Does a fifth force of nature exist or not?

We know that four physical forces rule the universe today: gravitational, electromagnetic, strong nuclear and weak nuclear, according to the standard model.

The gravitational force keeps us bound to Earth and the Earth to its orbit. It is all about the pull force, not the push one. Electromagnetic force works between two charges. As a result of this force, we have electricity, magnetism and light. We have harnessed this force in full measure and experience it in our daily life, from light to computers to cars. Among the rest of the forces, strong and weak nuclear operate within the atomic nucleus. The strong nuclear force is responsible for the binding of atomic nuclei. The weak force leads to radioactive decay, which is responsible for radiocarbon dating. It is also the force responsible for volcanoes, earthquakes and continental drift. 

Some scientists describe the subatomic world as a massive zoo, where a number of animals are yet to be discovered. This is what happened to Attila Krasznahorkay and his team during their experiment at the Institute for Nuclear Research in Debrecen, Hungary.

They saw odd results of sudden unexpected jumps in the emission of particles while they were hitting element lithium-7 with protons. After repeated results of the same jumps, they published a paper declaring they have discovered a new particle called ‘dark photon’. Dark photon would pave way in knowing the still unknown dark matter, they said.

The inability of the standard model of particle physics to explain dark matter has motivated many theorists to propose various exotic-matter particles and force-carriers, including ‘dark photons’, which are photons that carry the electromagnetic force. More than 80% of the universe’s mass is considered to be made of this dark matter. Because light has no effect on it, we know nothing about it.

But we know about the existence of dark matter simply because something is pushing the Earth, Sun and galaxy apart, leading to accelerated expansion of the universe. This expansion has been proved thanks to observations made by the Hubble telescope, Doppler effect and Einstein’s general theory of relativity. Now they say that there will be time in the far future when you see no more stars in the sky! They would have moved away too far. Attila’s report suggests the existence of a new, light boson only 34 times heavier than the electron.

While the Hungarian team said that they found a link to the dark matter well within the atom unknown to us so far, others who interpret their result and data tell a different story. Did they go wrong in interpreting their own results? Did they see what they wanted to? A team of scientists from University of California, Irvine led by Jonathan Feng has published a paper after scrutinising the already published Hungarian results with new interpretation. Jonathan and his team are of the opinion that the data reveals the proof of long suspected existence of the fifth force in the universe. This force, unlike the other four, exists between electron and neutron in the atomic world. This coupling is contrary to the standard model of physics known to us so far.

But the particle isn’t a dark photon, they say. They believe the particle could be ‘protophobic X boson’ instead. This particle would carry an extremely short-range force that acts over distances only several times the width of an atomic nucleus.

While a dark photon would couple electrons and protons, the new boson would couple electrons and neutrons. While the Hungarian team is absolutely confident about their result, the US researchers are conducting more experiments to find out more. Since the universe is a pretty massive entity filled with many things unknown to us, it would help in conducting more experiments in this arena to find out if there is a fifth force of nature or not.