going through puberty right now, at least the United States.
Maybe your voice is already pretty low for going through puberty, Harry.
I'm not gonna ask you if you're growing hair in
any new places. I don't want to know. Is the
universe growing hair in new places? I hear that things
(06:17):
are pretty hairy in Mars. Black holes are growing hair.
People talk about hairy black holes these days. That's totally
a physics topic. Are black holes black haired or blonde? Well,
that's the question, is like, how many characteristics can a
black hole have? You know, because in the in the sense,
it's just a collection of matter compressed down to a
tiny scale. I know, black holes can rotate. We know
(06:38):
they have mass, and the question is, you know, basically,
can they have other attributes? You know? Okay, so this
is a really interesting and important question. How old is
the universe? And we were wondering how many people out
there know how old the universe is? Yeah, which is
interesting from two points of view. One is do people care?
How they spend any time thinking about it? Is it
important to people? And two, if they do care, do
(07:01):
they know the right answer or they operating under completely
false pretenses for how old kind of creation is? Yes, So,
as usual, Daniel went out there to his university and
asked the question how old do you think the universe is?
Here's what people had to say. I think thirteen billion years?
And do you know how we know that number? I
(07:23):
believe we look way out as far as we can
and detect the early gases from the universe, and then
we extrapolate based on the distance we're looking. I think
something like that fifty walk one years, fifty one years?
(07:43):
Oh wait, wait, world or inniversity, the universe, the university
and the universe to bill two billion? And do you
know how we know the age of the universe by
the Big Bang? Yeah, big, big theory and looking at
how far the stars are right two? Not the university,
(08:04):
the whole universe. Oh, I'm sorry, villain. All right, And
do you know how we know the age of the universe?
How do we measure it? Starts six billion years? Okay?
And you know how we measure the age of the universe.
I'm guessing it has to do with some type of
carbon dating materials that don't all right, cools, thanks, billion
(08:27):
years billions that your best guests older than twenty six
years old? And you know how we measure the age
of the universe and the idea or how would you
figure it out if you had to? I don't know,
grabbing ripples biologist, all right, thanks very much? All right,
pretty good. A lot of pretty good guesses, right, Yeah,
A lot of people guess sort of in the range
(08:48):
of billions of years, right, which is totally respectable. Um.
I think my favorite answers were the people who misunderstood
my question and they thought I was asking them how
old is the university and which it just turned fifty
at a big party, etcetera. But when they said fifty,
I didn't really understand that misunderstood. I thought for a
moment that they thought the universe was fifty years old,
(09:08):
and I thought, oh my god, I've met some really
young Earth creation is how do I respond, you know,
like to keep a straight face. I'm trying to be respectful,
you know. Um, and then I understood, oh no, they
just missed her mishearth question. Well, when you're young and
you're in college, the university is your universe in a way, right, Yeah, exactly,
that is the in their whole life. Um. I like
(09:28):
the guy who said, I don't know at least twenty
six years old, right, which is tells you a little
bit how self centered some college students are. But you know,
everybody gave it their shot. He's like, yeah, the universe
was here when I was born, so obviously at least
twenty six years old, that's right. And maybe that's the
only information that matters to that guy, you know, like,
who cares as long as it was around for me,
nothing else is important. Yeah, I guess his universe started
(09:50):
twenty six years ago. Yeah exactly. But you know he's
actually using a strategy to measure the universe which scientists use,
which is how old is stuff in the universe? The
universe has to be at least as old as that.
So while his you know, focus on himself, isn't that
helpful in determining the age of the actual universe. He's
got a good idea there about how to figure it out.
(10:10):
How old is the oldest thing that I know about?
That should give you give you at least like a
minimum age of the universe. Yeah, exactly, so he even
though he's a biologist, he sort of invented that strategy
on the fly. Well, I think it's important. Let's start,
first of all, talking about what it means to ask
how old the universe is? Like, what is the age?
What does the term the age of the universe mean? Yeah,
(10:33):
that's right, that's the kind of answer somebody would give it.
They're trying to evade a question, right, how old you Well,
what do you mean by age? I mean, do you
mean conception moment of birth? Right? Um. But there's actually
a really good analogy there, because human age is a
little fuzzy. Like if you're conceived on a certain day
and then you're born premature, you know you are older
(10:53):
than you otherwise would have been, right, Um. Whereas if
you stayed in your mother's womb longer, you're technically younger,
even though you know it doesn't really matter, which is
kind of arbitrary, right because technically you're body and your brain,
all your parts started earlier than your birth. Yeah, and
we're not taking a position here, and there's a fetus alive,
(11:17):
and maybe that's why, maybe that's why we do that.
But you know, actually I heard that in other cultures
they define age a little differently, like in someone like
in in the US, when you're born year zero, right,
and the clock starts then. But in other cultures, when
you're born, you're one, and your age increases in the
new year, and everybody goes up one year in the
new year, where the concept of age is like how
(11:38):
many years have you been around in not exactly how
many years since your moment of birth. Um, So the
age of the universe is sort of a similar question, right,
Like how do you define the zero with the moment
of the universe equals zero? T equals zero. Yeah, let's
(11:59):
let's by what it means tigal zero. So what what
I physicists mean usually when they say T equals zero, Well,
it's not terribly well defined, is the problem. What we
can do is we can say, we know when now is,
and we can walk backwards from now to what we
know to be a very hot and dense state in
the very early moments of the universe, right like a
(12:20):
big primordial hot plasma which is nasty and wet and
all sorts of stuff is happening right like a baby
when it's born, like a baby, exactly, a big hot,
nasty mess. It probably wasn't as loud, I don't know,
maybe it was. Actually there was very on acoustic oscillations,
so it could have been a lot of screaming going
on UM. And we understand that very well, like we
can propagate that forward to get to our universe, we
(12:41):
can go backwards. But the problem is that just before
that is very fuzzy for us, Like we can't see
past that. For those of you who heard our episode
about the baby universe, we can't see earlier than like
three eighty thousand years UM after the Big Bang, and
so we don't exactly know what happened then and so
exactly how to define it. It's not clear like you'd
(13:02):
like to say T equal zero is the big Bang? Right? Yeah?
Isn't that what they usually mean that the universe started
with the Big Bang or we don't know, right, except
that we don't really have a great definition of what
the Big Bang is, right, Like, we don't know what
was the Big Bang? Was it a singularity that then exploded? Um?
Was it you know, some weird quantum blob? Was it inflotons?
(13:23):
Like that? Whole process is still very mysterious to us.
So we don't know exactly what happened and exactly how
long it took, so we can do you just blew
my mind a little bit. Yeah, scientists think Tiko zero
is the moment possibly of the Big Band, but you're
saying it's possibly, Like we don't really know what happened
around the time of Tiko zero. Yeah, and the I mean,
(13:44):
the whole definition of the Big Bang is still a
kind of bit fuzzy, Like some people think the Big
Bang is sort of still happening. Like what was the
Big Bang? It was this inflation of a dense amount
of matter into a hot promodial gas that was on
a macroscopic scale, right, really fast inflation and took less
than ten to the minus thirty seconds, right, and that
ever since then, things have been expanding, But things are
(14:06):
still expanding and they're still inflating, like we have dark energy,
which is just like a modern day analogy of of inflation.
So from some point of view, you could say, like,
the Big Bang is still banging. So then when do
you put to equal zero from the beginning of the
Big Bang? Like, we don't really understand very well the
physics of what happened in the early days, so it's
hard to define what T equal zero is. So you mean,
we can look back in our history, and there you
(14:29):
get to a point where you can look beyond and
you just assume that there's some sort of event beyond that.
But we can't see that's right. You don't have records
of your of yourself beyond pictures of you when you
were one year old, Like you don't you have no
idea what you look like before you were one years
old exactly. And so what you can do is you
can extrapolate. You can say, like, well, I know how
it happened when I went from one to two and
(14:50):
two to three and three to four, and I understand
the biology of and so I can extrapolate backwards from
one and think about what zero must have been like
and when zero was right, how long it took to
get to one, which is really the question when you
when you were conceived probably yeah, exactly. But if you
suspect that the physics happening down there between zero and one,
you know, just after the moments of the Big Bang,
(15:11):
we're different, we're interesting, um or maybe not typical of
what happened the rest of your life, then there's a
lot of uncertainty how to do that extrapolation. You can't
just blindly extrapolate, like what if the physics before I
was one years old were totally different, which means I
could be older than one year old when I think
I'm one year old. Yeah exactly. And it's not that
we think the laws of physics were different, but you
(15:33):
don't just different stuff was happening. Stuff we haven't seen, stuff,
we haven't had a chance to understand, um stuff. So
you know, we're extrapolating down, down, down, down down. But
we get to a region where we have don't really
have a lot of data to extrapolate into, so we're
skeptical of that extrapolation. But this is a very technical
discussion of like exactly when ti equal zero is. The
(15:54):
good news is doesn't really matter. What do you mean,
it doesn't matter. We just talk about how important was.
It doesn't really matter exactly when you define to equal zero,
because this uncertainty is a small number compared to the
age of the universe. Like we can extrapolate all the
way from now back to you know, less than a
million years after the Big Bang whatever that was, right, um,
(16:17):
And so there's an uncertainty there of like you know,
a million years, a couple of million years whatever for
what happened before the part we can extrapolate beyond. But
that's a small fraction we think of the age of
the universe. So if you want to say how old
is the universe, you can sort of sweep that question
under the rug. You can say, well, you know, how
old is it? How far back can we see? And
that's really to the age of the universe. So if
(16:39):
I said, Daniel, I hear you're forty three years old
plus or minus a million years, you would just sweep
that under the rug. I would say, no, that's an
accurate statement or a correct statement. Oh that's right. Technically
you are yeah plus or minus a million yeah, more
plus than minus but um, yeah, exactly. But I think
(17:00):
a better analogy would be like, you know, I'm forty
three plus or minus a day, you know, or a second.
Right there, These are details on the scale of the
times we're talking about. But you know, we want our
listeners to really understand the nitty gritty, and so the
exact definition the age of the universe is a little
bit fuzzy because those first few fractions of a second
especially are not well understood. Okay, so when we say
(17:23):
the age of the universe, we really mean how old
the universe is since some mysterious thing happened called the
Big Bang. That's right, exactly, and even deeper, right, we
don't know what happened before that, So it's just an
arbitrary thing to call that t equal zero. Right. It
could have been that before the Big Bang there was
another universe which had like a big bang of its
(17:45):
own and a big crunch. It's not really a different universe.
It's just like part another cycle. And this could have
been happening forever. So when you talk about the age
of the universe, you really can only talk about the
age since this early state that we understand. What happened
before that is a little question mark, Like the universe
could have just started before that it could have gone
on forever before that. Okay, let's let's get into how
(18:07):
we know all this stuff, but first let's take a
quick break. Okay, Daniels, settle this for us. How old
do physicists think the universe is? Years old? I mean,
(18:31):
that's how long? So what else is important? Um? You know,
the most accurate age of the universe currently is thirteen
point eight billion years. That's how long we think the
universe has been expanding since that hot, dense, nasty mess
at the very beginning. Okay, And just to put them
into perspective, the Solar system is four point five billion
(18:53):
years old, that's right. So solar system has only been
around for the last third of this party. There was
ten billion years almost when we didn't even have our star, right, Wow,
So the two thirds of the universe there was nothing
where we are. Oh, there might have been stuff, right,
there might have been other stars, there might have been
globular clusters or gas or whatever. But our star took
ten billion years to even form. Wow. Okay. And by that,
(19:17):
by the same account, the Earth itself is about four
billion years old, that's right. Yeah, it took less than
a billion years for life to start on Earth. Yeah,
and then to put that in scale, my families university,
you see, Irvine is fifty years old, right, so now
the party has started. Well, the United States is only
about It always blows my mind a little bit. In
(19:39):
the United States, it's only like two d and fifty
years old, lessan two fifty years old. I know. My
brother keeps reminding me of that because his university is
like three times as old as our country. Right. He's
at Oxford, so they have traditions, they have like probably
have silver ware over there that's older than our country.
So he's he's a younger brother and he's like trying
to find something to get to tab over. You aren't
(20:02):
always aren't younger brothers always doing that? No, he is
an academic rock star at Oxford, and so he gets
to um, he gets to look down and the rest
of us at fairly new universities. Okay, so thirteen point
eight billion years old? That's how old the universe we
think it is? And how do how do we know that?
How do we know there is there a birth certificate?
Is there like DNA evidence? Well, I've been asking your mom,
(20:24):
but she claims had not been around then. So we
have to figure it out for ourselves. Um, there's basically
two ways that we we know the age of the universe,
And this is really classic science strategy. Is like, find
two completely separate, independent ways of asking the same question,
and then if they agree, then awesome. You think probably
you haven't figured out and if they don't agree, then
(20:46):
you know something's wrong. Like two independent experts, yeah, or
two suspects more like like if you're a detective, you're
trying to figure out, um, you know, who did something.
You find two suspects, you separate them, You ask them
questions separately. If they tell you all the same details,
they're probably telling the truth, right. If they give you
totally different stories, then you know they're lying. So science
is sort of like that. Okay, so what's the first
(21:06):
way that we know how old the universe is? The
first way is just looking for old stuff. Like if
you find something in the universe that's fifty billion years old,
then you know the universe is at least fifty billion
years old. Right, It's not very complicated. So you just
look around and you try to figure out how old
is the stuff around us, And that's it's a sort
of a lower limit on the age of the universe.
(21:26):
So if you find a rock that's sixty billion years old,
then you know the universe must be at least sixty
billion years old, that's right. Yeah. Or if you find
an unpaid bill from fourteen billion years ago, right, then
you know you know your universe is about to end,
that's right. You know exactly they're coming for you. Um, yeah,
and um. But that's a tricky thing to do, right,
(21:48):
how do you know the age of stuff? Right? We've
changed one question how do you know the age of
the universe into another question, which is how do you
know the age of stuff we see around us? Right? Yeah, Well,
what's the oldest stuff that we know about? Then? Yeah,
the oldest stuff that we know about is stars basically,
I mean, there's this a caveat there with the cosmic
microwave background, which we we know, um is a little
(22:10):
bit older, but that's more difficult to age. But direct
stuff that we can see that we can ask the
question how old is it our stars? And we look
around and we look for really really old stars and
and and this is a tricky thing to do. But
what you can do is you can look for blobs
of stars they're called globular clusters. These are collections of stars.
(22:30):
There's sort of like many galaxies. I mean, they have
a whole different name from them because of the sized distinction.
But they're called globular clusters. He didn't like mini galaxies galaxinos.
I thought that would have been good glaxin exactly. That
sounds like a nice pasta. I'll have the galaxins with anchovies, please. Um. Yes.
So you look at these globular clusters and you ask
(22:52):
how old are they? How old are the stars in
these globular clusters. And it's hard to know how old
an individual star is, but you can look at a
group of them and you can figure out how old
that group is, really, yeah, based on which ones are
still there and which ones are not there anymore. And
the reason is that stars have different life spans. Right,
So you form a bunch of stars, and um, they
(23:13):
form out of gas and dust. They coalesce with gravity,
and you get some really big ones and you get
some really little ones. Now, the big ones burn really
fast and they don't last very long, and the little
ones they burn a long time. They're like saving their fuel.
Remember stars burned by compressing hydrogen, right, and then they
glow and they burn it's its fusion and you can
listen to our podcast episode about that if you're curious
(23:34):
about that. Um But the big ones burn out pretty quickly.
So if you're looking at a population of stars really
really far away and you notice that they still have
a bunch of big ones in them, you know it's
pretty young because those ones would have burned out already
if it was old, like the cluster itself is young.
Like the cluster itself is young, exactly. And if you
find a club a group of stars the globular cluster
(23:55):
that only has little stars and it left, then you
know it's pretty old, and because has been time for
all the bigger stars to burn out. So what's the
oldest star that we know about? Or how old are
the oldest stars that we know about? Well, this is
really fascinating. It's been controversial because this is a hard
thing to do. You have to know how far these
things are away. You have to measure their light. There's
(24:15):
a connection between the color of the star and its size,
so it's a lot of intermediate steps. Right, you see
the color that tells you the size that you can
make a distribution of the sizes. There's a lot of
steps that go along, and there's a lot of uncertainty
and um. Things happen very quickly in the beginning of
a life cycle of a globular cluster, like the big
bright stars burn out fast. Near the end, things happen
(24:37):
more slowly, which means for really old stuff, the uncertainties
are pretty large. Like it's hard to tell the difference
between a ten billion year old globular cluster and an
eleven billion year old, but between one and two billion
is easier. So people have been looking at these things
for a while, and the oldest ones we found are
something like thirteen billion years old. That's a very recent estimate.
(24:59):
A till like twenty years ago, people thought they had
found globular clusters that were like twenty billion years old
or even thirty billion years old. Did you say thirty thirty? Yeah,
they think so, maybe the universe is thirty billion years old.
Well that's what they thought. For a while. They had
this one measurement from the stars that was saying like
twenty or thirty billion years old, and they thought, well,
let's compare that to the measure to other ways we
(25:21):
can measure the age of the universe. Now the most
current one that they in the end, they found some
some mistakes and they updated it, and they weren't like
you know, um, somebody goofed by adding one plus one
making three. You know, we just got a better understanding
of how stars evolved and how they burn and how
to do these calibrations. And now the more recent updates
are like thirteen billion years old. But for a while
it seemed like those globular clusters were suggesting the universe
(25:45):
is older than twenty billion years. So so there are
things out there in the universe that we're there when
the universe started that are still around today. Well not quite.
When the universe started, right, We're looking at stars, and
you know the universe started, there was the Big Bang.
There's a mess of plasma things spread out and cooled off,
and then stars formed from that gas and dust. Those
it called the first generation stars. None of those stars
(26:07):
are still around. We can't see those stars. Nobody's ever
seen those We're looking for them. It's people want to
understand it, but nobody's seen those stars. The o G
stars exactly back when stars were cool, man, back when
they were hot. Um, yeah, and then those didn't last
very long. And then they know they burned, they cool,
they exploded supernovas, and you have this, they gather their
back together. You have the second generation of stars. Remember
(26:30):
stars are in this cycle, right, They burn, they then
they explode and their fuel gets spread out into the universe.
Then the gathered back together and make another cycle. And
so the second or third generation of the sort of
the oldest stars that we can see so far. And
that's why it's a lower limit, right, we see something
super old. We don't know if the universe is older,
how much older than that the universe is. We just
(26:51):
know it's at least that old. It's like finding a
relic from an ancient civilization. You know that the civilization
is at least at all, but it could have been
around for much longer. Just because you haven't found something older,
it doesn't mean that it wasn't older. That's right, exactly.
It's such a lower limit. And currently that lower limit
is about thirteen billion years old. That's the oldest thing
that we found. So we're seeing things from the very
(27:13):
very early universe, not exactly from the beginning, right, but
from very very early on, which is pretty awesome. Right,
that's like the ancient history of the universe. It's I
think that's super cool. Yeah. Imagine like coming up to
these clusters and you're staring at something that's been around
for thirteen billion years old. Yeah, that would be pretty amazing. Yeah. Well,
I mean I'm already just flabbergasted looking down at the Earth. Right,
(27:35):
the Earth has been around for five billion years. It's
such an ancient rock. It's seen so much history. I
think about that when I you know, we just walk
across the planet, I wonder like, who else is stepped here.
That's one of the things that makes me love those
um footprints, Right, you can see like footprints of dinosaurs
from hundreds of millions of years ago, like they were
just like walking along boop um. You know, so much
(27:55):
has happened on this planet. We don't we're not even
aware of. There's so much history that's just been lost
that will never know. Okay, So that's one way we
know how old d universe is. What's the other way
we know? The other way is by looking at the
expansion of the universe. We know that the universe is
spreading out. Things are moving away from us, and they're
(28:17):
moving away from us faster and faster every year, and
we can measure that. We look out in the universe
and we see how fast things are moving away from us.
We can measure that by looking at how the light
from them is stretched. Things that are moving away from
you have their light waves stretched out longer, they turn
more red. Things that are moving towards you have their
light waves squeezed, they turn more blue. This is the
(28:38):
Doppler effect. It's the same effect that makes like a
police siren sound different as it's approaching you and leaving you. Right,
So we can use that to measure how fast things
are moving away from us. And if you remember our
podcast episode about dark energy and the expansion of the universe,
we have these really cool standard candles are called supernova
type one a supernova, and we we know how bright
(29:00):
they should be, and we can look at them, we
can measure their velocity, we know how far away they are,
so use that to measure how fast the universe is expanding.
That's important because remember we talked about the definition of
the start was really what we're doing when we're measuring
the age of the universes, we're saying how long has
the universe been expanding since that hot date. And if
you know, um, the expansion rate, then you can extrapolate backwards.
(29:23):
So we we we hit the rewind button from what
how fast we think the universe is expanding, and that
makes the university you watch it in reverse, makes the
universe go down, down, down, down down into a very
small blob. Yeah, exactly. The Ebreody starts talking finding because
of backwards. Yeah. And the critical thing is that you
have to measure the rate, right We have to know
(29:44):
the expansion rate to know how fast to rewind, and
we have to know the expansion right now, and the
expansion made a billion years ago and ten billion years ago.
And we can do all that because remember, the further
we look out into space, the further we're looking back
into history, and we can see the expansion and right now,
we can see it a while ago, we can see
it a long time ago. Like the history of the
universe is written out there in the stars, like you
(30:07):
can tell, yeah, exactly, how fascinating we're expanding throughout the
history of the universe. Yeah, and our history is out
there also. You know, light left the Earth um when
you were ten, and you you know, did something embarrassing
at your cousin's birthday party. Light from that event left
the earth and is still out there, and somebody could
capture it and see that, right, even though it happened
years ago, So all that information is still out there. Yeah,
(30:30):
so watch out, So watch out. Light come back and
and expose your ten year old antics. That's right. Well,
when the aliens come, they'll have seen it, right, so
they'll know who's been naughty and who's been nice. Santa
is an alien? Oh? Did I just reveal that on
the air. Oops? Yes, Santa is an alien. Um. I
mean Santa can do a whole bunch of stuff that
(30:52):
nobody else can do, right. I think having him be
an alien with supertech is really the only reasonable expert
would explain it. Santa myth boom, We just saw that
mystery right there. Well, this is a perfect point to
take a break. So if you know the expansion rate
(31:18):
the universe, you can rewind back and we actually measure
the expansion RDE two different ways. One is just by
looking at how things are moving right right these stars.
The other is by looking at the cosmic microwave background.
This is the light from the very early moments of
the universe. That also tells us how old the universe is. Yeah,
it contains an incredible amount of information about what was
(31:40):
going on in the early universe, how much dark matter
there was, how much normal matter there was, how dense
it was, all of that stuff and all that information
in the end can tell you about the expansion rate
of the universe. Um. But you can extract the expansion
rate directly from that. That's actually the most precise way
to do it UM. And then once you know the
expansion rate, you can rewind the universe to figure out
(32:01):
how old it is. And that's the measurement that tells
us it's thirteen point eight billion years, and the uncertainty
on that it's about twenty one million years. So it's
pretty accurate plus or minus twenty one million years, depends
on your scale. But it's kind of interesting that, you know,
scientists hit the rewind button, right, we look at into
the stars, we hit we pressed the rewind button. We
see it all compressed, and then we sort of stop
(32:23):
once it gets really small, right, because we a we
can't rewind further, but also kind of conceptually right, like
we we can't imagine there being anything before that or
we can't imagine anything surviving being that small. Yeah, and
we have to ask questions like what does it even mean?
You know, Um, space and time started at the Big Bang?
So can you count before the Big Bang? You get
(32:45):
into really really difficult philosophical waters. Absolutely, um. And you know,
it's only recently that we've known this, Like this seems
to like going to be an important piece of information.
It tells me something about who I am and how
to live my life and how meaningless it is. But
it's sort of a new piece of information. You know,
Like a hundred years ago, people thought the universe was
steady state, right, that there was just a bunch of
(33:07):
stars out there and they've basically always been there, and
the universe wasn't expanding or contracting. It didn't have a
interesting history or a moment of birth. It's just been
around forever. This was a hundred years ago, right, only
only a hundred years ago, so from most of human history.
First of all, for most of the ministry, we didn't
understand anything about anything, right, so we were basically completely
all ignory missus um. You just exalted most of humanity.
(33:30):
But go ahead, I mean, in the best possible. Way
Um but yeah, um, And only about a hundred years
ago do we even figure out that there might have
been a beginning, that there was this expansion, which suggests,
you know, that that that there was that if you
rewound it, you got back to a very early, hot,
nasty state. A hundred years ago, we thought the universe
(33:51):
had been around forever, right, So yeah, like forever infinity right? Yeah?
So what was that like to learn that the universe, uh,
to go from age of the uni versus infinity to
agees you know, in the in the billions of years.
And it wasn't until the fifties that we had any
sort of accurate estimate because these things are hard to measure.
It's taken decades to get the technology and the math
and the physics models. So it's in the fifties that
(34:12):
really had the first accurate estimate of the universe's age
about fourteen billion years wow. Okay, so the universe is
thirteen point eight billion years old plus or minus twenty
one million years old. And so what does that mean?
What does that What does that tell us about how
the universe came to be or where it's all going?
(34:35):
It tells us something about how far we are along.
You know, we know that we've we've been around for
long enough for galaxies to form, right, for galaxies to
spin for a while, for stars to form and explode
and coalesce again in form and explode. Right, we're not
in the very first few moments of the universe. But
we don't really know much more than that. Yeah, and
more important, we don't even know how old the universe
(34:56):
is going to be, right, We don't know how old
the universe is going to be around. So we could
be in a very early part of the universe, or
we could be in a really late part of the universe.
We don't really know. No, we have no idea exactly. Um,
it could be that in a trillion years. There are
life forms that are studying the age of the universe
and they think about this little this first little bit,
the first fifteen billion years as like the big bang.
(35:19):
Right to them, this could have just been like the
engine just getting started, you know, platform from stars and galaxies.
We don't know, and we don't know if this part
of the age of the universe is typical, right, Like,
it could be that things go along and everything turns
to black holes and they have like only black holes
for a trillion years. Right, Um, so we really don't know.
(35:39):
When is the puberty of the universe? Right things changing?
Is it already grown up? We don't know. So maybe
the real question we should be asking, the one that's
less rude, is how young the universe is? Young? Is
the universe exactly? Hey, universe, how do you feel? You're
feeling pretty good? You got some joint pain. You've been
planning for your retirement. Yeah, you know, like if you
(36:01):
knew you were going to live to a thousand years old,
you would say things like, oh, I'm only forty two
years young instead of forty two years old. That's right.
If I knew I was going to live to a thousand,
I would have started saving for retirement a lot, a
lot earlier. You want to be retired for nine thousand,
nine hundred and sixty years. No, honestly, I'm never going
to retire. I mean, I have tenure. Why should ever
(36:22):
retirement to sit in my office for the next year
and you're already retired mentally mentally retired? You know you
do your best work and you have tenure. That's exactly
the point. You're free to think and expand and go
to crazy places in your career, like recording a podcast
with a cartoonist, right, yeah, sure, yeah, And the universe
(36:43):
is fifty years old. Universe's fifty years young, alright, everyone.
So that's the answer to the question how old is
the universe? And how do we know? Or how young
is the universe? How young isn't the universe? Oh my god, Universe,
you look good. You're looking sparkly. That's right, keep burning bright, Universe.
(37:04):
You're happy to be around. See you next time. Thanks
for tuning in. If you still have a question after
listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
at Facebook, Twitter, and Instagram at Daniel and Jorge that's
(37:26):
one word, or email us at Feedback at Daniel and
Jorge dot com.
Hey, Jorge, I've been meaning to ask you a really
important question. Yeah, go ahead, How old are you? How
old am I? That? Isn't that a rude question? It's
a little bit rude, but I want to mask it
by saying that I'm interested scientifically. I just want to know, like,
how did the Jorge begin? Did you start with a
big bang? Well, I'm not sure how my mom would
describe it. Am I getting better with age? Is that
(00:30):
kind of why you're asking? Yeah, it's Orge like a
fine wine that just gets better and better and more valuable,
or sort of like yesterday's banana. I have been working
on my earthly bouquet and under tones of cherry and oak.
I'll give you ninety points on the wine scale. Don't
you think we should focus on bigger topics? Perhaps? Yeah?
(00:51):
I think asking the age of stuff is a really
good way to figure out like where it came from
and why it's important and uh, and you know where
it's going to go and the whole context of every thing.
So yeah, I'm interested in how old you are, But
I'm also interested in how old the Earth is, or
how old the Solar system is, or how old the
galaxy is or even how old is like everything? You
(01:11):
want to be rude to everything. Yeah, I want to
ask your mom if she was around during the Big
Bang and so she can tell us all about it.
Your mom is so old she witnessed the Big Bang. Hey, look,
you're the one who brought your mom into this. Hi'm
(01:42):
Borning and I'm Daniel, and I'm about forty two years old.
Forty two years is the perfect age, actually, since that's
the answer to life, the universe and everything. Yeah, that's
why I brought it up, because you know, I'm the
answer to everything. They didn't notice you highly avoided staying
in your age. I thought I was doing. Did you
(02:03):
think that was sly? I just kind of avoid that,
didn't Yeah, and now that's double stubble sly. Oh my goodness,
can you can you go for a triple sly? Well,
let me tell you from the advanced age of forty
three that forty two is a good year. You should
enjoy yourself while you're young. You should go out there
and you know, enjoy your fitness and your your flexibility,
(02:25):
because when forty three comes around, everything changes, really peak life,
no jokes aside. For me, every year has been better
than the last so so far, forty three is the
best year I've ever had. Awesome? Oh what are we
talking about? This is our podcast Daniel and Jrnean explained
the universe. This is not just us chatting about random stuff.
(02:46):
This is our podcast where we try to explain the
whole universe to you, from front to back, from start
to finish. Today's topic how old is the universe? How
long has all of creation been around this amazing, beautiful, crazy,
chaotic mess that we find ourselves in. How long has
(03:07):
this party been going on? Are we at the beginning
of the party? Is a party ending? We're the best
moments of the party in the very early evening and
we've missed it already. Is the universe equivalent of forty two?
Or is it all downhill from here? That's right. Let's
hope that, like my life, every year in the universe
just gets better than the last. Right, that would be
pretty nice. Um, But I think it's a it's a
(03:29):
really important question. It's interesting not just from a you know,
academic physics point of view, like can we figure this out?
But I think it's one of these great questions that
touches on something. I think everybody wants to know the
answer to right, like how did it all start? And
where is it? Where is it going to go? Yeah,
it's pretty amazing to imagine not knowing how old you are.
Can you can you imagine not knowing how old you are?
(03:51):
That is kind of hard to imagine. I think actually
a lot of people in the world used to not
know like when they were born or how old they were,
and their parents were to tell them, oh, you were
born in the summer, it was several years ago. And
you know, I think a lot of people don't keep
track of their age. But you're right. For most modern people,
we know exactly how old we are, and that is
a big part of our identity. Yeah, I wonder if
you could figure it out, Like if you if I
(04:11):
went into your brain and erased that little bit of
neurons that store how old you are, if you could
piece it together just from your memories. I think if
you slice my brain open, yeah, you would find rings
and probably be able to count them and figure out
how old that was. Don't recommend doing that at home.
By the way, people said, where your old book comes from? Them? Yeah,
(04:32):
if I was a fine one, I think I would
be I would taste them sassy but unpretentious. Yeah, and
I'm a little nerdy, just a little bit of nerty,
just a little PhD in physics, nerdy but not not overpowering,
just enough in its undertones. Yeah, but yeah, I imagine
how disorienting it would be not to know how old
you are. Absolutely, I guess I'm trying to say. It's
(04:53):
that it's important to our identity to know how old
we are. Yeah, it is. And it's important identity to
know how old human civilization is, Like what is our history?
How long have people have been crawling along this planet?
How long have people been people? Right? That tells you, um,
you know of something about the context and of your
own life. And I think even more interesting is how
(05:13):
long our lives are compared to how long the world
has been around? You know, like we live a hundred years?
Is that long compared to the lifespan of the Earth
or in the universe? Is the universe two hundred years
old and I'm gonna live a hundred or is it
a tiny flicker in this vast, incredibly old universe? Right?
I think that helps us understand like whether we mean
(05:34):
anything spoiler, we don't yeah, kind of like where does
it Where do our lives fit in the history of
everything else? Yeah? And uh, even more interesting, I think
the unanswerable is not just a question of how long
are our lives compared to the history of the universe
so far, but how much history is left in the universe? Right?
Are we in the very, very beginning stages of the universe?
(05:56):
Is the universe of baby or is it middle age? Right?
We have a whole other podcast about that. So these
questions are important, I think. Yeah, I feel like we're
going through puberty right now, at least the United States.
Maybe your voice is already pretty low for going through puberty, Harry.
I'm not gonna ask you if you're growing hair in
any new places. I don't want to know. Is the
universe growing hair in new places? I hear that things
(06:17):
are pretty hairy in Mars. Black holes are growing hair.
People talk about hairy black holes these days. That's totally
a physics topic. Are black holes black haired or blonde? Well,
that's the question, is like, how many characteristics can a
black hole have? You know, because in the in the sense,
it's just a collection of matter compressed down to a
tiny scale. I know, black holes can rotate. We know
(06:38):
they have mass, and the question is, you know, basically,
can they have other attributes? You know? Okay, so this
is a really interesting and important question. How old is
the universe? And we were wondering how many people out
there know how old the universe is? Yeah, which is
interesting from two points of view. One is do people care?
How they spend any time thinking about it? Is it
important to people? And two, if they do care, do
(07:01):
they know the right answer or they operating under completely
false pretenses for how old kind of creation is? Yes, So,
as usual, Daniel went out there to his university and
asked the question how old do you think the universe is?
Here's what people had to say. I think thirteen billion years?
And do you know how we know that number? I
(07:23):
believe we look way out as far as we can
and detect the early gases from the universe, and then
we extrapolate based on the distance we're looking. I think
something like that fifty walk one years, fifty one years?
(07:43):
Oh wait, wait, world or inniversity, the universe, the university
and the universe to bill two billion? And do you
know how we know the age of the universe by
the Big Bang? Yeah, big, big theory and looking at
how far the stars are right two? Not the university,
(08:04):
the whole universe. Oh, I'm sorry, villain. All right, And
do you know how we know the age of the universe?
How do we measure it? Starts six billion years? Okay?
And you know how we measure the age of the universe.
I'm guessing it has to do with some type of
carbon dating materials that don't all right, cools, thanks, billion
(08:27):
years billions that your best guests older than twenty six
years old? And you know how we measure the age
of the universe and the idea or how would you
figure it out if you had to? I don't know,
grabbing ripples biologist, all right, thanks very much? All right,
pretty good. A lot of pretty good guesses, right, Yeah,
A lot of people guess sort of in the range
(08:48):
of billions of years, right, which is totally respectable. Um.
I think my favorite answers were the people who misunderstood
my question and they thought I was asking them how
old is the university and which it just turned fifty
at a big party, etcetera. But when they said fifty,
I didn't really understand that misunderstood. I thought for a
moment that they thought the universe was fifty years old,
(09:08):
and I thought, oh my god, I've met some really
young Earth creation is how do I respond, you know,
like to keep a straight face. I'm trying to be respectful,
you know. Um, and then I understood, oh no, they
just missed her mishearth question. Well, when you're young and
you're in college, the university is your universe in a way, right, Yeah, exactly,
that is the in their whole life. Um. I like
(09:28):
the guy who said, I don't know at least twenty
six years old, right, which is tells you a little
bit how self centered some college students are. But you know,
everybody gave it their shot. He's like, yeah, the universe
was here when I was born, so obviously at least
twenty six years old, that's right. And maybe that's the
only information that matters to that guy, you know, like,
who cares as long as it was around for me,
nothing else is important. Yeah, I guess his universe started
(09:50):
twenty six years ago. Yeah exactly. But you know he's
actually using a strategy to measure the universe which scientists use,
which is how old is stuff in the universe? The
universe has to be at least as old as that.
So while his you know, focus on himself, isn't that
helpful in determining the age of the actual universe. He's
got a good idea there about how to figure it out.
(10:10):
How old is the oldest thing that I know about?
That should give you give you at least like a
minimum age of the universe. Yeah, exactly, so he even
though he's a biologist, he sort of invented that strategy
on the fly. Well, I think it's important. Let's start,
first of all, talking about what it means to ask
how old the universe is? Like, what is the age?
What does the term the age of the universe mean? Yeah,
(10:33):
that's right, that's the kind of answer somebody would give it.
They're trying to evade a question, right, how old you Well,
what do you mean by age? I mean, do you
mean conception moment of birth? Right? Um. But there's actually
a really good analogy there, because human age is a
little fuzzy. Like if you're conceived on a certain day
and then you're born premature, you know you are older
(10:53):
than you otherwise would have been, right, Um. Whereas if
you stayed in your mother's womb longer, you're technically younger,
even though you know it doesn't really matter, which is
kind of arbitrary, right because technically you're body and your brain,
all your parts started earlier than your birth. Yeah, and
we're not taking a position here, and there's a fetus alive,
(11:17):
and maybe that's why, maybe that's why we do that.
But you know, actually I heard that in other cultures
they define age a little differently, like in someone like
in in the US, when you're born year zero, right,
and the clock starts then. But in other cultures, when
you're born, you're one, and your age increases in the
new year, and everybody goes up one year in the
new year, where the concept of age is like how
(11:38):
many years have you been around in not exactly how
many years since your moment of birth. Um, So the
age of the universe is sort of a similar question, right,
Like how do you define the zero with the moment
of the universe equals zero? T equals zero. Yeah, let's
(11:59):
let's by what it means tigal zero. So what what
I physicists mean usually when they say T equals zero, Well,
it's not terribly well defined, is the problem. What we
can do is we can say, we know when now is,
and we can walk backwards from now to what we
know to be a very hot and dense state in
the very early moments of the universe, right like a
(12:20):
big primordial hot plasma which is nasty and wet and
all sorts of stuff is happening right like a baby
when it's born, like a baby, exactly, a big hot,
nasty mess. It probably wasn't as loud, I don't know,
maybe it was. Actually there was very on acoustic oscillations,
so it could have been a lot of screaming going
on UM. And we understand that very well, like we
can propagate that forward to get to our universe, we
(12:41):
can go backwards. But the problem is that just before
that is very fuzzy for us, Like we can't see
past that. For those of you who heard our episode
about the baby universe, we can't see earlier than like
three eighty thousand years UM after the Big Bang, and
so we don't exactly know what happened then and so
exactly how to define it. It's not clear like you'd
(13:02):
like to say T equal zero is the big Bang? Right? Yeah?
Isn't that what they usually mean that the universe started
with the Big Bang or we don't know, right, except
that we don't really have a great definition of what
the Big Bang is, right, Like, we don't know what
was the Big Bang? Was it a singularity that then exploded? Um?
Was it you know, some weird quantum blob? Was it inflotons?
(13:23):
Like that? Whole process is still very mysterious to us.
So we don't know exactly what happened and exactly how
long it took, so we can do you just blew
my mind a little bit. Yeah, scientists think Tiko zero
is the moment possibly of the Big Band, but you're
saying it's possibly, Like we don't really know what happened
around the time of Tiko zero. Yeah, and the I mean,
(13:44):
the whole definition of the Big Bang is still a
kind of bit fuzzy, Like some people think the Big
Bang is sort of still happening. Like what was the
Big Bang? It was this inflation of a dense amount
of matter into a hot promodial gas that was on
a macroscopic scale, right, really fast inflation and took less
than ten to the minus thirty seconds, right, and that
ever since then, things have been expanding, But things are
(14:06):
still expanding and they're still inflating, like we have dark energy,
which is just like a modern day analogy of of inflation.
So from some point of view, you could say, like,
the Big Bang is still banging. So then when do
you put to equal zero from the beginning of the
Big Bang? Like, we don't really understand very well the
physics of what happened in the early days, so it's
hard to define what T equal zero is. So you mean,
we can look back in our history, and there you
(14:29):
get to a point where you can look beyond and
you just assume that there's some sort of event beyond that.
But we can't see that's right. You don't have records
of your of yourself beyond pictures of you when you
were one year old, Like you don't you have no
idea what you look like before you were one years
old exactly. And so what you can do is you
can extrapolate. You can say, like, well, I know how
it happened when I went from one to two and
(14:50):
two to three and three to four, and I understand
the biology of and so I can extrapolate backwards from
one and think about what zero must have been like
and when zero was right, how long it took to
get to one, which is really the question when you
when you were conceived probably yeah, exactly. But if you
suspect that the physics happening down there between zero and one,
you know, just after the moments of the Big Bang,
(15:11):
we're different, we're interesting, um or maybe not typical of
what happened the rest of your life, then there's a
lot of uncertainty how to do that extrapolation. You can't
just blindly extrapolate, like what if the physics before I
was one years old were totally different, which means I
could be older than one year old when I think
I'm one year old. Yeah exactly. And it's not that
we think the laws of physics were different, but you
(15:33):
don't just different stuff was happening. Stuff we haven't seen, stuff,
we haven't had a chance to understand, um stuff. So
you know, we're extrapolating down, down, down, down down. But
we get to a region where we have don't really
have a lot of data to extrapolate into, so we're
skeptical of that extrapolation. But this is a very technical
discussion of like exactly when ti equal zero is. The
(15:54):
good news is doesn't really matter. What do you mean,
it doesn't matter. We just talk about how important was.
It doesn't really matter exactly when you define to equal zero,
because this uncertainty is a small number compared to the
age of the universe. Like we can extrapolate all the
way from now back to you know, less than a
million years after the Big Bang whatever that was, right, um,
(16:17):
And so there's an uncertainty there of like you know,
a million years, a couple of million years whatever for
what happened before the part we can extrapolate beyond. But
that's a small fraction we think of the age of
the universe. So if you want to say how old
is the universe, you can sort of sweep that question
under the rug. You can say, well, you know, how
old is it? How far back can we see? And
that's really to the age of the universe. So if
(16:39):
I said, Daniel, I hear you're forty three years old
plus or minus a million years, you would just sweep
that under the rug. I would say, no, that's an
accurate statement or a correct statement. Oh that's right. Technically
you are yeah plus or minus a million yeah, more
plus than minus but um, yeah, exactly. But I think
(17:00):
a better analogy would be like, you know, I'm forty
three plus or minus a day, you know, or a second.
Right there, These are details on the scale of the
times we're talking about. But you know, we want our
listeners to really understand the nitty gritty, and so the
exact definition the age of the universe is a little
bit fuzzy because those first few fractions of a second
especially are not well understood. Okay, so when we say
(17:23):
the age of the universe, we really mean how old
the universe is since some mysterious thing happened called the
Big Bang. That's right, exactly, and even deeper, right, we
don't know what happened before that, So it's just an
arbitrary thing to call that t equal zero. Right. It
could have been that before the Big Bang there was
another universe which had like a big bang of its
(17:45):
own and a big crunch. It's not really a different universe.
It's just like part another cycle. And this could have
been happening forever. So when you talk about the age
of the universe, you really can only talk about the
age since this early state that we understand. What happened
before that is a little question mark, Like the universe
could have just started before that it could have gone
on forever before that. Okay, let's let's get into how
(18:07):
we know all this stuff, but first let's take a
quick break. Okay, Daniels, settle this for us. How old
do physicists think the universe is? Years old? I mean,
(18:31):
that's how long? So what else is important? Um? You know,
the most accurate age of the universe currently is thirteen
point eight billion years. That's how long we think the
universe has been expanding since that hot, dense, nasty mess
at the very beginning. Okay, And just to put them
into perspective, the Solar system is four point five billion
(18:53):
years old, that's right. So solar system has only been
around for the last third of this party. There was
ten billion years almost when we didn't even have our star, right, Wow,
So the two thirds of the universe there was nothing
where we are. Oh, there might have been stuff, right,
there might have been other stars, there might have been
globular clusters or gas or whatever. But our star took
ten billion years to even form. Wow. Okay. And by that,
(19:17):
by the same account, the Earth itself is about four
billion years old, that's right. Yeah, it took less than
a billion years for life to start on Earth. Yeah,
and then to put that in scale, my families university,
you see, Irvine is fifty years old, right, so now
the party has started. Well, the United States is only
about It always blows my mind a little bit. In
(19:39):
the United States, it's only like two d and fifty
years old, lessan two fifty years old. I know. My
brother keeps reminding me of that because his university is
like three times as old as our country. Right. He's
at Oxford, so they have traditions, they have like probably
have silver ware over there that's older than our country.
So he's he's a younger brother and he's like trying
to find something to get to tab over. You aren't
(20:02):
always aren't younger brothers always doing that? No, he is
an academic rock star at Oxford, and so he gets
to um, he gets to look down and the rest
of us at fairly new universities. Okay, so thirteen point
eight billion years old? That's how old the universe we
think it is? And how do how do we know that?
How do we know there is there a birth certificate?
Is there like DNA evidence? Well, I've been asking your mom,
(20:24):
but she claims had not been around then. So we
have to figure it out for ourselves. Um, there's basically
two ways that we we know the age of the universe,
And this is really classic science strategy. Is like, find
two completely separate, independent ways of asking the same question,
and then if they agree, then awesome. You think probably
you haven't figured out and if they don't agree, then
(20:46):
you know something's wrong. Like two independent experts, yeah, or
two suspects more like like if you're a detective, you're
trying to figure out, um, you know, who did something.
You find two suspects, you separate them, You ask them
questions separately. If they tell you all the same details,
they're probably telling the truth, right. If they give you
totally different stories, then you know they're lying. So science
is sort of like that. Okay, so what's the first
(21:06):
way that we know how old the universe is? The
first way is just looking for old stuff. Like if
you find something in the universe that's fifty billion years old,
then you know the universe is at least fifty billion
years old. Right, It's not very complicated. So you just
look around and you try to figure out how old
is the stuff around us, And that's it's a sort
of a lower limit on the age of the universe.
(21:26):
So if you find a rock that's sixty billion years old,
then you know the universe must be at least sixty
billion years old, that's right. Yeah. Or if you find
an unpaid bill from fourteen billion years ago, right, then
you know you know your universe is about to end,
that's right. You know exactly they're coming for you. Um, yeah,
and um. But that's a tricky thing to do, right,
(21:48):
how do you know the age of stuff? Right? We've
changed one question how do you know the age of
the universe into another question, which is how do you
know the age of stuff we see around us? Right? Yeah, Well,
what's the oldest stuff that we know about? Then? Yeah,
the oldest stuff that we know about is stars basically,
I mean, there's this a caveat there with the cosmic
microwave background, which we we know, um is a little
(22:10):
bit older, but that's more difficult to age. But direct
stuff that we can see that we can ask the
question how old is it our stars? And we look
around and we look for really really old stars and
and and this is a tricky thing to do. But
what you can do is you can look for blobs
of stars they're called globular clusters. These are collections of stars.
(22:30):
There's sort of like many galaxies. I mean, they have
a whole different name from them because of the sized distinction.
But they're called globular clusters. He didn't like mini galaxies galaxinos.
I thought that would have been good glaxin exactly. That
sounds like a nice pasta. I'll have the galaxins with anchovies, please. Um. Yes.
So you look at these globular clusters and you ask
(22:52):
how old are they? How old are the stars in
these globular clusters. And it's hard to know how old
an individual star is, but you can look at a
group of them and you can figure out how old
that group is, really, yeah, based on which ones are
still there and which ones are not there anymore. And
the reason is that stars have different life spans. Right,
So you form a bunch of stars, and um, they
(23:13):
form out of gas and dust. They coalesce with gravity,
and you get some really big ones and you get
some really little ones. Now, the big ones burn really
fast and they don't last very long, and the little
ones they burn a long time. They're like saving their fuel.
Remember stars burned by compressing hydrogen, right, and then they
glow and they burn it's its fusion and you can
listen to our podcast episode about that if you're curious
(23:34):
about that. Um But the big ones burn out pretty quickly.
So if you're looking at a population of stars really
really far away and you notice that they still have
a bunch of big ones in them, you know it's
pretty young because those ones would have burned out already
if it was old, like the cluster itself is young.
Like the cluster itself is young, exactly. And if you
find a club a group of stars the globular cluster
(23:55):
that only has little stars and it left, then you
know it's pretty old, and because has been time for
all the bigger stars to burn out. So what's the
oldest star that we know about? Or how old are
the oldest stars that we know about? Well, this is
really fascinating. It's been controversial because this is a hard
thing to do. You have to know how far these
things are away. You have to measure their light. There's
(24:15):
a connection between the color of the star and its size,
so it's a lot of intermediate steps. Right, you see
the color that tells you the size that you can
make a distribution of the sizes. There's a lot of
steps that go along, and there's a lot of uncertainty
and um. Things happen very quickly in the beginning of
a life cycle of a globular cluster, like the big
bright stars burn out fast. Near the end, things happen
(24:37):
more slowly, which means for really old stuff, the uncertainties
are pretty large. Like it's hard to tell the difference
between a ten billion year old globular cluster and an
eleven billion year old, but between one and two billion
is easier. So people have been looking at these things
for a while, and the oldest ones we found are
something like thirteen billion years old. That's a very recent estimate.
(24:59):
A till like twenty years ago, people thought they had
found globular clusters that were like twenty billion years old
or even thirty billion years old. Did you say thirty thirty? Yeah,
they think so, maybe the universe is thirty billion years old.
Well that's what they thought. For a while. They had
this one measurement from the stars that was saying like
twenty or thirty billion years old, and they thought, well,
let's compare that to the measure to other ways we
(25:21):
can measure the age of the universe. Now the most
current one that they in the end, they found some
some mistakes and they updated it, and they weren't like
you know, um, somebody goofed by adding one plus one
making three. You know, we just got a better understanding
of how stars evolved and how they burn and how
to do these calibrations. And now the more recent updates
are like thirteen billion years old. But for a while
it seemed like those globular clusters were suggesting the universe
(25:45):
is older than twenty billion years. So so there are
things out there in the universe that we're there when
the universe started that are still around today. Well not quite.
When the universe started, right, We're looking at stars, and
you know the universe started, there was the Big Bang.
There's a mess of plasma things spread out and cooled off,
and then stars formed from that gas and dust. Those
it called the first generation stars. None of those stars
(26:07):
are still around. We can't see those stars. Nobody's ever
seen those We're looking for them. It's people want to
understand it, but nobody's seen those stars. The o G
stars exactly back when stars were cool, man, back when
they were hot. Um, yeah, and then those didn't last
very long. And then they know they burned, they cool,
they exploded supernovas, and you have this, they gather their
back together. You have the second generation of stars. Remember
(26:30):
stars are in this cycle, right, They burn, they then
they explode and their fuel gets spread out into the universe.
Then the gathered back together and make another cycle. And
so the second or third generation of the sort of
the oldest stars that we can see so far. And
that's why it's a lower limit, right, we see something
super old. We don't know if the universe is older,
how much older than that the universe is. We just
(26:51):
know it's at least that old. It's like finding a
relic from an ancient civilization. You know that the civilization
is at least at all, but it could have been
around for much longer. Just because you haven't found something older,
it doesn't mean that it wasn't older. That's right, exactly.
It's such a lower limit. And currently that lower limit
is about thirteen billion years old. That's the oldest thing
that we found. So we're seeing things from the very
(27:13):
very early universe, not exactly from the beginning, right, but
from very very early on, which is pretty awesome. Right,
that's like the ancient history of the universe. It's I
think that's super cool. Yeah. Imagine like coming up to
these clusters and you're staring at something that's been around
for thirteen billion years old. Yeah, that would be pretty amazing. Yeah. Well,
I mean I'm already just flabbergasted looking down at the Earth. Right,
(27:35):
the Earth has been around for five billion years. It's
such an ancient rock. It's seen so much history. I
think about that when I you know, we just walk
across the planet, I wonder like, who else is stepped here.
That's one of the things that makes me love those
um footprints, Right, you can see like footprints of dinosaurs
from hundreds of millions of years ago, like they were
just like walking along boop um. You know, so much
(27:55):
has happened on this planet. We don't we're not even
aware of. There's so much history that's just been lost
that will never know. Okay, So that's one way we
know how old d universe is. What's the other way
we know? The other way is by looking at the
expansion of the universe. We know that the universe is
spreading out. Things are moving away from us, and they're
(28:17):
moving away from us faster and faster every year, and
we can measure that. We look out in the universe
and we see how fast things are moving away from us.
We can measure that by looking at how the light
from them is stretched. Things that are moving away from
you have their light waves stretched out longer, they turn
more red. Things that are moving towards you have their
light waves squeezed, they turn more blue. This is the
(28:38):
Doppler effect. It's the same effect that makes like a
police siren sound different as it's approaching you and leaving you. Right,
So we can use that to measure how fast things
are moving away from us. And if you remember our
podcast episode about dark energy and the expansion of the universe,
we have these really cool standard candles are called supernova
type one a supernova, and we we know how bright
(29:00):
they should be, and we can look at them, we
can measure their velocity, we know how far away they are,
so use that to measure how fast the universe is expanding.
That's important because remember we talked about the definition of
the start was really what we're doing when we're measuring
the age of the universes, we're saying how long has
the universe been expanding since that hot date. And if
you know, um, the expansion rate, then you can extrapolate backwards.
(29:23):
So we we we hit the rewind button from what
how fast we think the universe is expanding, and that
makes the university you watch it in reverse, makes the
universe go down, down, down, down down into a very
small blob. Yeah, exactly. The Ebreody starts talking finding because
of backwards. Yeah. And the critical thing is that you
have to measure the rate, right We have to know
(29:44):
the expansion rate to know how fast to rewind, and
we have to know the expansion right now, and the
expansion made a billion years ago and ten billion years ago.
And we can do all that because remember, the further
we look out into space, the further we're looking back
into history, and we can see the expansion and right now,
we can see it a while ago, we can see
it a long time ago. Like the history of the
universe is written out there in the stars, like you
(30:07):
can tell, yeah, exactly, how fascinating we're expanding throughout the
history of the universe. Yeah, and our history is out
there also. You know, light left the Earth um when
you were ten, and you you know, did something embarrassing
at your cousin's birthday party. Light from that event left
the earth and is still out there, and somebody could
capture it and see that, right, even though it happened
years ago, So all that information is still out there. Yeah,
(30:30):
so watch out, So watch out. Light come back and
and expose your ten year old antics. That's right. Well,
when the aliens come, they'll have seen it, right, so
they'll know who's been naughty and who's been nice. Santa
is an alien? Oh? Did I just reveal that on
the air. Oops? Yes, Santa is an alien. Um. I
mean Santa can do a whole bunch of stuff that
(30:52):
nobody else can do, right. I think having him be
an alien with supertech is really the only reasonable expert
would explain it. Santa myth boom, We just saw that
mystery right there. Well, this is a perfect point to
take a break. So if you know the expansion rate
(31:18):
the universe, you can rewind back and we actually measure
the expansion RDE two different ways. One is just by
looking at how things are moving right right these stars.
The other is by looking at the cosmic microwave background.
This is the light from the very early moments of
the universe. That also tells us how old the universe is. Yeah,
it contains an incredible amount of information about what was
(31:40):
going on in the early universe, how much dark matter
there was, how much normal matter there was, how dense
it was, all of that stuff and all that information
in the end can tell you about the expansion rate
of the universe. Um. But you can extract the expansion
rate directly from that. That's actually the most precise way
to do it UM. And then once you know the
expansion rate, you can rewind the universe to figure out
(32:01):
how old it is. And that's the measurement that tells
us it's thirteen point eight billion years, and the uncertainty
on that it's about twenty one million years. So it's
pretty accurate plus or minus twenty one million years, depends
on your scale. But it's kind of interesting that, you know,
scientists hit the rewind button, right, we look at into
the stars, we hit we pressed the rewind button. We
see it all compressed, and then we sort of stop
(32:23):
once it gets really small, right, because we a we
can't rewind further, but also kind of conceptually right, like
we we can't imagine there being anything before that or
we can't imagine anything surviving being that small. Yeah, and
we have to ask questions like what does it even mean?
You know, Um, space and time started at the Big Bang?
So can you count before the Big Bang? You get
(32:45):
into really really difficult philosophical waters. Absolutely, um. And you know,
it's only recently that we've known this, Like this seems
to like going to be an important piece of information.
It tells me something about who I am and how
to live my life and how meaningless it is. But
it's sort of a new piece of information. You know,
Like a hundred years ago, people thought the universe was
steady state, right, that there was just a bunch of
(33:07):
stars out there and they've basically always been there, and
the universe wasn't expanding or contracting. It didn't have a
interesting history or a moment of birth. It's just been
around forever. This was a hundred years ago, right, only
only a hundred years ago, so from most of human history.
First of all, for most of the ministry, we didn't
understand anything about anything, right, so we were basically completely
all ignory missus um. You just exalted most of humanity.
(33:30):
But go ahead, I mean, in the best possible. Way
Um but yeah, um, And only about a hundred years
ago do we even figure out that there might have
been a beginning, that there was this expansion, which suggests,
you know, that that that there was that if you
rewound it, you got back to a very early, hot,
nasty state. A hundred years ago, we thought the universe
(33:51):
had been around forever, right, So yeah, like forever infinity right? Yeah?
So what was that like to learn that the universe, uh,
to go from age of the uni versus infinity to
agees you know, in the in the billions of years.
And it wasn't until the fifties that we had any
sort of accurate estimate because these things are hard to measure.
It's taken decades to get the technology and the math
and the physics models. So it's in the fifties that
(34:12):
really had the first accurate estimate of the universe's age
about fourteen billion years wow. Okay, so the universe is
thirteen point eight billion years old plus or minus twenty
one million years old. And so what does that mean?
What does that What does that tell us about how
the universe came to be or where it's all going?
(34:35):
It tells us something about how far we are along.
You know, we know that we've we've been around for
long enough for galaxies to form, right, for galaxies to
spin for a while, for stars to form and explode
and coalesce again in form and explode. Right, we're not
in the very first few moments of the universe. But
we don't really know much more than that. Yeah, and
more important, we don't even know how old the universe
(34:56):
is going to be, right, We don't know how old
the universe is going to be around. So we could
be in a very early part of the universe, or
we could be in a really late part of the universe.
We don't really know. No, we have no idea exactly. Um,
it could be that in a trillion years. There are
life forms that are studying the age of the universe
and they think about this little this first little bit,
the first fifteen billion years as like the big bang.
(35:19):
Right to them, this could have just been like the
engine just getting started, you know, platform from stars and galaxies.
We don't know, and we don't know if this part
of the age of the universe is typical, right, Like,
it could be that things go along and everything turns
to black holes and they have like only black holes
for a trillion years. Right, Um, so we really don't know.
(35:39):
When is the puberty of the universe? Right things changing?
Is it already grown up? We don't know. So maybe
the real question we should be asking, the one that's
less rude, is how young the universe is? Young? Is
the universe exactly? Hey, universe, how do you feel? You're
feeling pretty good? You got some joint pain. You've been
planning for your retirement. Yeah, you know, like if you
(36:01):
knew you were going to live to a thousand years old,
you would say things like, oh, I'm only forty two
years young instead of forty two years old. That's right.
If I knew I was going to live to a thousand,
I would have started saving for retirement a lot, a
lot earlier. You want to be retired for nine thousand,
nine hundred and sixty years. No, honestly, I'm never going
to retire. I mean, I have tenure. Why should ever
(36:22):
retirement to sit in my office for the next year
and you're already retired mentally mentally retired? You know you
do your best work and you have tenure. That's exactly
the point. You're free to think and expand and go
to crazy places in your career, like recording a podcast
with a cartoonist, right, yeah, sure, yeah, And the universe
(36:43):
is fifty years old. Universe's fifty years young, alright, everyone.
So that's the answer to the question how old is
the universe? And how do we know? Or how young
is the universe? How young isn't the universe? Oh my god, Universe,
you look good. You're looking sparkly. That's right, keep burning bright, Universe.
(37:04):
You're happy to be around. See you next time. Thanks
for tuning in. If you still have a question after
listening to all these explanations, please drop us a line.
We'd love to hear from you. You can find us
at Facebook, Twitter, and Instagram at Daniel and Jorge that's
(37:26):
one word, or email us at Feedback at Daniel and
Jorge dot com.
Hosts And Creators
Daniel Whiteson
Kelly Weinersmith
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