Talk:Equivalence principle

"a free-floating (weightless) inertial body will simply follow those curved geodesics into an elliptical orbit. An accelerometer on-board would never record any acceleration." I'm quite certain that an object approaching from a distance, in a hyperbolic trajectory, cannot enter into an orbit without experiencing acceleration (actually, deceleration). So-called "ballistic capture" of spacecraft by other bodies always involves at least some maneuvering, or else the involvement of a moving third body to temporarily alter the shape of the geodesic.

The article is tagged "citation needed" since 2011, weasel-worded phrases (November 2018), and failed verification (June 2018). There is also a great deal of unsourced content including equations. The B-class criteria #1 states; The article is suitably referenced, with inline citations. It has reliable sources, and any important or controversial material which is likely to be challenged is cited. Reassess to C-class. — Preceding unsigned comment added by Otr500 (talk • contribs)

Hello, I am following the excellent discussion by user `69.243.124.241` regarding the "uniform gravitational field" and hope to clarify a point of confusion that seems to be created by the article's text.

I see a direct contradiction between the article's foundational "Concept" and its "Definitions" section.

1. The "Concept" section introduces Einstein's core thought experiment by claiming equivalence between "being on the surface of the Earth" and "a spaceship in deep space accelerating at 1g." 2. The "Weak equivalence principle" section, however, states that the principle applies in a "uniform gravitational field." It then immediately clarifies that this uniformity is necessary to "eliminate... tidal forces" which, it explicitly states, originate from a "radial divergent gravitational field (e..g., the Earth)."

This is a logical impasse. The article's foundational example ("the surface of the Earth") is explicitly defined by the article itself as being non-uniform and possessing tidal forces, while the principle's definition ("uniform gravitational field") is explicitly defined as requiring the elimination of those forces.

My question is: How can the article simultaneously claim the "surface of the Earth" scenario is equivalent to the rocket, while also defining the Earth's field as fundamentally *different* from the "uniform" field required by the principle's own definition?

Should the "Concept" section be corrected to clarify that Einstein's thought experiment only holds for a fictional, non-existent "uniform gravitational field," and not for the "surface of the Earth" as it currently, and contradictorily, states?2001:1C00:461A:5300:B72:CEE8:42CD:C28D (talk) 20:35, 24 October 2025 (UTC) [reply ]

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