Dark matter has eluded us for many decades. Even our most advanced particle colliders and sophisticated underground detectors have come up short. But it may be that we can finally solve this mystery with a much simpler experiment, involving a ray of light, a good clock, and the planet Mars.

The universe is expanding and that expansion is accelerating under the power of dark energy and eventually all matter and energy will be dispersed over such unthinkable distances that nothing can stop space from blowing up infinitely. Unless of course cosmologists blundered and dark energy doesn't even exist. Then it's back to the drawing board.

According to quantum physics, the universe should have collapsed on itself in the instant after the Big Bang due to all particles being 100 million billion times heavier. Recent observations of the universe existing suggest that this may not have happened. Even more recent experiments at the Large Hardron Collider have failed to find out why. In particular, why the Higgs boson is light enough to allow the universe to exist. This is part of something known as the hierarchy problem, and some consider it to be the most important unsolved problem in physics.

They say fusion is 50 years away, no matter when you ask. Then why are billions suddenly being pumped into fusion startups? Yes to train LLMs, but there's a reason the technobrats are bullish on fusion in particular. The fact is, the technological challenges have been chipped away and in many cases solved over the past decades, and there's really no one deal-breaker difficulty remaining. One of the final challenges is deciding on the physical vessel to contain our mini artificial stars--and we have some pretty sci-fi options that are nearly ready to go.