One of the interesting things about a photon is that it does not have a separate antiparticle (such as an electron versus a positron). Basically, a photon is its own antiparticle.

Back in the 80's, Photon was a moderately popular diversion. Based off of (ripped off of) lazer tag, Photon was a more team-oriented sport. Two teams, a red and a green team would descend into an arena, and attempt to play a game that could only be described as capture the flag, without the flags.

Your objective was to shoot your enemies as many times as possible, which was a given in any lazer tag-esque game. For big points, you'd could also go and to shoot the enemy's power base thingie 3 times, located deep within their base. It was usually well protected, as well, so it wasn't as easy as just running in, pulling the trigger 3 times, and running back out.

The arena featured fog, strobe lights, many twists, turns, dead ends, sniper locations, and an 80's techno soundtrack. The music ranged from crappy to not half bad.

Scoring:
Shooting the enemy's base 3 times: 200 points
Shooting an enemy: 10 points
Shooting a teammate: Priceless, ahem, -30 points
Getting shot: -10 points

Every time you were shot, you had to go to a recharge station, to power your equipment back up. The equipment itself was large, and when I last played it (around age 8 or so), probably weighed at least a quarter of my total body weight. It consisted of a Helmet, Armor, a battery pack, and the gun itself. Each suit had LED lights according to the team's colors, so while the arena itself was fairly dark, you could still see your teammates and opponents well enough to shoot them.

Most Photon locations were equipped with a fairly large arcade, as well as a balcony where people, for the price of $.25, could shoot at the players. I don't recall if the players were deactivated if shot by the spectators, but I believe the spectators had a score readout near their gun. This made the game more interesting, as when I couldn't cough up the money to actually play the game, I could go shoot those who could. Of course, this paled in comparison to actually playing the game, as the fun of being shot at yourself, and trying for the opponents target was lost.

There was also a show on television based upon Photon, but I cannot recall of it's details, other than it had Photon gun wielding monsters of some type, and all the bad guys were on the green team. If I find anything further, I will update this node.

Despite my young age, I was placing within the top 4 or 5 each game. The team sizes were roughly 11-12 per team. I vaguely recall getting some compliments for doing so well while being so young.

Alas, my favorite Photon location, in Ocean City, Maryland, has seen some drastic changes. For 8 or 9 years after the photon franchise folded, it was home to a wax museum. This was really awkward, seeing wax dolls occupy the space where I used to shoot people. Seeing the remnants of the targets (they were an octagonal shape, if I recall correctly) was also difficult to adjust to. Finally, in the past four years, the Wax Museum closed, and a 90's clone of Lazer-Tag/Photon (Lazersport, I believe), opened up in the same building.

Interesting fact: According to the Theory of Relativity, photon particles have not aged a second since the Big Bang.

Source: The Elegant Universe, by Brian Greene

That blows my mind. I can (after a bit of contemplation) understand how they can travel through space--time has stopped from the perspective of the photon, but from any other perspective, it continues on regardless. But...well...what happens from the perspective of the photon?

No, scratch that I don't understand how the damned thing can travel through space. How can it travel through space without it's perspective travelling through the intervening time?

Also, when scientists manage to slow a photon down, does it begin to age?

A quantum of electromagnetic energy. The photon is the gauge boson responsible for carrying the electromagnetic force.

Making Photons

A photon is emitted when an atom dumps some of its energy. An excited atom, one in a high energy state, has an electron in a higher energy orbit than normal. Nothing likes having more energy than it needs, so the electron will drop to a lower energy state. The difference in energy between the two levels is emitted as electromagnetic radiation, a photon.

How the atom gets in the excited state in the first place can be through many mechanisms. A commonly exploited example is electronic excitation in the cathode ray tube. Electrons accelerated in the tube strike the phosphor on the front of the screen, exciting the electrons in the phosphor atoms to high energy states. They then decay back to lower energy states, emitting a photon on the way. We see these photons.

The same thing can happen in the nucleus of the atom. If one of the nucleons is in a high energy state it can drop to a more desirable low energy state by emitting the excess energy as a photon. The energies involved in a nucleus are orders of magnitude greater than those for the electrons around the nucleus, so the photon has much more energy and we label it gamma radiation.

Wave or Particle?

Well, both. The wave-particle duality, as it's known. All matter, not just light is both a wave and a particle. Most of the time light is a wave, an electromagnetic wave. It is only when it interacts with something that is assumes a particle-like nature. For example, when the light travels towards your eye it is as a wave. Then when the light falls on your retina it can only deposit energy in distinct lumps, or quanta - so it appears particulate. This is true for all matter, just it is more noticeable for light.

You can neatly explain the double-slit experiment 'paradox' by thinking of light in this way. The light remains as a wave during its passage through both the slits and a standing wave pattern is set up on the other side. This standing wave is the quantum mechanical wave function, which directly relates to the probability of observing a photon at a given position. It is only when the light interacts with the screen that it appears as a particle. A full quanta of energy must be deposited.

Photon Mass

Mass is a confusingly misused term. We all know Einstein's rather famous mass-energy equivalence, E=mc², and it's fairly obvious that photons have energy, so they must have mass, right? Well, no. The correct way to interpret E=mc² is to use it define the energy of an object when it is not moving, or rest energy, E₀, in terms of a fixed quantity, it's mass. This is sometimes emphasised by calling this value the rest mass, but this isn't helpful, a particle only has one mass, it may have variable energy depending on how fast it is travelling, but mass is constant.

When a particle is moving the total energy is given correctly by, E² = m²c⁴ + p²c², where p is momentum. You can see if the object is at rest then p²c²=0, and the equation reduces back to E₀=mc². In the case of a massless, but moving, particle then it reduces to E=pc. This means that a particle can have energy without mass. You can't stop photons so they always have momentum.

Theoretically, if photons did have mass we would see deviations from the Coulomb inverse square law. It is photons that transfer the electromagnetic force, they are gauge bosons. If they are massless then they can have infinite range and the 1/r² law holds true, if they have mass, they become limited in their range so the 1/r² rule will not hold anymore. Experimental tests for photon mass concentrate on finding such deviations. The upper limit for photon mass so far stands at 3x10^-27 eV, which is about 10^-46 kg.

Other stuff

The photon is a boson. This means that many photons can exist with the same energy states at the same time in the same place. Not all particles are like this, the Fermions exclude each other from being in the same state - electrons for example, otherwise atoms would collapse. Because the photons can have the same state it is possible to superimpose many of them with the same energy in the same place, this is basically what a laser is.