A WISE search for large extraterrestrial civilizations: a complementary approach to traditional SETI

Jason - yeah you're aligned and white great okay okay so welcome ladies and gentlemen to your weekly City seminar series today we're very very honored to be joined by Jason Wright who's come across to us from Penn State University where he's an assistant professor there Jason did a BA at Boston University and the topic of his thesis was probing magnetic fields of Brock Locke globular Bok globular Z 335 rz-34 to 335 I'll get that corrected by Jason as soon as he comes on to me and then he did his PhD at Berkeley with Geoff Marcy on stellar magnetic activity and detection of exoplanets and then since 2009 he's been assistant professor at Penn State University he's involved with the center of exoplanets and for habitable worlds the Penn State astrobiology Center and he's also a curator and uh maintainer of the EXO planets orbits database which you can access through his website his interests and career as focused on as I mentioned exoplanets and he's published recently on the nearest old open cost to rupprecht 147 and small and he's involved in small and cool kepler planet candidates with high-resolution imaging on HST and very relevant to today's talk is some research into constraining abundance of Kardashev two and three types of all eyes Asians from larger IR surveys which I don't want to talk too much about but I'm sure Jason's going to fill up the next day off for us with that topic so please join me in welcoming Jason thank you I'm excited to be here and excited to learn that I'll be getting a City Institute coffee bug so I'm going to be talking about our search for extraterrestrial civilizations which is a form of SETI search for extraterrestrial intelligence when we think of SETI we traditionally often think of communication SETI and in particular radio SETI using radio telescopes to try and find radio transmissions from extraterrestrial civilizations and one of the the first and most important papers on this topic or first but an early one was by Nikolai Kardashev who calculated what at what frequencies one might want to go looking for extraterrestrial communication and he did this by looking at the radio spectrum of the Milky Way and he argued that if you wanted to transmit a lot of information and save power you would want to work where the background was low and there wasn't a lot of noise from the galaxy and so he argued that if you had a galaxy that was filled with civilizations communicating that most of their power would be where the background was Louis and they'd have less background where it was higher and so he inverted the spectrum of the Milky Way and he came up with this spectrum here the big black spectrum as the expected spectrum of extraterrestrial civilizations and he noted that there were two strange radio sources that had been discovered that didn't quite have the right frequencies we'd had roughly the right shape and we're very unusual adjusted that perhaps these could be galaxies filled with alien intelligence communicating with each other and so that was a CT a21 and CT a 102 and so these objects had a brief life in pop culture as galaxies where alien civilizations live the birds wrote a song about one of them he it turns out these are quasars so very interesting in their own right a new class of Astrophysical objects not extraterrestrials I was sorry can I just interrupt you just for one second because we're not getting the video from your main screen through here so I know that I apologize for this for our in-house audience we're getting that screen rather than your there was a fix to this I know that we played around with before the talk my apologies for our online we're trying now person talkie which one are you getting now getting the earth still there is it possible that suggests that you're not getting a live feed yeah you want me to restart it that want that I'll try to ask that how do they think cutting that might break things if I was you yeah is it possible to mirror them alright okay I I will mirror it sorry yeah still getting yeah that's what I figured yep my apologies I'm just going to want pull the camera back a bit so that we can get the slide ank you there we go yeah well it's not optimal but alright that's good enough my apologies for interrupting it soon all set alright so um Caro Sheff was interested in calculating how loud radio transmissions would need to be and so to calculate how loud the radio transmissions were to see if we could detect them he needed to estimate how much power an alien civilization civilization would have available to it for transmission and so he classified three types of ore scales of extraterrestrial civilizations by their total power supply available that in principle they could use to communicate so a class-one civilization on Kardashev scale was equal to humanity's present-day energy supply I guess the 1964 energy supply class 2 is significantly more powerful it envisioned a civilization that had as at its disposal an entire solar luminosity so it could command the energy of its star and in class 3 civilization would have a galactic luminosity and could command all of the Starlight in its entire galaxy and principle to try and estimate these transmission powers so this is actually a very useful scale for describing how large alien civilizations might get in this talk I'm going to refer to it but I'll use a slight modification of it instead of just referring to total power supply we're going to use a loser definition for these things Zubrin adopted it so a k1 or type-1 carted off civilization was a plan expanding civilization that could command essentially all of the resources of a planet including all of the Starlight that falls on to the planet so then a k2 would be a class to civilization that can command all of the resources of its stellar system its solar system and a significant fraction of the output of the star even if it doesn't get all of it and this is sort of a fanciful representation of what that might look like if you could harness a lot of stellar energy and a k3 is a galaxy spanning civilization or super civilization so app and galactic civilization that commands most of the resources and energy of the galaxy so when I say at k2 it's a circumstellar civilization I mean when I say k3 I mean an entire galaxy filled with an extraterrestrial civilization so without introduction let's start with the big question where is everybody else where's everybody else Enrico Fermi posed this question famously and so it's often called the Fermi paradox that if there's life throughout the universe where is everybody because the time it would take them to get here the time it would take them to cross the galaxy is actually quite short compared to the age of the galaxy so it seems like they should have been here already and yet evidence of alien civilization is has not been discovered yet and that that is the Fermi paradox it's been called the great silence space seems really quiet in 1973 Michael Hart argued that the reason we don't hear anything is because we're alone there's no one else in the Milky Way and we're never going to find anything and he divided other resolutions to the paradox other reasons why we might not have detected alien civilizations into four categories which he argued were all very unlikely or very contrived so the first category was physical objection you would argue that interstellar space travel is just infeasible the stars are too far apart you can't travel to other stars and so you're stuck on the planet where life arrived arrived arose even four billion year old civilizations no matter how arbitrarily technologically advanced you just can't get to the next star sociological solutions would argue that all aliens lack either the will or the coordination to colonize the Milky Way galaxy or that they're somehow deliberately hiding themselves from us and making sure that we don't find out about them so that that would ascribe some sort of a sociological motivation in capability to alien species there was a temporal argument that just says it takes a long time to cross the galaxy no one's managed to do it yet it just takes too long for life to arise and fill the whole galaxy and of course the last category is that they're out there we just are missing them we just don't notice them so for instance wood ants as a social species if they could think about the problem would they recognize humans as another social species or are we just so far beyond what an ant could possibly comprehend that they would just see us as a force of nature and not understand what they were looking at which is possible but I'm going to I'm going to actually argue that there is a giveaway signature that we would see so let me walk through each of these because this is actually in my opinion a very powerful argument and when it needs to be contended with in any SETI program so first of all the physical objection that you just can't build an interstellar probe for some reason is contradicted by the fact that we've already done it so within 80 years of developing powered flight humanity launched what would become an interstellar probe in the Pioneer and the eventually the Voyager spacecrafts so you can certainly build interstellar probes and if in 80 years you can do that the step further to actually colonizing another star is a problem of engineering but there's clearly no law of physics or ultimate engineering problem with launching interstellar spacecraft so I think we can say that one that's that's an objection that doesn't hold um there's the sociological argument and I think this is an underappreciated objection that Hart made to all sorts of arguments like this that maybe the aliens are all hiding from us or they've all developed virtual realities and that's much more interesting than the real universe or they're just fundamentally and curious and they don't explore the universe or they're just very shy and don't want us to know they're there or whatever and hardsub poet's counter-argument to this was that we shouldn't ascribe a single culture to alien species unless the all of the other species in the Milky Way in the universe have some sort of a hive mind where they all agree to do the same things we should expect them to have subcultures the same way we have subcultures and we all don't agree on we should be doing um also unless they somehow never evolve or change their minds then every few generations you get new subcultures and so just because today they've decided that they're going to be shy that doesn't mean in a hundred years they're not going to want to go out and see what's going on so you have subcultures within a species and you have subcultures that across time as well and unless they can communicate faster than light which as far as we know is impossible then if they're on different stars on opposite sides of the galaxy they can't coordinate their actions so even if they had a hive mind or we're inclined to all do the same thing the message here is what we should do is going to take tens of thousands of years to get across the civilization so it's physically impossible for a large civilization across the galaxy to coordinate its actions so you have to have lots of cultures so for most sociological solutions to work you have to ascribe one of these possibilities for why we don't see anything - all subcultures of all species for all time across all species and that seems quite infeasible so we call this the monocultural fallacy the fallacy that you can think up a reason that a culture wouldn't contact us and then try and ascribe it to every culture across the Milky Way galaxy so either there's so few cultures well basically this doesn't work the next argument was temporal that it that perhaps they haven't had time but they've certainly had time to fill the Milky Way galaxy it takes less than a hundred million years or so for a spacefaring civilization that can colonize a nearby star to colonize the entire galaxy and that's a that's a maximum amount of time and here's why so there have been a lot of optimistic scenarios on how long it would really take and for instance if you have the ability to build some sort of super engine that can drive you at ten percent the speed of light then it takes you a million years to drive that ship from one end of the galaxy to the other and so if you have a lot of those ships then you can cross the galaxy in a million years it takes something like a million years to fill the gap see with colony so that's very fast the galaxy is 10 billion years old pessimistically you say okay well maybe it's very hard to go very fast but is it hard to go very fast you can get gravity assists just because your ship isn't very fast doesn't mean it can't go very fast our interstellar probes did not get all of their velocities from rockets they got them from gravity assists from planets in the solar system and you can do the same thing for instance with a binary star if you fly near a binary star Freeman Dyson in 1963 showed if you go between them you can get 300 kilometres a second which is a part in a thousand of the speed of light and if you go between some black holes that are in orbit around each other you can even get up to 100 the speed of light without any fancy kind of whoop drive or whatever you have you just get near them and they send you off quite fast you don't even have to get that fancy there are stars in the Milky Way that do not orbit in the plane they orbit in a big halo around the Milky Way their relative velocity to the Sun is a partner thousand of the speed of light there are some near the Sun we could use them for gravity assists and get up to part ten to the thousand or pardon a thousand of speed of light and at the very minimum you have the planets like we do so the slowest you could really argue that you can travel through the galaxies the speed of planets around stars which is around light and that is in fact how fast our spacecraft go so those give you some long crossing times for the galaxies but it turns out even if you have very slow chips you still populate the galaxy very quick I've been speed at which a civilization is going to grow if it can colonize nearby stars is not the speed of the ships it's the speed of the stars so let's build a quick little model to illustrate what I mean let's just say we've got a colony and it's going to start colonizing the stars near it and they're very slow at building these ships it takes them ten thousand years to get up the will in the organization to build a colony ship and send it off but just to the nearest star and let's say that they don't have any kind of special engines they're just going to use the planets in their system and their best cruise speed is the speed of planets 30 kilometers a second so that's the speed that we can send things out so this is a pretty pessimistic assumption for a civilization that can build colony ships to go to another star will assume pessimistically that they have zero technological advancement they never get any better at doing what they do or speed up and will so that they only colonize the very nearest systems they don't get really ambitious and trying across the galaxy and that they don't use any of the halo stars or the binary stars that we talked about before so if you have that colony how long does it take that one colony to populate the whole galaxy well the crews time to the nearest star is about a hundred thousand years at that speed in that time you'll have launched ten colony ships to the ten nearest stars but the stars are moving and by the time the first colony ships arrive the ten nearest stars have all been replaced by ten other stars because the stars are all getting mixed up so now you have ten new stars to populate so you're not going to saturate the stars nearby with colonies you'll have this constant supply of fresh stars coming by because the stars are mixing themselves up so the colonies even if you wait 10,000 years that's not a pause in the expansion of your civilization because the stars are drifting apart and they're all drifting apart at independent trajectories in different directions and they are going to start populating their nearest stars and then those stars will populate those stars and so the civilization does not expand as a bubble and you won't expect to see so called Fermi bubbles or Fermi voids where this is the part of the galaxy that has the civilization and the rest of it doesn't for slow ships it's the stars themselves that spread the galaxy and it mixes quite quickly so the chances of actually catching a distant galaxy that's transitioning from a single spacefaring civilization to a pan galactic civilization are very small because the transition only takes at most 100 million years and they're 10 billion years old so that's a one percent chance of catching it in the act and if they have fast ships the transition is faster so the chances are smaller so when you work out this reasoning the corollary that Michael Hart argued was that nearly all galaxies should have either zero spacefaring civilizations they never got off the ground or they should be filled with spacefaring civilization so there should not be any in between and therefore he argued the Milky Way is either filled with them and for some reason we can't see them or we are the first to arise in the Milky Way so this is pretty pessimistic if we want to find alien civilizations in the Milky Way and in fact he was pretty pessimistic about the whole thing and that was the reason he made the argument but I'm going to argue the opposite I say that this analysis is very optimistic so heart said communication SETI is quote probably a waste of time and money which I very much disagree with but unless spacefaring life is unique to earth and I mean unique in the universe unless we're unless we really are the only civilization in the whole universe that spacefaring that if he's right other galaxies should be filled with advanced civilizations and so if we go looking for them we should find them and I'll argue that we can find them if they're out there and of course if he's wrong then the Milky Way should be filled with circumstellar civilizations and we should find them in the Milky Way so either we should see galaxies filled with them and the Milky Way empty or the Milky Way filled with them and other galaxies filled with them too unless somehow we are really the only spacefaring civilization in the whole you so we should test this hypothesis we shouldn't see this as oh we should stop or oh we should look we should go out and follow both paths and see if we can find them in other galaxies and find them in the Milky Way so the way I propose to do this is by using both communication SETI and what's sometimes called artifact setting my favorite example of artifact SETI comes from a paper by Luke Arnold in 2005 and he argued that spacefaring civilizations that need a huge amount of energy will build mega engineering projects around their stars so k2 civilizations need to build big solar collectors big energy radiators and we should be able to see these in silhouette when they pass in front of the star and so he pointed out that the Kepler spacecraft would be very sensitive to this sort of thing so as a toy model he said imagine that there was some big engineering project that was not a circle well it wasn't a disk it wasn't a sphere planets or spheres and so they have circular cross-sections so when a planet passes in front of the star there's a characteristic signature of that if you had something other than a circle like a triangle just not because they'd build triangles but because it's not a circle then the difference between the signal Kepler would see between the triangle and the circle had a characteristic signature and that difference was detectable Kepler could tell the difference between circles and non circles so Kepler would actually be very good at detecting mega engineering projects around other stars he went further and pointed out that as long as you're building these things and you know earthlings and other aliens can see them you could even do something clever like make your mega engineering project have some funny shape to communicate information and say not just I'm not a circle but something interesting like I have lots of louvers that maybe can change and signal you maybe you would arrange the objects in a pattern first one goes in front of the star then two then three then five and so you have some sort of prime number sequence going on that's clearly of extraterrestrial intelligence so it's a neat way that you would signal and it doesn't require you to transmit in radio waves and it would last a very long time so the knee little paper a cute idea and it basically predicted it said look if cap was looking at something and you see transit depths that are changing by a factor of five every time the thing goes around maybe what you're really looking at is an assortment of signaling objects so I thought it was pretty interesting when in 2012 Rapoport at all published the discovery of a transiting object around a star whose transit depths varied by a factor of five now they didn't happen in the pattern that Luke Arnold predicted but it was basically what he was talking about now this is generally the the explanation for this that Rapoport came up with is that this is an evaporating planet the planet is losing material and that material isn't a big tail behind the planet it's a turbulent tail sometimes it's thick sometimes a thin and so you see variable amounts of obscuration due to that object but it's interesting that Luke Arnold almost predicted this the this paper did not cite the Carnales argument probably because they hadn't read the paper I would guess another form of artifacts Eddy the form that I'm going to talk about was first proposed by Freeman Dyson in 1960 who pointed out that energy is never used up it's just converted to a lower temperature we think if we use energy and like it's gone or something like that but energy is conserved when my computer takes the energy from the power outlet and shows this talk and does calculations when it's done with that energy it has to get rid of that energy and so my computer heats up when you use up the energy from the breakfast you ate you warm up and you radiate it away you have to get rid of it or you heat up or not so if a civilization uses energy that energy must emerge as waste heat in the infrared we say it's waste heat but it doesn't mean that we've wasted it we've used it quite well to do interesting work we just can't keep it when we're done with it or we'll heat up so if a civilization ak2 we're using most of its star's energy then the star well it wouldn't be radiating that energy away so we'd see it being dimmer than it should be or perhaps not there at all but it would be a very bright infrared source because that energy has been reprocessed by a civilisation and is radiating away in the mid-infrared and this is a totally general approach there's no way out of this if energy is used it has to come out as mid infrared radiation and I'll justify that in a bit so there are some real advantages to this approach in looking for extraterrestrial civilizations it only assumes fundamental physics really bottom of the pyramid fundamental physics it assumes you have to conserve energy and I'm comfortable with that assumption it assumes the laws of thermodynamics which are as fundamental as physics gets and uh it also assumes maybe more subtly that there's no obvious new physics that you can't somehow tap a violate conservation of energy or thermodynamics or do something else in some special way that would avoid the heat that inevitably comes out from energy use and the reason I say obvious is just because there's a way to do it if there's any alien civilization that didn't figure it out then we would detect them so if you don't detect anyone either everyone figured out how to hide it's obvious and useful or you're going to see someone it also doesn't make any sociological assumptions about alien behavior or whether they would want to communicate or how they would try to communicate or what they would do because you can't avoid using energy and you can't avoid getting rid of that energy once you've used it it also can be applied out to extremely large distances radiation travels a long way and you can actually detect the amount of waste heat or mid and phred radiation coming off of galaxies at the edge of the universe so this works very well now this approach also has some disadvantages which is why it's not what everybody always does all the time it only really applies easily to very large power supplies stars themselves give off heat in mid infrared so the amount of power of a civilization has to be comparable to that of the Stars natural emission or you're not going to notice that it's there so you're talking about really large power applies really large civilizations I'll get to I'll give birth as an example but write a single planets waste heat would not be obvious against the star you would actually have to resolve the planet with the telescope and we we can't do that for small rocky planets close to their stars yet um also there's a lot of other reasons you would see MIT infrared radiation from a star or from a galaxy so there's a lot of contamination from objects that have a lot of what astronomers called dust it's more like smoke or soot very fine particles but those particles absorb starlight and then they rear 88 and some of that radiation a small amount comes out at mid infrared wavelengths so that's going to confuse things also if you see something it's a long road to prove its alien in artifact study because you haven't seen a signal you haven't seen the prime numbers necessarily you haven't seen something that's clearly intelligent you've just seen something anomalous and so you need to figure out what else it could be and rule out every conceivable naturalistic explanation so for instance when Rapaport discovered that planet that object and saw the variable transit depths they didn't jump to aliens they looked for and found a very plausible naturalistic explanation so this actually could brings us to a philosophical challenge of SETI that anyone do instead he has to contend with Arthur Clarke asserted that any sufficiently advanced technology is indistinguishable from magic so magic here is the suspension of natural law right there are physical laws that run the universe there's natural explanations for everything and if there's a sufficiently advanced alien technology it will appear to violate those laws because they just know more about them than we do but science assumes that the universe is governed by natural law if science encounters some new observation that doesn't make sense we don't jump to aliens or miracles we always reach for naturalistic explanations that's what science is that's why Lou Cardinale probably didn't get a citation other than not having read the paper in all likelihood with that evaporating planet because science says you have to reach for the laws of physics and so if Clark is right then SETI risks if you're not careful being inherently unscientific because it assumes that you can identify an apparent suspension of natural law as such and say there's no way that that could be natural that's got to be aliens and if you don't do that it leads to an aliens of the gaps kind of philosophy right anything we don't understand anything our models doesn't predict is aliens and that's the law Sophocles very problematic and unscientific so with communication SETI you avoid this because you're looking for signals that are clearly alien in nature and there's a lot of ways to distinguish communication signals from natural signals in the radio so we have communication SETI we have artifact SETI and I'm arguing that these are complementary approaches artifact SETI is hard-pressed to prove a phenomenon cannot be natural communication SETI is very hard because it has to cast what's really in a possibly wide net it's been described as looking for fish in the ocean thimbleful by thimbleful it's you have so many different frequencies you could search for duty cycles bandwidths powers what targets are going to look at it's an enormous problem and we have to look but we're going to be looking for a very long time if the signals are not very common and we just have no way of estimating how long it's going to take so they're complementary we should be using both to make sure the other is more successful artifacts Eddie can provide candidates this star looks especially bright in the mid infrared look at that one for communication SETI which can then jump to the end of the long line of reasoning of ruling out naturalistic explanations and say AHA there's the radio signal we've got it it's aliens and likewise if communication said he detects an anomalous signal but it's not clearly filled with information and we can't crack it and it could maybe be natural well then artifact SETI can go looking for other evidence of alien tech ecology and try to verify that that is what's going on or find the natural explanation for that so we need to be doing both so on the artifact set aside we're going to follow Dyson's approach and look for the waste heat from alien civilizations which is where we get this funny symbol G hat which stands for glimpsing the heat from alien technologies so this search is in three parts part one is we're going to look for kiiis we're going to look for whole galaxies filled with aliens which Michael Hart I would say has to argue must exist out there and we're going to do that around resolved galaxies that is we're going to use an infrared telescope called wise pictured here on the left and another one called spitzer on the right and they're going to we're going to use their surveys and look for galaxies that are clearly extended and we can really see if the whole galaxy has waste heat coming out of it the second phase is a k2 search we're going to get stars in the Milky Way that shouldn't have mid infrared excess but do and then the third part is we're going to look for very distant galaxies that are just little points and that turns out to be a different kind of search with different kinds of problems and opportunities so to do this we need to do what our cardio chef did we need to estimate how much energy is going to be emitted by these civilizations we have to parameterize that so that we can if we find nothing put upper limits on how big alien civilizations are so this is our parameterization alpha is a for absorption it's how much power an alien civilization collects from its star epsilon is energy it's how much energy they're generating by other means so it could be nuclear or coal or anything other than collecting sunlight gamma is how much power they're giving off as thermal photons it's their waste heat power and that's what we're looking for we're looking for their waste heat coming out and then nu is all the other ways you can get rid of energy so we don't get rid of all of our energy by waste heat sometimes we put the energy into a big radio transmitter and we beam signals into space so that's communication SETI and alpha and gamma are artifact SETI so with artifacts you look for starlight that's been blocked like the guard all did you look for the waste heat coming out like we're doing and with communication SETI you're looking for other ways that the power could come out we also have to talk about how hot the waste heat is if we want to know how much we're going to see how warm do their factories and computers and bodies get when they give off all of that energy that's the waste heat temperature and conservation of energy tells us that all the energy they generate alpha plus epsilon has to equal all the energy they give away and if those don't balance then they're gaining or losing energy and they can't maintain that for very long so we can estimate how much waste each should come out and how much power they have available for radio transmission from how much energy that they generate and because I don't want to work in megawatts I'm going to normalize everything by the amount of starlight available so for it k1 for us we normalize our power supply by how much sunlight hits the earth for a circumstellar civilization we normalize how much power they get by the total power output and for a k3 we say how much power the whole civilization has compared to the stars in the galaxy so if these values are 1 it means it's the same as all the Starlight so let me give you an example so we can put things in perspective let's use us our civilization and put it on the scale so alpha is a part in 10 to the minus 7 for us that means that one ten-millionth of the Earth's surface is covered by photovoltaic cells generating power for us epsilon is 10 to the minus 4 so we generate energy with fossil fuels we have some nuclear power all of that energy put together is one ten-thousandth of all the sunlight that hits the earth we're irradiate practically all of that into space we keep or turn into radio waves or something almost none of it on this scale so the waste heat we generate is a part in 10 to the 4 and the radio transmissions on the scale are very very small I don't know how to estimate them they're so small and the temperature is around 300 kelvins 250 Kelvin so like that so that gamma number means that the earth has an excess of heat that it gives off because we're generating energy with fossil fuels that it wouldn't have otherwise this isn't greenhouse warming greenhouse warming is an insulation effect this is actual direct heating of the earth by power plants and computers and everything in our cars and everything else that we do to generate energy so the earth is a little brighter than it should be by a part in 10 to 4 which is very very small and no one would ever really notice looking at us from afar but we're not a very big civilization yet so if you want to find this stuff in the mid-infrared you need the waste heat temperature to be around 300 kelvin or so hundreds of kelvin if it's too cold then you won't notice it because the waste heat is so far in the infrared it's so red that you wouldn't you wouldn't notice it so what are realistic values it might seem crazy to guess how warm the factories of alien civilizations might be but it turns out fundamental physics can put a pretty good constraint on this which is kind of surprising so the reason an alien civilization might operate at very low temperatures has to do the thermo dynamical argument about the maximum thermodynamic efficiency possible you might think that a huge civilization very advanced starved for energy could operate extremely efficiently and try to minimize all that waste heat coming out and to do that it has to lower its waste heat temperature by the laws of thermodynamics compared to the star that generated the energy so they also have to do something to get rid of this energy and the thing is if they go to very low temperature so they're extremely efficient the efficiency goes as one minus the waste heat temperature over the other temperature so if the waste heat temperature is small they're very efficient but to go to low waste heat temperatures means they have to be very big and the reason is if you want to radiate waste heat away then the amount of area you need to get rid of a given amount of energy scales is the waste heat temperature to the fourth power it's very steep and so that means that if you want to increase your efficiency from 90% to 99% so you already got a big one au sphere around your star using all the energy you say hey we're wasting some energy let's use that last nine of the last 10% that we're missing then you have to increase your area by a factor of 10 to the fourth so you've already done all this work to get 90% of the energy you can and if you want to get the next 10% you have to do all that work 10,000 more times over that's a very steep marginal cost for a little bit of energy so it's uncertain what the optimal size of this sphere that's radiating or all these surfaces is but it's probably somewhere around where you have things like solid metal and things like that around the temperature of the earth or so so as long as it's within about 150 Kelvin to 600 Kelvin that's a factor of 250 and engineering difficulty you're probably going to have your peak emission at somewhere between 5 and 30 microns which is right in the middle for red so there's a huge range of engineering difficulty that's all captured at MIT infrared radiation so that's my argument that we should be sensitive with these telescopes to just about any alien civilization so um I've argued it's all going to come from starlight that they're not going to have some other way of generating energy the reason for that is that there's as much energy available in sunlight as in any other source in the solar system the Sun light over the son's life is 10 to the 51 herbs of energy the mass energy of all of the planets put together is even if it were perfect it would be about the same if you could if you had some efficiency factor and how well you can extract the energy you're turning the mass and energy through fusion or something like that that only gives you something like 10 to the forty eight to ten to the fifty it's a fraction of that if you want to burn the planets the chemical energy available is many orders of magnitude smaller the kinetic energy is smaller the the only superior source of energy to sunlight is the Sun itself if you converted the Sun into energy but the sun's already doing that that's what nuclear fusion is and so sunlight the Sun the Stars really are the best source of energy in the galaxy so then would you really expect a civilization to need that much energy I mean we've only had a galaxy and stars for 10 billion years is that enough time for a civilization to grow so hungry that it would use that much energy and the answer is definitely enough let's use humanity as a case study here's how much energy humanity has used in the last few centuries and this is a logarithmic y-axis so this straight lines on this plot are exponential growth the energy use of the United States has tracked its population pretty well growing at about 3% a year doubling every 30 years giving you a factor of 10 every century so if we kept this up and we did it all with fossil fuels we'd have a horrible environmental catastrophe if we did it with solar power which is what I'm arguing you have to do in the long run you're going to hit a limit really fast right now we use a part in 10 to the 4 of all the sunlight our energy use goes up by a factor of 10 every century so we have 4 centuries left before we need solar panels to cover 100% of the Earth's surface we're about to hit a hard limit now we could switch to fusion power or something but we still have to get rid of that heat remember we're heating the earth with this energy so 400 years we have alpha equals 1 how long until we need the whole Sun at that pace it's about 1,400 years and we need the entire Sun and it gets worse because exponential growth is very fast the next factor of 10 comes in a millennium and so in 2,400 years we need every photon of all 200 billion stars in the whole galaxy this is not going to happen in 2400 years I said it takes a long time to fill the galaxy the point is we're going to hit technological limits on in a cosmic timescale almost no time at all we run right up to some limit like we're generating too much energy and then we need more technology and when we get the more technology we'll start climbing this curve again and in fact it's already happening Japan doesn't have a lot of land area but it needs a huge amount of power and nuclear power in Japan is not very popular right now and so they were looking into solar panels they don't have enough room for them so they're going to put them in space this is a real plan by the Japanese Space Agency to put solar panels in space and beam the energy back down to earth in Japan where they can then use this energy what they're effectively doing is collecting extra sunlight and this is what we're going to have to do we're going to expand off of the earth and collect extra sunlight now if you do this it won't work because you're just focusing sunlight back on the earth and you're just going to heat it up and that doesn't help but you don't need the energy here a lot of the energy we use is in things like giant data centers that use huge amount of energy to calculate our lives and do all of the work that we do and there's no reason is there I mean depending on what they're doing those data centers don't have to be here you could keep them up there and just send the information down or you could go up there maybe you're on the moon maybe you're on Mars maybe you're on a space station and you go up there and use the energy and so before you know it once you have that technology you're climbing that exponential curve again and you're headed toward using all the sunlight there is so can you use all the sunlight there's no physical limitation here available that mass isn't a problem there's enough mass in Jupiter to do it that would be hard but it's just energy we've got energy so you can build in principle enough collectors five meters thick if you want to collect all the sunlight that reaches the distance of Earth from the Sun and it doesn't have to be a solid structure this is sometimes called a Dyson Sphere after Freeman Dyson but you shouldn't be thinking of a solid sphere around a star that's not necessary it's probably not possible you just need a lot of collectors a lot of people going after energy and every other limitation you can think of that would stop us you can overcome with energy if you need more of something energy we'll give it to you you can get more food you can get more water you can get more anything you want if you apply energy and so the real limit isn't food or fresh water or something it's the ability to get rid of this heat so you don't overheat the planet it melts so I would argue that very small values of Alpha very small power supplies are inconsistent with old civilizations that are technologically advanced and keep having exponential power supply growth which comes just from being a species that that that that grows now it's possible that there's science we don't know yet in engineering and maybe there's better ways to generate energy than this so there might be alternative supplies of energy there might be new physics maybe there's a way to magically directly turn mass into energy maybe you throw things on to a black hole through the Penrose process and that generates large amounts of energy maybe you can tap the dark sector and there's zero-point energy you can have all the energy you want that's fine you still have to get rid of it you still have to rear a v8 it so it doesn't matter if you're actually getting it from the starlight if you're generating it in other ways then you might generate more energy than there is in starlight the the civilization around a star might be five times brighter than the star itself that only makes them more obvious so if that's not possible in starlight really is the best way to do things which i think is probably right then you expect alpha to be bigger the collection is more than the generation but it's still possible to get values near one that is to have power supplies comparable to the energy generated by a star so what about getting rid of it all why should it all come out as waste heat well it turns out there's fundamental physics here too because you have to get rid of your energy as waste heat again it goes back to this thermodynamic efficiency there's some maximum efficiency you operate at the maximum possible efficiency says that you're going to turn almost everything into something other than heat and get rid of it and so that's very good for communication setting because it means you're getting rid of this energy in some low entropy way like radio waves or lasers or something and so communication SETI is going to go find that because ADA is high and you're getting rid of almost all your energy that way but even then you have to get rid of the minimum waste heat which is your total luminosity and it scales with your temperature which I've already argued is not going to be very very low so even then minimum about 5% of your total luminosity so we should expect I think that very old large civilizations should have a lot of waste heat that they're giving off and by the way this is thermodynamic limits we don't come anywhere near these limits we do useful work we run marathons we run our computers we give talks and when we're done we radiate it all away anyway so for Humanity almost everything we give off everything we generate we radiate so fundamental physics says that these numbers should not be so tiny for large old civilizations that we won't see them so this is how we're going to go find them let's get really technical now and look at the spectrum that you would see from a large civilization just this slide I'll show a picture next so for large civilizations that are always teet like us we can approximate the flux we say that the Starlight gives off some energy some of that is absorbed its reradiating as waste heat there's a T to the fourth factor because the waste heat is brighter because it's colder and if we do an order of magnitude assumption then what we can see is that the flux in the mid-infrared goes as the waste heat temperature to the minus 3rd power the point is when T waste is very small that is like on earth you have a ways T temperature of something like 250 Kelvin compared to the star which is very hot then you convert a lot of flux from the optical into the bit infrared and things get very very bright very very fast by factors in my two examples here of 400 or 4000 depending on how much energy they're using so this is what it looks like this is a spectrum of a elliptical galaxy that's a galaxy without a lot of dust it's mostly just naked stars in black an old elliptical galaxy on the left is short wavelengths in particular optical light that you can see with your eyes and on the right are infrared wavelengths and what you see is in the vertical purple bands that's where the wise satellite that we're using can detect emission the bump all the way on the right by a hundred microns is dust dust gives off a lot of law wavelength lights if 1% of the star light in that galaxy we're being reprocessed by an alien civilization just 1% then the mid infrared radiation that wise detects would jump from the black curve to the red curve wise can tell if there is 1% of the star light in that galaxy being reprocessed by aliens now it's not that simple seeing an excess doesn't mean you see aliens and the reason is dust here's a spiral galaxy the spiral galaxy has a lot more dust and so the farmfreund flux is much higher the mid-infrared flux is also higher it's consistent with 10% of the star light being reprocessed by aliens so if you see a spiral with all this mid infrared light it could be that 10% of the lights and aliens or it could just be that it has a lot of dust like most spirals do so this is our confounder this is the problem that we're going to see MIT infrared radiation from things other than aliens but these two spectra are not identical there are still big differences that give away the dust the first is that the dust has this very funny spectrum in the mid infrared this is from polycyclic aromatic hydrocarbons it's a particular kind of dust and it's very characteristic so if you can take a spectrum of a galaxy then you can say oh that's dust that's about aliens never mind and move on to the next one the next big difference is that dust generally comes with molecules molecules have a lot of radio features and radios way off the edge here but radio telescopes can see oh I see carbon monoxide that's just dust don't worry about that meant infrared light and then of course there's this enormous difference here by a factor of 200 in the far infrared flux between the two scenarios and so you could also use a far infrared survey to distinguish unfortunately we don't have a very sensitive forum for its survey yet but when we get one it will be an excellent diagnostic of this sort of thing now if you do see a huge amount of mid infrared radiation that doesn't mean aliens even it's much more than this because there are really dusty galaxies so here's an extreme case of a nearby starburst galaxies and ultra luminous for red galaxies called up to 20 and it has a huge amount of dust but even so if 90% of the Starlight were being reprocessed into the mid-infrared that would still be more than this extremely star bursty dusty galaxy and so in this case what you can do is put some upper limit you say well the dustiest galaxies have mid infrared optical ratios that go up this high if we see more than that that's beyond any natural source that's a really suspicious object and we should go point our radio telescopes at it so that's what we're going to do we're going to look at stars we're going to look at galaxies and we look for excess mid infrared radiation and when we find something interesting we'll follow it up and try and find out if it's dust or not now if we look at a star it's going to be pretty tricky because stars can actually get much more red than whole galaxies can and almost arbitrarily mid-infrared bright but will be saved because a mission that is supposed to have launched by now but has been delayed by at least a month called Gaia will tell us how far away stars in the galaxies in the Milky Way are and so if we see a red star like wow that's a lot of mid-infrared right I'm very suspicious of that Gaia will tell us how far away it is and if it's very very very far away then it's probably either a distant galaxy that's been redshifted by cosmology or it's some sort of extremely dusty giant star there are these carbon stars and post asymptotic giant branch stars that are very dusty but they're also extremely luminous and so Gaia will tell us oh don't worry about that that's a giant star what we're looking for is something that's roughly the brightness of this luminosity of the Sun that's got too much mid infrared radiation so Gaia will let us split between zero parallax stars very distant objects that are galaxies and we can study them as galaxies giant stars which are probably giant dusty stars and they're a low priority for follow-up and things that are more like the solar luminosity which are excellent candidates for follow-up and in that case we can go ahead and take our mid infrared spectra and we can look and see if they're in a part of the galaxy where there's known to be a lot of dust in the star forming region or something like that but for the extended sources for galaxies it's simpler if you if wise looks up and it sees this dusty galaxy's red red red galaxy well we know that if they're extended they've got to be galaxies and if they're above the Galactic plane then they can't just be extended star forming regions in the Milky Way so that's going to say they're definitely galaxies and galaxies only get so red they only have so much been in for a mid infrared radiation so we can find the extreme ones the very largest k3s with the most energy will outshine the dustiest galaxies and will either detect them right away or say they don't exist and if they're really well resolved then we'll be able to actually use the morphology of the mid-infrared emission and this is an idea of it I got from dick Carrigan dick Carrigan who also works on this kind of artifact study let's look at this galaxy we'll turn on our mid infrared goggles there it is in the mid infrared now the galaxies there at the bottom is an elliptical galaxy doesn't it hardly has any mid infrared emission that's why it looks blue in this image and that's like that first example I showed we can rule out the existence of large extraterrestrial civilizations in that galaxy at the bottom using more than a few percent of the Starlight they aren't there now in the big spiral it's harder it's filled with mid infrared emission that's the dust but you can look at it that's the dust galaxies mixed stars mix themselves so if that were an alien civilization it would be everywhere but it's not it's clearly confined to the spiral arms where you expect dust so you can also put a limit on that galaxy and say this Andromeda does not have a large extraterrestrial civilization with huge amounts of energy so we can make this a little more formal and this which is called a color color plot we look at the amount of emission that's appearing at different wavelengths in the bands of Y's the first band the second band w1 w2 the point is that if things are very cold they have a lot more long emission than short emission or infrared far infrared than mid and Fred the near infrared it'll be to the right and it'll be up to the top things that have very little dust or little bit infrared emission will be in the lower-left so stars and elliptical galaxies don't have a lot of mid infrared emission they're in the lower left by zero zero and as you move up and right you find things that are dustier and dustier where do k3 civilizations live well it depends on their temperature and it depends on Alpha or gamma how what fraction they're using if they're not using any energy from the star light well it's just a naked star so they set at zero zero and then every dot here is another five percent of the star light that's being used by the alien civilization all the way up to one at the end of the blue so you see that if you're using more than 20 30 40 50 percent of the star light you quickly move up and to the right so if we take all the galaxies and Y's and we plot them up then we know which ones are the best candidates for being filled with alien civilizations because they're in the upper right and not on the lower left so where all of the points well this is where they land most galaxies or ellipticals or spirals corresponding to something like 5% of the star light being reprocessed in the mid infrared by the time you get to 30 or 40 percent reprocessing you have almost no sources so we haven't gone through all of these some of these sources aren't real some of them are actually solar system objects there's a lot of ways that you can be fooled and we have to be very careful with the data but you can see here the zeroth order result of the wise survey the universe is not filled with galaxies filled with aliens with huge energy supplies if it were possible to tap zero-point energy and have as much gaol energy as you wanted if you could outshine your star with all of your cool zero-point energy generators then there should be galaxies that are much brighter in the mid-infrared than they are in the optical and they would live way beyond the tip of this they're out there gamma batteries are way more than one and we don't see them they're not common at least and so we can actually put an upper limit on the whole universe we're seeing things out to cosmological distances here in the whole universe limit on how many very large power supplies there are so if there are aliens out there they have not universally figured out how to tap zero-point energy so we already know that we're not going to see that the universe is filled with advanced civilizations with huge energy supplies and we're going to see how much better we can do then that statement and this is new this is something that wise has taught us that we did not know before that satellite launched so there are a few science outputs we're not just looking for aliens here so the null detection if we see nothing up to some limit that's an upper limit on energy supplies of alien civilizations we will also look at the reddest objects the brightest mid-infrared objects in the sky and those are the most extreme and so by definition some of the most interesting objects in the sky to look at and we're also going to develop a comprehensive follow up strategy for our best candidates so when we see good things we want to know how to follow them up and see if they're alien civilizations we'll identify that strategy and we're already starting to think about what the optimal satellite would be to do this search what would it look like and so we want to know what we want to do next to put better limits and find these K 3 civilizations and test Michael Hart's hypothesis we might find entirely new classes of Astrophysical objects since this is artifact SETI we can't say that's it that's aliens so as scientists we have to first start with naturalistic explanations and that means we're going to find new potentially new classes of Astrophysical objects just like Kardashev identified objects that turned out to be quasars and um and Luke Arnold's prediction was interpreted in terms of an evaporating planet and we might find aliens who knows so what does a no result imply well civilizations with a large energy supply don't exist that's one possibility of why we don't see them that could mean they're logistically impossible for some reason it could mean they're physically impossible for some reason and it could be that civilizations inevitably stopped growing some projections of Earth's populations say it's going to level out somewhere 10 to in 12 billion people we just won't need a lot more energy maybe we'll never keep growing even after billions of years maybe they are inevitably short-lived for some reason maybe there's some galactic immune system that comes by and just you know scrubs out that little stuff growing on that planet over there every time it gets out of control it could mean there's some kind of new physics that we don't know conservation of energy thermodynamics maybe they can communicate faster than light and coordinate and make sure that they don't get seen but that has to be true of all of them it could mean that they inevitably operate at very low wet levels of waste heat temperature and so we can't distinguish them from dust or it could just mean that we aren't sensitive enough they never get to have very large values of gamma for some other reason so we're working on this we've defined how we're going to do this search we've been trolling through the data we've looked through most of the reddest objects we found a lot of red herrings and cleaned everything up and I hope to have some real hard numbers on upper limits soon and maybe some very interesting objects that we can pass along to the Allen telescope array and other communication SETI practitioners for follow-up is really interesting candidates so in conclusion communication and artifact SETI are complementary we should be doing both I think hearts analysis is optimistic not pessimistic either the Dyson Sphere search we're going to do we'll work or the galactic search is going to work one or the other eventually even if we don't have the technology to do it yet we're only going to get better at this and more sensitive we're very likely to see alien waste heat in the mid-infrared not at much lower temperatures because of that T to the fourth engineering problem wise and Spitzer are going to give us these upper limits and in the future future space missions will tighten those and a null result if we see nothing either means we're alone or there's new physics we don't understand that they inevitably tap that make them invisible to us for some reason and it's obvious which means we'll discover it eventually and that's exciting too Thanks I don't think there'll be any questions after this look no that's why I'm gonna ask one while everybody's thinking of their question so um Jason what I was wondering if perhaps it might be possible for the Dyson Sphere civilization to collect that energy and reradiates specifically in just one beam direction exactly theme their heat away at least to reduce their own detectability you know to to play like us if you beam the energy you lower your efficiency that's expensive so that's energy you didn't use so you could collect a lot of energy and then use that energy to beam that energy away hmm but then why did you collect it in the first place yeah so you can but it doesn't make it doesn't sort of make sense is something that you would spend a lot of engineering effort doing unless you did really want to hide yourself that's true um although it you're accomplishing anything by having yourself that way you're creating a lot of energy that might give you away and then using it to hide Rossano you could use the energy to drive a starship you can use the solar radiation to move the whole star and like a stellar engine it's been called um the other thing though is that's low entropy radiation and that's looks a lot like communication SETI that's the sort of thing you might look for in the optical right yeah so Andromeda is what 2 million light-years away or so right yet I think so so the light we're saying from Andromeda is 2 million years old two and a half million years old okay so maybe the light that you're looking for hasn't gotten to us yet right because the civilizations haven't haven't arisen in risotto the Andromeda galaxy is 10 billion years old and the light we're seeing is from two and a half million years ago so it's a factor of a thousand so we're seeing as it was one one thousandth of its life ago so it sort of be like you know me looking at you from I don't what it works out to a week ago or something like that you're more or less the same we just develop right now right there's an interesting idea that there might be an it's been called a an astrobiological phase transition that the Galaxy was inhospitable to intelligent life until now as a whole and right now all the civilizations are arising and that's that's that that's good because that avoids almost all of Michael Hart's arguments and that's very clever but there's no reason it should be the same time in every galaxy so unless the Milky Way is lucky enough to be the first one then other galaxies should already be populated so we can test that one which i think is really neat by looking at other galaxies every galaxy is an independent test of the idea that we're first in our own galaxy I I don't understand why kiiis would be rarer it seems like either there's something preventing them from existing or they should be everywhere because as far as we know nothing has changed in the past ten billion years in the universe well I agree for the most part 10 billion years a lot has changed but one or two billion absolutely well even even ten billion years I'm not I mean I suppose there's been more snow or processing a bit about supernovae rates gamma-ray burst rates density of amount of star form formation and stuff but but I agree I think that's right but the astrobiological phase transition argument are using something new but I think you're right I mean I mean there's not much has changed in 10 billion the earth is stable for 3 billion years and that seems more than enough time for a key three civilization I agree this puzzle is why it's called a paradox it really should be should be there so the wise mission came up with dozens or possibly hundreds of high mid-infrared radiating stars is that correct um well depending on how high you want to go it's found yeah it's not a lot of very minute Fred bright objects yes right and the vast majority of these are associated with star forming regions that's right proto stars and young stellar objects and things like that and carbon stars planetary nebulae it turns out are extremely mid-infrared right right right of course so what's the best candidates I mean do you have like a handful of them that look reasonable they're so nice old stars so the best candidates right now look a lot like the worst candidates except no one's ever noticed them before so the best candidates for the old that's amazing that's exactly what we're looking for and then we look in the literature and it's this very well known well studied carbon star like super famous and everyone has taken spectra and it's clearly just a carbon star and then we see another thing let's just like it and it's still exactly what we were looking for but no one's ever studied it before so it's probably a carbon star so is that a good candidate because it looks great or is it a bad candidate because it looks just like unknown false positive and that's what's so tricky about the point sources is that there's so many things they could be you just have no idea how much you should get invested in them and that's why Gaia will be so powerful because it'll tell us what's extra galactic with giant star luminosity and what is that luminosity that nomid in for a bright object has any right to be so you've probably eliminated about 80% of them so far um eliminated is hard you have this we have this grading scheme for how interested we are okay that grading scheme goes from A to F the FS are artifacts they aren't real objects the C's are well studied objects that looked good the B's are kind of interesting in the A's are the ones that we want to go after and we have dozens of A's and thousands and thousands and thousands of objects Thank You great talk my question was you seem to have left out the prime directive as a I haven't the prime directive is a great example of the sociological explanation the aliens have coordinated to leave us alone and make sure we don't know that they're there that's a deliberate coordination across all the species well I guess as a not just as a something one would choose to do but every civilization gets found by another civilization it gets ugly and they all learn that they should do it and so it's it's something that they the universe teaches civilizations it's interesting it could be a universal lesson if it's something they all learned or enough of them that they don't contact us that I guess would do it that's a interesting way around this it's sort of a yeah naturally learned sociological phenomenon it's interesting you're using lies and you're using spitzer yes to make these measurements and clearly if you have lots of measurements to make then you may be limited by the lifetime and the amount of time available on these two spacecraft where where are you in terms of you have do you have lots more sources to look at do you really depend on these two what do you have enough to simply say you don't care when they quit so Wise has finished its all-sky survey so we have the catalogue it's done and we're using it at the sensitives it's still running as an instrument but it's no longer doing this Big Sky Survey so it we're treating it as a finished mission and the the spitzer wavelengths were interested in it in the mid infrared that instrument has lost its coolant and it's no longer operational so we have fixed datasets we're working with spitzer also did not analyze the whole sky so it's very good for the the Dyson Sphere search because it did do the whole Galactic plane and it also did a deep stare at distant galaxies and so both of those surveys are good but they won't do the whole sky so we can't say no where in the galaxies or nowhere in the universe we can just find interesting candidates why is doing all sky lets us put real limits on things thank you icky aging very nice talk ie the motivation here is that for a better lifestyle you use more energy there's no doubt that that's very heavily correlated with our experience here I'm not sure that once you invent machine intelligence whether that paradigm continues but let's assume that it does so why wouldn't the really advanced aside there's just a suggestion we right look really advanced society say look back with g-type stars Sam dwarfs whatever let's go where the energy as are these black holes but those are hard to find a rare but there are bright stars around and they'll put out ten thousand times of course as much energy and if you hadn't have a bright star in a very cold area like in a Bach lobule which you know something about right yeah then you've got a tremendously better heatsink and a bright energy search you should look there I'm not sure the Bok globules are better heat sink than the CMB I mean a small C and B would ya be great but right that's maybe a long trip yeah I on the Gallic there that's how the Sun I'm just comparing it with the general interstellar medium um so the that's a good yes I agree that civilizations might find very massive stars or very young stars or black holes or the central black hole the galaxies as wonderful places to be but unless they all go there we should see the ones around ordinary stars too so if you're a civilization living around this star unless you pack everyone up and leave to go to that bright star then we should see the ones that didn't leave around that star so again it's it's the monocultural thing do they all do that or just a few it's problem of alien psychology yes with wise and Spitzer were pointed back at us yeah how far out could they detect us so there's detect and tell that something was anomalous at our presence on earth in terms of the waste heat increases the Earth's mid-infrared brightness by point zero one percent and that is probably too small to notice but there are other oddities about that point on one percent that you might think are strange so as the Earth rotates the hot spots come and go yes so that might be giveaway on the other hand we might just have a lot of volcanoes so it'd be hot you an alien civilization would be hard pressed to say we see their industry now they might see our bio signatures they might see how we affect the atmosphere they might see our radio transmissions but we are too small for the artifact the the waste heat approach to have made much of an effect yet but give us a couple hundred years and we might be able to do something about that and also historically as dr. shostek mentioned you know to improve our lifestyles so we've been generating more waste heat over time yes so it might there be an historical increase over time from yeah from zero to 0.01% so that might might be kind of hard to pick out because it probably get lost in just normal climate variations and things like that I would think and put in an ad for recent talk that was by jeffrey kuhn if you're online and want to see another time ago which one you mean yes i agree there was a question over here somebody puttan oh okay yeah yeah so I was wondering about you're talking about this power efficiency so as we get more handsome well just how efficient humans already using energy over time right you look at cell phones ten years ago you had to carry around us brick sure now we got little tiny things that slip over power that's right so yet you could make the argument that civilizations as they get more advanced get quieter that's here as we get more efficient at using the energy it's available to us so first of all that has not been historically true even today the per capita energy use of humanity has not gone down because yes our cars are more efficient than our grandparents car our refrigerators are more efficient they didn't use laptops and they didn't Google things where the Google servers did all of this work so that they could look at a cat or something I mean we do more stuff with energy then our grandparents did and so we have more ways of using energy maybe if you look at per capita energy use it's pretty flat actually and so the dominant driver of energy use turns out to be population growth and as more of the world gets more developed and as our insatiable appetite for cat videos just grows and grows we'll just keep using more and more energy the other argument I would make is efficiency is sort of linear right it's like how efficient is your car it's 90 percent or it's 10 percent it's 20 percent it's 90 percent energy growth is exponential and so unless you have exponentially improving efficiency the exponential growth of your population and energy use is going to outpace it Jason we have a couple of online questions actually probably have more online questions and we can get to tonight but I'll be directing you to answer those after the fact but he's one when we're looking back at civilizations across the universe are we not looking backward in time are we hoping that the aliens beat us at the race of evolution towards intelligent life right and I would I would argue that um the look-back time involved is small compared to the age of the galaxies and the likely age of the civilization so again it's it's the the amount of time we're looking back is not that long on in a cosmic sense so unless they just happen to arise arise in the last few million years which is unlikely we're not going to miss them because of look-back time yeah okay I'll um I'll be directing you to a couple more of those questions and I have a funnel we had a question a couple of questions Frank did you have one here too busy googling yeah we may not even have a single example of a civilization that has achieved a stable existence oh I that's that's sure true yeah and so is it possible then that civilization a stable civilization will end up inevitably stopping its growth at a certain point right just because of the limits to growth on the home planet sure and those limits include maintaining a healthy biosphere which cannot be maintained a healthy by growing exponentially yes ok so these are good good concerns the the there's two two things I want to say one is we could obviously destroy ourselves and never launch a colony ship that's definitely a possibility we're in this narrow range of time where we both have the ability to blow ourselves up and we don't have the ability to build a lifeboat but as soon as we have a moon base then a lot of its a self-sufficient then even if you nuke to the whole planet you still have the moon base and you can come back later or go to Mars and once you're on Mars you can't even conveniently get rid of the moon base even if you wanted to because Mars is far away once you're around a nearby star you're now a hundred thousand light years away and now you have independent colonies so that we're in the narrow range where we have nukes but we don't have colony ships and once you have colony ships I'm already got to be basically immortal there's basically no way to get rid of all of these civilizations all over the galaxy at once now you also talked about population growth and if that's stable then why would you necessarily go out but it's not population pressure that drives colonies right if you have 20 billion people on the planet and that's too many building a colony ship and going to Mars doesn't relieve the pressure because you're not going to move 10 billion people and even if you did you're going to double your population before you've set up the other colony so population pressure isn't what drives colonization because it doesn't help the problem and the people that go in colonize aren't it's crowded here they're like I want to live over there and so even if we achieve stable population that doesn't mean that we're not going go to other stars I think that would be my answer I saw some designs for adiabatic computing that allows you to use no energy for computation are you familiar with any of those I'm not but I believe you wouldn't would it make sense that an advanced civilization would come up with a design like that in that if that in that case then they would not use energy to do computation because the computations are free but that doesn't mean they won't use energy also the other question is if you were in the best of a civilization you wanted to hide wouldn't you proudly locate the telescope's of the civilizations that are trying to search for civilizations and try to do simulations that would appear as if there's no salvation - this wouldn't be like much more energy efficient and give me like a the I think this is a pudding glasses over your telescopes that Aryan hypothesis that we're inside a big planetarium and what's really going on is very different you lift up the screen and oh there are all these yeah so is it possible maybe to like a that's right um um yes we're so much more efficient so there's one class of there's one class of solution I left out which is sometimes called the solipsistic class which says you simply cannot trust what you see so either we're in a planetarium or we're all in the matrix or whatever and that we just can't trust our observations and I don't know what to do about that it's possible but I don't know so one this thing I do consider if you think about the number the amount of time we have left until the Sun this the earth becomes uninhabitable that's maybe a billion years and if you think about the proportion of time that life has existed on earth from the beginning of of life till we can't exist here it's about like you know 80% along the timeframe now if like if intelligent life was really you know impossible like you know very improbable we would probably find ourselves at 99.9 percent of the time for existence right no I don't follow that argument if if life is very unlikely to occur if intelligent civilizations are very unlikely to occur that doesn't we mean they all carry themselves close to the end not 80 percent I don't think so you've got a lot of star star years where it could arise throughout the galaxy and you don't know and art in our existence essentially no I know but you're saying if it's very rare yeah then you expect at the end of the bed at the end of the start of this habitable cycle of time we can talk about it later but I'm pretty sure that's not how it works yes low mass stars are fascinating targets for intelligent civilizations I agree my question this is my skill as your mago absolutely and it gives you a chance you said you talked about immortality and the challenges there those robots they are living the life of Orion and they're speaking to Drake Equation to each other see very relevant to your talk I'd say please join me in thanking Jason freeze great so I

Channel: SETI Institute

Views: 39,411

Rating: 4.5833335 out of 5

Keywords: seti talks, Extraterrestrial Life (Cryptid Classification), Search For Extraterrestrial Intelligence (Organization)

Id: fI8rYMuLNeA

Length: 82min 52sec (4972 seconds)

Published: Tue Nov 12 2013

Reddit Comments

[u/youarefeelingsleepy]

SETI Talks are great. I wish I lived in an area where I could spend an afternoon listening to these talks in person.

I found that Jason T Wright has a blog. Here is a link on his site where he describes some of this work.

A WISE Search for Kardashev Civilizations