welcome to the science for the public lecture series science for the public is an organization committed to bringing science information and issues to the general public this is our website for our program discussing her new book mapping the heavens also her a cutting edge research in astrophysics in addition to her academic position as a theoretical astrophysicist at yale dr knot and also currently holds the sophie and tai cobra a professorship of the dark cosmologist center at the niels bohr institute university of copenhagen her list of distinctions is long so we refer you to her website or to her event page on our website but we should mention that dr knot is an elected fellow of the american physical society in that she was also elected to an honorary professorship for life at the the formation of the first black holes she's also committed to communicating science to the general public this commitment is reflected in her articles in new york review of books and most especially in her splendid book mapping the heavens the radical scientific ideas that reveal the cosmos this book illustrates so well the difficult path of most breakthroughs in astronomy and cosmologist from resistance to acceptance often a very long transition we're delighted for the opportunity to talk about dr not a rajan's book and her own exciting research in astrophysics we're very honored to welcome heard tonight well home thank you a real pleasure to be here and i'm going to ask to start with talking about your book one of the best things about the book is it shows the fits and starts of introducing radical new ideas most of them were sort of rejected initially in astronomy is that true absolutely and i think part of what i wanted to show in the book illustrate through these examples of many of the radical ideas that we take for granted today the existence of dark matter of black holes the fact that the universe is not just expanding but the expansion is accelerating all of things we take it take as a given at this point but the process by which these ideas were first proposed they were contested and how they were eventually accepted is kind of complicated but it's a complication and in that complication you actually see many wonderful aspects of the human side of science the fact that scientists are human it and science is a human endeavor and so you have the passions of the scientists jealousies ambitions and personality clashes that kind of play out in the process and it's also true that the process of acceptance is extremely nonlinear ideas you would imagine are so much more complex that they would have taken a much longer time to get accepted but then you see it is the interplay of ideas and instruments so it's science so the ultimate arbiter is data so when you have overwhelming evidence in support of an idea then you know i scientists first of all we are trained to think and to reason and therefore you cannot but be persuaded by the evidence so i mean ultimately it's you know instruments and idea is that really help us shift our thinking in terms of these ideas that met with resistance to begin with what do you have any big favorites well since my own walk center principle on trying to understand the nature of dark matter by actually mapping it and you know the origin and the growth history of black holes i have to say the idea of dark matter the existence of dark matter and that of black holes are sort of two of my favorites and also the illustrious a sort of very different ways in which science works so for example the idea of a black hole originated from a mathematical solution so it was an elegant mathematical solution slightly perverse mathematical solution and so it was not believed to correspond to anything real so it was never believed for a long time for almost thirty forty years that you could actually have a real astrophysical object that would be a black hole it was a mathematical solution so it started from a theoretical idea and then eventually we found them and so on right but in the case of dark matter it's entirely the opposite there was no theoretical conception of dark matter it was found in the data and evidence was found in the data and then sort of a theoretical edifice sort of was built around it and it turns out now that this theoretical idea of dark matter is fundamental to our conception of how structure forms in the universe let me get this get something clarified here i think most people know that our baryonic matter the stuff that's all around us that we do perceive is minuscule in the universe but it's still a hard thing to get your head around that's about four percent that is right and dark matter that stuff we can't it's about twenty six percent of the overall sort of mass energy mentor you have the universe and ninety percent or more of the total matter content so the ordinary atoms baryons that  anything in the periodic table even the most you know the biggest most massive elements the biggest animes in the periodic table they constitute four percent and by and large we know that because the majority of baryonic matter in the universe is hydrogen and helium we actually know right after the big bang after the first three minutes we know how much was actually made because all the other elements are synthesize in the centers of storage here that happens over much later cosmic times so you know we have a it's remarkable but that we do have a really good inventory of everything in the universe well all the matter and that's of a saying well we don't know what dark matter is made it's true what the particle is we know it must have you know form sometime very early in the universe and that it is copious and it's mirrored everywhere but we don't know what it is at on that you've mentioned that it is there is scaffolding in which all structure in the universe including the galaxies and the stars in the galaxies form they are the dark matter is distributed in the universe it because gravity is the only force that's felt by dark matter they don't interact with any other forces they're not electrically charged these don't have to particles so all the dark matter interacts by the force of its own gravity so it flows in the universe so it actually flows into this filament restructures in the universe and what we find from our current understanding of galaxy formation is that dark matter is so many are very smoothly pretty much everywhere but are regions where you have these flows these filaments and those filaments intersect where you have a lot of clumpiness so you have a lot of concentration of dark matter so the way to think about it is because gravity is the only force and town when you have a small over dense sort of concentration of dark matter it tends to grow because gravity will pull in more stuff and it will tend to grow and this is a region that starts out having a little bit of an excess of dark matter over time progressive lee becomes really over dense and dark matter but those regions are very interesting because those are the very regions where galaxies and up forming and that was sort of determined at the very very early stages of the universe think it's a particle absolutely ok that's so there's you know there was a proposal that to circumvent the idea that it was actually a particle because we've not found it yet right and this idea called is referred to as modified newtonian dynamics and there the the proposal is that it's not a particle but it's just that the newtonian force law the force of gravitation the one over our squared law is actually and i hear more and more cold dark matter so they are very slow part don't interact massive they don't interact with each other or with anything basically it will be fascinating to learn more about that in terms of these ideas meeting with resistance sometimes for very long periods could you give us something examples of that right so i think that you know part of the normal process of science is being open minded and to contest ideas so that's part of the method of side is right however when some really radical ideas are proposed or over and beyond th normal contestation which is part and parcel of the intellectual process of science you have individual personalities and you have their egos you have their ambitions which get involved in it so i think you know one of the cases that is particularly interesting is the discovery the observational discovery of dark matter so first of all you know it is such a radical idea that it was discovered and then forgotten and then  discovered many times so fritz zwicky who was a scan tanker of ron of our who was at cal tech right it was brilliant so he came up with the idea of dark matter by looking at the motions of galaxies in these distant objects are called clusters so it turns out we now know that clusters are the largest repositories of dark matter in the universe and therefore the motions of galaxies that are bound in clusters about a thousand  bound by the gravity of the dark matter they are whizzing around much faster than they would if there was no further unseen matter and zwicky managed to measure the speeds of these galaxies and notice that they could not be reconciled with all that we see and so he proposed this idea of dunkel material some dark matter that's invisible right and it was nine hundred thirty three you know it was not taken as seriously and then in one thousand thirty seven he further noticed that if you do have such a large concentration of dark matter as for einstein's predictions from the theory of general relativity that the presence of mass is going to deflect light he said these regions of the sky should actually be huge light deflectors and that therefore they would be these gravitational lenses and that we should be able to see sort of deform shapes of bag around distant galaxies when we view the universe through these clusters through regions where you have these clusters and he predicted that right and i think thirty seven and that was not taken seriously either in fact the first observation of a gravitational lens which was confirmed a cluster lens was nine hundred eighty seven  mentioned is everywhere so it's distributed not just in clusters of galaxies but also in galaxies so individual galaxies like our own have a big halo of dark matter that extends well beyond where the light is and so in the nineteen sevent rueben and can't afford they actually measured the speeds of stars in galaxies spiral galaxies in particular from the center outward and once again like as wiki found that they were moving around much faster indicating there was something else that was contribution to gravity that was on c but you know they made these measurements in the early seventy's and it was such a radical claim but they actually just sat on the data for a few years before they actually had have so and it turns out finally they published it and simultaneously they were talking about these results but they were very cautious in claiming that there was this new sort of invisible entity because theorists you know people's yahoo and all stryker were noticing that in fact for the stability of galaxies to understand why galaxies are stable in an expanding universe they put forward ed and so when that convergence happened right then you know the idea was really accepted but it's amazing that these things these are all central to modern astronomy one after the other in your  know this is just our or the last hundred years have been incredible yes and i think it is really the growth in technology both with instruments and cameras and capabilities you know our ability to launch satellite and  to circumvent the earth's atmosphere as well as big build very large telescopes on earth and computing yeah i think there is support that he hangs converging that has really made a huge difference yes i want to ask you about that the about the technology i have one real quick question first about the delusions and so on can you give us an example of a situation where people saw things that were  rarely you know sort of imagined that they were that which you know one of the interesting things is how our imagination goes beyond interpretation what i've seen you know there's always interpretation when you see something in a distant object you look through a telescope you're obviously you know this is the beautiful thing in cosmology right you never do controlled experiments so it's not like you know you have a microscopic right and you can manipulate your specimen and then see what happens what you see is what you get so there you are and there's a layer of interpretation and the desire to discover the possibility of life elsewhere the possibility of water on mars was just such a strong driver that you could see that they were you know lowell particularly was very excited at the possibility and really believed that we may not be the only intelligent beings finding you know evidence i think it's kind of coming nice full circle yet on that though is there are a strong person or physicists who maintain this  idea of of life out there and other people who don't where do you fall in this so i mean i think that you know i think it serves to remind us that you know copernicus really got us started by moving the pivot away from us right and i think it was the beginning of what has now culminated in this incredible revolution of understanding our place in the cosmos and the realisation with the discovery of thousands of planets around here by at ours right so now we think that there are actually more planets than there actually stars in the universe because you can have stars that have multiple planet right and the fact that statistically with such a large number of possible worlds and many that we think are probably habitable given our understanding of life and the possibilities for life and its origin i definitely believe that there could be life elsewhere i mean the thing that i am sort of tickled by is that it's quite possible that life as a really know it might not know what turns up might not be recognizable to us as life because i was stephen jay gould famously said right even if we replay the tape of evolution on earth yes it's unlikely that we would be the end product so i think i believe that there are definitely life forms whether they are anything like us recognizable to us  or intelligent in the ways that we come we have come to define intelligence is an open question exactly but it's interesting how this has shifted it wasn't very loyal ago when people that went looking for ex planets were told your career is over if you try this just nothing out there and now look and it's changing very rapidly and they absolutely i'd like to switch to your work which is this very cutting edge material and you have a diverse of of a focus in this regard in can i start with the black holes there early early black holes th seems to be full of i don't know controversy a lot of difficulty can you give us some background yeah so i think what is intriguing about the early black holes is the seeds come from one of the first class so now we know that every galaxy including our own appears to have a super massive black hole million times the mass of the sun but sitting right at the center and the question is how did a black hole start out as a seed what was a mass of the seed how early in the university have to form that seed in order to end up with this kind of population at the end of it right so one thing we know is that black  either be active or dead and they're active when they're feasting on gas and growing and emitting in the process because of the way gas siphons onto them as the gas is falling on to them it gets heat distances in fact the most distant objects in the universe that we've detected so far tend to be quasars so what we have now found is that we found find a population of extremely bright quasars that are in existence when the universe was seven percent of its current age a fraction of it is right and the traditional thinking was that the may of the way you make the first black hole seed is that you make the first star which then exhaust all its fuel explodes and leaves behind a little seed black hole and then that seed consumes all this gas and sort of eventually build a city but the problem is that these bright quasars appear to be powered by black holes that are a billion times crunch even if we overfeed black holes there's a timing problem well you'd have to have huge huge stars still would have to do a stores or you would have to have a very steady supply of gas that would be constantly feeding into the black hole so you have this sort of you know rapid feasting sort of making these very obese black holes so an alternative suggestion that many of us to work on including my research group is that perhaps from the get go it's a very natural explanation that perhaps from the get go you could make seeds that were much more massive could you make seeds that were one hundred thousand times the mass of the sun rather than ten times the mass which you would get from the end product of a star and so then the idea is what is the kind of physics that is needed in order for a black hole to form so rapidly to such a high mass from the get go very early in the year when you work out what conditions you need so basically what we rapidly in the early universe making it to the center of a galaxy but the galaxy has not assembled yet so what you really have is just gas mostar some more and so the idea is that these are pretty girl lactic black holes or direct collapse black holes and it turns out that the conditions under which this can happen or ubiquitous in others so this can happen but the question of course is once matter goes into a black hole there is no information about the initial conditions so looking at the black hole at the center of the milky way today we cannot tell whether the initial c was aware of it was a very massive yes yes so the only possible indication you could have is by looking at the end vironment when these seeds actually form so very early in the universe so that's when you would have some inkling of how the black hole assembled we caught assembly ok but a major thing is it didn't come they didn't come from stars necessarily we have been taught by being we've been prejudiced to certainly believe that it started with stars these individual stars they collapse you get a black hole then you get a galaxy but you're saying no it could start in this other way so that is certainly interesting the other is i guess that they're all over the place there in every galaxy  you know they don't actually have to form in every early galaxy galaxies in the universe grow by merging with each other i see it turns out that even if you see one in five one in ten very early on in the universe as a result of merging over cosmic time you could end up with one in the center of every galaxy like our own i say ok now we've got that part out of the way then then in terms of other areas of your own work should we talk about the lensing oh absolutely but before that you know the question is it's all great to have these theoretical ideas right so what is the observational evidence where is it going to come from so james webb space telescope has a satellite that is going to be a telescope in space that's going to be launched in twenty eighteen is going to access so it has cameras that are sensitive and very long wavelengths which is the infrared and you know in the universe from early times light gets stretched a longer and longer wavelengths as it comes to us so the longer we are able to detect wavelength more sensitive detectors that we have the further back in time we can go and so this telescope has instruments on it which are going to be sensitive in the right wavelength rain to detect the first growing black hole that is a really exciting and how else you know we may well be able to settle the question and i think in nature we're probably happens as you probably form black hole seeds both ways and i don't think it's one or the other but the question is the most massive black holes in the universe probably require these very massive seeds from the get go and it would be very nice to catch one in action right as i don't i think everybody is in this field must be very excited actually wait for the web to go up hubble space telescope to actually detect these gravitational lensing effects that me clarify that you wouldn't have been able to do this with optical telescopes on earth would have found these distorted  but they would have been fuzzy sitting in the kind of science i'm doing what them so for example the cluster of galaxies which is sort of in the foreground has a huge amount of dark matter and it turns out now we know that it contains dark matter some of which is small be distributed some of which is quite heavy and it distorts the shapes of galaxies that lie behind it so when we look through a galaxy which is say normally projected on the sky looks like a little circle  gets stretched out yes if light actually passes through regions of space time that have a huge pothole generated due to dark matter so the presence of dark matter causes huge bumps in space time and light travels along space time follows that hole and so we end up seeing a very very distorted shape for a gal as i believe in your book you have images of this as well this is dramatic images just what is very interesting is because sometimes these bottles can be so deep that you can have a beam of light and that comes through and it actually gets split so you end up seeing multiple images of not say but multiple multiple there just of the same object and in reality you have only one object in the air but we see copies of it yes and these copies are very very interesting to detect because they offer us important constraints on modeling so what we do is we look at these distorted shapes and we back out the amount of dark matter that's actually causing these deviations and so we're able to map the dark matter so the more detail we can get out of hubble space telescope images in terms of the distortions the better we can actually map that dark matter so for example now we have these the latest data from this project called the hubble frontier feels project very deep a look at six clusters and we've reconstructed the dark matter distribution in those six regions and what we find is we can look at the reconstruction that we have it with theoretical predictions of the dark matter theory the cold dark matter theory which we which we can compute using simulations computers in a giant computer simulations so simulations that  is so troubling about cold dark matter so if you look at a lot of the observational data you look at a theoretical understanding everything fits rather nicely there are a few gaps here and there but that could be our own limitation in terms of the accuracy of measurement and so on and so forth and lack of understanding of some physics of galaxy formation but by and large things fit very very well the awkward embar is a thing of course we keep coming back to this we don't know what the part of whatever it is the other shows up really well you do really sophisticated modeling and so on to i don't think that kind of thing is as for the mill you're with us but you mentioned big data which is a big thing and your ability to really check your make a model and then you really check it with with with what you find what's happened with that how does this evolve now yeah so i think what has been pretty incredible is the sophistication both of our understanding of the physics and mathematical techniques that we have for sort of the paper and pencil theoretical work that can be done as well as the sophistication in computing that actually allows us to render our models and change and perform experiments if you will i want to go back to the point i raised is very similar which is that we can now in a computer simulate with a bunch of initial conditions and instantiation of version of the universe and then we can change the initial conditions and we can rerun the simulation and produce another piece of the universe another chunk of the universe so it kind of allows us to produce a sample of universes to test observational data but what is really sort of problematic about this is you know is sort of from the epistemic point of view is that you really are getting out what you're putting in a way right so i can pick properties for the universe initial property  then i can let it go i can let gravity do its trick and run it for thirteen point eight billion years and look at what a slice of the universe should look like today i can change the initial conditions and i can read run it right but i still am constrained by what i put in as initial assumptions right so this is very tricky in science the scientific method because if you look at  experiments and chemistry or biology what you do is you have a specimen you manipulate it you change conditions of you know temperature salinity ph and you look at how the sample evolves changes and you can make a record and then you understand it right so you are actually inferring by doing a whole bunch of independent experiments right so we don't have that power in cosmology yet we've devised these wonderful technique of cosmological large sophisticated salut simulations that allow us to sort of mimic the universe and make measurements so we make these mock measurements relations and then compare that to real data to see how well the correspondence is and you know given that we have this scheme as i said this called dark matter model works incredibly well both on galaxy scales on cluster scales and the only sort of places where there's a little bit of tension on the tension is really about the detailed understand it's our lack it reflects our lack of understanding of the physics of star from and what went so you know i think that the problems that are the hardest to crack are the ones in which you have to integrate sort of small scale behavior and larger scale so there's a there's a what we call technically is a challenge of the scales of physical scales that you need to resolve so for example in a simulation for example to form stars you would not only need to understand how individual molecular clouds interact but you would also need the entire cosmic context over where in a galaxy the star forming clump is sitting that is composed of these molecular clouds and so you would need to model the large scale flows of gas in the universe that dark matter network as well as the detail physics and chemistry yes those cloud right because you know ultimately what really you need to very low density gas so to be able to win the same calculation zoom in on where all this action is happening on small scales and then zoom out to see the context to get it right is a huge challenge that's very grateful for that explanation of what you have to say it kind of drugs even you know and actually although i sort of talked about how gas makes it to the black hole it's the same problem for understanding how gas actually flows requires because of the dark matter in particular we're talking about a particle that there is i don't know where the word is convergence of the largest scales in the universe and the smallest i don't know if it's all the way to quantum but the you're dealing with this this enormous stretch is that true and what does that do to your thinking because the right times they didn't have to do that right so i think that it's absolutely true that in a way the way to tackle these problems is to kind of synthesize what's happening on many different and so you know there are techniques that we kind of partition the problem and we try to do it and then patch the solutions to get sort of a more synergistic understanding and yes that there is actually no escape but to do this in a way but in a way i think that what is what is nice about tackling these huge scales for sure is that you realize how significant and insignificant you are we are as humans right doing this age so we have this cognitive capacity to make sense of all of this yeah which is incredible but on the other hand there are limits to our understanding so some limits come from our actual innate capacities day right i wonder if there's a space for a really big ego i would think that everywhere yes well in spite of that  exactly we are about out of time but i'd like as just a finishing statement from you is what do you think is say one or two of the biggest is issues today in cosmology where we're going and so on so i think that the figuring out the nature of dark matter and dark energy i think are the big open questions and you pick the harvest and i think that instrumentation actually in space something like lego but in space to do that and that's a foot so that project is called lisa and there was a prototype that recently was sent up and it actually performed better than expected so that we don't have a technological hurdle anymore so i think you know there are many windows that remain to be opened for us you know that will explain to us what the doc matter particle might be so you never know they may be  experiment of direct action dark matter experiment that might yield a result any day now or we have all these large astronomical surveys that are being done to really pin down when dark energy takes hold in the universe and starts to dominate we know that dark energy is dharma today it's the dominant component and it is driving the accelerating expansion of the universe today and we know that it probably picked up about seven to eight billion years ago and we want to really understand that in order to figure out what it could be so the current understanding is that it could be maybe some kind of you know energy that is associated with space itself that kind of vacuum energy and it could have been generated by some fields very early in the universe etc etc so there are sort of many models in play we don't really have a leading model actually and so we need a lot more data to figure out how to construct a viable model so i think all of these big questions stand to be answered our at least exciting developments in the coming decade or two and it sounds as though you're optimistic that you actually are going to be able to identify some of this one one sort of the reason i really wanted to write the book is that you know much as i am optimistic about the science of been slightly pessimistic about the misunderstanding of science the distrust of science yes  but i really do believe there are two that part of that mistrust and disbelief comes from the lack of understanding of the process of science of how and actually science works and in particular i think the have to be opened up and then understanding uncertainty and risk and i think you know evaluating that because that's where you know where science and society collide right sort of policy issues and understanding future risk and uncertainty and how that plays out and how as our understanding gets more refined we get a better estimate of the answer to and the risk i think the fact that you know one has to always stay open to changing mind i think is very difficult because the pace of change pace of technological processes progress has been so rapid in the last fifty years that i can understand why it's a challenge but i really think that today are more disposed to this they're not locked up in little villages all over the world which are you know centuries and centuries people were and locked into a particular world view so that this is changing and then people discover hey this is really neat you don't know what's happening next  misconceptions about science when they are clarified i think you know hopefully people will understand how wonderful sciences as a method to make sense of the world were you made a great contribution s