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Scientists made a startling cosmic discovery in 1998. They came to the realization that the universe is not only expanding but also seems to be speeding up with time due to an invisible force. That enigmatic force would soon be recognized as dark energy, one of physics’ biggest mysteries. It would complement the equally perplexing—if not more so—aspect of our cosmos known as dark matter, a general term scientist initially used to describe the invisible, halo-like barriers that keep galaxies from simply disintegrating in 1933. (Yet another power that is invisible to human eyes.)
The elusive nature of dark matter and dark energy is difficult for us to comprehend with our eyes, but math allows us to measure it. And on Wednesday, astronomers set the most accurate boundaries yet for the make-up and development of our universe, including the dark universe, in a series of studies published in the Astrophysical Journal. The researchers discovered that the universe is made up of roughly two thirds dark energy and one third matter, largely in the form of dark matter, using a potent analytical tool called Pantheon+. They believe that 66.2% of the cosmos is dark energy and that the remaining 33.8% is made up of both dark and visible matter.
Pantheon+’s unpredictable operation may be much more fascinating than the results. To put it briefly, the researchers used a variety of strong cosmic flashlights to look back in time and record the universe’s contents as they were more than 10 billion years ago. I refer to Type 1a supernovae as “flashlights.” These star explosions can be detected from distances billions of light-years away from Earth because they are so luminous that they outshine entire galaxies. Similar to flashlights, they illuminate the endless tunnel of space and time as opposed to illuminating a long hallway. In fact, they were crucial in the 1933 and 1998 discoveries of dark matter and dark energy, respectively, which led to the discovery of the dark universe.
To the next level, thanks to Pantheon+. The analysis’s researchers concentrated on the more than 1,500 supernovae that together illuminate nearly three-quarters of the known cosmos. Wow, in fact. According to astronomer Dillon Brout of the Harvard-Smithsonian Center for Astrophysics, “with this merged Pantheon+ dataset, we obtain a precise image of the cosmos from the time when it was dominated by dark matter to when it became dominated by dark energy.” According to Brout, “this dataset offers a rare opportunity to watch dark energy turn on and drive the universe’ evolution on the largest scales up to the present day.” This might resolve several scientific disagreements. The Pantheon+ legacy will eventually go beyond the dark universe.
The analytical technique provided incredibly encouraging data in support of the Standard Model of Particle Physics, a cornerstone of scientific theory, and verified the cosmos is indeed expanding at an accelerating rate. This framework essentially describes how every single particle that has been observed acts both alone and in interactions with one another. It also forms the basis for many of the most popular theories concerning what the dark cosmos is really made of.
According to Brout, “We are able to place the most exact limitations on the dynamics and history of the universe to date. The cosmos has developed over millennia, and the best hypotheses for dark energy and dark matter continue to stand up, we can declare with greater certainty than ever thanks to our analysis of the facts. In other words, Pantheon+ might be telling us that we should put an end to some alternative, unrelated to the Standard Model hypotheses of dark matter and dark energy. Those hypotheses could be… flawed.
We must also discuss my own favorite result of using Pantheon+ datasets. It could finally put an arduous, ongoing argument between physicists to rest. We might finally be making progress in understanding the Hubble constant. Kind of. In essence, we are aware of the exponential expansion of the cosmos. We can really watch it happen as it happens. On the precise rate at which that expansion is occurring, however, scientists cannot agree. The Hubble constant is the key to the answer, but different approaches to calculating it appear to produce different results.
We may now have the most accurate local measurement of the universe’s current expansion rate, according to a Harvard press release, after combining the Pantheon+ sample with data from another research cooperation. (The word “local” is crucial. That will be added later.) In a summary, the group determined the Hubble constant to be 73.4 km/s/Mpc (km/s/Mpc), with an astonishing 1.3% uncertainty. In other words, the research predicts that space itself is expanding in the nearest universe at a rate of more than 160,000 miles per hour for every megaparsec, or 3.26 million light-years, according to the press release. For context, this value falls between the historic measurement of 72 km/s/Mpc from 2001 and later reports of 74 km/s/Mpc. But compared to another leading measurement, which points to a constant of 69.8 km/s/Mpc, it is fairly far out. Yes, there is still a difference. The constant for Pantheon+ is also based on “local” data.
The Pantheon+ team underlines that this is the case because “observations from an altogether different period of the history of the cosmos foretell a different scenario.” In this sense, adding a new, opposing Hubble constant might not be resolving the Hubble tension, but rather escalating the already contentious discussion? It’s complex, as I’ve already stated. In contrast to what they expected, Brout said, “we’re finding that our data rules out many of these choices and that the significant gaps remain as intractable as ever. We assumed it would be feasible to find clues to a creative solution to these difficulties in our dataset.
But ultimately, because Pantheon+’s findings are so impeccable, perhaps they can at least clarify where the Hubble ongoing argument is at issue. According to Brout, “several recent hypotheses have started pointing to strange new physics in the very early cosmos.” But such unproven theories must hold up to scientific scrutiny, and the Hubble tension is still a significant obstacle. There are so many challenging problems, conundrums, and, let’s be honest, outright obstacles in physics. But I like to think of these difficulties as inspiration to keep the industry moving forward and brains active. It was for this reason that Pantheon+ was first developed. At the very least, we have advanced in understanding the truth about the shadowy side of our world thanks to this mechanism. Alternatively, Pantheon+ “gives us our best chance to constrain dark energy, its origins, and its evolution to date,” as Brout puts it.