Why did Zidane head-butt his opponent in the World Cup final? Do the French not fight with their fists?

He’s a soccer player! No fist on the ball, no fist on the opponent. Also, the Italian provoked him. France should have won.

A laser converts electricity into light with higher efficiency than any other device - semiconductor lasers can be more than 50% efficient! Unfortunately, this means that for every watt of power you deliver to an enemy Stormtrooper/Cylon/Romulan, you have to absorb a watt of energy inside the laser.

So you not only need a big power supply to run your laser - you also need a big refrigerator to keep it cool.

Gunpowder is far less efficient than a laser, but it has a far, far higher energy density than batteries. And, while a bullet being fired generates a ton of waste heat, the majority of that heat goes into the bullet, the shell casing, the vapor from the combustion, and the surrounding air - all of which are immediately thrown away. If lasers were so cheap that they could be used once before being thrown away, then they would make much better weapons.

Because you’d need a fairly hefty power source to power relatively delicate, sometimes perishable, often toxic devices that may turn out to be much bulkier than the power source itself. But if you dropped the laser on someone, I’m sure it’d hurt.

Well, we can represent the universe as a 3-dimensional manifold. But we currently know very little about 3-dimensional manifolds that beyond properties of manifolds in general, especially when compared to our knowledge of 3-dimensional manifolds, like spheres and toroids. There is much work being currently done on 3 dimensional manifolds, but even with a greater knowledge, in order to gather enough data to determine the exact shape of the universe would likely take until long after the sun has burnt out.

Still, it is possible for the universe to be bounded but not have an edge. The universe could be a hypersphere, much like the surface of the earth. There’s only a finite amount of space on the earth, but you could walk in a straight line from any point on the earth and continue in that direction ad infinitum. That’s because the surface of the earth is a 2-dimensional space that is bent in 3-dimensional space as a sphere. So too, imagine the universe as a 3-dimensional space bent in 4-dimensional space as a hypersphere. This is the model of the universe it seems most physicists consider if they in fact care about the overall shape of the universe. Me, I like to think the the universe is a 3-torus, just cos that would be cool.