The hypothetical ‘chameleon’ particles have thought to be a participant in the dark energy phenomenon that explains our ever-expanding universe. The problem is: these stealthy particles are hard to detect in a lab setting. Scientists from the University of California, Berkeley plan to snare the ‘chameleons’ out of their hiding.
To understand ‘chameleons’, we need to understand dark energy
In the early 1990s, it was thought that the expansion of the universe had to be slowing down because of the gravitational forces of attraction pulling all matter together. However, sovernovae sightings by the Hubble Space Telescope (HST) in 1998 revealed that the expansion of the universe was accelerating due to gravity, not slowing down. Since then, the name ‘dark energy’ was used to describe anything that could be attributed to the expansion of the universe. Dark energy constitutes roughly 68% of the cosmos, with dark matter making up about 27%. It turns out that what we call ‘normal matter’ makes up a paltry 5% of the universe. Two main theories surround the dark energy phenomenon: The ‘cosmological constant’ theory, which has now been abandoned, states that the space has its own energy that would not get diluted as more space comes into existence. This could therefore cause accelerated expansion. The second one derives from quantum theory of matter and outlines energy from the existence of temporary particles, whose properties change with time and space making them dynamic.
‘Chameleon’ particles are dynamic and camouflaged
‘Chameleons’ are one of the hypothetical particle candidates for explaining dark energy. They are thought to exert forces a million times weaker than gravity. These particles are difficult to detect because they behave differently in surroundings with different densities. In the empty space, chameleons would have a small mass and be able to exert long-range forces needed to push the universe apart. However, in the much denser lab setting, they would have a large mass exerting virtually undetectable, short-range forces. The scientists attempted to defeat this limitation by using an atom interferometer.
Chameleon-induced forces may function at the same scale as gravity
In the experiment involving the interferometer, they dropped atoms of the element cesium over an aluminium sphere, and used lasers to detect the forces the atoms experienced. They found no trace of any other force than gravity, thereby ruling out ‘chameleon’ forces thought to be weaker than gravity. However, this could leave room for the possibility that chameleons may function at the same scale as gravitational forces. Fine-tuning the experimental conditions may reveal chameleons, or other dark energy particles, in the future.
Dark energy exploration often involves ruling things that cannot be true out than find things that are. Though without conclusive evidence, this study has brought us one step closer to what the dark energy could entail.