The Universe is constantly expanding ever since the Big Bang emerged 13.7 billion years ago. Despite the name of the theory, we must think of the Big Bang not as a literal ‘bang’. We must perceive the Big Bang as a constant expansion of the Universe, which means that we’re currently living within the ‘bang’ itself.
As for dark energy, it’s the ‘glue’ that makes the Universe expand at an accelerated rate. We don’t know exactly what dark energy is and how it works, but we also know that it makes up 70% of the Universe.
Skeptical people will always exist, and this article is dedicated to them. You have all the right to be skeptical, and questioning any information you receive is highly recommended.
Discovered a century ago
Way back in the 1920s, when the world was recovering from the Second World War, an American astronomer named Edwin Hubble made one of the most significant discoveries in the history of science. Once he looked into the depths of the Cosmos through his telescope, he concluded something revolutionary: the galaxies are moving away from us at tremendous speeds, as he could observe the redshift caused by the Doppler effect. Not only that Hubble discovered over a century ago that the Milky Way was not the only galaxy from the Universe as scientists previously thought, but he also concluded that our Universe is expanding,
New method: measuring how galaxies gather
Thankfully, there are other ways to measure cosmic expansion. Galaxies clusters have formed due to Baryon Acoustic Oscillations (BAO). When gravity tries to pull galaxies closer to each other, dark energy’s role is to drive them apart. Thus, galaxies have formed into superclusters separated by large voids. The size of the voids allows scientists to measure the Hubble parameter.
Recently, a team made some new measurements for the galaxy clusters. They found out once again that the Universe is spatially flat. This means that the light we see from very far galaxies has traveled in a basically straight line to us. They concluded this relying on the fact that the structure of the voids depends on both the overall shape of space and dark energy.
The conclusion is simple: the Universe is expanding, it’s ‘flat’, and dark energy is not a hoax or just some spooky name from the sci-fi movies.
Furthermore, Einstein’s biggest blunder was to claim once that the Universe is NOT expanding at all. But the illustrious scientist acknowledged his mistake. The Universe expands at speeds even faster than the speed of light, and nobody knows why for the moment.
Do we live in a Multiverse?
Although this idea was for a long time just a scenario for the cartoons and sci-fi movies, scientists in the recent years had been taking a lot more seriously the hypothesis that there are many other Universes more or less like our own. In fact, most astrophysicists nowadays are certain that we’re actually living in a Multiverse, but by definition, we would never be able to travel to a neighboring Universe.
Max Tegmark, a prestigious Swedish-American physicist and cosmologist, reminded us all during a conference that if we look back in the history of mankind, humans underestimated nature tremendously. First, we thought that Earth and the Sun are all that exist, then we discovered other planets, exoplanets, and, ultimately, other galaxies. A similar thing could happen again, as our Universe might be just an insignificant portion in a vast ocean of other Universes that we can call the Multiverse. The String Theory is perhaps the most compelling and notorious theory that claims the existence of other Universes.
There you have it: before asking ourselves why the Universe is expanding or what dark energy actually is, we should consider thinking at a much bigger scale.