Is Gravity Really A Force?

[-Yasmin-]

As we all know, in school we are taught gravity IS a force. However, the truth is that according to the theory of general relativity gravity is NOT a force, rather a curvature in spacetime. Can someone please explain the evidence of why gravity is NOT a force.

[Ken4155]

Listen, Yasmin, if Gravity wishes to identify as a force, who are we to argue? :-))

[Hopkirk]

I don't think physics boffs can actually explain gravity yet.

[jim360]

There are a few answers to this, but the main point is that the definition of force refers to an interaction between (at least) two objects. In General Relativity, what happens instead is that one object curves space, and another object then freely moves within the curved space, so that it's no longer a direct interaction.

Having said that, gravity is still not fully understood, and General Relativity is certainly not the final explanation of gravity. In a more complete picture, it's expected that gravity will be explained in terms of a new particle, called the graviton, which then directly allows two bodies to interact. No complete description of a graviton exists, and none has ever been observed. But, if it were, then it would put gravity back on the same footing as the other basic forces (electromagnetism, and the strong and weak forces), because all of those also have "exchange" particles, eg the photon is the exchange particle of electromagnetism.

[jim360]

Just to add, though, that for many practical cases, there's no reason to worry about whether gravity is a force or not. It behaves as near as dammit to one when working out how most of the planets move, or planning rocket journeys to the moon etc.; it's only when you get close to black holes or the like that modelling gravity as a pure interaction force fails, and you start to care that it's "really" a curving effect in space-time.

[Old_Geezer]

Until we have a quantum theory of gravity maybe take general relativity with it's spacetime to be a good approximate viewpoint of what's sort of occurring ? But no one's forcing you.

[Milvus]

There was a programmed on BBC4 a couple of weeks ago by Prof. Jim Al-Khalili called Gravity and Me: The force that shapes our world. It goes through our understanding of gravity throughout time and covers the curvature of time theories, which Prof J. now believes. It's available on BBC iPlayer

[Bazile]

Ask Isaac Newton to recall his little encounter with a fruit

[Hymie]

See this youtube item for more on this – but it feels like a force to me.

[douglas9401]

Think how different things might have been if Isaac had been sitting under a particularly bushy rocket plant.

No need for all those wasted years trying to make Granny Smith achieve escape velocity.

[Rev. Green]

I'd call gravity a pseudo force because it is exactly proportional to the mass of the object, like other pseudo forces such as centrifugal force and Coriolis force. "Real" forces, like electromagnetism, are independent of mass.

[davebro]

I watched the BBC4 program on catch up & found it fascinating. The fact that space and time are not independent of each other & that gravity affects them both (or it) is a difficult concept for me to grasp.