Question

is there any relation between aging and gravitational field? what s the actual cause for aging?

Answer 1

Gravitational time dilation is at play for ISS astronauts too, and it has the opposite effect of the relative velocity time dilation. To simplify, velocity and gravity each slow down time as they increase. Velocity has increased for the astronauts, slowing down their time, whereas gravity has decreased, speeding up time (the astronauts are experiencing less gravity than on Earth). Nevertheless, the ISS astronaut crew ultimately end up with "slower" time because the two opposing effects are not equally strong. The velocity time dilation (explained above) is making a bigger difference, and slowing down time. The (time-speeding up) effects of low-gravity would not cancel out these (time-slowing down) effects of velocity unless the ISS orbited much farther from Earth.

The key is that both observers are differently situated in their distance from a significant gravitational mass. The general theory of relativity describes how, for both observers, the clock that is closer to the gravitational mass, i.e. deeper in its "gravity well", appears to go slower than the clock that is more distant from the mass. This effect is not restricted to astronauts in space; a climber's time is passing slightly faster at the top of a mountain (a high altitude, far from the Earth's center of gravity) compared to people at sea level. As with all time dilation, the local experience of time is normal (nobody notices a difference within their own frame of reference). In the situations of velocity time dilation, both observers saw the other as moving slower (a reciprocal effect). Now, with gravitational time dilation, both observers—those at sea level, versus the climber—agree that the clock nearer the mass is slower in rate, and they agree on the ratio of the difference (time dilation from gravity is therefore not reciprocal). That is, the climber sees the sea level clocks as moving slower, and those living at sea level see the climber as moving faster

Answer 2

Aging is caused by error in cell replication and malfunction. Cells can enter into senescence, apoptosis (cell death), or remain metabolically active. Aging happens as a result of cell death and senescence. Senescence is when cells are still active (secreting cytokines) but are not metabolically active. Cytokines result in inflammation and damage to nearby cells. Essentially cells enter into senescence due to ROS (reactive oxygen species) and other damages to the cell via exposure. For example UV radiation (sun exposure) pesticides in food, toxins in the air we breathe, etc.