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What is the “cosmic calendar”? What are some important scales in the universe? Why is it so hard to judge “importance” of events? I discuss these questions and more in today’s Ask a Spaceman!

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Music by Jason Grady and Nick Bain. Thanks to Cathy Rinella for editing.

Hosted by Paul M. Sutter, astrophysicist at The Ohio State University, and the one and only Agent to the Stars (http://www.pmsutter.com).

 

EPISODE TRANSCRIPTION (AUTO-GENERATED)

The next time you're in a jungle, and for the purposes of this introduction illustration, I'm gonna assume that you go to the jungle often. But the next time you're in a jungle, I want you to just pause for a moment. Just pause. Stop moving, and just pay attention. Just listen.

Just watch. Just let yourself be absorbed by the nature around you. Look around very carefully and listen very carefully. You might notice some things. You might notice some things that you may not have noticed if you're walking through the jungle just crashing through with your machete, you know, doing jungle y adventure things.

You might notice some birds starting to fly around or nest. You might notice some bugs crawling around. Maybe there's a jaguar prowling by. And if you pay a lot of attention for enough time, you'll even see the trees growing. There's a lot of different things happening in a jungle all at the same time, and they all have different timescales.

Right? Like, from the perspective of a tree that's slowly growing over the course of decades, that's a slow thing, right? Compare that to, like, a bug that might be alive for a week and is crawling around fast as it can trying to get food. And even your own perspective, your own human perspective where you can be in this jungle for maybe a day and that's your entirety of your jungle experience. There's all these different timescales associated with different things in the jungle.

I want you to keep this jungle y metaphor in mind of how you can just sit somewhere in nature and experience different kinds of timescales and different kinds of activities all happening simultaneously and in parallel. I want you to keep in mind because I'm gonna rant about the cosmic calendar. You you may have heard about the Cosmic Calendar. It is the device used in the Cosmos series, and I've seen it a few other places, where it lays out some major cosmic events, and it does so by taking the past 13,800,000,000 of cosmic history and compressing it down into a single Earth solar calendar year, and then just marking the dates of important events. So all of the earliest moments of the Big Bang happened, you know, in the first few minutes.

The first stars appear in, like, February or March, and I don't remember the details because I didn't bother to look it up before recording this podcast, but, you know, you get the picture. The first stars appear in, like, February, the first galaxies come online in March, Milky Way shows up in like May or June, our own solar system is born in early fall, your life appears on the Earth in late fall, Your vertebrates come on in, like, December or something. Humans finally show up on the scene on, like, December 27 or something, and then we invent writing in in the last second of the last day or or something like that. You get the picture. And, yeah, I get the point.

I get the point. One point is to lay out some major cosmic milestones, which is nice. Another point is to show us how utterly small and insignificant and inconsequential are human lives and experiences. In fact, all of humanity is on cosmic scales, and I'm totally on board with it. I kind of wrote a book about it.

But if you actually read my book, you see that there's a twist at the end. I guess I'm gonna kinda spoil it if you haven't read it. Yes. It's true that humans haven't been around on the Earth for a very long time compared to cosmic time scales. Not gonna argue that fact.

What I'm gonna argue with is does it matter? Does our time here on Earth, does the length of time that humanity has existed, does it really matter? Is that the proper yardstick? Or meterstick, for my international friends. Is that the proper ruler for measuring significance in the universe?

Because it's using one time frame, you know, the the length of time it takes for the Earth to orbit the sun, and the universe has been around for 13,800,000,000 of those, and it's gonna compress it down into a single one of those, and and and does that necessarily make sense? Like, Does it make sense to say that, Oh, compared to the lifespan of a tree and how slowly it grows, a single bug's lifespan is insignificant? Yes, that's true, but that doesn't mean the bug doesn't get to be a major player in the story of the jungle. Right? The bug could decompose material that provides nitrates to feed the tree and etcetera etcetera.

Just because the bug doesn't live a long time compared to the tree doesn't mean the bug is not important. Different physical processes in the universe have their own important space and time scales associated with them, And so it only makes sense to talk about those processes in the space and time scales that make the most sense for those processes. And like I said with the jungle, a single system, and when did this become one of my most used words, system, you know, a system could be anything from a bunch of particles in a box, to the weather on the Earth, to your human body, to a solar system, to a galaxy, to the whole entire universe, just a system. A system can have multiple time and space scales associated with it, and it doesn't always make sense to just apply one space and time scale to the whole thing, and use that to measure significance and importance. So I'm gonna give you a few examples before returning to the universe itself.

And, by the way, thanks to Ogi Jay via email for the question that led to today's episode. So I'm gonna start with nucleons. You know, protons and neutrons, everyone's favorite nucleons. They're small, like 10 to the minus 27 kilogram. That's small.

They're a big player when it comes to atoms. You know, the number of protons determines which element you are, where you're on the periodic table. These are the things that participate in nuclear reactions, binding the nuclei of atoms together. The nuclear fusion and fission, like all this. Protons and neutrons, important stuff, right?

What's the right scale for measuring important things in the life of a proton or neutron? Well, you could use, say, how quickly they interact with each other. So how often? You know, neutrons and protons are glued together inside of a nucleus with gluons. I wish I was making that up.

The strong force. That is strong force steps, so go listen to that one. Classic. Used a bunch of, Three Musketeers analogies if I remember right. So how often does a proton talk to a neutron?

A good number to keep in the back of your head. It's very very approximate, but it's it's around a femtosecond. A femtosecond, that's 10 the minus fifteen seconds for how quickly a proton and a neutron talk to each other. Like, if they need to send something by mail, it's like a femtosecond later, the the proton gets it. Okay.

That's one timescale. What about decay times? Right? If you if Neutrons and protons are very stable inside of a nucleus, but if you pull a neutron outside of an atom, it becomes very unstable, and in about fifteen minutes, it'll decay. It'll disappear.

Fifteen minutes for a neutron to disappear. So that's like the quote unquote life time of a neutron. So now we have two numbers associated with protons and neutrons. We have ten to the minus fifteen seconds, and we have fifteen minutes, which are worlds apart. What about the decay time of a proton?

It might be that protons never decay, and they have a lifetime of infinity. But in some grand unified theories, they have very long lifetimes, but are still finite, somewhere around ten to the fifty years. I mean, who's keeping track once you get up to that point? So we'll just use it. Ten to the fifty years.

So here are the three important time scales for protons and neutrons. Ten to the minus fifteen seconds, fifteen minutes, and ten to the fifty years. Which is the important one? How do you make a calendar? How do you pick one time scale to use for your calendar?

Or what about you? Yes. You. What's the right time scale to measure you? I mean, we have our lifetime, you know, seventy years plus or minus.

Okay. That's one measure, pretty standard measure, but there's other things going on inside of you that have their own rhythms, their own clocks, like your heartbeat. Heartbeat is roughly one second. So does it make more sense to chop up life into seconds? Sometimes it does.

What about electrical signals? It takes like a tenth of a second to blink, a third of a second to react. So again, that's seconds, a breath. You take a breath every few seconds. So it seems like when it comes to your body's own internal communication, seconds are much more important than any other timescale.

There are some other cycles, like every month you contribute to to Patreon. That's patreon.com/pmsutter where you can keep this show going. That's right. Just a few bucks a month, however much you wanna contribute, keeps this show going by paying my bills because this is my job. That happens every month.

That's a very important time scale. You have your circadian rhythm. You know? So you have this daily rhythm too. What is the right time scale for people?

Is it seconds? Is it days? Is it years? The answer is yes to all of them. It depends on the question you're asking.

You can even talk about things like the sun. The sun has a lifetime of around ten billion years, but in the core, it's processing somewhere around 620,000,000 tons of hydrogen are getting fused every single second. There are these giant granules, these boiling things on the surface of the sun that will have a lifetime of a few like, a dozen minutes or so. They'll rise to the surface, and then ten, twenty minutes later, they'll slink back down. There's a sunspot cycle of every eleven years from peak to peak.

And, hey, if you were to change something in the core, this is amazing. If you were to, say, shut off nuclear reactions in the core or change the reaction rate in the core or just do something in the core, it would take somewhere around a hundred thousand years before the surface of the sun changed. That's how long it takes for changes in the sun to make their way through the entire volume of the sun. So what's the right time scale for the sun? Is it fractions of a second for its nuclear reactions?

Is it dozens of minutes for the granules to appear and disappear on the surface? Is it years to measure this sunspot cycle? Is it hundreds of thousands of years because that's the amount of time it'll take to change the sun if you wanted to? Or is it billions of years for its lifetime? The answer is yes to all of them.

All those timescales are important and they're all important simultaneously. It depends on the question you're asking. Even galaxies, same story. You know, they have lifetimes of billions of years, but they rotate once every, say, two hundred million years or so. But there's supernova going off inside them that change their chemical makeup, can change their structure, can send flows of material going out, those happen a few per century.

What about star formation? Galaxies are made of stars, and there's new stars coming online every year, a few new ones every year. So what's the right time scale for galaxies? Say it with me. All of them.

Years, centuries, hundreds of millions of years, billions of years, all those time scales are important when it comes to galaxies. And to just pick one and say this is how we're gonna measure importance in a galaxy is a mistake. I'll do one more. If you had noticed, we're getting bigger and bigger with every example. I'm gonna talk about clusters of galaxies.

Talked about them recently. Awesome things. By all accounts, very, very big. So you might think there's only one time scale that could apply to something so big. But what is that number?

So I I mentioned briefly in the last episode that around 80% of clusters are nice and round and uniform, 20% are ugly trainwrecks, and based on this, and we think the trainwrecks are caused when clusters collide with each other, so it suggests, you know, just running the numbers, some back of the envelope calculations, that after a galaxy cluster collides with another, it takes about a billion years to fully relax and settle in. So maybe that's the right time scale. Right? A billion years. That's how long it takes for a cluster to find its identity.

But they have lifetimes in the trillions of years. Trillions of years. Galaxy clusters are the largest gravitationally bound structures in the universe, and they'll stay that way for a long time. But they have these supermassive black holes in their cores that can eject jets in giant bubbles, that can heat up the intercluster medium. There's almost a heartbeat inside of clusters due to these active galactic nuclei, due to these jets and bubble systems, and that's on the level of, like, millions of years.

And at the same time, the galaxies themselves that are in a cluster are moving around at hundreds of kilometers per second. So what's the right time scale for clusters? All of them. Millions of years, billions of years, trillions of years, all those numbers matter when it comes to a cluster of galaxies. So what about the universe?

What about our cosmic calendar? 13,800,000,000 years old. If something takes a small amount of time compared to 13,800,000,000, is it insignificant? You know, humans have only been around for two hundred thousand years, so, obviously, we're not important. Is that a valid argument?

You can guess what my answer is. It's no. Let me give you some examples. Let's talk about inflation. When our universe was 10 to the minus 34 old, that's like a billionth of a billionth of a billionth of a billionth of a second old, very young, the universe underwent this period of incredibly rapid expansion where its radius grew by, like, a factor of 10 to the 52 or something ridiculous.

It just got big really fast, and it got big in about the same amount of time, in, like, a billionth of a billionth of a billionth of a billionth of a second. Like, whoosh. Faster than that. Inflation was perhaps the most dramatic thing to ever happen in our entire universe's history. Right?

Completely changed the character of the cosmos. Completely got rid of all space time defects, rapidly expanded the universe, made it cold and empty, took tiny, tiny fluctuations in space time itself and turned them into very tiny differences in density that would someday grow up to become the largest structures in the universe. When inflation decayed and ended, it filled the universe with matter and radiation, the same matter and radiation that hangs around today. Probably the most dramatic thing to ever happen in the universe, and it was over and done in a billionth of a billionth of a billionth of a second. Where does that go on the cosmic calendar?

When you're taking thirteen point eight billion years and compressing it down to a single calendar year, where do you fit a billionth of a billionth of a billionth of a billionth of a second? Where does that go? Can you even write it down? And yet, it's kind of important. According to the cosmic calendar, this should be almost meaningless, but it's not.

What about the formation of the elements? Right? Nucleosynthesis in the early universe, the formation of all of the protons and neutrons, the hydrogen, the helium, the a little bit of lithium, but who cares about lithium, honestly? That got started when our universe was fifteen minutes old, lasted, like, ten minutes. Think about that.

Start to finish, this podcast episode, in that same amount of time, the universe fashioned, forged all the hydrogen and helium, which would someday go on to become stars and galaxies and fuse to higher elements and build planets in you and me. It happened in a time less than this podcast. Where does that go on the cosmic calendar? That's gotta be insignificant. Right?

Because it lasted a dozen minutes, and yet, kind of important. What about what about the cosmic microwave background itself? Cosmic microwave background was generated when our universe was 380,000 years old, when our universe transitioned from being a hot dense plasma to being a slightly less hot, slightly less dense, but very neutral gas. It was a phase transition. The phase transition lasted about ten thousand years.

Took the universe about ten thousand years to figure itself out. Three hundred eighty thousand years in, and it took ten thousand years. Where does that go on the cosmic calendar? Well, in our cosmic calendar, when we look at humanity, humans have been around for, like, what, two hundred thousand years, plus or minus, A little bit? That's roughly the same amount of time it took for the universe to start generating the cosmic microwave background.

And it took the universe ten thousand years. We've been writing for six thousand years, plus or minus. Interesting endpoints. Right? The end of the cosmic calendar is the rise of humanity and writing, and here we are.

Take that exact same slice of time. You know, the last minute, the last hour, whatever it is. Whatever that is, take that exact same amount of time, that same fraction of the year, and put it in January, and there's your Cosmic Microwave Background. There is the second to last major phase transition of the Universe. Huge, important, game changing epoch.

Barely gets a mention in the Cosmic Calendar. The early universe was incredibly exotic. You know, forces and energies that will never be seen again. It was operating on different timescales than we are today. It was the universe itself.

It's like the jungle. There's all sorts of important things happening on all scales all the time. Yes, there's the big lifetime, the thirteen point eight billion years. That's important for sure. But then there are these major epochs, especially in the early universe, that were critically important, but didn't take long, quote unquote, to do at all.

And at the same time as the universe is evolving, galaxies are doing their things, stars are doing their things, people are doing their things, protons are doing their things, and they're all important. Like, how do you measure? How do you mark out the important times in the growth of something like the universe? I don't think taking that thirteen point eight billion years and compressing it down to a single calendar year is the smartest move because it's picking one time scale. It's picking one thing to mark, to delineate.

And it's arbitrarily saying, okay, if you don't take up a lot of time, a lot of fraction on the cosmic calendar, then in some sense you're not important, You're not significant. Well, that's not true at all. I guess my point is this. One of the goals of the cosmic calendar was to show how insignificant human existence is because we haven't been around for very long. Well, my point is that just because you're not around for very long, doesn't mean you're not important.

Thank you so much for listening, and please, you can contribute to patreon.com/pm. Sorry. It really is. I can't thank you enough because it it is supporting all of this science outreach. It's it's what I do, folks.

And I'd like to thank my top Patreon contributors this month. John, Matthew k, Helga b, Justin z, Matt w, Justin g, Kevin o, Duncan m, Corey d, Kirk b, Barbara k, Nooter Dude, Chrissy, Eric m, Steve c, and Digital Neo. Those are just the top ones. There's a lot of other people joining this crazy party. That's patreon.com/pmsudder.

And you can always always buy my book, pmsutter.com/book for links how to get it on Amazon, Barnes and Noble, or you can order autograph copy directly from me. Also leave a review on iTunes. That always helps. And keep sending me questions. Hashtag ask a spaceman, or go to AskASpaceman.com.

And or email AskASpaceman@gmail.com. And I will see you next time for more complete knowledge of time and space.

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