Yes, I think human interstellar exploration (and yes, maybe even colonization) might be possible, after a fashion. But to get there, we're going to have to master at least two entire technological fields that don't yet exist, even before we start trying to blast compact disc sized machines up to relativistic velocities. And that's without considering the difficulty of how to cram an industrial infrastructure capable of building more of itself, of a machine capable of surviving in deep space — the equivalent of those 300,000 NASA technicians and engineers — into the aforementioned CD-sized machine ...
If we succeed in doing it, it's going to look nothing like the Starship Enterprise. Or even New Horizons. The whole reference frame we instinctively assume when we hear the word "ship" is just so wrong it's beyond wrong-ness.
(There's an alternative to shipping around uploads via laser that merits investigation: if we can do uploading, and if we can make memory diamond — which would seem to be a reasonable expectation of a mature machine-phase nanotechnology — then the 80g payload of the reference starwisp ought to be sufficient to carry about 2 x 10^24 bits, which corresponds to 20,000 stored uploads per "passenger ship". This might well be energetically cheaper than using a laser to transmit uploads, giving us an unexpected long-haul corollary to Tanenbaum's law.)
Stars and Other Solar Systems Could be Closer Than We Currently Think
NASA Infrared survey could find brown dwarf stars that are closer Alpha Centauri.
My article was mentioned in the 114th comment in the Charlie Stross article thread
NASA's wide field infrared survey project was examined in more detail as well
Universe Today: There have been microlensing events with suggests that Brown Dwarf stars are far more common than previously believed.
Michael Werner, Spitzer's project scientist at JPL: "It's clear now that brown dwarfs are about as common as all other kinds of stars put together,"
Relying heavily on data from the Jet Propulsion Laboratory-based Spitzer space telescope, astronomers for the first time have observed "baby" brown dwarfs in the earliest stages of formation..
Brown dwarfs are dim celestial objects that seem to be neither fish nor fowl. But it turns out they begin life more like stars than planets, according to a recent paper by a team based at the Centro de Astrobiologia in Madrid.
Astronomers thought that brown dwarfs had to be part of the process of star formation, but the newest images suggest that brown dwarfs can be formed through a completely independent process. Like stars, they are formed through gravitational collapse.
Brown dwarfs lack the signature feature of stars: they can't convert hydrogen into helium through nuclear fusion. They are too small and too cool to ignite nuclear fusion
Even without Brown Dwarf systems there are large planetoids in the Oort comet cloud and in the Kuiper belt. Fusion powered ships and colonies could be set up throughout the Kuiper belt and Oort comet cloud.
Winterberg's advanced deuterium rocket was designed specifically to leverage the common deuterium resources that are available all over space (our solar system and other solar systems). Comets, asteroids and planets are deuterium gas stations for fusion space ships.
Relatively Near Term Interstellar Enabling Space Technology
1. Mach effect for space propulsion would be huge and may only require better bulk dielectrics. It would enable speeds up to close to the speed of light and could enable faster than light wormhole travel.
Where does the kinetic energy of a Mach-drive vehicle come from?"
Simple, it's the cosmological gravity/inertia or gravinertial field created by the rest of the mass/energy in the universe. This idea is at the heart of Mach's principle as stated by Ernst mach in the late 1800s. In other words when an M-E drive accelerates itself and anything attached to it, the momentum and energy books for this acceleration step are balanced by subtracting the equivalent energy from this cosmological gravinertial field, which IMO, simultaneously lowers the overall temperature of the causally connected universe. So the Mach drive is just an electric motor that has replaced the driving electric and magnetic fields with the gravinertial field as the intermediating agent.
2. Speculation on combining mach effect propulsion and IEC fusion
3. Winterberg's advanced deuterium fusion rocket design
Winterberg's design to obtain a high thrust with a high specific impulse, uses propulsion by deuterium micro-bombs, and it is shown that the ignition of deuterium micro-bombs is possible by intense GeV proton beams, generated in space by using the entire spacecraft as a magnetically insulated billion volt capacitor. The design could have exhaust that is 6.3% of the speed of light. A multi-stage fusion rocket could achieve 20% of the speed of light with exhaust at that speed.
There are several near term nuclear fusion candidates for more energy production and for space travel.
Fusion propulsion if IEC (Bussard) fusion works
Cheap energy from nuclear fusion would also rapidly boost the GDP of civilization by many times.
4. 60 Tesla superconducting magnets could allow tests of gravitational field propulsion
5. 32 Tesla YCBO superconducting magnet project targets 2012
Larger and richer Interplanetary Civilization Can Afford Interstellar Projects
Here is a projection of how if we transition to rapid economic growth we can be a Kardashev 2 civilization within 250 years.
100 Years of growth at the Above Mentioned Growth Rates
3% 18.7 times larger
4% 48 times larger
5% 125 times larger
10% 12528 times larger (China level growth rates of the last 35 years)
20% 69 million times larger (Fast growing company or mutual fund)
30% 191 billion times larger
50% 271,000 trillion times larger
At the sustained levels of 20%, 30% and 50% annual growth the civilization would progress to and exceed Kardashev Level 2, capturing and using all of the energy (or the equivalent) energy of the Sun.
The Risk of Superweapons
I think there will be a need to be in spaceships and to be highly mobile most of the time. This would be a precaution against advanced super weapons. I think future technology will make it relatively easy to blow up a star. Powerful kinetic energy weapons will also provide a stronger offense than defence (if you can fly around a solar system willy-nilly in millions of interplanetary ships and can get up to 10% or even 1% of light speed easily then there is a lot of kinetic energy). Therefore, it will be safer to live in spaceships when there is advanced technology all over (common and cheap nuclear fusion, molecular nanotech etc...). Space colonies without propulsion is fine if you knew with certainty that things would be peaceful, but even if your civilization is peaceful you do not know about unknown neighbors or about internal radicals.
(Some ideas that I have seen about novaing a star - a sufficiently large gamma ray laser or anything else that could cause unusual hot spots in a star that disrupt the mechanics inside in a way that cause it to nova.)
Defences will improve. A more near term example, is a suggestion that I have for re-inventing civil defense against nuclear weapons on earth. However, even if you can make something able withstand powerful forces, the offensive weapons will improve too and you might need to run away quickly and advanced civilizations would be prudent to maintain that ability.