# Do a lot of questions about black holes have answers with wrong information?

According to Does it matter if answers are correct?, a lot of wrong answers on Physics Stack Exchange are getting more upvotes than downvotes. Also this answer and this answer both appear to have wrong information. They both appear to have been written by people who don't understand how black holes work.

According to the first answer, we never see an object cross the event horizon so when it gets bigger, we see it move out with the event horizon as the black hole gets bigger. I believe the real answer to the first question is that when a small object falls in, we can make the approximation that the black hole doesn't gain mass and only gains mass later when it consumes a star and if it doesn't consume any massive object until a long time after it consumes a small object, then before it consumes the massive object, in one coordinate system, space is flowing into the black hole in an approximately Newtonian way and flowing in faster than light beyond the event horizon. After the black hole consumes the star, the closer to the event horizon you look, the longer ago you see that region of space from and if you look close enough, you see it the way it was before the black hole got bigger so you see the object from a time when it was really close to the event horizon before the black hole consumed the star and it looks really wierd looking through the space around a larger black hole to space the way it was before the black hole got bigger.

According to the second answer, if you fall into an evaporating black hole, the black hole will evaporate before you reach the event horizon. I figured out what I believe to be the correct answer that I later saw as an answer on Astronomy Stack Exchange that somebody else independently figured out but I can no longer find that answer. I believe again that the shrinking of the black hole doesn't change the fact that you can treat it as though space is flowing into the black hole and flowing faster than light beyond the event horizon. In theory if light were entirely a particle and was composed of infinitely many of them, a falling object wouldn't emit the final photon that will escape out into space nor would its emitted light get red shifted to a longer wavelength than the Schwarzschild radius before half the black hole evaporates away so if an object falls in, then after half of the black hole evaporates away, you will see the object the way it was before it reached the event horizon while the black hole was bigger and it will also look very weird.

• (1) If you want to ask for clarification about the physics content of those specific answers, you should ask a follow-up question on the main site. The issue is subtle. (2) There are plenty of answers all over the site with wrong information. Both of the answers you link have been downvoted by other users on the site (despite currently having nonnegative answer score). – rob Aug 17 at 21:06
• @rob I already asked one at physics.stackexchange.com/questions/422436/…. I also saw a question on Physics Meta that I can no longer find about the problem of so many bad answers getting upvoted. – Timothy Aug 17 at 23:26
• Your last paragraph looks odd. The space flowing is just a coordinate choice i.e. the Gullstrand-Painlevé coordinates. In the early days of GR these were used because they remove the singularity at the horizon, however the metric is not diagonal so these days we'd use Kruskal-Szekeres coordinates instead. Space is definitely not flowing. Neither coordinates describe a time dependent geometry i.e. growing or shrinking black hole. – John Rennie Aug 18 at 9:52
• All of relativity is plagued by (a) multiple different ways to chose numeric conventions, (b) different ways to structure the language you use in talking about the subject, and (c) both misconceptions and shallow understanding ascribable to pop-sci treatments. Most of the 'wrong'ness caused by (a) and (b) can be dealt with by asking the author to clarify conventions and style. In most cases errors attributable to (c) are best dealt with by commenting and providing a better answer. – dmckee Aug 18 at 13:46