Can be accidental, can have already happened.
Must be a human-built object.
Must have a method for propulsion (whether or not such method is on itself).
Minimum mass of the object: 10 grams
To my knowledge, the fastest man-made object of that size was a manhole cover, and it only reached 66 km/s instead of 3,000: https://en.m.wikipedia.org/wiki/Operation_Plumbbob
https://en.wikipedia.org/wiki/Breakthrough_Starshot
A semi-serious project. Using solar sails. Each probe supposedly contains a computer chip. And weighs less than 10 grams.
The plan is to launch lots of them, but if each individual one weighs < 10 grams, does that count?
@DonaldHobson oof, yeah those wouldn't count but that's exactly the kind of thing I'd be curious about. Alas, I set my threshold too high. Maybe they'll make a bigger one!
@KongoLandwalker I'll have to think on this, but roughly something like a railgun projectile, an object with a solar sail, etc., where another object is providing the thrust
@Stralor so, railgun and solar sail are NOT adequate for this question? Like they are passive perceptors of the interaction
@Stralor what if some nucleus, created in the thermonuclear explosion (Fe for example), reaches the speed?
@Stralor Earth is ok. If humanity goes the black-hole path to resolve this market, then the object will likely be destroyed and we would not be able to extract the info from it's locally installed clock, we would only be able to to an approximation.
@Stralor what if we discover a black hole in the solar system, send a probe into it, and parts of probe are converted into jets of matter beamed out of the solar system at relativistic velocities? Does the 10 gram threshold hold in this case for the total matter converted and ejected from the black hole?
@Stralor Personally I think it would be more useful for us to bet on intact objects due to the ambiguity of whether at all and for how long pieces count as the same object. Like, would ejecta from a rocket engine count? Would Bomb shrapnel count? etc.
If we're excluding things that can technically be human-made but not human-invented (e.g. helium), then would artificial elements (e.g. Oganesson) or molecules (e.g. a carbon buckyball) be the smallest thing that counts?
If your intention was spaceships, then maybe being self-propelled should be a requirement (so nothing inside an accelerator)?
@Stralor hmm but it misses out on stuff like ground-to-space lasers pushing objects. maybe it's not a perfect fit
@Stralor how about self- or externally-propelled? So the acceleration has to happen outside of the device, excluding projectiles launched from particle accelerators but including solar/laser sails