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Iheartscience
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If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
You can view it the other way: they are trying to make the other 3 forces work with GR. Our current formulations of QCD etc. only work in flat space.Iheartscience said:If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
In my eyes that's just a word game, using a peculiar set of definitions of "gravity", "force" and "fictitious". The contact force that I feel now, while sitting in my chair, is very real (deforming my buttocks approx. in accordance with Hooke's law) and it's definitely caused by the Earth's gravitation. And I won't participate in discussions about word games.Iheartscience said:If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
Iheartscience said:If gravity is a fictitious force
It is really hard to tell whether when posters assert that gravity is a fictitious force they are simply playing word games(I speak from recent experience discussing these notions around here) as suggested by #3, but I wonder if for instance #4 is drawing some kind of distinction between the term interaction and the term force, if so I'd be curious to know about it. Are gravitational tidal forces the non-ambiguous term that the OP should be referring to? Are the latter fictitiour or not?Iheartscience said:If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
The tidal effects of gravity are not fictitious, so they do need to be unified with the other fundamental interactions. The "fictitious force" aspect is already unified by the fact that the other interactions can already be expressed in a manifestly covariant manner.Iheartscience said:If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
loislane said:I wonder if for instance #4 is drawing some kind of distinction between the term interaction and the term force
loislane said:Are gravitational tidal forces the non-ambiguous term that the OP should be referring to? Are the latter fictitiour or not?
The contact force is definitely not caused by the Earth's gravitation. As suggested by the name, it is caused by the contact with the chair (and Hookes law).harrylin said:The contact force that I feel now, while sitting in my chair, is very real (deforming my buttocks approx. in accordance with Hooke's law) and it's definitely caused by the Earth's gravitation
+1 on this. Also, there are tidal effects involving time that I think are not reasonable to label as "forces". I refer to say "tidal effects", although I am not perfectly consistent in doing so.PeterDonis said:The term "gravitational tidal forces" is ambiguous too,
harrylin said:In my eyes that's just a word game,
This is not simply semantics. There are physical similarities between fictitious forces and local gravitational forces.loislane said:It is really hard to tell whether when posters assert that gravity is a fictitious force they are simply playing word games
I can't bear the suspense, can you unveil the ultimate unambiguous term that should be used and formulate the OP's question precisely, as it should be asked?PeterDonis said:Yes, it is, at least in ordinary language. (In the language of, for example, particle physicists, the two terms mean the same thing; they both refer to the same terms in the mathematical equations.) A "force", as I was using the term in #4, is something you can measure with an accelerometer. An "interaction", as I was using the term in #4, is basically the thing that a particle physicist would call an interaction (or a force).
The term "gravitational tidal forces" is ambiguous too, because we can measure the effects of tidal gravity purely by looking at freely falling objects, which are not subject to forces in the sense I used the term in post #4 (accelerometers attached to them read zero). What are often called "tidal forces" in pop science treatments are really non-gravitational forces (electromagnetic in the most common cases) exerted by one part of an object on another when the object as a whole is moving through curved spacetime.
The reason these distinctions are important is that without them, people like the OP are led by our imprecise language to ask questions like the one in the OP, whose answers would be obvious (if the questions even occurred to them in the first place) if our language were more precise.
loislane said:I can't bear the suspense, can you unveil the ultimate unambiguous term that should be used and formulate the OP's question precisely, as it should be asked?
Then I think we should avoid talking about "gravity" being a "fictitious force" altogether (outside the Newtonian context), don't you think?PeterDonis said:There isn't one. The unambiguous expression of the physics involved is in math, not ordinary language. Using the unambiguous math, the OP's question cannot even be posed.
Or simply irrelevant to physics, as much of such causation musings.DaleSpam said:Saying that it is definitely caused by Earth's gravitation is simply untrue.
loislane said:Then I think we should avoid talking about "gravity" being a "fictitious force" altogether (outside the Newtonian context), don't you think?
Iheartscience said:If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
loislane said:Then I think we should avoid talking about "gravity" being a "fictitious force" altogether (outside the Newtonian context), don't you think?
In a local context with clarificatin to what the term refers it seems fine to me.loislane said:Then I think we should avoid talking about "gravity" being a "fictitious force" altogether (outside the Newtonian context), don't you think?
Even that is debatable. The equivalence principle also holds for the Newton potential, i.e. it can always be gauged away by a local acceleration. Newtonian gravity can also be described as spacetime curvature, by Newton-Cartan formulation.Mister T said:Altogether, yes. Without the caveat regarding the Newtonian context, because in Newtonian physics gravity is a real force.
One thing that distinguishes real forces from fictitious forces in Newtonian physics is the presence of a Third Law partner. A real force is an interaction between two objects, a fictitious force isn't.
Gravity is a fictitious force according to GR (General relativity).Iheartscience said:If gravity is a fictitious force, why some scientists try to unify it with other real forces of nature?
A fictitious force, also known as a pseudo force, is a force that appears to act on an object in a non-inertial frame of reference, but is actually a result of the motion of the frame of reference itself.
Gravity is not considered a true force because it is a result of the curvature of spacetime caused by the presence of mass or energy. In other words, objects with mass or energy cause spacetime to curve, and this curvature causes other objects to be pulled towards them. This is not a force in the traditional sense, but rather a result of the geometry of spacetime.
Even though gravity is not a true force, it still has a very real and tangible effect on objects with mass. This is because the curvature of spacetime caused by massive objects is strong enough to influence the motion of other objects, causing them to be pulled towards the source of the curvature.
The concept of fictitious forces helps us to better understand the underlying principles of gravity and how it works. By recognizing that gravity is not a true force, we can better understand its effects and how it relates to other fundamental forces in the universe.
Yes, other examples of fictitious forces include centrifugal force (the apparent force experienced by objects in a rotating frame of reference) and Coriolis force (the apparent force experienced by objects in a rotating reference frame due to the rotation of the Earth).