Scientists are trying to answer one of the biggest open questions in physics
More than 70 years ago, an idea arose in the physicist community: to use magnetic fields and the spin property (internal angular momentum) of the electron, to cause a body from the world of large objects to exist in two places at the same time, i.e. to be in a state of "superposition". A research group, led by Prof. Ron Pullman from the Physics Department at Ben-Gurion University of the Negev, recently succeeded in realizing the idea, and even proposed an advanced version of a device that may provide future answers to one of the central questions in physics: Is there a connection between quantum theory and gravitation?
In the 20th century, two revolutions took place in the field of physics: relativity (which also deals with gravitation) and quantum theory. Both are still the pillars of modern physics. One of the open questions in this field is why we do not succeed in uniting these two successful theories in the framework of one theory that will be called quantum-gravitation?
Prof. Pullman's research group proposed a way to conduct an experiment that would test the relationship between the two theories. At the core of the idea is a device (a unique interferometer) based on the principles of quantum theory and capable of allowing one body to exist in two places at the same time. There are many types of interferometers, but the interferometer developed by Prof. Pullman and his group members is particularly important because it is suitable for working with particles of large mass (which, naturally, are exposed to a relatively large gravitational interaction). The unique device, which the group was able to develop, is a "full loop interferometer based on the Stern-Gerlach effect" or in short a "magnetic interferometer".
Exactly 100 years ago, an experiment was carried out in which the "Stern-Gerlach effect" was discovered, named after the physicists Walter Gerlach and Otto Stern. A beam of silver atoms is launched towards a screen, as it crosses a magnetic field of varying strength. The magnetic field split the atoms into two rays. The quantum explanation for this splitting is that the atom is actually a small magnet that can only be in one of two directions with respect to the magnetic field, and thus two magnetic forces act on it. The internal magnet of the atom (which is related to its internal angular momentum) is given the name "spin".
In the 50s it was theoretician David Bohm who proposed to create a complete loop of splitting and recombining the rays: after the splitting, a magnetic field would stop the rays and direct them back towards each other, so that the rays would unite again into one beam, after making a complete loop. This is how the magnetic interferometer was created. After a body has existed in two places at the same time (the two branches of the beam), it again unites into one body, and through measurements performed on this one body, it is possible to learn about differences in the conditions experienced by the body in the two orbits, conditions such as the gravitational interaction.
In fact, it was very difficult to implement such a loop. It was necessary that the parts of the split atom not only be returned to the same place but also at exactly the same speed. The scientists from Ben-Gurion University of the Negev were able to control the magnetic field with a particularly high level of precision using a chip (such as computer chips). In addition, the beam of atoms they used was not a beam of silver atoms, but of rubidium atoms that underwent a process of deep cooling to a temperature close to absolute zero (minus 273 degrees Celsius), so that the scientists' control over the properties of the atom was very high.
A few years ago, the group performed another experiment with a similar purpose, when they used an atomic clock consisting of a single atom that was placed in two places at the same time, one closer than the other to the Earth (according to the theory of relativity, time is affected by gravity). However, to reach unequivocal results in this experiment, significant improvements in the performance of the atomic clocks will be required. Now the group proposes to put in the interferometer a body with a very large mass, such that the gravitational forces acting on it will not be negligible. In this way, one experiment will be obtained, in which the quantum theory will operate, which allows one body to exist in two places at the same time, alongside the theory of gravitation, the force it exerts depends on the size of the body's mass. Only by combining the two theories together will it be possible to explain the experiment.
To prove the feasibility of the ambitious experiment, the research group, called the 'Atomic Chip Group', carried out a preliminary experiment, with the support of the National Science Foundation. In this attempt, the scientists used single atoms, and on the other hand, implemented the entire process that would be required to do this with a heavy mass. "This achievement has an important meaning," says Prof. Pullman, "since it is possible that the creation of such a Stern-Gerlach interferometer, with a large mass, will give us New clues regarding the quantum nature of gravity, and thus we may be able to solve one of the great mysteries of modern physics."
Now that there seems to be a practical way to do this, the group will begin, together with other groups around the world, in the realization of the experiment.
The research team included: Dr. Yair Margalit, Mr. Or Dovkovski, Dr. Zhifan Zo, Mr. Omer Amit, Dr. Yonatan Yaffe, Dr. Samuel Mukuri, Dr. Daniel Rorlich, Prof. Anupam Mazumder, Prof. Sugato Bose, Dr. Karsten Henkel and Prof. Ron Polman.
Prof. Ron Polman lives in Tel Aviv and is the father of four daughters. He is a human rights and peace activist, and also an environmental activist. He also invests his energy in sports and extreme sports, from volleyball, through snowboarding to flying. Ron is also known as the one who tattooed an exact copy of the number engraved on his father's arm in Auschwitz.
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