The Knowledge: How to Rebuild Our World From Scratch (30 page)

Most societies devise their own system of measures for distance, volume, or weight. These units are usually on a human scale relevant to everyday life: a pound weight represents a handful of meat or grain, and the second is a division of time corresponding roughly to the heartbeat. Indeed, many of these traditional units have been directly based on the dimensions of the body, such as the foot, inch (thumb), cubit (forearm), and mile (one thousand Roman paces). However, the problem with these units is that they vary not only from person to person, but often
involve incredibly cumbersome conversion factors: the mile, for example, is equivalent to 1,760 yards, 5,280 feet, or 63,360 inches. What you ideally want is a standardized set of units that are interrelated and incorporate a convenient hierarchy of scale.

The system used today throughout the global scientific community, and almost universally for national administration and commerce, is the metric system devised in the 1790s amid the reorganizing fervor of the French Revolution.
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This international system of units (SI is the French acronym) defines just seven fundamental units, including those for length, mass, time, and temperature; every other measurement can be naturally derived from combinations of these units. Smaller or larger multiples of the core unit are restricted to the convenience of base ten, and indicated with an agreed prefix. For example, the meter is the standard unit of length, with smaller objects described in parts of a meter—a centimeter as a hundredth, a millimeter as a thousandth—and larger distances as multiples, such as a kilometer stretching 1,000 meters.

Alongside the meter, a second base unit is that of time—the second. Building from just these two base properties, using combinations or ratios of them, you can derive a great many other units. Multiplying two distances together (such as the length and width of a rectangular field) yields a measure of area, and consequently area always has units of distance squared. Multiplying three dimensions gives a volume, with units of length cubed. Dividing a quantity by time tells you how quickly it is varying—giving you a rate of change. So dividing a distance by time provides a unit of velocity, such as kilometers per hour, and
dividing by time again indicates how rapidly something is speeding up or slowing down: acceleration and deceleration. Units can be combined in ever-deeper degrees of derivation to describe further physical properties. The kilogram is the base unit for mass, and the density of a body—and so whether it will float or sink—is found by dividing its mass by volume. Combinations of mass and velocity yield measurements of the momentum and energy of a moving object.

So how can you reconstitute this system of measures and units from first principles in the post-apocalyptic world, if no graduated jug, set of scales, working clock, or thermometer can be found?

Starting with the meter as the primary base unit, you can derive many others from it. Build a cube-shaped container with each interior side exactly 10 centimeters long (one-tenth of your meter). The internal volume of this box is 1,000 cm
³
, or one liter. Fill the container with ice-cold, distilled water, and the water will have a mass of exactly one kilogram. Use a set of well-constructed balance scales (hang a straight, stiff rod from its midpoint if you need to) and you can use this liter of water to create any fraction or multiple of this unit by moving the mass closer to or farther from the pivot. To bring time into the fold you can utilize the pendulum we encountered in the last chapter. The length of a pendulum that swings each way (i.e., a half-period) in exactly one second is 99.4 cm, and even if you used a meter-long pendulum it would still be accurate to within three milliseconds—a hundred times less than the blink of an eye.
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So, building from the meter alone you can reconstruct the metric units for volume (liter), mass (kilogram), and time (second).

But how do you define the length of the meter for the survivors of the apocalypse, to allow them to unpack everything else from it? Well, the line drawn along the bottom of this page is exactly 10 cm long, and so from this seed the other units can be reconstructed.

All of these quantities discussed so far can be measured with very rudimentary implements—a graduated ruler or balance scales—but how would you go about devising from scratch an accurate gauge, meter, or instrument for measuring less physically tangible attributes, such as pressure or temperature? The general principles needed to design novel instruments will be essential for the scientific scrutiny of the inner workings of the world, particularly when you stumble across strange new effects and want to understand them.

One of the very first scientific instruments you will need to invent is intimately related to the puzzling observation that a suction pump can never raise water from a well more than about 10 meters, as we saw in Chapter 8. Fill a long tube with water, seal it at both ends, and then dangle it down out of a tall tower. Dip the lower end into a basin of water and remove the bottom seal. Water will flow down out of the tube by gravity, but not all of it, and you’ll find that no matter how you set up the experiment, the remaining water column is always about 10.5 meters tall (curiously, this is the same as the maximum height that a suction pump can raise water from a well). At the top of the tube you’ll notice a clear space left behind as the water drained away and where the air has not been able to reenter—a vacuum. The weight of the water column is held up by the force exerted at the bottom by the overbearing ocean of air—the atmosphere. Changes in the surrounding pressure are revealed in the rising or falling height of the column: it is a working pressure gauge. Using a denser liquid makes for a more practical barometer, and atmospheric pressure equates to only 76 cm of mercury (rather than more than 10 meters of water).

Such a barometer can be built out of any glass tube—and the elegance of such an arrangement is that it is naturally invariant in relation to the diameter of the tube used (as long as the diameter is constant along its length). The thicker the mercury column the more weight is pulling it down, but this is perfectly balanced by the increased force of atmospheric pressure pushing it back up—any mercury-column barometer will immediately give you the same answer, regardless of the details of its construction.

Once a novel instrument becomes available, it offers an unprecedented means for investigating the world and often leads to a rapid burst of new discoveries. For example, try hiking your new barometer up a mountain to explore how atmospheric pressure changes with altitude, or look for patterns and correlations between the finely fluctuating air pressure at your location and the weather. Medics today still quote blood pressure in units of the height of a corresponding mercury column: around 80 mmHg is the normal value between heartbeats.

Measuring temperature demands a little more cunning. The temperature of different objects is revealed to us by our own senses—we can feel whether something is hot or cold. But how do you build a device to precisely measure that subjective experience, to put a number on something’s hotness? The trick is to look for physical effects that correlate with your personal sensation: you’ll notice that as substances get hotter they also often expand. The next step then is to build a device designed to exploit this physical phenomenon for an objective expression of temperature. A simple heat-sensing device can be constructed with a long thin tube of glass, partially filled with liquid, and then sealed at both ends—such an arrangement maximizes the visible effect of expansion. Strap the tube to a ruler, and the height of the top of the fluid column provides a proxy for the temperature encountered. You can now measure the temperature of objects relative to each other, independent of your subjective perception.

But the fluid column height seen at different temperatures in a
particular instrument, and thus the measurement you get, will be entirely dependent on the dimensions and other idiosyncrasies of its construction (unlike the simple barometer we already looked at): you won’t be able to compare your results against anyone else’s. What you need is a standardized scale that anyone can derive and mark on their own instrument. And for that you need a way of determining fixed points: events or states of matter that always occur at exactly the same temperature and so can serve as a thermometric benchmark. It seems natural to base a temperature scale on water, as the changes in state of this substance occur over a range relevant to everyday life—from an icy winter’s morning to a steaming saucepan. Once you’ve got an upper and lower fixed point nailed down, it’s then a simple matter of regularly subdividing the range in between into a convenient round number of graduations to give a meaningful temperature scale. The Celsius scale is based on the freezing and boiling of water
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as fixed points, defined to occur at 0 and 100 degrees, respectively. But rather than using water itself as the fluid, you’ll realize that mercury expands far more uniformly for an accurate thermometer. For thermometers capable of operating at temperatures beyond the boiling point of mercury, for use in a kiln or furnace, for example, you will need to exploit other physical phenomena. Your investigations of electricity, for instance, will reveal that the resistance of a wire often increases with temperature.

This, then, is the fundamental process for devising reliable means for measurement of any attribute. As the recovering civilization discovers
strange new phenomena of nature, new fields of scientific research emerge. Means of isolating the properties of these phenomena and translating them into something that can be reliably measured must be devised before they can begin to be understood and exploited for technological applications. For example, when electricity was first stumbled upon, investigators struggled to quantify the properties of this new phenomenon, resorting to subjectively rating the intensity of the shock they received. But as the phenomenon was investigated, some of its repeatable effects were noticed and could then be employed for measurement—using the motor effect to deflect a needle around an ammeter dial, for example. And these scientific instruments aren’t just gizmos for the laboratory: they are also the thermometer that reveals your child’s fever, the meter monitoring the flow of electricity into your home, the seismometer serving as a sentinel for foreshocks presaging a larger earthquake, or the spectrometer detecting trace indicators in your hospital blood test.

These devices for measuring the world, and the standardized units they count in, are the basic tools of science. Knowledge of the world can be gleaned only by attentively inspecting it, or even better, by carefully arranging contrived circumstances to investigate a particular aspect in detail. This is the essence of the experiment.

An experiment is a way of artificially constraining a situation, to attempt to remove other distracting or complicating factors so you can focus tightly on how just a few features behave. An experiment is asking a clearly worded question of the universe and eagerly watching how it responds. Experimentation addresses the dissatisfaction with what nature happens to display for you, and forces it to reveal tightly defined facets of itself as you poke in different ways. Once you have controlled all the complicating factors and pinned down just one, you’ll then move on to the next, and so on, systematically interrogating the system until you understand how all the parts fit together.

As well as your instruments to extend the human senses and to
measure the results of different tests—a thermometer, a microscope, or a magnetometer—the meticulously constrained scenario demanded by a particular experiment often requires new contraptions: specially constructed scientific equipment designed to create specific conditions for you to study. Just as important, observations and results of your experiments need to be recorded numerically—adorning qualitative descriptions of what happened with measured, quantitative precision. But far beyond merely using enumeration to accurately compare different outcomes, the language of mathematics can be adopted as a powerful tool for precisely describing the behavior and patterns of nature, and the interrelationships between her parts. An equation summarizes a complex reality into its condensed essence. The upshot is that you can calculate the expected outcome in new, unobserved situations—you can make precise predictions.
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But for all of its careful observations, intricate experiments, and condensed equations, the absolute essence of science is that it offers a mechanism for you to decide which explanation is most likely to be the right one. Anyone with imagination can construct a tale that neatly accounts for the ways of the world—where rain comes from, what happens when something burns, or how the leopard got its spots. But these are no more than entertaining diversions—etiological Just So stories—unless you have a reliable way of selecting which one is more likely to be correct.

Scientists construct a best-guess story based on their prior knowledge and what’s already been established, called a hypothesis, and design particular experiments targeted to test different predictions of this story—systematically poking and prodding the hypothesis to check
how well it works, or to inform the choice between competing proposals. And if this account withstands the tests of experiments or observations many times, and is not found wanting, then it becomes a well-founded theory and we can have confidence in using it to explain other unknown aspects. But even then, no theory is ever inviolate: it could itself be torn down later, undermined perhaps by new observations that it cannot account for, and replaced by an explanation that offers a better fit to the data. The essence of science lies in repeatedly admitting you were wrong and accepting a new, more inclusive model, and so, unlike other belief systems, the practice of science ensures that our stories become steadily more accurate over time.

In this way, science isn’t listing
what you know
: it’s about
how you can come to know
. It’s not a product but a process, a never-ending conversation rebounding back and forth between observation and theory, the most effective way of deciding which explanations are right and which are wrong. This is what makes science such a useful system for understanding the workings of the world—a powerful knowledge-generating machine. And this is why it is the scientific method itself that is the greatest invention of all.

But in the hardships of a post-apocalyptic world, you’ll not be immediately concerned with accruing knowledge for its own sake—you’re going to want to apply that understanding to helping improve your situation.