Imagine you sit down and pick up your favorite book. You look at the image on the front cover, run your fingers across the smooth book sleeve, and smell that familiar book smell as you flick through the pages. To you, the book is made up of a range of sensory appearances. But you also expect the book has its own independent existence behind those appearances. So, when you put the book down on the coffee table and walk into the kitchen, or leave your house to go to work, you expect the book still looks, feels, and smells just as it did when you were holding it.
Expecting objects to have their own independent existence –
independent of us, and any other objects – is actually a deep-seated assumption
we make about the world. This assumption has its origin in the scientific
revolution of the 17th century and is part of what we call the mechanistic
worldview. According to this view, the world is like a giant clockwork
machine whose parts are governed by set laws of motion. This view of the world
is responsible for much of our scientific advancement since the 17th century.
But as Italian physicist Carlo Rovelli argues
in his new book Helgoland,
quantum theory – the physical theory that describes the universe at the
smallest scales – almost certainly shows this worldview to be false. Instead,
Rovelli argues we should adopt a “relational” worldview.
What does it mean to be relational?
During the scientific revolution, the English physics
pioneer Isaac Newton and his German counterpart Gottfried Leibniz disagreed on
the nature of space and time. Newton claimed space and time acted as a
“container” for the contents of the universe. That is, if we could remove the
contents of the universe – all the planets, stars, and galaxies – we would be
left with empty space and time. This is the “absolute” view of space and time.
Leibniz, on the other hand, claimed that space and time were
nothing more than the sum total of distances and durations between all the
objects and events of the world. If we removed the contents of the universe, we
would remove space and time also. This is the “relational” view of space and
time: they are only the spatial and temporal relations between
objects and events. The relational view of space and time was a key inspiration
for Einstein when he developed general relativity.
Rovelli makes use of this idea to understand quantum
mechanics. He claims the objects of quantum theory, such as a photon, electron,
or another fundamental particle, are nothing more than the properties they
exhibit when interacting with – in relation to – other
objects. These properties of a quantum object are determined through experiments and include things like the object’s position, momentum, and energy. Together
they make up an object’s state. According to Rovelli’s relational
interpretation, these properties are all there is to the object: there is no
underlying individual substance that “has” the properties.
So how does this help us understand quantum
theory?
Consider the well-known quantum puzzle of Schrödinger’s cat.
We put a cat in a box with some lethal agent (like a vial of poison gas)
triggered by a quantum process (like the decay of a radioactive atom), and we
close the lid. A quantum process is a chance event. There is no way to
predict it, but we can describe it in a way that tells us the different chances
of the atom decaying or not in some period of time. Because the decay will
trigger the opening of the vial of poison gas and hence the death of the cat,
the cat’s life or death is also a purely chance event.
According to orthodox quantum theory, the cat is neither
dead nor alive until we open the box and observe the system. A puzzle remains
concerning what it would be like for the cat, exactly, to be neither dead nor
alive. But according to the relational interpretation, the state of any system
is always in relation to some other system. So, the quantum process in the box
might have an indefinite outcome in relation to us but have a
definite outcome for the cat.
So, it is perfectly reasonable for the cat to be neither
dead nor alive for us, and at the same time to be definitely dead or alive
itself. One fact of the matter is real for us, and one fact of the matter is
real for the cat. When we open the box, the state of the cat becomes definite
for us, but the cat was never in an indefinite state for itself.
What does this tell us about reality?
Rovelli argues that, since our world is ultimately quantum,
we should heed these lessons. In particular, objects such as your favorite book
may only have their properties in relation to other objects, including you. Thankfully,
that also includes all other objects, such as your coffee table. So, when you
do go to work, your favorite book continues to appear as it does when you were
holding it. Even so, this is a dramatic rethinking of the nature of reality.
On this view, the world is an intricate web of
interrelations, such that objects no longer have their own individual existence
independent from other objects – like an endless game of quantum mirrors.
Moreover, there may well be no independent “metaphysical” substance constituting
our reality that underlies this web.
As Rovelli puts it:
We are nothing but images of images. Reality, including ourselves, is nothing but a thin and fragile veil, beyond which … there is nothing.
Peter Evans, ARC Discovery Early Career Research Fellow, The University of Queensland
This article is republished from The Conversation under a Creative Commons license. Read the original article.