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Requirements for the force field: It must be resistant to all small arms fire, melee weapons, some explosives, and be able to prevent any damage to the user from these weapons.

It has to use a REASONABLE amount of energy, not like nuclear plant level amounts of energy, the user must be able to make, use, and carry the force field with today's technology.

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    $\begingroup$ 30 minutes to accept an answer is pretty short, considering that you have got only 2. If you wait at least 24 hours you have more chances of getting more answers. $\endgroup$ – L.Dutch - Reinstate Monica May 18 at 13:52
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    $\begingroup$ Considering we don't have any similar mechanism to the one you're proposing nowadays, "with today's technology" might be the biggest limiting factor here (unless the Illuminati are at it again, hiding useful technology from the rest of the world) $\endgroup$ – ProjectApex May 18 at 15:41
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    $\begingroup$ @TheDaleks Asking on Physics SE sounds like a non-starter. Even basic prior research by the OP (a minimum requirement on Physics SE) would tell them that such a device is impossible with existing technology (or anything remotely possible for the near future). I'm pretty sure it would be closed as e.g. non-mainstream physics. $\endgroup$ – StephenG May 18 at 17:20
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    $\begingroup$ I'm pretty sure the answer to this is "it wouldn't work". We live in real life, with current technology, and we don't have force fields of the type you describe despite the fact that they would be enormously useful in a huge variety of circumstances. Could you bend on at least some of the requirements in the question, in order to make it answerable? $\endgroup$ – Upper_Case May 18 at 21:34
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    $\begingroup$ Just to set a realistic expectation. (A) Since there are no real-life force fields of the type you're asking about, any answer that explains how it could be done is wrong. (B) If, perchance, someone could answer the question, they wouldn't answer it here... they'd be running to the patent office. $\endgroup$ – JBH May 18 at 22:37
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One explanation could be that you have a magnetic (or electrically charged) fluid held in place by a potential well- as the fluid moves away from the minimum of the potential well it gets 'pushed back' into the centre by the field acting on it (kind of like a marble in a half-pipe).

Any force upon the fluid, such as from gunshots or shrapnel would be dispersed due to the surface tension (akin to how liquid armour could be used), with the fluid resetting back to it's original position in the potential well after taking the hit.

Effectively, you have a wall of fluid held in place by an electric or magnetic field that soaks up any impacts for you.

However, this is not really something that could be practically done with today's technology (otherwise militaries would be already doing it)

Edit: alternatively, a more 'traditional' scifi force field could be an incredibly strong cathode (a negatively charged plate). As atoms have negatively charged electrons surrounding the nucleus, when become very close to the cathode they will be repelled as they have like charge, meaning objects should be prevented from passing. (Edit again: the force exerted on the incoming projectiles will also be exerted on the cathode in the negative direction, so your field might be able to stop bullets and other objects will a comparatively low momentum, but the cathode would probably break if you apply too much force on it, like driving a car into it.)

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    $\begingroup$ Just slightly deflecting a bullet with magnetic fields we could realistically use today is extremely difficult and that's under optimal conditions (powerful magnets below the muzzle). These EM field ideas won't do anything to stop a bullet - it's just going too fast to be affected by a local field for long enough to slow down significantly. Any field large enough to do the job would require a huge power plant and the resulting fields would likely kill the human just as quickly. The fluid is already constrained to move slower than the speed of sound in it - the field does nothing useful. $\endgroup$ – StephenG May 18 at 17:37
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    $\begingroup$ @StephenG I don't deny that any forced-field is far beyond today's technology, as I mentioned in my answer. OP's question can't be fully answered, so I gave an answer of how it could be done and said it can't be realistically be achieved using modern technology. $\endgroup$ – Jack May 18 at 18:27
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Frame challenge: it wouldn't

Your requirements are:
* Resistant to all small arms fire, melee weapons, some explosives,
* Prevent any damage to the user from these weapons.
* Use a 'reasonable' amount of energy
* Can be carried and built by an individual
* Producible with today's technology.

It's hard to prove a negative, but I will state that this is impossible, with the evidence being that if such a device were possible, it would be seen in active use by militaries around the world, since it would be tremendously useful.

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    $\begingroup$ As the question is written at the time of my comment, this is the ONLY valid answer. $\endgroup$ – JBH May 18 at 22:38
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    $\begingroup$ Your answer summarizes my opinion of this. If it was possible with modern technology, someone would've already made it, if for no other reason than to be cool. This is some Sci-fi piece for such a thing to exist, let alone work through an energy source that's easily available/ can be easily made. $\endgroup$ – ProjectApex May 18 at 23:19
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    $\begingroup$ @nullman that’s definitionally not today’s technology. $\endgroup$ – Daniel B May 19 at 8:48
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    $\begingroup$ Or the entire question is based on a misunderstanding of what force and energy are. $\endgroup$ – Mad Physicist May 19 at 13:43
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    $\begingroup$ @Demigan, you seem to be ignoring the OP's requirements. His requirements, as written, are IMPOSSIBLE to meet. That's the whole point of a frame challenge. "Improbable" makes it sound like it's actually possible, somehow, for those requirements to be met. If you think it is, you should either post your answer or run to the patent office. $\endgroup$ – JBH May 20 at 7:47
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It must be resistant to all small arms fire, melee weapons, some explosives, and be able to prevent any damage to the user from these weapons.

You are just giving a fancy description of a carbon fiber or polymeric shield, like those used by anti-riot forces

cop with riot shield

Riot shields are typically made out of transparent polycarbonate between 4–6 millimetres (0.16–0.24 in) in thickness. Shields are designed to be shatter resistant, though are typically not ballistic resistant. Some shields used to counter rioters offer a form of ballistic protection against lower velocity ammunition fired from handguns or shotguns. However, ballistic shields are instead used in situations where heavily armed resistance is expected.

The electromagnetic force keeping together the molecules of the shield is what takes care dissipating the energy of the weapons.

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    $\begingroup$ @DatOneNerd: "Energy" is not a thing, it is a number describing the capacity of a physical system to do work. There is no such thing as energy disconnected from the physical system. So I understand that you don't like plexiglass; well, fine: but in this case you must indicate what kind of physical system you like. $\endgroup$ – AlexP May 18 at 13:42
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    $\begingroup$ @DatOneNerd and what is ENERGY to you? Because energy as we know it won't stop projectiles or explosions, nor will to form a tangible field on its own. $\endgroup$ – ProjectApex May 18 at 15:55
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    $\begingroup$ Since ballistic shields weight in at an average of 7.4kg and E=MC^2 that would make it a 666 petajoule energy shield. Though they are not very efficient for your power input since they can be penetrated by bullets with as little as 4KJ of force $\endgroup$ – Nosajimiki May 18 at 19:05
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    $\begingroup$ One issue of plexiglass shields compared to sci-fi-style energy shields is that they can't be compacted to almost nothing when not in use. $\endgroup$ – John Dvorak May 18 at 22:08
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    $\begingroup$ @JohnDvorak I'd be curious to see how much the generators of the supposed energy field could be miniaturized when not in use. Like the microscopes: 300x magnification, easy peasy, carry it by hand; 1000x-20000x - electron microscope - takes the entire desk, use a trolley to move it around. $\endgroup$ – Adrian Colomitchi May 18 at 23:46
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Plasma Shields are the closest thing to energy shields that modern science understands. They are not a mature technology, but they can at least in theory do what you are asking according to modern understandings of science and engineering. They work by using lasers, electricity, microwaves, and/or magnates to rapidly polarize and heat up the air between the vehicle and an attacker in a way that creates a temporary "high density" plasma field.

What plasma shields are already publicly specced to do:

The primary military use of plasma shields today is that they can block explosive shockwaves, lasers and other electromagnetic weapons, and radiation. They are not speced to stop missiles, bullets, or melee attacks, but the science already exists or is very close to existing for them to be able to.

How plasma shields can be developed to meet your needs:

There was a government program a few years back called Plasma Point Defense that was theorised to be able to use plasma to detonate missiles too, but it was abandoned because the technology to make an "eye safe" missile shield did not exist yet: basically the shield was so bright you would burn your retinas using it. Newer plasma shield programs such as MILI-Flash and RESLIFE are solving this issue by finding ways to make darker high energy plasma shields. So, although they don't exist yet in any declassified capacity, expect to "eye safe" missile shields in the next few years.

No current shield can block a kinetic attack directly because solid matter is not meaningfully affected by a plasma shield pulse; however, if your setting prominently features energy based small arms such as a plasma pulse, laser, radiation, or electrolaser weapons those could certainly be blocked with existing technologies.

That said, there are ways to protect against bullets and melee that don't require stopping the bullet or blade. One way a plasma shield can already do this is to make it much harder to target you. Plasma bursts like those created by PASS create a bright disorienting burst around you which can make you much harder to see precisely enough to know where to shoot, blind a melee attacker who gets too close, and interfere with computer aided targeting sensors. You just need to give your soldier something similar to transition welding goggles to make sure he is not blinded in the process.

Another application that could exist in the very near future using only technology that already exists is resistive tracking. A plasma shield creates a thin layer of atmospheric pressure which a bullet can easily pass through, but PASS style shields can create very controlled pulses of plasma by design. Stellar Photonics for example is currently working on one that can generate hundreds controlled pulses per second. While the official purpose of this project is to make a crowd control system similar to PASS, If such a shield were programmed to track the path of a bullet, it could make enough of these small wakes in the bullet's flight path to stop or deflect small arms similar to flying through a really thick and turbulent shield window.

I'm not sure exactly how much power they use, or how small they can be made, but all the milliaray designs I am able to find are intended to be installed on aircraft, tanks, and humvees and powered by non-nuclear power sources. Based on this, I do not believe you could fit a shield on your person, but vehicles can project shields up to 100m. So, you will not have anything like a Gungan personal shield, but if you look at the way Fambaa shields work to protect squads of nearby infantry, something similar to that is feasible under modern tech.

enter image description here

Another approach, and the most effective one IMO is to consider a shield part of a layered defensive system. Modern body armor is getting REALLY good to the point that gun makers are having a really hard time now designing bullets of reasonable size that can penetrate them. 4 layers of NNF treated kevlar is all it takes to stop most bullets. Add in ceramic plating and you can very quickly armor yourself against most military calibres of bullets and melee weapons at a fraction of the weight it used to take just a few years ago. If you accept that your armor is part of a layered defense strategy, then a plasma shield would protect you from explosive percussion, electrocution, radiation, and lasers etc which would otherwise be able to bypass modern armor.

https://www.sciencealert.com/boeing-has-patented-a-plasma-force-field-to-protect-against-shock-waves https://www.youtube.com/watch?v=ZJpRtY21PPI https://www.popularmechanics.com/military/research/a8626/the-pentagons-wall-of-light-laser-shield-15008409/

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    $\begingroup$ What, no link to an actual description of the "plasma shields"? I for one have difficulty picturing how "lasers, electricity and microwaves" can convert the "air between the vehicle and the attacker" into a "high density" anything. (Plus I have no idea what a "plasma field" could be. Plasma is a state of aggregation of matter, not a field.) $\endgroup$ – AlexP May 18 at 21:31
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    $\begingroup$ So, emphatically not current technology. $\endgroup$ – Daniel B May 19 at 0:23
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    $\begingroup$ I would say it's closer to current tech than most people realize, but not effective against everything. But that's okay because the areas where plasma shields lack, modern armor has come a LONG way in the past few decades. As non-newtonian fluids and graphene become more common in armor, needing energy shields for stopping knives and bullets isn't particularly necessary. $\endgroup$ – Nosajimiki May 19 at 1:10
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    $\begingroup$ Plasma Windows are firmly a real-world technology, They can hold back multiple atmospheres of pressure though. My off-the-cuff math (probably wildly wrong) says that being able to hold back 9 atmospheres is 19000 ft-lbs of pressure. Which is a LOT more than inflicted by a handgun's meager 300 - 500 ft-lbs. So if I'm right they could definitely stop a bullet. DISCLAIMER: my math sucks balls. $\endgroup$ – Ruadhan May 19 at 9:22
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    $\begingroup$ 9 atm is less than 150 psi. Assuming the projectile has a frontal surface of 1 square inch and has 300 ft-lbs of energy, it would take over 2 feet to stop under that pressure. Also, plasma windows require about 20 kW per inch of window diameter, so you'd need a small generator or a very large battery to power it. $\endgroup$ – AI0867 May 19 at 10:09
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I'll give a slightly different take on the question.

In reality, there are two different components to 'science/technology': Theoretical Knowledge, and Technical Capabilities to Test/Implement Theoretical Knowledge. Let me give you some example of this.

First off, Gut bacteria and the fecal transplant. Fecal Transplants is the result of an idea: that some maladies are the result of missing necessary microbes required for healthy digestion. Now here's the thing: testing this isn't actually all that difficult. I mean, the first case of FMT was in 1958, and it didn't start becoming a mainstream practice until a few decades ago - wayyy past the time where we had the technology to test such hypothesis. But the timing wasn't due to limitations in testing technology or such - it was simply a limitation in our knowledge of the field.

Likewise, RSA Cryptography. The implementation of the core parts of RSA isn't actually all that difficult. It was devising the approach that was the hard part. The state of technology at the time wasn't limiting advancement - technically, RSA could've been developed decades prior... its just that nobody thought of it (or needed to think of it.)

(And on the flip side... there are all sorts of places in physics where we simply don't have the technical/engineering ability to even test the predictions.)

So... how does this relate to your original question?

You want forcefields, with today's technology.

It's possible that it's possible. Oh, it's not possible with our current knowledge, but it's entirely possible that we have the technical capability to do so right now, but it requires simply making some novel thought/discovery - that if we had that breakthrough of creativity/ingenuity, that we'd have forcefields within a few years.

It could be that forcefields require us to unlock some deep core underpinning of gluon interactions...

... or it could be that all it takes is using a set of three ultra-low sound emission speakers pointed at a patch of air containing silicate dust, and the harmonic pattern causes the silicate dust to rigidly orient in place.

Or other such, "Uh, well, I never thought of even trying that!" method. Some advancements aren't due to intricate engineering... some are just due to a person thinking, "Dude, why isn't this bacteria growing on this mold?" or "Hey, why did this antenna melt my chocolate?" or "Wait, what the heck did this Nitric Acid do to this rubber?" We didn't end up with Penicillin, Microwaves, and Vulcanized Rubber because they finally became possibilities... we ended up with them because we discovered a novel use of technological capbilities we already had.

Well? Who's to say that forcefields not existing isn't due to insufficient engineering... but us simply not having the novel thought to make them a possibility? Your difficulty is going to be coming up with a possible novel thought that doesn't sound completely outlandish or too McGuffin-y.

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When all the requirements are taken together, the requested technology simply isn't possible (not with today's technology). Let's relax the current technology requirement a bit (and the power requirement, as it turns out).

Now, you never actually specified that the force field need be electromagnetic in nature. One approach could be a swarm of nanobots that could solidify momentarily into momentum/energy-absorbing configurations.

It would be tricky to build capable nanobots, of course. And, powering the swarm would be an issue; there's probably no way around needing an power source with at least nuclear-level energy density (antimatter would be a compact though very complicated and potentially very dangerous option).

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As everyone has explained, "force fields" are totally impossible for numerous reasons.

The only thing that is similar in effect (but not in paradigm):

your character (blue) is in force-field jail.

imagine simply a frame (gray), perhaps 3m x 3m, which will be the "force field".

It houses a number of incredibly advanced robotic laser guns. (perhaps ten or so)

enter image description here

the lasers simply shoot in to the plane of the "force field" and they can swivel on that plane.

By incredibly advanced, I mean three things...

  1. insanely powerful
  2. unbelievably fast pointing
  3. there's an amazingly fast/accurate visual system which tracks everything coming near the "force field" plane.

Simply ... any thing which comes in to the "force field" plane - anything at all, a bullet, a hand, a beach ball - gets utterly zapped by the lasers.

(The item would then be utterly destroyed, the remains might fall harmlessly the floor, or in the case of say "a hand" the person would pull back their hand in agony/terror, exactly as in a 'real" force field.)

Note that

We can, literally , build this now - !

(Amazingly, I have built such a contraption for a client! Off the shelf tracking camera systems (such as in industrial applications) are commonly available, and lasers with a servo are easy. Obviously, the ones you can build now can only track moderate size objects (perhaps only if tagged with IR tape) moving at moderate speeds, and the lasers do nothing other than add a red dot!)

Conceptually, that's the only way you could build a "pseudo force field" using known physics, and indeed today's technology stretched a bit.


However ... "plasma windows" ...

Thanks to informative comments on this page, it is worth noting that "plasma windows" (be aware they are currently tiny) are a thing:

There's literally a "take it for what it's worth" wiki article on "plasma windows as sci-fi force fields" - !

https://en.wikipedia.org/wiki/Plasma_window#Similarity_to_"force_fields"

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    $\begingroup$ This is similar to Iron Curtain shields en.wikipedia.org/wiki/Iron_Curtain_(countermeasure) which are in use today. They use explosives instead of lasers, but the principle is the same. $\endgroup$ – Nosajimiki May 19 at 13:20
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    $\begingroup$ Why would the debris fall harmlessly to the floor? You didn't change the mass of the incoming projectile and it has kinetic energy in a certain direction. You might change it into liquid blobs or tiny (super-heated) liquid droplets but you don't want to stand down-range of this "shield." You'd be better off super-heating one side of the projectile as it comes through and attempting to change the trajectory by blowing material off the side of the projectile. But you can't really disintegrate it to the point where it's not dangerous. $\endgroup$ – Scott Whitlock May 19 at 14:36
  • $\begingroup$ a fair point, @ScottWhitlock $\endgroup$ – Fattie May 19 at 15:34
  • $\begingroup$ great point, @Nosajimiki-ReinstateMonica $\endgroup$ – Fattie May 20 at 12:29

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