Have you ever wondered how our units of measurement came to be? Why do we measure a gram by the mass that we do instead of by some other arbitrary mass? Why is a meter the length that it is?

You might be surprised to learn that the story of how we measure things is not as precise as you might expect. For instance, the metric system itself is ultimately determined by a bunch of scientists who sit on the International Committee for Weight and Measurements. Since doing good science requires that our units of measurement remain relatively constant, it's a weighty responsibility, but also one that occasionally requires an overhaul.

The last big overhaul of the metric system came in 1960, when the meter was officially changed from being measured according to an actual meter-long metal bar, to being based on a particular distance that light travels in a vacuum. Now for the first time in nearly 60 years, a new overhaul is coming ... and it will forever change how we think about the kilogram, reports Science Alert.

Currently, the kilogram is the last of the seven basic units in the International System of Units (SI), or metric system, that is still defined by a single physical object, known as the International Prototype Kilogram (IPK). It's an actual lump of metal, made of 90 percent platinum and 10 percent iridium, that's sitting in a vault in France. Replicas have been made, but without this lump of metal, we'd have no true point of comparison to make sure they're accurate.

As you might imagine, this isn't the most reliable system. In fact, scientists have noticed that the IPK has actually changed mass over the years as it has shed or gained atoms just like any physical object might. That's not good, since so many scientific assumptions are based on the mass of a kilo staying the same.

There might finally be a solution, however. A new proposal, set to go into effect in 2018, has recommended that the mass of a kilogram be based on Planck's constant, which is the quantum of action in quantum mechanics. This would tie the kilogram to a constant property of nature instead of to the IPK, a substantial upgrade.

The reason it has taken so long for the International Committee for Weight and Measurements to make this upgrade is that scientists have had a particularly difficult time calculating the precise value of Planck's constant. But an agreement was seemingly reached in 2014, and no major objections have arisen since.

Three of the other basic units, the ampere (which measures electrical current), the kelvin (which measures temperature), and the mole (which measures the amount of substance, in chemistry), are also receiving upgrades in the new proposal.

For most people, these changes won't mean anything. The differences in measurements are minuscule. But scientists will certainly appreciate the upgrade, which will lead to more precise calculations.

The event has been dubbed a "once in a lifetime" overhaul, though by anchoring the metric system in the fundamental laws of physics, future overhauls should become less necessary. That is, assuming that our understanding of the laws of physics doesn't radically change anytime soon.

So by 2018, assuming that no major objections are raised concerning Planck's constant, the IPK will go from invaluable hunk of metal locked away in a vault, to just another lump of matter. Sentimentality aside, that should actually be a comforting thought for those who aren't comfortable with change.

Bryan Nelson ( @@brynelson ) writes about everything from environmental problems here on Earth to big questions in space.

The kilogram will no longer be defined by a single lump of metal in 2018
All standard units of measurement will be defined by a constant property of nature — and be more precise.