It probably goes without saying: Trying to understand the entire universe is nearly impossible. Fortunately, it’s also really simple. We’ll try to find some middle ground, honoring both the simplicity and the impossibility.

First, there’s only one universe¹. That’s good news and bad news. Only having one thing to study means there’s less to be looking for, but it also means we can’t compare this universe to others. There’s no “control” group when you study the universe. It’s all or nothing.

Well, actually, it’s “all.” It contains everything. This is a good definition of the universe: the container of all space and the backdrop for all of time. Within that time and space you have a kind of gameboard, and all of the rules of the game and all of the pieces are played within.

For us, the question is, Where did that everything come from and what does that everything look like and how does that tell us anything at all about the beginnings? Oh, and also, where is it all going?

To get a sense of what we’re talking about, I like to show an image produced by the Hubble Space Telescope early in its career. But first, imagine holding a pencil, and then holding that pencil in your hand at arm’s length away from you, and then hold that pencil up to the sky and consider the amount of sky that is blocked by the very tip of the pencil. Got it? Just a little point in the sky. Oh, and make sure the part of the sky you’re looking at is a dark part, not with any stars in the way. 

Take a moment to consider that penciltip of dark sky.

Okay.

So, that dark, minute fraction of a sliver of our view of the universe actually looks like this:

Each one of those blobs of light (remember, in this pencil tip of space) is a galaxy, an entire island of stars. Each of these islands holds on order of 100 billion stars, and there’s on order of 100 billion galaxies in the universe.² You can go ahead and multiply these together to get an idea of how many stars (each with possibilities of planets orbiting about) there are in the universe. I don’t know what to say about this number, actually. I write it out and stare at it but I don’t really understand it in any real way.³

So, this gives you a sense for the stuff out there, but we also want to consider the space that allows for all the stuff to exist. For us to start to get a handle on this, all we do is look in all directions and we see pretty much the same thing everywhere we look: galaxies. We say the galaxies are distributed homogeneously and isotropically, which is just to say that every direction and every place has the same distribution of galaxies. You might think this is obvious, but it didn’t have to be this way. And yet, we’re pretty happy that it’s this way because it tells us that space is all equivalent. There’s no place that’s any more specialized than any other. 

Also, the space goes on forever and ever. But it also has a finite amount of stuff in it, distributed uniformly. Okay, sure, that sounds obvious, too. Until you sit with that just a little longer. How can something go on forever, have a finite amount of stuff in it, and be uniform throughout? 

I’ll wait.

Okay, here’s how I picture this. I’ve invented a universe that I actually can step outside of. In fact, I can actually draw it on the page. I call it Circleland.⁴ Imagine that you can live on the line of the circle, but you can’t understand any space beyond that inked, one-dimensional curve. In fact, you can’t even tell that it’s curved or that it’s a circle. You just know that the line you can travel and see goes forward and backward, or left and right—I’m not sure how a Circlelander thinks about direction since there’s only two of them. At any rate, your only sense of space is along the one dimension that just keeps going, and you can only go two different directions. We, here outside of that page, might feel sorry for Circlelanders, but they don’t know any different, just as you don’t know anything other than three dimensions of space. After all, what else could there be? Your imagination might be a little bit limited simply based on your existence.

I bring this up because it gives us a useful way to picture space from the outside. We don’t normally get a chance to do this with the space we’re already in, so I like looking at other simpler spaces so I can imagine what extra dimensions look like.

Hold this picture for a moment.

Back in our own universe where we move around in three spacial dimensions as time moves us forward in another, we can observe distance galaxies that HST slurps up with such aplomb. In the early 1900s, Edwin Hubble observed that all distant galaxies were getting farther away from our own, and the farther away they are the more quickly they seem to be moving⁵. A rough sketch of this might look something like this, with arrows representing the perceived recession of galaxies from our own location:

To me, at first glance, this looks like we’re at some center and everything is flying out away from us; and it even looks as though the stuff that’s farthest has had a chance to move more and is now going faster, as if it had seen us coming. But this doesn’t make sense for a few reasons. First, we’ve realized that every time we think we’re at the center of the universe—or at the center of anything, actually—it becomes clear that we’re wrong. So we should have learned to inhibit that reaction by now, though that’s hard for us humans. We like to be at the center of lots of things. 

Maybe more convincing is the overwhelming evidence that the universe is the same everywhere and in all directions. If that’s the case, then we can’t be at the center. In fact, an infinite and smooth universe doesn’t have a center that you can exist at. This is hard to picture, but having Circleland as an analogy helps.

The center of Circleland can’t be visited or even seen or even pointed to by its residents. They only point along the surface of the circle. But if their circle gets bigger, expanding from that center they can’t see, look at what happens:

Your Circleland neighbors all are getting farther away from you; but if they are looking back at you they will claim that you are the one becoming more distant. In a sense you’re both right, and you’re both wrong. Not one of you is moving, it’s just that the space between is getting greater⁶. Everyone will agree on the observation that you are all getting farther away from one another. More interesting still: There’s more space between you and your more distant neighbor, so as the circle gets bigger that recession is faster. In other words, the farther apart two points are to begin with, the faster they’ll separate. Again, everyone will observe the same features of this expansion, feeling as though they’re staying in place (which is basically true) while everything else is getting more distant (also true, but not for the reasons we might naturally assume). 

Spend a little time with the idea of living on Circleland, and then think about the similarities to our own sense of space. I can’t point to the center of our own universe, but our expansion is such that we must be limited by our existence in the wretched prison of only three dimensions of space. There could be an expansion from some central point in another dimension, even if that point doesn’t exist in our standard three dimensions. 

Chew on this for a second. Maybe go get a snack. Take a deep breath. 

Once you’re ready, consider this: If everything is expanding, then where did it all come from? 

To me, this is the easier problem to solve. You just take the current pattern of expansion and you rewind⁷ it back as far as you can. Then you can answer the question, Where does it all start? 

In Circleland, it’s pretty clear that the start—and this would be the start of some kind of clock for the entirety of space’s existence—would be when the space itself was all condensed into a single point. You could say that it’s really really small, although at the same time it’s the entirety of an infinite universe. Ah, the paradox. I’d like to suggest it’s like some kind of poem or song, but the idea isn’t that it’s metaphorically small and big at the same time. It truly is both of these things at the same time.

This start from a what’s known as a singularity that holds all of our physical existence and marks the beginning of time is referred to as the Big Bang. This was originally supposed to be a sarcastic description of the ridiculousness of the whole idea, but the name stuck. To call it “Big Bang” is both an understatement and a ridiculous embellishment. It’s not just a “bang” or “big.” It’s everything’s beginning. But it’s also not an explosion into space, but the breath that inflates the very structure of space itself. As with so many things, I don’t really know what to tell you to make of this. It’s big and subtle and everything and very little all at the same time. 

To be sarcastic about a “big bang” feels merited in so many ways. It’s a ridiculous idea, audacious to claim that we know the beginning of the universe and the ability to rewind 13 billion years to describe the very moment in which the existence of all things began. You should very definitely be asking, How do we know that?

One piece of evidence is the very simple idea of taking the expansion we currently witness and rewinding it. While the process and details here are not simple, the basic idea is. When you look for patterns in motion you can extrapolate to see where the simple rolling ball has come from and where it’s going. The idea here isn’t much different. We see a certain pattern and we understand the basic rules. We can re-create the scene from those basic principles, and it’s easy to go back to a beginning point from that.

But this certainly shouldn’t be all that we use to make the claim. There should be more evidence to search out. So, we think about what an early, dense universe would feel like. Lots of subatomic particles in very close confines with lots of energy. Unlike our current regime in which particles are spread out and generally repulsive, these charges particles would be forced together in nuclear fusion. This produces two things: New forms of matter and the resulting energy from these reactions. 

The most basic and prevalent element in the universe is (and should be) hydrogen. It has a single particle at its center (a proton) that is completely uncomplicated by anything else. To make an element with anything else at the center you need to form these from smaller pieces. This happens in the center of our Sun right now, but it would also happen in a dense early universe. The net result would be a big production of the next most complicated element, helium, with its two protons and (typically) two neutrons. So, you would predict that if the big bang were a real occurrence, you should see higher amounts of helium than other elements besides hydrogen, and sure enough we do: about a quarter of the known matter in the universe is helium, way more than what stars could have produced on their own.

And also, there’s that energy. The cosmic microwave background, a radiated energy that would be everywhere throughout the universe, even as it has continued to expand, is a predicted indicator of this. You “see” some of this background energy in static on a television channel connected to an antenna but picking up no programming⁸. We can also study this and see that the energy is really smoothly distributed everywhere in the universe, though it’s just lumpy enough that you can imagine how the first seeds of galaxies formed from clumps of matter accumulating. 

So all of this helps us to understand the really big picture of the universe. It’s a simple picture, but there are big implications and big questions, like what makes the expansion? If gravity structures space itself and there’s all this stuff, why isn’t there enough to pull it all back? You might think about scenarios where the universe had so much stuff that gravity was more dominant; or the case in which the universe expanded more quickly early on so that gravity’s hold on space was much less. In either case you wouldn’t be here to be conscious of these very questions. It’s likely that there’s no other universe that you could exist in. On the other hand, there’s no other there must be multitudes of other universe possibilities, none of which could have had the right conditions for self awareness, not to mention scientific study.

But it’s more than simply the right universe. To be you, there has to be a galaxy with the right about of space and time, sure. But also you have to have more elements than simply hydrogen and helium. Carbon, nitrogen, oxygen, and so much else doesn’t come pre-fabricated in the universe we’re describing. You need more time and you need some kind of factory to produce the elements that make chocolate, Doritos, kittens, beer, and us. 

In truth, there’s quite a bit more to contend with here. Based on the overall proportions of the universe, you’d think we should have more hydrogen and helium, but it’s not as pervasive on Earth as on other, cooler planets. There are some interesting dynamics going on there, but for now let’s focus on the elements we deem essential to Earth and our existence.

We organize the elements on this periodic table. Essentially, this should be your ingredients label. This codes elements according to when they were discovered by humans:

It’s interesting to see that when things were discovered isn’t necessarily in any kind of order. There are some surprises, like the fact that helium eluded us for so long even though it’s the second most abundant element in the entire universe. Part of the reason is that helium doesn’t interact with other elements very often. The other reason is that it isn’t as abundant on Earth as it is on other planets or the Sun.

Anyway. I just thought you should know that or stick it somewhere in the back of your psyche for some other time when you’re wondering what to think about. The real task at hand right now is to question why we have anything beyond hydrogen in the first place. All the rest of it has to have evolved in some other fashion. It turns out that the energy factories of stars have to convert one form of matter to another, and the generalization of this process (known as nuclear fusion) is that you end up with elements—waste products, really—that are higher up on the periodic table. This other version of the periodic chart shows the various origins, as far as we know, of these more complicated and essential (to us) elements:

In a nutshell, the materials that you are assembled from have to have come from really energetic reactions that combined lighter elements together. Carbon, for example, would in most cases be formed by three subsequent collisions and fusings of helium. But that isn’t very likely unless the helium is really close together, moving very fast (we’ll see later this means high temperatures), and there’s a whole bunch of it really concentrated. This is exactly the kind of environment you’d expect in the core of a star. 

The trick is that if we’re made of stuff that was sourced in other stars, then those stars would have had to have already cycled through their entire existences and then shed all their materials for us to re-form in the creation of another star. Our Sun, then, is a recycled collection of parts from which we get to rebuild. You are star stuff, as they say. What you are created from and what you continue to build from and what you continually interact with (breathing, eating, touching, etc.) has all been on the insides of another distant, long forgotten star. 

I can say with great confidence that I know this isn’t all there is to it. You aren’t simply the byproduct of a universe with just the right conditions, nor are you the simple amalgamation of elements that happen to have been recycled in long dead stars. Of course there’s more to figure out. The nature of life itself is way more than the sum of these elements or the final outcome of all these events. But this story—a universe that gives time and space for the development of elements that can then be use in the creation of compounds that can be stirred together in the right conditions and temperatures and stewing to allow for Doritos and kittens—still has more to it. Physics is a big part of this, and we’ll keep working out those pieces.

1. Okay, well, there’s only one universe that we can study by harvesting evidence about time and space and all that’s contained there. We don’t study other universes because we can’t collect data on them. We’re “trapped” in our own universe so we don’t have a way to test ideas about others, or even know if they exist at all.  ↩︎
2. This is an approximation on the low end of all likely calculations. I didn’t want to exaggerate, after all. ↩︎
3. And yet, that number of stars is less than the number of water molecules in a teaspoon. ↩︎
4. As far as I know, no one else has invented Circleland. I’d like to think it’s my own baby universe. But I got the idea from a more complicated universe called Flatland,the subject of a piece of fiction written in the late 1800’s by Edwin Abbott. You should look it up: https://en.wikipedia.org/wiki/Flatland ↩︎
5. We say they were “redshifted.” The light from these most distant galaxies was stretched out to longer wavelengths. This is most pronounced the farther away the galaxy is. ↩︎
6. Upon reading this statement a second time, I recognize that this is both super simple and ridiculous. ↩︎
7. I’m trying to decide if “rewind” is always going to make sense as a verb. If you grew up with cassette tapes and VHS like I did, this is naturally the right action. If you grew up with CDs or mp3s or streaming services then there’s no “rewind” because there was nothing that was ever wound in the first place. I’m sure you’ll be fine and your lives will all be fulfilling and interesting, but I can’t help but think that you missed out on something. ↩︎
8. When I was growing up, we could turn the dial to channel 3 or 4 and see this regularly because I lived far enough out of town that we didn’t have cable and there were plenty of empty channels. I imagine that there are many people today who have never seen a television channel that’s empty like this. It looks about as exciting as you would imagine, just a bunch of static flashes and a white noise that sounds less interesting than rushing water. But if you imagine that some of those flashes are harvested from energy from the beginning of the universe, it becomes a little more exciting. ↩︎