Gravitational Mass: The gravitational mass of an object is the ratio of the gravitational force applied to an object and the strength of the gravitational field.
Einstein's Thought Experiment:
Inertial Mass: The force applied to an object divided by the acceleration it produces.
These two are identical for all intents and purposes on earth and would only become significant if we accelerate in deep space where the gravitational forces are negligible.
Einstein's Thought Experiment:
Consider two scenarios: If there is an astronaut doing an experiment of dropping a ball in a stationary elevator on earth or in an accelerating elevator. Einstein states that the observations would be identical and the astronaut would not be able to determine whether he is in an accelerating frame of reference or in a gravitational field. This is called the principle of equivalence.
Bending of Light:
Light bends in the presence of bodies with large masses. Evidence: During a solar eclipse in 1919, Arthur Eddington found that stars behind the sun were shifted outwards as shown:
Gravitational lensing:
Light from distant galaxies behind other galaxies reach the earth because of bending of light. This allows us to see them and is evidence for general relativity.
The distant galaxy appears as a ring around the galaxy in front which is called the Einstein ring.
Time ticks slower in accelerating frames of reference. Consider an beam of light being shone at a wall inside a room that is moving at constant velocity and in a room that is accelerating:
To an observer in the room accelerating, the light appears to be hitting the same spot as he is stationary with respect to the event. But to an observer outside the room, the light appears to be taking a curved path. As the speed of light is constant and the distance that light travels increases according to the observer (curved distances are longer than linear ones), time must be slowing down.
This is why light ticks slower closer to bodies with large masses, as light bends around them.
Bending of Light:
Light bends in the presence of bodies with large masses. Evidence: During a solar eclipse in 1919, Arthur Eddington found that stars behind the sun were shifted outwards as shown:
This proves that light from the stars bends due to the presence of a body of large mass like the sun which provides evidence for general relativity.
Gravitational lensing:
Light from distant galaxies behind other galaxies reach the earth because of bending of light. This allows us to see them and is evidence for general relativity.
The distant galaxy appears as a ring around the galaxy in front which is called the Einstein ring.
Time ticks slower in accelerating frames of reference. Consider an beam of light being shone at a wall inside a room that is moving at constant velocity and in a room that is accelerating:
To an observer in the room accelerating, the light appears to be hitting the same spot as he is stationary with respect to the event. But to an observer outside the room, the light appears to be taking a curved path. As the speed of light is constant and the distance that light travels increases according to the observer (curved distances are longer than linear ones), time must be slowing down.
This is why light ticks slower closer to bodies with large masses, as light bends around them.
