Science & Technology (Commonwealth Union) – The speculation as to what exactly is the relationship between empty space and light has been on the minds of scientists for years.
Astronomers may have possibly found evidence of one of quantum mechanics’ most unusual predictions: that even apparently empty space can influence how light behaves.
Known as vacuum birefringence, this phenomenon was proposed nearly nine decades ago by Werner Heisenberg, one of the key figures in the development of quantum theory. He theorised that a perfect vacuum is not truly empty, but instead contains fleeting “virtual particles” that constantly appear and disappear.
A research team, including Dr Marcus Lower from Swinburne University of Technology, investigated this quantum effect by studying a magnetar — an extremely rare type of neutron star known to produce the most powerful magnetic fields in the universe.
Their findings may represent the first evidence of vacuum birefringence occurring within a magnetar’s intense magnetic environment. The discovery could provide a new way to investigate the hidden quantum properties of the universe. The study was published recently in Nature.
In the presence of an extraordinarily strong magnetic field, the ocean of Heisenberg’s predicted virtual particles should influence the way light travels, causing it to bend and polarize in distinctive patterns — a phenomenon known as vacuum birefringence. However, only rare cosmic objects called magnetars possess magnetic fields powerful enough for this subtle quantum effect to become detectable.
Dr Lower is a member of an international research team that studied the magnetar 1E 1547.0–5408 (commonly referred to as 1E1547) with NASA’s Imaging X-ray Polarimetry Explorer (IXPE). The observations were complemented by data from the NICER X-ray telescope aboard the International Space Station and Murriyang, the CSIRO-operated Parkes radio telescope in Australia.
Dr Lower’s measurements from Murriyang, combined with further analysis carried out on Swinburne University’s Ngarrgu Tindebeek supercomputer, may represent the first direct evidence of this quantum phenomenon, which had previously existed only as a theoretical prediction.
Dr Lower highlighted the fact that although vacuum birefringence was first proposed in the 1930s, scientists have yet to obtain a definitive experimental confirmation of the effect until now.
By precisely monitoring how the radio waves released by the magnetar change their oscillation direction — known as their “polarisation state” — as the object spins, researchers determined that the magnetic and rotational axes of 1E 1547.0–5408 are almost perfectly aligned. They also found that the magnetar is being observed nearly directly along one of its poles. This particular magnetic and viewing arrangement makes 1E 1547 an excellent target for detecting the effects of vacuum birefringence.
The researchers then uncovered two key indicators that this quantum effect is occurring around the magnetar. They discovered that the X-rays detected from 1E1547 by IXPE showed exceptionally strong polarisation, and that the direction of this polarisation remained aligned with the magnetar’s magnetic field, matching the behaviour seen in its radio emissions.
Dr Lower indicated that due to the immense strength of the magnetic field, Heisenberg’s virtual particles become organised and aligned with the direction of the field.
“By carefully tracking the direction the radio waves and X-rays oscillate as the magnetar rotates, the team found that the alignment of 1E1547’s magnetic and rotational poles were ideal for detecting vacuum birefringence.”
If validated, this breakthrough could provide a new window into how the laws of quantum physics operate under some of the most extreme conditions found anywhere in the universe.
Dr Lower notes that the remarkable result may soon be strengthened through further observations, with additional data and more advanced computer modelling helping researchers distinguish the vacuum birefringence effect from other phenomena taking place around magnetars.
