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In certain theoretical scenario's a human can be in a gravitational field where he would age half as fast as on earth's surface.

However, for light to travel half as fast in one direction, we are talking about gravitational compressions and time-space distortion that already would kill even most invertebrates. If light travels half as fast upwards, and the same speed laterally to the gravity centre, we are talking about disintegration of matter into strands?

Is that true? It would mean that life can only survive gravity fields that make time distortions in the order of 1% and less?

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    $\begingroup$ Are you asking about the maximum gravitational gradient (tidal force) across a human before it affects our health? That seems like a question for biology. $\endgroup$ Jan 22, 2015 at 23:15
  • $\begingroup$ I think that time passes twice as slowly if light travels twice as slowly, and for that to happen on a 1/2 ratio, the matter would be so close to a black hole, it would have already compressed to the density of something like a neutron star. Thanks for the awesome answer, have read the wiki articld, have to read more about compression of matter and distortion of time space when light travels twice as fast away than towards the gravity centre. $\endgroup$ Jan 22, 2015 at 23:50

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The only requirement for strong gravitational time dilation is that the gravitational field be strong. A person can be in a strong gravitational field and not even know it - for instance, an astronaut in orbit around the Earth is in the Earth's gravitational field (which is only slightly weaker than at the surface), yet feels weightless. Spaghettification (which is shockingly the correct technical term) occurs if there is a strong gravitational field gradient, that is to say there is a substantial difference between the gravitational force on say the head of a person as compared to the force on their feet. If this differential (tidal) force exceeds the tensile strength of, say, bone or ligaments, biologically speaking very bad things are likely to happen. However, a strong gravitational field does not necessarily imply a strong gradient in that field. For instance, a typical stellar-class black hole will spaghettify a human outside the Schwazschild radius, but a typical supermassive black hole will not, even though the gravitational field is stronger$^{1}$.

$^{1}$ Before asking me to support this statement with calculations, please at least read the wikipedia article I linked, and ideally go look up or do the calculation yourself, it's been done many times before.

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  • $\begingroup$ But if a person is experiencing extreme gravitational time dilation in free fall, wouldn't that imply that they would either be orbiting at relativistic speeds, or else dropping into the singularity fast enough that they wouldn't notice (still implying relativistic speed)? Or would time dilation still occur if an object wasn't moving? $\endgroup$
    – Michael
    Jan 23, 2015 at 5:37
  • $\begingroup$ Still occurs if not moving, but if not orbiting and not falling, that means thrusters, which means large acceleration, which could be quite painful/harmful. Is orbiting/plunging at relativistic speeds problematic for some reason? (As long as you don't collide with any stray particles, that is). $\endgroup$
    – Kyle Oman
    Jan 23, 2015 at 6:11

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