24 August 2019 | New Scientist | 35The mysteries don’t end there. Quantum
theory also seems to violate the principle of
locality, which says that objects or events must
be near one another to interact. In classical
physics, for example, the gravitational or
electrical force between two objects depends
on their distance: the closer they are in
space, the stronger the force between them.
Quantum theory, meanwhile, introduces
entanglement, a phenomenon that allows
objects to seemingly influence each other
instantaneously over any distance.
Einstein notably believed that these
blemishes indicated that quantum theory
was wrong, and that a truer, deeper description
of nature was out there. He wasn’t the only
quantum pioneer to express doubts. Louis
de Broglie, who first predicted the wave-like
aspects of matter, was another sceptic, as was
Erwin Schrödinger, whose famous thought
experiment of the dead-and-alive cat was
designed to highlight the absurdity of
quantum theory’s prediction of alternative
realities. In the present day, quantum
dissidents include notable physicists such as
Roger Penrose and the Nobel-prizewinning
theorist Gerard ’t Hooft.
Arguments about whether quantum
mechanics is a complete theory of reality
have usually been carried out in isolation. But
the route to a deeper and truer understanding
of nature may lie in connecting the problems
of quantum theory with other big, open
problems in fundamental physics.
The most obvious one is how to develop a
quantum theory of gravity. Gravity is the only
one of nature’s four fundamental forces not
to have a quantum-mechanical description.
It is described by Einstein’s general theory of
relativity as an effect resulting from massive
objects warping space-time around them.
General relativity and quantum theory seem
to be fundamentally incompatible, not least in
the way the former describes a smooth,Quantum theory is our most successful theory of material
reality – but we might already have the outline of something
better, says physicist Lee Smolin
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INFeatures Cover story
to seek what might lie beyond it. I believe we
already have the outline of what this deeper
answer looks like. We are only at the start
of this work, but by digging down into the
fundamental principles that underlie reality,
and weeding out what is right and what is
wrong about our current ideas, we can see
glimpses of a truly unifying picture of physics.
It comes at a price: to go beyond quantum,
we must totally upend long-held ideas of how
the universe hangs together.
It is easy to state the basic problem of
quantum mechanics as a theory of reality:
it doesn’t tell us what is happening in reality.
It has two different laws to describe how
things and events evolve. The first applies
most of the time, and describes quantum
objects as wave-like entities embodied in a
mathematical construction known as a wave
function. These objects evolve smoothly
in time, exploring alternative realities in
“superpositions” in which they aren’t
restricted to being in any one place at any one
time. That, to any intuitive understanding of
how the world works, is distinctly odd.Curiouser and curiouser
The second law applies only under special
circumstances called measurements, in which
a quantum object interacts with a much larger,
macroscopic system – you or me observing
it, for example. This law says that a single
measurement outcome manifests itself.
The alternative realities that the wave function
says existed up to that point suddenly dissolve.
These two laws exist in parallel, in apparent
contradiction of one another – a fundamental
failure of our understanding known as the
measurement problem. Attempts to do the
obvious, and derive the second law from the
first, have so far failed. We are left with only
statistical predictions of what is going on in
the quantum world before it is measured.Beyond weird
Q
UANTUM mechanics is often called
a theory of the very small. In reality,
it explains phenomena on a vast range
of scales – from elementary particles and their
interactions, through atoms and molecules, all
the way to neutron stars and the supernovae
that spawn them. So far, essentially all
its predictions have been confirmed by
experiments. It is the most successful theory
of material reality we have ever had.
So why have so many physicists, from
Albert Einstein onwards, taken the view
that quantum theory is wrong?
The reasons lie in its mysterious nature,
in the phenomena it doesn’t explain and the
answers it doesn’t give. That is reason enough