36 | New Scientist | 15 February 2020
of causation back through Earth and cosmic
history to the moment the carbon atoms
within the apple were first manufactured
in a supernova – and beyond that almost to
the big bang and time’s beginning.
The thing is, that apple was always going
to fall; it can’t choose to jump or decide not to
fall. Agency is different. From our perspective
at least, our decision-making is discretionary;
there is none of the inevitability that marks
out physical laws. And the chains of causation
behind our actions are very complex, running
through psychological influences brewed by
nature, culture and nurture.
Our current physical laws don’t try to
explain this. “We think of ourselves as
coming from outside the causal order and
somehow intervening in it, making things
happen,” says philosopher Jenann Ismael
at Columbia University in New York. That
strange detached position is maintained –
albeit with an additional twist – even in the
weird world of quantum theory, our most
advanced underlying theory of material
reality (see “No ‘I’ in collapse”, page 38).
The god-like status we accord ourselves
is highly suspicious to many physicists.
“If I’m saying that something doesn’t
boil down to the laws of physics, then I’m
basically positing something supernatural,
that’s outside natural laws,” says Matt Leifer
at Chapman University in California.That has been a popular way out for
natural philosophers over the years, in
various forms of mind-body dualism: the
idea that the mental and physical realms
are separate, and the rules of one don’t apply
to the other. But that hardly seems a tenable
position within modern science. “Being a
full-on dualist is quite hard because it does
look like, for instance, when I put lots of
serotonin in your brain, your mental states
change,” says Knox. “The question is how
you think that could work if you think there’s
two kinds of separate stuff.”
“If there’s evidence we should carve out a
different realm for organic things or people
or whatever, then by all means,” says Carroll.
“But I’m made of atoms, my laws of physics
purport to explain atoms, and it would seem“ Our decision-
making has none
of the inevitability
that marks out
physical laws”
Agency is bound up with
several other fundamental
concepts that philosophers,
physicists and others
struggle to get to grips with.
That starts with...LIFE. In the early 1990s,
an advisory panel to
NASA defined life as “a
self-sustaining chemical
system capable of Darwinian
evolution”. Others dissent.
Typical defining characteristics
include being born and
dying, metabolising, growing
and reproducing. Some
life forms are known to
exhibit more complex
characteristics, including...INTELLIGENCE. Broadly, the
ability to learn stuff and solve
problems. Artificial machine-
learning systems can do those
things too, so life probably isn’t
a prerequisite. But AI is still
far away from the “general
intelligence” of humans and
some animals that allows
knowledge gained in one area
to be applied elsewhere. This
is possibly bound up with...CONSCIOUSNESS.
A perennial head-scratcher,
consciousness starts with
the observation that some
things are aware they exist.
Some conscious beings argue
that explaining this state inpurely physical terms will
always fall foul of the “hard
problem”: that certain aspects
of it, such as individual
experiences of colour or pain
or love, can only ever be felt
inwardly. The difficulty of
defining consciousness
satisfactorily leads some
physicists to prefer...AGENCY. This is at least
expressed outwardly, in
actions that change the
external world. Human-
type agency is arrived
at intentionally, through
internal decision-making
processes, which throws
up thorny questions of...FREE WILL. Often seen as
the opposite of determinism
(everything is pre-determined),
free will in its strongest sense,
the complete freedom to act
independently of any causal
influences at all, almost
undoubtedly doesn’t exist.
The sort of free will we
experience – agency that can
be free of immediate physical
causation – isn’t necessarily
incompatible with either the
deterministic laws of classical
physics or the indeterminate
probabilistic laws of quantum
mechanics. The question is
how agency fits in with those
laws – and whether it should
(see main story).LIFE, AGENCY
AND EVERYTHINGby far the most likely hypothesis that the laws
of physics explain me.”
The central conundrum becomes what sort
of physical laws can unify two very different,
conflicting views. “We see agents that make
choices and exert a causal influence on what
happens in the world, and then science comes
along and says, ‘You’re actually a bunch of
particles or atoms and you’re just obeying
differential equations’,” says Carroll. “What
we want to figure out is how those things can
both be true at the same time.”
For Carroll and many others, the answer
lies not in mysticism, but in emergence.
This is the idea that behaviours and
properties that are inscrutable when you
look at single components of a complex
system pop into existence when you view
things as a whole. There are plenty of
precedents. The temperature or density of
a gas, for example, doesn’t mean much at
the level of single molecules. Look at all the
molecules of the gas together, however, and
they are measurable quantities that explain
physical change: how temperature differences
cause heat flows, for example, or how a gas
pushes a piston when compressed.
The catch is that human brains are
phenomenally complex. A fully grown one
contains nearly 100 billion interconnected
neurons, and we are still far from establishing
how they produce the felt states of our