# Timeline of falling into a blackhole

For some "average sized" black hole, how long would it take for a distant (spacesuit-wearing!) astronaut to:

• be able to see the gravitational lensing with the naked eye
• clearly feel the gravity gradient
• reach a lethal gravity gradient
• cross the event horizon

Ultimately I'm interested in the subjective experience of a human falling into a black hole. Would it be drawn out and unpleasant? Or is it that by the time the gradient would be painful, there'd be barely any time at all before annihilation?

• Actually, this is a problem I remember doing in my cosmology class. There are some really good questions here having to do with proper time versus coordinate time, the relationship between the mass of the black hole and the gradient of its gravitational field, and a few other things. If I find some quantitative calculations I remember doing I'll try to answer the question. Dec 18 '13 at 4:26
• Thanks @astromax, would appreciate an attempt at an answer, and cheers for a counter opinion on this question's appropriateness. Dec 18 '13 at 4:35
• Yes - the conclusion I remember coming to is that the larger the black hole mass the closer you could come to the event horizon without feeling this differential tug between your head and your feet. The smaller mass black holes are actually the more lethal ones in terms of tidal forces as you approach the event horizon. However, the amount of time it takes you to get to the event horizon as seen from an "outsider" if I'm not mistaken is infinite. I'll have to double check to see if that's actually the case. Dec 18 '13 at 4:39
• I'm actually teaching a cosmology class next term. One of the homework sets assigned I believe has this particular question. I'll post the answer when I figure it out. Dec 18 '13 at 4:42
• I calculated questions 2/3 for a super-massive black hole once; it's still up on physics: physics.stackexchange.com/questions/38837/… - maybe that helps. (tidal forces can be painful, ouch) Dec 18 '13 at 16:01