What Is Nothing?

Thank you to M1 Finance for supporting PBS. This is a video about nothing. Like, it’s actually about nothing. What is nothing? Well, let’s think about it. Think about nothing. Are you picturing a black void? An empty room? Open space? Actual space? Or are you trying as hard as you can to not think about anything at all? The thing is, no matter how hard you try, you can’t think about nothing. But I can think about this. This is something that means nothing. But is zero nothing if it’s something? Are there other nothings? Or is nothing just an idea we came up with so we could better understand all the somethings in the universe? And if nothing is just the opposite of everything, does it actually exist?

[OPEN] Hey smart people. Joe here. I was just sitting here doing nothing. Well, actually, I was doing a lot. Sitting is something, but I wasn’t exactly trying to sit. I just let gravity take care of that. But I was also doing a lot of things that I wasn’t even aware of. I was breathing. Pumping blood through my body. I was digesting the food I ate earlier. Transforming the energy in that food into heat. It takes a lot of doing something just to be alive.

Nothing is a word we use a lot. What’s so funny? Nothing. What’s wrong? Nothing. What are you up to tonight? Nothing. What did you learn? Nothing. Most of the time when we say “nothing” we don’t actually mean nothing. “The absence of all magnitude or quantity. Not any thing. Nonexistence.” The idea of complete and total nothingness, a true, empty void, has bothered many great minds throughout history. And depending on where in history we look, the idea of nothing has existed, and not existed. And existed again, and then not existed.

Here are five pieces of candy. I’m going to share them with you. Wow. Thanks. Ok… I gave away five pieces of candy. How many do I have now? Zero. This feels like the easiest math problem ever, but for much of human history, we didn’t have any way to explain what’s left on the table. Because even this most obvious kind of nothing is not an idea we’ve had forever. We had to invent it so we could better describe reality.

Evidence of counting dates back at least 5,000 years. But zero, the numeral, showed up way after that. Exactly who invented zero and when, we don’t know for sure. But what we do know is that the first zero wasn’t a number meant to be used in calculations, like 5 – 5 = 0. It was just a placeholding symbol. The numbering system we use today is a “positional” system. It’s based on powers of ten. And the value a digit represents depends on where in the number it sits. We don’t even really think about this when we look at numbers, but this zero isn’t just a number. It represents none of something.

Here’s what I mean. When you read 2021, you know that’s two thousand, twenty, and one years. That zero isn’t the zero that’s halfway between 1 and minus 1. It’s just a symbol to hold that place that means “no hundreds.” So if we saw this number (2201), now the zero means nothing in the tens place. You probably learned all of this before you could even add and subtract. But this way of using zero was a major innovation in how humans think about numbers, one that was separately developed by many cultures from the Mayans to the Babylonians. But zero as a placeholder is not the same as mathematical nothing. As in what’s left of my candy.

Indian astronomers may have been the first to consider nothing as “something.” A number with no value. It started with a strange question: What happens when you subtract a large quantity from a small one? This was another big shift in how people thought about numbers, because if I have 5 pieces of candy, you can’t take 7 of them. There’s not 2 pieces of un-candy here. It doesn’t work… unless you think of numbers like this. This is a number line. Negative on one side, positive on the other. And a very important point in the middle. They called it Sunya, the nothingness. And they developed a symbol for it. A squashed egg-shape that looks pretty familiar.

Other mathematically advanced cultures like the Greeks didn’t use nothing or zero as part of their math, because their way of looking at the universe simply didn’t allow zero to exist. The Greeks tended to think of numbers using geometric shapes. To them, “pi” wasn’t 3.1415 yadda yadda. To them, pi is the ratio of a circle’s circumference to its diameter. Explaining zero with geometry, or shapes? Describing a shape with no sides would mean trying to explain something that isn’t there. A void. Zero is an important part of modern geometry. But the idea of a void, of nothingness, went against the prominent philosophy of Ancient Greece. There’s an old saying: “Nature despises empty space.” You can tell it’s old, because no one uses the word despises anymore. The saying means “nature dislikes empty space” or “nothingness” and it’s what ancient Greeks like Aristotle and his friends believed.

Aristotle came up with this thought experiment: Drop a marble in honey, and it’ll sink pretty slowly. Drop a marble in water, or some medium thinner than honey, and it’ll move faster. The less stuff there is to move through, the faster something moves. By Aristotle’s logic, something moving through a void, true nothingness, would move infinitely fast… it just didn’t make sense. So to Aristotle and his friends, the “void” was impossible. Instead, they believed that what we think of as empty space was filled with a mysterious substance, a fifth element beyond Earth, Water, Air, and Fire: the Aether. What later came to be known as “quintessence,” which literally means the fifth essence, an invisible something… everywhere there seemed to be nothing.

But another group of ancient Greek thinkers began to think nothing was real. They developed an idea called “atomism”: that everything is made of lots of tiny, indivisible things. Not quite the same as “atoms” as we think of them today, but lots and lots of small somethings moving in nothing… in a void. Where there are no atoms, there is just emptiness.

But what is “empty”? This box is empty, right? Of course, technically, scientifically speaking we know this box isn’t empty. Obviously, there’s air in the box. A cubic meter of air, down near the ground, has something like 10 trillion trillion air molecules. That’s definitely something. And that’s not all that’s in here. There’s dead skin, and other dust particles, and germs. But what if we sucked all that stuff out? Would we be left with truly nothing? Well, totally empty space might be impossible. We think of the vacuum of space as nothing. But there is stuff even in the emptiest places in the universe. One cubic meter of the interstellar space between galaxies contains maybe as few as 100 particles, but still something. Beyond particles, electromagnetic radiation, from x-rays to radio waves, exists everywhere. And just consider this: that no matter where we look, in any direction, we see electromagnetic radiation dating from the earliest days of the universe, traveling everywhere as the universe itself expands. There are some particles we can’t detect, and particles that seem to blink in and out of existence. Even the particles we do see are thought to be just visible blips of energy fields that permeate the entire universe, like waves cresting above an invisible ocean. Beyond all this, we think dark energy is a property of space itself, a something that’s everywhere space is, even if we can’t observe it. Space isn’t nothingness, it’s somethingness.

But what about at the very beginning of our universe? Maybe there was some nothing that our universe expanded into? According to most models of physics, there can’t be anything outside the universe, because the universe is, by definition, everything. The universe didn’t expand into empty space. Space and everything in it… expanded. When ancient Greek thinkers said that a truly empty void couldn’t exist… we’re realizing they were right, just for the wrong reasons. Unless… dark energy… is quintessence?! No. There are other ideas of nothing. Like absolute zero. The molecules and atoms that make up matter are always moving around. Temperature is a measure of those atoms’ kinetic energy. The faster atoms move around, the higher the temperature. If we reduce temperature enough that atoms themselves are totally still, that’s absolute zero. But while we’ve managed to get within a fraction of a billionth of a degree, no one has ever actually cooled anything to absolute zero. And here too, modern physics tells us getting to absolute zero is probably impossible anywhere in the universe, because of quantum effects at scales even smaller than atoms.

It’s taken us 3,000 years of trying to understand the universe to realize that outside of math, nothing can’t exist. And that’s a lot to think about. Let’s go back to thinking about nothing for a minute. Except we can’t. So what is your brain doing when you try to do nothing? The few pounds of mushy tissue in your skull accounts for just 2 percent of your body mass, but it uses 20 percent of your energy every day. In 1953, one scientist wanted to find out how much oxygen the brain consumes during vigorous thought. So he had some people do math problems and monitored how much energy their brain was using. Oddly enough, the resting brain appeared to be just as active as the calculating brain. That experiment didn’t get much attention, but new technology has let us see even clearer that the brain is up to something when we’re doing nothing. When your mind is wandering, when you’re not consciously focusing on the outside world, certain parts of the brain spring into action. A neural “nothing network.” Gram for gram, these brain regions use 30% more energy than regions involved in conscious thought. And these same regions become less active when we focus on something specific. Scientists think these brain regions may be where daydreaming happens. Why spend all this energy letting our minds wander? This seems to be when our brain analyzes past experiences so we can adjust our future behavior. Some scientists think that when our minds wander, or even meditate, it helps us process and store memories. Thinking about nothing, or trying to, may help us write the inner story of our lives.

So. We can’t make nothing. We can’t find nothing. We can’t think nothing. We can’t do nothing. But we can’t become nothing either. Even when we die, the atoms and elements that make up our bodies, the molecules in brains that held all our conscious existence, all of this will eventually become something else. Not us, but not nothing. And even when you or I are one day not here, we will leave memories behind in other people’s consciousness. All of us can still be something, even when, one day, we’re not here. Nothing is… a lot. And as always, I hope you learned… something. Stay curious.

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