GRT - Essence:
Newton thought the Earth- gravity space and the Earth-gravity time
are absolute independent conceptions.

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Einstein showed that the Earth- gravity space and the Earth-gravity time
are relative conceptions. The Earth- gravity space and the Earth-gravity time
are dependent on its mass and speed. If the mass and speed of our Earth
were different then our Earth space and Earth time would be another.
The same is about every gravity system.
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Israel Socratus

 

Einstein showed ( GRT ) that some kind of moving mass
can create reference frame of gravity space and gravity time