Comment by maggit | Hacker News Reader

Comment by maggit | Hacker News Reader

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> I really don't understand the question "is gravity a force?"

The question is not "is gravity a force?". The question is "What is gravity?"

An accepted answer, what I was taught in school, and what I would answer if you asked me is "it's a force". And labeling something as "a force" has huge implications for people that know what that label means.

If a four year old asked me "What is gravity?", I'd know better than to give him a label, because he wouldn't know what a force is from school. Obviously.

If it turns out gravity is not really a force -- if modelling gravity as a force breaks down at some point -- that's a good fundamental result. It is a falsification of the theory "Gravity is a force". (So the line of thought goes: "What is gravity?", "It is a force!", "Is gravity really a force?", "Perhaps not!")

How is this not helping us attaining a deep understanding? How is this not advancing science? How is this any different from any science?

> If it turns out gravity is not really a force ...

It definitely isn't. The word "force" implies a Newtonian model for physics. Under general relativity, gravity isn't seen as a force but a consequence of curved space-time.

The title was probably chosen by an editor without deep knowledge of the subject. It doesn't accurately describe the article's content either.

I humbly bow to anybody's superior knowledge of physics.

To clarify, I wasn't actually trying to say anything about physics, just about science. So it would have been better phrased as a hypothetical; If we assume that gravity is currently best modeled as a force, why is it valuable (nay, essential) to question whether or not it actually is a force? I hope I answered that hypothetical properly :)

> Under general relativity, gravity isn't seen as a force but a consequence of curved space-time.

But why does the presence of matter cause spacetime to curve?

If you want to argue that gravity isn't a force, I don't think it's enough to say "it's a consequence of curved spacetime". I think you have to answer the question of why it curves. I'm not aware of an answer to that question. If there isn't one, as I suspect, then I would say, there's your force of gravity: you're just describing it as acting on spacetime itself rather than on the objects in that spacetime.

I was taught in school that there were four forces- strong, weak, EM and gravity. Gravity was the one that was always hardest to fit into a GUT model (people suggesting looking for a particle called a gravitron, for example, which intuitively I always thought was bullshit), and based on what I've read since school it's hard for me to believe that gravity belongs in the list of "the four forces."

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