The public face of science focuses on its accomplishments: what
it has nailed down about our universe. There
is an understandable tendency to de-emphasize the unknown, especially for those
issues that persist in being mysterious despite long and costly efforts. For
some of us, particularly science fiction lovers, this tendency to put a cork in
the mystery bottle is sad because we love the unknown.
Media reports on science give the impression that science
has erected a solid framework for understanding the universe, except for a few
interesting issues yet to resolve. A
“standard model” has been constructed for all of the elementary forces and
sub-atomic particles that make up our world, and the universe has been reduced
to a tidy pie-chart that shows how little of ordinary matter makes up our
universe. “Dark matter” and “dark
energy,” which gobble up most of the pie, are presented as things we have a handle
on, understand well enough to put a precise percentage on them in the big pie
chart of the universe.
Reports of the discovery of the Higgs boson in 2012 said
that it put the last building block into the standard model and confirmed its
validity. Confirming the Higgs boson,
which was predicted by standard model physics, was a great achievement, but
there are wide dark patches in elementary physics that aren’t explained at all
by the standard model. In fact, darkness
overwhelms the light. One of the dark areas is the “dark energy” of the
universe. What is termed “dark energy” is whatever is causing everything in the
universe to accelerate away from everything else. Because it’s accelerating, it means there is
some force driving everything away from everything else, some kind of energy,
like when you step on the gas. But what
that energy is, is a complete and total mystery. The astronomers who discovered the
acceleration in 1998 were expecting, based on currently accepted theories, to
measure how fast the well-known outward expansion of the universe was slowing down, not speeding up. In the words of Alex Filippenko, one of those
astronomers, it was as if “we were doing a multiple-choice exam and the right
answer was not one of the choices.” In
the twenty ensuing years, little progress has been made in solving the mystery,
in spite of the many references to dark energy as if it were a familiar thing. A calculation was made of how much energy
must be involved to make the universal expansion accelerate like it does, and
that energy is so enormous that it must account for 68% of everything in the
universe, including all the stars, planets, and galaxies.1
That’s where the percentage in the pie chart comes from. We don’t know anything more about it than
that. It defies any explanation. The
best guess of what it might be comes from high-energy physics, in which a universal
energy field known as a scalar field might behave as the “dark energy”
does. The Higgs is such a scalar
field. But there’s no field in the
standard model that explains the accelerating universe. There are other big
holes in the standard model. Like
gravity. No explanation at all for it,
or how all those particles in the standard model that make up mass as we know
it are affected by or affect gravity. Or
why neutrinos have mass, also discovered in 19982,
and which is unexpected according to the standard model. Dark matter
is a different matter entirely, being something that is known to be affected by
gravity and affects how galaxies spin and move around in clusters but is
otherwise not detectable, making it something unlike any other kind of
matter. Calculations based on how much
it affects galaxy movements indicate its total mass must be 27% of all the
matter in the universe, far more than the ordinary matter we and our earth and
our sun are made of, which is less than 5%.
Whatever dark matter and dark energy are, they don’t seem to be in the
standard model.
Some of the biggest mysteries of the elementary particles
and forces in the standard model are associated with their quantum nature. Personally, the big mysteries of dark energy
and dark matter leave me a bit stunned, but the mysteries of quantum mechanics
make me say “Wow, that’s amazing!” Quantum mechanics originated in the discovery
that the smallest amounts of energy must come in well-defined chunks, even for
things that behave precisely like waves, like light and infrared radiation.
This discovery was made by Max Planck at the end of the 19th century
to explain why light with really short frequencies, in the ultra-violet range,
is radiated by hot things at lower intensities than other light in the
spectrum: it is limited by being broken up into little chunks. This defines the spectrum of light that we
see from stars, including our sun, which is a spectrum that is really important
to us. Sunlight would be very different
and the ultraviolet would kill us all if it weren’t for the exact size of these
light chunks and the way they determine the intensity of the different colors
in the rainbow. And it also determines
the way that electrons arrange themselves in atoms, which in turn determines
everything about chemistry.
Experiments at the very small quantum level reveal some
really mysterious behavior, which is still mysterious after nearly a century of
experiments, theorizing, and debating. This bizarre behavior and the history of
thinking about it is elucidated in a couple of excellent books published in
2018. In Adam Becker’s What is Real?
The Unfinished Quest for the Meaning of Quantum Physics, the emphasis is
very strongly on the word meaning in
his title. The major theme is the great
divergence between practical application of the mathematical theory of quantum
mechanics and our understanding of what it all means. This divergence hasn’t narrowed since the
math of quantum mechanics was formulated almost a century ago. Unlike Newton’s theories of gravity, mass,
and other forces, which can be explained intelligibly in words and picture
concepts, quantum mechanics simply cannot.
“Nobody understands quantum mechanics,” said Richard Feynman3,
who greatly advanced its science. In
discussing why a young physicist’s career disintegrated, Steven Weinberg, one
of the great contributors to the standard model, quoted a colleague as saying,
sadly “He tried to understand quantum mechanics.”4 Some of the most fundamental equations of
quantum mechanics were formulated by Werner Heisenberg, who arrived at them by
“careful guessing” based on experimental results. Heisenberg’s resulting “matrix mechanics” and
Schrรถdinger’s
wave function, which is used today, only describe the probabilities of what
will happen during interactions of fundamental particles. Many of the debates among physicists in the
early days of quantum mechanics argued that the mathematical theory gave
correct predictions but wasn’t satisfactory because it was unintelligible.5 There’s no “mental model,” only equations
that describe probabilities. This
bothered Einstein so much he disavowed quantum mechanics, in spite of his early
contributions to it.
Becker traces the history of efforts to understand the foundations
and meaning behind the equations, which continue while the “shut up and
calculate” consensus has proceeded to use the mathematical theory to produce
results used in many practical applications including nuclear reactors,
micro-electronics, particle accelerators, and, unfortunately, weapons. What stands out is how research and debate on
the fundamentals is always relegated to the backwaters of physics, dismissed
and even disparaged by the mainstream pursuing practical results. Yet the biggest mysteries in quantum
mechanics are in its fundamentals. Some
of the most outstanding are:
- How can something be in two places at the same
time, which quantum experiments have proved true? (This is known as the non-locality problem,
to give it the proper jargon.)
- How can physical processes be random, governed
by probabilities rather than deterministic cause and effect? (Known as the
indeterminism problem.)
- How can objects at the quantum level be in two mutually
exclusive conditions at the same time? (Known as superposition. This is the
famous “Schrodinger’s cat” problem in which an experiment that would kill the
cat in one quantum condition but not in the other are in superposition, but
before the experiment is performed the cat can be either, or neither, or
perhaps both dead and alive.)
- What is the role of the “observer” in events at the quantum level? (Known as the measurement problem.) As per the problem with Schrodinger’s cat, the quantum superposition of mutually exclusive conditions collapses whenever a measurement is made. What makes this transition from the micro, quantum world to the macro world occur? Some have seriously suggested it is an effect of human consciousness.
Anil Ananthaswamy’s Through Two Doors at Once – The
Elegant Experiment That Captures the Enigma of Our Quantum Reality, uses a
famous quantum experiment, the “double-slit” experiment, to illustrate a number
of the fundamental features of quantum mechanics. It’s got some of the best plain-language
explanations of quantum phenomena I’ve seen.
The double-slit experiment displays the wave-particle duality of quantum
chunks of light, which we know as photons.
Light shining through two vertical slits in an otherwise opaque barrier
displays evidence of being a wave. Just
like circular water waves generated by dropping two stones at the same time on
a pond surface, the waves of light going through two narrow slits produce
circular waves that pile up on each other downstream at some locations wherever
two wave crests coincide and cancel each other wherever a wave bottom from one
circle and a crest from the other coincide.
With light, this shows up as a pattern of light and dark vertical bands
on a photographic plate catching the light on the far side of the slits from
the light source. But when the light
source is reduced to almost nothing, the light comes through in those little
chunks, and individual photons appear on the photo as small dots, one at a time
in sequence over time. You would think
there could be no light and dark bands because each photon, which is an
irreducible quantum chunk, must go through only one slit. And indeed, each photon dot on the photo
shows up in only one location. But over
time, amazingly, the photon dots build up a pattern of vertical bands, just as
if they were waves! How could this be
possible? No one knows. This is an
example of the non-locality problem.
Each irreducible chunk must be present in some weird way in both of the two
pathways through the two slits to the photo film. If there’s only one slit there’s no light and
dark bands.
The book traces the history of double-slit experiment
results and more elaborate experiments with mirrors and beam splitters that also
demonstrate photon non-locality. These
latter share with the true double-slit experiment the key ingredient: they
provide two simultaneous potential pathways for the photons, which then cause
photons to show up as if they are interfering with themselves. Also described
in Ananthaswamy’s book are experiments which show how beams of electrons, that
is, matter instead of light, also display the same wave-particle duality. This is really important, since we don’t
normally think of matter as being composed of waves, do we? Yet the papers reporting experiments proving
this behavior with electrons using early electron microscopes in the 1950s sat
untranslated from German in an obscure publication for years, unknown even to
famous physicists who speculated in the 1960s that it might be demonstrated
some day. The demonstration just wasn’t
important to the practical probability calculations that physicists were most
concerned with.
The slow progress in the foundations of quantum physics only
deepens the mysteries. This is wonderful
for people who like to speculate. But much
of the speculation about quantum mysteries today in science fiction is based on
misunderstandings. For example, the
potential for human consciousness to mysteriously affect quantum
phenomena. As described by the careful
history related in Becker’s book, there is no basis for this particular
weird idea, which some physicists have postulated; there are more likely
explanations for the collapse of quantum superpositions when measurements are
made. On the other hand, the locality
problem – one thing spanning a large space across which random changes are
instantaneously correlated, has been irrefutably proven by experiments proving
something called Bell’s theorem.
Some of the most interesting areas for valid speculation appear to be:
- Indeterminism: What are the implications of the randomness
in nature that appears to be fundamental according to quantum mechanics? Can it be the basis for a concept of free
will?
- Non-locality: How can things be in two places at
once, and can there be instantaneously correlated random changes in two objects separated by a large distance,
violating the speed-of-light limitation of Einstein’s relativity? What does this mean for our concepts of space
and time?
- Consciousness: Can quantum superpositions and quantum randomness somehow be important in understanding how our brains produce consciousness? (This speculation would be how quantum mechanics affects consciousness, not the other way around.)
But the biggest thing to wonder about is whether the
seemingly bizarre behavior of quantum phenomena might be giving us a peek at
some underlying reality that explains them.
Informed speculation on the fundamentals of quantum reality might just
provide a breakthrough that shutting up and focusing on refining the
calculations could never arrive at.
There’s plenty of mystery in the universe for us to wonder
about.
[1] The
mass of stars, planets, galaxies and all other matter are converted to energy
for this calculation using Einstein’s famous equation E = mc2,
energy is equal to mass times the constant speed of light squared.
[2]
Scientific American, November 4, 2014. https://www.scientificamerican.com/article/nova-experiment-neutrino-mass-mystery/
[3] Richard
P. Feynman, The Messenger Lectures, 1964, MIT
[4]
Weinberg. S., Dreams of a Final Theory, 1992, p. 84.
[5]
The German word Anschaulichkeit was used in the debate, which means picturable,
intelligible, intuitive, or clear. This was a major theme of the great summit
of early quantum physicists known as the Fifth Solvay conference in 1927,
described in detail in Bacciagaluppi and Valentini, Quantum Theory at the
Crossroads, 2009: https://arxiv.org/abs/quant-ph/0609184v2
