This episode is sponsored by CuriosityStream. Get access to my streaming video service,
Nebula, when you sign up for CuriosityStream using
the link in the description. Without the stars no life would exist on Earth
or any other world which might harbor it, but could stars themselves host life? Sometimes in science fiction, particularly
in what we call Space Opera, where the science is very subordinate to the fiction if present
at all, we’ll see an alien race that evolved to live inside stars. At first this notion can seem rather fantastic,
and indeed it probably is, but we’ll look at some ways in which it could conceivably
occur either naturally or by artifice. We will focus particularly on the idea of
a star or stellar object being a conscious mind itself, and indeed that notion long predates
science. Mankind has had a lot of deities down the
millennia but perhaps the most common is a Sun God, Ra or Amun of Egypt, Apollo or Helios
of Greece, or Sol of Rome being but a few of many dozens of such deities we have recorded,
and doubtless there are more we do not. Indeed we name our sun Sol when wishing to
distinguish it from other stars and it is from that we get the term solar system. Of course much of that will depend on what
we mean by life and also what we mean by a star, both in terms of what counts as a star
and where exactly a star ends and space begins. One might argue that just as life on Earth
occupies only the thinnest edge of Earth’s crust, Earth and the other planets occupy
but the edge of our own Sun, whose total mass outnumbers all those worlds combined by 500
to 1. And as we’ll see today, one example of a
conscious stellar object that definitely can exist inside known science, the megastructure
known as a Matrioshka Brain, while fundamentally run on a star in its basement, might well
be far larger in diameter than what we usually define as our solar system. But we should start with the basic concept,
as usually presented in fiction: That some entity or species dwells inside a star much
like our own. Could this be? Well, not anything running on biochemistry
to be sure, or any chemistry. The substances with hottest melting point
are still lower than the surface of the Sun and while you still technically can have liquid
or gas-based chemistry of course, without the ability of large complex molecules to
form and persist, it’s hard to imagine any complex self-replicating organism coming into
being. We’ll offer some challenges to that in a
bit, but we must first mention that our Sun, for all that we call it a yellow dwarf, is
actually rather large and hot as stars go. Indeed you won’t hear yellow dwarf as often
anymore, it’s a nomenclature dating back to when most stars we could detect were unsurprisingly
the brightest of them, and brightness rises with mass of star far faster than it diminishes
with distance. Indeed most stars in this Universe are red
dwarfs, not a single one of which is visible to the naked eye, including Proxima Centauri,
the star closest to Earth. Since we saw those biggest and brightest stars
first, much bigger than ours, we concluded ours was rather small. And again we now know it is not, and the bigger
a star is the hotter it is. Indeed many red dwarfs have a temperature
of just over 2000 Kelvin, and there are a handful of metals that remain solid at that
temperature and some alloys as well. You could, for instance, drop a ball of tungsten
onto such a star and it would not melt. Initially anyway, the thing about stars is
that when we refer to their surface we’re talking about where they become opaque, not
some solid bit of star or sea of fire, that is part of why it’s very hard to say where
a star begins and ends, and arguably it’s much further out in space, all the way to
where inner planets would be. At our sun’s surface the density of matter
is actually much thinner than the air we’re breathing and such a ball of tungsten would
simply fall down till it reached a place that was hot enough to melt it. Though a sufficiently large and hollow one
might maintain a total density lower than whatever it was at a depth where that sphere
would melt and just float around. Most of the metals with that sort of temperature
resilience are not the more plentiful ones, red dwarf stars are also fully convective,
meaning their contents bubble about and metals don’t just sink to the center. So one could imagine some scenario akin to
what we think might have occurred on Earth for proto-cells, essentially a big bubble
forms of some substance and things begin happening in it. Tungsten and Tantalum and Rhenium and Molybdenum
might be the basic building blocks, as they could remain solid at such temperatures, and
many others would still be a liquid and might serve some parallel role to water. It’s quite a stretch but we could probably
make such a thing, so nature might too. I don’t think beings made of hollow metal
spheres are what most people picture when thinking of sun-life, usually we think something
more like a Phoenix, but most of us don’t picture aliens as being made of a bunch of
spheres either even though that is not a bad description of us. Humans aren’t particular spherical, at least
if they watch their diet, but plenty of the cells inside us are and you might get some
truly titanic organism living in a star, made of such building blocks. After all stars are quite enormous so if your
basic building block of life was meters across, not micrometers, you could still have such
organisms without getting crowded. Especially inside a Red Giant, which are vastly
larger than our Sun but quite cool in their upper layers. Of course, life might not need to necessarily
run on chemistry either. Probably the most critical part of life is
having an abundant energy source and stars certainly have that. Though not so much for those coolest red dwarfs,
who are so weak in their illumination that we didn’t even know they existed for the
longest time, in spite of being the majority of stars. Presumably anyway, by modern theory you can’t
have a star below a certain mass needed to kindle hydrogen fusion, but we do have a close
tier beneath the red dwarf, or M stellar classification. Indeed we have three nowadays, L, T, and Y. Class L dwarfs are either just barely above
the mass minimum for hydrogen fusion or below it, a Brown Dwarf, and are cool enough to
allow metal hydrides and alkali metals. Beneath that we have the Methane Dwarfs, Stellar
Class T, and these obviously can have methane on them and range between 550 and 1300 Kelvin,
and I should note that while Class M red dwarf stars outnumber all the classic stars combined,
these smaller Class L and T stars might outnumber them too, and since they live so long relative
to stars, barring collisions they would only grow in number as time goes by. The more time you have, the more chances for
life, if possible, to make itself pop up and grow in complexity, something we’ll want
to keep in mind when we get to discussing stellar remnants in a bit. Our smallest stellar class, arguably sub-stellar,
is the Class Y, or coolest anyway. Temperature and mass are not always tightly
linked, particularly for stellar remnants such as Red Giants, but this class of Brown
Dwarfs can be much cooler, indeed the coolest yet detected is cooler than Earth, though
most of the handful we’ve spotted are warmer. Needless to say if we’re treating these
as stars, or at least as stellar objects, a place larger than Earth and dense in material
and about our temperature has to be considered a plausible option even for carbon-based life,
and we would expect them to have an abundance of a lot of other life-related molecules such
as water, ammonia, and methane. We also have an entirely different type of
star classification, the Class C or Carbon Star, a Red Giant whose atmosphere contains
more carbon than oxygen, red giants not being terribly long-lived and about as dense as
what we think of as outer space, this wouldn’t seem likely to spawn life either but you might
get a lot of carbon objects forming nearby as that star died back down to a white dwarf. A key notion where life is concerned, we aren’t
necessarily talking about what exists now either, but what may arise in the future,
and as stars create more and more heavy elements not only do we get more planets and new types
of stellar classifications as we get metal richer stars, but we get more time for life
to develop. If the origin of life is a statistics game,
the longer things go on and the more heavier elements you have, the more likely you’d
see it arise in surprising places. However, we keep talking about life in a star,
and should not ignore that many stars aren’t really singular, they’re binaries and often
have quite a lot of exchange of material between them if they’re closer. I could imagine some life emerging in such
a matter stream between binaries but more to the point, I could imagine a lot of smaller
objects forming and hanging around such a binary as an asteroid belt equivalent rather
than some inner planet like Mercury. In such a case we might see near-stellar asteroid
or comet clouds have life emerge on them and slowly form a natural dyson swarm around that
star, or some life forming further out and migrating there as they developed a higher
tolerance to heat and light. We looked at such notions more in our episodes
Void Ecology and Space Whales. This is one scenario for a conscious stellar
object to form, not unlike the notion of some ocean planet developing algae mats that slowly
evolved into a single sentient planet brain, only at the stellar scale. This might be much easier in a binary system
where there was a lot of debris forming around and swirling about, both near and far from
the stars, in very large and rich asteroid belts. Speaking of planets brains though, something
we’ve noted before in discussion of digital consciousness or mind augmentation and cybernetics,
is that the signals our neurons send each other move around at less than a millionth
of light speed, so if you replaced those neurons with some optical analogue sending signals
by light, a brain the size of Earth – possessed of the same number of neurons just very spread
out, would operate at the same speed as our own minds. Your typical white dwarf incidentally is about
the size of Earth, albeit far hotter, denser, and made of degenerate matter. They do cool with time and would also tend
to have very large clouds of debris from their red giant phase hanging around, so we could
conceivably see life emerge in a cloud around one, and given the size it’s possible that
if those smaller organisms communicated at light speed, as would not be too bizarre if
they lived in a near vacuum, that you could get something akin to a single big brain that
had communication delays on an order of the human brain. This is the big problem with megacomputers
built around stars, such as the Matrioshka Brain, they have almost incomprehensible computational
power, or thought capacity if we’re thinking of this in Artificial Intelligence or Digitally
uploaded mind contexts, but they have immense signal lag time. Now if you just want raw computation and capacity
that’s fine, it’s only an impediment to a single large brain. Now a Matrioshka Brain is a specific type
of Stellar Computation Engine that relies on many concentric layers around a star recycling
energy from the lower layer to be maximally efficient, but it’s become a bit of a blanket
term for any stellar-scale computing engine. You can see the episode Matrioshka Brains
for details on why those layers are helpful but if we just took the raw power of our Sun
and converted that to computation under modern performance per watt, you’d get around 10^38
FLOPs or about 10 billion, trillion times what we currently estimate would be needed
to simulate a human mind, or enough to simulate the minds of the current population a trillion
times over again or a trillion times faster than now. That’s very approximate incidentally as
there’s too many unknown to bother with precision calculation and because it’s very
unlikely we’ve reached peak computational performance per watt, indeed we’re still
only running at less than a billionth of what the Landauer Limit on classic computing is
for Earth’s temperature, and you can multiply that by at least a hundred inside a Matrioshka
Brain since that limit is temperature dependent, half the temperature, twice the computation
with the same power, and a Matrioshka Brain would likely have its outer layers out past
Pluto where things were much colder and be gaining around an order of magnitude more
computation simply by the multi-layer recycling approach that gives it its name of Matrioshka,
from those dolls within dolls, Matrioshka Dolls. Again see that episode for details. However the problem there is that it would
be very hard to set that up as a single brain, as its various thoughts, even moving at light
speed, would take forever to occur. As we said, converted to light speed rather
than chemical signaling, you could spread a brain out to Earth-size and have it run
at normal human speed, but if we’re talking a construct the size of Pluto’s orbit to
take advantage of the cold, that’s around a million times Earth’s diameter and means
it would take a couple years to experience what took us a minute. Of course it could potentially have around
a trillion, trillion, trillion times the computational capacity needed to emulate a human mind, so
it kinda cancels out and then some, slow but massive. Thing is that since Pluto’s orbit is around
a million times Earth’s size, that outer layer would have around a million-squared
or a trillion times the surface area, so could be running about a trillion-trillion times
the computation of a human brain in an area small enough to run a brain at light speed
with human-neuron signal lag times. Whether you want to run a trillion-trillion
simulated people in such a spot or a trillion entities a trillion times smarter than a person
or whichever, you have a ton of thinking without the light lag issue coming up that a singular-conscious
Matrioshka Brain would have. So I suspect that would be preferred, or possibly
some multi-layered or multi-tiered hive mind. Now as we noted in Civilizations at the End
of Time, in cases for using black holes or iron stars as your Conscious Stellar Object,
be it a single mind or many, as the Universe ages that light lag issue becomes less important
because everything is running at maximum cold on small sips of power, hyper-efficient but
slow anyway. You can’t take advantage of Landauer’s
Principle of hyper-efficient cold computing unless you let your switches and chips cool
down to that temperature before flipping them again so you have to run slow anyway. And while they enjoy far more energy in the
long term and far more efficiency with that energy, they have very little actual power,
less than a light bulb rather than a normal star, so in the very late Universe you might
see these stellar computers or minds favor the singular consciousness approach as light
lag just wouldn’t matter as every has to run super-slow anyway. Now this is an artificial construct, though
we could doubtless make something that was arguably organic, or at least self-replicating
and conscious, that acted similar. However this lag time issue applies to any
megamind and is far worse for those using chemistry. The notion of a planet-wide mind evolved from
some ocean-spanning algae mat is interesting but probably unlikely just from the huge signal
lag whereas smaller mats would be dumber but run at more plausible timeline. In nature, unlike in the lab, brains are expensive
and need to serve a purpose that enhances survival and it’s rather hard to imagine
how a super-smart but super-slow consciousness could pop up. Even if it has no predators – which is usually
thought to drive brain evolution, the predator-prey cycle – its individual components aren’t
just going to evolve and keep a mutation that let them link up to form a bigger mind, and
pay for that extra energy and resources to maintain it – if it isn’t helping them
survive. The same probably would apply to anything
seeking to evolve inside a cold star or in a cloud of debris around one. I find it quite plausible we’d make life
that lived in a cloud around a star, either a classic Dyson Swarm or some void-ecology
equivalent like we discussed in that episode. I even think it’s possible if not too plausible
that such a thing could arise naturally from some organism that began in very-low-gravity
environments where adaptation to vacuum might be easier and necessary to spread out. That they might slowly disassemble all the
rocks and debris in their system to make a natural dyson swarm to take advantage of all
that light, with some semi-organic equivalent to ultra-thin solar panels taking the form
of plant leaves. However, I can’t see a single consciousness
emerging over an entire star, inside or around it, either naturally or really even artificially
at this stage of the Universe. Not because it isn’t possible – and inside
anything but the coolest star probably isn’t – but because it lacks an obvious survival
track or advantage. Needless to say, for a civilization considering
building such an object, that might not matter much and the motive is fairly obvious. While a single consciousness would be incredibly
slow, and would presumably need to be composed of lots of levels of sub-minds to act like
an hierarchy of a hive-mind, the thing is about as close to a god as you can make under
known science, and even it’s faster but dumber sub-minds many layers down, which we
might think of as layers of an angelic choir or demigods for context, would each be beyond
anything we can plausibly comprehend in terms of modern intellect. Such a thing is both awesome and terrifying,
which is probably appropriate considering how Sun Gods tended to be regarded by our
ancestors, their literal artificial equivalents would be Conscious Stellar Objects of incomprehensible
mental might. We’ve a couple quick announcements but first,
we were talking today about how you might host vast numbers of artificial minds on Matrioshka
Brains, but we recently explored the alternatives to artificial intelligence in our Nebula Early
Release, After AI. In that episode we asked what a civilization
might be like that abandoned pursuit of artificial intelligence or barely survived a machine
rebellion, and if you’d like to catch that or our Nebula-Exclusive series, Coexistence
with Aliens, you can try out our Nebula Streaming Service for free as a bonus with Curiositystream,
which you can also try out for free using our link in this episode’s description,
curiositystream.com/isaacarthur. Curiositystream has thousands of top-notch
and thought-provoking documentaries available for watching, and during the current crisis
they are offering a 40% off “Stay at Home Deal”, if we’re going to have to social
distance ourselves, let’s at least spark some curiosity while we’re doing that, and
again you can try Curiositystream and Nebula out for free by using the link in this episode’s
description, curiositystream.com/isaacarthur. So I’m back from my honeymoon and Sarah
and I had a great time, we just wanted to thank everyone for all the well-wishes, not
to mention gifts that folks sent us. The wedding was a bit different, with all
the social distancing requirements, but as a silver lining a lot more folks were able
to join us for the livestream of that then could have fit in the building. Lots of folks have been trying the livestream
approach and I suspect that will be a trend that continues even after the crisis. Speaking of livestreams, we did have to skip
last month’s but we will have our usual monthly livestream Q&A to close out the month,
Sunday, May 31st. Before that though we’ve got two more episodes,
starting this Thursday with a look at antimatter, how we can produce and store it, and what
uses it might have besides blowing things up. Then the week after that we’ll return to
the alien civilizations series to consider the notion of aliens who come in peace, and
actually mean it, in Benevolent Aliens. For alerts when those and other episodes come
out, make sure to subscribe to the channel, and if you’d like to support future episodes,
you can donate to us at Patreon or our website, IsaacArthur.net, linked in the episode description. And if you enjoyed this episode, don’t forget
to hit the like button and subscribe to the channel. Until next time, thanks for watching, and have a great week!
