සිංහල ලිත් ඉලක්කම්
෦ ෧ ෨ ෩ ෪ ෫ ෬ ෭ ෮ ෯
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Paradox
puts objectivity on shaky footing
මා දාර්ශනිකයකුවත් විද්‍යාඥයකුවත් නො වෙයි. මෙහි පහත
පළවන්නේ අගෝස්තු 21 වැනි දා සයන්ස් සඟරාවෙහි පළ වූ ලිපියක්. එහි කියැවෙන්නේ
නිරීක්‍ෂකයන් දෙදෙනකුගේ මිනුම් ඒ දෙදෙනාට සාපේක්‍ෂ බවයි. නිරීක්‍ෂකයන්ට එක ම
මිනුමක් ගැන එකඟතාවකට පත්විය නොහැකි බවයි කියැවෙන්නේ. මිනුම් ඊනියා සාධක (facts) සාපේක්‍ෂ බව කියනවා.
යථාර්ථය වාස්තවිකත්වය ආදිය ඇත්තේ දුර්වල පදනමක බවයි කියැවෙන්නේ. බටහිර විද්‍යාව
අවසාන වශයෙන් යැපෙන්නේ මිනුම් මත. දෙදෙනකුට මිනුමක් ගැන එකඟ වීමට නොහැකි නම් කාගේ
පිහිට ද? අර facts are sacred කතාවට මොකද වෙන්නෙ?
කවුරු හරි අහන්න පුළුවන් බටහිර විද්‍යාව කියන දේ ඇත්ත ද කියල. එය පට්ටපල් බොරුවක්. මා කියන්නෙ බටහිර විද්‍යාවේ කතා (හිතළු) ඇතැම් විට හරි යන බව මිස හරි බව නොවෙයි. වාස්තවිකත්වයක් නැතැයි කියන එක එහෙමත් නැත්නම් යථාර්ථයක් නැහැයි කියන එක යථාර්ථය ද කියල අහන්නත් පුළුවන්. එහෙම කීමත් හරියන දෙයක් වැඩ කරන දෙයක් පමණයි. අප ජීවත් වන්නේ වැඩ කරන සංකල්ප ප්‍රවාද ආදිය සංස්කරණය කර ගෙන. යථාර්ථයක් ඇතැයි කීම වැඩ කරන කතාවක් නො වෙයි. එය හුදු හිතළුවක් පමණයි.
Paradox
puts objectivity on shaky footing
IN SECTION: IN
DEPTH | QUANTUM THEORY
Quantum test of
venerable thought experiment suggests facts are relative
By George Musser
Nearly 60 years
ago, Nobel Prize–winning physicist Eugene Wigner captured one of the many
oddities of quantum mechanics in a thought experiment. He imagined a friend of
his, sealed in a lab, measuring a particle such as an atom while Wigner stood
outside. Quantum mechanics famously allows particles to occupy many locations
at once—a so-called superposition—but the friend’s observation “collapses” the
particle to just one spot. Yet for Wigner, the superposition remains: The
collapse occurs only when he makes a measurement sometime later. Worse, Wigner
also sees the friend in a superposition. Their experiences directly conflict.
Now,
researchers in Australia and Taiwan offer perhaps the sharpest demonstration
that Wigner’s paradox is real. In a study published this week in Nature
Physics, they transform the thought experiment into a mathematical theorem
that confirms the irreconcilable contradiction at the heart of the scenario.
The team also tests the theorem with an experiment, using photons as proxies
for the humans. Whereas Wigner believed resolving the paradox requires quantum
mechanics to break down for large systems such as human observers, some of the
new study’s authors believe something just as fundamental is on thin ice:
objectivity. The puzzle could mean there is no such thing as an absolute fact,
one that is as true for me as it is for you.
“It’s a bit
disconcerting,” says co-author Nora Tischler of Griffith University. “A
measurement outcome is what science is based on. If somehow that’s not
absolute, it’s hard to imagine.”
Some physicists
dismiss thought experiments like Wigner’s as interpretive navel gazing. But the
study shows that the contradictions emerge in actual experiments, says Dustin
Lazarovici, a physicist and philosopher at the University of Lausanne who was
not part of the team. “The paper goes to great lengths to speak the language of
those who have tried to merely discuss foundational issues away and may thus
compel at least some to face up to them,” he says.
Wigner’s
thought experiment has seen renewed attention in recent years. In 2015, Časlav
Brukner of the University of Vienna tested the most intuitive way around the
paradox: that the friend inside the lab has in fact seen the particle in one
place or another, and Wigner just doesn’t know where it is yet. In the jargon
of quantum theory, the friend’s result is a hidden variable.
Brukner sought
to rule out that conclusion in a thought experiment of his own, using a
trick—based on quantum entanglement—to bring the hidden variable out into the
open. He imagined setting up two friend-Wigner pairs and giving each a particle,
entangled with its partner in such a way that their attributes, upon
measurement, are correlated. Each friend measures the particle, each Wigner
measures the friend measuring the particle, and the two Wigners compare notes.
The process repeats. If the friends saw definite results—as you might
suspect—the Wigners’ own findings would show only weak correlations. But
instead they find a pattern of strong correlations. “You run into
contradictions,” Brukner says.
In 2018,
Richard Healey, a philosopher of physics at the University of Arizona, pointed
out a loophole in Brukner’s argument, which Tischler and her colleagues have
now closed. In their new scenario they make four assumptions. One is that the
results the friends obtain are real: They can be combined with other
measurements to form a shared body of knowledge. The researchers also assume
quantum mechanics is universal, as valid for observers as for particles; that
the choices the observers make are free of peculiar biases induced by a godlike
superdeterminism; and that physics is local, so that one observer’s choices do
not affect another’s results.
Yet the
analysis shows the contradictions of Wigner’s paradox persist. The team’s
tabletop experiment, in which it made pairs of entangled photons, also backs up
the paradox. Optical elements steered each photon onto a path that depended on
its polarization: the equivalent of the friends’ observations. The photon then
entered a second set of elements and detectors that played the role of the
Wigners. The team found, again, a mismatch between the observations of the
friends and the Wigners. What is more, when they varied exactly how entangled
the photons were, they found that the mismatch occurs for different conditions
than in Brukner’s scenario. “That shows that we really have something new
here,” Tischler says.
It also
indicates that one of the four assumptions has to give. Few physicists believe
superdeterminism could be to blame. Locality is already under fire in quantum
theory, but a failure in this case would imply an especially potent form of
nonlocality. So some are questioning the tenet that observers can pool their
measurements empirically. “It could be that there are facts for one observer,
and facts for another; they need not mesh,” says study co-author and Griffith
physicist Howard Wiseman. It is a radical relativism, still jarring to many.
“From a classical perspective, what everyone sees is considered objective,
independent of what anyone else sees,” says Olimpia Lombardi, a philosopher of
physics at the University of Buenos Aires.
And then there
is Wigner’s verdict: that quantum mechanics itself breaks down. Of all the
assumptions, it is the most testable, by efforts to probe quantum mechanics on
ever larger scales. But the one position that doesn’t survive the analysis is
having no position, says Eric Cavalcanti, a co-author at Griffith. “Most
physicists, they think: ‘That’s just philosophical mumbo-jumbo.’” Now, he says,
“They will have a hard time.”
George Musser is a
journalist based in New Jersey and author of Spooky Action at a
Distance.
