The Power of Inertia

A foundational principle of physics is also my most helpful decision-making tool

© 1995 Watterson/Dist. by Universal Press Syndicate

in·er·tia /iˈnərSHə/ (noun) — a property of matter by which it continues in its existing state of rest or uniform motion in a straight line, unless that state is changed by an external force.

de·ci·sion-mak·ing /dəˈsiZHənˌmākiNG/ (noun)— the action or process of making decisions, especially important ones.

The idea that ‘an object in motion tends to stay in motion unless acted on by an outside force’ is something most people remember faintly as a thing they learned in a science class they tolerated but have never used or cared about since. I am here to suggest that this concept — inertia — is not only Newton’s first law of motion but also the most powerful force acting upon your life, and that noticing its effect allows you to harness its power for your benefit. Not in some vague mystical sense tinged with the charlatanism of self-helpery, but in a direct and practical way.

My initial recognition of inertia as a social concept was related to employment. People I knew who began working jobs sooner in what ultimately became their chosen profession held more senior positions and were earning more than those who took a longer amount of time to find and invest time in their true calling. This may strike you an obvious observation. To wit: The sooner you start the farther you tend to go. But it wasn’t until I started noticing the same concept taking effect in other areas of life that I realized a deeper principle could be at work.

For example, a related concept has to do with forming habits. Habits are a technique for doing something more often (akin to grooves formed from repeated use which, in turn, form a path from which it’s more difficult to deviate), but the benefits resulting from this frequency (i.e. familiarity, understanding, or expertise) have to do with the power of inertia. The more often you do something the more you will tend to continue doing it. Or, as Annie Dillard phrased it: “How we spend our days is, of course, how we spend our life.”

Pairing these aspects of continued motion — start time and frequency — naturally leads you to the financial domain and the idea of compound interest. This refers to interest calculated on the initial amount and also on the accumulated interest of previous periods. It’s interest on interest, which means as you deposit more cash you’re also increasing the amount of earned interest at the same time. The cumulative effects of compound interest are why parents and other advice-givers implore us to start saving for retirement as early as possible, and to keep our money in a retirement account full of index funds rather than under a mattress or in a new car. The sooner you start the more you will benefit, oftentimes even more than if you started later but deposited larger amounts. This idea keeps you focused on long-term payouts — whether with money, relationships, health, activities, habits — rather than short term gains. The ability of time to accumulate effects is often underestimated, which is why this idea of inertia is an important one to keep in mind.

Physicists are very familiar with the unexpectedly large cumulative effects of continuous motion, not only because of the nature of their jobs but because of their tool: math. The earth orbits the sun as a result of its tendency to stay in motion while being acted on by the curvature of spacetime, and we feel this motion as gravity. (Einstein famously showed that gravity is acceleration) Gravity is the reason a toy car rolls down a wooden slope for a few seconds and lands at the bottom. If you want to know the car’s speed at any point, you use calculus to find its derivative at a given moment in time. You can plot all of those moments onto a graph and connect them into a line or curve, and the slope (“rise/run”) of that graph line at a given point is the toy car’s speed (“miles/hour”) at that very moment. Easy enough. But what if you want to know the cumulative effects of all those tiny changes in speed? What does the accumulation of all those little instantaneous changes look like? That’s the integral, and the integral is the entire area underneath that single graph line you drew. That’s a huge amount compared to the little line that merely forms its upper boundary. This is why scientists and mathematicians are more likely to have an intuitive feel for the power of accumulation than non-physicists like me. I needed to borrow their tools in order to share their intuition.

This gravity example brings me to another point about the power of inertia, which has to do with how easy it is to stop something. To get something moving from a resting position takes more effort than keeping it in motion once it’s already going. This is a physical fact of real world objects. You probably have an intuitive feel for this concept, having had to push a heavy door or bowling ball and finding it requires much less effort once it has picked up a little speed. You’ll also grasp the idea that a slow moving bowling ball that’s just getting going is easier to stop than one at full speed halfway down the lane. The amount of inertia something has varies according to its mass. The more inertia something has, the more mass it has. A more massive object has a greater tendency to resist changes once set into motion. I use this fact to remind myself that bad habits, undesirable relationships, or terrible jobs are easier to quit sooner rather than later. They grow more heavy the more inertia they accumulate. This inertial decision-making tool is actually the inverse of the others: The sooner you try to stop the easier it is. And, conversely, the longer something heavy stays in motion the harder it is to stop.

Then there is the converse of Newton’s first law itself: not only does an object in motion tend to stay in motion, but an object at rest tends to stay at rest. What you do you tend to continue doing, which includes nothing at all. Inertia usually explains why people remain in jobs or relationships they don’t like.

After identifying this heuristic for myself I started to see inertia everywhere. This is important, because metaphors aren’t just about being clever in spotting resemblances, they’re actually helpful. They provide a way to think about abstract things more simply and intuitively. Not only that, but once you attach a word or concept to something the more you will tend to notice it. Words help us, quite literally, to see.

Here are some other ways I’ve applied the idea of inertia as a tool — or what the philosopher Daniel Dennett calls an ‘intuition pump’ — when it comes to making decisions:

  • When thinking about investing in cryptocurrencies I decided to invest sooner, when the cost of low and upside of potential appreciation enormously outweighed the downside of losing my investment, rather than wait to see if the prove legitimate and viable first and lose the ability to accumulate effects.

Fine, you may be saying, but why in the beginning did you claim that inertia is “the most powerful force” acting on our lives? Surely there are other forces or ideas that are more important like, say, hard work, or mindfulness, or health, or love, right? Yes, all of these things are tremendously important, but all of them are beholden to the idea of inertia explored here.

The sooner you start the farther you tend to go and the more you will benefit.

The more often you do something the more you will tend to continue doing it.

The sooner you try to stop the easier it is.

What you do you tend to continue doing, which includes nothing at all.

Cicero once claimed that gratitude is not only the greatest all virtues, but the parent to all others. I would make the same claim of inertia: it’s not only the greatest of all my decision-making principles, but the parent to all others.

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