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We've all seen science fiction movies where a beam of some kind hits a person, and the entire person is affected but nothing else. For example, an ice blast freezes a person, their clothes, and their shoes instantly, but not the floor. Or a phaser disintegrates a person's body without leaving a trace, but their clothes fall harmlessly to the floor.

In every case, a collection of objects (composed of various materials) is affected in its entirety, but adjacent objects are untouched.

I'm wondering, how might such a system work? What process could enable a reaction to completely affect a desired target and all associated material (clothing, handheld objects, etc), but discern and ignore unrelated adjacent objects (such as the floor, a chair, etc)?

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    $\begingroup$ Would you accept 'it's impossible' as an answer? $\endgroup$ – DaaaahWhoosh Sep 4 '15 at 18:00
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    $\begingroup$ I call it "the Hollywood Effect" $\endgroup$ – bowlturner Sep 4 '15 at 18:06
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    $\begingroup$ @DaaaahWhoosh Half the stuff we talk about at Worldbuilding is impossible. I'm looking for "plausible," not "genuinely possible." For example, one could isolate the target in a force field as part of the firing process, that sort of thing. $\endgroup$ – Nerrolken Sep 4 '15 at 18:11
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I've often thought that seemed pretty implausible. Well, elements of it are plausible.

A death ray -- a laser or phaser or whatever -- that works by burning someone up would likely affect a person's body but have very limited effect on the air around him. Consider what happens when you open a hot oven to remove, say, a cake. If you touch the sides of the oven, or a metal baking pan, you'll be badly burned. But you aren't afraid to be touched by the hot air in the oven, even though it's the same temperature as the metal pan. Air is so much less dense than metal that even though it's the same temperature it contains very little heat, i.e. very little actual energy.

If he's standing on dirt or rocks, the heat ray wouldn't have much effect on them either, as the heat conductivity of dirt and rocks is also pretty low.

If he's standing on a wooden floor, I'd expect the floor to catch fire, or at least that there'd be a circle around him that becomes charred and blackened. If he's standing on a metal floor in the starship, I'd expect the floor to become hot and everyone standing near him to at least have to be dancing as their feet are burned.

Likewise, if he was sitting on a wooden chair, I'd expect the chair to be burned up along with his body. If a metal chair, it should at least be glowing a nice cherry red. If a plastic chair, it if doesn't burn it should at least melt.

But I presume the real reason is that the producers are trying to maintain a PG rating. If someone really invented such a death ray, I suspect that what would really happen when you used it is that you'd burn a hole in the person you're shooting at, and he'd have burned guts falling out of his chest and in general be a pretty ugly, grisly mess. Or if it could really vaporize a person, that it would leave charred stumps of arms and legs behind. That would have been way to ugly to show on TV in the 70s and 80s. Maybe today it would be acceptable. But still, they probably don't want to show the heroes killing people in an ugly way. When the hero kills someone it usually has to be neat and clean. Also, I'd guess the special effects for believable burnt leg stumps is more expensive than a glow and the person disappears.

Personally, I often wonder how when a person is thrown back in time or travels to another dimension or whatever, he's always transported with his clothes and whatever he was carrying, but he never seems to bring along a chunk of the ground or the floor or anything else around him. I recall one science fiction book I read years ago -- forget the title -- that had the hero thrown into the future by being caught in a beam from some experimental machine, and the author threw in a line about how he was lucky that his whole body was caught in the beam, but it did leave behind the heel of one shoe. I suppose as the physics of such things is all made up, one could invent some equally made-up explanation.

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    $\begingroup$ Heel of a shoe: Pebble in the Sky, or an homage to it. Asimov's first novel, IIRC. $\endgroup$ – JDługosz Sep 6 '15 at 6:55
  • $\begingroup$ @JDługosz Could be. I remember the story was by Asimov though I don't recall the title. $\endgroup$ – Jay Sep 6 '15 at 7:02
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One option that you might want to look into is harmonic frequencies. I can't find much information on it, and I'm pretty sure that its actual usefulness has been greatly exaggerated, but the general idea is that different substances resonate at different frequencies, and hitting such objects with those frequencies cause them to vibrate, and sometimes even break.

Based on this concept, it may be possible to find the right frequencies for the molecules you wish to freeze/burn/vaporize/whatever, and output those frequencies with sufficient power to cause a reaction. This reaction would be localized to only the molecules you wanted to affect, which could be used in some situations to target individual objects as you suggest.

However, there are a lot of cases where this won't target just one object, such as when you're trying to destroy a container that's made of the same material as the floor (or even the machine you're using to destroy it), or if you want to cause harm to one person but not another. There is also the problem of targeting unknown materials, as it will be difficult to lock onto the right frequencies without knowing what frequencies you need. Then there is the problem with the Doppler Effect, which will make it hard to use this method on moving targets. And finally, there is the question of how much power it would take for sound to have your desired effects. For this last one, you might have to add some extra material, such as a form of plasma that is attracted to harmonic vibrations (or something that actually exists, though nothing comes to mind).

In the end, though, I don't think it's ever going to be possible to achieve the kinds of things you see in the movies without an army of nanobots you control with your thoughts, and even then I still think it would be better to use more conventional means.

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  • $\begingroup$ The container and the floor have a junction--it's not solid. Perhaps this reflects the energy. (Note that such a system can't target a creature and it's clothes, though.) $\endgroup$ – Loren Pechtel Sep 5 '15 at 22:46
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A variation might be to affect some classes of materials. How many sci-fi battles take place on wooden floors? Eary space-age SF probaby assumed ship decks etc. are made of metal. But carbon fiber in epoxy might behave like organic material.

In real life, it was discovered that a particular UV laser will affect the bonds of much (living) organic material and make it disintegrate without burning or wven heating the neighboring tissue. I think that's just a matter of power to make it into a blaster-type weapon. For now it's used in delicate eye surgery.

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I'm not sure the exact numbers but in science everything has a specific heat. The specific heat is the amount of heat per unit mass required to raise the temperature by one degree Celsius. So if two objects within close proximity and a laser or freeze ray pointed at an object heated/froze the object. Nearby objects wouldn't be affected if the specific heats were varied enough.

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The main problem is not to destroy the target, there are already good answers on the way to make it precise and letal. The problem is to aim, to chose where the death ray is going to hit and what it is going to destroy.

Pick your laser, your death ray or your phaser, then set up the best viewfinder ever on it : mind-controlled viewfinder.

This is not a complete fiction :

Some scientist from Berkley did register some brain waves to recreate some pictures : just look at the video

This is far of perfect, but it does already exist, ok ?

Second sci-fi fact : we can already move things with mind

These are existing technologies. In the future we can imagine a helmet/brain wave reader that can be installed on you when you use your weapon. You target your ennemy with your mind, weapons, clothes and shoes included. Everything you picture in your mind is locked by your very precise laser weapon, and nothing else.

I don't think that's as impossible as it sounds, because this is a way to never miss your target and totally erase the collateral damages.

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