A Strange End

In the world of modern high energy physics, there exists one type of particle that can single-handedly reduce the entirety of the Earth to a smoldering rock. That particle is whats known as a "strange" particle, a hadron (mass made of quarks) composed of quarks so massive that it needs to gain mass in order to maintain stability, and it gains mass by energizing the quarks of ordinary matter into massive "strange" quarks and then assimilating it. The process feeds upon itself and will continue until all the matter surrounding it has been converted and assimilated into one super massive particle, which will remain stable for an unknown period of time. It is comparable to some sort of viral/bacterial particle, changing and accumulating the matter around it in order to sustain its own stability.

While this type of doomsday particle exists only in theory, the fact that theory allows it is a scary thought indeed. The accidental production of one tiny little particle can destroy all of the Earth. In the future, should this particle ever become realized, it will posses the same threat to entire planets as what threat nuclear weapons posses against our cities today.

Dyson Sphere, Take II

A long long time ago some genius physicist by the name of Dyson predicted that as technology evolved and population grew, the only way to meet an advanced civilizations energy demands is to build a massive superstructure that would completely enclose the sun, capturing most of its energy for our use. Simple mathematics will reveal that such a massive undertaking is simply impossible because the amount of matter required to construct such a large structure simply does not exist within our solar system. This mathematical argument convinced me for a short while, but then an alternate solution presented itself.
The sun emits so much energy across so broad a spectrum that if we only captured a small spectrum of its emission, the energy gained would still be significant. While the Dyson sphere will capture all of the sun's rays, it would be possible to capture only the ionized energy by projecting via magnetic containment several panels of plasma-state gasses with distinct focal points on generators. While most of the visual light from the sun will pass through the plasma, ionized particles will be reflected to energize a generator. The same particles that power our auroras will then be shoved onto conductors where their excess electrons energize the circuits projecting the plasma barrier, and excess energy is shipped off elsewhere for consumption.
The concept is still a far ways off, but its a lot closer to reality than the massive Dyson sphere. The technology to contain plasma already exists, as with the ability to produce electricity when given a supply of ions.