The Hidden Truth About Units: Why Physics Constants Aren’t as Fundamental as You Think

By J. Rogers

We like to think of the laws of physics as fixed, universal truths. The speed of light, the weight of a kilogram, the tick of a second—these seem like unshakable foundations of reality. But what if we’ve been fooled? What if these "constants" are just accidents of human history, shaped by arbitrary choices about how we measure the world?

Turns out, they are. And realizing this changes everything.

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The Speed of Light: A Unit Conversion, Not a Cosmic Law

We’re told the speed of light is 299,792,458 meters per second. But that number isn’t written into the fabric of the universe—it’s just a conversion factor between two human-made units: the meter and the second.

• 
  If we had defined the meter as half the distance light travels in a second, the speed of light would be 599,584,916 m/s—but nothing about light itself would change.

The takeaway? The speed of light isn’t "fundamental"— the number c with units of m/s just defines the meter against a second, it is just a bridge between our definitions of space and time.

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The Second Is Arbitrary (Thank You, Earth’s Rotation)

Our entire system of time is based on Earth’s rotation:

• 1 second = 1/86,400 of a day

• But Earth’s rotation is slowing down (thanks, tides!)

• 
  We later redefined the second using atomic clocks (9,192,631,770 oscillations of a cesium atom), but that’s still a human choice.

What if Earth spun twice as fast?

• 
  A "second" would be twice as long in our current seconds.

• Frequencies (Hz) would halve—a 440 Hz musical note would now be 220 Hz.
  
  

• Planck’s constant (h) would numerically halve, because energy-per-frequency would scale differently.

The takeaway? Even time itself is measured in arbitrary chunks.

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Planck’s Constant: Just a Unit Exchange Rate

Quantum mechanics tells us energy comes in packets:

$$\mathrm{<span\; style="background-color:\; white;">E</span>}<span\; style="background-color:\; white;">=</span>\mathrm{<span\; style="background-color:\; white;">h</span>}<span\; style="background-color:\; white;">\times </span>\text{<span style="background-color: white;">(frequency)</span>}$$

But h (Planck’s constant) isn’t a law of nature—it’s just how we convert between energy (Joules) and frequency (Hz). And since Joule has units of mass and length, then how we convert between frequency and energy depends on how we define that length and mass units of measurement. 

• If we had defined energy units based on atomic vibrations instead of mechanical work, h could have been 1 (or any other number).
  
  

• Its value (6.626 × 10⁻³⁴ J·s) is just a receipt for how we defined Joules and seconds.
  
  

The takeaway? Planck’s constant is a unit translator, not a cosmic rule.

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Temperature, Energy, and the Boltzmann Constant

The Boltzmann constant (k) links temperature (Kelvin) to energy (Joules):

$$\mathrm{<span\; style="background-color:\; white;">E</span>}<span\; style="background-color:\; white;">=</span>\mathrm{<span\; style="background-color:\; white;">k</span>}<span\; style="background-color:\; white;">\times </span>\mathrm{<span\; style="background-color:\; white;">T</span>}$$

But k exists only because we defined temperature separately from mass and length.

• If we had said 1 K =  1 Hz = 1 kg  and set the meter so c=1 m, then k = 1 J/K by definition.
  
  

• Instead, we tied temperature to water’s freezing point, we scale the kg to be an absurd number of atomic masses, and set c to the length it has in meters, forcing k to be a weirdly small number (1.38 × 10⁻²³ J/K).
  
  

The takeaway? Even temperature is just equivalent to frequency, mass, and energy in different costumes.

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What Really Matters: The Dimensionless Numbers

If all our units are arbitrary, what’s left? 

Pure ratios:

1. 
   The fine-structure constant (α ≈ 1/137)

   • 
     Governs electromagnetism’s strength

   • No meters, seconds, or kilograms—just a number

2. 
   The proton-electron mass ratio (≈ 1836)

   • A proton weighs ~1,836 electrons

   • Doesn’t care about grams or pounds

3. 
   The cosmic microwave background temperature (2.725 K)

   • Only meaningful relative to other temperatures

These are the true laws of physics—not the unit-laden "constants" we’re used to.

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The Big Picture: Physics Without Human Bias

Our units are like a language—useful, but not fundamental. If aliens measured the universe in totally different units, their "speed of light" would be a different number, but the underlying physics would be identical.

So next time you hear about a "fundamental constant," ask:

• Is this a real law of nature?

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  Or just a conversion factor between our arbitrary rulers and clocks?

The answer might surprise you.

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Want to go deeper? Try recalculating physics equations using different unit scales—you’ll see the numbers change, but the relationships stay the same. That’s the beauty of reality: It doesn’t care how we measure it.

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Further Reading:

• 
  How the kilogram was redefined using Planck’s constant

• 
  Why some physicists want to abandon units entirely

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  The search for truly dimensionless constants in nature

Would you prefer a universe where the speed of light is 1 by definition? Or do you like our messy, human-centric units? Let us know in the comments! 🚀