PBS Space Time Season 2015 Episode 18 Is Gravity an Illusion?

Is Gravity an Illusion? That's the question posed by the 18th episode of PBS Space Time's season 2015. The answer is a bit more complicated than a simple yes or no, but the episode unpacks the science behind why gravity might appear to be an illusion.

The hosts of PBS Space Time, Gabe Perez-Giz and Matt O'Dowd, start by discussing the history of scientific inquiry into gravity. For centuries, scientists have been trying to understand the force that keeps us all from floating off into space. Isaac Newton's law of universal gravitation helped to explain some of the basic principles behind gravity, including the fact that the force between two objects is proportional to their masses. But as physicists delved deeper into the mysteries of the universe, they began to question whether gravity really is a fundamental force or if it might be something else entirely.

One of the first challenges to the idea of gravity as a fundamental force came from General Relativity, the theory developed by Albert Einstein. This theory presented a new way of thinking about gravity, proposing that it's not actually a force at all but rather the curvature of spacetime. In other words, objects with mass create curves in the fabric of spacetime that cause other objects to move towards them. General Relativity has been incredibly successful in explaining a wide range of gravitational phenomena, from the orbits of planets to the behavior of black holes.

However, some physicists believe that General Relativity may not provide a complete picture of gravity. One idea that's gained traction in recent years is the concept of emergent gravity. This theory suggests that gravity is not a fundamental force but rather emerges from other, more fundamental aspects of the universe. For example, it's possible that gravity could be an emergent property of the behavior of subatomic particles or the geometry of spacetime.

Another potential explanation for why gravity might appear to be an illusion comes from the idea of dark matter. Although we can observe the effects of dark matter on the movement of galaxies, we don't actually know what it is or how it works. Some physicists have suggested that dark matter could be an indication that our understanding of gravity is incomplete. They propose that dark matter may actually be some kind of modified gravity that interacts differently with ordinary matter than we currently understand.

Despite these challenges to the idea of gravity as a fundamental force, most physicists still believe that gravity is a real phenomenon that can be measured and observed. The hosts of PBS Space Time compare it to the concept of temperature. While we can't directly observe temperature, we can measure its effects and create models that accurately predict how it will behave under different conditions. Similarly, while we may not fully understand the nature of gravity, we can measure its effects and make predictions based on our current understanding.

In the end, the answer to whether gravity is an illusion is both yes and no. It's true that our understanding of gravity is still evolving and we may not yet have a complete picture of how it fits into the larger framework of the universe. However, it's also true that gravity is a real phenomenon that affects every single one of us every single day. PBS Space Time's exploration of this complex topic is thorough and engaging, providing viewers with a deeper understanding of one of the most fundamental forces of nature.