Kind: captions
Language: en
why weren't we pushing towards economic
fusion and new materials and new methods
of heat extraction and so forth because
everybody knew Fusion was 40 years away
and now it's four years away
the following is a conversation with
Dennis white nuclear physicist at MIT
and the director of the MIT plasma
science infusion center
this is the Lex Friedman podcast to
support it please check out our sponsors
in the description and now dear friends
here's Dennis White
let's start with a big question what is
nuclear fusion is the underlying process
that powers the universe so as the name
implies it fuses together or brings
together
two different elements technically
nuclei that come together and if you can
push them together close enough that you
can trigger essentially a reaction what
happens is that the the element
typically changes so this means that you
change from one element to another
chemical element to another underlying
what this means is that you change the
nuclear structure this rearrangement
through equals mc squared releases large
amounts of energy so Fusion is the
fusing together of lighter elements into
heavier elements and when you go through
it you say oh look so here are the
initial elements typically hydrogen and
they had a particular Mass rest Mass
which means just the mass when they're
with no kinetic energy and when you look
at the product afterwards it has less
rest mass and so you go well how is that
possible because you have to keep Mass
but mass and energy are the same thing
which which is what equals mc squared
means and the the conversion of this
comes into kinetic energy namely energy
that you can use in some way and that's
what happens in the center of stars so
Fusion is literally the reason life is
is viable in the universe so Fusion is
happening in our sun and what are the
elements the elements are hydrogen that
are coming together it goes through a
process which just probably gets a
little bit too detailed but there's it's
a somewhat complex catalyzed process
that happens in the center of stars but
in the end stars are Big Balls of
hydrogen which is the lightest it's the
simplest element the lightest element
the most abundant element most of the
universe is hydrogen and and it's
essentially a sequence through which
these processes occur that you end up
with helium
so those are the primary things and the
reason for this is because
helium has features as a nucleus like
the interior part of the atom that is
extremely stable and the reason for this
is helium has two protons and two
neutrons these are the things that make
up nuclei that make up all of us along
with electrons and because it has two
pairs it's extremely stable and for this
reason it when you convert the hydrogen
into helium it just wants to stay helium
and it wants to release kinetic energy
so stars are
basically conversion engines of hydrogen
into helium and I mean this also tells
you why you love Fusion I mean because
our sun will last you know 10 billion
years approximately that's along the
fuel will last but to do that kind of
conversion you have to have extremely
high temperatures it is one of the
criteria for doing this but it's the
easiest one to understand and why is
this it's because
effectively what this requires is that
these hydrogen uh ions or which is
really the bare nucleus so they have a
positive charge everything has a
positive charge of those ones is that to
get them to to trigger this reaction
they must approach within distances
which are like the size of the nucleus
itself because the nature in fact what
it's really using is something called
the strong nuclear force there's four
fundamental forces in the universe this
is the strongest one but it has a
strange property is that it while it's
the strongest force by far it only has
impact over distances which are the size
of a nucleus so to get put that into
what does that mean it's a millionth of
a billionth of a meter okay incredibly
small distances but because the
distances are small and the particles
have charge they want to push strongly
apart namely they have repulsion that
wants to push them apart so it turns
when you go through the math of this the
average velocity or energy of the
particles must be very high to have any
significant probability of the reactions
happening and so the center of our sun
is at about 20 million degrees Celsius
and on Earth this means it's one of the
first things we teach you know entering
graduate students you can do a quick you
can do a quick basically Power Balance
and you can you can determine that on
Earth that it requires a minimum
temperature of about 50 million degrees
Celsius on Earth
to perform Fusion to get enough Fusion
that you would be able to make get
energy gain out of it
so you can trigger Fusion reactions at
lower energy but they become almost
vanishingly small at lower temperatures
than that
first of all let me just link around
some crazy ideas so uh one the strong
force just stepping out and looking at
all the physics
is it weird to you that there's these
forces and they're very particular like
it operates at a very small distance
then gravity operates at a very large
distance and and they're all very
specific in the standard model describes
uh three of those forces extremely well
and there's and this is one of them and
yeah this is one of them and it's just
all kind of works out there's a big part
of you that's uh you know an engineer
that used to step back and almost look
at the philosophy of physics
so it's interesting because as a
scientist I see the universe through
that lens of essentially the interesting
things that we do are through the forces
that are get used around those and
everything works because of that
Richard Feynman had I don't know if
you've ever had Richard fine it's a
little bit of a tangent but she's never
been on the pocket he's never been on
the podcast he was unfortunately passed
away but wanted like a like a hero to
almost all all physicists and then part
of it was because of what you said he
kind of looked through a different lens
at these but typically look like very
dry like equations and relationships and
he kind of I think he brought out the
Wonder of it in some sense right for for
those he posited what would be if you
could write down a single not even
really a sentence but a single concept
that was the most important thing
scientifically that we that we knew
about that in other words you had only
one thing that you could transmit like a
future or past generation it was very
interesting it was um so it's not what
you think it wasn't like oh strong
nuclear force or Fusion or something
like this and it's very profound which
was he was that the reason that matter
operates the way that it does is because
all matter is made up of individual
particles that interact each other
through forces that was it so just that
atomic theory basically yeah
which is like wow that's like so simple
but it's not so simple it's because like
who thinks about atoms that they're made
of like I I this is a good this is a
good question I give to my students how
many atoms are in your body like almost
no students can answer this but to me
that's like a fundamental thing by the
way it's about 10 to the 28. out of 28.
so that's uh you know trillion or you
know million trillion trillion or
something like that yes so one thing is
to think about the number and the other
is to start to really Ponder the fact
that it all holds together yeah it all
holds together and you're actually that
you're more that than you are anything
else yes exactly yeah no I mean there
are people who do study such things of
the fact that if you look at the for
example the ratios between those
fundamental forces people have figured
out oh if this ratio was different by
some Factor like a factor of two or
something I was like oh this would all
like not work and I look you look at the
sun right it's like so it turns out that
there are key reactions that if they had
slightly lower or probability no star
would ever ignite and then life wouldn't
be possible it does seem like the
universe set things up for us that it's
possible to do some cool things but it's
challenging so that that keeps it fun
for us yeah yeah that's the way I look
at it I mean the you know the Multiverse
model is an interesting one uh because
there are you know Quantum scientists
who look at and figure I was like oh
it's like oh yeah like Quantum science
perhaps tells us that there are almost
an infinite you know variety of other
universes but the way that it works
probably is it's almost like a form of
natural selection it's like well the
universes that didn't have the correct
or interesting relationships between
these forces nothing happens in them so
almost by definition the fact that we're
having this conversation means that
we're in one of the interesting ones by
default
yeah one of the somewhat interesting but
there's probably super interesting ones
we I I tend to think of humans as
incredible creatures our brain is is an
incredible Computing device but
I think we're also extremely cognitively
limited I can imagine
alien civilizations that are much much
much much more intelligent uh in ways we
can't even comprehend in terms of their
ability to come to construct models of
the world and to do physics to do
physics and Mathematics I would see it
in a slightly different way it's
actually it's because we have
um we have we have creatures that live
with us on the earth that have cognition
right that understand and move through
their environment but they they actually
see things in a way or they sense things
in a way which is so fundamentally
different it's really hard like the TR
it's the problem is the translation not
necessarily intelligence so it's the
perception of the world so I have a dog
and when I go out and I see my dog like
smelling things there's a realization
that I have that he sees or senses the
world in a way that I can never like I
can't understand it because I can't
translate my way to this we get little
glimpses of this as humans though by the
way because there are some parts of it
for example Optical information which
comes from light isn't now because we've
developed the technology we can actually
see things you know I've had I get this
you know as a one of my areas of
research is spectroscopy so this means
the study of light you know and I and I
get this quote unquote see things or
representation of them from you know the
far infrared all the way to like hard
hard x-rays which is several orders of
magnitude of the of the light intensity
but our own human eyes like see a teeny
teeny little sliver of this yeah so that
even like bees for example see a
different place than we do so I don't I
I think if you think of there's already
other intelligences like around us in a
way in a limited way
um because of the way they can
communicate but it's like those are
already baffling in many ways yeah so if
we just focus in on the senses there's
already a lot of diversity but there's
probably things we're not even
considering as possibilities for example
uh whatever the heck Consciousness is
could actually be a door into
understanding some physical phenomena
we're not I haven't even begun
understanding so just like you said
spectroscopy there could be a similar
kind of spectrum for Consciousness that
we're just like we're like these dumb uh
the descendants of Apes like walking
around it sure feels like something to
experience the color red but like we
don't have
it's the same as in the ancient times
you experience physics you experience
light it's like oh it's bright and you
know yeah yeah and you construct kind of
uh what's interesting we might actually
experience this faster than we thought
because we might be building another
another kind of intelligence yeah and
that that intelligence will explain to
us how silly we are there was an email
thread going around the professors in my
department already of uh so what is it
going to look like to figure out if
students have actually written their
term papers or it's chat
chat GPT
um uh it was so as usual as it is where
you we tend to be empiricists in my
field so of course they were in there
like trying to figure out if uh if it
could answer like questions for a
qualifying exam to get into the PHD
program
T which was it they didn't do that well
at that point but of course this is just
the beginning of it so we have some
interesting ones to go eventually both
the students and the professors will be
replaced by Chad GPT yeah and we'll sit
on the beach I really recommend you know
this I don't know if you've ever seen
them it's called the day the universe
changed
James Burke he's a science historian
based in the UK um he had a had a fairly
famous series on on public television
called connections I think it was but
the one that I really enjoyed was the
day the universe changed and the the
reason for the title of it was that
um he says the universe is what we know
and perceive of it so when there's a
fundamental insight as to something new
the universe for us changes of course
the universe from an objective point of
view is the same as it was before but
for us it has changed so he walks
through these these moments of
perception in in in in the history of
humanity that like changed what we were
right and so as I was thinking about
coming to to discuss this you know
people see Fusion oh it's still far away
or we've been it's been slow progress
It's like when my when my godmother was
born like people had no idea how Stars
worked
so you talk about like that day that
Insight the universe changed it's like
oh this is the I mean and they still
didn't understand all the parts of it
but you know they basically got it it's
like oh because of the because of the
understanding of these processes it's
like we unveiled the reason that there
can be life in the universe that's
probably one of those days the universe
changed right yeah and uh remember 1930s
yeah it seems like technology is
developing faster and faster and faster
I tend to think just like with your gbt
I think this year might be extremely
interesting just with how rapid and how
profitable the efforts and artificial
intelligence are that just stuff will
happen where our whole world is
transformed like this
and we're there's a shock and then next
day you kind of go on and you adjust
immediately uh you probably won't have a
similar kind of thing with uh nuclear
fusion with energy because there's
there's probably going to be an opening
ceremony and stuff yes an announcement
it'll take months but with uh with
digital technology you can just have a
immediate transformation of society and
then it'll be this gasp and then you
kind of adjust like we always do and
then you don't even remember just like
with the internet and so on how the days
were before and how did it worked before
right yeah I mean Fusion will be because
it's energy it's it's nature is that it
will be um and anything that has to do
with energy use tends to be a slower
transition but they're the most I would
argue for some of the most profound
transitions that we make I mean the
reason that we can live like this and
sit in this building and have this
podcast and people around the world is
is at its heart is energy use and it's
intense energy use that came from the
evolution of starting to use intense
Energies at the beginning of the
Industrial Revolution up to now it's
that it's like it's a Bedrock actually
of all of these but it doesn't tend to
come overnight yeah and some of the most
important some of the most amazing
Technologies one we don't notice because
we take it for granted because it
enables this whole thing yeah which is
energy which is amazing for how
fundamental it is to our society and way
of life is a very poorly understood
concept actually just even energy itself
people confuse energy sources with
energy storage with energy transmission
these are different physical phenomena
which are very important for so for
example
you know you buy an electric car and you
go oh good I have an emission free car
and uh ah but it's like so so why do you
say that well it's because if I draw the
circle around the car I have electricity
and it doesn't emit any anything okay
but you plug that into a grid where you
follow that wire back there could be a
coal power plant or a gas power plant at
the end of that oh really I mean so this
isn't like carbon free oh
and it's not their fault it's just you
know they don't like the car isn't a
source of energy the underlying source
of energy was the combustion of the fuel
back somewhere plus there's also a story
of how the raw materials are mined in
which parts of the world uh with sort of
basic respect or or deep disrespect of
human rights that happens in that money
so the whole supply chain there's a
story there that's deeper than just the
particular electric car with a circle
around it in the physics or the science
of it too is the energy use that it
takes to do that digging up which is
also important and all that yeah anyway
so yeah we wandered away from Fusion but
yes it's beautiful but it's very
important actually to in the in the
context of this just because you know
those of us who work in infusion and
these other kinds of
um sort of disruptive Energy
Technologies it's it's interesting I do
think about like what would it what is
it going to mean to society to have an
energy source that is like this that
would be like you know which has which
is such completely different
characteristics
for example you know free unlimited
access to the fuel but it has technology
implications so what does this mean
geopolitically what does it mean for how
we how we distribute wealth within our
society it's
it's very difficult to know but probably
profound yeah we're gonna have to find
another reason to start wars uh for
instead of resources we've done a pretty
good job of that over the course of our
histories yeah uh so we talked about the
forces of physics and again sticking to
the philosophical before we get to the
specific technical stuff E equals MC
squared you mentioned how amazing is
that to you that energy and mass are the
same
and what does that have to do in your
clear Fusion
so it has to do with everything we do
it's the fact that energy and mass are
equivalent to each other they're just
the way we usually comment to it is that
they're Just Energy just in different
forms can you intuitively understand
that yes but it takes a long time I
um having for all but usually often I've
I teach the um the introductory class
for incoming nuclear engineers and and
so we put this up as an equation and we
go through many iterations of using this
uh to how you derive it how you use it
and so forth and then you usually in the
final exam I would give I would
basically take all the equations that
I've used before and I flip it around I
basically instead of thinking about
energy is equal to mass is sort of mass
is equal to energy and I asked the
question in a different way and usually
about half the students don't get it it
takes a while is to get that intuition
yeah
um so so in the end it's interesting is
that this is is actually the source of
all free energy because that energy that
we're talking about is kinetic energy if
it can be transformed from Mass so it
turns out even even though we we used
equals MC square this is burning coal
and and burning gas are and burning wood
is actually still equals mc squared the
problem is that you would never know
this because the relative change in the
mass is incredibly small by the way
which comes back to Fusion which is that
E equals m c squared okay so what does
this mean it tells you that the the
amount of energy that is liberated in a
particular reaction when you change Mass
has to because c squared is that's the
speed of light squared it's a large
number it's a very large number and it's
totally constant everywhere in the
universe which is which is another weird
thing which is another weird thing and
in all rest frames and the actually the
relatively stuff gets more
difficult conceptually even until you
get through it anyway so you go you go
to that and and it's in what that tells
you is that it's the relative it's the
relative change in the mass we'll tell
you about the relative amount of energy
that's liberated and this is what makes
fusion and you asked about Fusion as
well too this is what makes them
extraordinary it's because the relative
change in the mass is very large as
compared to what you get like in a
chemical reaction in fact it's about
it's about 10 million times larger
and that is at the heart of why you use
something like Fusion it's because that
is a fundamental of nature like you
can't beat that so of whatever you do if
you're thinking about and why do I care
about this well because Mass is like the
fuel right so this means Gathering the
resources that it takes to gather a fuel
to hold it together to deal with it the
environmental impact it would have and
fusion will always have 20 million times
the amount of energy we lease per
reaction that you could have those so
this is why you know we consider it the
ultimate like environmentally friendly
energy source is because of that so is
it is it correct to think of mass
broadly as a kind of storage of energy
yes
you mentioned it's environmentally
friendly so
nuclear fusion is a source of energy
it's cheap Clean safe so easy access to
fuel and virtual Unlimited Supply no
production of greenhouse gases little
radioactive waste produced allegedly uh
can you can you sort of elaborate why
it's cheap clean and safe I'll start
with the easiest one cheap it is not
cheap yet because it hasn't been made at
a commercial scale right flies when
you're having fun yes yeah yeah
but yes not yet but we'll talk about it
actually we'll we'll come back to that
because it it this is cheaper or or a
more technically correct term that is
economic that it's economically
interesting is is really the primary
challenge actually a fusion at this
point
um but really we can get back to that so
what were the other ones you said um so
cheap actually when we're talking about
cheap we're thinking like asymptotically
like if you take it Forward yeah several
hundred years uh that's sort of because
of how much availability there is of
resources to use of the fuel you have
the fuel we should separate those two
the fuel will all the fuel is already
cheap it's basically free right what do
you mean by basically free so if if we
were to be using fusion
um fuel sources to power your and it's
like that's all we have is fusion power
plants around and we were doing it the
fuel cost per person or something like
10 cents a year it's like it's free okay
this is why it's hard to in some ways I
think it's hard to understand Fusion
because people see this and go oh if the
fuel is free this means the energy
source is free because we're used to
energy sources like this so we you know
we spend resources and drill to get gas
or oil or we chop wood or we make coal
we find coal or these things all right
so Fusion this is what makes fusion and
it's also
um it's not an intermittent renewable
energy source like wind and solar so say
but this is this makes it hard to
understand so as you're saying the fuel
is free why isn't the like why isn't the
energy source free and it's because of
the necessary Technologies which must be
applied to basically recreate the
conditions which are in stars in the
center of stars in fact so there's only
one natural place in the universe that
fusion fusion energy occurs that's in
the center of stars so that's going to
bring a price to it depending on the the
cost and sorry the size and complexity
of of the technology that's needed to
recreate those things and we'll talk
about the details of double Technologies
and which parts might be expensive today
and which parts might be expensive in
200 years exactly it will have a
revolution I'm certain of it um so about
clean so clean is at its heart what it
does is convert it basically converts
hydrogen into it's it's it's heavier
forms of hydrogen the one the most
predominant one that we use on Earth and
converts it into helium and some other
products but primarily helium is the
product that's left behind so helium
safe inert gas you know in fact that's
actually what our sun is doing is
eventually going to extinguish itself
because it'll just make so much helium
that it doesn't it doesn't do that so in
that sense clean because there's no
there's no emissions of of carbon or
pollutants that come directly from the
combustion of the fuel itself and safe
safe
we're talking about very high
temperatures yeah yeah so this is also
the counterintuitive thing so you I told
you temperatures which like 50 million
degrees or it actually tends to be more
like about 100 million degrees is really
what we aim for so how can 100 million
degrees be safe and it's safe because it
is
this is so much hotter than anything on
Earth where everything on Earth is at
around 300 Kelvin you know it's around a
few tens of degrees Celsius
and what this means is that in order to
get a medium to those temperatures you
have to completely isolate it from
anything to do with terrestrial
environment it can have no contact like
with anything on Earth basically so this
means what we this is the technology
that I just described is it
fundamentally what it does is it takes
this Fuel and uh it isolates it from any
terrestrial condition so that it has no
idea it's on Earth it's not touching any
object that that's at room temperature
including the walls of the containment
even including the walls of the
containment building or containment
device or even air or anything like this
so so it's that part
um that makes it safe in this and
there's there's actually another aspect
to it but that that fundamental part
makes it so safe
um in in the main lines
approach diffusion is also that it's
very hot but there's very very few
particles
in at any time in in the thing that we
view the power plant and the actually
the more correct way to do it is you say
there's very few particles per unit
volume so in a cubic centimeter and
cubic meter or something so we can do
this so right now we're although we
don't think of air really as there's
atoms floating around us and there's a
density because if I wave my hand I can
feel the air pushing against my face
that means we're in a fluid or a gas
which is around us that has a particular
number of atoms per cubic meter right so
it's about this actually turns out to be
10 to the 25th so this is one with 25
zeros behind it per cubic meter so we
can figure out like cubic like cubic
meters about like this yeah the volume
of this table like the whole volume
um okay very good so like Fusion there's
a few of those so Fusion like the
mainstream one of fusion like what we're
working on at MIT will have a hundred
thousand times less particles
per unit volume than that so this is
very interesting because it's
extraordinarily Hot 100 million degrees
but it's very tenuous
and what matters from the engineering
and safety point of view is the amount
of energy which is stored per unit
volume because this tells you about the
the scenarios and that's what you worry
about because when those kinds of
energies are released Suddenly It's like
what would be the consequences right so
the consequences of this are essentially
zero because that's less energy content
than boiling water
because of the low density because of
the low density so if you take water is
at about 100 million to a billion times
more dense than this so even though it's
at much lower temperature it's actually
still it has more energy content so if
for this reason
um you know one of the ways that I
explain this is that if you imagine a
power plant that's like powering
Cambridge Massachusetts like if you were
to which you you wouldn't do this
directly but if you went like this on it
it actually extinguishes the fusion
because it gets too cold immediately
yeah so that's the other one and the
other part is that it does not and
because it works by staying hot rather
than a chain reaction it can't run out
of control that's the other part of it
so by the way this is what very much
distinguishes it from fission it's not a
process that can run away from you
because it's it's basically thermally
stable
what does thermostable mean that means
is that you want to run it at the
optimization in temperature such that if
it deviates away from that temperature
the reactivity gets lower and and the
reason for this is because it's hard to
keep the reactivity going like it's a
very hard fire to keep going basically
also it doesn't it doesn't run away from
you it can't run away how difficult is
the control there to keep it at that it
varies from from concept to concept but
in generally it's fairly it's fairly
easy to do that and the easiest thing it
can't it can't physically run away from
you because the other part of it is that
there's just at any given time there's a
very very small amount of fuel available
to fuse anyway so this means that that's
always intrinsically limited to this so
if it even if the power consumption of
the device goes up it just kind of burns
itself out immediately yeah so you are
the just to take a tan another tangent
on tangent you're the director of mit's
plasma science at Fusion Center uh
we'll talk about maybe you can mention
some interesting aspects of the history
of the center in the broader history
of uh MIT maybe brought a history of
Science and Engineering in the history
of human civilization but also just the
link on the safety aspect you know
um
how do you prevent you know some of the
amazing reactors that you're designing
how do you prevent from destroying all
of human civilization in the process
what's the safety protocols Fusion is
um interesting because it's not really
directly weaponizable because what I
mean by that is that you have you have
to work very hard to make these
conditions and which you can get energy
gain from from fusion
um and uh this means that the the when
we design these devices with respect to
application in the energy field is that
they you know you
the while while they will because
they're producing large amounts of power
and they will have hot things inside of
them this means that they have like a
level of industrial Hazard which is very
similar to like you would have like in a
chemical processing plant or anything
like that any kind of energy plant
actually has these as well too
but the underlying under underneath the
core technology like can't be directly
used uh in in a nefarious way because of
the power that's being emitted it just
basically will if you try to do those
things typically it just stops working
so the safety concerns have to do with
just regular things that uh like
equipment malfunctioning
uh melting of equip like all this kind
of stuff that yeah it has nothing to do
with Fusion necessarily yeah I mean
usually what we worry about is the
viability because in the end we build
pretty complex objects to realize these
requirements and so what we try really
hard to do is like not damage those
components which but those are things
which are internal to the to the fusion
device and and it's this is not
something that you would
um consider about like it would as you
say destroy human civilization because
that release of energy is just
inherently limited because of the fusion
process so it doesn't say that there's
zero so you asked about the other
feature for that it's safe so it is the
process process itself is intrinsically
safe but because it's a complex
technology you still have to take into
account consideration aspects of the
safety so it produces ionizing radiation
instantaneously so you have to take care
of this which means that you Shield it
you think of like your dental X-rays or
or treatments for cancer and things like
this we we always Shield ourselves from
this so we get the beneficial effects
but we minimize the harmful effects of
those so there are those aspects of it
as well too yeah so we'll return to
mit's plasma science the future Center
but let us Linger on the uh destruction
of human civilization uh which brings us
to the topic of nuclear fission what is
that so the the process that is inside
nuclear weapons and current nuclear
power plants so it relies on the same
underlying physical principle but it's
exactly the opposite a few which
actually the names imply Fusion means
bringing things together fission means
splitting things apart so fission
requires the heaviest instead of the
lightest and the most unstable versus
the most stable uh elements so this
tends to be uranium or plutonium
primarily uranium so take uranium so
uranium-235 is one of the that this is
one of the heaviest unstable elements
and what happens is that this is a
fission is triggered by the fact that
one of these subatomic particles the
neutron which has no electric charge
basically gets in proximity enough to
this and and triggers an instability
effectively inside of this what is
teetering on the border of instability
and basically splits it apart
and that's the fission right the
fissioning
um and so when that happens because the
products that are and kind of roughly
splits in two but it's not even that
it's actually more complicated splits
into this whole array of lighter
elements and nuclei and when that
happens there's less rest Mass
uh uh laugh than the original one so
it's actually the same so it's again
it's rearrangement of the strong nuclear
force that's happening
um but that's the source of the energy
and so in the end it's like so this is a
famous graph that we show everybody is
is basically it turns out every element
that exists in the periodic table all
the things that make up everything have
uh have a remember you asked a good
question it was like so should we think
of mass as being the same as stored
energy yes so you can make a plot that
basically shows the relative amount of
stored energy in all of the elements
that are stable and make up basically
the world okay in the universe and it
turns out that this one has a maximum
amount of of stability or storage at
iron
so it's kind of in the middle of the
periodic table because this goes from
you know it's roughly that and so this
what that means is that if
um if you take something heavier than
iron like uranium which is which is more
than twice as heavy than that and you
split apart if you somehow just
magically you just split apart as
constituents and you get something
that's latter that will because it moves
to a more stable energy state it
releases kinetic energy that's the
energy that we use kinetic energy
meaning the movement of things so it's
actually an energy you can do something
with and fusion sits on the other side
of that because it's also moving towards
iron but it's do it has to do it through
Fusion together so this leads to some
pretty profound differences as I said
they have some underlying physics or
science
um uh proximity to each other but
they're literally the opposite so Fusion
why is this it actually goes into
practical implications of it which is
that fission can happen at room
temperature
it's because there's this neutron has no
electric charge and therefore it's
literally room temperature neutrons that
actually trigger the reaction so this
means
um in order to establish uh what's going
on with it and it works by a chain
reaction is that you can do this at room
temperature so Enrico Fermi did this
like on a on a University campus
University of Chicago campus the first
sustained you know chain reaction was
done underneath the squash court
with a big blocks of graphite you know
it was still don't get me wrong an
incredible human achievement right but
that's you know and then you think about
Fusion I have to build a Contraption of
some kind that's going to get to 100
million degrees okay wow that's a big
difference the other one is about the
chain reaction that namely fission works
by the fact that when that fission
occurs it actually produces free
neutrons free neutrons particularly if
they get slowed down to room temperature
trigger can trigger other fission
reactions if there's other uranium
nearby or physometers so this means that
the way that it releases energy is that
you set this up in a very careful way
such that every on average every
reaction that happens exactly releases
enough neutrons and slows down that they
actually make another reaction one
exactly one and what this means is that
because each reaction releases a fixed
amount of energy you do this and then in
time this looks like just a constant
power output so that's how our fission
power plant works and so either the
control of the the chain reactions is
extremely difficult and extremely
important for it's very important and
when you intentionally design it that it
creates more than one fission reaction
per per starting reaction that it
exponentiates away
but which is which is what a nuclear
weapon is yeah so how does an atomic
weapon work how does a hydrogen bomb
work asking for a friend yeah
yeah so um at its heart what it how what
you do is you very quickly put together
enough of these materials that can
undergo fission with room temperature
neutrons and you put them together fast
enough that what happens is that this
process can essentially grow
mathematically like very fast and so
this releases large amounts of energy so
that's the underlying reason that it
works
so you've heard of a fusion weapon so
this is interesting is that it is it but
it's dislike Fusion Energy in the sense
that what happens is that you're using
Fusion reactions to but it's simply it
increases the gain actually of the
weapon rather than
um it's it's not a pure at its heart
it's still a fission weapon you're just
using Fusion reactions as a sort of
intermediate Catalyst basically to get
even more energy out of it
but it's not directly applicable to to
be used in an energy source does it
terrify you just again to step back at
the philosophical that humans have been
able to use physics and
uh engineering to create such powerful
weapons
I wouldn't say terrify I mean we should
be
this is the this is the progress of
human every time that we've gone access
you talk again you know the day the
universe changed those really changed
when we got access to new kinds of
energy sources but every time you get
acts and typically what this meant was
you get access to more intense energy
right that's and that's what that was
and so the ability to move from burning
wood to using coal to using gasoline and
petrol and then finally to use this is
that
is that both the potency and the
consequences are elevated
around those things it's just like you
said the
the way that Fusion nuclear fusion would
change the world
I don't think unless we think really
deeply we'll be able to anticipate some
of the things we can create there's
going to be a lot of amazing stuff but
then that amazing stuff is going to
enable more amazing stuff and more
unfortunately or uh depending how you
see on it more powerful weapons well
yeah but see that's the thing Fusion
breaks that Trend in the following way
so one of them so Fusion doesn't work on
a chain reaction
there's no Chain Reaction zero so this
means it cannot physically exponentiate
away on you because it works and
actually this is why Star by the way we
know this already it's why stars are so
stable why most stars and suns are so
stable it's because they are regulated
through their own temperature and their
Heating
because what's happening is not that
there's some probability of this
exponentiating away is that the energy
that's being released by Fusion
basically is keeping the fire hot
and these tend to be you know and when
it comes down to thermodynamics and
things like this there's a reason for
example it's pretty easy to keep of
constant temperature like in an oven and
things like this it's the same thing
infusion so this is actually one of the
features that I would argue Fusion
breaks the breaks the trend of this is
that it's it has more energy intensity
than than fission on on paper but it
actually does not have the consequences
of control and sort of Rapid Release of
the energy because it's actually it the
physical system just doesn't want to do
that yeah we're gonna have to look
elsewhere for the weapons with which we
fight World War III
fair enough uh so
what is plasma that you may may have not
mentioned you mentioned ions and
electrons so what is plasma what is the
role of plasma and nuclear fusion so
plasma is a phase of matter or state of
matter so
unfortunately our schools don't it's
like I'm not sure why this is the case
but all all children learn the three
phases of matter right so and what does
this mean so we'll take like Waters an
example so if you if it's cold it's ice
it's in a solid phase right and then if
you heat it up the temp it's the
temperature that typically depends sets
the phase although it's not it's not
only temperature so you heat it up and
you go to a liquid and obviously it
changes its physical properties because
it can you can pour it and so forth
right and then if you heat this up
enough it turns into a gas and a gas
behaves differently because there's a
very Sudden Change in the density
actually that's what's happening so it
changes by about a factor of ten
thousand in density from the from the
liquid phase into when you make it into
steam atmospheric pressure all very good
except the problem is they forgot like
what happens if you just keep elevating
the temperature you don't want to give
kids ideas they're going to start
experimenting they're going to start
heating up the gas it's good to start
doing anyway so you
um it turns out that once you get above
it's approximately five or ten thousand
degrees Celsius then you hit a new phase
of matter and actually that's the phase
of matter that is for all pretty much
all the temperatures that are above that
as well too
um and so what does that mean so it
actually changes phase so it's a
different state of matter and the reason
that it becomes a different state of
matter is that it's hot enough that what
happens is that the atoms that make up
remember go back to Feynman right
everything's made up of these individual
things these atoms but atoms can
actually themselves be
um which are which are made of nuclei
which contain the positive particles and
the neutrons and then the electrons
which are very very light very much less
mass than than the nucleus and that
surround this this is what makes up an
atom so a plasma is what happens when
you start pulling away enough of those
electrons that they're free from the ion
so almost all the atoms that make up us
up and this water and all that the
electrons are in tightly bound States
and basically they're extremely stable
once you're about five thousand or ten
thousand degrees you start pulling off
the electrons and what this means is
that now the medium that is there its
constituent particles have mostly have
net charge on them
so why does that matter it's because now
this means that the particles can
interact but through their electric
charge in some sense they were when it
was in the atom as well too but now that
they're free particles this means that
they start it fundamentally changes the
behavior it doesn't behave like a gas it
doesn't behave like a solid or a liquid
I mean he's like a plasma right and so
why is this why is it disappointing that
we don't speak about this it's because
99 of the universe is in the plasma
State it's called Stars
and in fact our own Sun at the center of
the sun is what clearly a plasma but
actually the surface of the sun which is
around 5500 Celsius is also a plasma
because it's hot enough that is that in
fact the things that you see sometimes
you see these pictures from the surface
of the Sun amazing like Satellite
photographs of like those big arms of
things and of light coming off of the
surface of the Sun and solar flares
those are plasmas what are some
interesting ways that this forced state
of matter is different than gas
let's go to how a gas works right so the
reason a gap and it goes back to
fireman's Brilliance and saying that
this is the most important concept the
reason actually solid liquid and gas
phases work is because the the nature of
the interaction between the atoms
changes and so in a gas you can think of
this as being this room and the things
although you can't see them is that the
molecules are flying around but then
with some frequency they basically
bounce into each other and when they
bounce into each other the exchange
momentum and energy around on this
and so it turns out that the probability
and the distances and the scattering of
those of what they do it's it's those
interactions that set the uh about how a
gas behaves so what do you mean by this
well so for example if I take a a an
imaginary test particle of some kind
like I spray something into the air
that's got a particular color in fact
you can do it in liquids as well too
like how it gradually will disperse away
from you this is this is fundamentally
set because of the way that those
particles are bouncing into the
probabilities of those uh the rate that
they go at and the distance that they go
out and so forth so this was figured out
by Einstein and others at the beginning
of the Browning motion all these kinds
of things these are these were set um up
at the beginning of the last century and
it was really like this great Revelation
wow this is why matter behaves the way
that it does like wow
um
um so but it's really like and also in
liquids and in solids like what really
matters is is is is is how you're
interacting with your nearest neighbor
so you think about that one the gas
particles are basically going around
until the until they actually hit into
each other though they don't really
exchange information and it's the same
in a liquid you're kind of beside each
other but you can kind of move around in
a solid you're literally like stuck
beside your neighbor you can't move like
yeah
plasmas are are weird in the sense is
that they're it's not like that so and
it's because the particles have electric
charge this means that they can push
against each other without actually
being in close proximity to each other
it's not that's not an infinitely true
statement which we go together it's a
little bit more technical but basically
this means that you can start having
action or exchange of information at a
distance
and that's in fact the definition of a
plasma that it says these have a
technical name is called a coulomb
collision it just means that it's
dictated by this Force which is being
pushed between the charged particles is
that the definition of a plasma is a is
a medium in which the collective
behavior is dominated by these
collisions at a distance
so you can imagine then this starts to
to give you some Strange Behaviors
um uh which I could I could quickly talk
about like for example one of the most
counterintuitive ones is as plasmas get
more hot as they get higher in
temperature then the collisions happen
less frequently
it's like like what that doesn't make
any sense when particles go faster you
think they would Collide more often
but because the particles are
interacting through interacting through
their electric field when they're going
faster they actually spend less time in
the influential field of each other and
so they talk to each other Less in an
energy and momentum exchange point of
view it's just one of the count one of
the counter-intuitive aspects of plasmas
which is probably very uh relevant for
nuclear fusion yes exactly so if I can
try to summarize
what a nuclear fusion reactor is
supposed to do
so you have what a couple of elements
what are usually the elements usually
deuterium and tritium which are the
heavy forms of hydrogen hydrogen you
have those and you start heating it
and then as you start heating it I
forgot the temperature you said about
100 million no first first it becomes oh
first it becomes a plastic so it's a gas
and then it turns into a plasma at about
10 000 degrees and then so you have a
bunch of electrons and ions flying
around and then you keep heating the
thing
and uh I guess as you heat the thing the
ions hit each other rarer and rarer Yes
except oh man that's not fun so you have
to keep heating it
um such that uh you have to keep hitting
into the probability of them colliding
becomes reasonably high and so and also
on top of that I'm sorry to interrupt
you have to prevent them from hitting
the walls of the reactor that's exactly
somehow so you asked about the the
definitions of the requirements for
Fusion so the most famous one or some
sense the most intuitive one is the
temperature and the reason for that is
that you you can make many many kinds of
plasmas that have zero Fusion going on
in them and the reason for this is that
the average so I mean you can make a
plasma at around 10 000 in fact if you
come by the way you're welcome to come
to our laboratory at the psfc I can show
you a demonstration of a plasma that you
can see with your eyes instead of about
10 000 degrees and you can put your hand
up beside it and all this and it's like
and nothing there's zero Fusion going on
so you have uh so what was the
temperature of the plasma about ten
thousand degrees you can stick your hand
in well you can't stick your hand into
it but there's a glass tube you can
basically see this yeah yeah and you can
put your hand on the glass too because
it's what's the colors of purple it's
yeah it's purple yeah
it is it is kind of beautiful
um yeah plasmas are actually quite uh
astonishing sometimes in their beauty
actually one of the most amazing forms
of plasma is Lightning by the way which
is is instantaneous form of plasma that
exists on Earth but immediately goes
away because everything else around it
i