[ExI] Expansion of the Universe

[Anders Sandberg]

On 30/12/2012 17:20, Tomaz Kristan wrote:
> The fastest way to go around should be on the tip of the laser beam, 
> which prints a machine into the dust of a distant planet. A machine 
> which do the same. And so forth, across the galaxies.
>
> This should be possible with a smart laser modulation, I think.

Why?

If you use a Gaussian beam with a waist width W it has divergence angle 
lambda/(pi W) where lambda is the wavelength. If you want to manipulate 
atoms, you need a waist width less than a nanometre, and a wavelength of 
the same size. That gives you a divergence angle of around 18 degrees. 
So if you want to build something in the Andromeda galaxy 2.5 million 
light years away, you need a laser aperture about 800,000 light years 
across. Somewhat bigger than our galaxy...


-- 
Anders Sandberg,
Future of Humanity Institute
Philosophy Faculty of Oxford University