From Physics to Logic Gates: How Computers Become Possible

Learn the 3 physical requirements for computation, why structure matters more than material, and how Boole and Shannon made logic hardware-real.
Binary numbers

When I decided to study how computers really work from scratch, I kept asking one question:

Why do computers begin with logic gates?

Where do those “rules” come from?

And came to the conclusion:The physical world doesn’t run on logic — it runs on physics.

Logic is just the language we invent to describe stable patterns we observe in reality.

Logic is a model of stable physical behavior

We constantly meet systems that behave predictably:

Computers are possible because the physical world allows some behaviors to be reliable enough that we can treat them as symbols.

Three physical requirements for computation

For computation to work, a system must support three things.

1 - Distinguishable states

A system must represent one state as reliably different from another.

In digital electronics, we simplify continuous voltages into two buckets:

But note, real circuits aren’t perfect, so what matters is noise margin: there must be enough separation that small variations don’t flip meaning.

If a signal can’t be distinguished reliably, you don’t have information, you have ambiguity.

2 - One outcome under identical conditions

Under the same conditions, the system must not “contradict itself”.

Same inputs, same environment, same circuit → one outcome.

If the same setup sometimes produces conflicting results, the system can’t be trusted. That’s not computation, that’s randomness.

3 - Repeatable behavior

This is the practical version of determinism: Same setup = same result (reliably, over and over).

If a transistor sometimes conducts and sometimes doesn’t under identical conditions, you can’t build a CPU. You can’t build memory. You can’t build anything layered on top.

Computation is about structure, not material

Computers are made of silicon, but computation is not “about silicon”.

You can build reliable logic using:

The material changes engineering constraints (speed, size, cost, energy, reliability). But the computation itself stays the same as long as the structure is preserved.

So what is “structure” here?

Structure means the constraints that make a medium behave like a machine:

A computer is a pattern of states and state-transitions that implements abstract rules, and physics is the medium that carries those states.

An analogy: the song and the instrument

A song can be played on a piano, a guitar, or a violin. The instrument changes the sound, but the melody and rhythm remain. In computation:

George Boole: turning reasoning into a formal structure

In the 1800s, algebra was mostly treated as “letters standing for quantities. Boole asked a different question:

What if algebra is really about rules, not about numbers?

What if symbols represent classes of things and the operations represent how we combine them?

That gives you operations like:

This wasn’t electronics yet. It was a pure structure: a symbolic system with precise rules.

Claude Shannon: connecting the structure to switches

Decades later, Claude Shannon made the bridge physical. He showed that switching circuits (like relays in telephone systems) can be described using Boolean expressions, and that Boolean expressions can be built as switching circuits.

That was the key leap: logic as mathematics → logic as hardware

Once you can build Boolean structure out of physical switches, two things become possible:

From math to decisions

The final insight is that outputs can control future behavior. The result of one logical step can become the condition for the next:

That is the physical root of control flow. And that’s why computers begin with logic gates: they are the smallest reliable building blocks that turn physical stability into symbolic rules.

In the next article, I’ll introduce logic gates directly — what they are, why their truth tables look the way they do, and why some sets of gates are “universal”.