Dark energy permeates the universe. It can cause entire galaxies to move, yet it remains invisible. In early 1998, researchers discovered that the universe is expanding too rapidly, an unexpected result. Approximately 15 billion years ago, during the Big Bang, the universe underwent a sudden expansion, increasing its size by a factor of 1050 in an instant. However, this tremendous expansion gradually slowed down over time due to the gravitational forces pulling planets and stars closer together.
“We have evidence of this accelerating expansion thanks to several extremely bright stars,” explained Jean-Philippe Uzan, an astrophysicist at the Paris Institute of Astrophysics. “These stars, at the end of their life cycle, emit extraordinary light, illuminating the universe like a spotlight. The advantage is that the brightness of these stars remains stable, allowing us to use them as an effective means to measure the distance between us and the dying star. The closer we are, the brighter it appears.”
Astronomers have cataloged a significant number of these extremely bright stars, calculating the distance between them and Earth. “Overall, the extremely bright stars appear dimmer than before. This means we are increasingly farther away from them than predicted. In other words, the universe has been expanding faster, increasing the distance between Earth and the bright stars.”
This expansion of the universe became the first evidence for the existence of dark energy. Researchers were left with no choice but to invent the concept of “dark energy,” a form of matter that “pushes” (as it drives galaxies apart) to explain the acceleration they observed. However, it is unimaginable what particles might carry this energy.
Another piece of evidence was discovered in October 2003, this time from photons, the particles that carry light. American researchers focused on long-traveling photons that pass through galaxy clusters with diameters of hundreds of millions of light-years before reaching Earth.
Typically, the energy of a photon is not affected by the journey it takes. That is the theory on paper. In reality, photons gain a tiny bit of energy from an external source. This anomaly can only be explained by the influence of dark energy, which helps photons escape gravitational pull.
These speculations are bringing scientists closer to understanding dark energy, but it has yet to be proven. Nevertheless, this source of energy constitutes a large portion of the total energy in the universe.
(Source: CAND)
