On 2024-06-08 17:40:15 +0000, Luigi Fortunati said:
In the video https://www.youtube.com/watch?v=R3LjJeeae68 at minute 6:56
it states that there is no measurement that can be made to distinguish
whether you’re being accelerated or whether you are sitting still on the >> surface of a planet.
So, I ask: what stops us from measuring the presence (or absence) of
tidal forces? If tidal forces are there, then we are stationary on the
surface of a planet, if they are not there, we are experiencing a
non-gravitational acceleration.
Consider a situation where you are not sitting on a surface of a planet
but acclerated by a real non-gravitational interaction; and this happens
near a planet or a star: you can measure a tidal force (if your instruments are big and sensitive enough).
In the video https://www.youtube.com/watch?v=R3LjJeeae68 at minute 6:56
it states that there is no measurement that can be made to distinguish whether you’re being accelerated or whether you are sitting still on the surface of a planet.
So, I ask: what stops us from measuring the presence (or absence) of
tidal forces? If tidal forces are there, then we are stationary on the surface of a planet, if they are not there, we are experiencing a non-gravitational acceleration.
Hendrik van Hees il 10/06/2024 14:10:37 ha scritto:These are preconceptions well tested with high precision for centuries.
Or to put it simpler. In a local inertial reference frame, realized by a point-like non-rotating body in free fall, you observe (e.g., by using pointlike test particles) only the "true gravitational forces", i.e., the tidal forces.
If you sit on the surface of a planet, you are not in free fall, because there are (electromagnetic) forces keeping you there.
That's why the accelerometer of your smart phone at rest on Earth shows an acceleration of 9.81 m/s^2, because it measures accelerations relative to a local inertial frame of reference! See, e.g.,
Your reasoning is based on two preconceptions.
The first is that the accelerometer measures accelerations (and insteadI don't know, what's evident in your misconception. By definition bodies
it only measures forces) and the second is that free fall is an inertial reference system despite its very evident mutual acceleration towards
the other body (also) in free fall.
Luigi Fortunati
Hendrik van Hees il 11/06/2024 10:46:14 ha scritto:
The first is that the accelerometer measures accelerations (and insteadI don't know, what's evident in your misconception. By definition bodies
it only measures forces) and the second is that free fall is an inertial >>> reference system despite its very evident mutual acceleration towards
the other body (also) in free fall.
which move without any interactions except the gravitational interaction
are by definition in free fall, and according to the equivalence
principle such bodies define a LOCAL (!!!!) inertial reference frame.
The inertial reference frame is one where no forces act.
In free fall, tidal forces act and, therefore, you and Einstein are
wrong when you say that free fall is an inertial reference (whether
local or non-local).
Luigi Fortunati
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