How would you aim a probe at another star as mentioned in this thread?
Isn’t the Milky Way revolving as well as moving? Since the probe would take, let’s say 500 years, wouldn’t the star not be there when you got there? How would you pick out the star amongst all the others since the relative position would change as you got closer?
Stars are definitely in motion and you would have to account for this in your navigation. Over a long enough journey, you might even need to take the effect of the aggregate mass of the Galaxy into consideration. As for the position, it is pretty easy to measure the lateral movement of a star with respect to Sol with a reasonable degree of precision, using a combination of methods. On the other hand, the radial distance and movement is really a rough guess beyond a few dozen light years based on the luminosity of the star and (if it is moving fast enough) minor relativistic frequency shifts in its characteristic spectrum. It would be really embarrassing to get there only to find out that you’ve somewhat overshot the target and don’t have enough push-juice to get back.
Right now, just going around the Solar System is a significant challenge, and we know the positions of planets to within a few kilometers or less. Crossing interstellar distances without a good set of charts is a great way to get lost and end up on the wrong side of an event horizon.
Stranger
Questions and Answers | Sten's Space Blog discusses the difficulties of covering the distances involved. They come up with 18,000 years using the slingshot method we use today, and discuss ion drives.
Navigating would rely on our extensive knowledge of the distances and velocities of nearby stars and of galactic mechanics (though offhand I bet the galactic rotation wouldn’t be important in aiming for nearby stars). And. surely, it would rely on built-in intelligence. This spacecraft would have to be able to identify known stars and measure the angles between them, and maybe doppler shift velocities too. It would have to be able to decide how best to use its fuel to keep getting closer. I’m thinking unmanned, but it’d be the case either way.
You’re being facetious, right? Or is local interstellar space really so littered with black potholes that they present a real hazard to navigation?
Better have a female pilot, then. She can ask for directions.
Nay, just hyperbole. There are a few people who think that the missing dark matter could be explained by a distribution of sub-stellar mass black holes, but that doesn’t accord with our current understanding of black hole thermodynamics and we otherwise see no evidence of this in our observable neighborhood.
Stranger
It should be noted that the bounds of “our observable neighborhood” are so poor in this instance as to be almost meaningless. Basically, our best data amount to “There are no primordial black holes within interplanetary distances of us”. There could still be plenty between stars.
However, even if there are plenty between stars, there’s still a heck of a lot more empty space between them. You could cross the entire Galaxy blindfolded without having to worry about colliding with any of them (nor with a star, nor anything else larger than a mote of dust).
Sure, but we don’t see any signs of radiation emitted by infalling particles (which are admittedly pretty sparse in the interstellar medium) or any other expected signs of micro black holes dominated by quantum effects. So, either our expectations are wrong, and interstellar space is littered by benign gravitational singularities, or there aren’t many out there. Either way, I agree that they wouldn’t really pose much of a hazard; even a superJovian mass black hole would have a sphere of influence much smaller than the total volume of space transited.
Stranger
Yes, but those effects are all expected to be faint enough that even if there are a goodly number out there, we’d still expect to see the same null results we do see. Primordial black holes are only bright by comparison to their size, but in absolute terms, they’re not all that much.
FWIW 500 years is an exceptionally lowballed figure. Our fastest probe to date would take something on the order of around 20,000 years to arrive at Proxima Centauri which is the next closest star to earth. Hitting a moving target 20,000 years from now would be quite a feat. You really would need some sort of terminal guidance ability once the probe got in the vicinity.