- Quantum mechanics states reality doesn't exist until it's measured
- This means a particle's past behaviour changes based on what we see
- Experiment using an atom and laser beams has proven this to be true
- How the atom behaved depended on how it was measured at end of test
The universe doesn't exist if we stop looking at it.
This
is according a famous theory in quantum mechanics which argues that a
particle's past behaviour changes based on what we see.
Now, scientists have performed a new experiment proving this theory to be true on the scale of atoms.
The bizarre nature of reality as laid
out by quantum theory has survived another test, with scientists
performing a famous experiment and proving that reality does not exist
until it is measured
According
to the rules of quantum mechanics, the boundary between the 'world out
there' and our own subjective consciousness are blurred.
When physicists look at atoms or particles of light, what they see depends on how they have set up their experiment.
To
test this, physicists at the Australian National University recently
conducted what is known as the John Wheeler's delayed-choice thought
experiment.
The experiment involves a moving object that is given the choice to act like a particle or a wave.
Wheeler's experiment then asks - at which point does the object decide?
Common sense says the object is either wave-like or particle-like, independent of how we measure it.
But
quantum physics predicts that whether you observe wave like behaviour
or particle behaviour depends only on how it is actually measured at the
end of its journey.
This is exactly what the Australian team found.
'It
proves that measurement is everything. At the quantum level, reality
does not exist if you are not looking at it,' said Associate Professor
Andrew Truscott.
Despite the apparent weirdness, the results confirm the validity of quantum theory.
Quantum
theory governs the world of the very small, and has enabled the
development of many technologies such as LEDs, lasers and computer
chips.
The
ANU reversed Wheeler's original concept of light beams being bounced by
mirrors, and instead used atoms scattered by laser light.
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'Quantum
physics predictions about interference seem odd enough when applied to
light, which seems more like a wave,' said PhD student Roman Khakimov.
'But
to have done the experiment with atoms, which are complicated things
that have mass and interact with electric fields and so on, adds to the
weirdness.'
Physicists at the Australian National
University recently conducted what is known as the John Wheeler's
delayed-choice thought experiment . Pictured is Associate Professor
Andrew Truscott (left) with PhD student Roman Khakimov
Professor
Truscott's team first trapped a collection of helium atoms in a
suspended state known as a Bose-Einstein condensate, and then ejected
them until there was only a single atom left.
The
single atom was then dropped through a pair of laser beams, which
formed a grating pattern that acted as crossroads in the same way a
solid grating would scatter light.
A
second light grating to recombine the paths was randomly added, which
led to constructive or destructive interference as if the atom had
travelled both paths.
When the second light grating was not added, no interference was seen as if the atom chose only one path.
However,
the random number determining whether the grating was added was only
generated after the atom had passed through the crossroads.
If
you choose to believe that the atom really did take a particular path
or paths then you have to accept that a future measurement is affecting
the atom's past, said Truscott.
'The
atoms did not travel from A to B. It was only when they were measured
at the end of the journey that their wave-like or particle-like
behaviour was brought into existence,' he said.
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