# Strong equivalence principle

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roineust

1. When a gravitational wave passes through earth, it 'squashes' the form of earth, hence gravity geometry is changed, hence gravity at any given point on Earth change at that moment, be it a small change as may be.

The only reason for that change in gravity, as the gravitational wave passes through, is the above mentioned change in the form of earth, when the gravitational wave passes through it, i.e. depending on the angle from which the gravitational wave arrives, Earth shape changes, for example, from a slightly squashed form to an even more squashed form. In the case of other angles of attack of the gravitational wave, gravity is influenced, by other changes in the form of the mass that the gravitational wave passes through.

2. And the above has a lot to do with what the strong equivalence principle states: that in order to say that acceleration and gravity are equivalent, we must ignore the shape or form of the celestial mass, usually a round mass, which produces the gravity ('earth'). Ignoring that round shape means, having a measuring equipment small enough ('local'), so the round geometry properties of that mass gravity can be ignored, which then could be considered as gravity measured by the equipment, as if its geometry was shaped in a straight line and not in a curved or a round line.

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Mentor
It sounds like you are asking about changes that are not directly due to the gravitational wave itself but are primarily due to a change in the Earth's metric secondary to a change in the shape of the Earth caused by the gravitational wave. Is that what you are asking about?

As you have been told before, you should use unambiguous terminology. "Gravity geometry" and "gravity pull" and "gravity magnitude" are ambiguous.

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roineust
roineust
I don't have the vocabulary to ask this precissly, is the subject in question totally not undserstood, because the use of umbigous terms? If it is somwhat undserstood, but first should be asked using correct terms, what would be the correct phrasing for laymen?

I have taken off 'pull', what should i write instead of 'magnitude', just delete it as well? ..'magnitude' taken off as well...'arrive' taken off as well.

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Mentor
I don't have the vocabulary to ask this precissly,
OK, we need to start there. The question (I think) you are asking is about exceptionally precise concepts. That requires exceptionally precise vocabulary in both the asking and the answering.

Here is a vocabulary list. You need to start here. Before you can ask an unambiguous question and understand the answers you need to know all of this vocabulary and the concepts each term refers to.

Mathematical concepts:
Tensor
Vector
Scalar
Manifold
Metric
Coordinate chart
Basis
Christoffel symbols
Riemann curvature
Covariant derivatives

Basic GR concepts:
Spacetime
Spacetime interval
Timelike
Spacelike
Lightlike
Worldline
Four velocity
Schwarzschild coordinates
Schwarzschild metric
Minkowski (inertial) coordinates
Minkowski (flat) spacetime
Stress energy tensor
Einstein field equations
Ricci curvature
Weyl curvature

Gravitational wave concepts:
Background metric
Linearized equations
Perturbation

Please open new threads about any unfamiliar concepts. I like Sean Carroll’s Lecture Notes on General Relativity first few chapters for this material. I also like Susskind’s lecture videos on the topic for a light intro.

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