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<p data-start="47" data-end="160">[even opfrissen waar de
theoretische natuurkunde ook al weer was gebleven...]</p>
<h2 data-start="47" data-end="160"><br>
</h2>
<h2 data-start="47" data-end="160">Locality and Its Discontents: A
Philosophical Essay on the Rift Between General Relativity and
Quantum Physics</h2>
<h3 data-start="162" data-end="226">1. Introduction: A Fracture at
the Heart of Modern Physics</h3>
<p data-start="228" data-end="612">Modern physics rests on two
intellectual pillars of extraordinary success: <strong
data-start="303" data-end="325">general relativity</strong> and
<strong data-start="330" data-end="348">quantum theory</strong>.
Each has reshaped not only scientific practice but also our
deepest philosophical intuitions about space, time, causality, and
reality itself. Yet these theories appear to stand in conceptual
tension—perhaps even contradiction—over the principle of <strong
data-start="599" data-end="611">locality</strong>.</p>
<p data-start="614" data-end="987">General relativity is a theory of
spacetime and gravitation grounded in local causation: physical
influences propagate continuously through spacetime at finite
speeds, ultimately limited by the speed of light. Quantum theory,
by contrast, seems to allow — and in some interpretations demands
— <strong data-start="908" data-end="934">non-local correlations</strong>,
most strikingly manifested in quantum entanglement.</p>
<p data-start="989" data-end="1305">This essay examines this dispute
not merely as a technical inconsistency, but as a philosophical
conflict about what the world is like. The disagreement is not
simply about equations; it is about whether reality is
fundamentally local, separable, and continuous, or whether it is
irreducibly holistic and relational.</p>
<hr data-start="1307" data-end="1310">
<h3 data-start="1312" data-end="1378">2. Locality in General
Relativity: The Geometry of Causation</h3>
<p data-start="1380" data-end="1750">In <strong data-start="1383"
data-end="1405">general relativity</strong>, developed by <strong
data-start="1420" data-end="1461"><span
class="hover:entity-accent entity-underline inline cursor-pointer align-baseline"><span
class="whitespace-normal">Albert Einstein</span></span></strong>,
gravity is not a force transmitted through space but the curvature
of spacetime itself. Matter tells spacetime how to curve, and
spacetime tells matter how to move. Crucially, this interaction is
<strong data-start="1659" data-end="1668">local</strong>: what
happens at a point in spacetime depends only on its immediate
neighborhood.</p>
<p data-start="1752" data-end="2080">Einstein’s equations are <strong
data-start="1777" data-end="1809">local differential equations</strong>.
They encode a vision of the universe in which causal influence
propagates smoothly, respecting light cones and prohibiting
instantaneous action at a distance. This structure underwrites
relativity’s commitment to causality and its compatibility with
special relativity.</p>
<p data-start="2082" data-end="2157">Einstein’s philosophical
commitments here were explicit. He famously wrote:</p>
<blockquote data-start="2159" data-end="2263">
<p data-start="2161" data-end="2263">“The field at one point of
space has no immediate influence on the field at another point
of space.”</p>
</blockquote>
<p data-start="2265" data-end="2510">This locality principle was not
merely a mathematical convenience; it was, for Einstein, a
metaphysical requirement for intelligibility. Without locality,
physics risked collapsing into what he regarded as “spooky” and
unscientific correlations.</p>
<hr data-start="2512" data-end="2515">
<h3 data-start="2517" data-end="2582">3. Quantum Non-Locality:
Entanglement and the EPR Challenge</h3>
<p data-start="2584" data-end="3016">Quantum mechanics, however,
seems to violate this ideal. The most dramatic challenge emerged
in the <strong data-start="2684" data-end="2697">EPR paper</strong>
of 1935, authored by <strong data-start="2719" data-end="2760"><span
class="hover:entity-accent entity-underline inline cursor-pointer align-baseline"><span
class="whitespace-normal">Albert Einstein</span></span></strong>,
<strong data-start="2762" data-end="2803"><span
class="hover:entity-accent entity-underline inline cursor-pointer align-baseline"><span
class="whitespace-normal">Boris Podolsky</span></span></strong>,
and <strong data-start="2809" data-end="2850"><span
class="hover:entity-accent entity-underline inline cursor-pointer align-baseline"><span
class="whitespace-normal">Nathan Rosen</span></span></strong>.
The authors argued that quantum mechanics was incomplete because
it allowed distant systems to exhibit perfect correlations without
any mediating local interaction.</p>
<p data-start="3018" data-end="3114">Einstein derisively referred to
this as <em data-start="3058" data-end="3083">“spukhafte
Fernwirkung”</em>—<em data-start="3084" data-end="3113">spooky
action at a distance</em>.</p>
<p data-start="3116" data-end="3478">Quantum entanglement appears to
permit two particles, separated by vast distances, to behave as a
single system. A measurement performed here seems instantaneously
correlated with an outcome there. Importantly, this correlation
does not transmit usable information faster than light, but it
nonetheless resists any explanation in terms of local hidden
variables.</p>
<p data-start="3480" data-end="3665">Einstein’s concern was not
primarily about faster-than-light signaling; it was about <strong
data-start="3565" data-end="3581">separability</strong>—the idea
that spatially distinct systems possess their own independent real
states.</p>
<hr data-start="3667" data-end="3670">
<h3 data-start="3672" data-end="3748">4. Bohr’s Reply:
Complementarity and the Limits of Classical Intuition</h3>
<p data-start="3750" data-end="3941">Einstein’s great opponent in
this debate was <strong data-start="3795" data-end="3836"><span
class="hover:entity-accent entity-underline inline cursor-pointer align-baseline"><span
class="whitespace-normal">Niels Bohr</span></span></strong>,
who rejected the demand that quantum mechanics conform to
classical intuitions of locality and realism.</p>
<p data-start="3943" data-end="4150">Bohr’s response to the EPR
argument was subtle and famously opaque. He insisted that quantum
phenomena cannot be understood apart from the experimental
contexts in which they are measured. According to Bohr:</p>
<blockquote data-start="4152" data-end="4240">
<p data-start="4154" data-end="4240">“There is no quantum world.
There is only an abstract quantum mechanical description.”</p>
</blockquote>
<p data-start="4242" data-end="4504">For Bohr, the mistake lay in
assuming that physical properties exist independently of
measurement. Entanglement did not signal non-local causation but
rather the failure of classical categories—like separable systems
and definite properties—to apply universally.</p>
<p data-start="4506" data-end="4704">Philosophically, Bohr embraced
a form of <strong data-start="4547" data-end="4576">anti-realist
epistemology</strong>: physics does not describe reality “as it
is,” but rather what can be meaningfully said about nature under
specific conditions.</p>
<hr data-start="4706" data-end="4709">
<h3 data-start="4711" data-end="4762">5. Bell’s Theorem: The Death
of Local Realism</h3>
<p data-start="4764" data-end="5016">The debate might have remained
philosophical were it not for the decisive intervention of <strong
data-start="4854" data-end="4895"><span
class="hover:entity-accent entity-underline inline cursor-pointer align-baseline"><span
class="whitespace-normal">John Bell</span></span></strong>
in 1964. Bell proved that no theory based on <strong
data-start="4941" data-end="4958">local realism</strong> could
reproduce all the predictions of quantum mechanics.</p>
<p data-start="5018" data-end="5275">Bell’s theorem transformed the
issue from interpretation to experiment. Subsequent tests—most
notably those by <strong data-start="5129" data-end="5170"><span
class="hover:entity-accent entity-underline inline cursor-pointer align-baseline"><span
class="whitespace-normal">Alain Aspect</span></span></strong>
and later loophole-free experiments in the 21st century—have
overwhelmingly supported quantum mechanics.</p>
<p data-start="5277" data-end="5328">Bell himself was clear-eyed
about the consequences:</p>
<blockquote data-start="5330" data-end="5415">
<p data-start="5332" data-end="5415">“The idea that correlations
can be explained by local causes is no longer tenable.”</p>
</blockquote>
<p data-start="5417" data-end="5599">What quantum theory seems to
demand, then, is not merely non-locality, but the abandonment of a
classical worldview in which the universe is composed of
independently existing parts.</p>
<hr data-start="5601" data-end="5604">
<h3 data-start="5606" data-end="5660">6. The Deep Conflict:
Spacetime vs. Entanglement</h3>
<p data-start="5662" data-end="5973">Here the tension with general
relativity becomes acute. General relativity presupposes a <strong
data-start="5751" data-end="5780">local spacetime structure</strong>;
quantum theory, through entanglement, seems to transcend spacetime
entirely. Entangled systems are not “connected” through space but
are described by a single, non-factorizable quantum state.</p>
<p data-start="5975" data-end="6286">Philosophically, this suggests
a striking reversal: spacetime, once regarded as the fundamental
arena of physical reality, may be emergent rather than
fundamental. Some contemporary approaches to quantum gravity—such
as holography and spacetime-from-entanglement proposals—explicitly
entertain this possibility.</p>
<p data-start="6288" data-end="6470">Yet these approaches also raise
troubling questions. If spacetime emerges from entanglement, what
becomes of causality? What replaces locality as the organizing
principle of physics?</p>
<hr data-start="6472" data-end="6475">
<h3 data-start="6477" data-end="6531">7. Interpretive Responses:
Escape or Revolution?</h3>
<p data-start="6533" data-end="6595">Several strategies attempt to
reconcile or evade the conflict:</p>
<ul data-start="6597" data-end="6913">
<li data-start="6597" data-end="6687">
<p data-start="6599" data-end="6687"><strong data-start="6599"
data-end="6627">Hidden-variable theories</strong>, such as
Bohmian mechanics, accept non-locality explicitly.</p>
</li>
<li data-start="6688" data-end="6799">
<p data-start="6690" data-end="6799"><strong data-start="6690"
data-end="6721">Many-worlds interpretations</strong> deny
collapse and reinterpret non-local correlations as branching
structures.</p>
</li>
<li data-start="6800" data-end="6913">
<p data-start="6802" data-end="6913"><strong data-start="6802"
data-end="6858">Relational and information-theoretic
interpretations</strong> downplay ontology in favor of
operational consistency.</p>
</li>
</ul>
<p data-start="6915" data-end="7067">None, however, fully resolves
the tension with general relativity. <font color="#ed333b">Either
locality is abandoned, or spacetime itself is demoted from
fundamental status.</font></p>
<hr data-start="7069" data-end="7072">
<h3 data-start="7074" data-end="7125">8. Philosophical Reflections:
What Must Give?</h3>
<p data-start="7127" data-end="7428">At its core, the dispute
between locality and non-locality is a dispute about <strong
data-start="7205" data-end="7232">metaphysical commitment</strong>.
Einstein sought a world that was intelligible, separable, and
objective. Quantum theory, as it stands, offers a world that is
holistic, context-dependent, and resistant to classical
description.</p>
<p data-start="7430" data-end="7633"><font color="#ed333b">The
philosophical cost of quantum non-locality is high: it
challenges our understanding of causation, individuality, and
even reality itself. Yet the empirical success of quantum
mechanics is undeniable.</font></p>
<p data-start="7635" data-end="7718">Perhaps the deepest lesson is
one of <strong data-start="7672" data-end="7694">epistemic
humility</strong>. As Bell once remarked:</p>
<blockquote data-start="7720" data-end="7820">
<p data-start="7722" data-end="7820">“We have an unromantic
picture of the world that works, but we do not know how to think
about it.”</p>
</blockquote>
<hr data-start="7822" data-end="7825">
<h3 data-start="7827" data-end="7871">9. Conclusion: An Unfinished
Synthesis</h3>
<p data-start="7873" data-end="8110">The conflict between general
relativity and quantum physics is not merely a technical problem
awaiting better mathematics. It is a philosophical crisis that
forces us to reconsider the foundations of explanation, causation,
and ontology.</p>
<p data-start="8112" data-end="8366">Whether the future belongs to a
radically revised notion of spacetime, a deeper non-local theory,
or an as-yet-unimagined synthesis remains unknown. What is clear
is that locality—once the bedrock of physical reasoning—can no
longer be taken for granted.</p>
<p data-start="8368" data-end="8570" data-is-last-node=""
data-is-only-node="">In this unresolved tension, physics reveals
its most philosophical face: not as a catalogue of facts, but as
an ongoing struggle to make sense of a reality that continually
exceeds our conceptual grasp.</p>
<p><br>
</p>
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