Interstellar travel by dark matter and mini black holes

[skeptical]

Interesting article on the New Scientist web site.
Dark power: Grand designs for interstellar travel - space - 25 November 2009 - New Scientist

Two proposals for ways humanity might, in the future, travel between the stars.
1. Similar to Bussard ramjet, but using dark matter. Apparently dark matter is supposed to contain two types of neutralinos that annihilate each other with the relase of vast amounts of energy. If it can be trapped and compressed together, the results are stupendous! Acceleration to close to light speed is theoretically possible.

2. Mini black hole. The exact size needed is about one million tonnes - about the size of an atom - which will give off Hawking radiation, thus acting as an energy source able to accelerate a starship to close to the speed of light.

The suggestion is that alien civilisations may be zipping about the galaxy using one or both of these. If they use black holes, their ships should be detectable with a gravity wave detector, tuned to high frequency waves.

Obviously both of these methods are highly speculative, and humanity is a very long way off being able to use either. But in 500 years, who knows?

 

[chrispenycate]

Right, you've told me how to get the em vee squared – the energy – what do I do to get the mv - the conservation of momentum, the reaction mass thrown back along the path you're accelerating along? Which, to get anywhere near light speed would be well over ninety percent of your original mass (and the amount of mass needed to accelerate a mini black hole is - interesting.

It is a standard error to assume that enough energy, and your problem's solved; actually you've the two conservation laws to consider.

 

[skeptical]

chris

With method 1, you are tossing dark matter backwards, which is substantially massy. The principle of the ramjet includes collecting, and accelerating backwards.

With method 2, the black hole is losing mass from Hawking radiation. This is being ejected backwards. A million tonnes adds up to a lot of mass.

Any other questions?

 

[chrispenycate]

chris

With method 1, you are tossing dark matter backwards, which is substantially massy. The principle of the ramjet includes collecting, and accelerating backwards.

With method 2, the black hole is losing mass from Hawking radiation. This is being ejected backwards. A million tonnes adds up to a lot of mass.

Any other questions?

A million tonnes of mass to accelerate, too.

Your maximum ejection speed is c, so the closer you get to light speed the less force you get in the accelerate direction, and the more "friction" you experience in picking up more mass to eject; as photons, if possible, and dark matter doesn't seem too well adapted for that.

Of course it's good for slowing down, another very real problem.

 

[skeptical]

The biggest problem here is that no-one has the faintest idea how to interact with dark matter, to permit that form of starship, or with black holes, no-one has the faintest idea of how to manufacture or discover a mini black hole, or how to handle it once available.

Whether these ideas ever reach practical fruition is a matter of speculation, but I cannot see anything happening for a hell of a long time.

 

[Nik]

Um, any-one trying to patent variations on 'Tame Black Hole Rocketry' may be referred to Charles Sheffield's McAndrew Chronicles...

FWIW, I'm not happy about invoking immense amounts of 'Dark Matter' like a 'modern aether'. I recently read in New Scientist (1000mph car issue) that a nearby intra-galactic gas cloud probably has ~100 times more mass than previously thought...
Smith's Cloud - Wikipedia, the free encyclopedia

That's just the nearest and easiest to study of so many in our galaxy, suggesting that finding the 'missing mass' may not take new physics...