Frank Wilczek
Nature, Volume 410, March 8, 2001
Scientists have to struggle
with words that don’t fit reality.
____________________________
Language is a social creation.
It encodes the common experience
of many people, past and present,
and has been sculpted mainly
to communicate our everyday needs.
Ordinary language
is most certainly not a product
of the critical investigation of concepts.
Yet scientists learn,
think and communicate in it
during much of their lives.
Ordinary language is therefore
an unavoidable scientific tool
-rich and powerful,
but also quite imperfect.
One scientific imperfection of language,
perhaps the most obvious, is its incompleteness.
For example,
there are no common words
for several of the most
central concepts of quantum theory,
such as the linearity of state-space
and the use of tensor products
to describe composite systems.
To be sure,
we've developed
some applicable jargon
-'superposition' and 'entaglement',
respectively, are the words we use-
but the words are unusual ones,
not likely to convey much to outsiders,
and their literal meaning is misleading to boot.
Although it creates cultural barriers
and contributes to the balkanization of knowledge,
such enrichment and slight abuse of language
is not conceptually problematic.
Much more insidious,
and more fundamentally interesting,
is the opposite case: when
ordinary language is too complete.
When something has a name,
and is commonly employed in discourse,
it is seductive to assume
that it refers to a coherent concept,
and an element of reality.
But it need not.
And the more pervasive the word,
the more difficult it can be to evade its spell.
Few words are more pervasive than 'now'.
According to his own account,
the greatest difficulty Einstein encountered
in reaching the special theory of relativity
was the necessity to break free from the idea
that there is an objective, universal 'now':
«[A]ll attempts to clarify this paradox satisfactorily
were condemned to failure as long as the axiom
of the absolute character of time, viz., of simultaneity,
unrecognizedly was anchored in the unconscious.
Clearly to recognize this axiom
and its arbitrary character
really implied already
the solution of the problem.» [1]
Einstein's original 1905 paper
begins with a lengthy discussion,
practically free of equations,
of the physical operations involved
in synchronizing clocks at distant points.
He then shows that these same operations,
implemented by a moving system of observers,
leads to different determinations
of which events occur "at the same time".
As relativity undemines 'now',
quantum theory undermines 'here'.
Heisenberg had Einstein's analysis
specifically in mind when,
in the opening of his seminal paper
on the new quantum mechanics in 1925,
he advocated the formulation of physical laws
using observable quantities only.
But while classical theory
has a naïve conception of particle's position,
described by a single coordinate
(a triple of numbers, for three-dimensional space),
quantum theory requires this to be
replaced by a much more abstract quantity.
One aspect of the situation
is that if you don't measure the position,
you must not assume
that it has a definite value.
Many successful calculations
of physical process
using quantum mechanics
are based on performing
a precise form of averaging
over many different positions
where a particle 'might be found'.
These calculations would be ruined
if you assumed that the particle
was always in a definite place.
You can choose to measure its position,
but performing such a measurement
involves disturbing the particle.
It changes both the question and the answer.
Einstein himself was never
reconciled to the loss of 'here'.
In his greatest achievement,
the general theory of relativity,
Einstein relied heavily
on the primitive notions
of events in space-time
and (proper) distance
between nearby events.
These notions rely
on unambiguous association
of times and places
-'nows' and 'heres'-
to individual objects of reality
(though not, of course,
on the existence of a universal 'now').
Understandably impressed
by the success of his theory,
Einstein was loath
to sacrifice its premises.
He resisted modern quantum theory,
and did not participate in the sweeping success
in elucidating problem after great problem.
Ironically, the sacrifice he feared
has not (yet) proved necessary.
On the contrary,
in the modern Theory of Matter,
we retain 'nows' and 'heres'
for the fundamental objects of reality.
These primitives are no less important
in the formulation of the subatomic laws
of quantum theory than in general relativity.
The new feature is that
the fundamental objects of reality
are one step removed
from the directly observed:
they are quantum fields,
rather than physical events.
It is possible to avoid
ordinary language and its snares.
Within specific domains of mathematics,
this is accomplished by constructing
exact definitions and axioms.
Purity of language is also forced on us
when we interact with modern digital computers,
since they do not tolerate ambiguity.
But the purity of artificial languages
comes at a great cost in scope,
suppleness and flexibility.
Perhaps computers
will become truly inteligent
when they learn to be tolerant
of ordinary sloppy language
-and then use it themselves!
In any case, for us humans
the practical and wise course
will be to continue to use
ordinary language, even for
abstract scientific investigations,
but to be very suspicious of it.
Along these lines,
Heisenberg's considered formulation, put forward
in The Physical Principles of Quantum Theory in 1930,
was: «[I]t is found advisable to introduce
a great wealth of concepts into a physical theory,
without attempting to justify them rigorously,
and then to allow experiment to decide
at what points a revision is necessary.»
Looking to the future, after 'now' and 'here',
what basic intuition will next require reformulation?
As the nature of mind
comes into scientific focus,
might it be 'I'?
Perhaps the following remarks of Hermann Weyl,
stimulated by deep reflection on the aspects
of modern physics discussed here and stated in his
Philosophy of Mathematics and Natural Science (1949),
points in that direction:
«The objective world simply is, it does not happen.
Only to the gaze of my consciousness,
crawling upward along the life line of my body,
does a section of this world come to life
as a fleeting image in space
which continuously changes in time.»
____________________________
[1] Einstein, A. "Autobiographical notes",
in Albert Einstein, Philosopher-Scientist (Ed. Schilpp, P.)
(Library of Living Philosophers, 1949).
……………………………………………...
Frank Wilczek is in
the Massachusetts Institute of Technology,
Cambridge, Massachusetts 20139, USA.
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