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(This message was added in version 6.7.0.) in /home4/scienrds/scienceandnerds/wp-includes/functions.php on line 6114Source:https:\/\/www.quantamagazine.org\/how-nearly-nothing-might-solve-cosmologys-biggest-questions-20230725\/#comments<\/a><\/br> \u201cThe Hubble tension has lasted a decade so far because it is a hard problem,\u201d said Adam Riess<\/a>, an astronomer at Johns Hopkins University who uses supernovas to estimate the Hubble constant. \u201cThe obvious issues have been checked and the data has improved, so the dilemma deepens.\u201d<\/p>\n Now, the hope is that studying nearly nothing could lead to something big.<\/p>\n Voids are regions of space that are less dense than the universe, on average. Their boundaries are defined by the immense sheets and filaments of galaxies that are woven throughout the cosmos. Some voids span hundreds of millions of light-years, and together, these bubbles make up at least 80% of the universe\u2019s volume. For a long time, though, no one paid much attention to them. \u201cI began my research in 2011 with around 200 voids,\u201d Pisani said. \u201cBut now we have roughly 6,000.\u201d<\/p>\n The bubbles have a tendency to expand because inside them, there isn\u2019t much matter to exert an inward gravitational pull. The stuff outside them tends to stay away. And any galaxies that start inside a void get tugged outward by the gravitational pull of the structures defining a void\u2019s edge. Because of this, in a void \u201cvery little happens,\u201d Pisani said. \u201cThere are no mergers, no complicated astrophysics. This makes them very easy to deal with.\u201d<\/p>\n But each void\u2019s shape is different, which can make it tricky for scientists to identify them. \u201cWe want to make sure our voids are robust,\u201d Pisani said. \u201cHow empty does it have to be, and how do I measure it?\u201d<\/p>\n It turns out that the definition of \u201cnothing\u201d depends on the type of information astronomers want to extract. Pisani and colleagues started with a mathematical tool called a Voronoi diagram, which identifies the shapes that make up a 3D mosaic. These diagrams are typically used to study things like bubbles in foams and cells in biological tissues.<\/p>\n In the current work, Pisani and her colleagues tailored their Voronoi tessellations to identify about 6,000 voids in the data from an enormous galactic mapping project called the Baryon Oscillation Spectroscopic Survey<\/a> (BOSS).<\/p>\n \u201cVoids are complementary to the catalog of galaxies,\u201d said Benjamin Wandelt<\/a>, an astrophysicist at Sorbonne University in Paris who was not involved in the study. \u201cThey are a new way to probe cosmic structure.\u201d<\/p>\n Once Pisani and colleagues had their map of voids, they set out to see what it could reveal about the expanding universe.<\/p>\n Every cosmic void is a window on a great cosmic conflict. On one side, there\u2019s dark energy, the mysterious force that causes our universe to expand ever more quickly. Dark energy is present even in empty space, so it dominates the physics of the void. On the other side of the conflict there\u2019s gravity, which attempts to pull the void together. And then matter\u2019s clumpiness\u00a0adds wrinkles to the voids.<\/p>\n Pisani and her colleagues,\u00a0including\u00a0Sofia Contarini<\/a>\u00a0of the University of Bologna, modeled how the expansion of the universe would affect the number of voids of different sizes. In their model,\u00a0which kept a handful of other cosmological parameters constant, a slower expansion rate produced a higher density of smaller, more crumpled voids. On the other hand, if expansion was faster and matter didn\u2019t clump as readily, they expected to find more\u00a0<\/b>large, smooth voids.<\/p>\n The group then compared their model predictions with observations from the BOSS survey. From this, they were able to estimate both clumpiness and the Hubble constant.<\/p>\n They then juxtaposed their measurements with the two traditional ways to measure these values. The first method uses a type of cosmic explosion called a Type Ia supernova. The second relies on the cosmic microwave background (CMB), the radiation left over from the Big Bang.<\/p>\n The void data revealed a Hubble constant that varied by less than 1% from the CMB\u2019s estimate. The result for clumpiness was more muddled, but it also aligned more closely with the CMB than with Type Ia supernovas.<\/p>\n Perplexingly, the voids in the BOSS survey lie closer in space and time to more recent Type Ia supernovas \u2014 making it a bit surprising that the void measurements align more closely with the primordial CMB. Wandelt, though, suggested that the results might reveal a new understanding about the universe.<\/p>\n \u201cThere is one deep insight that makes my hair stand up,\u201d he said. Inside voids, structures never formed and evolved, so voids \u201care time capsules of the early universe.\u201d<\/p>\n In other words, if the physics of the early universe was different from the physics of the present day, the voids may have preserved it.<\/p>\n Others think it\u2019s too soon to draw any conclusions from the new results.<\/p>\n Even with thousands of voids, the study\u2019s error bars are still too large to say anything conclusive. \u201cThis analysis is extremely well done,\u201d said Ruth Durrer<\/a>, a theoretical physicist at the University of Geneva who did not take part in the research. But, Durrer noted, the results haven\u2019t reached statistical significance \u2014 yet. \u201cIf Alice wants to be in the club of amazingly good Hubble constant measurements, she has to get to the 1% limit, which is a huge challenge,\u201d Durrer said.<\/p>\n Pisani said she considers the work to be a proof of concept. It will likely take another decade \u2014\u00a0and the help of future missions such as NASA\u2019s Nancy Grace Roman Space Telescope and SPHEREx Observatory \u2014 to accumulate enough void data to be on a par with the conflicting CMB and Type Ia supernova measurements.<\/p>\n Durrer also points out that maybe these arguments \u2014 the attempts to reconcile cosmic tensions \u2014 are all much ado about nothing, and that the observational disagreements could be pointing to a reality that scientists shouldn\u2019t be trying to erase.<\/p>\n \u201cThe supernova and CMB groups are doing measurements that are very, very different,\u201d she said. \u201cSo there may be new physics that explains why we shouldn\u2019t be seeing the same thing.\u201d<\/p>\n Editor\u2019s note: Alice Pisani receives funding from the\u00a0<\/em>Simons Foundation<\/em><\/a>, which also funds this editorially independent magazine. Simons Foundation funding decisions have no influence on our coverage. More details are\u00a0<\/em>available here<\/em><\/a>.<\/em><\/p>\n<\/div>\n <\/br><\/br><\/br><\/p>\n
\nHow (Nearly) Nothing Might Solve Cosmology\u2019s Biggest Questions<\/br>
\n2023-07-26 21:58:21<\/br><\/p>\nBuilding Bubbles<\/strong><\/h2>\n
Something From Nothing<\/strong><\/h2>\n
The Future of Absence<\/strong><\/h2>\n