What are the biggest mysteries facing modern astronomers? What questions do I wish could be answered in my lifetime? What are most astronomers working on right now? I discuss these questions and more in today’s Ask a Spaceman!

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EPISODE TRANSCRIPTION (AUTO-GENERATED)

happy 2/100 episode, everyone 200 down and at least 200 more to go. And to celebrate our likely unending quest into complete knowledge of time and space, I wanted to recount my most favorite outstanding questions in modern astronomy like last time. This will be a list of five top mysteries in astronomy like last time. We're only going to focus on astronomy, you know, maybe for the 3/100 episode we'll do this again, but for physics, and we're going to have less preamble today because I already said most of it last time. But just in case you're not a fan of the biggest discoveries of the past and are more of a forward thinking kind of person, here's how to get on my list. Number one breath. Many people are working on the same problem from a bunch of different angles. There are lots of problems out there, but not every problem captures the imagination and curiosity and interest of a large fraction of the astronomical community. Number two depth.

This is actually a difficult problem and requires a lot of different people. Taking different approaches requires observations and theory and lots of just sitting around talking, trying to figure it out. Number three potential, while not guaranteed solving this mystery, will probably lead to a radical changing of the way we understand the universe. And even making progress itself will have a substantial impact, even if it all leads to nothing, because the tools and techniques and insights we gain just to try to tackle the problem will give us lots of cool, new ideas about the universe and, lastly, neatness, not orderliness. But how nifty, interesting or intriguing. The problem is based solely on my own sensibilities. And so, given these categories, we can already move on to our honorable mentions today, which go to galactic evolution, star and planetary formation, solar weather and, uh, everything related to dust.

Unlike the last episode, which focused on specific results in individual breakthroughs and discoveries today, we're going to look at broader categories of problems. Why will problems always seem larger until they have a solution? Mysteries are just a list of things we don't know, and it's handy to group those lists into categories to help us navigate and assign funding. But once we make a breakthrough, the mysteries collapse into a known solution, and I should mention that this list probably leans heavy into cosmology because, you know, I'm a cosmologist. And so the things I personally find interesting are going to appear more often, but also because cosmology really is at the forefront of our biggest questions and mysteries. Yes, I know I'm biased, but bias is everywhere, and at least I'm being upfront about it. So as we continue our celebration of the 2/100 episode of Ask a Spaceman, I can't believe I made it this far. When I started this podcast years ago, I had no idea that I would still be going at it today.

But we are not stopping now. Presented in no particular order, it's up to you to decide rankings. The top five mysteries in modern astronomy. Mystery number one. Is anybody out there? Are we alone in the universe? It's one of those questions that has been asked by dozens of cultures across the world and throughout time, and that's only the ones we have written records for. I'm sure every single human who has looked out at the horizon or up into the endless dark sky is wonder. The same thing is this It is this all we are, Even if you couldn't imagine that those tiny dots of light in the sky were suns unto themselves, most of them with worlds circling around them. The question lingers in the back of your mind. You know of your family, your extended network, the trading patterns of your culture, the people you fight with or cooperate with. That's true 100,000 years ago, and that's true. Today you hear stories of more distant lands, exotic and strange, people who eat a dairy byproduct known as cheese.

And then you, you wonder, Is there any more? There's the people I know than the people I hear about. Is that it? Are there people that I haven't heard of yet? Are there people that anybody hasn't heard of yet? Our modern search for life outside of the Earth is just a continuation of that exact same line of thinking, because by now in the 21st century, there's nobody left to meet. Yes, there are some uncontacted tribes, but they've made it pretty clear that they want to be left alone. There's nobody else. There are no horizons left on the earth. And so we look to those distant stars with their orbiting worlds and wonder. Is there anyone else? Starting in the 20th century, this question moved from speculation, philosophy and even theology into the camp of science. We openly wondered if Martians were running around on the surface of the Red Planet building canals. We were wondering if more distant planets hosted their own civilizations and we had ways to check. We could point a telescope at them and see if anyone was looking back.

So far, no one's looked back, but that hasn't stopped us. I like to think of the search for life as encompassing three separate domains. One life in the solar system. This is Mars. Has there been microbial life on the surface of Mars when it was warm and wet with water? Has any of that life clung to a meager existence? Today, there are back and forth debates about whether liquid water can exist on the surface of Mars. There's this weird seasonal fluctuation in the amount of methane in the Martian atmosphere, which might be a sign of life. Or it might just be some weird Martian chemistry. We don't know there's a Venus where is largely a hell world, but the upper atmosphere has pretty decent temperatures. If you don't mind the sulfuric acid, you know, minor inconvenience. But maybe there's some interesting chemistry going on there. There are the ocean worlds of the outer solar system, these moons locked in layer after layer of frozen water ice.

But underneath that ice are liquid water oceans. Some of those worlds, like Europa, have more liquid water than the Earth does, and they are completely blocked off from sunlight. But that's not a problem for some forms of life on earth. And then you get the weirdos like Titan, which have seas of liquid methane on the surface, where if life existed on that world, it would follow completely different biochemical pathways than life does on the Earth. It would be completely and truly alien to us, but still alive. And so we're developing missions to go exploring in our own solar system. Then there are the searches for intelligent life. This is SETI, the search for extraterrestrial intelligence, which relies on techno signatures. Does anyone have a radio out there, or do they build a giant shell around their star? Something obvious that signals their existence to the rest of the galaxy or wider universe, and we can pick up on that.

And then there's the third domain, which is the search for literally anything else. So, for example, looking for a life on exoplanets, using the transit method, waiting for planets to cross the face of their star. That light filters through the planet's atmosphere on its way to the earth, and we can detect the presence of molecules. And some of those molecules are signs of life, some biosignatures or searching for the precursors of life throughout the galaxy, like amino acids and proteins and all sorts of cool stuff. Organic compounds to try to get a gauge on how rich the galaxy could be with life. So far, all three of these approaches have come up empty, just as they have for thousands of years. But that doesn't mean we have to stop trying. Mystery number two. The darkness becomes us. I'll be the first to admit that it's somewhat embarrassing to state that we understand less than 5% of the universe, and that's not a matter of we've only mapped 5% or cataloged 5%.

No, this has nothing to do with volume. It has to do with ingredients. 95% of the contents of the universe are of a form unknown to modern physics, period. We have no idea what it is. We have no idea what's going on. We have no idea if it's simple or complicated or somewhere in between. We have no idea all of human history, all of the progress of physics, all of our achievements and advances in knowledge gained all our work. Generations of it and all we've managed to understand is less than 5% of what's out there. One big chunk of it we call dark matter. This goes all the way back to the 19 thirties and astronomer Fritz Zi I can't ever get tired of saying that name, who was looking at clusters of Galaxies and looking at the motions of Galaxies within them. And he realized that the Galaxies were moving too fast, that there wasn't enough gravity among the Galaxies by themselves to explain how fast the Galaxies were moving. The the cluster should have just ripped themselves apart billions of years ago, but there they were.

He suspected there was some form of hidden mass that he could not see in his observations. He called it dark Matter, but then moved on to other projects. The whole community ignored the problem for decades, until another astronomer in the seventies, Vera Rubin, discovered that Galaxies themselves were rotating far too quickly and should have flung themselves apart long ago. Since then, there have been many, many more observations of the cosmic microwave background, the large scale structure of the universe. All these independent lines of evidence point to the same thing. There is some form of matter. This is not a problem with our theory of gravity. This is not a problem or a shortcoming of our models. This is a component of the universe. Around 2025% of all the universe is dark matter. It is some form of matter that is invisible. It does not interact with light or other matter, and we have no idea what it is. The other big chunk between 60 70% of the universe is dark energy, which was accidentally discovered in the late 19 nineties.

There were two teams of astronomers looking at distant supernova that were out there to measure the deceleration of the universe. The thinking is OK. Our universe is expanding, but it's made of stuff. All that stuff has its own gravity, which can pull in on that expansion and gently glide that expansion down to a halt. They did not measure deceleration. Instead, they measured acceleration. Since then, there have been countless independent observations that measure the exact same thing. It's not going away. It's not some little gremlin in supernovae. It is a real thing of our universe. We call it dark energy because it's a really cool name, great for marketing. We don't know what it is. We don't know why the expansion of the universe is accelerating. We just don't know. We just don't. And I realized I didn't place dark matter and dark energy on my biggest discoveries list last episode. But here they are as the biggest mysteries. Well, that's because we don't yet know how important the discoveries are. After a few more decades of work, we may discover OK, dark matter is just some species of particle that we hadn't included in the standard model yet, but there it is, and, uh, dark energy is some sort of vacuum energy related to various quantum fields, and we don't learn anything new, and it doesn't lead to a new advance in understanding.

It's a mystery right now. We can't gauge its importance, but I can tell you that the vast majority of the cosmological community is obsessed with it. Yours truly included. The vast majority of my own research papers have been about dark matter and dark energy. We have made a lot of attempts to understand these twin darkness is theoretical advancements, trying to model what particle the dark matter could be, or species of particles or what the candidates are. We've used particle colliders to try to generate dark matter particles. We've made better observations of the history of growth of structure in the universe. Try. We've tried to pick apart the cosmic Web like like digging into a cupcake and and looking at it with a microscope to figure out what the ingredients are. We. The hope is that over the next decade or so, we'll bring the uncertainties on our measurements of dark matter and dark energy down low enough that something interesting will pop out and help us sort out one theory over the other.

But That's pretty much the best we've got right now. I need to take a quick pause here, folks, to tell you that this show is sponsored by better help. And I gotta tell you, Adulting is really hard. It turns out that being a grown up is harder than being a quantum physicist. There are so many things that require balance. There are so many demands on your time and your attention and your energy, and it's so easy to get out of balance and to get burned out. I've personally found therapy, a powerful tool for dealing with all the balancing issues in my life, of how to balance a personal and professional and family and in career. And, you know, there's a lot going on, and therapy has helped guide me through that to find just the right balance. And so I encourage you to give therapy a try, and I'd like you to use better help.

It's entirely online, designed to be convenient and flexible, suited to your schedule. Just fill out a brief questionnaire and you're off to the races with a licensed therapist. Find more balance with better help. Visit better help dot com slash spaceman today to get 10% off your first month. That's better. Help HE LP dot com slash spaceman. And once we're in balance, we can start tackling the whole quantum physics thing. Mystery number three In the beginning, this is another case of one of those giant questions that has gone unanswered for millennia. And when we first discovered modern cosmology with Hubble's results in the 19 twenties that a Galaxies exist and B, they don't like us, they are receding away from us, and we live in an expanding universe. We created in those observations and with Einstein's general relativity, modern cosmology, which has its foundations in the Big Bang theory.

And for a while we thought we were on the cusp of figuring it all out. We finally had a story to the universe based on evidence and observation. You know, many cultures from around the world and throughout history have come up with beautiful, powerful stories about the origins of the cosmos and our place in it. But this was the first real time that the practice of science got to take a crack at it. And don't get me wrong. The Big Bang theory is powerful. And all the ways that other major cornerstone theories like evolution and germ theory are, it can explain a wide variety of natural phenomena using only a few simple statements. I mean, in this case, what powers the big Bang is this. We live in an expanding universe. That's it. That's the simplest, shortest, most summarizing E. If that's not a word, it should be way to state our modern understanding of the history and evolution of our entire universe. We live in an expanding universe. It was smaller yesterday. It's not so small today and tomorrow it will be even bigger. This simple statement leads to all sorts of observational consequences.

From here you get the cosmic microwave background, you say, 01 time, the universe was so small and so hot it was a plasma. And then it cooled off and released light boom CMB. Oh, when our universe was really young, it was so hot that all the protons and neutrons were smashed up against each other and then kind of coalesced into the first hydrogen and helium boom nucleosynthesis. Oh, a long time ago, there were no stars. There were no Galaxies. But as time went on, gravity did its thing and structures formed and generally got bigger as the universe expanded. Boom structure, formation. What a beautiful, powerful story. But there's this little problem, the problem of the beginning. How did it all start? Where did it come from? Like I said, these are giant questions, and the big bang gets us so close we can get nearly to the beginning. We can understand, with an extreme and alarming amount of confidence, the physics of the universe when it was 10 minutes old.

How insane is that? Earlier than that? It gets a little sketchy, though. The problem is is that our knowledge of physics gets in the way. Or rather, our lack of knowledge of physics gets in the way the further back in time we go, the smaller and hotter the denser and more extreme the universe becomes. Our theories start to break down, and eventually we just run out of chalkboard space. And so we have a whole host of questions involving both known unknowns and unknown unknowns. Did inflation really happen? If so, how did it go down? What split matter from antimatter? Where did dark energy and dark matter originate. What was our universe like when it was the second? What were the conditions? What are the equations of physics that describe those conditions? We understand the universe when it was 10 minutes old. We have a vague understanding of what it was like when I was 10 seconds old. But before that, our physics just can't handle it. We're so close. And what about the singularity? General relativity tells us that the Big Bang began at a point of infinite density.

Well, we know that's wrong. We know that general relativity is breaking down, that the equations are just throwing up their hands and walking away without even saying goodbye. But we don't have a correct theory to replace it. We have no way to grapple with the earliest moments of the universe. There is no tool in our physics tool belt that can help us. What created the universe? Does that question even even make sense? Does a multiverse exist? These questions can keep someone like me up at night, and they do. What's not a mystery is patreon, and yes, I know this is another obvious one, not a mystery, because I really do have the best audience ever, and I want you to know that it's not just about the money. Seriously, If all patreon were to go away tomorrow, I would still do this show because you you have an insatiable curiosity and I'm here to do my best to serve it. Thank you for the privilege of giving me the opportunity to serve your curiosity.

Patreon dot com slash PMS Sutter Mystery number four Ouch. One of my favorite spots is in New Mexico, Northwestern New Mexico. There's a park, a Chaco canyon. It's named for the native people that used to live there about 1000 years ago. The Choco people, we don't know what they called themselves. Uh, they left no written language, but we call them the Chaco, and you can go out on a hike. And you can, uh, walk into the desert up into some cliffs and you can see these cliffs and then some of the cliffs have overhangs on them, and some of the overhangs contain petro grass, these paintings on the rock that are baked into the rock. So they've been there for 1000 years. And there's one particular pet graph that has a hand print a crescent moon and a star. And that's a very intriguing pattern to put there, because if you stand there and place your right hand where that handprint is, and if you know that the Choco people were living in this area about 1000 years ago, you can take any astronomy software, run the clock back about 1000 years and wait for the crescent moon to be at that position.

Buy your handprint and what do you see? A supernova? They were not the only ones. Chinese astronomers noted the appearance of a guest star around the same time the Europeans curiously did not, although this was not exactly a peaceful, stargazing period of time in European history. So maybe they get a pass. Cultures around the world would marvel as new stars would appear in the sky, some so bright that they could outshine the full moon and then fade into obscurity. In less than a month. Taco Bra wrote about one in 15 72 with the most awesome title for a book ever. His title was concerning the star new and never before seen in the life or memory of anyone. I mean way to put it all out there in the title. Good for you, Tyco. He discovered that it was an astronomical object and not just something happening in the atmosphere, which was a big deal, that these new stars weren't just flashes of light in our own atmosphere. They were happening in the heavens.

His greatest student, Johannes Kepler, totally copied his former boss in 16 04 and wrote his own book, Tela Nova, The New Star. Another supernova appeared. Today we know a lot about these guest stars or new stars or Nova. We know that some are regular nova, that these come about when you have a binary star and it's a white dwarf orbiting a giant star. And the giant star spills its atmosphere onto the white dwarf and builds up this layer of atmosphere on the white dwarf until it crunches, ignites a nuclear fusion and flashes releasing a nova. Some of these are supernova. We have both type two and type one A. Sometimes giant stars die and explode, releasing a tremendous amount of energy. Sometimes that nova process gets a little haywire, and instead of just the hydrogen atmosphere going nuts, the entire white dwarf cracks open in an uncontrolled fusion reaction, the world's largest nuclear bomb.

We know of some of these nova as killer nova, which is what happens when neutron stars merge together. And we know of some of these as hyper nova, which are like supernova but even cooler. We're not exactly sure how those happen. It might be related to the formation of a black hole when a giant star dies. The thing is, there are a lot of high energy events happening throughout the universe all the time. And this is one of the great directions that astronomy is moving in in the 21st century, something the nerds call time, domain, astronomy or transient astronomy. But for us, we can just call it astronomy for the impatient. So much is happening in the sky all the time, which is a rather radical idea. We're used to the stars being the stars. Occasionally there might be a little bleep or bloop or flash here or there, but largely the firmer stays firm. But once you develop the sensitivity and you have high powered telescopes, you can see that there are things happening all the time.

Nova Supernova Kan Nova. Hyper nova gamma ray bursts fast radio bursts, quasars, tidal disruption events. The universe is alive, and some of these events blink in and out of existence in less than a second, and we don't understand most of them. We still don't understand exactly how supernova work about how a giant star dies. We have the general picture, but we do not understand the details. We actually have a lot of difficulty in our theories and simulations in getting stars to actually explode. We don't understand how gamma ray bursts work. We don't understand how hyper novae work. We don't understand how fast radio bursts work. We have general pictures, but the physics is so extreme here, and the events are so rare they happen all the time. But they're so fast, so it's hard to catch that we only have vague outlines. Why do we care? Well, one, because it's cool stuff happening in the universe, and that's our job as astronomers is to find it.

And two is because nature is giving us particle colliders for free. A typical supernova that the cosmic rays ripping through our atmosphere right now charged particles traveling close to the speed of light are billions, if not trillions of times more energetic than our most powerful particle colliders. Nature is giving us laboratories of high energy physics that we can't even hope to match on the Earth. Understanding the high energy, transient, short term universe means we get to understand fundamental physics. Mystery number five. Of course, it's black holes. Do I need to say more? It's black holes. Look, they're not just interesting astrophysical objects. Black holes represent the boundaries of known physics specifically, and why black holes continue to be so interesting and exciting. Decades after their discovery is that black holes are a window into one of the thorniest problems in all of physics.

The marriage of quantum mechanics and general relativity. All of modern physics, rests on two great pillars. Our understanding of the subatomic world through the language of quantum mechanics, which gives us an understanding of electromagnetism and the weak and strong nuclear forces, an understanding of how subatomic particles interact of how atoms form. And on the other side we have general relativity, which explains the force of gravity and the force of gravity alone, and the relationship between space and time and matter and energy. These two theories are incompatible with each other. When we try to develop a quantum theory of gravity, just infinities appear everywhere and we can't make progress when we try to apply the language of space, time to particles themselves, infinities appear and we can't make progress. We don't know how to unite these two pictures. We feel it's not guaranteed, but we feel like there should be a unified theory. One set of equations that can describe all of physics.

We feel like it should be. There doesn't have to be, but we feel like it's there. And so we have this nasty problem that we've been unable to solve for ages, and there's not even a guarantee that we'll be able to solve it. Maybe we're just not smart of enough. Our dumb monkey brains can't figure it out. And there's some alien civilization riding around in Andrada being like we figured that out long ago. What's your problem? I don't know, but black holes might offer us a way through, and there are not one but two ways they can do it. One is the singularity. General relativity tells us that the center of a black hole is a point of infinite density, which is not possible. We know that's wrong. We know that's stupid. Come on, Albert, go home. You've said enough, but we don't have a theory of quantum gravity to replace it, to tell us what is happening at the center of a black hole. So we're trying to understand the centers of black holes because that is a place where we know that general relativity breaks down and that quantum gravity must take over in the second place.

And this is a little more surprising is the event horizon. See, the event horizon is the boundary of a black hole. It's the region that if you cross it, you can't get out, and there's nothing physical there. It's just an imaginary line in space time. But if you cross it and you try to leave, you'll find that you have to travel faster than the speed of light to escape. And everything was fine about event horizons. Nothing was super special about them until that jerk Stephen Hawking discovered that black holes aren't entirely black, that they actually emit a little bit of radiation. The most important thing here is that he showed that the event horizon is really a quantum surface that interacts with gravity. It's like a singularity, but we can actually touch it. You know, if we could actually travel thousands of light years to the nearest black Oh, we could actually touch an event horizon, and we wouldn't exactly live to tell the story. But we could do it. The event horizon of a black hole is a quantum surface. It is a place where quantum mechanics is is intersecting with general relativity, and it's accessible, which is why there's so much interest in event horizons and firewalls and information paradoxes.

It's because that's an intersection point. If we can understand that, we might be able to crack quantum gravity and gain a deeper understanding of the fundamental workings of nature. But we can't, like, go to a black hole. And so it all remains theoretical exercises, and so the mystery remains. But wait, there's more. Black holes aren't just mysteries of exotic physics. They also play a role in the wider universe, which is something we also don't fully understand. We don't know if primordial black holes exist. If if the conditions of the early universe were enough to spew tiny black holes that continue to flood the universe. That's pretty cool. We don't know. Giant black holes play a role in galactic evolution. They release heat and radiation into their galactic environments, which regulates star formation. It's possible that we wouldn't exist today if it weren't for the supermassive black hole in the center of the Milky Way that if there wasn't that black hole, then all the stars would have just burned and lived their lives and formed in less than a few billion years.

And then that'd be it. Black holes regulate star formation in Galaxies by releasing heat and preventing the formation of too many stars at once. But we don't know exactly how that relationship works. Speaking of giant black holes, the biggest black holes are tens of billions of solar masses, and we don't know how they got so big so quickly. We push our observations of the early universe back to the first generations of stars and Galaxies, and there are giant black holes right there saying, Hey, how's it going? I'm here, too. How does that work? We don't know. There are mysteries everywhere. These were just five mysteries, and I don't know about you, but I can't wait to see what mysteries we solve and what new ones we uncover. Next. Thank you for following me on this journey of 200 episodes of ASA Spaceman. We've got at least 200 more to go, and I can't wait to see what continued explorations of complete knowledge and time and space will bring us. Thank you, Thanks. Especially to Mark J on email, Jordan on email and at POSA on Twitter for the questions that led to today's episode.

And, of course, thank you to my top patreon contributors. That's patreon dot com slash PM center to help support this show. The top ones this month are Justin G, Chris Eels, Barbara K, Duncan M, Corey D, Justin Z Nalla Scott M, Rob H, Justin Lewis M John W, Alexis Gilbert, M Joshua, John S, Thomas D, Simon G, Aaron Jessica Kay and Valerie H. Again, that's patreon dot com slash PM Sutter. Keep the questions coming. We've only done 200 episodes. We're just getting started, folks. That's ask us spaceman at gmail dot com or ask us spaceman dot com. There's a place on the website where you can drop me a line and I will see you next time for more complete knowledge of time and space.

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