Is Gravity An Illusion?

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Cites Omar Nagib · 2015-07 · Physics Stack Exchange · on “Why does a free-falling body experience no force despite accelerating?”

Before telling you why an observer in free fall does not feel any force acting on him, there are a couple of results that should be introduced to you. Newton's second law is only valid in inertial frames of reference: To measure quantities like the position, velocity, and acceleration of an object, you need a coordinate system $(x,y,z,t)$. Now the coordinates that an observer in uniform motion(constant velocity) uses is what we call an inertial frame of reference , and the coordinates of an observer in non-uniform motion is what we call a non-inertial/accelerated frame of reference Now $\vec{F}=m\vec{a}$ is only valid in inertial frames of reference. This means that only observers in uniform

Cites Harlequin · 2018-12 · Physics Stack Exchange · on “Shouldn't a cold object feel less gravity?”

The premises for my question are, Gravity isn't a force but curved spacetime [this video] "If gravity isn't a force, how does it accelerate objects?" [LINK] (complicated answer) If the answer below, to the question linked above, is correct, I feel it's easier to understand: "Even objects "at rest" (in a given reference frame) are actually moving through spacetime, because spacetime is not just space, but also time: apple is "getting older" - moving through time." [LINK] Time is the result of causality [LINK] -- to my understanding this means that something ages because of the interactions of its smaller parts, and at the speed of light for example, those interactions don't happen hence time doesn

Cites Pankaj Bhambhani · 2020-04 · Physics Stack Exchange · on “How does the Equivalence principle explain "what goes up must come down"?”

Apologies if this is a dumb question, I am mostly self-taught when it comes to physics. I recently came across this video by PBS Space Time ( Is Gravity an Illusion? [this video] ) which talks about the Equivalence Principle, where a box falling freely in a gravitational field can be considered an inertial frame, and a stationary frame in a gravitational field is equivalent to a frame accelerating in the opposite direction of gravity. He illustrates this by saying that an apple in free-fall is an inertial frame while the surface of the earth is not, and really it is the surface that is accelerating upwards relative to the apple. This leads me to think about the case where an apple is thrown up fr

Cites vibhum mohan · 2023-06 · Physics Stack Exchange · on “Where does the acceleration that doesn't change our co-ordinate in space that ground applies comes from? (General Relativity)”

I saw this video of veritasium [this video] I have this question... [LINK] if I am being accelerated by ground with 9.8 m/s2 then where this acceleration is actually coming from? I mean what I've understand is this one equation of General Relativity says that zero co-ordinate acceleration should be there for us just to stand still and not floating in a curved spacetime but there should be a force (i.e. Normal Force) accelerating the ground and hence us giving rise to an acceleration which is equal to the (spacetime curvature times our velocity through time squared part of the equation). If acceleration is actually a deviation from geodesic rather than a result to force then I didn't understand ho