Shedding Light on the Dark Universe

[Music] on a clear dark night we can all Marvel at a crystal Sky brimming with stars and Beyond what we can see with the naked eye powerful telescopes confirm an expansive Cosmos chalk full of galaxies and stars and swirling clouds of gas and dust and planets and comets and asteroids but here is the amazing realization telling the mass and energy of everything in the cosmos that we can see accounts for less than 5% of what there is the rest more than 95% is invisible to even the most powerful telescope imaginable because it is all dark the dominant ingredients in the makeup of the cosmos do not emit or reflect light and so have been named dark matter and dark energy but if we can't see the dark side of the cosmos how do we know it exists well scientists have deduced the Dark Universe indirectly by its effect on the universe that we can see and among the scientists who were the earliest champions of a cosmic dark side was James pebles one of the most influential cosmologists of our time pees has played a critical role in numerous cosmological advances including the discovery and decoding of the cosmic microwave background radiation a decisive tool for analyzing the Dark Universe and refining cosmological Theory contribution that earn peoples the 2019 Nobel Prize in physics welcome Jim thank you so much for being here so so many people who go into science or mathematics often tell stories that they knew from when they were like four or five years old that this is what they wanted to do but I gather for you the journey was a little bit more circuitous than that true true um I think as a as a student in high school I was unsatisfactory not because I was at all rebellious but because I was a dreamer I didn't pay much attention to the courses I passed them but I didn't participate in any sports activities communal activities um I was a dreamer and and was that like by yourself yes bl by myself in books or um well you know my father was handy with his hands and he liked to build things I like to build things I like to mess around with with electric motors transistors Transformers um and uh because I was not paying attention I went into engineering which I did because I knew Engineers built things and I knew I built things so that seemed right I mean you say you were not paying attention meaning I didn't ask anyone I just entered ah the University of Manitoba okay um where I discovered at the engineering department that what I really liked were those courses in physics so I transferred and it was the best thing I could have done right and was there a particular course in physics that really made it clear that that's what you wanted to do more important I think it been important one Professor which is what you need uh who took an interest in me taught a good course that taught me a lot about physics and then he declared uh he had been a graduate student in physics at Princeton uh 10 years earlier and he decided you should go to Princeton so all right can I went and it was wonderful of course it was a big fish in a small pond becoming a little fish in a very big pond but I survived yeah and I gather at that time at Princeton you had two really iconic individuals who are starting to think about gravity but in very different ways John Wheeler is the one who you know we in the theoretical Community know well but of course Bob Dicky yes was there as well can you give a sense of their different approaches well you you you summarized it well to John a Wheeler Johnny uh general relativity was such a beautiful theory that it was almost certainly a good approximation to reality Bob dicki uh certainly understood Theory well but he was a brilliant experimentalist he had spent 10 years after arriving at Princeton doing laboratory what might call Quantum Optics he decided that gravity experimental gravity had languished since the 30s when difficult experiments were done but was technology that was so much more crude than what could be done with the electronics that came out of the second world war so Bob decided to set up a program of tests of gravity physics including the old classics but do them better with modern Electronics now like oos experiment for example yes uh many others testing active and gravitational Mass equivalence yeah very clever experiments so uh it I am a theorist but his work was much to my taste so I started with him he is the one who said you might consider looking into the expanding universe theory I did and where do you think that came from from from Dicky was was he just starting to think about cosmology and applying general relativity whether was it air um not in the air U although Bob and and John were were quite close and familiar they had very different worldviews John well Einstein's general theory of relativity is so elegant to Bob it's a theory and you don't trust theories until he'd been tested and so he's he was looking for tests all kinds he had a quite a quite a large group of graduate students doing lots of very interesting experiments um and of course gravity figures large in the theory of the expanding universe so he became interested in it that's why he suggested I started working in it and did he have a specific idea I gather yes he did yep yeah um he decided that uh of course you had that old problem what was the universe doing before it was expanding yeah uh one idea that people had discussed it was a bounce Universe collapsed bounced I guess Tolman was pushing that Tolman was pushing that it's a natural notion Bob noticed um and worked out the elegant physics of that in a collapse it's going to be thermodynamically in irreversible going to produce a lot of entropy which would be largely in radiation so this universe that's now expanding would be expected to contain a sea of radiation that radiation would be expected to have a specific spectrum that is to say the intensity at each wavelength uh uh he uh had invented during the war of microwave radiometer a device capable of very sensitive measurements of radiation uh he suggested to two of his young people in his group David Wilkinson and Bri and Peter R why don't you build a radiometer to see if there's anything there and he said to me so casual remark why don't you think about the consequences of this experiment whether a detection or non- detection right now A non- detection would have been interesting yes oh yes and of course it has implications you have a real challenge if the universe uh in the very early stages of expansion were called yeah because the protons would fuse to make heavy elements and that's not the way our universe is made most of the Barons they already hydrogen and helium so of course there's a way out you postulate to gener neutrinos and so that that's a possibility to consider I of course worked on that but turns out um the radiation is there and it has been wonderfully instructive now the discovery of the radiation is itself an interesting sociological SL physics story oh yes oh yes you know it goes a long way back already in the early 1940s people observed Interstellar atoms and molecules by the absorption of light from stars behind them uh the molecules cause absorption line the atoms cause absorption lines a discovery was that uh the molecule CN Cyanogen carbon and nitrogen stuck together is absorbed observed in interstellar gas in emiss in in absorption and startlingly it's observed in absorption in the first excited level remember in quantum physics energies are quantized in an isolated system it was a puzzle why should uh the Cyanogen in interstellar space be in an excited level right one possibility slightly mentioned maybe there's a sea of thermal radiation that's pushing it up to this first excited level then again uh when people started at Bell Laboratories in northern New Jersey started thinking about Communications by microwaves which had to me the rather unhappy consequence of producing those cell phones that I see our students at Princeton University walking around staring at rather than admiring that beautiful campus but among other detrimental effects among others um 1959 engineers at babbs developed very sensitive detectors to use in Communications they found that the receivers were receiving a little more noise a little more electromagnetic radiation than they could account for that for that was a dirty little secret at Bell Telephone Laboratories in northern New Jersey and this is before penius and Wilson Oh yes right five years before um it remained a PR little secret until penus and Wilson two young people from physics 1964 decided Well we ought to find out the source of this radiation they work very they're to be credited for refusing to give up the search for the source of this radiation and you know I'm I'm impressed that the the their their their bosses allowed them to keep going this in a commercial yeah research laboratory but one you know B Labs at that time had had had had had they had a monopoly on the telephone now they were controlled and so they couldn't charge too much money but they had a lot of money a lot of Revenue yeah and they SP resulted in Freedom right oh boy transistors it's just a very impressive place anyway they allowed these guys to keep going pens and Wilson also did something very sensible they complained why can't we find the complaints actually eventually reached Princeton where uh Bob dicki had as I said suggested the two of his young young members of his group uh build a radiometer of the kind that b bobit had invented during the war to look for this radiation so the two met and the recog recognition wow maybe this is maybe that noise in microwave radiation came from the early Universe now often the story is told that the next step was a telephone call yes um so we well we were having lunch in Bob's office back lunch uh phone rang uh Bob answered uh I could see David Wilkinson's ears pop up mention of well sources uh radiation leakage through the an through the joints of the of the microwave pant microwave channels um and it was pretty clear and then Bob turned and said well we've been scooped you know I'm often asked what was our what was our emotional reaction to that yeah and what was your emotional reaction to that you have to bear in mind this experiment was a blind search in the dark no guarantee that anything would be detected of course it was not detected that's interesting but still um the fact that Bell had shown that there is something there to be further studied experimentally and to study theoretically that's my job to find this implications was very exciting so uh it's often said well you must have been chagrined but certainly not me that was a real exciting moment how about the more experimentally oriented members of the well they had something wonderful to do so David Wilkinson spent the entire rest of his career yeah and I spent the entire rest of my career just following Bob's suggestion now you and penius and Wilson the two two groups I gather agreed to write two separate papers right one on the experimental discovery of the microwave background radiation and one more on the explanation and prediction from a cosmological perspective followed the the first being the the detection the second the implications now when you look at the experimental paper I've always been taken by the fact that there's zero mention of anything but the experimental detection not even a word about cosmology was that agreement or did penius and Wilson just want to State the facts and and not muddy it with any potential theoretical interpretation that's probably a good motivation but um I don't know I never discussed it with in fact Bob dicki directed the papers I don't know whether he suggested or whether pen Wilson realized you made a very good point let's not money in the water right right now of course history shows that the Nobel Prize was awarded for this discovery to penus and Wilson some have suggested that there could have been a more generous spreading out of the prize perhaps to Bob you know so what's your view of that well I was totally disgusted um I I deeply respect the Nobel Prize and the Nobel committee those people work really hard to get it right they work really hard but this was this is a brainless move it it should be penus Wilson dicki dicki invented the instrument he suggested the use and he told the Bell people what they may have found it was obvious um how how did he how did he take that did he show any sense of well I remember he was a little chagrined a little chagrined you should understand uh the people at the Nobel committee uh work really hard yeah but they're people they make mistakes right right now the other interesting part of the story is that in time you and and others recognize that there'd have been even earlier intimation of these ideas from gamma and and alfur can you just give us a sense of that backstory well so gamov had the deepest physical intuition of anyone I've ever encountered just dazzling uh I maybe it's inevitable that such brilliant intuition must go along with a certain dislike of authority so uh gamov you know during the 30s he was one of the leading authorities in nuclear physics at the time uh shortly after the uh World War II that is relevant he was finishing the Third Edition of his book on nuclear physics why wasn't he part of the effort at lelos to develop the atomic bomb everyone else was there it was his refusal to take take seriously in the notion of security yeah so but brilliant character in 1948 he wrote a paper with with Ral elfer uh and uh since beta since Alpha and Gamma look like the second and third letters of the Greek alphabet he put in by hand the name of Hans beta to write a paper famously known Alpha Beta gamma uh the paper assumed a cold start to the expanding Universe it's totally wrong right later in that same year his intuition Hit Upon what was totally right the notion of a hot Universe with many of the physical considerations that were then fleshed out by di by centuries of by many people uh it's so funny that in the first of the papers where he got it right a hot big bang he mentioned the alphabeta gam paper and saying due to a numerical error but it wasn't a numerical error this is gamov right I don't care about that old paper uh anyway gamov got many of the ideas right but because he was such a flighty person and because shortly after two brilliant papers in 1948 he streamlined the idea down to a theory that was just not logical so um his theory dropped out of sight yeah it wasn't forgotten by everybody but me I a physicist knew nothing about this so I had to start from scratch gamma Theory didn't didn't make its way into the textbooks yeah in particular you know the wonderful series of theoretical physics by oh land land they they had they had a third of their book on classical theory of fields is G relativity Theory ironic because it is then was not a theory that was at all well tested it did it included the notion of the expanding universe but they introduced a footnote this may be all wrong because the universe may not be homogeneous right they didn't mention um the hot big bang they didn't mention gamov and so I didn't know about gamov so that was eventually the connection was made by the time of those two papers you mentioned our paper has references though I have to admit among those references was Alpha Beta gamma I hadn't done the homework to recognize that that paper is wrong I let it get in there yeah and the and but there's also an alfer Ralph alfer paper with Hermon on the uh CNB and predicting as a 5 degree background temperature that was their great contribution yeah following gamma's two papers in 1948 they pointed out that uh in this Theory you would expect that the uh universe is filled with a near uniform sea of radiation at a very well well determined temperature around 5° or maybe 8° or close enough yeah to be consistent with what was later discovered yeah incidentally I mentioned the Cyanogen temperature it was 2.3k 2.3 Kelvin alha 5 Kelvin the observation 2.32 75 right right wow no it's amazing yeah and so we now had evidence that this thermal background is there which is giving us evidence of the hot big bang approach to cosmology but as you said you didn't stop there this is really the beginning because now you have this Relic from The Big Bang you can start to push further so what was the the the next step in trying to understand this radiation what it means the very first Next Step the key step is this R does this radiation really have a thermal spectrum that is to say you give me one parameter a temperature I'll tell you the intensity of each wav link yeah attempts to check that were very difficult because you had to get above the atmosphere to reach the peak of the radiation and getting above the atmosphere and doing experiments is really difficult yeah the result was that during the 70s there was a persistent indication of an anomaly that the Spectrum isn't quite thermal that was a horrible that that really made me uneasy because it's easy to imagine that the early Universe was energetically mixed up enough to produce radiation enough to have Disturbed the Spectrum if it did that then the distribution of radiation across the sky is giving you a measure of some complex process that was a horrible thought it wasn't until the early 80s when John Ma and others flew the definite experiments that showed wow it's exactly almost exactly thermal that meant that the small departures from an exactly uniform thermal C was telling you about the nature of departures from uniformity in the m distribution suddenly you had the prospect of a Precision test compute the evolution of the mass distribution predict its present properties and then measure them and that was really key because you could make these computations very reliably they're just linear perturbation Theory and that means because you can also make Precision measurements that you had a wonderful tight test of theory against observation which is very new in a realm of cosmology which which so it made a convincing case that we are on the right track right and so just to review that key idea you're saying that small in homogeneities in the matter distribution they would be centers around which additional mass and a kind of snowball gravitational effect would accumulate giving rise to galaxies so this is essential to understanding how these structures exist the word snowball is is a is a hazardous Point galaxies are complex yeah and so their properties aren't really a very good test of the expanding Universe it's the slight departures from uniformity in the radiation and in the large scale distribution of the galaxies that you can compute reliably and you can measure pretty reliably and my goodness they agree and in fact there's a a beautiful graph which shows the anisotropies in the microwave background radiation against the measurements well here's the uh this is the black Body Curve this is what made me feel good and early 1980s is that's John Mather is there a second one that shows ah interesting that uh there were many attempts to measure the intensity of this radiation as a function of wavelength two people drove experiment that got it right John Ma's experiment was proposed to NASA 15 years before the measurement beautiful work required but enormous effort to make that measurement in the Year John Mather submitted a proposal to NASA herb gush lead author in this measurement flew a rocket herd gush is a Canadian University of British Columbia more more modest funding at the time in Canada uh he couldn't fly a rocket that is adequate to carry the shielding that was needed but he flew it anyway he made the first attempt at the measurement of the spectrum from outer space 15 years later and many failed attempts shall I mention an example of the horrors of Rocket measurements why not solid fuel rocket it carries up the rocket the instrument explosive bolts release the instrument it goes ahead and leaves the rocket behind but some of the solid fuel in the rocket didn't burn CAU fire after the instrument package had been released and the rocket ran ahead of the instrument package and sprayed it with noxious chemicals oh gosh it's a tough life you have to be tough yeah uh eventually though within months the two got the measurement both would have made the case that it's thermal radiation John Mather received the Nobel Prize for that measurement well deserved well deserved yeah herb gush got the Deep respect of his colleagues but nothing more so is that another example of the Noel committee trying their best but perhaps not getting it yes thank you yeah you know I'm from Canada and so a certain shavinism yeah maybe apparent here so this is the curve that establishes the black body spectrum that any of you viewers here or in digital you take a basic physics class and statistical mechanics thermodynamics you learn about this curve a a box at thermal equilibrium will have this particular Spectrum right and then amazingly the deviation from perfect thermal Spectrum was the the next major result that allowed one to really as you say do Precision tests and you understand it was the absence of serious deviations which would have meant serious deviations in from non from linearity in the early Universe would have made uh the whole thing very impossible right but there it is you can you can be quite sure the early universe is quite tranquil slightly disturbed by growing departures from moment geneity now to take this to the next step you introduced into cosmology another idea which has been with us ever since dark matter in particular cold Dark Matter so can you explain the trajector in your thinking that leads to that step the Galaxy distribution is quite clumpy that's fine gravity would naturally draw things together and make a clumpy distribution of something was almost exactly smooth but to move around the matter to make it that clumpy would seriously disturb the microwave radiation so how do I understand that the microwave radiation is so very smooth well the matter is so clumpy the way out had to be an ad hoc guess that most of the matter in our universe is not made of the Barons electrons protons neutrons of a standard Theory but rather something invented ad hoc dark matter let it be cold to begin with because that's simple it's the first thing to try and also it keeps the pressure low presumably that's right so it's easier to compute yeah and uh ask yourself the question would this scenario work the idea is simply that uh as gravity is drawing matter together bionic matter together it will in radiation but if most of the matter is not bionic and does not interact with the radiation then it won't disturb the radiation very much so already in 1982 I had computed the first the DI the quadriple moment I had a prediction it's sort of fun to realize how long it took to check that prediction what couple of decades yeah but but it was found then of course we get to this um the bionic matter and the radiation in the early Universe strongly interact because the temperature is high enough to strip atoms of the electrons the electrons scatter off the radiation strongly enough to tightly couple them the electrons scatter off the ions tight strongly enough to couple them so ions electrons and radiation act as a fluid which has a pressure which means uh if it's Disturbed from uniformity it will oscillate like a wave that oscillation like a wave means that the final Mass distribution and the final distribution of the radiation uh are uh computable if the if the departures from uniformity are small so you can use linear Theory and here uh are dazzling results recently obtained The Wiggles uh you understand of course resonance which is a key thing if I had a bottle I would blow across his top and I would make a tone which is set by the boundary conditions in the bottle the university has boundary conditions it must start smooth and it must end these this coupling when the radiation Falls to a temperature of about a th000 Kelvin when the electrons can combine with the ions and that lets the radiation free to move to move and the matter free to move so you can compute all that uh in this graph uh The Wiggles are the results of those that resonance lucky and unlucky modes modes that grow and modes that diminish uh that can be computed the solid curve assumes particular values for parameters such as the mass density in Dark Matter the mass density in bionic matter uh the abundance of helium which matters um and the solid curves are adjusted to fit those constraints the data points are data points they're not at all well measured in the radiation at the very small L value and L is like a wave number it's a reciprocal of a length so that's large length scales where we don't have a very good sample of the universe because you could only see so much of it the rest spectacular agreement and even more spectacular to me the distribution of galaxies of large scales is measured in a very different way so you have different theories matching data obtained in very different ways and getting a consistent story it's really dazzling shockingly dazzling that a calculation that really can be done on paper and pencil you know can can yield something so precise about the nature of the universe at large yeah nature seems to operate that way yeah and uh it gives us very important point you don't trust a theory until you've had it tested and what you just saw is a really demanding test that it convincingly establishes the hot big bang general relativity Theory as a remarkably good approximation to reality now there was another anomaly that you were paying more attention to than most at this time regarding the expansion rate of space in fact I've read in various places that people would find it irritating when you'd bring up this issue at times but it turned out again to be right so maybe give us some ins on what that was all about right so Einstein another spectacularly intuitive person and maybe better self-controlled than GMA uh Einstein decided in first he introduced his general theory of relativity in in 1915 it was a spectacular intuition um so beautiful that many people accepted it but it it was not based on much empirical evidence on the other hand so then two years later he decided Well I'm going to try to apply this Theory to the structure of the universe for reasons that no one has ever explained to me he decided that the universe is uniform in the large scale average why did he assume that Simplicity Simplicity uh he found that this universe uh would not stay static of course it's it's obvious that the universe is static it's not changing of course it is changing uh but to keep the universe from collapsing under Gravity he introduced a term he added to his his field equations of general relativity so it it was got in urine the name the cosmological constant that added term um Einstein later emphasized was added only because he had to fit the observations he did not realize there was an observation that the universe is expanding as soon as he learned that he decided the cosmological constant must go but uh now in the 1990s the early 1990s uh it was becoming very clear that if you didn't put the cosmological constant into Einstein's field equations then uh then the Motions of the galaxies indicated a mass density that is quite large small small small compared to what you would expect from the rate of expansion at the time people were so impressed by the Simplicity of Einstein's field equation and of a homogeneous near homogeneous Universe uh and so impressed I think by the two facts that the cosmological constant is disliked by Einstein and because if you accept standard quantum physics then the Z Point Energy of the electromagnetic field would add up to an absurdly large cosmological constant the only solution something caused the cosmological constant not to be there that was very convincingly convinced many people surely there is not a cosmological constant but I was doing uh studies of how the galaxies are distributed how they're moving and to make that story fit I had to assume a mass density considerably less than was required by this universe without the cosmological constant so I proposed adding the cosmological constant that did offend people yeah um I remember one young person very capable now a great scientist saying you're only doing this to annoy and do you know the old Lewis Carol be be be to your little boy whenever he sneezes he only does it to annoy because it knows it teases and and I I must admit that I kind of enjoyed going to conferences in the 1990s and pointing out the evidence for the cosmological because I knew it teased right and just from the physics standpoint the cosmological con with the right sign would yield an outward push that's exactly that would assist the expansion that would solve the problem right so now in that me in that um image you saw of the oscillating the computation it it has a cosmological constant that um well it's needed and what size were you suggesting back then were you giving a numerical oh I was but I don't remember these things instead it's a dimensionist measure what is the ratio to the pionic density and I don't even remember that was it like sish or is that a hint U I adjusted it to fit the measurements okay which were only the mass density is the essential point and it was I think reliably nailed down to a factor of two right so it was and then the beautiful thing is 1998 when the observations from the distant exploding Supernova yeah gave an answer that showed there was a cosmos that produced that produced the um Nobel Prize yeah um just a magnificent result that people had been trying to achieve ever since the 30s people knew it would be a critical measurement yeah um but you know if we' had only that uh it would have been unsatisfactory how do you know that Supernova at Red shift 1 are really very similar to Y the year 2000 give plus or minus one the first detections of these oscillations were found and were found to require a cosmological constant so you found that more convincing yes really because it's a it's simpler simple to compute uh and whereas the evolution of supernova is impossible to compute right so I was I was not convinced by the Supernova I deeply admired it those people did a great thing yeah but as a practical matter it was the radiation that uh who his anisotropy was detected that convinced me now does it bother you or maybe that's the wrong way of framing it does it make you wonder about the fact that these dark entities the dark matter the dark energy they're kind of patches yes they are in order to make things work they're not something that we've directly detected that's right bare patches and where do you come down on that is that do you view them as sort of a temporary fix or are they the answer that ultimately will be directly confirmed I can't believe there they're more than a temporary fix got to be more interesting has to be a wonderful challenge for the next Generations learn how to make a more realistic model for the nature of matter in the universe dark and light and so the failure to detect Dark Matter over many decades now yes where where does that leave you on thinking we just have been looking the wrong way or it's a more exotic species or yeah uh nobody ever guaranteed that we could make a any sense of the universe around us and I've often wondered why were people so sure that the Universe operates in a rational way you see equally early examples of it um T ta o brde 2,000 years ago had a theory for the Motions of the planets it was it was an ad hoc Theory circles but yet he managed to get very good predictions yeah uh and I guess he wasn't particularly worried about the fact that well why are circles so very you do what you can yeah so far we have not found any flaw in the use of dark matter and dark energy cosmological constant and so we'll stick with it but we certainly lust after hints of failure of the standard theory that will hint to a better a still better Theory because it will have have more interesting properties for the Dark Sector would you be surprised if say 30 50 years from now the Dark Sector has been replaced by some new theoretical idea some new force of nature something of that sort right I I certainly don't expect that the be the main outlines of the standard Theory we have now are wrong yeah but in detail I think they got to be wrong and who knows maybe tomorrow you'll hear news of detection um or maybe you will never know never a guarantee that we can solve all the problems of that are opposed to us yeah for sure so in terms of anomalies with the standard Theory there are a variety of hints of things to come right one of which is the so-called Hubble tension yes when you measure the expansion rate of the universe basically in two different domains early Universe later universe and try to extrapolate they don't quite meet yes do you think that's a big clue number one I'm impressed that they almost meet you're comparing what happens in the universe Lo recently and in the remote past that they should agree at all is startling to me but of course they don't agree that maybe because of systematic errors it would have to be I think in the local Universe measurements uh systematic errors may be the culprit uh or maybe and this what I'm hoping for this is a true anomaly which is telling us there's something observably wrong with a standard Theory so let's look for what it is and of course let's also look for more anomalies and maybe if we have enough we'll see how they all fit together you think James web Space Telescope observations are going to resolve this particular anomaly only know if you try yeah right so it's still very much up in the air but but one can hope as we go forward and it's good to be looking in lots of directions by lots of ways yeah you as you've gone forward to refine cosmological Theory scientists you the community at large have taken on problems which in an earlier age reviewed as we'll get to that at some point but we're not ready to yet and among those for instance are questions that inflationary cosmology has tried to address this idea that in the early Universe there was some phase of Rapid expansion driven presumably by some energy that mimicked a cosmological conent of a very large value in the early universe and drove everything outward there's controversy now about inflation although I think some of the inflationary proponents may get angry at me for calling it a controversy but but there are differing opinions right now the inflationary structure where do you come down on this I have to respect these beautiful theoretical ideas after all Einstein's general theory of relativity based on almost pure thought has wonderfully successful I got to respect that and I've got to respect the possibility that inflation is in the same line but I don't trust it until we have some evidence and unfortunately it's very difficult to get evid empirical checks so that early on on so I say yes let a thousand ideas Bloom and meanwhile wait and hope we can think of something that contest these ideas now now one of the particular issues there there a number but some people bristle at a fairly generic quality of inflationary models which is they make our universe not the only universe so the inflationary fuel that drives a rapid expansion it's not exhausted by the expansion in our realm and the leftover fuel roughly speaking gives rise to other Big Bangs in other Realms now for someone like you who wants things to be tested which of course is the way science is meant to progress does the idea of other universes seem nutty to you or or are you willing to sort of allow for a tested Theory to make untestable predictions um it should be done but how much how how seriously should we take the ideas yeah I'm quite comfortable to hear about the Multiverse um but I might mention one point yeah we talk about eternal inflation but Eternal inflation is very clear can be Eternal into the future but it can't be internal back in the past yeah we run into these logical problems as well as imp iCal problems and we pay attention to them and do you think we'll ever be able to deal with the issue of the past I mean the question that I'm asked most frequently both by students and by the general public is okay you've got this big bang idea okay maybe inflation but what got it started right why was there the inflaton field you know why was there any expansion in the beginning at all we're waiting out of our subjects you think so yes and with subject are we waiting into speculation many many possible ideas but you think that it will resist scientific explanation do you think that there are questions of that sort that will simply be beyond the reach of the methods of science I I dislike definite statements so I say it certainly looks likely that we will not be able to answer all questions and how do you feel about that is that just the way it is or no one told us we could find answers to all questions I'm I'm amazed at how well we've done yeah and I'm sure we'll be doing even better there's a great future ahead of you all in in in physics it's a good subject uh but you're not going to get all answers that's just to me obvious so the big one that live nits asked a long time ago why is there something rather than nothing that is among those presumably I I don't lose sleep over that question so as we turn to the Future there are a number of missions that are planned we've we've made reference already to obviously the discovery of the microwave background radiation then the confirmation of the black body Spectrum with Kobe and also the Canadian experiment that that you described the anisotropies that came from Kobe and then we got a lot more information from w map and and from plank MH we have James web up there now doing remarkable work what of the upcoming missions are you excited about well we've reached a point in this subject where there are two lines of Investigation first you can do measurements that have already been done much better and you should do that better you perhaps will find that what look like close AG green ment of theory and experiment Isn't So Close maybe there's an anomaly that's very important to be done but you know in the rush to advance the science you do tend to leave behind little Oddities that you feel well we'll get to that later yeah and we don't there are in cosmology many questions that remain open that are a little outside the general line of approach of the big experiments to do a big experiment you got to be pretty sure that you know the answer and to find deviate find big missing pieces of the puzzle you have to step back and start thinking and maybe do a small experiment I'm I'm I'm I Harbor The Hope and I'm working on it that there are puzzles that were left behind in the rush to advance that are pointing us to issues that are going to teach us how to do better in cosmology do you have any that you can share with us as some final words in our conversation here of where you're putting your attention at the moment do we have a photograph of a galaxy do we have a photograph of a galaxy imagine that there is one because we will make it look that way in the digital version of the program okay a beautiful one is named Messier 101 nearby face on spiral wonderful uh it's a gorgeous image do you see the blue patches that's where groups of stars are formed relatively recently among the groups of stars there are some that are much more massive than the sun they are far more luminous they're hot blue that's what makes the blue patches you notice red patches that's where these massive stars have produced enough ionizing radiation that they produced patches of plasma in the plasma the dominant ion is hydrogen its recombination line is a big fat line in the red notice a glow of yellow toward the center that glow extends across that whole galaxy it is a light of stars similar in Mass to the sun astronomers have shown that in our patch of our galaxy there are at least as many planets around stars as there are stars this is showing us a system that we can never reach it's it's 10 million miles 10 million light years away uh in which there are some 10 to the 9th planets on which all sorts of things of wonderful things are happening that we the human race will never see that's one cautionary remark I like to explain the other is the Fantastic spiral galaxy the evidence is from observations of other galaxies that this galaxy is thin like a discus all the way to the center that thin discus is not obtained in numerical simulations of the formations of galaxies within the parameters of the standard hot big bang cosmology it's a real deep puzzle why is this thing so thin and why do the spiral arms go all the way to the center and I'm might point to the enlargement on the left from the Hubble Space Telescope instrument you see how the spiral arms extend almost to the center where there's a bright spot that's a million solar masses of stars that's a big number but trivial compared to the mass of this Galaxy 10 to the 10 10 the 10.5 in Stars uh in our galaxy there's a massive black hole in the center is there a massive black hole in the center of this galaxy I'm really hoping J wst turns its power to that little spot and determines whether or not the G stars are moving in such a way as to indicate the presence of a black hole in the very center we don't know where black holes come from that's one big puzzle yeah the other is uh we don't understand why the mass around the black hole is so darned close to smooth and moving so slowly that it can form a spiral arm a beautiful set of puzzles right here before our very eyes and do you anticipate Insight on that from numerical computational studies that are more refined in understanding the Dynamics they've been working on it for years and very refined and so far no one has found a Galaxy to my way of thinking that matches the properties of this one that means there's something we've left out of the computation my bet is what is it what did we leave out well no it's up to you you need to discover what we left out of this Theory great challenge for all of you one final question before we end here one recent result from the James web Space Telescope is that early galaxies seem to not conform to what we would have thought from the standard cosmological scenario they're they're brighter at earlier times and more massive and more massive what do you what do you think about that well I I it's another example of the fact that we don't really understand well how galaxies form and so that another valuable clue but do you have any nope no guesses of where that's going to go again another challenge for all of you both live and digitally who are watching this it's been a fascinating conversation Jim thank you so much for joining us please join me in thanking Professor Jim [Applause] [Music] p [Music]

Channel: World Science Festival

Views: 122,812

Keywords: Brian Greene, what is dark matter?, how to detect dark matter, dark energy, dark matter, galaxies, particles, natures dark side, farthest reaches of space, antimatter, dark fluid, Standard Model, Supersymmetry, Large Hadron Collider, world science festival, best science talks, 2019, James Peebels, Nobel, prize

Id: rRWIcpZqnXQ

Length: 57min 18sec (3438 seconds)

Published: Fri Sep 01 2023