2024-09-04 13:31:35
When scientists argue, it’s often about the big picture. More than a hundred years ago, a debate centered on nothing less than the question of how vast the universe is. Is the Milky Way the only one, or is it much bigger? The question was answered when astronomers first determined the distance of the Andromeda Galaxy in 1923. In the 1960s, the discovery of the cosmic microwave background clarified the long-standing debate as to whether the universe existed forever or was created in a big bang. Now there is another debate, this time about the question of how fast the cosmos is actually expanding.
The two groups have been insisting on their findings, albeit using different methods, for a good decade. One is led by Nobel Prize winner Adam Riess from Johns Hopkins University in Baltimore and says the cosmos is expanding more rapidly than previously thought. No, other scientists disagree. From the data from the European special telescope Planck, they derived a somewhat slower expansion of the cosmos. Now astronomers led by Wendy Freedman from the University of Chicago want to finally solve the controversial issue with new measurements.
The prospect for “new physics” is once again disappointing
Whether the cosmos expands a little faster or slower can have a big impact. A few physicists hope that behind this small but important difference there is a “new physics”, i.e. previously unknown laws of nature, which may also provide an explanation for what lies behind the mysterious dark matter and dark energy. . All we know for sure about the former is that its energy helps slow down the expansion of the universe, and the only thing we know about the latter is that it speeds it up.
But if Wendy Freedman and her team from Chicago are right, then the hope for new physics will not be fulfilled. Because the measurements using the James Webb Space Telescope showed that the difference between the results of the Planck data and the findings of the Adam Riess group did not exist, Freedman and colleagues wrote in a paper submitted to the “Astrophysical Journal”: The um Riess group is simply incorrect, the representative rate according to the values determined from measurements with the Planck satellite. After Freedman’s article appeared on the preprint server “arxiv.org” at the beginning of August, it took only nine days for Riess and his team to publish the correction: No, the results they had compiled over the years were not wrong. never. , doesn’t even have the light of James Webb.
In the light of standard candles
The main point of the dispute is the central mass: it is called the Hubble constant, or H0 for short, after the American astronomer Edwin Hubble. Indeed it is not constant, but it refers to the current of the science and describes the relationship between the escape velocity of the galaxy as a result of the expansion of the Universe and its distance from the Earth. H0 is one of the most important parameters of the universal standard model, which is why the difference that has been debated is also called the “Hubble problem” or “Hubble tension”.
Now the value of H0 can be determined empirically in two different ways. Riess and his team used the “classical” method used by Edwin Hubble himself in the 1920s: using the Hubble telescope, they determined the distances of the stars using Cepheids – bright giant stars that appear according to the actual brightness they can be compared. Because this light can be used to determine their distance, Cepheids serve as “standard candles”. The escape velocity of the stars is then determined based on the redness of the light emitted by them. In this way, Adam Riess and his team determined a value for H0 of 73 kilometers per second per megaparsec, where one megaparsec corresponds to a distance of 3.26 million light years.
The echo of the Big Bang contradicts this
Scientists working with data from the European Planck mission used a completely different approach. Until 2013, the satellite measured the temperature distribution in the cosmic microwave background, which is also called the “echo of the Big Bang”. Although H0 is not directly apparent, it can be indirectly determined from the analysis of the distribution of the prevalence. The generally accepted method gives a Hubble constant of 67.4 kilometers per second per megaparsec. The difference between the two values is significant, meaning that it cannot be explained by statistical measurement errors.
Like Hubble and Riess, researchers led by Wendy Freedman chose the standard candle method. However, they used the new James Webb telescope for their measurements, whose bright images show the Cepheids better. In addition, they used two other types of standard candles to measure the distances of neighboring stars: stars that show a light flash at the end of their growth stage, and carbon-rich pulsating stars that shine in the infrared spectrum.
According to Freedman and his colleagues, this improved the accuracy of their measurements. Because Cepheids are by no means perfect standard candles. Their light, which varies from model to model, is not exactly known as Edwin Hubble himself believed. The Chicago team’s analysis provides a numerical value for the Hubble constant that varies between 68.8 and 71.1. The result matches the result from the Planck data within the range of measurement errors, Freedman said. “The numbers are consistent with the current biological model without the need to add additional new physical elements.”
For the research team led by Riess, the new results are not very convincing. The devil is in the details: Depending on the properties assumed for the three standard candles, different values for H0 will result. In their publication, Riess and his team presented values for the Hubble constant, which was also determined using all three standard candles. All of them are significantly higher than the result from the distribution of cosmic background radiation. Researchers from Baltimore also criticized the fact that Freedman and his team had measured the velocities and distances of eleven stars. This is a very small number for determining the global accuracy constant.
Neither the work of Freedman’s group nor the response from Riess and his team has been reviewed by independent scientists or given the green light for publication in a regular scientific journal. The Hubble crisis will be possible for a while: As long as both sides insist on their values and the difference cannot be explained, the basic explanation of the Big Bang theory will remain understandable. This is a very interesting situation for scientists. Because nothing is more desolate than a world in which there is nothing left to explore.
#endless #debate