Experiment confirms quantum theory weirdness: Reality doesn’t exist until measured

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.

Physicists at The Australian National University (ANU) have conducted John Wheeler’s delayed-choice thought experiment, which 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 behavior (interference) or particle behavior (no interference) depends only on how it is actually measured at the end of its journey. This is exactly what the ANU 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 from the ANU Research School of Physics and Engineering.

Despite the apparent weirdness, the results confirm the validity of quantum theory, which governs the world of the very small, and has enabled the development of many technologies such as LEDs, lasers and computer chips.

The ANU team not only succeeded in building the experiment, which seemed nearly impossible when it was proposed in 1978, but reversed Wheeler’s original concept of light beams being bounced by mirrors, and instead used atoms scattered by laser light.

“Quantum physics’ predictions about interference seem odd enough when applied to light, which seems more like a wave, 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,” said Roman Khakimov, PhD student at the Research School of Physics and Engineering.

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 counter-propagating 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 observed 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 one chooses to believe that the atom really did take a particular path or paths then one has 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 behavior was brought into existence,” he said. The research is published in Nature Physics.

5 thoughts on “Experiment confirms quantum theory weirdness: Reality doesn’t exist until measured

  1. If the universe doesn’t exist until measured, then there must be a “god”, or someone outside the universe to initiate the chain of measurements, so that humans can exist and measure whether it is a particle or a wave.

    H’mm…I might doubt some of these conclusions.

  2. “However, the Bohr-Einstein debate has already been resolved, and in favor of Einstein: What Einstein desired and Bohr deemed impossible–an observer-free formulation of quantum mechanics, in which the process of measurement can be analyzed in terms of more fundamental concepts–does, in fact, exist.”

    From Quantum Theory Without Observers http://www.math.rutgers.edu/~oldstein/papers/qts/qts.html

    But if you read the article, the team begin by demonstrating that the helium atoms exists, by collecting and isolating it, then try to say that after this same the helium atom does not exist until they later measure it. The damn thing seems to be flickering in and out of existence. Clearly the authors are confused.

    Also we ought not to get too excited about the “observation” part of this. Observation here really means “physical interaction with the experimental apparatus”. No person can observe a single atom. Thus observation boils down to *physical interaction*. If you design the apparatus to interact with a wave it will, and if you design it to interact with a particle it will do that. And in reality particles are interacting with each other constantly. “Observation” has nothing to do with it. That’s just a conceit.

    The trouble here is that, as so often happens, these scientists are just not very good at thinking philosophically.

  3. Reality in the universe is a matter that we can only appreciate in a subjective manner. We will never be able to know what something is absolutely, but only can manage to understand it in our discernible ways. In quantum physics this inability to have complete knowledge is high-lighted by the incompleteness theorem, but we should not think that this problem is unique to small particles. So any scientific knowledge which is claimed to be about reality should be doubted.

  4. In an effort to make quantum theory seem even weirder than it already is (and it’s weird enough), science writers always substitute “look at” for “measure” so people think OMG I have to actually look at it? No, that’s not the case at all. Measurement, in quantum mechanics, is basically just short-hand for an interaction that rises above the quantum universe into the universe we understand. Reality is real all the time. It’s just that the “duality” (particle vs wave) is directly influenced by how we measure it (ie, cause an interaction with the underlying quantum state) which we then interpret. It seems like it’s got some sort of intelligence, but that’s just us bad science writing. It’s not. It exists in the state it exists all the time. Whether it expresses itself as a wave, particle, both, or neither, is dependent on how we measure it, but that has nothing to do with reality “not existing” if an intelligent actor isn’t looking at it. That’s metaphysics, basically. It’s an unfalsifiable question and irrelevant.

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