The Universe’s Mysterious Expansion Rate and Its Mystifying Implications
In the realm of cosmology, one of the most perplexing enigmas is the ongoing debate about the rate of expansion of the Universe. The standard model used to predict this phenomenon is known as Lambda-cold dark matter (ΛCDM) and relies on detailed observations of the cosmic microwave background (CMB) – the residual light from the Big Bang.
As the Universe expands, galaxies move away from each other. This expansion is governed by “Hubble’s constant,” which is approximately 43 miles (70 km) per second per Megaparsec (a unit of measurement in astronomy). As galaxies move further away, they accelerate. However, recent conflicting data has emerged, indicating a “Hubble tension” due to a larger expansion rate calculated from nearby galaxies and supernovas than predicted using the CMB.
This leads to a hypothesis presented in our new paper – the possibility that we reside within a vast void in space. Our study suggests that living within such a void could distort local measurements of the expansion rate through material outflows caused by denser surroundings exerting a stronger gravitational pull. Though unexpected, this theory proposes that we may be situated near the center of a void with a density approximately 20% below the universal average.
To explore this concept further, we introduced an alternative theory, called Modified Newtonian Dynamics (MOND), which deviates from the ΛCDM model. MOND challenges the need for “dark matter” by proposing that Newton’s law of gravity weakens when gravitational pull diminishes, explaining galaxy rotation speed discrepancies. Our model examines how the universe would appear within a MOND framework, allowing local measurements of the expansion rate to fluctuate depending on our location.
Recent observations have supported our model, where the average velocity of matter (bulk flow) consistently demonstrates an exceptional speed, a departure from what the standard model anticipates. This poses a challenge to popular Hubble tension solutions, indicating that structure growth exceeds ΛCDM’s predictions on large scales.
This revelation raises questions about the dominance of gravity on cosmic scales, hinting at potential extensions to Einstein’s theory of gravity to address our emerging cosmological challenges. It serves as a compelling call to reexamine our understanding of cosmic expansion on a grand scale, as we navigate a shift in gravity’s theory that may revolutionize our current state of cosmology.
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