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Dr. Christopher S. Baird

Why is gravity not a real force?

Category: Physics      Published: August 5, 2022

By: Christopher S. Baird, author of The Top 50 Science Questions with Surprising Answers and Associate Professor of Physics at West Texas A&M University

star warping spacetime
Gravitational effects are the result of spacetime curvature. Public Domain Image, source: Christopher S. Baird.

Gravity is indeed a real force, but not in the traditional sense. In other words, gravity is not a direct, classical, action-at-a-distance force between two objects. However, in the broader sense, gravity is indeed a force because it describes the resulting interaction between two masses. Gravitational effects are fundamentally caused by the warping of spacetime and the motion of objects through the warped spacetime. However, the end result is as if a force was applied. Therefore, the most accurate approach would be to call gravity an "emergent force," meaning that what looks like a direct force is actually emerging from more fundamental effects (the warping of spacetime). With this in mind, it is perfectly reasonable to call gravity a real force.

Interestingly, all of the fundamental forces are actually emergent forces and not classical, action-at-a-distance forces. If you insist on calling gravity not a real force, then you must call all of the fundamental forces not real forces. It is more accurate to call them all emergent forces. For instance, two electrons repel each other through the electromagnetic force. However, the one electron does not exert a literal, direct, electromagnetic force on the other electron. Rather, the more fundamental description is that the first electron creates a quantum electromagnetic field in the space surrounding it, and then the other electron moves and interacts with this electromagnetic field. The end result is that it looks like the second electron experienced a force from the first electron. On the fundamental level, there are no action-at-distance forces. It is really just certain objects creating and/or warping certain fields and then other objects moving and interacting with these fields.

Some scientists think that even calling gravity, electromagnetism, and so forth "emergent forces" can be misleading because it makes people think of action-at-a-distance forces. They prefer to avoid the word "force" entirely and instead prefer the name "interaction." For instance, instead of saying that one electron exerts an electromagnetic force on another electron (which is perfectly reasonable to say as long as you know you are talking about electromagnetism as an emergent force), some scientists prefer to say that the electrons participate in the electromagnetic interaction.

Topics: field, force, gravity, mass, spacetime