Diamond prices are down 60% since a 2011 high, and they are still falling. It's not all down to lab-grown diamonds, demand is down too, especially in China.
No one can lab-grow gold yet, so its rarity and scarcity protect its value, but that will end too. It's just a question of when. China launched an asteroid touch-down mission this week, which will make it the 4th country/region to do so, after Europe, the US & Japan.
How soon will it be feasible to mine asteroids? Who knows, but a breakthrough in space propulsion might mean the prospect happens quickly when it does. It's possible gold has twenty years or less of being high value left.
The $80 Billion Diamond Market Crash Leaves De Beers Reeling
Eh they are already moving a good clip relative to the earth, nudging them in this direction would be the easier part of the equation. Stopping them when they get here is probably where you want to focus your energy... No pun intended
I have absolutely no idea what you're talking about.
They are talking about not returning mined material from asteroids but about changing the trajectory of asteroids so that they collide with Earth. But if you do so, the asteroid would likely be destroyed, leaving little to mine, so it would have to be stopped (or slowed down) before reaching the ground.
Oh, right. I totally forgot about that part, I thought they were talking about diamonds.