Actually, it was supposed to be microwaves not a laser. And the idea was to provide all the acceleration early on, not over centuries.
How were you supposed to stop?
The Starwisp wasn’t intended to decelerate. Forward advanced another suggestion using a higher frequency laser that would use a large detachable reflector that would reflect the beam back to the main craft for deceleration; unfortunately, if you work out the numbers, the payload mass per surface area ended up being some absurdly high number; for even a small payload the required reflective area would be larger than the system itself, several hundred light-hours across.
Solar- or beam-powered propulsion across interstellar distances simply isn’t practicable, no matter how you spin the numbers. Manned interplanetary transit is only a modest extension of existing technology (and by modest I mean something that could be developed in 20-30 years), but interstellar travel is strictly in the realm of science fiction at this point.
Stranger
Not true. That’s only half (or likely less than half) the info needed to build a human. The environment it develops in is just as important.
But the instructions to construct a body are all in the genome, except for some extra floaty bits like the mitochondria that can be mixed and matched. All you need to make a body is some form of uterus or in vitro environment. Someone has to care for and raise the resulting organism, which is definitely a non-trivial task, but still much more manageable than keeping a sustainable population alive in a closed environment with no external source of power or resources for decades or (more likely) centuries.
Stranger
Maybe Detroit is secret test version 1.0 
A solution to the energy requirements?
Not sure what’s supposed to be new about that; the possibility has been known for decades. There’s no reason in principle that it wouldn’t work, but a decent chunk of the energy produced would be wasted in neutrinos. And of course it’d be very expensive to construct the first one.
Someone better at math than I am would have to check the lifespan/mass ratio for black holes. The article states that a black hole with a 3.5 year lifespan would weigh around 600,000 tonnes. The figure I once heard was that the “last ten million tonnes” would evaporate in ten seconds. That’s a significant difference.
A “phenomenal amount of engineering” indeed would have to done to be able to compress enough photons into a small enough space to form a micro black hole. I once heard that even though photons are bosons, that at extreme densities subtle quantum effects come into play that cause scattering. Is this true? And even if you could form a micro black hole I don’t see how you could feed it to maintain its mass- getting enough baryonic matter into a vanishingly small event horizon against a stupendous radiation pressure sounds difficult to say the least.
Still, unless something like catalyzed proton decay is possible, a micro black hole is about the only way we know of to truly convert matter into energy with high efficiency.
Once you get down to holes that small, it’s tricky to calculate the lifespan, since it depends on counting all of the particle modes that are available to be emitted, and a hole that small could emit far more particles than we’ve ever produced in the laboratory. And this is aside from any quantum gravitational effects of which we’re completely clueless, and which might plausibly start showing up for micro holes.
It’s not so much extreme densities as extreme energies. Basically what happens is, if you get photons of sufficient energy, they’ll produce electron-positron pairs, which will interact and then re-combine into photons. Since these are virtual particles, this can in principle happen at any energy, but it’s much easier when you have enough energy to actually make the particles for real. And I imagine that it’d require energies high enough for this to be significant to make an artificial black hole, since you’d need to localize the beams extremely precisely.
Well the paper that the article came from was published Aug 2009. Full paper:
So all you need to make a human is another human!?
Two, traditionally.
Actually, the density is important too. Even if your photon has an energy >1 Mev , big enough to create an electron-positron pair, you can’t get real particles because you need a way to conserve momentum. This requries two photons. Since you are trying to focus light from the Sun, you don’t have to worry about 1 Mev photons, but you do have to worry about what happens when the density of photons becomes so high that the electric fields exceed the breakdown strength of the vacuum. At these intensities electromagnetic fields become highly nonlinear and all the normal rules of optics break down.
Larry Niven did cover it in A World Out Of Time, and in fact it’s used as a minor twist- the renegade pilot of a ramscoop is planning to accelerate his ship to near the speed of light, assuming the ship’s original, relatively sedate itinerary is just unimaginativeness on the part of his former commander, and he has already begun to do so when his commander hacks his ship’s computer and explains to the pilot that he’ll be throwing his life away because as he accelerates the ship will suffer increasing damage from friction.
That assumes a magnetic only bussard ramscoop.
Electrostatic designs ARE drag free, but have their own problems.
Combining the magnetic and electrostatic system will result in low or no drag, and
increased scoop radius, all for the same power input:cool:
I was assuming perfectly inelastic collisions between the scoop and the ISM particles, without regard to how the scoop was constructed. I take it then that the electrostatic designs do something to salvage some of the energy from the collision?
Man, just barely. The theory of general relativity was published in 1915. That was 94 years ago.
As far as I can see.
Actually, the c limit comes from special relativity, not general, which was developed in 1905, the “Miracle Year”. Which means that the world record holders for longevity would have been talking then, but not much of anyone else.