The demonstration, which turned ideas of the great Isaac Newton on the nature of light, was incredibly simple. It “can be repeated with great ease, whenever the sun is shining,” said the English physicist Thomas young in November of 1803 members of the Royal society in London, describing the experiment, which is now called the double slit experiment. And young was enthusiastic youngster. He came up with an elegant and carefully thought-out experiment, demonstrating the wave nature of light, and thereby disproved Newton’s theory that light consists of corpuscles, i.e. particles.
But the birth of quantum physics in the early 1900-ies have indicated that light was composed of tiny indivisible units or quanta of energy which we call photons. The young’s experiment carried out with single photons or even with individual particles of matter such as electrons and neurons, is a mystery that raises questions about the nature of reality. Some even used it to claim that the quantum world is affected by human consciousness. But do a simple experiment can demonstrate this?
Can consciousness determine reality?
In modern quantum form, the young’s experiment involves shooting individual particles of light or matter through two slits, or holes carved in an opaque barrier. On one side of the barrier is a screen, recording the arrival of the particle (say, a photographic plate in the case of photons). Common sense leads us to expect that the photons will take place or through one, or through another slot and accumulate the relevant passage.
But no. The photons fall in certain parts of the screen and avoid the other, creating alternating bands of light and dark. These so-called interference fringes resemble the picture of the meeting of two waves. When the crests of one wave are aligned with ridges of the other, you get constructive interference (bright bands), and when crests are aligned with troughs, you get destructive interference (dark).
But using the device takes only one photon at a time. It seems that the photon passes through both slits at once and interferes with itself. This is contrary to the common (classical) sense.
Mathematically speaking, through both slits is not a physical particle or a physical wave, but the wave function is an abstract mathematical function that represents the state of a photon (in this case position). The wave function behaves like a wave. It falls on the two slits, and new wave come out on the other side of the cracks propagate and interfere among themselves. Combined wave function allows to calculate the probability, where there may be the photon.
A photon has a high probability of being where the two wave functions constructively interfere, and low — where the interference is destructive. Measurement — in this case, the interaction of wave functions with a photographic record leads to a “collapse” of the wave function, its collapse. In the end, she points to one of the places in which the photon materializes after the measurement.
This is obviously caused by the measurement wave-function collapse became the source of many conceptual difficulties in quantum mechanics. Before the collapse there is no way to say for sure where the photon; it can be anywhere with non-zero probability. There is no way to trace the trajectory of the photon from source to detector. Photon unreal in the sense in which a real aircraft flying from San Francisco to new York.
Werner Heisenberg, among others, interpreted this math the way that reality does not exist until observed. “The idea of an objective real world whose smallest particles exist objectively in the same sense in which there are stones or trees, regardless of the fact that we observe them or no, — impossible,” he wrote. John Wheeler also used the variant of double slit experiment, to declare that “no elementary quantum phenomenon is a phenomenon until it is registered (“observed”, “it is written”) phenomenon.”
But quantum theory absolutely does not give any clues to what is considered “measurement”. It just postulates that the measuring device should be a classic, without defining where that line between classical and quantum, and leaving the door open for those who believe that the collapse causes the human mind. Last may, Henry Stapp and his colleagues said that the double slit experiment and its modern variants suggests that “conscious observer may be necessary” to give meaning to the quantum field, and that the basis of the material world is transpersonal mind.
But these experiments are not empirical evidence of such allegations. In the double slit experiment done with single photons, it is only possible to verify the probabilistic predictions of mathematics. If the likelihood surface in the process of chambering tens of thousands of identical photons through a double slit, the theory says that the wave function of each photon imploded — due to unclear a particular process called measurement. That’s all.
In addition, there are other interpretations of the double slit experiment. Take, for example, the theory of de Broglie-Bohm, which States that reality is both wave and particle. The photon is sent to the double slit with a certain position at any point and passes through one slit or the other; hence, each photon has a trajectory. It passes through a pilot wave which penetrates through both slits, interferes and sends a photon in the place of constructive interference.
In 1979 Chris gudni and his colleagues at the College Birkbeck in London modeled the prediction of the theory on the trajectories of particles which pass through a double slit. Over the past ten years, the experimenters confirmed that such trajectories exist, though, and used a controversial technique known as weak measurement. Despite the controversial, experiments have shown that the theory of de Broglie-Bohm is still able to explain the behavior of the quantum world.
More importantly, this theory does not need observers or measurement, or non-consciousness.
It does not need so-called theories of collapse, from which it follows that wave functions collapse at random: the greater the number of particles in a quantum system, the more likely the collapse. Observers simply record the result. The team of Markus Arndt of the University of Vienna in Austria tested these theories, sending larger and larger molecules through the double slit. The theory of collapse predict that when the particles of matter become heavier than a certain threshold, they can no longer remain in a quantum superposition and pass through both slits simultaneously, and this destroys the interference pattern. The team of Arndt sent a molecule with 800 atoms through a double slit and still saw the interference. Search threshold continues.
Roger Penrose had our own version of the theory of collapse, in which the higher the mass of the object in superposition, the faster it collapses to one state or another because of gravitational instabilities. And again, this theory does not require the observer and of any consciousness. Dirk Bouwmeester University of California, Santa Barbara examines the idea of Penrose with one version of the double slit experiment.
The conceptual idea is to not just put the photon in a superposition of passing through two slits simultaneously, but to put one of the slits in a superposition and get to be in two places at the same time. According to Penrose, replaced the gap will either remain in a superposition, or collapses with the photon on the fly, which will lead to different patterns of interference. This collapse will depend on the mass gaps. Boumeester working on this experiment for ten years, and may soon prove or disprove the statements of Penrose.
In any case, these experiments show that we can not yet make any statements about the nature of reality, even if these statements are well backed up by mathematically or philosophically. And given the fact that neuroscientists and philosophers of mind disagree about the nature of consciousness, the claim that it leads to the collapse of the wave functions, it would be premature at best and wrong at worst.
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