# Can an entity trapped past the event horizon detect getting turned into Hawking radiation?

Assuming your space ship survives engaging with the accretion disk and any spaghettification issues:

(1) I’ve read that the crew can’t tell if they’ve already crossed the event horizon. There wouldn’t be a point where some crew member would analyze the recent path and what they could see what’s outside the windows on the way and go “oh sh#t”?

(2) Black holes lose mass through Hawking radiation. Once you cross the event horizon, you seem to be part of the black hole. So couldn’t the part of the black hole that goes away (to balance the outgoing HR) be part of you? Assuming you had super space sensors, could you detect missing parts and conclude you’re past the event horizon?

• This diagram i.sstatic.net/677y2.jpg shows coordinate timeslices. The red line is when the black hole evaporates and no longer exists anywhere above this line. So nothing can cross the horizon before the black hole completely evaporates and disappears. (Technically, the black hole evaporation event is in the past light cone of all falling observers while they are still outside.) Also, you become a part of a black hole not when you cross, but while approaching the horizon from outside. So you too evaporate before crossing the horizon. Thus your question is based on a wrong premise. Commented Sep 16, 2023 at 6:24
• If your question is not about the Hawking radiation, but how to know you’ve crossed the horizon, then there is a simple way. If you are in a free fall, just look back and measure the redshift of the starlight exactly behind you. When this redshift is exactly 1 (the wavelengths are doubled), you are at the horizon. See this for details: physics.stackexchange.com/questions/420721 Commented Sep 17, 2023 at 5:10
• I'm more interested in the Hawking radiation part. Your second comment gives a way to detect if you're at the horizon. When relative to that detection does the evaporation (as mentioned in your first comment) happen? Commented Oct 22, 2023 at 2:20
• Per classical GR, all outside events happen before anything reaches the horizon. Evaporation is an outside process, except it is not classical, but quantum. As such it breaks GR at the horizon by the Information Paradox (e.g. how can you evaporate before crossing the horizon?). Thus, if the Hawking radiation exists, then GR is no linger predictable starting from the quantum scale distances to the horizon and we have no alternative validated theory (Quantum Gravity) to replace GR there. One way or another you are destroyed (by the firewall or something else) just before you reach the horizon. Commented Oct 22, 2023 at 18:51