Sean Carroll's Mindscape: Science, Society, Philosophy, Culture, Arts, and Ideas - 243 | Joseph Silk on Science on the Moon

Episode Date: July 17, 2023

The Earth's atmosphere is good for some things, like providing something to breathe. But it does get in the way of astronomers, who have been successful at launching orbiting telescopes into space. But gravity and the ground are also useful for certain things, like walking around. The Moon, fortunately, provides gravity and a solid surface without any complications of a thick atmosphere -- perfect for astronomical instruments. Building telescopes and other kinds of scientific instruments on the Moon is an expensive and risky endeavor, but the time may have finally arrived. I talk with astrophysicist Joseph Silk about the case for doing astronomy from the Moon, and what special challenges and opportunities are involved. Blog post with transcript: https://www.preposterousuniverse.com/podcast/2023/07/17/243-joseph-silk-on-science-on-the-moon/ Support Mindscape on Patreon. Joseph Silk received his Ph.D. in Astronomy from Harvard University. After serving on the faculty at UC Berkeley and Oxford, he is currently Professor of Physics at the Institut d'astrophysique de Paris, Université Pierre et Marie Curie, and Homewood Professor of Physics and Astronomy at Johns Hopkins University. He is a Fellow of the Royal Society, the National Academy of Sciences, the American Astronomical Society, and the American Academy of Arts and Sciences. Among his awards are the Balzan Prize, the Henry Norris Russell Lectureship, and the Gruber Prize in cosmology. His new book is Back to the Moon: The Next Giant Leap for Humankind. Johns Hopkins web page Google Scholar publications AIP Oral History interview Wikipedia

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If you know the feeling, you should know the facts. The eczema medication you're taking may not be right for you. Visit MyRawtruth.com and talk to your dermatologist about your symptoms and treatment options. Hello, everyone. Welcome to the Mindscape podcast. I'm your host, Sean Carroll. If you are a working cosmologist and you're studying the cosmic microwave background, in particular how density perturbations in the microwave background grow into galaxies and large-scale structure, et cetera,

one of the first things you have to learn about is matter falls in to some overdense region, and then photons stream out, and the photons streaming out damp the oscillations and the growth of structure in that pre-CMB era. This phenomenon is called Silk damping, after today's guest, Joseph Silk, who first wrote about it in 1968 in a paper on galaxy formation and the cosmic background radiation. Pretty amazing when you think that we only discovered the cosmic microwave background radiation in 1965. Joe Silk has gone on to be a leading theoretical cosmologist for decades now. I've known him for a long time. And for example, after we discovered the antisotropies in the cosmic microwave background from the Kobe satellite in 1992, it was clear that Joe Silk's group at Berkeley at the time was one of the very small number of leading places,

which was training up young people to tackle this new set of puzzles. So it was slightly surprising to me when Joe recently gave a colloquium at Johns Hopkins, and it was not about recent wrinkles in cosmological theory, it was a sales pitch for going back to the moon and building telescopes there. Now, obviously, there is a relationship here, any working cosmologist wants more data, better data, and the moon provides an excellent place to build telescopes

and get more cosmological data. but the thoroughness of the case that Joe made and the interest in all the different aspects of it, I thought was very impressive. In fact, I learned thereafter that Joe has a new book out called Back to the Moon, the next giant leap for humankind, where he takes very seriously the idea that not only

should we travel back to the moon in our little spaceships, we should put people there, have a settlement, and do science. He makes a very explicit case for the different kinds of telescopes that you can build, and also for other benefits of being on the moon, including mining rare earth elements and things like that. So this is a very fun conversation because it's a intersection, right, of science issues. You know, why can't we just build a big telescope on Earth or in orbit or whatever?

What's so special about the moon? But also practical, technological, and political issues. Who's going to do this? Do we have the money? What is the case for it for people who don't necessarily care a lot about modern cosmology? And, you know, I think it's kind of persuasive. I think that, you know, the case is actually pretty darn good. Opinions may differ. That's perfectly okay.

But it is something that the human race is going to be confronted with the possibility, the opportunity to do in the near-term future. So I'm happy that we're thinking about it at a high level. Let's go. Joe Silk, welcome to the Mindscape podcast. Thank you for inviting me. You know, I was in the audience for a colloquium that you gave at Johns Hopkins, where we are colleagues, and I've known you for decades now as a famous, accomplished theoretical cosmologist, and here you are advocating to travel to the moon. So I presume there is some story there, or at least there's some, I know there's an intellectual connection in terms of the science that can be done, but how did you in particular decide that building telescopes on the moon was what you really wanted to put some. effort into? Well, I was getting very frustrated with the progress in cosmology that I was seeing

around me. My colleagues have made immense advances in cosmology when I began in the field, which is, I guess, maybe half a century ago, I had to think of it. But there were uncertainties in measuring parameters such as the Hubble constant other things, in almost 50% of the uncertainty and we live with that you know we spent our early careers debating you know issues of 50% uncertainty back as of two unknowns yeah suddenly over the past decade as we've brought in much more precise surveys especially of just in galaxies we've made in enormous use of the microwave background also as that cosmological tool the fluctuations of that background our errors, our

systematics, now have dropped to maybe 2%. But it seems that the same questions are still plaguing us. You know, how did you all begin? And you know, what is the meaning of it all?

The universe does seem to be accelerating. We've learnt that from this enormously improved data. But what does that mean? Where does all that come from? And so, We're hoping that with the next generation of surveys, with better and better telescopes, my colleagues are hoping at least, they'll get some answers. But I'm very, very pessimistic because what I've seen is that over the years I've been in the field, we had this outrageous hypothesis at the beginning from Lemaître, George Lemaître, that there was a cosmological constant universe is accelerating at the moment. and we didn't understand it at the time

we still don't understand it but all the recent studies converge on the met with a visual hypothesis the constant and no you need to seem some deviations to understand the physics better to see what's really going on and I saw no prospect in not just the current surveys

but the next generation of surveys actually making real progress because all we've seen is convergent So I decided that we're going to do something radically different to make a breakthrough here. And eventually it seems that putting telescopes on the moon is going to be the way to do that over the long term. That'll be the next step forward in cosmology, I think. I mean, it's a fascinating answer, which I didn't anticipate. So it all comes from the cosmological constant problem and the issues that it arises.

I mean, you're right that cosmology is often inspired by these very big questions. Why are we here? How did it all begin? And then the working cosmologist ends up measuring the amplitude of density fluctuations to some percent or something like that. I mean, do you think that there is this kind of prospect for answering those bigger questions if we just get better telescopes? Well, let's see. It's more than just the causal constable, because we have to go back also to the beginning. which is now pretty much to everyone in the field, the theory of inflation,

it's the most significant advantage of cosmology since the time of George Dementra in basically a century. But we have no proof. We don't understand how inflation really began. Now, there is a fascinating hypothesis that we're trying to test, namely that as inflation came to an end, it generated gravitational wave modes that left their imprint on the microwave background. So we have many experiments, beautiful experiments set up to look for those,

and no doubt they will give us some answers in 10 years, but the problem is that there is absolutely no guarantee they will achieve success because the predicted value of this distortion is totally uncertain. If we're lucky, we're optimistic, they'll find it. They'll find the missing growth. But the chances are it could be almost at any level. And so my view is, why don't we do some cosmology with a guaranteed return, which will tell us the answer. And so that's what really drove me towards this next stage, which I can tell you about

to do with doing something on the moon. Yeah, no, we'll definitely get there. but I'm just intrigued to ask one more question along these lines while I have you here, which is what is the probability that you personally would put on inflation or something very much like inflation being true in the real world? I would like to think it's 50%. It's such a compelling theory to me, but it also raises questions as to how it began. So for that reason, I won't go all the way to a high probability,

and it's so compelling that I wouldn't give you a much lower one. So 50%, I think, is a fair answer, which means you'll better do a lot of work to get any better for that. That is exactly my probability. So I'm very glad that we're on agreement here. I think that a lot of our colleagues put it a lot higher, which worries me a little bit sometimes. So going back to the moon then, that's a big thing. We've been to the moon once before, the Apollo missions, et cetera. Why don't you set some context by telling us what the previous moon missions accomplished and why they ended?

What's different now? It was a long time ago. It was 50 years ago. Oh, that's exactly right. I mean, the Apollo three, the Apollo accomplishments were marvelous, actually. They were inspired by JFK, of course. He had this driving ambition to demonstrate to the world that he could out split the Russians, having been taken aback by that at the time.

And he did it amazingly in half a decade. And the budget they put into that was enormous. It was a significant fraction of our gross national product in the US. So we'll never see days like that again. But nevertheless, it's clear as time has gone on that we want to go back to the moon because that is our next major frontier in scientific exploration. for many reasons. And if we put telescopes on the moon,

I think we can answer some really incredible questions about the universe. And perhaps the biggest question of all is what was there out there before there were any stars, before there are any galaxies? We call that era the dark ages. And so I think we can ultimately penetrate the dark ages only from the moon. And do I remember correctly reading that at the peak of Apollo, NASA's budget was something like 4% of the U.S. total budget, and now it's more like 0.4%. That's absolutely correct. But you must remember that 0.4% is still an awful lot of money, and it's more than enough to finance the Artemis program, which is the current program. to get humans back on the moon and more than just back on the moon, but to build a space station around the moon and do many other things.

Well, let's fill in some of that because I'm not actually up on it. So the Artemis program is happening, right? Like NASA is doing it and it involves boots on the moon. That's exactly right. So the first goal is to get boots on the moon. and the interesting thing that is spurring this along at great intensity is China is doing exactly the same thing

they have a program to have the first astronauts back on the moon in 2026 and NASA wants to match that and if anything get there before the Chinese and it's not a question of getting just anybody on the moon in both countries announced that they want to get the first woman on the moon. Which is an amazing breakthrough.

And among the astronauts in training on the NASA-ESA side, there are even astronauts of color and even one disabled astronauts. So I think that's, you know, our boundaries are changing. But it'll be much more than putting astronauts on the moon, of course, but that's the first step. And you mentioned a space station.

I've heard about this. There's the lunar gateway that is going to be in orbit around the moon rather than orbit around the Earth. That's correct. So that's the next step. And the reason is that you want to go to build a facility from which you can easily land on the moon without creating too much havoc in lunar dust, et cetera.

It's so much easier than going directly from the Earth. You have a space station with pods in from which you can send landers down to the surface. That's how we did the Apollo program, right? We sent an orbit around the moon, which dropped the pods onto the surface. So it's the same idea

and from this orbiting space station will be dropping that. That'll be where the astronauts reside at first. One can just make that a more homely sort of place, a safer place to live than initially on the surface of

the moon. And so that's where they'll be, and we'll have once coming down, the long-term goal of the space station will also be to launch a rocket's into interplanetary space further afield, and also back to Earth, of course. So it'll be a major hub for exploration. But we'll start off in orbit around the moon, because that's such a much easier place to develop. And just to calibrate our expectations here, this is all stuff on the NASA side that is in the budget, right? This is not just a plan that they're dreaming up and trying to sell to Congress. This is the ongoing stuff is happening for this project. That's correct. And this all comes out of the standard NASA budget. It's a small fraction, of course, not so much of the NASA budget,

but of the total GDP. But this is enough to keep the whole Artemis program going for the next decades. Plan B made over-the-counter emergency contraception legal more than 20 years ago. It's a safe, effective backup birth control option that helps prevent pregnancy before it starts by temporarily delaying ovulation. Plan B is the number one OBGYN recommended brand and the only one that you can find at all major retailers in all 50 U.S. states. There's no minimum age requirement and you don't need an ID to buy it. You can order it through DoorDash and other major delivery platforms too. That's freedom to be. Use us to direct. As

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the way difficult. Talk today with your doctor or pharmaceutical, patrocinoed by GSK. Are there other countries besides the U.S. and China

who are interested in this? It's an amazing race at the moment between the primary players are the U.S. and China is there, they have so far the largest spacecraft and the

largest manned crew space programs, but Smaller spacecraft are being launched by many other countries. They're driven actually by availability in the past recent years of commercial launches, which are eager to expand their horizons for future exploitation of the moon. And so they're available and they're being sponsored by, but not just by NASA to develop spacecraft, but also they're available on the international scene

for any country to buy a launch vehicle, to use one to send stuff to the moon. But in the past three miles alone, there have been launches by Israel and by the United Arab Emirates, both in which were unsuccessful, but they're being planned, they're going to repeat them,

and they were designed to send small lunar rovers to the moon to do surveying of terrain. That incidentally is what we have. to be doing now thinking of because one of the major issues is going to be how to use the moon, have to exploit the moon. And for that we need information and that means basically doing sort of the end of the moon, both from satellites and from on-site robes. And when you mentioned the commercial spacecraft, this is, I presume, SpaceX, Blue Origin, companies like that? Yes, and there are probably a dozen small companies now, not just in the U.S.

but one or two are in Japan, etc., which are trying to make a commercial business out of the moon. Of course, the moon is very high on the list of tourist destinations. And so that will be another goal, as well as exploitation of the surface of the moon, resources that we can use on the Earth. Would you go as a tourist to the moon if you could afford it? Were I much younger, yes.

I jump in the thought. Right now, I don't think my mobility would get me, well, even though the gravity is lower, that would help me in. Got to get there first, though, yeah. But it's interesting because I guess that is a consequence of these private companies building their own space vehicles is that other countries can get into the game much more easily, as long as they have money. They don't need the technological know-how necessarily. Yeah. Yeah, so what's quite amazing is that the cost is coming down rapidly of these transport vehicles that take us to the moon.

The commercial industry is very good now at modest payloads of tons, a few tons, perhaps. The major payloads, which are just for the moment in the domain of Storix, of NASA, of China, Russia, too, which can carry tens of tons of payload. those also are rapidly developing. And the net effect, all of this is the cost per kilogram of delivery to the moon is going down rapidly. So it's a whole new ballgame for doing things on the moon. Yeah. And so let's just segue into what we want to do on the moon. I mean, obviously, the skies are dark and clear.

But tell us more in some more detail, like what is the call for cosmology and astrophysics? Well, before we do that, there is competition. Before we get to science, science is at the back of the queue. There's no question of that. But let me tell you what I want the major driver is right now to go to the moon, and that is to exploit the moon, to do mining on the moon. Now, the mining is really, really simple to start with, okay? Because all we want to mine is ice.

amazingly there are craters near the poles of them are many craters which are in permanent shadow they have such high

rims the sun never gets too high in the horizon because they're polar they're near the poles or too low and so they're very cold

in fact the temperature measured in these dark craters to be as low as 30 degrees Kelvin of absolutely zero just incredible

which is great for astronomers, it's also great for ice. And what was discovered a decade ago was that these crafters are full of ice, many of them. So what do you do with the ice? Well, the idea is it's got two immensely important uses. One is you can break it down into hydrogen, oxygen, and liquidify the two. You have rocket fuel. And then you also have oxygen, but habitat use. And so suddenly we can now imagine designing, and we have energy sources obviously from the hydrogen two. So now we can obviously design habitations on the surface of the moon,

aiming at exploiting the dark craters, the shadowed craters near the poles of the moon. So that's the first goal. And that's a major step, because that will be the key to doing everything else on the moon. Do we know how much water ice there is? It's hard to be totally quantitative, but our leaders, the agencies, are convinced there's more than enough to supply a rocket fuel for a very long time. They're eager to exploit that.

But overall, maybe this is jumping ahead a bit, but if we want to build things on the moon, we are going to have to crate up a lot of tonnage of material from the earth to the moon, right? Like we presumably we can't mine iron very easily. In fact, the lunar regolith is a very rich source of all the elements you might need to, for example, build electronics, and you can easily make cement with lunar dust and water and do structures on the moon. So everything is in place and it is envisaged over the moon. next decade or tune will be manufacturing locally on the moon.

So you won't have to ferry everything to the moment. One could do more as anything one wants with local materials. So that's part of the planning. Does that include the raw materials for breathable air? Indeed, yes. But basically you have the ice and the oxygen. So that will give us the atmosphere we need. And you can get enough, you know, gas is from lunar regular.

to mix of the oxygen to make it safer. So that's to be done. So let's, I want to ask more details about that, but let's get the motivation more explicit here. I presume that as an astronomer, cosmologist, you want to build telescopes. Are there specific kinds of telescopes that are especially better on the moon

than just say in orbit? I mean, we're doing pretty well with JWST, which is not on the moon. So the problem is GWST is a pretty small telescope really. I mean, eight meters, it's not even that we can build larger ones on the earth, actually. You've gone to 39 meters as the current while, large sunner construction. That's far with the limit. We'll never build a bigger one.

The problem is that what you want to do is to ideally look very far away with your telescopes, but also look in detail even nearby. with incredibly high resolution, both in terms of the spectrum and the light gathering power. And it turns out that to really do a good job of that, you need a much larger telescope than we can currently launch into space. And so let me give you the optimal example of this, which is if you could imagine building a telescope that was one. kilometer across on and you can only do that on the moon very hard in space too but in principle you can go to a dark

crater and fill the crater with with mirrors and combine the beams etc we could have thought of ways of doing this and if you could combine those beams together and i can explain how that's on a second but the first point is that with such a huge diameter an incredible resolution suddenly you could get a resolution of millions of of a second of up that millions of times better than you can do on the Earth, just limited by the size of the telescope, actually. And once you get that sort of resolution, you can imagine looking at nearby planets, planets that are twins of the Earth actually,

around nearby stars, stars tens or hundreds of light years away. And with that exquisite resolution, you could study these planets, some of which are twins of the Earth, actually, and we have no idea what's going to be. going on in those planes at the moment. But with this resolution, you could look at the cloud cover. You can look at the mountain tops. You could see the glimmering of the oceans against sunlight from the

host star. You could look with spectroscopy into the atmosphere in detail for signs of life-like indicators, methane or whatever, for example, pollution from industrial or even nuclear fuels, that sort of thing. Tiny amounts you could suddenly see, provided you had a big enough telescope. So in some sense, a big telescope is the key

to really answer one of the biggest questions we have, namely, are we alone in the universe? To me, that's one of the most exciting goals. And just to finish, you wonder how on earth you do this? Well, you go to a dark crater, which already is very cold. So it's a great place to build telescopes. It's very dark all the time. and you string your camera from the rims of the crater.

Okay, and so you build telescopes on the basin to basically all focus their beam at the camera is strung from the rim. And the only challenge really is to combine those beams. And that's a simple question of basically quantum physics, really, because we're finally learning. We've done this now for essentially, two telescopes on the earth.

We now would have to do this to hundreds of them to combine beams together to make them coherent. So all these many small telescopes that give me the equivalent of one big one. But that is possible. It's technology impossible. It means developing much better beam

combiners with ideas from quantum physics that were on the way to doing that. So I could see that in 10, 20, 30 years will a telescope like this could answer one of their biggest problems. That's great. And just to try to dig into the details a little bit more for the audience, or maybe for me and the proxy for the audience,

I know that in radio astronomy, a technique like this is often used, right, where we use different individual dishes and combine them into one big telescope. That's harder to do, more rare to do in optical or infrared astronomy, me because the wavelength of the light is shorter, I presume. Is that it? Is it more to it than that? No, there's more to it than that. The other problem is the atmosphere, the Earth's atmosphere. It makes it incredibly difficult because it gives you scattering the turbulence, etc. in the atmosphere invisible. That means it's incredibly hard to cohere these beams together.

It's long wavelengths. It's easier. It shruglyness. It becomes almost impossible, which is the greater advantage you're going to the moon, but you have no atmosphere. And so that makes a huge difference. It doesn't mean to say it's easy to do, but it's going to make it a challenging project, but I think we can do it. So that answers the other question I had is the primary advantage of the moon. I mean, one of them is obviously the atmosphere is not there. But another one presumably is that there's less gravity, so maybe it's easier to build a giant structure without it collapsing under the force of gravity. Is that a benefit at all or am I being fanciful? That's exactly right. And I'm sure that this idea of using a natural crater to combine a lot of

small telescopes together, that's one design option. Another one might be to build a coherent, much larger telescope than anything we can build all the earth because there are no winds to shake the structure, gravity is much lower, you would be able to support the structures much more easily. So that would be another direction to go in, and we will need to discuss that in enormous detail, the designs, the pros and cons. Probably we'll end up with both approaches eventually. Is the reason to use a single crater, if we're going to have many dishes, and physical dishes, and then combine them together into one effective telescope, I'm wondering why we don't just scatter them all over the moon rather than putting them in a crater, but maybe it's just colder

in the crater? Yeah, and it's also dark all the time. So that's a big difference, but it's colder. And, I mean, the extremes of temperature when you're not in the crater, the moon are enormous. They go from, you know, incredible heat to incredible cold. And it's very hard to design a structure that can operate, you know, with a high sensitivity under those extreme conditions, whereas in a dark crater, you have much more control on a thermal environment, and so it's a much more stable situation where you'd want to

build your telescopes. I was going to say maybe it's also just hard to do it in a very cold environment, but presumably satellites and existing orbital telescopes do that all the time. That's right, and one would be working with robots on the moment, I'm sure, as well. So it wouldn't necessarily need a human presence right at the telescope. Certainly for installation he might, but eventually it would not. So you've made a very good evocative case for super high resolution pictures of Earth-like planets elsewhere. So let's, you know, let our hair down a little bit.

What do you think we're going to see? Do you think we're going to see life on a whole bunch of other planets? Do you think that we'll see intelligent life? Look, we have no idea. The problem is that, you know, we've theorized a lot of the origins of life. We simply don't understand it. There are a number of theories out there, you know, ranging from, you know, origins in some muddy, shallow parts of oceans, et cetera, life emerging onto land, et cetera.

But, you know, all this is just a guess. what we only have one example actually on the earth we are eager to go to Mars for a very good reason we know once upon a time that had an atmosphere that had flowing water it's pretty arid now there's no evident signs of life on Mars you haven't seen them yet but the thought is if we go to Mars and dig deep maybe we'll find some you know some dried bacteria

or something or perhaps even more that we give us clues. But right now we have nothing. Another option is there are one or two moons, one in particular around Saturn, with Enceladus, which is covered in ice,

but we know that beneath that ice there are water oceans. We found that out by a recent satellite, a recent mission, shooting a probe in, and we saw the water splash out. Why an amazing experience. So that ocean, Cold Ocean is another place where we're going to go back to and look for life.

But frankly, I can't imagine that that would be, you know, even if we found something, it would be terribly interesting from this question of life in the universe, etc. So we have to do that, of course, but I think our best bed is to look for planets that I essentially like the Earth, but as they have rocky cores, they have atmospheres, they're not too far from the hostile, which is like the sun, not too close, so they're wouldn't get, you know, they wouldn't be burnt to a cinder really on the surface. And so we now know that there are many such planets.

Our best estimate is billions in the Milky Way. And so all of these are potential sites of life. But because we have no idea where the chances of life is one in a billion or one in hundreds of billions or maybe one in a hundred, it's all open, we have to look. And so the way do we look is we try to get a sample of these exoplanets. And the trouble is that with a small telescope, such as the one that our agencies are planning to do life searches,

like the best one that we have that came out of a recent study, was a six-meter telescope designed to get exquisite images of the atmospheres of nearby exoplanets, So it had very high resolution. It has a device for shielding the blinding light from the star, so you can actually see the planet to some extent against the star. The trouble is with a six-meter telescope, you have a sample of probably 20 X of planets around the nearest stars

that you can have the sense to really study. And that simply is not enough. So my dream is, you know, with a, let's say, a hundred meter telescope on the moon, or an even larger one, would suddenly improve that sample from, you know, tens, thousands of extra planets and improve our odds of finding something interesting. So that's the reason we want to build bigger telescopes, and we can best do that from the moon. It would not be affordable anywhere else, actually.

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Is it going to be just, are we so prepared for it? Have we priced it in? Or is it going to be a shock to the system? I think over the years we priced this in with all our warnings about UFOs and the hikes. So I think people are certain subset of population are ready for this, I would say. Most of us, perhaps are not. And the chances are, of course, if you do find something interesting,

we're discussing something many light years away from us, so it's hard to see any dramatic communication. Right. And it's very unlikely, just to put a cap on this, it's easy to imagine extraordinarily primitive life, right? Single-celled organisms, whatever. And maybe it's possible to imagine super advanced life that has gone way beyond us because they've been technological

for a billion years now. But it's very unlikely we will find peers out there. there in our galactic neighborhood nearby? That's probably right. It'll be one extreme or the other. I think I would agree with that. And the worrying thing, of course, is that when we try to extrapolate to life around stars that have been around for billions of years longer than our sun, any like there would have had a billion years or so advanced on the earth, the making life. The trouble is, we have no idea whether that life would have survived that million years.

You know, there are so many potential catastrophes. We're going through on the Earth now. Who knows what, how challenging that would be over longer time scales. So, on the other, it's possible, of course, is a sort of a science fiction way to tell us that it could be a very intriguing in a highly advanced long life. I guess we're open to this. Do you have a favorite answer to Enrico Fermi's question

about where all the aliens are? I fear for the worst that they're simply they're incredibly rare. That's not the worst. The worst is that they're common and they always blow each other up or something like that, right? I guess. Yes, okay. Okay. The most up too, of course, which is another worry if we are too far in finding them.

But it's not just exoplanets and life that we'd be looking for. I mean, we started off by talking about cosmology. So, like, what would these giant telescopes do for the working cosmology? Well, okay, so let me turn to the other aspect of telescopes, which is radio astronomy. So the advantage of doing radio is that you can penetrate the universe and see what happened before the first stars. So let me explain why that is. Galaties are made of gas clouds that come together.

And so these gas clouds are the building blocks at the universe, and we know roughly that they, You know, each one probably must wear a million solar masses, a million times the mass of the sun. And that's simply because you need a certain amount of gravity there for them to condense as gas clouds. And that's our best calculation of how big they should be. And so then you do this very simple estimate, which says, well, we know that our Milky Way galaxy is many billions of times the mass of the sun. That's its mass. therefore it must have formed from millions of these smaller gas clouds. They are the building blocks.

That's the raw material from which we were made. And so how on earth do you find these things? Well, the idea is you look back in time before the first galaxy, both of our stars, and you look for gas clouds. Now, the way you would do that is you use the tool of the astronomers to measure hydrogen gas, which is the 21-centimeter line of atomic hydrogen. And so that can be excited and gives you an absorption or an emission. It's excited.

It's the electron spin levels that are excited and de-excite. So they give you an emission or if they're excited, they will give you an absorption against something distant, some background radiation. So that's the idea. The trouble is if you want to look at this radiation, are from way back in the past, it's highly redshifted. So from 21 centimeters, you suddenly have to start thinking about 10 meters, because that's roughly how far back you want to go to get to where the first clouds were

that made the first galaxies, and there should be many, many of them. Now, you can't go back too far because you run to the microwave background, and that sort of mixes everything together. But it's when the background radiation cools down, as the units expands, but the matter then cools down even further. And so you can see it as a cold shadow against the cosmic microwave backgrounds.

That's the idea, and the typical wavelength will be tens of meters. Okay, so that tells you what you're going to look for, a signal or a shadow against the fossil radiation from the Big Bang, but you can only do that in a place where the radio environment, the radio astronomical signals can get to us. The trouble is on the earth. We have an ionosphere, which surrounds us.

You hear that when you listen into the radio, you turn between stations, you hear this crackle and pop, right? That's all from the ionosphere. And when you look at low-frequency radio waves, 10-meter-ish-wet radio waves, the ionosphere is opaque. Nothing can get to us from the distant universe. It just bounces off the ionosphere.

So what do you do? Well, you go to somewhere where there's no ionosphere. So you go into space. That's fine. When you go into space, which we're certainly doing, the trouble is the Earth is a huge source of radio emission from things like FM stations, from cell phones, maritime radars, you name it.

Space is not so simple if you want to. a lot for this ring signal from the beginning. So there's only one place that is nearby, not so nearby, but it's the far side of the moon. And it turns out the far side of the moon

is the most radio quiet place in the entire inner solar system because the earth just doesn't shine there in radio sense. Okay. So it's blocked completely. So our dream now, and it's more than a dream actually,

is to put radio telescopes on the far side of the moon. Now, the first remark is that these are really simple radio telescopes. They're just like your TV antennas. I mean, nothing more. They're what we call dipoles. There's metal wires, basically,

which you have to correlate together with wires or cables or something, and put the signal together, and then you've been the signal up to an orbiting satellite, which beams it back to work, for example. So that's the sort of thing we're going to start off doing. And if we have enough sensitivity, then that will give us a glimpse of the dark cages, of these clowns that were there before the first galaxies.

And so that, we think, is the new horizon for astronomy. It's totally unexplored directly. The new frontier, if you like, we haven't been there yet. We're going to go there. And then we're going to learn amazing stuff when we go there. Well, we do have these hints from JWST that there are galaxies that are younger than we thought and bigger than we thought. They assemble very early. And some people have worried or wondered whether this is a challenge to our models of galaxy formation.

Do you think that that's a real worry or just like an inducement to learn more? Well, I think the basis of all this, the problem with all of this, is that we do not have a theory of how stars form. And what we're looking at is the consequence of star formation in these very distant galaxies. So we based almost all our knowledge of star formation, and what we measured in the military way and very nearby galaxies. And to extrapolate that from a current vista point of 10 billion years after the Big Bang back to near the beginning, 100 million years after, is a really dangerous and toxic thing to do.

You have no idea what we're doing, actually. So what we can do is observe, of course, and we do see things that seem slightly strange, far away, not what we had predicted. But I think at this point, the jury is out. we just don't know if this is due to some slight increased efficiency of making stars. Maybe there were more massive stars back then at the beginning of the galaxy. All these things are postulated. Or is it something radically new?

Extra objects forming galaxies, that we're expected. So it's very dangerous to say that there is something radically new going on before you fully understand the standard physics, the simple explanations that we don't have by far not mastered at all yet. So all I can say about this is that we need a lot more data, and that data is going to come in the next year or two. And with all that data, we're suddenly not have samples of tens of these galaxies,

what we have now. We have hundreds, thousands, hundreds of thousands, and only then we'll be able to come to a more definitive statement about what's going on back there. You don't want to panic right away? You want to just collect more data? Absolutely. It's panicking will, you'll be wasting your time. That's my. Good. I mean, I think these are compelling cases for the exoplanets, high resolution, imaging and so forth in spectroscopy and also peering into the dark ages cosmologically.

Are there, before we move on to technology questions, are there other science targets that are especially appropriate for building facilities on the moon, whether or not in astronomy? Well, here's the major science target, which is an extension of the Dark Ages search. Suppose we do go there. We're building experiments to go there, actually. There are one, two, they're already. Job will come to. But suppose we start getting data from these many hydrogen clouds from the beginning. Well, the beautiful thing about this is there are so many of these clouds.

I mean, when we do surveys of galaxies to get. information about the size of the universe, the content of the acceleration of the universe, expansion of all this stuff. We're dealing with billions of galaxies, maybe. If we can start harvesting the data from the dark clouds, we'll suddenly be getting trillions of clouds in our surveys. Now, that means immensely more information, what you can then analyze to do cosmology with.

And so our cosmology now is limited, as we said at the beginning, to one or two percent accuracy. But with all this, you know, let's say a hundred thousand, a million size, information even, will suddenly be able to get an accuracy that surpasses that by a hundred thousand. I mean, fraction of a percent accuracy in determining the puzzling parameters of cosmology. So that's the dream. And there's one more aspect of this, which, to me is even more incredible, is the only robust test of the inflation theory, okay, is that the fluctuations from the beginning do have these primordial wells and twists and things.

That's common to all there is in inflation. This is not just the gravity wave, doesn't tell us the whole other story. But this is just intrinsic to the fluctuations. And the only way you can never see those is when we have enough sensitivity. And so it seems to be true that with these telescopes on the far side of the moon, if we make them large enough, we'll have the sensibly to actually pin down the details of whether inflation actually occurred or not. We're able to test one of its, I think, most robust predictions, which are these what we call non-Galcianities from the beginning. Yeah. So that's a goal for me, a major goal.

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50, I've learned some things, like the value of the family, the importance of the work,

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Talk today with your doctor pharmaceutical, patrocino for GSK. I guess I shouldn't pass up the opportunity

while we have you here. I did talk to Adam Rees, our joint colleague, a while back about the

Hubble tension, about the apparent disagreement between measuring the Hubble parameter using early things like

the microwave background versus using more nearby stars and galaxies. Apparently it's still a

looming issue out there. Do you have a favorite prognostication as to going to happen? Is there new physics lurking there, or do we set to get our measurements in order? Well, I discuss this a lot with Adam, but let me just say that I, I'm very concerned that

all the data that comes from using stellar indicators, super and over indicators, which Adam is the world's expert on, et cetera, it's a little bit like climbing a distance ladder to get to the things far away. And you can never be very strong. certain about the first rung on that ladder. It might be unstable. You might fall down. So now, many of us are completely certain. It's a robust, very solid ladder. But nevertheless, it is an indirect way of getting far away. Ideally, what we'd like are what we call geometrical indicators, which don't rely on going up a ladder, but are just direct measures of distance. And I would say, until we get those securely in place,

for me, the jury is out because there are worries just about the observational issues and systematics that come from from using Explodity supernating and, you know, other types of stars to build

your distance letter. So I think we're still beginning to explore the natures of the environments of these different distance indicators. They don't all agree with each other. And I don't, I'm not convinced that we have a robust forward would wait there, rather wait until we get some geometrical indicator, which will come in the next

end years. Okay, very good. Thank you for that update. So let's be much more down to earth. I mean, we're both theoretical physicists at heart, but in writing this book, I forgot to mention you've written a book. I will mention it in the intro, I promise. But back to the moon, the next giant leap for humankind, you must have dug into some of the

technological challenges involved with literally going to the moon. I mean, you've already mentioned very briefly that you envision both human beings building things, but also robots building things. Is it going to be almost all one or the other? What do you imagine to be the mix of people and construction and so forth? Well, it's such an a rapidly involving situation. I would have said a year ago that if you you could

a lot with robots but you need humans very close by to guide them because a robot has to respond instantaneously but what's happened

this past year is amazingly the development of visual intelligence at such an amazing speed. So now I do not quite see what the

limits are actually of robotic deployment of telescopes on the moon for example. Right. So basically, if you put a robot on the moon with a certain goal, we're more confident now that it could figure out how to solve puzzles maybe than we were a year ago. That's right. How to, you know, if it's easy, if there's a crevice in front of it, you know,

you know, it might take seconds to get instructions from the Earth and what to you next. I suspect before very long we'll figure out ways of having, you know, self-guiding robots that can cope with any conditions they come across. So that that's what, I think it's an amazing area that's developing so rapidly. It's hard to take where we're going. It's easy for me in my brain as a very long-term science fiction reader to imagine robots building telescopes on the moon. Is that, do we really appreciate what the challenges are there?

Well, you know, I think you need human intervention, right, basically, because there are just so many surprises that you have to have someone on, on the spot to look out for. But again, I don't see what the limits are for the robots at this point. And we're forecasting what's going to happen probably on a 20 or 30 year time scale

in these big telescope projects and the range of which AI has developed so rapidly in the past two years. How on earth can we forecast where we may be? And, you know, there's time. It's all crazy. Yeah. So what is the biggest challenge

besides the fact that it's far away? I mean, obviously you're in vacuum, there's dust. The dust is, there's no atmosphere, but there is dust, right? Right. So let's talk about the dust. So lunar regolith is everywhere. It's very abrasive dust, actually. So it's not good for telescope mirrors.

So we will need to think of ways to shield the mirrors somehow from the dust. Now, one interesting aspect is this, that the dust is photocharged by ultraviolet light and levittates, okay, because of the charge, okay? So it rises in the day, but at nighttime, it falls down. So the hope is that in a homely dark crater, dust will be much less of a problem, which is why you probably want to go there rather than some random place on the moon to build a telescope. So I don't know.

I mean, that's something we're discussing. And obviously, there are also ways of self-reparing devices that can self-enil, etc. to develop protection against us, too. So I think these problems are going to be surmountable by our engineers. Have we learned a lot from the experience with Martian rovers? That I cannot say. We've certainly experienced micrometeore impacts on the web telescope already, and that has not been a major disaster.

And one might expect there are similar issues on the moon. So I think we should be able to use our experience to cope with that too. What about moon quakes? Are those an issue? So moon quakes are known to be far, far weaker than earthquakes. by an enormous factor. And so they're often caused by asteroid impacts or some minor settling of the moon,

but they're relatively minor things. I don't think they're any danger at all. The one area where they've come up recently has been we want to actually one of the first things we'll do on the moon is put down seismometers in various places. Now, Apollo did this, but we know I have much better ideas and models and building seismometers. And the reason we want to do this is we want to measure the shaking of the moon, because that's basically like a gigantic gravity wave detector.

Ah. You know, so you imagine right now we've measured gravity waves with basically having laser beams that are four kilometers long. our future ones will have 40 kilometers long. We measure the shaking of these beams by a passing gravity wave from emerging black holes. On the moon, 4,000 kilometers. You can suddenly do something different, okay? You can measure lower frequency gravity waves,

just like longer together. And you can measure the inspirerating of black holes that come together to give you the ones we've seen already. So it's a whole new chapter on gravity wave astronomy, which will do with CITUES, isomometers on the moon and various devices based on them, et cetera, which you're planning to. And that's, again, fairly known technology. So it shouldn't be too hard.

And I think that will be one of the only things we do on the storm. I had not ever heard that idea. That's a wonderful one. Is it clearly superior in some ways to just building satellites and bouncing lasers between them? It's complementary. So right now, our best satellite, a main satellite project, has a separation of the satellites of a million kilometers, new balance lasers.

So this is a very, very different frequency from the one measure on the moon. So after that, we're debating formation, flying of satellites with a few thousand kilometers separation. And that would be much, more or less equivalent to what we do on the moon.

So it would be a complementary activity to what we do on the moon, actually, with satellites. But that's a future thing, too. All right, so we've listed, the moon is far away, it's cold, there's no atmosphere, there's dust, there's moon quakes,

Are there any other worries that we haven't anticipated yet? Well, you have to support people, of course, and we need them somewhere, and I think one of the big worries is going to be a physical state of people that suffer long stays on the moon. This is one of the reasons why we want to put them in a space station around the moon. So we've done that on the earth, and I don't know how well people realize this, but when our, astronauts come back from the space station after a six months stay there. If you probably have noticed, you see them in chairs. They are not able to walk very well. And I'm not sure what other problems they may have,

but on the moon, there could be longer stays. It could be worse. So I think we have things like this to learn from and understand much better. And of course, issues about radiation, exposure, etc. like that. It'll all be far, far worse on Mars. Don't worry about that. The moon is an easy step forward. That's not that people do.

Mars, I worry about it. In the science fiction stories, our space stations always have rotations so they can mimic artificial gravity. But as far as I know, that's not in the plans of any current NASA program or anything like that. I think that's right. That's right. You don't really want to do that for an orbiting space station probably. Okay.

And do you, I mean, how much of the program of doing astronomy on the moon and other things is beholden to a larger program of getting people there on a regular basis? So it's all part of the same story. So I think the here is why I think we have to be patient. We have to realize that science, astronomy telescopes have not. at the head of the queue for the moment. But on the other hand, that gives them an enormous advantage. Because we're going to build infrastructure here for the moment, not just the orbiting space station,

but having moon of rovers, doing construction of the moon, et cetera, et cetera. And all of this will take some enormous budget, which is being planned, and it's partly spurred on by international rivalry. Right. Okay. It's clear that, you know, if the US doesn't do this, China, well, et cetera, et cetera. And it's not even clear there where we're young.

We have to have better coordination, of course, as whole of the story. But anyway, all of this will be very expensive. So if I were to imagine spending a few percent of the cost of the infrastructure on science, that would be enough to build all the telescopes I've talked about. And the reason I'm confident of that is let me give you an example. the space station and the shuttle were built at some, you know, multi-billion dollar, whatever expense. And we would never have had the Hubble Space Telescope without those things.

Okay. Hubble was a few percent of the total, right, that we put into that other infrastructure in space. And you can make a similar argument for the moon. All the telescopes I've talked about would be a few percent of the total of this amazing, story that we're going to build on the moon and do things on the moon. So it seems to me it's not too crazy to imagine big science projects. They're cheap, relatively speaking. This is probably an unfair question, but is there any hope for international cooperation here rather than rivalry? I think it's essential. We better have this because even right now,

I think we're very worried. NASA's very worried, for example, that they know the Chinese, are putting science experiments on the moon. Probably, if anything, on a faster time scale, the national is, although there's been the competition between the worry is that, you know, if the Chinese are there first, they say, I want this crater for my experiment, you know, that's a desirable crater. There aren't that many dark craters.

There are a quarter of 50 or something. I mean, you know, who takes what? The choice real estate. I haven't also told you this, that these dark craters, some of them have immensely high rims. and those rims are always in sunlight, permanent sunlight, because they're so high, they see the sun. So they're the places where you can pipe in solar power into your dark crater. Ideal for doing experiments.

Ideal for many other things too. It'll be competition for them. So I hope we don't result. You know, I got there first. That's mine. We have to have coordination. We've done this in the past. The best example is Antarctica.

I don't know how well known this is, but there are, I think, some 70 different search stations in different countries in Antarctica, all very nicely allocated, no rivalry, no wars. But we've done that. We know how to do this. Of course, the commercial stakes there are much, much less than what I wait to some of them own. So it's a different ballgame. But I hope we can have something similar to guidance. Let's fill in a little bit the commercial stakes, because I'm interested. in the motivation for private companies or individuals to go there also. I mean, we hear talk about mining, tourism and so forth. Do you have a feeling for how realistic that is? What are the resources up there on the moon that you can't just get easier down here on Earth? So the resources are this, that the moon has been bombarded by asteroids and meteorites over billions of years.

And now this happened on the Earth too, but they burn up in the Earth. atmosphere. On the moon, they cover the surface with valuable raw materials. And so the moon has enormously larger reserves of rare earth elements like European, vanadium, etc. That are essential for much of what we do on the earth in terms of high technology. Yeah. Where computer screens to, you know, windmills, whatever, all sorts of things. On the earth, when running outer supplies. We know that European, for example, has probably 1,000 users of supply sector on the Earth. Other rare earth's a little longer. But on the moon, we have enough to keep us going through a million years. Thousands of times more resources. And so it's an incredibly

interesting target for the mining companies. You know that as resources get lower, the price goes up, so it's going to become incredibly expensive scene on the earth. What is more, it's even worse than that because mining rare earths is a really toxic process. And right now, China dominates the rare earth industry. Mostly for that reason, they would take the risks. Now, it's not clear, and they also have the dominant reserves on the earth. So there are two reasons there. So going to the moon will open up new possibilities for mining. It will be something that will last for thousands of years. It'll be a major investment. And it's such an incredible. attraction for the big mining companies, that I think that we're going to do that regardless.

Yeah. But if we mine on the moon, we have to survey the moon. And that involves a whole other story. But that will be what's going to be happening in the next 10 years, choosing the best mining sites on them. I guess maybe I just have trouble imagining this, but how do you ship all that stuff back from the moon to the earth? That sounds very expensive. Well, not really because right now we're going through this dramatic leap in space cargo development where we have many launches at the 110 level capacity.

We're in the process of building two. One has flown successfully. The NASA SLS, the starship has not yet flown successfully, but both will have of order a hundred ton payload. And what is more, Starship, when it does eventually work, will be unlike the NASA spacecraft, recyclable, reusable,

which is bringing down enormously the payload costs. So I don't think that's going to be a real problem. We'll be able to, over the next decades, have efficient ways of shipping whatever we need back to Earth, there'll be some price. when it'll be nevertheless a source of enormous profit for the mining companies in principle. So if you had to guess, you don't have to, but if you wanted to, when would you anticipate the first helscope seeing first light on the moon?

Well, actually in three years' time. Okay, good. Let me explain that. So not necessarily the most useful first light, but this is radio. telescope. And so two projects are under planning now to go up in 2026. One of them is a single antenna. It's designed by NASA, the Palm of Energy, and it will go on the far side and will look for the shadow of the dark agent. So that's the first thing we're doing. A simple dipole antenna on the far side of the moon. The Chinese already landed something on the far side, the first

antenna, but it didn't bring back data because the local electronics was so noisy. It was designed badly. They didn't mask that out. But the new instrument built in this case by NASA will solve that problem. The only difficulty is that it'll go to the far side. It landed there. but battery power is limited. So it doesn't have large enough batteries to survive more than one night on the moon, which is 14 days long. So the problem is that it won't get enough data. So we'll need to, we have to develop power, you know, battery power. And we're not quite there yet.

Meanwhile, on exactly the same time scale, a Chinese have solved this problem. So they're sending a flotilla of. of nine spacecraft to orbit around the moon, one mother ship and eight smaller antennas, like 10E, and they basically orbit the moon, far side to near side, every two hours. So they take their data on the far side.

They fly in formation, so they act together like an interferometer, a giant radio telescope, and they take their data, then radio it back to Earth. So that, it seems to me, has the best chance of getting the first science signal from the far side of the moon and that's going to happen soon.

And then on the longer time scale, we have much more dramatic projects. In radio astronomy, we know we'll lead much more than nine antenning. We'll lead hundreds, maybe even thousands. And so we're designing projects to do just that on the far side of the moon. But that's going to take much longer, of course. I love the idea of the simple, cheap, fast radio telescope, because once there is any working model, it becomes much more real in people's minds, right? It will help inspire them to the next step.

Exactly. That's right. And that's the beauty of one of the current NASA programs where they have commercial spacecraft, which carries small payloads, and they've been able to sell projects to other countries. You know, I mentioned there was an Israeli project, a UAE project also, and they'll be continuing. to land small lunar rovers in these cases on the moon. That's their immediate goal. India is very much involved too. They want to do surveying of the moon with their next generation of lunar orbiters.

So it's a huge and interesting competition now. It's interesting how it comes and goes. It was 50 years and then we went quiet and now we're back again. It seems like with earnest. But maybe for the very last question, let's reflect a little bit on how the scientific community goes about things like this. I mean, these are obviously very big, ambitious goals that you were discussing here. I worry that sometimes scientists are almost too cynical in an attempt to be realistic.

Like, they hear these giant plans, and of course, if you're the one proposing them, you'll be very enthusiastic. But others are going to be like, eh, that's, you know, a load of hot air. We'll never get there. How well does a scientific community do in coming together over these big plans and are there ways we can do better? Right now, I would say the scientific community is doing a slightly better job than our political communities in planning for experiments on the moon. We have conferences in which participants include different space agencies, not just, the US, but also was one recently with both China and India very well represented, describing their projects for lunar astronomy on the Vostok.

So all of this is happening. I think overall we still need better coordination internationally to make sure that when the commercial aspects which are driving all of this really get underway, there is some suitably peaceful strategy for negotiating for sharing

international coordination. Right now we don't have that. I think we have a window maybe a few years to develop this. As the political situation improves perhaps we'll get there. Right now it seems impossible to imagine this happening, but

I'm optimistic. What we want to do is avoid the Wild West, basically, on the moon. That's the hope, summer. I think it's good to be optimistic about these things. Certainly, it's an ambitious program, and I'm very excited about everything you've told us. So, Joe Silk, thanks very much for being on the Mindscape podcast. It's been a real pleasure, Sean.

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