between now and when the sun gets too hot to handle, there will be hundreds of stars approaching within 0.5LY, and we may be able to hop across the gap and colonize them even with fairly slow ships.

I figure YES by three lines or reasoning:

1. Antimatter. It's the universe's cheat code. Or some other form of hand-wavium. Physics is so clearly not all figured out yet.

2. It's tough to look at the last 1000 years of progress, then look ahead to the next 8000 and think, "oh that'll be too hard."

3. Doesn't really matter if it happens or not. Mana will be won or lost based on how this market fluctuates short-term. I think the overwhelming majority of bettors will read this as "is 9999 sufficiently far away to be sci-fi?"

@DanHomerick How is antimatter "hand-wavium"? We've produced it in labs and know pretty much exactly how it works.

@IsaacKing in order for it to be a useful form of energy storage or propulsion, we'd need a bunch of engineering breakthroughs so as to produce it, store it, and utilize it far more efficiently than we can now. With a distant-enough future, it's easy to wave away any concerns that those breakthroughs might not arrive.

@DanHomerick I wouldn't call that handwaving; they're difficult engineering problems for sure, but with our current scientific knowledge I think we can say with upwards of 95% confidence that it's possible to build such a drive given unlimited funding.

@IsaacKing the efficiency of current antimatter production methods is about 10^-9. But with reaction mass exiting the ship at ~0.05c you'd only need about 1/400 as much energy as the laser. So current total global energy production for a year would be enough to get a ~2 gram probe up to speed

@JonathanRay Wait, why is it less energy than the laser? Photon drives have the highest possible specific impulse.

I think a light sail that's very thinly distributed wouldn't necessarily have issues with collisions. Especially if different cells only connect intermittently with each other. If there's a collision then maybe a few cells are lost and that's it, not the whole spacecraft.

There's probably a way of doing it with a swarm of light sail cells that can coordinate with each other and self-heal

Accelerating something like that to 10% the speed of light doesn't seem that hard

Just need a big laser

Could even make it more exotic by having the sail cells gather matter from collisions to make more cells. Or fire particles at the cells along the path of the laser beam for them to use.

The idea of feeding the cells with a particle beam is nicer because the relative velocities can be, in theory, adjusted to make the collisions very mild

Considering that particle accelerators are technology we already have, doesn't seem that implausible we could get something like this to work by the year 9999

If you allow for beaming light and matter at a swarm of cells like this then it also allows you to do tricks like use the matter as propellant to slow down past a certain point. Or split the swarm in 2 and use one half as a mirror to slow the other half down. All kinds of tricks are possible in theory.

@MalachiteEagle Light sails are hopeless because they accelerate so slowly that you can't get much acceleration from a single close approach to a star. You'd need a series of thousands of hyperbolic close approaches to different stars, and you'd need to be able to fold away the light sail to reduce drag in between the close approaches.

in theory a light sail could get up to speed eventually, but it would take way more than 7000 years.

@JonathanRay i'm talking about light sails illuminated by powerful lasers in the above comments

@JonathanRay therefore possible to achieve 10% rapidly

the energy requirement for laser propulsion is absurdly high. The current total global energy production going to a 50% efficient diode laser would be enough to accelerate a 500kg probe at about 1g. You need about 1/10 of a year at 1g to get up to 10%c at a distance of 0.005ly. Then you have unavoidable beam spreading proportional to wavelength/diameter. Diode lasers are limited by the band gap, and the highest band gap is under 7ev which is a limit of 177nm. With an aperture of 50m that's going to spread out to 837km at a distance of 0.05ly. If you go into the soft x-ray wavelengths (1nm) the laser efficiency will be less than 1% and then the beam only spreads out to 4.75km. There's unavoidably a minimum probe size for any complex electronics to survive the journey, because of radiation from from interstellar neutral hydrogen which can't be deflected colliding with it at 0.1c = 9MeV. This minimum thickness of shielding is probably >500kg/m^2. See below calculation that you'd need 33cm of lead = 3300kg/m^2 to match the radiation levels on a mars trip.

@JonathanRay say the meat of the probe is a very narrow cylinder with lots of shielding in the front of it, and then you have a very wide sail around that, to keep the total mass under 500kg. The beam spreading issue still makes the energy requirements prohibitively high, and you'd probably also have problems with radiation embrittlement of whatever you use to make the sail.

@JonathanRay here’s a simpler way to think about this if you move away from the single massive probe idea. Instead of a 500-kilogram craft trying to pull off 1 g of acceleration, imagine a large swarm of ultralight sail-cells, each carrying only tiny amounts of mass and extremely miniaturized electronics. You can spread your total payload across thousands or even millions of these minuscule craft, which drastically reduces the shielding requirements and solves a lot of the problems you raised. Because each individual cell is so light, it doesn’t need anything close to 33 centimeters of lead. It can rely on thin, well-chosen materials or even just radiation-hardened components, and if some portion of the swarm fails, enough cells can survive to keep the mission going.

With this approach, you don’t need to pump out 1 g of continuous thrust. You can work with a much gentler acceleration—like a fraction of a g over weeks or months—powered by a sustained laser beam or phased array. The moment you shed the requirement for huge acceleration in short bursts, the energy requirements become far less daunting. There are already concepts for phased-array lasers or free-electron lasers with better-than-1% efficiency, and they can operate at near-UV or X-ray wavelengths. Even with diffraction limitations, a large phased array can form a beam that stays tight enough across interstellar distances to impart enough momentum to these lightweight sails. The idea is to let the swarm soak up laser photons over time rather than trying to slam it with all our global energy in one enormous pulse.

If you do the math in a simple way, radiation pressure acting on a perfectly reflecting sail provides twice the laser power divided by the speed of light as the net force. Over a long enough period, the resulting low but steady acceleration adds up to 10% the speed of light, and you don’t have to waste power aiming for any quick 0-to-60 sprint. Because the sails are so light, the total thrust needed per cell is easily within range if you use a big but realistic power source and spread it out over a timescale of months. Beam spreading isn’t fatal for a swarm spread over kilometers instead of a single compact craft, and each cell can collect enough photons over its small cross-section to keep accelerating. You can even imagine strategies to mitigate interstellar collisions, like letting the swarm spread out so the cross-sectional density is low, or using partial sacrificial shielding on the forward cells.

It’s basically a completely different engineering setup than the 500-kilogram probe you’re calculating for. When you swap that big, monolithic spacecraft for a cloud of many lightweight, resilient pieces, the trade-offs change dramatically. The swarm can take some hits without failing entirely, and it can operate on much smaller per-unit power and shielding budgets. That’s how it becomes plausible to shoot for 10% the speed of light without requiring the absurd scaling you get from the single heavy-probe scenario.

@MalachiteEagle heavy radiation bombardment will entropize any small features. The way you rad-harden electronics is by making the transistors huge. Then you can't do much complexity.

The slower the acceleration, the farther away it gets before you reach target speed, the more you get fucked by the aforementioned beam spreading. The beam will be kilometers across before you get up to speed. Each nanoprobe needs guidance and propulsion systems to reunite with the others at the destination, too, and that puts a floor on size besides the radiation problems.

@JonathanRay The most rad-hardened CPU today can take about 30J/g of radiation and weighs 0.5kg. At 10%c you're colliding with interstellar protons at 9MeV to the extent of 0.0043W/cm^2. Supposing it's 2cm by 2cm, and assuming 25% of the incident energy becomes gamma rays, and half of that goes towards the electronics, without shielding you're looking at a survival time of 8 days. You need to last for 40 years to get to the nearest star. The secondary gamma ray spectrum probably peaks around 1MeV and the half-value-layer of lead for that is ~1cm. To extend 8 days into 40 years you need ~11cm of lead. Perhaps an artificial superintelligence can design a much better and smaller rad-hardened CPU. But like I said heavy radiation will randomize any small features in anything.

@JonathanRay I loved reading this exchange. Cool ideas