The planet Earth is the laboratory for the study of the fifth force

Picture of the experimental setup. It depicts the long-range spin-spin interaction (blue wavy lines) in which the spin-sensitive detector on Earth’s surface interacts with geoelectrons (red dots) deep in Earth’s mantle. Illustration: Marc Airhart (University of Texas at Austin) and Steve Jacobsen (Northwestern University).

Picture of the experimental setup. It depicts the long-range spin-spin interaction (blue wavy lines) in which the spin-sensitive detector on Earth’s surface interacts with geoelectrons (red dots) deep in Earth’s mantle. Illustration: Marc Airhart (University of Texas at Austin) and Steve Jacobsen (Northwestern University).

The Earth, in particular ferrous minerals that make up the mantle of the planet, will be the ideal laboratory for the study of a hypothetical fifth fundamental force of nature, a  long range spin – spin particle interaction.
This is what say physicists led by Larry Hunter of Amherst College in Massachusetts in a paper published on Science. The consequences of the experiment could also provide new information on the nature of the lower mantle of the planet Earth.

The four fundamental forces in nature are gravity, electromagnetism and the strong and weak nuclear forces. The hypothetical fifth force can be thought as a kind of magnetism not decreasing with the distance. Each quantum particle has a certain spin, whose value determines the force exerted on the particle when it interacts with a magnetic field. Two spin particles interact as two magnets and their interaction is effective only at short distances, because the intensity of the force is inversely proportional to the cube of the distance.

Larry Hunter and co – workers are looking for a long range spin-spin interaction between particles. The fifth force should be mediated by an exotic particle called unparticle, whose existence was first postulated in a 2007  by Howard Georgi. The ordinary particles are characterized by their mass, momentum and energy. According to theory, it is not possible to scale all quantities by a factor without changing the nature of the particle. The unparticle has this characteristic, it is scale invariant by changing mass, momentum and energytogether. The unparticle are just a guess, no one has ever detected yet.

Since the interaction of the hypothetical fifth force is felt at a great distance and is very weak, scientists had the crazy idea to use all the electrons of the mantle as source to measure the interaction with the particles in the lab. Scientists have created a density and spin orientation map of electrons in the Earth’s mantle (they called them geoelectrons) by studying the characteristics the Earth’s geomagnetic field. Although scientists have not found the fifth force, they have quantitatively established it should be very weak. If the force exists, it is so weak that gravitational force between two particles, for example an electron and a neutron, is a million times stronger.

As a possible result, the study might eventually provide geophysicists with a new tool that allow them to directly study the inaccessible depths of the planet Earth.

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