FUNDAMENTAL BUILDING BLOCKS 285
soon as it is observed. The very
act of measuring a quantum system
seems to “shunt” it into one state
or another, forcing it to “choose”
its option. In the world we’re
familiar with, a coin toss results in
a definite heads or tails, and not
one, the other, and both at once.
Copenhagen fudge
In the 1920s, Niels Bohr and Werner
Heisenberg attempted to sidestep
the measurement problem with
what became known as the
Copenhagen interpretation. It holds
that the act of making an observation
on a quantum system causes the
wave function to “collapse” into
the single outcome. Although
this remains a widely accepted
interpretation, many theorists find
it unsatisfactory since it reveals
nothing about the mechanism
of wave function collapse. This
bothered Schrödinger, too. For him,
any mathematical formulation of
the world had to have an objective
reality. As Irish physicist John Bell
put it, “Either the wave function, as
given by the Schrödinger equation,
is not everything, or is not right.”
Many worlds
Everett’s idea was to explain
what happens to the quantum
superpositions. He presumed
the objective reality of the
wave function and removed the
(unobserved) collapse—why should
nature “choose” a particular version
of reality every time someone
makes a measurement? He then
asked another question: what then
happens to the various options
available to quantum systems?See also: Max Planck 202–05 ■ Werner Heisenberg 234–35 ■ Erwin Schrödinger 226–33
Hugh Everett III
Born in Washington DC, Hugh
Everett was a precocious boy.
At 12, he wrote to Einstein
asking what held the universe
together. While he was studying
mathematics at Princeton, he
drifted into physics. MWI—his
answer to the riddle at the heart
of quantum mechanics—was
the subject of his PhD in 1957,
and led to him being pilloried for
proposing multiple universes. A
trip to Copenhagen in 1959 to
discuss the idea with Niels Bohr
was a disaster—Bohr rejectedeverything that Everett said.
Discouraged, he left physics for
the US defense industry, but
today MWI is regarded as a
mainstream interpretation of
quantum theory—too late for
Everett, an alcoholic, who died
at just 51. A lifelong atheist, he
asked for his ashes to be thrown
out with the trash.Key works1956 Wave Mechanics
Without Probability
1956 The Theory of the
Universal Wave FunctionThe MWI says that all possibilities
do, in fact, occur. Reality peels
itself, or splits, into new worlds,
but since we inhabit a world where
only one outcome occurs, this
is what we see. Other possible
outcomes are inaccessible to us,
since there can be no interference
between worlds and we are fooled
into thinking that something is lost
every time we measure something.
While Everett’s theory is not
accepted by all, it removes a
theoretical block to interpreting
quantum mechanics. MWI does
not mention parallel universes,
but they are its logical prediction.
It has been criticized for being
untestable, but this may change.
An effect known as “decoherence”—
whereby quantum objects “leak”
their superposition information—is
a mechanism by which MWI might
be proved to work. ■“Multiverse” is an installation
of 41,000 LED lights at the National
Gallery of Art in Washington DC.
It was inspired by the many-worlds
interpretation.