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Paul M. Sutter of “Ask a Spaceman.”
While Pamela and Fraser were at Ohio State University for a symposium in October, they caught up with Paul M. Sutter from Astronomical Observatory of Trieste, who is a visiting scholar at the OSU Center for Cosmology and Astro-Particle Physics. His specialty is cosmic voids. Paul also hosts the “Ask a Spaceman” podcast.
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Female Speaker: This episode of Astronomy Cast is brought to you by Swinburne Astronomy Online, the world’s longest running online astronomy degree program. Visit astronomy.swin.edu.au for more information.
Fraser: Hey, everyone, Fraser here. So this is a very special episode of Astronomy Cast that we recorded in middle of October with Paul M. Sutter and he is a fellow at the Astronomical Observatory of Trieste and a visiting scholar at the Ohio State University Center for Cosmology and Astro-Particle Physics. Pamela and I were in town at OSU doing a symposium and we were able to get a little bit of Paul’s time to talk about his specialty, which is cosmic voids. So we’re talking about these big gaps in the largest scale structure of the universe.
And so the conversation goes on for half an hour, 45 minutes and it’s sort of a round table with the three of us, standard Astronomy Cast style and I think you’re really gonna enjoy it. So if you want more information on Paul you should follow his podcast, which is called Ask a Spaceman. And you can find that wherever good podcasts are distributed. All right. Enough. Enjoy the show.
Female Speaker: This episode of Astronomy Cast is brought to you by 8th Light, Inc. 8th Light is an agile software development company. They craft beautiful applications that are durable and reliable. 8th Light provides disciplined software leadership on demand and shares its expertise to make your project better. For more information visit them online at www.8thlight.com. Just remember, that’s www.the digit 8 T-H-L-I-G-H-T.com. Drop them a note. 8th Light. Software is their craft.
Fraser: So once again we are pleased to announce that Casper Mattresses is our sponsor for Astronomy Cast. They’ve been sponsoring us now for like a year and I know it’s working out really well for them. And it’s working out really well for us as well. I think, as people may or may not know, we got our sample mattress. I then had to leave mine in the States so I ended up buying another mattress for my bed. I got the king size one. And now I bought another one for the spare bedroom so now I’ve got two Casper mattresses in the house, plus the one that they gave us as a trial. How is your Casper mattress working out Pamela?
Pamela: So mine aren’t multiplying the way yours are. I still have just the one. It’s on my daybed and it makes me happy. That combination of latex foam and memory foam, you don’t overheat in the summer and now that it’s getting to be winter I can snuggle up in bed and I don’t have to wait for the mattress to warm up. I just snuggle into my blankets and I’m good to sleep.
Male: Yeah, and this is the part that I hadn’t tested out before because mine was down in Louisiana, it was very hot. And now as it’s getting colder here in Canada, it’s great. As you said, it’s not like you jump into a cold bed. And what’s great about these mattresses is it’s a risk free trial and return. You can order one. It comes in this crazy box that you open it up and then a transforming mattress pops out of this box. And you can try it for 100 days and then if you don’t like it, the delivery’s free and you can get it returned as well.
Pamela: And they’re made right here in the United States. So it’s not like they’re shipping to you from China, you’re not waiting for them to cross on some weird boat, they’re just getting shipped to you in this magical box with a magical tool for you to – it’s really kind of amazing. They just expand out like those magic pill creatures you get at the science museum. But it’s a mattress, not a dinosaur.
Fraser: And so they’re $500.00 for a twin size, $950.00 for a king size mattress, which is what you would pay, less than what you would pay, if you go down to the mattress store. So if you wanna try out a Casper mattress, wanna buy one, go to casper.com/astro. Use the promo code Astro and they’ll give you $50.00 off the price of a mattress, so it gets to even a better deal. So once again, thank you so much Casper for sponsoring Astronomy Cast. I’m sure this isn’t the last time you’ll hear from them or us. Thanks a lot.
Fraser: So who are you and what do you do?
Paul: Who are you? Is this an interrogation? What’s going on here?
Fraser: Pretty much.
Paul: I am Paul Sutter. I am a astrophysicist. And I work here – at two places actually, I’m bi-local. I’m funded by research fellowship position in Trieste, Italy, but my wife and my family live here in Columbus, Ohio. And so I’m a visiting scholar here at OSU Center for Cosmology and Astro-Particle Physics, CCAP if you’re feeling affectionate.
Fraser: So, now, you do a whole bunch of stuff and what would you say is the specialty? What kind of research do you do mainly?
Paul: Yeah, I have two main specialties nowadays. One is on the topic of what are called cosmic voids and the other is the topic on the first stars in what’s called the Epoch of Reionization in the very early universe.
Fraser: All right. So we looked at the things you do, we cross-reference it among the episodes that we’ve already talked about, and one of the things that we haven’t spent really any time directly on is talking about this idea of cosmic voids.
Pamela: That’s because they’re empty.
Paul: Yeah, yeah, so you’re saying –
Fraser: We’re gonna talk about nothing.
Paul: There’s a hole in your knowledge and that hole can be filled with the holes. This is perfect. This is where I come in.
Fraser: Yeah, this is where you come in.
Paul: Because you know that joke about how a specialist is someone who knows more and more about less and less? I’m the world’s leading expert on nothing and I am so proud of this fact.
Fraser: But there’s something to this nothing.
Paul: I suppose.
Fraser: So why don’t we at least talk about the bare minimum here.
Paul: Yeah, yeah, yeah, so to get started we have to zoom out. We have to go to the very biggest scales in the universe. And we have to go to such big scales that entire galaxies with 300 or 500 billion stars are just a single point of light. So that’s the scales we’re talking about. We’re looking at the whole entire universe at once. And we notice something about the way the galaxies are arranged in our universe. They’re not just scattered around randomly. And this was actually a surprising discovery. When we first started mapping the universe in the late ‘70s and early ‘80s, we kind of expected the galaxies to be just like you spill sand on a table, it’s just random.
Pamela: And this is that Hook or Gellar diagram with the man standing up in it.
Paul: Yep, yep, exactly. We noticed like, wait a minute, wait a minute. The galaxies are doing something; they’re arranged in a pattern. And as we build bigger and bigger surveys and mapped out more and more of the universe, it became apparent that the galaxies are arranged in a pattern that we call the cosmic web because it kind of looks like a spider web. There’s long strings of galaxies, there’s dense clumps where the strings connect to each other, there’s sheets of galaxies, like big two dimensional walls. And then there’s these big empty spaces with no galaxies at all.
Fraser: So what was the mechanism that created that structure in the universe?
Paul: Yeah, so this is one of the coolest things I think about in cosmology, is the source of the structure in the universe on the grandest scales actually comes from submicroscopic fluctuations in the very fundamental fabric of space time. In the very early universe, and I mean early, like 10-40 seconds after the big bang. There’s all these virtual particles that are being created and destroyed, there’s this quantum foam concept that fundamental space time is roiling and boiling, it’s not smooth at all.
And there was an event in the early universe called inflation where it took these submicroscopic, super fundamental fluctuations and inflated them, made them bigger to be like microscopic, not submicroscopic, now they’re microscopic. And that laid the seeds of structure. Because there are some places in the universe that were a teensy little bit more dense, and some places in the universe that were a teensy little bit less dense, and then over time, over 13 billion years, those little pockets, the ones that are a little bit more dense, have a little bit more gravity so they attract a little bit more matter, and a little bit more, and more attracted, more gravity, more stuff.
And you build up structures and then those places that were a little bit empty, all their stuff gets sucked out of them. They get pulled towards what become the clusters and the ropes and the filaments and the walls and they leave behind those evacuated spaces. So actually, this large scale structure pattern that we see in the universe today was seeded at submicroscopic, subatomic scales over 13 billion years ago.
Fraser: That’s kind of amazing. Go ahead.
Pamela: What’s totally awesome about this is because light takes time to travel we can see this entire process happening.
Paul: Yeah, exactly. Exactly.
Pamela: We look back to the cosmic microwave background, we see the initial hot and cold spots that traced out these densities whether they be over or under, we look at the early universe when the first stars are turning on and reionizing the universe and we see the structures. They’re a lot more; well, homogeneous across that epoch of time. And as we get closer and closer to now, the universe gets more and more like lacy Swiss cheese instead of baby Swiss cheese.
Paul: Exactly. And the universe will continue to evolve for billions of years. So the cosmic web that we see today is an evolving thing, it’s a changing thing under the influence of gravity and under the influence of the continued expansion of the universe. So eventually the structures that we have now will continue to glue themselves together and eventually the walls will disappear because they will gravitationally collapse. The filaments, the ropes, those will get sucked down into the clumps. And eventually the cosmic web that we see will be replaced by isolated spheres, isolated clumps of gigantic clusters of galaxies. There’ll be no more ropes, no more filaments, no more webs.
Fraser: And the voids will, I guess, just disappear at this point. There’ll just be the one big connected void.
Paul: Yeah, exactly. In fact, there’s some recent evidence, some analysis and simulations that suggest that cosmic voids are actually all connected to each other, even in the universe today. Which means that if you found yourself in a cosmic void one of these empty patches in the universe; you could travel to any other cosmic void in the universe without ever passing through a dense clump, without ever crossing a wall or a filament or a cluster. That there already may be completely connected together and that this connection will only continue to be enhanced as time goes on.
Fraser: Right.
Pamela: Space is mostly empty.
Paul: Yeah, that’s why it’s called space.
Pamela: Right. Right. You and I are mostly empty space no matter what our bathroom scales may say. And it starts to be the smaller you are, the further you can go without having anything on your horizon. And it’s evolving more and more towards nothing.
Paul: Yeah, and since these cosmic voids fill up most of the universe, between 70 and 90 percent of the volume of the universe is just these empty spaces with hardly any matter in it. This means that if you live somewhere, like on the Earth, you do not live in a void. Because by definition you’re somewhere with lots of stuff and that means you’re not in a void. But that also means wherever you live, you’re always right next to a void because the clusters and the filaments, where all the matter is, it’s so thin compared to the vast expanses of these voids, you’re always on the edge of a cliff. So we’ve actually mapped this out and our local super cluster, our own galaxy, is right on the edge of a very vast, incredibly vast void.
Fraser: Do they have a name for that void?
Paul: The Bootes void. I believe it’s called – I believe it’s both the largest and closest void. I could be wrong about that.
Fraser: And give us a sense of scale. Because I know that our super cluster is hundreds of megaparsecs across, right? Hundreds and hundreds of light years across.
Paul: So a typical galaxy cluster, which is the largest gravitationally bound structure in the universe, usually a few thousand galaxies all bound together, usually around one, maybe one and a half or two megaparsec across. It depends on how you define what is the edge of a cluster. A typical void is around 20 to 40 times larger and they can go up to be 100 times larger.
Pamela: And what’s kind of amazing is a lot of work, a lot of telescope time has gone into trying to answer just how empty are these voids? And I have seen some great researchers like Martha Hayes presenting where it’s like, “And we found a galaxy. Just one. One galaxy in this void.”
Fraser: So you’ve got an area that as you said, that’s 20 times bigger than a typical galaxy cluster, but there is one galaxy in that entire void.
Paul: Check this out. This is something super cool about – okay, I think everything about cosmic voids is super cool, but here’s one thing in particular. We do a galaxy survey and when you do a galaxy survey you have a certain limit to the brightness of galaxies that you can capture in that survey. If they’re too dim, not enough stars and stuff, you just won’t see it because your telescope isn’t big enough; you didn’t look at the sky long enough. You do that survey and you’ll map out this giant cosmic web.
Now let’s say you picked out one of the voids, any void at random where it looks completely empty. And you decided to zoom in on that void and do a more detailed survey with more time to try to pick out faint galaxies, small galaxies. You will find in that void a population of small galaxies and those small, dim galaxies will be arranged in a cosmic web. So each void contains like a faint cosmic web. And then if you look inside one of those subvoids and do it again, you will find a very faint cosmic web. Eventually you’ll run out of galaxies because there’s only so much gas in the universe. So if we look in simulations and we look at dark matter, which is like the skeleton of this cosmic web, this keeps going.
Pamela: It’s fractal.
Paul: Now I can’t use the F word, technically, because fractal cosmology has this very storied history. Like Mandelbrot, you know the Mandelbrot stuff, he thought the whole structure of the universe was totally fractal, there was maybe some evidence early on and say, “Oh, the answer is fractals everywhere.” In the early ‘90s this view became highly – not something that reasonable people would talk about. So I don’t like to use the word fractal, but in these cosmic voids, and we’ve actually seen evidence of this in our analyses, that there is a certain self-similar structure to the voids where you can zoom in and you recover similar kinds of properties and you zoom in and you recover similar – there’s a fractal-like nature –
Pamela: And the problem here, for those of you who are missing the mathematical subtleness of this, is when you say something is fractal in the noncolloquial way, if you say something is fractal in the highly technical mathematical way, you can identify something’s fractal number. So for instance, different modern artists you can tell their paintings apart because the splatter patterns have a different fractal number. Well, it turns out that you can’t really say something is fractal if the number that describes how the structures scales changes. And the web that’s inside of the void may not have the same fractal number as the parent. Therefore, you can’t actually say it’s fractal in the specific scientific sense, but you can say it’s webs all the way down.
Paul: Right. It’s self-similar, sure.
Fraser: Now all of the fractal astronomers can save their emails now.
Paul: Yeah, don’t bother.
Fraser: They don’t have to send them.
Paul: I have seen one author in one paper describing this phenomenon, call voids a non-lacunar multifractal. I’m not exactly sure what those words mean, but it sounds pretty cool.
Fraser: It sounds recursive to me.
Paul: It sounds – and eventually this scale does break – these properties do break down because eventually you get down to things like galaxies themselves. Like I’m not a fractal, I’m not self-similar, last time I checked. So this is only within a certain range of very –
Fraser: Right. It’s not a series of Pauls nesting inside each other, like Russian nesting dolls, to the vastest scales of the universe.
Pamela: That would be highly disturbing. We like one Paul, we do not need –
Paul: Yeah, one Paul is more than enough.
Fraser: So, right, but I think if we get down to that smallest scale, if I’m an astronaut floating around, it I’m a [inaudible] that suddenly appeared in the middle of one of these cosmic voids, what’s around me?
Paul: Yeah, I’ve gotten this question before. If our intelligent life arose in one of these very dim galaxies that inhabit the voids, what would the universe look like? The answer is it wouldn’t look much different. Our night sky is dominated by 6,000 really, really close stars all right? Whether you’re a void galaxy or a galaxy in a cluster that’s not really gonna change. Maybe the colors will change, the population of stars will change, but the night sky won’t look much different. And then you won’t have something like the Andromeda galaxy that’s barreling in on us, you won’t have that.
Fraser: Right. So in perfectly dark conditions, you won’t see that fuzzy spot off in the distance.
Paul: Yeah, yeah, yeah.
Pamela: You wouldn’t have the Large and Small Magellanic Clouds.
Paul: Probably not. Exactly. Your galaxy will probably be smaller and dimmer in general, fewer stars; it will be [inaudible].
Pamela: No grand spiral design because that requires friends.
Paul: Probably not. Yep, exactly. But then when you start doing cosmology, when you’re the Edwin Hubble equivalent, all the other answers come out pretty much the same.
Fraser: Right. But then, I guess in the medium term is you had the beginning power telescopes, you wouldn’t see any other galaxies. And then as you got really powerful telescopes, then you would start to see galaxies –
Paul: And then it’s like, “Oh, man. There’s all sorts of stuff in the universe.”
Fraser: Right. It all just happens to be billions of light years away.
Pamela: The what our galaxy’s debate probably would have been delayed until probably the ‘60s.
Paul: That’s a good point.
Fraser: Yeah, and but let’s not even have a galaxy. You’re an astronaut floating in the middle of space right in the center of one of these voids, far away from all the galaxies.
Pamela: Centers are special places. It makes us feel uncomfortable.
Fraser: So now what are you seeing around you? You’re seeing nothing, but –
Paul: It would be the same thing as if you were – imagine rocketing off of the Milky Way and being transported far enough away where you can’t even see a disc of the Milky Way, any structure, it’s just like a blob of light or a fuzz of light. And you would see that if your eyes are actually capable of detecting that miniscule light, the sky around you would be filled with these pin pricks of light, but these aren’t stars, these are entire galaxies.
Fraser: Right. And what is the actual density of the stuff that’s around you? We can imagine here on Earth we’ve got the air, we’ve got air pressure, when you’re in the middle of the solar system you’ve got the interplanetary medium and its particles zipping around. And if you get out into the intergalactic medium then the density goes down even more, just a few hundred or thousand particles per square meter. So how undense is the middle of these voids?
Paul: Right. Right. So we actually decide this by definition so that we can make progress. If you take the mean density of the universe, if you took every bit of matter and dark matter and radiation and everything and smeared it out uniformly across the universe, that’s your mean density. Voids are by definition anything around less than 20 percent of that mean density. And that definition gets you something like 80 percent of the volume of the universe. By contrast, something like a galaxy cluster, one of these large agglomerations of galaxies, by definition are around 200 times the mean density of the universe. So you’ve got a lot of stuff crammed into very, very tiny volumes.
Fraser: Right. So you would still have occasional atoms of hydrogen floating around you.
Paul: Oh, there’s still gas in the voids, there’s still dark matter in the voids. There are regions, there are pockets that are completely, truly totally void of matter, but usually we think of voids as just the less empty kind of basins in the universe rather than the holes in the cosmic web.
Pamela: At that background level of stuff that’s flying around, the voids are still going to be filled with those high energy particles that are released in supernova events. There’s –
Paul: Oh, yeah, there’s high energy neutrinos, there’s the cosmic microwave background, there’s distant starlight. There’s all that kind of background fluff that makes up the character of the universe.
Pamela: It’s the structures that decide they need to be elsewhere because gravity.
Paul: Exactly.
Fraser: And so what does studying those voids really kind of tell you about the past and future evolution of the universe?
Paul: Yeah, like the story that we told of the growth of the structure of the universe is just if you were to slice open a cupcake, right? And you see all these tiny little holes and you see little structures of delicious food. If you change the ingredients in the cupcake, you change the structure at the end of it. And you could change the recipe, if you change how long you cooked it you end up with a different kind of cupcake. If you change your recipe for Swiss cheese you end up with different kinds and sets of holes in your cheese.
And so by looking at the structure of the universe and trying to follow and track its evolution, we learn about dark energy, we learn about the properties of dark matter, we learn about the mass of the neutrino. Because if you change these fundamental components, you’re changing the recipe of the universe and you end up with a different thing after 13 billion years. And – go ahead.
Pamela: One of the coolest tangible ways of looking at this is we know that dark matter and regular, we call it baryonic matter, all has been around since the beginning. And those initial overdensities, as the material, whether it be dark matter or baryonic matter, tried to flow into those overdensities, the baryonic matter, as it lit up, as stars formed, as radiation pressure became a thing, those baryons stopped being able to fall in because they were getting pushed out. But dark matter, it doesn’t care. It doesn’t want to interact with anything.
So it’s in trying to figure out how do we balance that dark matter that is perfectly happy to flow anywhere gravity is pulling, versus the baryons which can be pushed around? It’s in balancing just those two ideas, baryons versus dark matter, that gets us to the starting points of all of our models.
Paul: And here’s a question that will let you think about how important voids are. Where does dark energy live?
Fraser: Everywhere.
Paul: Everywhere. Okay, do you – when you bought this coffee this morning, did you care about the influence of dark energy?
Fraser: No.
Paul: No, because there’s all sorts of complicated physics on top of that effect of dark energy. There’s electromagnetic radiation, there’s the gravity of the earth.
Pamela: All I care about is the chemical bonds right now. Coffee is chemical bonds.
Paul: Yeah, exactly. Exactly. You don’t care about this dark energy that’s kind of permeating the fabric of space and [inaudible].
Fraser: Right. Trying to care my coffee apart.
Paul: Exactly. In the voids dark energy is dominant because there’s so little other stuff. That’s where dark energy lives. That’s where dark energy has its influence on the universe is in the voids.
Pamela: And this leads to some really neat physics. There was a talk I saw years ago, I wish I could remember who gave it so I could give them credit, but they were talking about a galaxy potential merger that wasn’t going to happen because as the two galaxies came together the one didn’t have enough gravitational potential energy to overcome both the velocity of the galaxy that was flying past and the effects of dark energy.
Fraser: Right. So the universe is expanding those two galaxies apart from each other faster than they could come together.
Pamela: And it was right on the boundary between becoming a future merger and two galaxies that pass in the night because of that cosmic expansion.
Fraser: Right. And I know some cosmologists have a problem with the idea that the Laniakea Supercluster, that a certain point when objects cannot even come together because of their mutual gravity, because the dark energy’s pushing them apart faster then they’re coming together. Can you really call it a gravitationally bound structure when it’s not gonna form into a big cluster in the far, far future. It’s gonna fly apart and eventually be completely invisible to one another.
Paul: Yeah, and what’s driving this flying apart is the voids getting bigger and matter is continuing to stream onto the gravitationally bound clusters and those clusters are getting farther apart because the voids in between them are expanding. They’re inflating like little bubbles.
Fraser: Now we’ve only known about dark energy since whatever, 1998, so we’ve known about cosmic voids probably a lot longer than that.
Paul: Right.
Pamela: But we knew the universe was expanding.
Fraser: We knew, but what impact did the discovery of dark energy have on our understanding of how these voids formed and [inaudible].
Paul: Yeah, so when we first discovered cosmic voids and this large scale structure of the universe, that was actually a bit of a surprise, like I mentioned. So we actually had to figure out where could this structure actually come from and that led us onto some very fundamental theories of the way the early universe worked. And so pretty much any kind of universe you can design you’ll end up with some population of voids, with some sets of properties of sizes and shapes, you’ll find that. And when we discovered dark energy the whole community just said, “Oh, crap.”
Pamela: It made the math so much worse.
Paul: It made the math so much worse.
Fraser: Einstein was right.
Paul: Einstein was right.
Pamela: We’re okay with that part. It’s the math that we dislike.
Paul: It’s the math part and it’s like, “What in the world is this dark energy stuff?” We just don’t know. So now the program for the past 15 years and the program continuing to the next 20 or 30 years isn’t even in the ballpark of trying to understand what dark energy is. We’re just trying to measure it more precisely. Like has it been constant for 13 billion years? Is it getting faster or slower? We’re just trying to measure it and so we’re trying to come up with any kind of probe we can from multiple different directions to just try to measure it.
Pamela: And this is where we’re investing in our future with the WFIRST spacecraft that’s coming, there’s the Hobby-Eberly Telescope Dark Energy mission. We actually, if all goes well, will be working with us with CosmoQuest. We’ll be working with the McDonald Observatory team. It’s gonna take every eye we can possible get trying to track out the dark matter through how it deforms light. That’s unfortunately all we’ve got and the dark energy as it’s traced by supernova and other effects.
Fraser: But has dark energy led – at a certain point dark energy became more and more dominant and had more and more of an impact, like a blowing wind that’s increasing, right? It’s accelerating the effect in the creation of these voids, right?
Paul: Yeah, exactly. And so when I said dark energy it dominates in these voids. We say about 5 billion years ago dark energy kind of overwhelmed the universe.
Pamela: And it’s not that it changed, it was just that things spread out enough that it could become the dominant factor. The way to think about it is if you’re on roller skates and someone starts pushing on you and the push is constant, you’re initially moving very slowly, but over time you pick up more and more and more speed. Well, it’s kind of been happening that way with our universe where gravity was like originally, “I’ve got it. I’m holding you all together.” And now gravity’s like, “Don’t got it.” And it’s that dark energy push that is racing everything apart out of control.
Paul: And it’s this process – it started in the voids because they were the least dense parts of the universe. They were the least resistant. And so when you start playing with dark energy models, maybe it’s a little bit hotter and faster, maybe it’s a little bit slower, maybe it oscillates, you see the effects in the voids first. It changes how they expand and how they grow and merge together and live, before it affects the universe on average as a whole.
Fraser: And so I know some of the simulations of the entire universe, these supercomputer simulations, have gotten pretty good at simulating the universe that we see today and then using that, I’m sure there’s some kind of number for dark energy that they’re putting into the simulation. So you mentioned maybe it’s increasing, maybe it’s decreasing, maybe it oscillates. What, based on the most recent kinds of simulations, do we think dark energy was doing over this time?
Paul: Yeah, as far as we can tell, and this is a statement that carries like a 10 or 20 percent uncertainty with it –
Fraser: How many sigmas would we get here? Zero?
Pamela: It’s more like two sigma.
Paul: Yeah, it’s like the universe is – or dark energy consistent with it being totally constant. Constant across space and constant across time for this whole time. We cannot detect any deviation from there.
Fraser: Which is a relief for the possibility the universe will tear itself apart in the future.
Paul: Yeah, yeah, if you’re afraid of the big rip scenario, this phantom dark energy scenario, that’s a good thing. If you’re trying to find any theoretical hook where you can develop some model of what dark energy is, it’s a bad thing because this flat, constant –
Pamela: Doesn’t match anything we’d imagine.
Paul: It doesn’t match anything we can imagine and because it’s like the simplest answer, it’s like there’s nothing there to give the theorists anything to work with to find anything different. They have their pet theory and then their pet theory looks like this plain old vanilla model like –
Pamela: Right. And dark energy isn’t that much energy. We’re talking about just a couple of protons worth of energy per cubic meter. So there’s more energy in a sneeze than there is in dark energy.
Fraser: So you described this earlier on, that these voids are increasing and eventually the voids themselves will disappear. So how long do you have a job for?
Paul: To any funding bodies I have enough work to do at least until tenure.
Fraser: Right. But I’m thinking in billions of years.
Paul: Oh, billions of years, okay. You know, that’s a good question. Usually we stop our simulations at the present day because that’s the limit of our observations. But you can run these forward and see the voids begin to merge, see the structure continue to collect. The problem with running simulations forward is that depends on the exact properties of dark energy. If dark energy is constant we’ll have one kind of universe ten billion, 50 billion, 100 billion, 100 trillion years from now. If dark energy is even a little bit different, that tiny little bit adds up over these billions of years and you end up with a completely different future history of the evolution of voids and the evolution of structure.
Fraser: Right. But somewhere between a few dozen billion years and a trillion years you’ve still got work in this before you have to look for a new career?
Paul: Yeah, yeah, let’s go with that. Yeah, before there’s no more distinct voids that we can identify with our algorithms.
Fraser: Well, Paul, thank you so much for taking the time to speak with us today. We really appreciate you talking about nothing and taking this whole episode to do it.
Paul: I could talk about nothing all day.
Pamela: And it’s great to just get to record live in the same room with Fraser and having you here that we can bounce new ideas off of, even if we are bouncing them off of nothing.
Paul: Off of nothing. Thank you so much for having me.
Fraser: Where can people find out more about you?
Paul: They can find more about me on my website, which is pmsutter.com. You can also follow me on Twitter, @PaulMattSutter, see the P and the M stand for Paul and the Matt, which that’s the name. And then also Facebook, Paul Matt Sutter, Instagram, Paul Matt Sutter.
Fraser: And you do a podcast.
Paul: And I do a podcast called Ask a Spaceman. So if you say, “Hey, spaceman, what is a cosmic void?” then I’ll just repeat everything I’ve been saying for the past half hour.
Pamela: And you can find out all of this at 365daysofastronomy.org.
Male Speaker: Thanks for listening to Astronomy Cast, a nonprofit resource provided by Astrosphere New Media Association, Fraser Cain and Dr. Pamela Gay. You can find show notes and transcripts for every episode at astronomycast.com. You can email us at info@astronomycast.com, tweet us @AstronomyCast, like us on Facebook or circle us on Google+. We record our show live on Google+ every Monday at 12:00 p.m. Pacific, 3:00 p.m. Eastern or 2000 Greenwich Mean Time. If you miss the live event, you can always catch up over at cosmoquest.org.
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