Ten years ago I lived in Boone, in the mountains of North Carolina. Boone has an interesting mix of the political spectrum. There are good old boys mixed in with flower children. It’s a bit of a hippie enclave amid a sea of conservatism. In one day, you hear a very wide range of what’s-wrong-with-the-world.

One of the few things everyone agreed upon was that there were too many tourists moving into town. Too many people in general. Overpopulation is a rare area where the left and right both see a problem. Except that the problem does not exist. It hasn’t for a long time. And it’s not going to become a worse problem in the future.

When the “population bomb” books starting coming out in the 70s, they were already wrong. Population growth was no longer accelerating upward; it was decelerating. How was that possible when the number of people on the planet was going up, up, up? To understand this is to understand the difference between velocity and acceleration.

When I throw a ball straight up into the air, I accelerate it with my arm, using my muscles to impart lots of energy into the ball. When I release the ball, it soars higher and higher. But it’s no longer accelerating upward. Even though it has velocity, that velocity is shrinking and shrinking. Pretty soon, the ball reaches the top of its flight and falls back to the earth.

Population growth is possible even when acceleration is negative, if it already has a lot of energy imparted. This is because acceleration can have velocity. It’s like stomping on the gas or letting off the gas. Letting off the gas gradually is one way to come to a complete stop. At any one point, it’ll look like you’re still accelerating (your foot is on the gas), and you’ll think your velocity will continue forever. But the direction of acceleration tells the whole story.

Another example, because it helps to hear it twice. This time with more accuracy about what acceleration is. Right now, you are experiencing the accelerating force of gravity tugging you toward the center of the earth. It’s just that the chair or floor is in the way. The heaviness you feel of your own weight is due to the acceleration of G, or gravity.

When a rocket sits on a launch pad, it is accelerating downward as well. It’s just not moving, because the concrete pad is in the way. So its velocity is zero while its acceleration is 9.8 m/s^2 downward. When the rocket fires, its acceleration slowly reverses. That downward arrow becomes smaller and smaller until it becomes zero. At that point, the rocket has zero velocity and zero acceleration. This is when the people who built the rocket feel their butts clench up. Velocity moves upward as the acceleration becomes positive, overcoming that constant 9.8 m/s^2 of gravity.

As the rocket shoots upward, velocity becomes massive. Here’s where we found our population explosion of the early twentieth century. Lots of velocity and lots of acceleration. But the rocket soon runs out of fuel and the nozzle goes silent. That was us decades ago, no longer accelerating upwards. Now the rocket is coasting. Soon, it’ll crash back to earth.

It may seem laborious to detail this interplay of velocity and acceleration, but numbers mean nothing without understanding where they came from and where they are going. Understanding trends is to understand numbers in motion. It requires some grasp of these concepts. If I tell you the replacement fertility value is 2.1 (the extra 0.1 to account for not every child surviving to adulthood), and then tell you that our current value is 2.5 globally, you’ll think we have growth with no end. Except that the number of children per couple was twice this number fifty years ago. Our foot has come off the gas in a very big way. By 2050, we will be close to the 2.1 number of mere replacement. That’s when the rocket starts falling back to earth. The nozzle is already sputtering, and there are zero indications that it’ll turn back on.

That year of 2050 is significant in that once you see it you won’t stop seeing it. That’s because any article or statistic meant to sow fear of population growth will only list that year and none further. It’s the last year we expect to see the world’s population tick upward. For the last twenty or so years I’ve seen that 2050 number from all the fear-mongers. It’ll be interesting to see how little effect this tactic has as we inch closer and closer to the actual year. 2040 is not so far away, and by then we will all be discussing population collapse in our everyday lives. It’s worth boning up on the subject and preparing for those discussions today.

I started thinking about this anecdotally many years ago, because of personal trends around me. My grandmother had nine siblings. I had two. Among my brother, sister, and myself we have zero children. Looking around at my peers, I noticed a handful having two kids, many having one or none, and almost nobody having five or more. I often wondered where all these extra billions would come from. For every couple you know isn’t having a child, think of how many who are having four to compensate. Or for every only child, how many parents have three children. Anecdote is not data, but the data supports your observations in this case. And it’s not just here.

Today, almost all population growth in the world comes from India and Africa, but they are also letting off the gas. They are the last sputtering of the rocket’s nozzle. The same trends will take place there as elsewhere, only slightly delayed. This makes sense, because lower fertility rates generally come after women have more wealth and opportunity. When women have the freedom to choose, some choose a balance of work and family, or to focus solely on work, or simply to not have kids. The lowering of the stigma of being single, of being gay, also contributes. Population explosion was mostly a measure of women and men not having the choice to not have kids. Now, many choose other focuses. And they have the means to do so.

There are all kinds of forces at play here to affect those choices. In agrarian societies, kids are a source of labor and wealth. In a consumer or services society, kids are a drain on finances. They have gone from being the workforce to being the work! Parents make choices accordingly. The aggregate of these choices is leading to a shrinking world population this century. What will that look like? Some people are absolutely terrified. But it’s difficult to understand why.

One fear is that demographics will change to the point that we can’t care for the elderly. There won’t be enough young people to work in an economy to support the aged and infirmed. This is a really, really weird fear considering that our current economy is based upon caring for a huge number of young people who are economically worthless and physically feeble. We care for children from the day they’re born to at least 18, if not 25. (My mother would say it never ends.) Parents spend a good 20-30 years making sacrifices for a demographic that doesn’t contribute much in return in the way of GDP. The idea that we can’t or won’t care for a population in their 80s and 90s is absurd.

It’s even more absurd because we are already showing how it will be done. Partly by the older populations taking care of themselves and each other. My mom doesn’t need any help in life (except with an occasional Friday NYT crossword), but she lives in a retirement community with a wide range of those needing help and offering help. She has never been more physically and socially active in her life, and I for one am counting the days until I can qualify for a neighborhood with a minimum age requirement. A small number of staff (not necessarily young themselves) is able to care for a larger group of people. Exactly what our school systems do now to care for a youth demographic reliant on others to feed and clothe them. We won’t have both of these challenges at the same time. Society will slowly shift from managing large groups of children to managing large groups of elderly. The amount of work may even be far less, and we will have many tools and advancements to help us by then. (We will also have an elderly generation that is wholly comprised of digital natives who will likely be clamoring for video games, VR headsets, social media, and Netflix).

The future will be very different from the present, and I believe in a good and interesting way. We will see more people my age living with their parents, and not just to help them but for the enjoyment and the company. This might seem alien, but we will adapt. Future generations will marvel at the idea of us having lived with three siblings all under the same roof, just as today’s generation marvels at the idea of ten siblings living together. Things change.

Another thing that will change in the future is the world’s racial makeup. Much of the political upheaval in the US and UK today is a reaction to these trends. Brexit was enacted amid tabloid headlines of the dangers immigrants posed, and Trump won largely on the promise to build a wall. The fear of racial shifts in the short term are an interesting contrast to the flow of racial makeup over the longterm. Populations are not static and never have been. If you watch a historical time-lapse, you’ll see adventurers from Asia sailing across the Pacific to the Americas, then a burst of Europeans appearing, then Africans. The mix moves and shifts. The United States will have briefly appeared mostly white, but it will only be a blip. Attempts to forestall the shifts or control them are both futile and misguided. (A recent report suggests that racist policies from the Trump administration will delay whites becoming a minority by a whopping five years. All that evil for the briefest of delays.)

Trying to control the racial makeup of a country is a bizarre fascination. For the racists, there will always be enclaves to go join, gated communities that are hostile to diversity, so why not enjoy the bunkered and sheltered life and stop worrying about population trends around you? One theory that rings true is that those who stomp on minorities do not look forward to becoming one. If you think being in a minority is bad, perhaps work harder to shore up equal treatment methods while you can. Because the population of the future is going to be darker than the present. If this disturbs you to any degree at all, you have some racism to work on. If it doesn’t disturb you how the Americas were conquered or how Africans were enslaved, then ditto. I think we can simultaneously accept that history has happened, know that history, be disturbed by it, love ourselves and each other in the present, and also grasp that the future will be alien to us. All these things are true.

Some very clever people will continue to attempt to sow fear about population changes. For many years these were the folks who thought the Earth couldn’t support us all. They were wrong. Now you’ll start hearing from those who say population declines will be the end of us. They are also wrong. At some point we will find an equilibrium. It might be a few billion. It might bounce up and down between some minimum and maximum. But we will never go back to the days of uncontrolled growth, because choices will not diminish going forward. There will be more and more interesting things to distract us and more control over our sexual outlets and our reproductive outcomes. What some fear, I believe, is that population contraction will lead to economic contraction. To which I say, “so what?” It is very possible that economic contraction means we no longer have the job specialists required to build large yachts, nor the compounding interest in a small number of hands to afford said yachts. That may be the end of some people’s worlds, but it won’t be the end of the actual world. Speculating about the future that awaits highlights our values, doesn’t it? As cities empty out and entire countries no longer have the growth needed to support their populations, we will probably gather in smaller pockets of the earth. Large areas will return to their natural state, and we will visit these areas and live only sparsely there. Will anything be lost if Venice is abandoned while Milan becomes more diverse? Sure. But only if you hold the naive belief that Venice was ever going to be permanent.

The very continents we live on will no longer exist some day. They will slide back to the magma while other continents rise. It’ll happen so slowly we won’t notice it, but shorelines have already changed in my lifetime. Demographics have shifted during my 45 years. That will continue. We won’t need to flee to Mars or fly off to the stars to see a new world, because one is forming as you read this. It’ll be very different, but we’ll still be here in some number, in some mix of colors, hopefully caring a lot less about measuring either of those things.