# The Elephant and the Event Horizon

Saw a pretty stunning piece on Nova recently (Monster of the Milky Way) on the absolute weirdness of black holes (they’re more surreal than you thought). Today found a New Scientist article on what happens to objects sitting at the rim of the event horizon. For 30 years, Stephen Hawking has maintained that all information was destroyed at the event horizon, even though this ran counter to one of the fundamental principles of physics. But now, after studying the work of a young theorist named Juan Maldacena, who essentially posits our universe as the holographic projection of a 5-dimensional counterpart. New Scientist:

Let’s say Alice is watching a black hole from a safe distance, and she sees an elephant foolishly headed straight into gravity’s grip. As she continues to watch, she will see it get closer and closer to the event horizon, slowing down because of the time-stretching effects of gravity in general relativity. However, she will never see it cross the horizon. Instead she sees it stop just short, where sadly Dumbo is thermalised by Hawking radiation and reduced to a pile of ashes streaming back out. From Alice’s point of view, the elephant’s information is contained in those ashes. There is a twist to the story. Little did Alice realise that her friend Bob was riding on the elephant’s back as it plunged toward the black hole. When Bob crosses the event horizon, though, he doesn’t even notice, thanks to relativity. The horizon is not a brick wall in space. It is simply the point beyond which an observer outside the black hole can’t see light escaping. To Bob, who is in free fall, it looks like any other place in the universe; even the pull of gravity won’t be noticeable for perhaps millions of years. Eventually as he nears the singularity, where the curvature of space-time runs amok, gravity will overpower Bob, and he and his elephant will be torn apart. Until then, he too sees information conserved.

Essentially, we end up with a large-scale paradox similar to the light-as-wave/particle paradox: In order to satisfy the laws of physics, objects have to simultaneously be intact inside the black hole and torn to shreds just outside of it. This bakes my noodle.

Thanks Milan

Music: Wire :: I Am The Fly

## 2 Replies to “The Elephant and the Event Horizon”

1. Years ago I read a book called “A World Out of Time.” Aside from being a really interesting novel, the book included one line, almost a throw-away superficial to the plot, that’s resonated with me ever since.

“The radius of black hole is infinite.”

Once I read that, I made a sort of intuitive leap toward understanding the theory of black holes. Not that I DO understand it, not by a long shot, but at least it seemed to make a lot more sense.

2. Erwin says:

It seemed to make a lot more sense.

Respect, absolute respect. Like with some rather complex subjects in maths I can work with the ‘rules’ involved in thinking about black holes, but that doesn’t mean it makes sense to me. Not by a long shot. I can’t get my head around them – but then again, with a radius of infinite, what do you expect? -E