Warp wrote:
>   With this taken into account, can you just go from Earth to the nearest
> black hole, get an enormous speedup and come back at 100x the speed and
> slam onto Earth at that speed? From a gravity assist only, I don't think so.
> I think it would be against conservation of energy.

I don't believe that's right.

Consider rolling a small ball at 10 kph on a level surface. It runs into a 
large heavy ball (say, 1000x the mass) rolling at 1 kph the other way and 
bounces off. Now the large heavy ball is rolling at 0.999 kph, and the small 
ball is rolling at 1000 kph (or 10,000 kph or something) back the way it came.

Clearly energy and momentum are conserved there.

You'd wind up changing the course of the black hole much less than you'd 
change the course of your spaceship, is all.

I also think the black hole would be better, because you can get closer and 
get a bigger time dilation from the gravity also.


>   There are also some practical things to take into accout:

We're talking about using black holes for time travel and you're considering 
practical things? :-)

> - The humongous amounts of radiation around a black hole would probably
> be enough to fry you to ashes in a fraction of a second, 

FWIW, it's the accretion disk that generates the radiation, so you could 
kill two birds with one stone by finding one without.

-- 
   Darren New, San Diego CA, USA (PST)
   "Ouch ouch ouch!"
   "What's wrong? Noodles too hot?"
   "No, I have Chopstick Tunnel Syndrome."

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