If Sci-Fi laser guns existed, do you think the bolts would act more like bullets or laser pointers in relation to how the various variables affect their path?
The thing about lasers is, they actually exist now. Which wasn’t true (or, at least, wasn’t as true) back when science fiction first picked them up as a concept.
A laser is, basically by definition, going to travel at, or very close to C. (Roughly 300 million meters per second.) So, if you’re thinking of slow moving projectiles that your eye can see and track, that’s never going to happen.
The other thing about lasers is, they’re just focused light. This is the same, basic concept as a kid with a magnifying glass, weaponized. It’s still going to reflect off, or burn through, anything it hits. It will also be basically invisible.
The only time you can actually see a laser beam, in real life, is if there’s particulate matter in the air, reflecting the light back to you. Smoke, fog, and dust will all pick up the beam, and reflect some back to you so you can see it. This isn’t a problem when you’re talking about a targeter or pointer; the beam isn’t particularly destructive, so this kind of blowback is harmless. But, when you’re talking about a weaponized laser, that starts to become a real concern.
This is a general truth about seeing things, by the way. For your eye to see something, light needs to strike it and bounce off, hitting your eye. Your eye processes that light, and tells your brain, “hey, there’s a thing here.” Lasers, by definition, avoid that until contact with their target. Thing is with a weaponized laser, the produced light is the weapon. So, if you can see it, you’re getting hit. Even if it’s bouncing off water vapor in the air.
Of course, as with any other variety of light, you can bounce it off a reflective surface. This means, the greatest defense against future soldiers with laser weapons may just be polished chrome surfaces. Not only would it reflect the laser off of it, it would send it back in the general direction of the original user or their buddies. Best of all, you couldn’t see exactly where it was going, because you don’t want that light being reflected back to you.
Now, there is a possibility it would burn through any dust or other atmospheric contaminants on the way through, leaving a faint, singed, after image of where the laser was fired, but in general, you wouldn’t be able to see the beam. Which isn’t that different from bullets, for that matter. There’s another possibility where it would reflect off something like water vapor or any other atmospheric obstruction, (the way lasers actually do), and diffuse to the point of worthlessness almost immediately. (To be fair, I’m not sure which is more likely to occur.) Either way, you’ve got a weapon that will face all kinds of problems on a battlefield.
If you’re trying for a hard-sci-fi setting, (meaning the science underpinning your setting is sound), then all of these factors will make lasers less appealing. If your setting is aimed at a less grounded, soft sci-fi, then lasers are (somewhat) less appealing, simply because their fantastical value has worn off. Lasers sounded like weapons of the future, when you couldn’t pick one up as a cat toy for $5 in most department stores.
With that in mind, you can try to keep the same weapon concept, but selectively trim off the issues, for your softer settings. Things like Star Trek’s phasers and disruptors aren’t, technically lasers, while Star Wars’s Blasters are an entirely different technology that you probably interact with in a non-weaponized capacity on a regular basis.
As with a large amount of stuff in Star Trek, whatever technology keeps phasers from reflecting around randomly is never clearly explained. The term itself is a portmanteau of phased and laser. So, it’s some kind of laser variant that won’t normally reflect (though it is shown happening a couple times in the franchise).
Disruptors are even more nebulous, and it’s helpful to remember this is more of a catch all term, including things like sonic weapons, up through a variety of molecular disruption weapons.
Star Wars uses the molecular disruption idea for their disruptors, when the writers want one, but basic blasters aren’t laser weapons. Blasters fire bolts of ionized gas, meaning they’re actually plasma weapons.
As with lasers, plasma is a concept we’re familiar with in modern day. In the simplest terms, it’s a fourth state of matter. You have solids, liquids, and gasses, with plasma sitting above gasses. Plasma is heavily affected by magnetic fields, meaning it is possible to contain and eject it with directed energy weapons (though, that’s not possible with current technology.) It’s not a very energy efficient technology, but you don’t need to worry about it reflecting back and killing the shooter because it struck a mote of dust en route to the target.
If you absolutely need an energy weapon that behaves more like a modern gun, firing glowing bolts of energy, plasma is probably your best bet.
There are problems. Magnetic fields on the target’s armor could mess with the plasma delivery, (which may help you understand that line about the Death Star’s trash compactor being magnetically shielded.) Also, any magnetic field it passes through on the way.
Plasma is also an option for beam weapons. In fact, the most destructive form of plasma you’ve probably encountered is a lightning strike. The electrostatic discharge instantly ionizes the atmosphere between the points, and you get a visible flash of light, followed by the sonic shock of that air being instantly converted into plasma.
Before I move on, it’s probably worth noting, most current plasma research is focused on power generation. That is to say, using magnetic fields to contain plasma for the purposes of safe fusion reactions.
Long term, plasma weapons are probably going to fall by the wayside for sci-fi the way lasers have. Most people don’t think of fluorescent lights as plasma, so the term sounds more fantastic than the technology really is. With refinement of magnetic containment technology, and the use of fusion as a power source, plasma weapons will probably lose a lot of their shine.
The railgun is another weapon you’ll see referenced in near-future sci-fi. Sometimes called gauss weapons, or mass drivers, these are, quite simply, a gun. Instead of using a chemical propellant, they use magnetic fields to accelerate a ferrous slug to speed.
I’m bringing them up for two reasons. First, it is one conceivable way to make a plasma weapon viable. Second, they actually exist.
Laser weapons are, at best, theoretical. Plasma containment and manipulation is an actively researched topic. Though the primary goal there is power generation, not weapons technology. Railguns do exist today.
Modern railguns are mounted weapons. You can stick these things on a naval vessel, or in a facility. They draw massive amounts of power to fire, but deliver a lot of destructive force on impact. Part of the reason is because they’re truly frictionless. You can accelerate their payload to speeds that would utterly destroy conventional firearms. You can also send payloads down range that are far harder than anything you’d ever load into a gun.
One of the mechanical limitations to modern firearms is, the bullet and barrel are in direct contact. When you fire a bullet, it, quite literally, scrapes the barrel on its way out. Part of the reason why we make bullets out of materials like lead and copper is because they are substantially softer than the steel barrel, and will result in significantly less wear.
When we do need to fire a round with something more solid as its payload, the harder core will be wrapped (called jacketed) by a softer metal. For example, a steel core round will have a copper or lead jacket, to protect the firearm. On impact, that coating will strip away fully, and the steel will (usually) punch through any light armor in its path. You’ll also see things like depleted uranium, or tungsten used as cores for armor piercing rounds.
With railguns, that’s not a consideration. Unless the material is magnetically inert, you can just drop it in, and fire it.
What we can’t do with a rail gun, is carry it around. Current technology is too energy intensive for that. But, if you’re looking at a future setting, where power generation is less of a consideration, then these may be an option. Ballistically speaking, they are guns, firing solid projectiles. The only difference is, they’re doing so at speeds that are impossible to achieve with conventional firearms.
I’m going through all of these, but all of them are built around the idea that we need something other than conventional firearms. That’s probably true, on a long enough timescale, but modern ballistic weapons are remarkably energy efficient, for their design. You have a cartridge which contains all of the necessary energy to propel a round at hyper sonic speeds. There are considerations like recoil, which can be minimized through mechanical developments. There’s also potential hybridization of other technologies into them, in order to make a more efficient design. But, if you’re working with a sci-fi setting, it’s worth considering that guns may stick around, simply because they work.
In a vacuum, lasers or plasma weapons are probably more desirable, because a mass projectile will continue traveling until it hits something, which could be in hundreds of thousands of years. But, a laser will eventually disperse to the point that it is too indistinct to cause damage.
In an atmosphere, a gun, or gauss rifle may be a much better option for the situation presented.