Ep. 404: The Difference Between: Can’t Know, Don’t Know, & Just Awaiting Better Tech

There the things we know, the things we don’t know, and the things we can’t know. How do we know which one is when when we’re deciding to fund research and direct our scientific inquiry.

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Female Speaker 1: This episode of Astronomy Cast is brought you by Swinburne Astronomy online, the world’s longest running online astronomy degree program. Visit for more information.

Fraser Cain: Astronomy Cast episode 404, what we know, what we don’t know, and what we can’t know. Welcome to Astronomy Cast, our weekly facts based journey through the cosmos. We’ll help you understand not only what we know, but how we know what we know. We say what we know and don’t know and can’t know quite a lot. Wow. My name’s Fraser Cain. I’m the publisher of Universe Today, and with me is Dr. Pamela Gay, a professor at Southern Illinois University Edwardsville and the director of Cosmo Quest. Hey, Pamela, how you doing?

Dr. Pamela Gay: I’m doing well. How are you doing?

Fraser Cain: I don’t know. I probably can’t know. No, I know. I’m doing good, doing good. The weather is lovely here, and it’s that time where we come back around to spring and we notice it.

Dr. Pamela Gay: It is true. I bike rode 36 miles this weekend, lapping in as much sunlight as I could, but we were only having Indian summer. So while my tulips are coming up, they’re going to get snowed on later this week.

Fraser Cain: No, we’re done with snow. It’s going to be nice from here on out. Okay, cool. So let’s do this episode.

Female Speaker 1: This episode of Astronomy Cast is brought to you by 8th Light Inc. Eighth Light is an agile software development company. They craft beautiful applications that are durable and reliable. Eighth Light provides disciplined software leadership on demand and shares its expertise to make you project matter. For more information, visit them online at Just remember, that’s Drop them a note. Eighth Light, software is their craft. Astronomy Cast is proudly sponsored by, training videos with personality for software professionals.

Fraser Cain: There are the things that we know, the things that we don’t know, and the things that we can’t know. So how do we know which one is which when we’re deciding to find research and direct our scientific inquiry. This just sounded like a great quote from – I can’t believe I’m saying this – Donald Rumsfeld. I’m trying to remember the gist of it, but it was something like there’s the unknown – there’s no known –

Dr. Pamela Gay: There’s the known.

Fraser Cain: There are the known knowns, there are the known unknowns, there are the known – sorry – you have the known unknowns, and then there are the unknown unknowns, the ones that we don’t know that we don’t know. And although it was used just five [inaudible] [00:02:58], it’s actually a really clever thing to categorize the world in, which is that when we direct our scientific inquiries, there’s this stuff that we already know. We know gravity makes things fall, and we know mathematically.

And then there’s the stuff that we know, but we just know that we don’t know it. And then there’s the stuff that we don’t know that we don’t know, and then there’s a whole other class of stuff, which Rumsfeld forgot, which is that we can’t know it. I think there’s a really good distinction that you put in. So let’s go back to the beginning here and talk about – you queued this topic up this week. What’s your philosophy here in approaching this?

Dr. Pamela Gay: Well, we get lots and lots of questions coming in, everywhere from Twitter to Facebook, so on and so forth, and some of them are related to things that we can’t answer, in which case we answer them to report [inaudible] people at a web link. But a lot of them –

Fraser Cain: Sometimes there some math.

Dr. Pamela Gay: Sometimes there some math, and I have, more than once, recommended people take college courses. But at the same time, there are a whole lot of questions we get where it’s like, “We don’t know that.” “What do you mean we don’t know that?” “Well, we can’t know that.” “What do you mean we can’t know that?” “Well, there are just some things the universe isn’t going to let us know.” Now, other times it’s like, “We don’t know right now. We need to build a bigger telescope.”

So it seems like there’s a lot of difficulty understanding the difference between the things that we’re going to know soon, we just need a bigger hammers. The things we just don’t know, just don’t know, could go in any direction, and then the things that people put forward that are absolutely not testable and we have absolutely no way of knowing whether or not they’re real.
Fraser Cain: So let’s come up with some example questions – the kinds of questions that we might get to which – let’s go with the, “We know it,” category. What’s some stuff that we just know the answer to?

Female Speaker 1: Well, stuff we just know the answer to is, what is the distance to Mercury? That was something that took us a long time to figure out, but now we know it very precisely thanks to things like radar. So that was the kind of thing that required the invention of better and better hammers – in this case, better and better optics and technology. So we know the distance to Mercury.

Fraser Cain: Right. We know how long it takes for Saturn to complete a rotation, which took a long time to figure out, and we’re not even entirely sure yet –

Female Speaker 1: It has pre [inaudible] [00:05:47] bars.

Fraser Cain: Yeah, we’re pretty close, which is amazing that’s a question that we don’t really directly know the answer to. But it took being able to measure the magnetic field of Saturn and calculate how long it comes around because watching the cloud churn around actually doesn’t help you get that really specific number because the thing is changing so quickly. So that’s another thing that we now know.

Dr. Pamela Gay: And there are things like we now know that galaxies form both bottom up and top down. They form both through the giant collapse of a giant cloud into a giant galaxy and through a whole bunch of small galaxies forming one by one and combining into bigger and bigger systems. This was something that’s only been figured out in the past couple of years. Even some of our early episodes we were like, “We don’t know,” and new technology, and this is only going to get better understood as James Webb space telescope comes online. So these are all problems that just took better hammers.

Fraser Cain: We know that quasars are super massive black holes that are actively feeding. We know that black holes exist, and that there’s a super massive black holes at the heart of the Milky Way. So these are – obviously, there’s lots of stuff that’s even simpler than that. And we now know that gravitational waves exist, although, we knew them back in the ‘70s thanks to the indirect observations of pulsars. But we know now that we have the ability to detect them. So those are things that we know. And I guess there are things that we know, but we know with more and more accuracy. So we know the age of the universe, and we’re bringing down those aerobars.

Dr. Pamela Gay: The expansion rate of the universe. When I was an undergrad, as I’ve said before, we were told, “Just use 100. It’s good enough. It makes the math simple.” Now, we have it a couple of significant figures.

Fraser Cain: We know the size of Pluto thanks to the New Horizons space craft that did a fly by and was able to finally provide a precise measurement, as opposed to one that had pretty big aerobars.

Dr. Pamela Gay: Now, these are all examples of things that people knew that we’d be able to measure once, give or take, Kepler coming along. We didn’t know we’d be able to measure the distance to Mercury until Kepler came along. But these are all things that, for the most part, we knew we would find the answer for one day, and finding the answer was part of the justification for building better telescopes, for building more exploratory spacecraft. These kinds of answers are the reason that we build facilities, the reason that we have robots roving our universe for us.

Fraser Cain: Yeah. It wasn’t necessarily one of its specific mission requirements was to measure the size of Pluto, but that’s one of the things that New Horizons was able to do. And you couldn’t have gotten that level of accuracy without sending a spacecraft that close to the dwarf planet. Okay, so those are the things that we know. We specifically chose the stuff that has been figured out within the last decade, maybe 100 years. So let’s talk about the things that we don’t know but can know.

Dr. Pamela Gay: So we’re starting to get a better understanding of, what is the size frequency distribution of planets around other stars, which puts another way is, we’re figuring out how often we find planets of different sizes around different kinds of stars throughout our universe. This is getting us, step by step, closer to being able to build better models of planet formation.

Prior to the 1990s, we could tell you nothing about planets in other solar systems other than, maybe they’re there. But at this point, we’re starting to build better and better technology that will get us better and better numbers that will start telling us where the other Mercuries are. Everyone talks about finding the Earth twin. I want to find the Mercury twin. We’re getting there.

Fraser Cain: That’s sad, but –

Dr. Pamela Gay: Hey, no one shows Mercury any love. I’m going to love the unloved planet.

Fraser Cain: Right. So if you were to put some rules to this, like the stuff that falls into this category, it’s the stuff that either we just haven’t even discovered any of them yet so it’s still an open question on whether or not these things even exist, like intermediate mass black holes or the largest mass of the population three stars – things that are at the very –

Dr. Pamela Gay: Is it testable?

Fraser Cain: Is it testable? Yeah.

Dr. Pamela Gay: The most straight forward way of looking at it is, is this a testable concept? Are there intermediate black holes? We can never prove the negative. That’s the problem with negatives. But we can prove the positive. We know what they would look and smell like – well, we don’t know what they’d smell like. We know what they would look like in outer space and how we should be able to detect them, and we just haven’t yet. The universe is a kind of big place. If there’s an ability to test for a thing, it’s knowable, but just not known yet.

Fraser Cain: Right. Okay, so let’s go with some other examples that you think are in the – even with the capabilities that we have right now or the observatories that are coming out in the next little while. What are some of those kinds of questions that we don’t know today that we should know – check back in ten years and we probably will know?

Dr. Pamela Gay: So just in our own solar system, Planet Nine, is there life on Europa? Is there life on Titan? Why is there is cliff at 55 AUs in the Kuiper belt population? All of these different things, it’s a matter of building a bigger telescope, looking in the right place, having the right timing. There’s a chance at solving all of these. Looking beyond our solar system, we’re going to be able to start to figure out at, what point do planets settle into their orbits? At what point do we see wild collisions still going on?

We’ll be able to get enough snap shots of solar systems at enough different points in their solar system evolution that we’ll start to understand not just the formation but the evolution, the nice model of other solar systems over time. Looking beyond solar systems, we’ll be able to get better and better understandings of how galaxies have formed, how the metallicity distribution of galaxies has changed. With the James Webb space telescope going on, there’s the potential to start to understand the gas and dust evolution and distribution in galaxies over time better than we can now, and this is all cool stuff – large scale structure formation in greater detail. There’s a whole lot of filling in the details that comes with identifying the known unknowns that are testable.

Fraser Cain: Right. I think the filling in the details one is great. Is there a Planet Nine? There might be a Planet Nine, and it may be so far away and so dim that it’s just outside of our capabilities, and it could take us hundreds or years to find it, but it is testable. You could find the little blip moving at the right rate, and then someone else could point their telescope at it and confirm it, and you could send a spacecraft there and find it.

So these are all within that capability, but there’s the stuff that – and as we said, the stuff where you’re really just narrowing down the aerobars. We’ll send another version of WMAP up, and it’s going to plonk, and it’s going to take the age of the universe down to within tens of millions of years. Let’s talk about that stuff that we can’t know and why.

Dr. Pamela Gay: Well, and this is where we start to get into things like, what’s outside of our universe? Are we one of many universes? Maybe?

Fraser Cain: What came before The Big Bang?

Dr. Pamela Gay: Yeah. Science just doesn’t have any tests that we can answer any of these questions, and it’s when you get into these untestable ideas – string theory is currently not testable, which is why it’s one of those things that makes me grouchy.

Dr. Pamela Gay: Yeah, we all know how much you hate string theory. But it’s not like there’s no hope because there are ideas to try and say, “Well, maybe you could test what came before The Big Bang if you could somehow find some evidence, some echo of what was here before somehow permeating the universe as we see it today, and that could give you some hint or clue on what came before it. so you can have stuff shift categories from, “We think we can’t know it,” to, “Maybe if this test turns out then that might tell us,” but most of the time it doesn’t.

Dr. Pamela Gay: But the things is a lot of these things are based on the, “Well, if turns out there’s underlying theory that completely invalidates or completely changes our present understanding of the universe that is designed by genius who doesn’t yet exist.” It’s when the shift to make something from untestable to testable requires rewriting our underlying physics that I start to get – I’m not sure that counts yet. That’s the alternate universe; new Einstein required way of looking at things.

Fraser Cain: Right, but we talked a bit about string theory. So there’s this idea that if you could – at the earliest moments of the universe, maybe the initial strings could’ve gotten their scale magnified into the comics microwave background, and maybe you could detect it in that – maybe there’s a test.

Dr. Pamela Gay: And it’s when someone can define a test based on not having to rewrite the physical laws that it makes it much more rational. When Einstein came along, he didn’t require us to rewrite Newton, he required us to expand upon it, and there’s a difference between having to rewrite the rules and expand on the existing rules.

If string theory can come up with ways that match everything we currently observe and says, “Here’s how you test it,” it’s the here’s how you test it part that’s still missing with people going, “Well, let’s see if we can figure out way to get from this place where string theory’s at to this place where the cosmic microwave background is at,” and saying, “We need to define a path between these two islands. Well, it’s hard to make a path over ocean if you don’t have a boat.

Fraser Cain: So what is the – we talked about some of these, and there’s a million of them – stuff that we don’t know and can’t know. Another thing that’s kind of interesting is that the laws of physics themselves will prevent us from getting to know things. There’s the uncertainty principle. I actually had a conversation with Lawrence Krauss a few years ago about this, and he said that there could very well be – our physics could take us to a place where we can’t probe any further; it’s just impossible.

Dr. Pamela Gay: Right, and it’s not just with the uncertainty principle. The speed of light is a frustrating limit that you might be able to tunnel from one point to another, but one of those points probably isn’t going to be the center of a black hole. So it’s quite possible that we’ll never actually understand, in a testably proven way, what the inside of a black hole is like.
Fraser Cain: Except with gravitational waves.

Dr. Pamela Gay: Yeah, those still aren’t really going to help.

Fraser Cain: Right. And then the other part is that there’s stuff – and you hinted at this. There’s stuff that is beyond our vision. It’s there. If we could get there, we could test it, but we can’t get there. The laws of physics absolutely prevent it – something that’s outside of the Hubble Sphere of us here, there’s stuff there most likely.

Dr. Pamela Gay: And we may never actually know if we live in a finite or infinite universe.

Fraser Cain: There’s a great example. So we may not be able to know, which is crazy.

Dr. Pamela Gay: See, I find it kind of awesome.

Fraser Cain: Really?

Dr. Pamela Gay: You get frustrated.

Fraser Cain: Yeah, I want to know.

Dr. Pamela Gay: And I’m like, no, it’s cool. We study to the limits of what we can understand, and there’s so much left. Why get frustrated when you haven’t figured all the stuff you can figure out, but there’s stuff that you can’t figure out?

Fraser Cain: And then I think of that last category, the one that we talked about, the Rumsfeldian unknown unknowns. That’s where I think the source of the most interesting scientific inquiry comes from is that Isaac Asimov, “That the most interesting thing is not eureka,” but that’s funny.

Dr. Pamela Gay: And this is where things like the LSST have so many people excited because this is an open-ended instrument. There are some instruments – I was grouchy last week about LIGO – that only solve one problem. But LSST is out there with the primary mission of making sure we don’t die by rock. But as it’s out there discovering all these asteroids that are part of its primary mission, it’s also going to be turning up, potentially, tens of thousands of things that flicker, flare, and move in the night and helping us know about things that are so low probability that we’ve just never seen them before, helping us notice things that you have to have systematic observations with that kind of cadence. It’s going to point out things that we can’t even speculate on, and it’s the fact that we can even speculate that is so cool because we know we haven’t watched the entirety of a stellar lifetime. It’s going to allow us to see some many stars at once with sufficient detail that we’re going to fill in all of those details of a star’s life.

Fraser Cain: The classic example of this surprise was things like dark energy where scientists were looking for one outcome and a completely surprising one came about, and it told us something about the universe that we had no idea. Before 1998, we didn’t know that 76 percent, or whatever it is, of the universe – we didn’t even realize that was part of the equation. And then suddenly, you now have to ask yourself, “What is that dark energy?”

Dr. Pamela Gay: So this is actually even worse than that. We had an equation that had the Lambda term, the term that we now use to express dark energy, and we made the choice to get rid of that term and say, “well, we see the universe is expanding. Clearly, Lambda doesn’t have a value that stops the expansion of the universe. Maybe it has a value, but that makes the math a whole lot harder so let’s not do that. All of the test cases in cosmology books and everything was the end. We assume Lambda equals zero, and, no. Lambda doesn’t equal zero, and to quote Chris Empian, one of my favorite moments of a talk ever, “Who ordered this?”

Fraser Cain: Yeah, that was most unexpected. But as we go back to some of these missions – you look at the mission from New Horizons to Pluto. We have lots of conversations with the mission scientists leading up to this, and I kept asking this question. Really, come on, just between you and me, you’re looking for the stuff that you weren’t even expecting that you weren’t even planning that was going to happen.

And, of course, that’s what they really want to see. Of course, we’d like to measure the magnetic field, and we want to know what the atmosphere does. But, hey, what a surprise, Charon and Pluto have vastly different terrains – sorry, Charon. Charon has this enormous chasm on it. Pluto has this incredibly young surface with glaciers of – or, sorry – mountains made of ice and glaciers of ammonia, stuff they never would’ve expected.

Dr. Pamela Gay: And this is part of what’s so awesome about building versatile instrumentation. SDSS is another one of those, “We’re just going to capture all the light and then see what we discover.” You have the science you know is going to happen. They knew they had a lot of science that would happen with certainty with Pluto. But then you build the instruments flexible enough that when you realize, “Wow, okay. The universe is more awesome than the human mind could ever imagine,” which is what we keep rediscovering because we can’t remember it for some reason. Until we can consistently remember the universe is more awesome than we can imagine, we need to just keep building flexible instruments that serve many science purposes, and, luckily, that keeps us safe when it turns out we need to do things we hadn’t anticipated.

Fraser Cain: So let’s talk about policy for a second then, which is that if you had your way and we could direct science funding more, I guess, away from the cogitating over the stuff that, maybe, we can’t even know, where would you put the funding, he says throwing a softball?

Dr. Pamela Gay: Yeah, it’s not a softball, and I don’t want to get hate mail. I think there’s a lot to be said for things that aren’t necessarily kitchen sink instruments. You have to have a certain amount of specificity.

But having really good high resolution spectrographs that are capable for brighter objects giving us really detailed understanding of what the chemistry is out there so we can confine our models, having some really good high resolution imagers that allow us to start to get at fine structures, but then also have the stuff that just collects as much light as possible and throws it into a lower resolution setup so we can see what’s at the beginning of the universe. At the end of the day, what you need is big glass, big collecting area – it’s not always glass. Radio needs other things.

Fraser Cain: Right, x-rays – whatever.

Dr. Pamela Gay: Attached both a really good high resolution set of instrumentation for the nearby universe and really good low resolution set for the most distant part of the universe.

Fraser Cain: If I could make this an analogy, it’s about listening to the universe as it is. It’s about listening to nature and letting nature tell us how it functions and how it operates. You need to build your theories, but the number of times – maybe the Higgs boson. I can’t think of a lot of times where – neutrinos – you worked out the math in advance for a particle that you thought might be there or an object that you think is going to be there and then 10, 20, 30 years later the thing came about. It’s a lot more about building those tools, getting them out there, collecting, and listening – being a really good listener – and then turning around and going, “What’s in here that weird?” Let’s try and figure that out.

Dr. Pamela Gay: And this comes down, in a lot of ways, to the Simon White Rocky Cold debate between high cost highly flexible instrumentation – the Hubbles of the universe – and the highly focused highly specialized instrumentation – Large Hadron Collider, WMAP Planck. And there are times when you need the Large Hadron Collider to find your Higgs and find out if supersymmetry is another Nobel Prize for Weinberg or not. But at the same time, I’m a huge fan of the ideals behind the great observatory program. This was the program that gave us Hubble Space Telescope, Chandra, Fermi –

Fraser Cain: Spitzer.

Dr. Pamela Gay: I think Spitzer was one of the great observatories – just took us all the way through the electromagnetic spectrum where you should focus in space. We didn’t launch radio telescopes – but gave us that full access to the universe. Having that full access to the universe allows us to be nimble in the face of new science.

Fraser Cain: I think, though, the Large Hadron Collider fits more as a generic tool. It’s a really powerful particle accelerator collider. All of the particle discoveries have come out of more and more powerful particle accelerators. So I think there’s value. I wouldn’t see it as a single purpose tool.

Dr. Pamela Gay: It’s very locked in on what it can collide and what energies it can access. So there’s a lot of work that – it’s not slamming together atoms. It’s not looking at a lot of the higher mass regime where you see things happening at the National Superconducting super collider – or National Superconducting Laboratory rather, at Michigan State University. We still have Fermi Lab. We still have various other laboratories that are building heavier elements.

Unfortunately, colliders, there are some that are tuned really well for creating heavier and heavier elements, there are some that are tuned really, really well for making medical isotopes, and there are some that are designed for making discoveries at different energies. LHC has a very narrow window on what it’s able to do, and this is why we have this whole suite of places that make atoms and molecules and particles go boom.

Fraser Cain: And I think that a lot of people make philosophical questions. They try and make that a scientific question, and that comes up quite a lot. You should read the comments on the YouTube Chat – YouTube channel of mine. I ask, “What came before the Big Bang,” or things like that. That’s the gist, like, this is a question that we can’t know, and yet, philosophy is what people turn to with certainty, which is not appropriate, I think.

Dr. Pamela Gay: Yeah. It’s the quote from R town that I may screw up slightly. “Truth is only known by the poets, the drunks, and the mad.”

Fraser Cain: That’s awesome. All right, on that note, thanks, Pamela.

Dr. Pamela Gay: Thank you.

Fraser Cain: Which one are we? Thanks. We’ll talk to you next week.

Dr. Pamela Gay: Okay, bye-bye.

Male Speaker 1: Thanks for listening to Astronomy Cast, a nonprofit resource provided by Astrosphere New Media Association, Fraser Cain, and Dr. Pamela Gay. You can find show notes and transcripts for every episode at You can e-mail us at Tweet us @astronomycast. Like us on Facebook or circle us on Google+. We record our show live on Google+ every Monday at 12 p.m. pacific, 3:00 p.m. eastern, or 2000 Greenwich Mean Time. If you missed the live event, you can always catch up over at

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