As you remember, this week in the world of physics and astronomy, someone fired a cannon: perhaps the expansion of the universe is not accelerating. An article appeared in the scientific reports of the journal Nature that partially refuted the fundamental observations that led to the modern view that dark energy accelerates the universe. Of course, we immediately decided to abandon this strange, incomprehensible and elusive idea. And they hurried.
The famous American astrophysicist Adam Riess, who received the Nobel Prize with his colleagues, spoke in defense of dark energy, guess what? "For the discovery of the accelerated expansion of the universe through the observation of distant supernovae." I published my note on Scientific American. Further from the first person.
After reading this article, you are confident that there is no need to revise our current understanding of the universe. All this work does is slightly diminish our confidence in what we know - but also that, by discarding the cosmological data upon which our understanding was built. She also ignores important details in the data she is looking at. And even aside from these issues, the headlines are wrong anyway. The study concludes that now we are only 99.7% sure that the universe is expanding at an accelerating rate, but this is hardly equal to "it is not accelerating."
The original discovery that the universe is expanding at an increasing rate was made by two teams of astronomers in 1998 using Type Ia supernovae as space-based measuring instruments. Supernovae - exploding stars - are some of the most powerful explosions in space, equivalent to a billion billion billion atomic bombs exploding simultaneously. Type Ia is a special type of supernova that, unlike other supernovae, they all explode at the same luminosity each time, probably reaching the critical mass limit. This similarity means that differences in their observed brightness almost always depend on how far away they are. Therefore, they are ideal for measuring cosmic distances. In addition, these objects are relatively common and so bright that we see them billions of light years away. We see what the universe was like billions of years ago, and we can compare this with how it looks now.
These supernovae are often referred to as "standard candles" for their consistency, but more precisely, they are "standardized candles" because in practice their accuracy can be improved and improved by taking into account small differences in their explosions, observing how long the explosion unfolds and how the color supernova blushes due to the dust between us and them. The search for a way to make more accurate corrections led to the discovery of an accelerating Universe.
That recent document that caused the media hype used a catalog of Type Ia supernovae compiled by the community (including us) that had been analyzed many times before. But the authors used a different method to enable fixes - and we believe that this undermines the credibility of their results. They suggest that the average properties of supernovae from each sample used to measure the expansion history are the same, although they have already been shown to be different, and analyzes of the past have accounted for these differences. However, even if ignoring these differences, they concluded that the chance of accelerating the expansion of the universe is about 99.7%.
In addition, the vast majority of astronomers believe that the universe is now expanding faster than billions of years ago, and this is not only supported by measurements of supernovae. This includes tiny fluctuations in the relict afterglow of the Big Bang (the cosmic microwave background) and the modern imprint of these fluctuations in the distribution of galaxies around us (the so-called baryonic acoustic oscillations). The present study also ignores the presence of significant amounts of matter in the universe, confirmed many times and in different ways since the 1970s. Other data show that the universe is expanding independently of supernovae. If we combine other observations with supernova data, we get not 99.99 percent confidence, but 99.99999 percent. That's for sure.
Promotional video:
We now know that dark energy, which we believe is causing the expansion of the universe to accelerate, makes up 70% of the universe, with the rest of matter. The nature of dark energy remains one of the greatest mysteries in astrophysics. But there is no active debate about the existence of dark matter, and no one is discussing the acceleration of expansion anymore, since this picture was cemented a decade ago.
There are many major new studies, both on earth and in space, with a top priority over the next twenty years to figure out exactly what this dark energy might be. At this point, we must continue to refine our measurements and question our assumptions. While this recent work does not disprove any theories, it’s very good that we can pause for a second and remind us how big the questions we are trying to solve, how we arrived at our current conclusions, and how seriously we should test every brick of our understanding.
ILYA KHEL