Illustration by Bud Cook September 2019, ScientificAmerican.com 33sible. The mathematics of quantum theory jumbles
together subjective and objective elements. His “QBist”
interpretation tries to strip away the subjective ele-
ments and reveal the real structure that lies within,
much as Einstein did with relativity theory.
Philosopher Richard Healey of the University of
Arizona has a related “pragmatist” view that quantum
theory is a representation not of the world but of the
interface between the world and a human or another
agent. We can use it to judge the probabilities of things
that might happen, just as a technical stock trader
buys and sells based on market trends rather than eco-
nomic fundamentals. Such a trader can become rich
without a clue what the companies are doing. Unlike
Fuchs, Healey doesn’t think that a description of phys-
ical reality is tucked inside quantum theory. That, he
thinks, will require an entirely new theory.
At the opposite pole, if you do take quantum theory
to be a representation of the world, you are led to think
of it as a theory of co-existing alternative realities.
Such multiple worlds or parallel universes also seem
to be a consequence of cosmological theories: the same
processes that gave rise to our universe should beget
others as well. Additional parallel universes could ex-
ist in higher dimensions of space beyond our view.
Those universes are populated with variations on our
own universe. There is not a single definite reality.
Although theories that predict a multiverse are en-
tirely objective—no observers or observer-dependent
quantities appear in the basic equations—they do not
eliminate the observer’s role but merely relocate it.
They say that our view of reality is heavily filtered, and
we have to take that into account when applying the
theory. If we do not see a photon do two con tradictory
things at once, it does not mean the photon is not do-
ing both. It might just mean we get to see only one of
them. Likewise, in cosmology, our mere existence cre-
ates a bias in our observations. We necessarily live in a
universe that can support human life, so our measure-
ments of the cosmos might not be fully representative.
Parallel universes do not alter the truth that we ex-
perience. If you suffer in this universe, it is little com-
fort that near duplicates of you thrive elsewhere. But
these other worlds are corrosive to the pursuit of
broader truth. Because the other universes are gener-
ally not observable, they represent an insuperable
limit to our direct knowledge. If those universes are
utterly unlike our own, our empirical knowledge is
not merely limited but deceived. The laws of physics
risk descending into anarchy: they do not say that one
thing happens rather than another, because both hap-
pen, and which we see is blind luck. The distinction
between fact and fiction is just a matter of location.EVEN SOME ASPECTS of fundamental physics that seem
firmly established are surprisingly subtle. Physicists
routinely speak of particles and fields: localized motes
of matter and continuous, fluidlike entities such as theH O W A P H Y S I C I A N
SEARCHES FOR ANSWERSThe answer to questions about human
life isn’t a certain thing, like measuring how a stone
drops to the ground in exactly so many seconds. If it were, it probably would not
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we know before we even start a study.
Still, the one core dimension across biomedicine is the ability to replicate, in
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we have been discouraged from doing this. Why waste money to do the exact
thing you had done before, let alone something someone else had done before?
But many researchers are realizing it is not possible to leave out replication studies.
To make replication work, though, it is essential to have a detailed expla-
nation of how the original study was done. You need the instructions, the raw
data and maybe even some custom-built computer software. For a long time,
scientists didn’t want to share that information, but that is changing. Science
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Dø§îî ̧Ux³ ̧Çx³D³läDß³ÍJohn P. A. Ioannidis, a professor of medicine at Stanford University,
as told to Brooke Borel