For many decades, quantum science has argued the validity and reality of vacuum birefringence, an effect where a highly magnetized vacuum acts as a prism for the propagation of light. That's because it was difficult to find evidence that it really exists until a strongly magnetic neutron star called RX J1856.5-3754 came along.
Vacuum birefringence came into the quantum science vocabulary when physicists concluded in 1936 that the effects of these virtual particles in space could really be measurable by twisting its polarization. The simplest comparison how it happens is like how liquid crystals do in LCD displays.
However, finding evidence of its existence is difficult because scientists need a very strong electromagnetic field when they measure it directly. Such electromagnetic force is impossible to create in the laboratory. However, space has its own laboratory in the form of neutron stars, which are born after a big star explodes and dies. When these stars collapse, they leave a small, dense core that continues to collapse. Neutron stars possess a great amount of electromagnetic fields that enhances the effect of vacuum birefringence to measurable levels.
Scientists believe without a doubt that the strong magnetic field of the neutron star polarizes gravity. However, they are very far away from the Earth so the moment their light reach the planet, the polarization is gone.
However, it was different in the case of the neutron star called RX J1856.5-3754 because when scientists from the National Institute of Astrophysics in Milan, Italy, and University of Zielona Góra, Poland led by Roberto Mignani, the light it gives out polarized from somewhere between 11 and 12 percent, high enough to suggest that vacuum birefringence is happening.
George Pavlov from Penn State was quick to dismiss it saying such amount of polarization can still happen without vacuum birefringence. If such is the case, the only way to prove this is to conduct missions that would look at the polarization of X-rays rather than just depending on visible light. This is possible in the next few years since NASA has planned to send three different missions in the future. After such time, we will then really prove if vacuum birefringence is indeed true.
