The Science Book

234

UNCERTAINTY

IS INEVITABLE

WERNER HEISENBERG (1901–1976)

F

ollowing Louis de Broglie’s

suggestion in 1924 that

on the smallest scales of

matter, subatomic particles could

display wavelike properties

(pp.226–33), a number of physicists

turned their attention to the

question of understanding how

the complex properties of an atom

could arise from the interaction

of “matter waves” associated

with its constituent particles.

In 1925, German scientists

Werner Heisenberg, Max Born,

and Pascual Jordan used “matrix

mechanics” to model the hydrogen

atom’s development over time. This

approach was later supplanted by

Erwin Schrödinger’s wave function.

Working with Danish physicist

Niels Bohr, Heisenberg built on

Schrödinger’s work to develop the

“Copenhagen interpretation” of

the way that quantum systems,

governed by the laws of probability,

interact with the large-scale world.

One key element of this is the

“uncertainty principle,” which

limits the accuracy to which we

can determine properties in

quantum systems.

The uncertainty principle arose

as a mathematical consequence of

matrix mechanics. Heisenberg

realized that his mathematical

method would not allow certain

pairs of properties to be determined

simultaneously with absolute

IN CONTEXT

BRANCH

Physics

BEFORE

1913 Niels Bohr uses the

concept of quantized light to

explain the specific energy

levels associated with

electrons inside atoms.

1924 Louis de Broglie

proposes that just as light can

exhibit particle-like properties

so, on the smallest scale,

particles might sometimes

show wavelike behavior.

AFTER

1927 Heisenberg and Bohr put

forward the highly influential

Copenhagen interpretation

of the way that quantum-level

events affect the large-scale

(macroscopic) world.

1929 Heisenberg and

Wolfgang Pauli work on the

development of quantum field

theory, whose foundations

have been laid by Paul Dirac.

Quantum tuneling

is explained by

Heisenberg’s principle.

There is a nonzero

chance that an electron

can pass through

a barrier even if it

appears to have too

little energy to do so.

Electron

Classical picture

Quantum picture

Electron

wave

Energy

barrier