Some particles are extremely unstable, lasting only fractions of a second. We can create and study them, even with such short lives, through instruments like the Large Hadron Collider (LHC), a giant particle accelerator that works by smashing beams of particles into each other at nearly the same speed light travels in a vacuum. The LHC is buried in a 17-mile-long (23 kilometers) tunnel under France and Switzerland, where it uses more than 10,000 powerful magnets to shape the beams into circles and steer them into each other. The resulting collisions make new and interesting particles.
The Standard Model of particle physics describes all of the known elementary particles and three of the four known forces that define how they interact with each other: the electromagnetic force, "weak interactions" and "strong interactions." Strong interactions are what holds some elementary particles together, like the protons and neutrons that make up an atom's center. Weak interactions are called "weak" because they work over much smaller distances than strong interactions -- less than the diameter of a single proton.
You might have heard that light acts like a wave, and electrons act like particles. In physics, when something acts like a wave, it acts like a lake -- it has ripples that go up and down in a regular way and is one big thing. When things "act like particles," they're more like a pile of very small rocks. You could count the rocks and know exactly how many there are. For a long time, scientists thought things acted like either waves or particles, but this isn't true -- peer inside an atom and things act like both. This is called wave-particle duality, and the Standard Model was developed in part to explain it.
How can something act as both a unique object and a wave? Subatomic particles are best described with fuzzy math. We don't know exactly where an electron is -- but we know the odds that it's at a certain point in a general area that is ringed by a boundary. Those odds are described with an equation called the wave function. When we measure behavior that looks like a separate object, we're focusing on the boundary. When we measure behavior that looks like a wave, we're focusing on the probability.
In 2012, scientists discovered the Higgs boson particle, which is an extremely unstable particle that gave mass to all particles with mass just after the Big Bang. The finding was an important validation of the Standard Model, which had predicted the existence of the particle.
The Standard Model has some holes, however. The most obvious problem is gravity -- physicists haven't found a way to incorporate gravity into the Standard Model. It's still the best tool we have for describing subatomic particle behavior -- it's extremely accurate, except for gravity.