One second of time-- that's it, you just had one. Who decided how long that was? If you think of it objectively, this [snaps] doesn't actually mean anything. It's a pretty arbitrary duration, right? Yet, even though it's arbitrary, we made it very precisely arbitrary. One second is not just one second; it's 9,192,631,770 microwaves of radiation coming off a caesium-133 atom inside of an atomic clock, and there are many of them all over the world. And still, why? Where did that come from? Why not round up to 10 billion, or down to 9 billion? Because time is something we invented. It doesn't actually exist. I mean, well, it's a debate, and that's what we're going to talk about. Have you ever sat around and thought about time? Not just like the time of day, like, the sun moving and stuff; the moving of the planet or the stars. Just time. What is it? Why is it? Who decides how fast it moves, how long things will be? What is time? Where does it come from? Is times even actually real, or is it just how our brains process this complicated and strange reality we all exist in? We're gonna tick through all these "tocks," so welcome to "Uno Dos of Trace." Every month, I pick a topic and I dig deep into it, breaking it into chunks so that we all understand it a bit better--myself included. I am no expert. This month, we're talking about time. Over the next five episodes, we're gonna dig into the history, the engineering, the psychology and relativity, the philosophy and physics, even the whole universe and the end of time. Let's kick into it.

[intro music]

(Describer) Title: Uno Dos of Trace. Science Explainers from a Professional Nerd

Hi, hi, hi. Trace here again. First, my fellow time lords, what is time? René Descartes and Immanuel Kant, 100 years apart, both had philosophies of time. And one said, "We do not appreciate "time objectively as a physical thing; that it is simply a pure form of sensible intuition." Which actually isn't that far off from what physicists today think-- that it has to do with how we perceive and not necessarily something objective. There are lots of philosophers and physicists and mathematicians and psychologists all who have attempted to define time. Think of it like the association and memory of successive perceptions, mathematical concepts, physical motions, like gravity, energy, or heat-- they're all connected to time. But perhaps that's just how our brain interprets what's already there. Because time is fluid. So I'm gonna answer the title question now-- "Time is a construct that we built "to help us better understand the increasing complexity of the universe and its changes." And whether time is flat, and it already has all happened, you know, like a DVD--flat circle, I know, it's a joke, but, seriously, that's one of the ways to think about it-- or whether we're creating time as we go remains to be seen. And we are going to talk about both. But time isn't a particle or a wave. It isn't a mass. But it might be affected or created by some of those. Okay, so anyway, let's just go back. What is time? Time is what we think it is. So what do you think it is? Let's do the five Ws-- what, where, when, why, and of course how. What is time? The dictionary definition of time is "the indefinite continued progress of existence "and events in the past, present, and future regarded as a whole." The etymology of the word "time" comes from Old English and Proto-Germanic, Old Norse and Swedish. You could say tima or timon or timi or timme, coming from "to divide." Time is experienced. Yes, sure, you can see the sun and the stars move. You can see the rotation and orbit of our planet. You can see things age and die around us. In that respect, time is very much real. But it's also kinda not. Time isn't really anything. There's no big, cosmic counter that's counting down to the end of time, or up from the beginning. Time isn't a thing at all. If it's real, it must exist somewhere, but there's no particle that determines time-- at least not that we know of. So where is time? We know that it is out there. Radioactive decay is done over time. There was something, now there isn't something. The stars and the galactic ephemera all move. Time is required to calculate those movements and those decays. Energy moves through the universe. Without time, there's no way to say when something was emitted and then absorbed, or at least not accurately. You are watching this, and the Earth moved like 110,000 kilometers in that time. Atoms--they decayed, they vibrated. Your screen emitted light that was then absorbed by your eyes. Time, in this respect, is real and it's measurable. But it's also not-- I know, it's so confusing-- at least, not in the way we think. So, let's assume that time is a thing and that time is real and measurable, because we can do both of those things. But now we get to the fun questions: How did time start? How is time? In a 1996 lecture, "The Beginning of Time," by Dr. Stephen Hawking, he said, "All the evidence seems to indicate "that the universe has not existed forever, but that it had a beginning, about 15 billion years ago..." He liked to relate that time is sort of like the South Pole. There's nothing south of the South Pole. The idea being, of course, that "south" was something that we invented, and that a "South Pole" is also something that we invented. But because we have time, we had to have a start. And so that would be the Big Bang, right? That idea alone-- what he just said, by the way-- is remarkable. Today we take it for granted that time has a beginning. We know when that beginning was. It was about 14 billion years ago. But at some point in human history, we have no idea when time started; we just knew that time existed, and it was continuing to flow around us all the time, like a rock in a river. We just knew that there was a river; we didn't know where it started, we didn't know where it went. And, honestly, even though now, we sort of know where the river comes from, we still don't know where we're going. At some point, thought many, a deity flipped on the light switch, or perhaps the Big Bang happened, and at that moment, time began. Again, the Big Bang, of course. It's--Big Bang singularity is separate from the Big Bang, the event. The event is what we're talking about; the singularity is still up for debate. The idea that all matter in the universe was a single point-- not actually matter; like all of the infinitely dense point of everything that exists-- energy, matter, everything, all of it-- no atoms or particles, just the energy of the universe in one infinitesimally small spot-- that is still debated. But that is the Big Bang singularity. The event itself--we're pretty sure that that happened. At least in some capacity, there was massive inflation all at once. And someone gave that universe a laxative, and all of a sudden, boom! We got the universe. It expanded faster than the speed of light for a little bit, and now we see the result, which is all of this energy and all of this matter in the universe moving, inflating, moving away from each other; the energy is moving. The galaxies are moving away from each other. The universe is expanding. It's called inflation, and we can see light from the earliest universe; it's still out there, at the very edges of everything, permeating everything-- the microwave background radiation scattered by the matter of the universe in every direction that we look. And this is, in part, how we know when time started. Because we know the speed of light, and we know how big the universe is, or at least the inflation speeds, so we can kind of calculate, roughly, how long it's been doing that. And from this, we can imagine time sort of like the surface of the Earth. Time has no edges, no boundaries; there's no inner edge of the expanding balloon of the universe-- it just goes. And it's not expanding into anything; it's just happening. So imagine if you're on this planetary surface that I've just invented that is time, and you start moving through time. You're walking along this surface. Unlike a real surface, you never come back to where you started-- it's imaginary--but time just kind of goes and goes and goes. And the Big Bang, like the South Pole, started time. That's maybe where you began. But the universe keeps it going, because the universe is getting less ordered. If you imagine the universe right before the Big Bang was this kind of infinitesimally small spot with no particles; it was extremely ordered, in some ways. And now it's getting more disordered, more messy, more scattered. And that disorder can be tracked. It's called entropy. But you have to track it, of course, over time. And that's where we get to the Second Law of Thermodynamics...

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(Describer) 2nd Law of Thermodynamics

...which is one of the things that physicists think is driving time--the arrow of time is essentially that there is more entropy in the universe today than there was yesterday. We can't track all entropy everywhere, so it might be local to us, but what we do know is that it is happening. So that's one way to measure time. But that doesn't necessarily mean that is time; it's just a way to measure it. So why does time exist? Because it does. On some level, we humans create time. But time also exists inherently. There's no, like, "if the tree falls in the woods and you're not around" riddle in my head for time. You know? Time still happens regardless of our selfish human perspective in that it's a measurable thing going on in the universe. If we were wiped out, would time cease to exist? I mean, by our reckoning, sure, but by universe reckoning, probably not. Again, I'm not an expert, so if you disagree, please let me know in the comments. But if time did not exist, then everything would be happening at once, which some physicists think is how it is. Some scholars believe time exists because space exists. One of those is, of course, Uncle Albert Einstein, from the 1910s, and he connected time as a part of space. So imagine a movie-- the drama, the excitement, the narrative, flowing, laid out--you experience it from beginning to end. that is not unlike time. Now imagine a DVD of that movie. It's flat, readable. Everything in the movie is right there--you could just look at it if you knew what you were looking at. Both of those are valid perspectives of time. We can experience it linearly, like a narrative, watching the movie as it plays out. But we can also look at it from above or from a different angle and see all of time, everywhere, and the whole story. Because time is part of space. In physics, space-time is a mathematical relationship. It's physical, it's measurable, it's quantifiable. Things with high mass end up distorting and warping space-time, and fast things experience time differently than slower things. And we're going to get to that in a little bit. We're still, like, in the first episode, okay? We're still just doing that right now. So when is time? This is a question, actually, that I love. As soon as I started researching it, I'm like: "When--when is time? When? When is now?" 'Cause technically, now was then. By the time I said "now" or even thought "now," time had passed; by the time I thought "now," and the time that I said "now," and by the time you heard "now," now was not the same thing. Think of a phone call where you call your friend across country; you can say out loud, "Can you hear me now?" And they say "Yep." But "now" arrived at their ears milliseconds after you said it, so it's not really the same "now," is it? It's then! And so now we're talking.

[laughs] Literally, now we're talking.

But now we're not talking; it was then! There's no such thing as now! Or even that time ticks at all. So much is created by our brains. Time is about perception, which means it's about neuroscience and human brains and biology--three things that I really enjoy-- plus physics and math, and astrophysical concepts, which I really enjoy, and quantum mechanics... This series is so fun. So it's all super interrelated and really nuts, but the main thing is, is time that is experienced. When it comes to experiencing time, though, I thin that we all know it's felt pretty darn slow lately, especially in this pandemic, and that's why I'm so happy to have Nebula as a creative outlet, even more so now that we've partnered with Curiosity Stream. A while back, I really wanted to start making this series and series like it, but I wasn't sure if it would work. I was worried that the algorithm might tank it, or I'd lose subscribers, and I just wouldn't be able to make it work. These existential questions haunt everyone who's creating video online. Like, imagine being a TikToker right now. It's not awesome because there's so much uncertainty. The great thing is, Nebula is a place where thoughtful creators like myself and tons of others can just make stuff. They can try things; we can experiment; we can enjoy what we do best, which is creating. I even got to call up Andrew Smyth from "The Great British Baking Show" and talk about the science of baking for an original series called "Working Titles." And it airs only on Nebula, and it was so fun, and it was such a breath of fresh air for my creativity, and I think you're gonna love it. I mentioned Curiosity Stream, too, because they love Nebula. They love it so much that if you join Curiosity Stream, you get Nebula too. And it's actually for a lower price than joining Nebula alone. On Curiosity Stream, I can get documentaries about space and technology, AI and futurism, and of course climate change and animals and even the Internet. Curiosity Stream loves Nebula so much that for a limited time, they are offering 26% off of all their annual plans-- 26% off; it's the best deal you can get anywhere. We fact-checked it. For less than $15 a year, a little over $1 a month, you can get Curiosity Stream, plus Nebula, and you're supporting creators that you love, and you can listen to David Attenborough narrating tales about hummingbirds, and Chris Hadfield taking you on a road trip through the universe. You can watch a Gen Z-er learn about Limp Bizkit over on Nebula for the first time, or explore the storytelling of video games and then go back to Curiosity Stream and watch a show about big data or about the Internet. To get all of this, you can use the link in the description; it's so easy. CuriosityStream.com/trace. Link down below--26% off for a year of both services. And you can feel good about it too, because clicking that link directly helps me keep this channel going. On top of all of that, today--the day that this episode airs here on YouTube-- you can get all five of the episodes over on Nebula. That's right-- all of the episodes as one, giant mega episode on Nebula right now. So, CuriosityStream.com/trace, promo code: TRACE, 26% off for the year, and you get both services; it's only, like, $1 a month, and it supports me directly. Thanks for considering it. I really hope that you find it a valuable service. I think you will. Let's go back, though, to the science of time. Honestly, I think this series might have broken my brain a little bit. I think I said "now" like 45 times. I don't know. Hey, I'm just here for y'all. So come back on Wednesday for "The Psychology of Time." Please subscribe. I'm Trace. And I will see you in the future.

(Describer) At tracedominguez on Twitter, Instagram, Patreon, and YouTube.