Daniel and Jorge Explain the UniverseWhat can slime molds teach us about dark matter?
Daniel and Katie talk about where the missing matter in the Universe might be, and how slime molds might help us find it.
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Hey Katie, how do you feel about mushrooms?
I'm a big fan. They actually make a mean pizza fung guy over here.
M that reminds me of the best pizza I ever ate. It was covered in morels and I still think about that pizza like twenty years later.
Yeah, they actually have these really good fried mushrooms, these local ones, and it was absolutely amazing. But yeah, that is that is entry level stuff, Daniel. If you're a real mushroom fan, you would be into the weirder varieties.
Oh, bring on the challenge, you know, hand in the woods, oyster mushrooms. I'm into all of it. Yum yum yum.
Well what about manticore's tongue?
Why is that real? Did you just make that up?
Wait until you see monkey's head.
Well, put it on a pizza and I will take a bite. Hi. I'm Daniel. I'm a particle physicist and a professor at UC Irvine, and I will taste any mushroom that isn't labeled as toxic.
I am Katie Golden, and I too will eat any mushroom as long as you eat it first. I am the host of the podcast Creature Feature, and I'm stepping in for Jorge. Or, as some theorize on the internet, we are actually sort of like two states of the same person.
Maybe if you eat the right mushroom, we turn into Jorge. Is that how it works?
I'll never tell.
The banana mushroom. Well, Welcome to the podcast Daniel and Jorge explain the Universe, in which we take a big juicy bite out of the weirdest, strangest, slimiest mysteries in the universe. We think that the whole universe deserves to be understood, deserves to be explained, and deserves to be explored, at least mentally by these funny little apes living on this weird little rock in the corner of the galaxy. We think all of it should make sense, and we do our best to tackle the biggest, weirdest, slimiest, amazing questions about this bonkers and beautiful universe and explain all of it to you. My friend and co Hostje can't make it today, so as Usual. We are very grateful to have Katie Usual host of Creature Future podcast. Katie, thanks again for joining us.
Yeah, absolutely, I am pumped to be on. I guess like the slimiest episode you guys have ever done.
Did you eat some slimy mushrooms to prepare yourself to get yourself in the right mental frame.
I just kind of licked the walls of a cave, a random cave, to get myself in the right mindset.
I think everybody out there just had their stomach turnover that mental image cave.
Not into cave cave tasting. I see you.
Oh well, and I suggest that nobody out there google cave tasting because you have no idea what might pop up. But today on the podcast, we're going to be taking advantage of Katie's knowledge of biology to try to bring together two very disparate topics to try to unify our desire to understand the whole structure of the universe, its shape, its form, its history together with the things that we see here down on Earth. You know, a lot of folks write to me and wonder about whether there are connections between the shape of the universe on the biggest scale, you know, this cosmic web with filaments and sheets of stars, and the patterns that we see down here on Earth, or the organization of the atoms, as if maybe there's some deep structure to the universe and it reveals itself on many levels.
Yeah, I love that. I think that there often seems to be this parallel between the facets of physics, like the kinds of behaviors that particles will exhibit and the behaviors that biological organisms will exhibit. So these patterns that we see for these you know, inorganic particles will pop up when you're looking at organic particle or organic organisms, and I just find that so fascinating.
It is fascinating because it hints at something really really deep. If you discover some basic mathematics about the way the particles organize themselves, and it also applies to the way sea lions build colonies and the way the galaxies organize themselves, that suggests that you've revealed something really really true about the universe, that there's an organizing principle of play that can unify them. You know. One of the first people to do this, as Isaac Newton. His theory of gravity could describe not just the motion of apples falling from trees, but also the motions of bodies in the heaven. And so to have this moment where you feel like, oh, I've discovered something which is true not just about what's around me, but also about what's in the sky and maybe about everything. That must have been an incredible moment. Of course, we know now that he was wrong about everything, but you know, the idea that you could potentially discover these organizing principles that work across incredibly distant length scales, because galaxies are hundreds of thousands of light years across and particles are ten to the minus twenty meters across, and so to imagine that you could have rules that describe everything on those scales, it's very tempting. It's very tantalizing, and I think that's why people look for these connections and that's why we're going to talk about some of those today.
Yeah, even Alan Turing would sometimes use his incredible genius level skills to make these connections between things like math and particles and biology, Like he explored the how animals can have things like stripes or spots like these clusters of melanin, and he worked out this whole kind of model with like the randomized movements of particles and sort of using that as a way to understand how you could get a pattern like stripes through the semi random movement of say like melanin cells. And it's really it's just so interesting how deep these things go, like these very broad mathematical or physics based principles.
Yeah, it's like the universe is a grand experiment and it's revealing the underlying rules as it plays out, and if you pay attention, you can spot them here, and you can spot them there, and you can learn things about galaxies by looking at things under a log in the forest.
The universe is the world's biggest escape.
Room, exactly. There are clues everywhere, you know. I was talking to my son about science fiction movies and he was asking me why I'm so picky about the science being right, and I was telling him that it was like a detective movie. You know, if you get a bunch of clues and they point you in one direction, and then at the end the clues didn't make sense or they're not consistent with the answer, then it feels pretty frustrating and disappointing. And I see every science fiction movie as sort of like a new mystery, like, what are the rules of this universe? How does it all come together? What clues are we getting? And so I want the clues to be accurate and not just to lead you astraya in to be nonsense.
Yeah, and you don't want to like accidentally frame a neutrino for murder or something.
I don't know, they're pretty sneaky, those neutrinos really weird, pretty suspicious. But you know, there is one organism which has inspired a lot of strange reactions in people to wonder whether or not it's intelligent, or whether or not its structure reveals something about the nature of the universe. And this is very weird entity called the slime Mold. And you know, my first interaction with the slime Mold actually came from a listener email. We had an episode about the book Semiosis, which is a science fiction novel in which plants organize and become intelligent in sort of a strange way that's not exactly penetrable by human intelligence, but you know, they can act, and they can think and they can plan in this novel, and one listener, Ian hanns Portman, from the UK wrote to me and said that it reminded him of one of his favorite pets, which were slime molds, and would I be interested in him mailing me some example slime molds. Oh, so, of course I said, sure, please send me these crazy creatures via the post, and he did so. He sent us some slime molds via the mail. Because they're very hardy, right, they can survive a long time. And my wife grew them for a while and then I think she threw them out and they ended up taking over our compost bin for a while. So they're out there now exploring southern California and gobbling up all the amazing treats that they can find.
Wonderful. I'm sure that won't sort of come back to bite us and say, one hundred milillion years.
But slime molds are fastenating because they are these tiny little creatures, but they also seem to exhibit some form of intelligence, and the way they organize themselves might provide clues as to why the whole universe organizes itself. The patterns of slime mold networks might reveal something which tells us about the structure of the universe and where all the.
Dark matter is, And I guess where all the compost heaps Jupiter's been keeping.
Yeah, maybe dark matter is just the compost of the universe. You know, it's just the universe's recycling.
Would that make black holes the sort of insyncorators of.
The universe universal garbage disposals? So I was curious if people had thought about this or understood that there might be a connection between weird, sticky blobs on forest floors and the structure of the universe on the grandest scale. So I went out to our cadre of Internet volunteers and asked them what they thought about a potential connection between slime molds and dark matter. Think everybody who participated, and if you would like to get similarly puzzling questions via email from me, don't be shy, write to me two questions at Danielanjorge dot com. So before you hear these answers, think to yourself, what do you think slime molds might tell us about dark matter?
And have no idea what a slime mold is, but I'm guessing it might be the movement of dark meta around the universe and objects how viscus and fluid it is where it fills in the gaps.
I actually don't know slime molds.
I know they can They've been shown to be.
Able to compute stuff, But what that has to do with dark matter, I have no idea.
I didn't expect to expect a question like this. I have no idea whatsoever slime molds, no nothing, I've got absolutely nothing. Sorry, best I can do.
Slime molds and dark matter.
I'm all in favor of mixing up stuff, but I don't see any connection between those two. Very curious to know what that is.
I have no idea what slime molds have to do with dark matter, but I imagine their growth or something in their molecular constitution that might be maybe affected by dark matter. I'm not sure.
I have no idea.
I have no idea what slime molds are.
When I think of slime, I just think of the green goo.
I'm sure that has nothing to do with what we're talking about.
I don't know what they say about dharma matter. I just know that they try to map something. I don't know too much, too many details about it, but it is interesting. How close can can you get with this model?
I don't know is there something about slime molds that we just do not know.
Like it's like the mystery mold of the universe. It holds all mold.
Together a man.
Maybe it just tells us there's more mystery here than we really thought there was.
All right, So a lot of confusion in these antsers. Not a whole lot of people had even heard of slime molds or had any idea what they might tell us about the universe. Does that surprise you, Katie?
Yeah?
Yeah, I mean I love slime molds, so I feel like everyone should love them as well. Obviously they are in a way cute. I suppose I try to find the cuteness in every organism or I guess like blobular cluster of organisms. So yeah, I really hope people gain some slime mold awareness through this.
I'm glad that you're pro slime mold, that you're really thinking about what the slimes need. They need human representatives to really speak up for them, advocates. Yes, our interest here is not just to think about what the slime mold needs, but to try to solve the mysteries of the universe, to think about where in the universe everything is and how it got there and how we can learn about it.
Yeah, Yeah, I am really curious because slime oulds are one of the most mysterious organisms on Earth. Their behavior and what exactly is going on with them is really interesting, and it's relative. There's a lot of room to explore still, so there's a lot unknown about them. There are a lot of studies and a lot of controversy. So I feel like the fact they are just so already so mysterious, it's just very intriguing that if we unlock some of these mysteries of the slime mold, we may be able to unlock some of the mysteries of the universe exactly.
Maybe slime molds are aliens and they're here to tell us the secrets of the universe.
They do look very alien like in just like there's sort of a blob, a growing blob. So if that is your image of an alien sort of a blob, I think there's been a few sort of B movies where an alien blob comes from outer space and then consumes people or takes over the world.
Well, I'd love to talk about B movies with blob aliens. Let's first talk about the structure of the universe where everything is and where everything isn't. So, as you probably know, the universe is not just the stuff that we see out there. Of course, there are galaxies, and there are stars, and there are planets, and there are huge clouds and gas and dust. But that only adds up to about five percent of all of the stuff in the universe. The rest of the universe is other stuff, stuff that we do not understand. A huge chunk of that, like twenty to twenty five percent is dark matter, something we know is out there. We know it's matter, we know it's stuff, we know it has gravity, but we don't know what it's made out of. And all that just adds up to about thirty percent of the universe. The other seventy percent of the energy density of the universe. If you took like a cubic light year of the universe and asked where is all the energy, seventy percent of that would be in something else called dark energy, which is accelerating the expansion of the universe, tearing it apart faster and faster every year. And while we'd love to dig into dark energy on every podcast because it's an amazing mystery, today we're focusing on sort of where is the stuff in the universe? Where is the matter by which we mean dark matter and normal matter.
How do we even know that dark matter exists? If it's something that's so mysterious and so seemingly extremely difficult to like directly observe it, What are the signs that dark matter exists? Like, is it sort of a negative space scenario where we are able to see the dark matter based on the things around dark matter?
Exactly? We can't see dark matter directly. The name dark matter itself is a little misleading because it makes you think of like a big dark cloud that would block your vision. But actually dark matter is more like invisible or transparent matter because lights is right through it doesn't give off any light, it doesn't reflect any light. You can't see it directly using light because it just doesn't interact with photons at all, And the only way that we can see it is through its gravitational effects on other things. And so that means, for example, that it holds galaxies together, because we think that all galaxies are swimming in these big dark matter halos that are compressing them and keeping them together as they spin really really fast. We also know that dark matter has played a huge role in determining the structure of the universe, Like why is there a galaxy here at all? It's because there was a big pool of dark matter that pulled together all these gas and dust to form stars. Without dark matter in the universe, that structure would take a lot longer to form, be like another ten billion years before the gravity of just the gas and the dust was able to pull it together to make stars. So dark matter really has shaped the universe, even though we can't see it directly.
So it's kind of like the invisible hand of the universe if we want to get all economics about it. But that is really interesting. Could you, I mean, if you gave me a spoonful of dark matter, like, could I feel it? Or would it just sort of destroy me? Would it start impacting the things around it? Would my office chairs start to float up and get sucked in around or pushed around? What is that sort of physical attribute of the dark matter? Because my sense of matter is matter is a physical thing that impacts things physically, whereas energy differs from matter, and that it's not like a it is it's hard for me to describe without the kind of just reiterating the physics concepts.
Yeah, it's a great question, but unfortunately, dark matter is not something that you can put on your pizza. Dark matter interacts with you gravitationally, which means that it pulls on you. It tugs on you gravitationally, but because it doesn't interact with you using electro magnetism, it passes right through you, the same way that like neutrinos can. Neutrinos come from the Sun and they shoot through the Earth and they don't stop. They don't obey the boundaries of your body or the walls or the ground because they don't see them. The universe is transparent to them. They don't have that way to interact, so they just ignore that kind of matter and pass right through it. The same is true for dark matter, which remember, is not out there in the universe. It's here surrounding us. It's all around us. It's in this very room that you are in. But if a piece of dark matter flew right through your brain, you wouldn't notice, and either would it, because you too cannot interact except through gravity, which is super duper weak. The only way we can even know dark matter is there is when there are enormous galaxy sized blobs of it having gravitational effects on the visible matter.
What you didn't see was me with a broom trying to sweep out all the dark matter. As you told me that it's here with me right now, So like it's scattered throughout the universe. But then you can have like these big sort of blobs of it as well that have a stronger impact on their surroundings.
Yeah, and these blobs have an amazing history that really shaped the whole structure of the universe. If you cast your mind back to very very beginning of the universe, everything was filled with like an even smooth amount of energy. No spot was any different from any other spot, because like, why would any spot be special. The universe doesn't have a center. No location is different from any other location, so everything is the same. But if everything is the same, then gravity can't really do anything because it's being tugged in every direction the same amount. But what happened very early on was that you got quantum fluctuations. You know, pairs of particles were created out of the vacuum just randomly, energy converted into matter and back, and so some places were a little denser than others, and then the universe expanded very very rapidly, so those little quantum fluctuations, which normally you would never notice and would have no gravitational impact, got blown up to enormous props. The early universe expansion is like a factor of ten to the thirty. That's ten with thirty zeros in front of it. Something used to be like a nanometer is now light years across, and so then gravity had something to hang on to. You could say, oh, this spot here is denser than its neighboring spots. I'm going to start tugging on those particles. And that's how structure was formed. It was the seeds that gravity needed to grab onto. And then you fast forward some millions of years and gravity has gathered that together into these huge sheets of dark matter. And where those sheets overlap with each other, you get even stronger densities, and those would call filaments. And where those filaments intersect with other filaments are the most powerful densities, and those are the intersections where galaxies form, because you get this intersection with a lot of dark matter, and it's like a lake with all the filaments sort of like contributing to it. Everything is flowing towards the densest spots and that's where galaxies formed. So these sheets and these filaments of dark matter really have to the whole structure of the universe.
Well, so we kind of started out as a puree and then became like Campbell's chunky chicken noodle soup. But yeah, that is I mean, even the way describe it does sound very biological. Things kind of coagulating and coalescing and pulling on each other. It sounds like something like milk curdling, which is really interesting. So dark matter has this huge impact on the universe. How do we How have we kind of observed that happening.
It's a great question because dark matter is kind of invisible. So some of this is a little bit theoretical. Some of this is like running simulations and saying, if we put all these rules into the universe, what kind of universe do we get? Do we get the kinds of structure that we see today. But of course we'd like to see the actual structure. We'd like to look out into the universe and observe how things really are. And the fascinating thing about these filaments is that connections between galaxies, right, Like our galaxy is floating in space, and there's another galaxy nearby, Andromeda. But there's not just empty space between us and Andromeda. There's an invisible filament of dark matter, but there's also a filament of normal matter. Not all of the gas in the dust ended up in the galaxies, A lot of it is actually between the galaxies. And so for example, like only ten percent of the matter is in galaxies. Like if you take a random proton in the universe, only one out of ten are in the galaxy right now. Another fifty percent of them are around the galaxies, like in a big blob of gas that hasn't yet fallen in but might soon. And the rest of it, like thirty percent of the stuff in the universe, we're not even sure where it is. It might be in these filaments between galaxies. It might be that there's huge amounts of gas lying along these filaments made by dark matter, but it's hard to tell. It's hard to see these things because the gas is so faint.
That's so interesting. So we've got like these almost these like tendons or strings that are connecting these galaxies, but not just connecting them, but also influencing the matter around them by pulling on it. Can we actually, like, when say we got just a really good telescope, could we actually see these filaments or would since dark matter is invisible, would we not really see anything.
We can see them a little bit, but it's very limited. So these filaments have lots of gas in them, and if the gas is hot, meaning the particles are moving really really fast, then they emit light. They emit X rays, for example, and we can see that with our X ray telescopes, and you might be confused, like, how can this gas be hot? We're talking about something in deep space between galaxies or remember that things can be hot, but they can also be dilute. It's not like hot in the sense that you could like hang out there in your swimsuit and have a nice time. You would definitely freeze if somebody dumped you in these filaments because there isn't a lot of heat there. But there are fast moving particles and those emit rays. So we have seen these filaments directly. The problem is that it's hard to see the whole cosmic web using these X rays because we're at one little spot of it. It's easiest to only see the really close parts. We'd like to see the whole map of the universe. Another way we can look at these is to see how light is absorbed as it comes to us from things behind these filaments. For example, quasars are very very bright sources of light. They are black holes that have swirling gas around them, and that gas is being squeezed by the tidal forces of the black hole and heated up to incredible temperatures and emitting these very very bright pencil beams of light. And when they pass through the filaments, some frequencies of light get absorbed based on what's in them. So we can use this to sort of like X ray these filaments to say, oh, here's one and it has some hydrogen in it. Oh, and look it also has some iron in it. How did that get there? So we can see sort of the nearest ones using X rays, and we can have a few like pencil beams through the universe to give us a sense for where some of the other ones are. But we don't have a great way in general to figure out where these filaments are.
That's really interesting, I mean it seems like basically trying to detect these filaments. It's like trying to sort of toss a marble at another marble, like another a mile away and hit it. So by observing sort of like how the effect it's having on light as it's passing through, we can kind of tell a little bit about them.
Yeah, but you need a source of light. You need like a conveniently placed quasar to show you where these things are. It's sort of like the way a laser beam in a dark room will show you where the dust is, but it won't show you where the dust is where the laser is not pointing, you know. And so if you have a few lasers through a room, you can see where the dust boats are, but most of the room is still invisible to you.
Wow. So we're really just relying on luck to be able to see any any sign of these filaments.
Yeah, and it's a huge mystery how much gas is in these filaments. You know, we're talking about a big chunk of the universe's budget is like unexplained, and people are used to the idea that dark matter is sort of like this missing chunk of the universe and that five percent of the universe is our kind of matter. Now we're talking about like thirty percent of that five percent, not some mysterious form of matter, but just like normal matter, protons and neutrons. We can't explain where all that stuff is, like a huge chunk with a third of the visible universe, the stuff we're supposed to understand is gone missing. This is called the missing baryon problem, and so understanding if it's in these filaments could really help us get a clear picture of, you know, the whole universe.
I mean, have we tried printing out posters with missing baryon call this number reward.
We've tried sending traps, you know, with nice hasty rushroom pizzas on them, but they don't seem interested.
So let me go grab a delicious pizza right now, and when we get back, why don't we talk a little bit about those slime molds and see what they're about, now that we've learned a little more about dark matter.
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All right, and we are back, and I have just polished off this wonderful slime mold pizza. Actually, no, don't do that. Don't eat unidentified slime molds. But Daniel, I mean, you have gotten to know a slime mold personally, so you've actually had a personal relationship with a slime mold. What did you learn in that relationship with that slime mold, the listener sent you.
I learned that slime molds are not as slimy as you might expect. You know, They're one of these weird creatures with multiple stages in their life that look very different. You know, like how caterpillars and butterflies are really the same creature, just in a different part of its life, and slime molds only are slimy in like one mode of their life, So sometimes they can look just sort of like a normal weird blob or like an actual mushroom or something sort of crawling its way across your countertop. So I was a little bit underslimed.
Yeah, that is one of the most baffling things about slime molds is they have a life cycle that's just very confusing, and it's almost like they turn into completely different sort of organisms throughout their life. I mean, this is not something unheard of for other animals. Of course, you know, the first person to see a caterpillar and then see a butterfly, I would have no idea this is the same animal. It goes through these very different stages, and it goes through a crawling stage, and then the chrysalis, this immobile sessile stage, and then a flying stage. So that must have been very mystifying for the first people to see these organisms. And of course slime molds are also really mysterious, and we were learning so much about them even now. But yeah, so the first thing I think to know about them is that it is not a single organism. It is generally speaking, these slime molds that you will see, like this kind of blob or splat mark is going to be a amalgamation of a bunch of individual organisms that are all interacting with each other like an ant colony or a b colony, but on a microscopic scale and smooshed together.
So it's like a community you're saying, not just like a single organism.
Yeah, I mean it. They will have stages in their life where they will be sort of a single organism, but yeah, the most of their life, and indeed, like the when we can actually see this thing that looks like a single organism, that is a cluster of these single celled organisms. So they used to be classified as fung gui. You know, we've talked about the mushroom, pizza and everything, but that's actually a somewhat outdated classification. So now they are just kind of their own thing. It's a very strange classification because it is like eight hundred species who are all sort of loosely related phylogenetically, but kind of lumped together as it's like the extra pile in terms of organisms, where we try to make these classifications and now we have this group of kind of weirdos that we don't know how else to classify them, so they all get lumped together as slime molds.
I mean, if I just google slime mold. For example, I see a bunch of interesting things. I see some weird yellow things with like what looks like veins in them, you know, these like transport networks. And then also see like weird purple blobs and weird pink things that look like mushrooms, and you know some things that just really do look like gelatinous cubes taking over the earth.
You know.
So are you saying this is sort of like a biological frontier? Is not something we really understand how they evolved and how they're related. It just sort of like a grouping of mysterious objects that are sort of similar to each other.
I mean, I wouldn't say it's completely mysterious. We have, I mean, researchers have discovered a lot about them, but it is a little more of a wild West situation than maybe some other organisms that we've studied. So basically they are. What we do know is they are eukaryotes like humans, plants, and animals. These are all eukaryots, but they are protists. So a protest is any kind of eukaryote that is not an animal, plant, or fungus. So it's just basically we know definitely what they aren't, so we know that they are not animals, plants, or fungus, so we kind of give them their own group. But in terms of figuring out how they are related at each of these slime mold species, you know, that is still a growing topic of research. And in fact, that a slime old you google, that yellow one probably is the Fyceerum polycephalum, which is that yellow blob. And I think we've actually shot that species of slime mold into space to just see exactly what is going to happen with it in a low gravity setting.
So do you think that they're going to land on the moon and partner with tartar grades to build the next alien empire?
I fear what would happen if they partnered with tartar grades. So they have a very strange life cycle. So during one stage of its life, it's an acellular organism, so instead of actually like at least for this fiseram polycephalum, So it differs depending on the slimeold, but like for that specific slime mold, it just has like one kind of cell that instead of just like dividing into multiple cells as it grows, it's just like one big kind of goofy blob. But you know, other types of slime molds are a group of individual unicellular organisms, and they can really a mass to large sizes. So some can be up to twenty kilograms in mass and they can be measure in square meters in size, which is alarming.
Twenty kilograms. Wow, that's like big enough to tackle somebody. I mean, has a slime mold ever taken down a person?
I don't think they have, just because they move so slowly.
What about like a cartoonist that was like sleeping in really late. Did you think it could eat Orge if he was not paying attention?
I think maybe yeah, if Jorge was staying up late at night finishing a cartoon and kind of slept in, maybe.
All right, Well, let's hope somebody warns him.
That's why you set alarm clocks so your local slime mold won't devour you as you sleep in.
So I think slime molds are fascinating because they have these weird life cycle and biologically they're really interesting. But also they seem to be able to like to do things. You talked about slime molds at these individual entities which sometimes come together to act communally, and it's amazing to me when they can do things as a group that an individual couldn't do. There's some example of these things like learning.
Yeah. Yeah, So they can either live freely or they will join together to form a multicellular aggregate. And this is where, yeah, it gets really weird and really interesting. So, like there have been multiple studies to see how they act as a group. I mean, you know, when you think about something like an ant colony and you leave a piece of food out, the ant colony is going to sort of act as a group. They'll form these lines of ants guided by pheromones to go pick up this food. But we can still kind of see these individual ants for slime molds when they get together. They're so small. What we're seeing is basically a blob or a slug seeming to act as one organism, even though it's made up of many individual organisms. So they will sometimes when they detect food, they will come together and kind of act together as if they are a single organism. And there's actually a study that was done that I was like kind of trying to see like whether slimold could figure out how to get to food and they would put these little oat flakes around in a little dish with the slime mold, and the slime mold was able to relatively efficiently figure out how to get to these oat flakes, and it actually somewhat resembled like the Tokyo train system because it was finding out roots to the oat flakes in a relatively efficient way.
I think that's super fascinating and that connects to the idea we were talking about at the top of the episode about having similar mathematical problems on different scales. You know, people wonder like, how could a slime mold replicate the Tokyo rail network? What does that mean? Well, think about, like how you build a rail network. You want it to be efficient. You want to be able to get from one place to the other with a minimal number of connections and the shortest distances. So you build this network between your cities. And the slime mold it seems like it's sort of solving a similar problem. It's like, if I have food in these locations, then where should I build my connections between them so I can most efficiently move my nutrients around and get my cells from one food source to the next. You know, where should I focus my energies, and it's amazing that the network that comes out of that, if you place like the oats in the same structure, is like the Japanese cities that it basically replicates the Tokyo rail network because it suggests that it's solving a mathematical problem, not like it's got a little chalkboard in there, but that effectively it's doing computing. You know, what is a computer other than like a physical representation of a mathematical problem. You get the universe in terms of transistors or whatever to solve a problem you've represented symbolically. And that seems like that's what the slime mold is doing. It's like basically doing slime mold computing. It's solving this optimization problem.
Yes, actually some researchers are interested in studying whether it could be used to build like a biocomputer and use the slime mold to form these logic gates in a biocomputer, so instead of using you know, a circuit board, you would have a guy living sort of bioboard.
Yeah, you can form computers out of all sorts of stuff. You know, people think about computers as like transistors and switches, flipping, and that is one way to use a computer, one way to design a computer. But anytime that you build something which solves a math problem where you're using the physical universe to represent your problem again an answer effectively, that's a computer. And so yeah, you could represent a computational problem as a challenge for a slime mold where the answer is how the slime mold builds its network, which is pretty cool. I also really like these studies that show that slime molds can like learn. And remember they had these experiments where they were basically torturing slime molds every ten minutes on the hour. They would like cool it down so it was uncomfortable for the slime molds and this lime molds would like react to that, and then when they stopped doing it, they like took a break. The slime molds anticipated it anyway, they were like, oh, oh, is it going to get cold, and they reacted before the cold snap would come. Would suggest that they have like some internal clock or something, some way to keep track of time and anticipate what's going to happen based on what's happened to them before. That's incredible to me.
Yeah, that's absolutely so strange because it is a question of exactly how do they store that kind of data, right, Like how are they storing this memory of the cold snaps? And I don't mean memory in terms of like a human memory like thinking back to something, but how a computer might store memory. So it is really it's spooky, it's really strange, and I think comparing it to a computer is so ampt because at this point, in terms of how we've developed computers, computers don't probably have a sort of conscious understanding or a cognitive system like it's AI is still a pretty distant goal at this point. And so sometimes these slime moolds will do things that make it seem like they are behaving in this very like conscious way or even altruistic way, but then when you look at the mechanisms behind it, it's actually this weird just probability mass. So slime molds like this study you mentioned with the researchers just torturing them when they are behaving as a collective as that mass, they will try to avoid hostile environments and get out of it. And one way they can do that is they will actually, like if they are on an environment and they want to kind of make sure that their spores will be able to get to another place. They will form a slug, and then that slug will somewhere and then will grow a stock like a plant, and then form like a fruiting body at the end that releases these slime old spores that can then go colonize another area. And it seems like the because remember this is made out of a bunch of individuals. The ones that are like on the base of the stock or forming the stock, the ones that are not at the fruiting body that get to release their spores. It seems like they are sacrificing for their comrades to be able to get to the tops where they can release their spores, but in fact they are probably not acting altruistically. It is simply sort of a probability distribution where they are all trying to climb up to the top, and only some can reach the top. But as they are all collectively trying to make this climb, they happen just by sort of the probability distribution of how these slime molds are going to stack up they form the stock and this fruiting body, and it's just it's purely math there's no slime mold cooperation or camaraderie going on.
What is it like to be a slime mold. We'll never know, but it's amazing that they have something that seems like an intelligence, ability to learn, to remember, to anticipate, though they have no central processing unit. There is no brain to these things. As you say, it all just emerges from the operations of these individual entities following local rules. That's really incredible to me. So let's take another break and we get back. We'll talk about how slime molds and the slime mold computing problems that they solve might give us a clue about the whole structure of the universe and where the dark matter is.
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All right, we're and it was my turn to go off and polish a pizza. But I imagine the pizzas I'm getting over here in southern California are not really as you know, amazing as the ones you get over there. How far are you from it really excellent pizza. If you want to go from zero to pizza, Katie, how long does it take you?
Well, there's a really good like forcatcha pizza place that's maybe a like five minute walk for me, and then yeah, there's and then there's another just traditional pizza place that's maybe a seven minute walk. So yeah, you know what, if you're a human and you want to live the slime mold life of trying to find the shortest distance between two points, finding a walkable city is a way to go because you can just walk right to a pizza place.
If I live there, then I think the map of my walking around with follow the slime mold map of the city. You know, the fission paths between pizza joints.
Yeah, your your oat flakes would be all the pizza joints around here. Yeah, exactly.
So we've been talking about the mystery of the structure of the universe. Where is some of the missing stuff in the universe, the normal matter, the protons, the neutronsy electrons, A lot of that might be between galaxies, but we can't see it directly. We also suspect that there are filaments of dark matter, these tendrils between galaxies that feed new matter into the dark matter halos and connect us and show us sort of the history of where things split apart, but we can't see them directly. And now we have on the other hand, this sort of slime mold computer that lets us think about networks and how to build them efficiently. So you might be wondering, like, what are these things have in common? There were some researchers in Santa Cruzo had an idea for how to use slime molds to build a map of these tendrils to these cosmic filaments. The idea actually starts with galaxies. You know, if you want to know where the filaments are, you want to know where the connections are between galaxies. Instead of looking for the filaments directly, why not just look for the galaxies, because galaxies are something that we can see. Galaxies are like the nodes of this network, right. We can see them because they generate a lot of light. They have billions and billions of stars in them. We could see them across the universe. And there's a huge number of galaxies, right. Quasars that we used to see the filaments when they shoot these like pencil rays of light and we can see them highlighting the filaments. Those are pretty rare. There aren't that many quasars in the universe. But galaxies are.
The goodness because if there were too many quasars, that would mean a bunch of black holes that we would all get be getting sucked into.
Yeah, an incredible radiation. But you know, if you hold up your finger, then like the size of your fingernail, for example, the size of your fingernail has like a million galaxies behind it, just in the observable universe. Like if the universe is infinite, then there's an infinite number of galaxies behind it. But just in the part that we can see. If you like focused hubble on that one spot in the sky, there'd be a million galaxies each with hundreds of billions of stars. You know, it's just it's mind boggling to hold this in your mind, but it's a really good way to get a sense for what the network is. It's like asking, we want to know where the trains run. Why don't you start out by looking for the stations and then figure out where the trains run in between the stations.
Just don't stand in between the stations on the railroad tracks with your camera because that's probably not a good idea exactly.
So that's the easy part, is to figure out where the galaxies are. We spend a lot of time looking at galaxies. We have a big catalogs of where galaxies are. But these folks are wondering, well, if you know where the galaxies are, does that tell you necessarily where the filaments are. You can't just draw a line between every pair of galaxy. You'd have like lines everywhere. Right, These filaments tend to cluster together places of larger mass. These filaments tend to form between the larger clusters of galaxy and the form between the neighbors. There's a bit of an optimization problem here, right, Like how do you find the filaments? You need to explain the galaxy clusters that we have. You can't just spread them everywhere. And so folks have this idea. They're like, maybe we need to use slime mold computing to find out what is the optimal way to place filaments between the galaxies that we can see to figure out where where those filaments probably are.
So, in order for that to work, the filaments, the dark matter filaments would have to have some kind of behavioral similarity to slime mold. So filaments have that push pull, attraction and repulsion sort of characteristics. And is that sort of the connection with slimeold. So if slimold has like an attraction to food and sort of a wanting to avoid scientists trying to torture it. What are sort of the analogous behaviors of dark matter filaments.
Well, it's all gravity, right. Dark matter creates those galaxies where there is more dark matter, then you get more dark matter halos, and you get more bowls for galaxies to formid so there's a tight connection between where the filaments are and where the galaxies form. They sort of like support and encourage and create each other. So that's the push, right, They help create each other, And there's also a pull. They pull on each other, sort of like tug on each other to make each other more compact. And so instead of just like spreading out in every direction, the dark matter pulls itself into these halos and into these filaments between them. And so that's why it's sort of like a push and a pull. As you say, like an optimization problem. You can't just spread out everywhere. You need to figure out like what is the best arrangement of dark matter? If I give you some dark matter, how would you sprinkle it around the universe to create the galaxy map that we see, Or was the best place to put it, and so they discover that slime wolds can help us figure this out if they turn this like dark matter filament problem into a food problem. So they did this. Of course in simulation, they didn't use real slime molds.
So they didn't put a pile of slime mold next to a powerful telescope and say, what do you think? What would you guys do you.
Guys are in charge, tell us where the look in.
This scenario would how would you behave?
So what they do is they put blobs of simulated the slime mold where they see the galaxies and then they simulated slime molds send out tendrils in every direction and if it finds another galaxy then it strengthens that connection. And so this is the part where it's like simulating how a slime mold explores its space. It's sending out tendrils and looking for stuff, and when it's successful, a slime mold will build a stronger network. That's how replicated, for example, the Tokyo train map. And so in the universe, these simulated slime molds start from galaxies and when they find other galaxies then they like enhance that connection between them. So there must be more of a filament here. So they're not actually modeling like the real physics of darkmap. They're like saying, if you had a simulated slime mold and you put in this artificial problem, would it solve that problem effectively? Can you use slime mold computing to figure out where the filaments should be?
What are the benefits of trying out sort of a slime mold model versus modeling physics? Is it that having some kind of physics model, we're still asking the questions that we would need to be able to make a physics model at this point.
You can do it with physics as well, but it's difficult because you don't know what the initial conditions are. Like, what we can do with physics is we can say, let's say we had a random universe and that's run a simulation of that and understand how the particles interact and how gravity works. What do you get? And you get a universe with tendrils and galaxies, But you don't get our universe, right, that's a different random universe. So because we don't know what the initial conditions of our universe are, it's hard to run that simulation and so you could try to run it backwards. So this is just like an alternative approach to say, like, maybe we can find a shortcut, a clever way to solve this problem using ideas from slime molds, so that we don't have to figure out, like how to run the universe backwards.
Man. Slime molds are so smart. They're teaching us about physics. It's so interesting and mind blowing to me because with slime molds, when we talk about their intelligence, it is not the kind of intelligence of a researcher sitting there programming this mimicry of or the slime mold. It's just the the intelligence of a pattern of like individual particles. Let's just call one of the unicellular organisms like a particle doing a behavior. What gets even more kind of like Russian nesting doll is you look at that individual unicellular organism and it is also basically just a domino effect of particles colliding with each other and interacting so like molecules setting off other molecules, and then that's how that unicellular organism is able to move around. And then you zoom back out and then many of these unicellular organisms so it's just it almost makes my eyes crossed just thinking about how many complex like basically little little individual units bonking into each other many many times, and how that can create such incredibly complex and seemingly very intelligent behavior.
Yeah, the same way that like a compute couter can seem intelligence. It can do complicated things, but at the lowest level, it's just following very simple rules a by flipping bits from zeros to ones. And of course we don't know if consciousness could arise from that kind of system, And we also don't know why intelligence and consciousness does arise from, like our biological system, which in the end is just a bunch of neurons zapping each other. So there is really a deep mystery there about the connection between the underlying rules and the emergence of consciousness. But I think it's really cool when you can take advantage of that and say, like, oh, let's model these systems, let's figure out what they're doing, and see if we can use that to solve this other problem. And it's awesome to see the connections between problems on the cosmological scale, like the filaments between galaxies and how the universe formed and how this weird goopy thing crawls across the forest floor. It really suggests that there are some mathematical connections there, that the problems are similar in some deep way. In the end, the galaxies and the slime molds are both just solving an optimization problem to figure out what's the best way to hang together.
I mean that makes me feel kind of more I guess connected to the universe. Where you know, it's not the way that these galaxies are behaving. It's it's similar to how something is seemingly simple, as like the slime mold that we can find licking the walls of your local cave or maybe not, maybe don't do that.
That has not been cleared by our legal department. By the way, I do not endorse cave licking here at your own risk.
I mean there are many there are Like splunking in cave licking are both only activities for highly trained individuals exactly.
Professional cave lickers were used for this podcast and at home, folks. But even these slime molds have taught us something about the nature of the universe. These guys were in this simulation and they now have a map of these cosmic filaments between the galaxies. And what they did is then they turned humble to one of these locations where they thought, maybe here's a cosmic filament. Our slime mold simulation tells us it should be there. We're able to see little hints of X rays emissions from what it was otherwise deep empty space. So they found new filaments using this simulation.
So if they get a Nobel prize, is that going to go to the slime mold or to the researchers who ripped off the slime molds mathematical model.
Well, you know, in the great history of professors taking advantage of their students, I think you'll probably just tossed them a few oat flakes and assume that that's enough. But this is a deep mystery in the universe, not just where are the filaments, but where is all the missing stuff? And so understanding where these filaments are might give us a clue as to like where those missing particles are. Are they really stretching between the galaxies what seems like otherwise empty space. Is there really a third of all the normal matter in the universe in these long bands between galaxies. It'd be incredible to discover that a whole third of the pie is really out there and what we otherwise thought was deep empty space.
I mean that makes me feel good, warm and fuzzy. It's like we're holding hands with other galaxies. It's not just it's a just cold empty nothingness.
We're all just part of the big galactic slime mold.
Ah.
That's gross, all right.
So thanks everybody for joining us for this fun conversation about the structure of the whole universe and how it's creeping along the forest floor of the cosmos, as well as the mysteries of slime molds and how we could take advantage of them to understand the questions of the universe. And thanks Katie for coming along and telling us about your cave liking habits.
Yeah. Absolutely, I hope people have an appreciation for even the slimiest, moldiest critters out there, because maybe they contain the keys to the universe.
And it never ceases to amaze me how is even possible for us to understand the universe at any scale, especially at these largest scales, using the tiny little networks encased in our skulls. And so I'm glad that our slime mold brethren have come to help us in that great cosmic detective mystery, the escape room of the Universe.
Is that just your way of saying everyone's got flying for brains?
I mean, if you ever taste in brains, they're pretty slimy, even on kids. All right, on that, mate, Thanks everybody for joining us. Tune in next time. Thanks for listening, and remember that Daniel and Jorge Explain the Universe is a production of iHeartRadio. For more podcasts from iHeartRadio, visit the iHeartRadio app, Apple Podcasts, or wherever you listen to your favorite shows. When you pop a piece of cheese into your mouth, you're probably not thinking about the environmental impact. But the people in the dairy industry are. That's why they're working hard every day to find new ways to reduce waste, conserve natural resources, and drive down greenhouse gas emissions. How is us dairy tackling greenhouse gases? Many farms use anaerobic digestors to turn the methane from maneure into renewable energy that can power farms, towns, and electric cars. Visit usdairy dot COM's Last Sustainability to learn more.
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