But the film also makes you consider a deeper question: Is there a true story, or is our belief in a definite, objective, observer-independent reality an illusion?
This
very question, brought into sharper, scientific focus, has long been
the subject of debate in quantum physics. Is there a fixed reality apart
from our various observations of it? Or is reality nothing more than a
kaleidoscope of infinite possibilities?
This month, a paper published online in the journal Nature Physics presents experimental research that supports the latter scenario — that there is a “Rashomon effect” not just in our descriptions of nature, but in nature itself.
Over
the past hundred years, numerous experiments on elementary particles
have upended the classical paradigm of a causal, deterministic universe.
Consider, for example, the so-called double-slit experiment. We shoot a
bunch of elementary particles — say, electrons — at a screen that can
register their impact. But in front of the screen, we place a partial
obstruction: a wall with two thin parallel vertical slits. We look at
the resulting pattern of electrons on the screen. What do we see?
If
the electrons were like little pellets (which is what classical physics
would lead us to believe), then each of them would go through one slit
or the other, and we would see a pattern of two distinct lumps on the
screen, one lump behind each slit. But in fact we observe something
entirely different: an interference pattern, as if two waves are
colliding, creating ripples.
Astonishingly,
this happens even if we shoot the electrons one by one, meaning that
each electron somehow acts like a wave interfering with itself, as if it
is simultaneously passing through both slits at once.
So
an electron is a wave, not a particle? Not so fast. For if we place
devices at the slits that “tag” the electrons according to which slit
they go through (thus allowing us to know their whereabouts), there is
no interference pattern. Instead, we see two lumps on the screen, as if
the electrons, suddenly aware of being observed, decided to act like
little pellets.
To test their commitment to being particles, we can tag them as they pass through the slits — but then, using another device, erase the tags before they hit the screen. If we do that, the electrons go back to their wavelike behavior, and the interference pattern miraculously reappears.
There
is no end to the practical jokes we can pull on the poor electron! But
with a weary smile, it always shows that the joke is on us. The electron
appears to be a strange hybrid of a wave and a particle that’s neither
here and there nor here or there. Like a well-trained
actor, it plays the role it’s been called to perform. It’s as though it
has resolved to prove the famous Bishop Berkeley maxim “to be is to be
perceived.”
Is nature really this weird? Or is this apparent weirdness just a reflection of our imperfect knowledge of nature?
The
answer depends on how you interpret the equations of quantum mechanics,
the mathematical theory that has been developed to describe the
interactions of elementary particles. The success of this theory is
unparalleled: Its predictions, no matter how “spooky,” have been
observed and verified with stunning precision. It has also been the
basis of remarkable technological advances. So it is a powerful tool.
But is it also a picture of reality?
Here,
one of the biggest issues is the interpretation of the so-called wave
function, which describes the state of a quantum system. For an
individual particle like an electron, for example, the wave function
provides information about the probabilities that the particle can be
observed at particular locations, as well as the probabilities of the
results of other measurements of the particle that you can make, such as
measuring its momentum.
Does
the wave function directly correspond to an objective,
observer-independent physical reality, or does it simply represent an
observer’s partial knowledge of it?
If
the wave function is merely knowledge-based, then you can explain away
odd quantum phenomena by saying that things appear to us this way only
because our knowledge of the real state of affairs is insufficient. But
the new paper in Nature Physics gives strong indications (as a result of
experiments using beams of specially prepared photons to test certain
statistical properties of quantum measurements) that this is not the
case. If there is an objective reality at all, the paper demonstrates,
then the wave function is in fact reality-based.
What
this research implies is that we are not just hearing different
“stories” about the electron, one of which may be true. Rather, there is
one true story, but it has many facets, seemingly in contradiction,
just like in “Rashomon.” There is really no escape from the mysterious —
some might say, mystical — nature of the quantum world.
But
what, if anything, does all this mean for us in our own lives? We
should be careful to recognize that the weirdness of the quantum world
does not directly imply the same kind of weirdness in the world of
everyday experience. That’s because the nebulous quantum essence of
individual elementary particles is known to quickly dissipate in large
ensembles of particles (a phenomenon often referred to as
“decoherence”). This is why, in fact, we are able to describe the
objects around us in the language of classical physics.
Rather,
I suggest that we regard the paradoxes of quantum physics as a metaphor
for the unknown infinite possibilities of our own existence. This is
poignantly and elegantly expressed in the Vedas: “As is the atom, so is
the universe; as is the microcosm, so is the macrocosm; as is the human
body, so is the cosmic body; as is the human mind, so is the cosmic
mind.”
Edward Frenkel, a professor of mathematics at the University of California, Berkeley, is the author of “Love and Math: The Heart of Hidden Reality.”
