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I am facing a great difficulty to come up with a working principle for a permanent force field on my spaceship which will only permits guest while simultaneously deny strangers or foe. The following are conditions applicable to my force field:

  1. Ability to transition between transparent and opaque for different viewing experiences.
  2. Rigid enough to withstand a direct hit from a 10 petawatt laser blast.
  3. Served as a permeable membrane which allows authorized/recognized spaceship to slip through unharmed without the need to power down.
  4. It can display advertisement in 4K UHD.
  5. Personnel can lean on it safely.
  6. Air tight.
  7. Trojan horse-proof? (Optional)

Note: kindly provides explanation should any or all of the above mentioned item sounds absurd/ridiculous/incorrect/out-of-place/un-achievable.

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    $\begingroup$ Only a severly wastefully person would be able to do all of that, it is severly inefficient. You would need a lot (like one every meter or so) of force field projectors, hologram projectors and scanners. Also 4k UHD would only like it fits on a small spaceship, I not sure you unerstands what it means. $\endgroup$ – Necessity Sep 6 '16 at 2:39
  • $\begingroup$ 4k UHD is a resolution spec. It fits on a watch and on the Grand Canyon. It only dictates how many pixels a display is divided into. Not how big they are. $\endgroup$ – candied_orange Sep 6 '16 at 2:58
  • $\begingroup$ @Necessity: I'm a complete moron when technology is concern and I'd only like the TV salesman to teach me those complex technical terms, it would be nice if you could help me out with the mistakes. $\endgroup$ – user6760 Sep 6 '16 at 3:18
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    $\begingroup$ Do you need a working principle? By Sanderson's First Law, "The author's ability to resolve conflict with magic is directly proportional to the reader's understanding of said magic," what really matters is not that you've nailed the principles down, but rather that the reader's understanding is sufficient to let you resolve conflict with this device. (High technology tends to be well supported by approaches designed for magic, so it may be a good tool to rely on here) $\endgroup$ – Cort Ammon - Reinstate Monica Sep 6 '16 at 3:43
  • $\begingroup$ Fun fact: Earth gravity is a permanent force field, holds pressure quite well and lets spaceships in. So it meets the requirements from the title. $\endgroup$ – Mołot Sep 6 '16 at 4:13
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I would suggest nanobots. If the force field is made of millions to billions if nanobots, it could solve the problem of both opacity and strength. The nanobots can have a part the creates the force field and a projection system that can display either whatever is on the other side, making the illusion that it is invisible, or display certain things from the computer.

The nanobots forcefield could be adjusted through a computer in the ship or building. Can be controlled via A.I. And manually. And because it is nanobots, you can set the nanobots individually or by group. You can program them to be stronger in fights and be weaker in normal situations.

Since it is nanobots, you can also program them to react to certain situations. For example,

If said person is recognized as friendly in computer, allow access.

If object is warmer than X degrees Celsius(or Fahrenheit), block it. You know, to block lasers.

As for how to recognize a person or alien, there are tons of detection systems, like retina scans, fingerprint scans, voice detection, x ray, etc.

Of course there would be some problems like maintanence and cost. But considering that it would be easier that molding an energy field, I say it works.

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    $\begingroup$ Wow! very creative not only you have downsize drones you even assign them to be guard dogs :) $\endgroup$ – user6760 Sep 6 '16 at 3:43
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    $\begingroup$ It's weird the number of times the situation of "I need a technology that does X, Y, Z!" is solved with "Use nanomachines." $\endgroup$ – Frostfyre Sep 6 '16 at 13:37
  • $\begingroup$ They're just that good. $\endgroup$ – CadmusMorale Sep 6 '16 at 14:51
  • $\begingroup$ I think Alistair Reynolds calls this a passwall in The Prefict. $\endgroup$ – JDługosz Sep 6 '16 at 21:11
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Ability to transition between transparent and opaque for different viewing experiences.

Liquid crystal does this. It's the same as in old calculator displays.

Rigid enough to withstand a direct hit from a 10 petawatt laser blast.

Since we can color change already to display advertisements turn white when under attack then black to cool down faster.

Served as a permeable membrane which allows authorized/recognized spaceship to slip through unharmed

Transmit security codes.

"It's an old code but it checks out. I was about to let them through"

without the need to power down.

Explosive decompression not your thing? At Willy's used force fields we stock the latest in dynamic envelopment technology. So smooth it didn't even wake this sleeping baby!

"Shush! Don't wake the baby."

It can display advertisement in 4K UHD

What? No smell-o-vision? Cheep no-panel display.

A display can emit light or it can reflect light. I say reflect so it withstands attack. Shine a light on this 2D hologram so people will buy more bachelor chow.

Personnel can lean on it safely.

Just make sure they carry the right security codes for personnel. Otherwise be prepared to update the "days without a safety incident" sign.

Air tight.

Willy sells only the best! Won't stand behind his product though. Likes it better inside where he can breath. All sales final.

Trojan horse-proof? (Optional)

Security is in the mind of the beholder.

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  • $\begingroup$ Wow! can you do my TV? $\endgroup$ – user6760 Sep 6 '16 at 3:11
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You're asking a lot of your force field. Your ? only mentions guest, so starting with that: A field that is SOLID permeable, but not air or perhaps even liquid permeable gives you a good start. A person or ship or such should have no problem getting through said field, and you could even expand that to something like and atmosphere in that it just gets "Thicker"/Stronger over a range that is related to the other requirements. I'd stick with a thin one though for some of your display opacity requirements. Solving those while still friend/foe decisions could instead be handled with an energy "attack" instead of being impermeable to others: verify anyone/thing that has permissions and DON'T fry it/them. Ballistics from foes then is handled in that un-tagged bullets or such get disintegrated coming IN, but outbound is still usable for defense purposes.

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As for your title question, the way to let guests in without decompressing, especially with a shield such as your describe, would be to have the shield kind of form its own airlock around the arriving guest and/or their vehicle.

So, when the vehicle approaches, and the shield gets the authorization, it becomes thinner and more flexible, and bends around the vehicle (like blowing a bubble), except instead of the vehicle taking off in the little bubble, when the shield can come together behind the vehicle and seal shut, it can open the front of the bubble and draws the shield-material back to the original shield location. The vehicle, and a layer of outside air, are welcomed into the shield (and possibly a breath of inside air was lost if the front began opening a hair before the rear opening closed).

Maybe the security codes will just allow the bubble to "pop" or something to let friendly vehicles really come in - so instead of an unfriendly vehicle hitting the rigid force field, and potentially cracking or popping the field - it gets enveloped, and the enveloped bubble can be kind of controlled to nudge at the inner vehicle to slow down, change directions, and maybe land in a specific place (more damage to the vehicle the greater force behind the nudges). They don't have access to your grounds or even the inside air while still enveloped, so it's not like being inside your force-field. But being surrounded by an airtight bubble you control is a pretty vulnerable place to be if they're foes, with a safety net for if they're friends with some technical problem in their codes or your reception.

As for the rest of your specifications, you need a material that's really flexible - since sturdy enough to lean on and flexible enough to bend around a spaceship are difficult to get side-by-side. The opaque-to-translucent can be a side effect of this flexibility (if it becomes more transparent as it thins, for example, but also weaker). Airtight will come with total enclosure (no gaps) since anything strong enough to lean on can already withstand the pressure, and the ability to project images on it can be done while opaque (think simple projector, it can potentially be more advanced but doesn't have to be). Ability to withstand a laser might come from being rigid enough, or with the ability to disperse the energy, or to "heal" damage by flowing more base material into any gaps.

Depending on your tech, you need force-fields with precision and flexibility. You can fill two layers of force-fields with something that fills your other properties (something liquid-ish and in a closed system, I'm thinking, that might be able to disperse force, pulling the fields part or together to thicken or thin, etc). Or, since that might end badly if you ever get a gap or a power fluctuation, maybe fill the space between two force-fields with something more solid-ish that alters its properties based on something controllable (temp, or pressure, or presence of electricity or something) makes it flexible enough to thicken or thin or fold around and incoming vehicle or be solid enough to lean on, and use more delicate local force-fields to shape and hold it while it is acting like a liquid.

You could have specific structured ports where a different material or property could let people or vehicles in or out, or you could control the field by sections, so that only the needed area becomes permeable or flexible, while adjacent areas keep their integrity. If your dome's made from an actual material, and just shaped and controlled with force-fields, you can have projecting images or absorbing or distributing energy as a property of that material a lot less expensively (physically expensive, that is, less effort) than making a pure-energy force-field do all that work.

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