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Language: en
man, you discovered dark energy. You're
a co-discoverer of one of the biggest
paradigm shifts in the history of
astrophysics, right? Since Hubble
discovering that the universe is
expanding, discovering that it is
accelerating. So, when you get a result
like that,
>> Yes.
>> I mean, man, I mean, I would be sweating
cuz I cuz I know how our colleagues are.
If if you
>> They're rough. They're rough. They're
rough. And chances are if you've gone
through everything
>> and you're like, I'm sure this is right
>> because we have so many and everybody's
so smart, somebody's going to be like,
no, you're in it. It's that they know
immediately, right?
>> So, how did your team receive this
result and how did you feel reporting
this result?
>> Yeah, very nervous. Um, you know, at
first you find something like this and
as I said, you're sure you're wrong and
but you know, you know the process to go
through. I'm going to go over all the
steps, check everything, do this, do
that. Right? Because you want to find
your own error first, right? Absolutely.
In fact, you want to find your error and
not even admit to anybody that you made
an error, right? You're a former
adviser, your colleagues, you're just
like, I'll just find
>> to mention you were pretty young.
>> Uh, correct. Correct. I was just you're
fresh out of graduate school. Wow. And
so, you know, I hadn't had any
significant results. And so, yeah, you
want to find your own error. And then um
when I couldn't and I had checked
everything, then I began working with
people on the team saying, "Look, I'm
seeing something funny. It's probably
going to go away, but can you just check
step B to C and can you check step C to
D? Can you reproduce?" And it was just a
series of farming out. And then Brian
Schmidt was, who's my colleague, he was
leading the team, did the final check on
the last step. So I remember he had
moved to Australia and I was in
California. So when I would send him an
email, it would take like 12 hours
before I'd get a response. Oh boy. So I
had a very sweaty night one night when I
was like, I've checked everything. This
is the final calculation is do you see
what it favors? And he wrote me back the
next morning an email that said, well
hello lambda. Okay. And now lambda is
you know the Greek symbol for what we
call the cosmological constant or dark
energy. And so
>> he saw the exact same thing.
>> Wow. that that is well Brian seems to
have had the belief in the result to uh
make such a bold statement. You
mentioned lambda.
>> Yeah.
>> So lambda shows up in Einstein's
equations as a constant that he inserted
and there's that historical story that I
hear people uh misquote. You know that
you know people often say Einstein said
that was his biggest blunder. But I saw
another um science communicator, Sabina
Hassenfeder, I think, who said, "No, he
didn't say that about that. That's not
what that was." But I don't know the the
the truth historically. Um but I do know
that when I look at that equation and I
attempt to interpret what it means, it
can be read in one of two ways. One way
is that dark energy is some stuff in
spaceime. And the other way is that dark
energy is the intrinsic energy density
of spaceime. What is your
interpretation?
>> Yeah. Um I mean you know so as it
depends on in this discussion which side
of the equation you put it on because
basically what you're trying to balance
what sorry what Einstein was trying to
balance was that he thought that the
universe was static that it wasn't
expanding or contracting. That's what
astronomers of the day told him because
astronomers of the day didn't know that
what we call galaxies were actually
outside the Milky Way. So they thought
everything was in the Milky Way. Nothing
is really expanding in the Milky Way.
>> A universe of one galaxy.
>> Right. Right. So they said, "Hey,
nothing's really expanding or
contracting." And he was like, "Wow,
that's a puzzle because this term in the
equation, which looks like kind of like
Newton's gravity, will cause things to
pull together. There must be something
pushing the other way." So he made an
amazing discovery, which is that
although the gravity of stuff of matter
is attractive, that the gravity of empty
space could be repulsive, could go the
other way, and that these two could be
in balance. And so he called this the
cosmological constant and he saw that it
could exist as as an extra term in his
equation. And this is important. There
was a place for it. I mean this isn't
like if if if Newton had had this
problem he would be stuck because you
know in his gravity there is no option
for something to be repulsive. But the
the curious thing is Einstein's gravity
recognizes different forms of
>> matter and energy as having different
gravity. And so energy itself can be
repulsive. It has a curious property
that we call negative pressure.
>> Exactly. That's what I was going to say.
You could have positive energy and
positive pressure which would be
attractive or positive energy and
negative pressure, right?
>> Which would be repulsive.
>> Correct. Correct. And so so that is how
we we attempt to understand it today as
though the universe is filled with this
kind of energy um that has this property
of negative pressure and so it has
repulsive gravity. I think Einstein
didn't even go that far. I think it was
a term in his equation that
>> with no physical interpretation.
>> Yeah. With with initially not a lot of
physical interpretation. It was just
what we would like to call a boundary
condition. Well the universe is static.
Therefore a term is there.
>> Wow. Um but uh and of course once he
learned about a decade later from Hubble
and others that the universe was
expanding he certainly thought this was
a mistake
>> and removed it. you know this question
of if whether he called it his biggest
blunder or not is more you know
anecdotal apocryphal you know who was he
talking to did they remember it
correctly but the sentiment is certainly
true that he thought
>> well if the universe is expanding I
don't even need this why did I come up
with it but you know once that once that
toothpaste was out of the tube right
there was no putting it back I mean he
demonstrated it could exist it may exist
there's even a physical interpretation
of it could be the energy of the vacuum
that quantum theorists uh wouldn't know
how to get rid of if they wanted to. And
so we have always been in this situation
of this ambiguity. Is it going to be
there or is it not? You know, and every
couple of decades somebody says, "I
think I see it." And then others were
like, "No, I don't." But it wasn't
really until 1998 that we saw the direct
consequence of it that is irrefutable.
>> Irrefutable. Now in 2025 is even become
stronger and stronger. Right. Yeah.