According to many of these theories, if extra dimensions do exist, gravitational waves would “leak” into those dimensions, causing the waves to weaken as they made their way across the universe. The scientists in the recent study measured how far the gravitational waves and the light waves from GW170817 traveled to reach Earth, but the researchers didn’t find any hints of the weakening that would be associated with extra dimensions.
In the wake of the GW170817 event, many studies ruled out some of the modified gravity theories by calculating the speed of gravitational waves to determine their travel-time delay. This new paper is able to dismiss a whole other set of theories, Bakertold LiveScience.
The new results exclude only large dimensions. As such, they do not place any constraints on the 10-plus dimensions predicted by string theory — a theory in physics that suggests everything is made up of tiny vibrating strings. However, the new findings do show that across scales of about 1 mile (1.6 kilometers) up to at least 80 million light-years, the universe is three-dimensional. The finding further dismisses even larger dimensions, but only if they have visible effects on physics on scales smaller than 80 million light-years.