Which gets you first when you are falling into a black hole, the black hole singularity or the cosmic background radiation?

black-holes cosmic-microwave-background tidal-effect

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That is an incorrect description of what happens.

If the black hole is small, the gravitational forces pull you apart before you get anywhere near the horizon. On the other hand, if the black hole is large, you won't even notice anything as you cross the horizon, until you hit the singularity and then you'll be pulled apart. Remember, from your point of view you are just free-falling, the event horizon only has meaning for the outside observers. The stars will look somewhat different during your fall because of the hole's gravitational lensing effect, but no fiery death by cosmic radiation.

From the outside observer's point of view this is all different: they will see you getting closer and closer to the horizon but never reaching it.

Some more detailed explanation about this (and many other things about black holes) is for example here: http://cosmology.berkeley.edu/Education/BHfaq.html#q3

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Qmechanic

Updated on May 21, 2020

Comments

Qmechanic about 3 years

If you look up while you are falling into a black hole you see the universe blue shifted, that is, you see the universe moving quickly forward in time compared to your local time. Since this effect increases as you get closer to the singularity, a star aimed at you could blast you with a billion years of radiation in maybe a second. Of course, no star will be perfectly aligned for billions of years. On the other hand, there is lots of cosmic background radiation coming at you from everywhere in the sky and it will be blue shifted too. So, how bad is it? Would this radiation cook you before you hit the singularity?
Scott Wales over 12 years

Yes, if the background radiation were constant, that would definitely be the case, but the universe is expanding. That means the background radiation is getting dimmer and dimmer, and as you fall, you see it getting dimmer faster. Is the universe expanding slowly enough so you fry, or is it expanding fast enough for one to get safely - if I may use the term - to the singularity. I assume it depends on your accelerating rate of travel.
Gergely over 12 years

Or you can try out what the process looks like with the Black Hole simulator: physorg.com/news185055769.html
Jerry Schirmer over 12 years

No. There are not necessarily any local effects at the horizon. Time dialation and blue shifting of radiation are global effects that describe the comparison of local reference frames at the horizon, and local reference frames far from the black hole. For a sufficiently large BH, a local observer wouldn't even know they're crossing the horizon.
Jerry Schirmer over 12 years

One side note: Likely, the most dangerous thing, if there is any nearby matter, is going to be the gamma and X-ray radiation from the nearby accreting matter.
Ron Maimon over 11 years

This is not incorrect--- it is accurate description of the Cauchy horizon.
ProfRob almost 8 years

According to Taylor & Wheeler's book on black holes this is not correct. The light that a freefalling observer sees from the outside universe is blueshifted and distorted. The blueshift reaches infinity at the singularity, whilst the light comes from a ring around the sky perpendicular to the direction of motion. The question seems legitimate and this doesn't answer it.
ProfRob almost 8 years

This is incorrect. You have described what an observer would see who is capable of hovering just over the event horizon. This is not what a free-falling obser would see at all. Nothing special happens at the event horizon.