New Paper Challenges Notion of a Vast Universe
The Universe, as we know it, might not be as expansive as previously thought, according to a new scientific paper. While cosmologists have long believed that the observable universe is just a small portion of a much larger and potentially infinite creation, this new study argues that the observable universe is mostly all there is.
One of the key reasons why scientists have speculated about the vastness of the Universe is the distribution of galaxy clusters. If the Universe didn’t extend beyond what we can see, distant galaxies would only feel a gravitational pull towards our region of the cosmos and not away from us. This would result in asymmetrical clustering. However, since galaxies cluster at a similar scale throughout the observable universe, it suggests that the universe is homogenous and isotropic.
Another indicator of the Universe’s size is the flatness of spacetime. If spacetime were not flat, our view of distant galaxies would appear distorted, making them appear larger or smaller than they actually are. However, the flatness of spacetime implies that the Universe is at least 400 times larger than what is observable.
The cosmic microwave background (CMB), the most distant light we can observe, also has implications for the size of the Universe. The CMB is almost a perfect blackbody, with small temperature fluctuations. To account for this uniformity, scientists propose a period of rapid expansion called early cosmic inflation. If this model is accurate, then the Universe could be approximately 10^26 times larger than what we can observe.
However, the new study brings string theory into the picture. String theory, often touted as a physical theory, is actually a collection of mathematical methods that can be used to develop complex physical models. Some string theory models are more promising than others, and theorists have defined a “swampland” of theories that aren’t considered promising.
The researchers behind the new study argue that most inflationary string theory models are in the swampland, meaning early cosmic inflation may not be a viable option. Instead, they propose considering higher-dimensional structures within string theory. By looking at a 3+2 or 4+1 universe, where the global structure can be embedded into an effective 3+1 structure, the authors suggest a model that matches observations and avoids the swampland. According to their toy models, the Universe may be only a hundred or a thousand times larger than the observable universe.
While this study remains speculative, it challenges the prevailing notion of a vast and infinite Universe. If early cosmic inflation is true, scientists should be able to observe its effects through gravitational waves in the future. However, if such evidence is not found, it might be worthwhile to explore string theory models that steer clear of the theoretical swamp.
The study, titled “A Small Universe,” was authored by Jean-Luc Lehners and Jerome Quintin and published on arXiv preprint.