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eggshaped
309179.  Wed Apr 02, 2008 10:38 am Reply with quote

This is quite complicated, but could be fun if we can nail it down. The question I'm proposing would be something like:

Question: What’s the best thing to do if you fall into a black hole?

Which should get panellists going, at least.

The idea is that if you find yourself past the event horizon, there is a longest-path that you will spiral down before you become part of the star's mass.

This longest-path is the default way you would fall, if you started to free-fall. In other words, like quicksand, the more you struggle, the more quickly you will die. Put on the thrusters, and you're hastening your demise because you'll go off the longest path.

The other cool thing, I think, is that as you fall, someone observing you from outside the event horizon would see you go slower and slower and appear to be virtually stopped in time.

Another fact about black holes is that they don't suck things in. You can orbit a black hole perfectly happily in the same way that you might orbit a sun.

All this is pretty hard physics, so it may be too hard for Stephen to explain in a couple of seconds, but I thought I'd throw it out there for some of the austere brains to ponder.

Here's a link anyway; there's loads out there if you google it.

PPV "Nature" article c&p-ed into a forum

 
dr.bob
309188.  Wed Apr 02, 2008 10:43 am Reply with quote

eggshaped wrote:
The idea is that if you find yourself past the event horizon...
<snip>
The other cool thing, I think, is that as you fall, someone observing you from outside the event horizon would see you go slower and slower and appear to be virtually stopped in time.


Just a minor point, someone from the outside would never see you pass the event horizon. They would indeed see you fall more and more slowly until you appear to stop on the event horizon.

Another point to bear in mind is that you'd be very lucky if you managed to pass the event horizon in one piece. Most likely is that tidal forces would rip you to pieces long before then.

eggshaped wrote:
Another fact about black holes is that they don't suck things in. You can orbit a black hole perfectly happily in the same way that you might orbit a sun.


Well, they do suck things in, but only in exactly the same way that any object with a gravitational field sucks things in. It's entirely true, and possibly surprising to those of you who don't have PhDs in astrophysics, that you can orbit a black hole perfectly happily :)

 
eggshaped
309200.  Wed Apr 02, 2008 10:50 am Reply with quote

Oh yes. Tidal forces. I did have that in my notes, but carelessly omitted it from the post.

Cheers Bobster.

 
eggshaped
309203.  Wed Apr 02, 2008 10:52 am Reply with quote

So from the safety of their orbiting spaceship, they'd forever see the look on your mangled face as your body is torn apart by gravity's tidal forces.

As the old saying goes. "Funny. But not for the victims."

 
eggshaped
309210.  Wed Apr 02, 2008 10:54 am Reply with quote

Wiki calls this tidal effect spaghettification and claims it comes from "Brief History of Time"; my copy of which is currently in Woking.

wik

Quote:
What is the best thing to do if you fall into a black hole.


Sit back and enjoy the ride, unless you've already been spaghettificated.

 
Flash
309219.  Wed Apr 02, 2008 11:04 am Reply with quote

Quote:
the austere brains

That'd be me.

I think this would be good, but quite difficult to pull off unless Stephen feels that he's really on top of it. Plus, we'll have the Boss in a right old two and eight.

How do we know this stuff? Does it mostly have to do with tremendously long sums?

One to ponder.

 
WB
312046.  Mon Apr 07, 2008 1:34 pm Reply with quote

Q. Who first forecast the existence of Black Holes?
A. An English country parson John Michell in 1783.

In 1783 Henry Cavendish delivered a paper to the Royal Society that forecast the existence of Black Holes. It was the contents of a letter to him from John Michell.

Michell accepted Newton’s theory that light was small particles. He reasoned that such particles emerging from a star would have their speed reduced by the gravity. He also knew that there was a critical speed (the ‘escape velocity’ w2GM/R - N.B. this is independent of the mass of the escaping object) needed to escape from a star’s gravitational pull. He wondered what would happen if the star’s gravitational pull was so great as to make the escape velocity larger than the speed of light (already known for 100 years from Ole Roemer’s experiments). Michell calculated that a star of the same density as the sun, but 500 times larger would have such an escape velocity. It would not allow light to leave and as such would be invisible.

Michells answer was right, although it would have to wait for Albert Einstein to correct his reasoning. Later Schwarzschild solved Einstein’s equations for the case of a black hole (singularity) and Robert Oppenheimer predicted that they could be formed from massive collapsed stars. The term ‘Black Hole’ was coined by John Wheeler in 1968.

(In 1796 Pierre Laplace made similar conclusions to Michell in his paper “Exposition du Systeme du Monde”. Both were too way ahead of their time to be taken seriously and their work was forgotten when the wave theory of light took over in the 19th century. Michell’s paper was only re discovered in the 1970’s!)

 
eggshaped
312587.  Tue Apr 08, 2008 9:29 am Reply with quote

This is funny, but "not for the victims".

Quote:
In Kuwait after the end of the Gulf War, the Kuwaitis celebrated by firing weapons into the air - and 20 Kuwaitis died from falling bullets.


moreover

Quote:
In Los Angeles, between the years 1985 - 1992, doctors at the King/Drew Medical Center treated some 118 people for random falling-bullet injuries. 38 of them died. Practically all of the injuries were due to happy holiday weekend revellers.


In this paper

 
Flash
312595.  Tue Apr 08, 2008 9:41 am Reply with quote

Yes, apparently if you're hit by a bullet it's more likely to be fatal if it's falling from the sky than if it hits you horizontally (because it's likely to hit your head). However, I was husbanding this topic for G for guns.

 
eggshaped
313960.  Thu Apr 10, 2008 9:59 am Reply with quote

Black holes leak out information. At least we think they do. It's called Hawking radiation and it proves that black holes can evaporate. Put very basically, in the vacuum around the event horizon, the laws of quantum mechniics allow for pairs of particles to come into existance, one of which can be sucked back into the black hole, while the other comes into the "rest of the universe".

Aaaaanyway. According to a new study, this information leaks out at a rate faster than a dial-up internet connection.

http://www.sciam.com/article.cfm?id=information-may-leak-from

 
dr.bob
314375.  Fri Apr 11, 2008 5:37 am Reply with quote

Bear in mind that Hawking Radiation is so far entirely theoretical and has never been observed. I mean, Stephen Hawking is an exceptionally clever guy, but he's been wrong before.

 
eggshaped
314382.  Fri Apr 11, 2008 5:43 am Reply with quote

Yes, that was the "At least we think they do" caveat.

I always wonder, that if the hawking radiation turns out to be wrong; what will Hawking be remembered for? Writing a fairly good coffee-table book about space? Leaving his wife for his carer? Or just being generally wrong about some stuff.

 
dr.bob
314398.  Fri Apr 11, 2008 5:53 am Reply with quote

It's hard to know with these scientists who become celebrities. At the end of the day, pretty much all scientists are eventually proved to have been "generally wrong about some stuff."

 
eggshaped
334555.  Mon May 12, 2008 9:11 am Reply with quote

The only person ever to be confirmed to have been hit by a meteorite was Ann Hodges.

Quote:
The “Hodges Meteorite” fell from the sky on Nov. 30, 1954, punching a hole in the roof of a house in the Oak Grove community, near Sylacauga, smashing a wooden radio cabinet and then landing on 31-year-old Ann Hodges, as she lay dozing on her couch. The meteorite, which weighed about 8.5 pounds, hit Hodges’ hand and hip and caused extensive bruising


http://uanews.ua.edu/anews2004/nov04/meteorite112404.htm

 
WB
334737.  Mon May 12, 2008 12:43 pm Reply with quote

Apart from "The Pope Hit by a Meteorite" by Maurizio Cattelan at the 2000 Apocalypse Show at the Royal Academy.

 

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