What would be the most limiting factor for a handheld plasma weapon or a wormhole or an alcubierre drive if they could exist? the answer is simple:


This is what limits most energy weapons, you can't carry around energy-dense things on the battlefield, cause the denser they are in energy the higher the risk of explosion, thank it to the fundamental rules of the universe.

With that being said:

Would it be possible to partially measure the entanglement and use out the conservation of energy to transport energy from one place to another while preserving the entangled state?

Partially based on this.

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    $\begingroup$ Hi. I don't see what is the difference between this and linked question. Can you highlight differences? $\endgroup$
    – Mołot
    Mar 12, 2017 at 18:36
  • $\begingroup$ @Mołot it's a proposed idea (more specifically a part of it) that I want to use, to make a (seemingly) perpetual motion monster. $\endgroup$ Mar 12, 2017 at 19:17
  • $\begingroup$ What does it mean to "partially measure the entanglement" and what energy would be derived from doing so? $\endgroup$
    – Schwern
    Mar 12, 2017 at 19:46
  • $\begingroup$ @Schwern I've seen something about the partial measurement and quantum energy teleportation somewhere on Physics SE, but I can't find it right now. I have something in my mind about what could they be, but those thoughts are incomplete. $\endgroup$ Mar 12, 2017 at 19:49
  • $\begingroup$ What the best solution is depends on what is fighting, how and why. $\endgroup$ Mar 13, 2017 at 1:00

3 Answers 3


"Would it be possible to partially measure the entanglement and use out the conservation of energy to transport energy from one place to another while preserving the entangled state?"

Whoa there, Geordi. Cool your tachyons. Let's deal with this more basic assumption first before we go all quantum...

"You can't carry around energy-dense things on the battlefield, cause the denser they are in energy the higher the risk of explosion, thank it to the fundamental rules of the universe."

...except for all the fuel, gunpowder, and explosives everyone carries around with them on the battlefield. And the liters and liters of gasoline we drive around with.

Let's deal with the assumption that "energy density == explosion". Hollywood would have us believe that EVERYTHING EXPLODES!!! Especially cars and sci-fi consoles. Reality... not so much. Energy density != explosiveness.

For example, gasoline and other hydrocarbons have some of the highest energy densities of any non-radioactive material, about 47 MJ/kg. Unlike what you see in the movies, gasoline is very hard to ignite. Gasoline must first be vaporized and mixed with air before it will ignite, this is why a thin film of gasoline will ignite, but drop a lit match in a bucket of gasoline and it will go out. This is why some cars are fitted with special fuel tanks that collapse as they empty to avoid having a bunch of vapor in a half-empty tank. This is also why we're allowed to drive around with 1.4 GJ of energy (40 L of gasoline @ 0.73 kg/L is about 29 kg) in our fuel tanks.

In contrast, explosives like TNT and gunpowder have a fairly low energy density, about 4 MJ/kg. We use them as explosives because when they ignite, they detonate which means they combust so fast there's a supersonic shockwave of expanding gases. A gasoline or black powder explosion is, in contrast, pretty slow.

We also use those particular explosives because they're very stable. Most require a detonation by a small amount of unstable explosive to themselves explode. For example, gunpowder is touched off by a small primer of mercury fulminate which can be set off by the hard shock of being struck by a firing pin. Whereas C4 explosive is so stable it can be shot, hit with a hammer, burned, and microwaved. It requires a detonator, a supersonic shockwave, to explode.

The question isn't how energy dense an object is, but how stable it is. Fissile materials like uranium and thorium have an energy density of 80,000,000 MJ/kg, but without a lot of work it's just a radioactive rock. Hydrogen has an even higher energy density if you put it into a fusion reactor.

And no, fusion reactors (probably) don't explode. A fusion reaction requires very high pressure generated by a magnetic field, otherwise the high temperature plasma simply blows itself apart in a small puff of hydrogen (you don't need a lot of mass in a fusion reactor). Once the magnetic containment fails, the pressure is released, the gas expands, and poof the reaction stops. You can also make fission reactors which are "passively-safe" meaning by its very nature it will shut down safely.

Your solution is to come up with a device that is very energy dense, but also very stable. If you're talking warp drives and plasma guns, I'm going to say a micro fusion reactor.

  • $\begingroup$ To be honest, I thought about anti-matter in this case, but guess the total, time, wich under the energy transfer happens, am I right? Will you continue this answer? $\endgroup$ Mar 12, 2017 at 19:15
  • $\begingroup$ @RedactedRedacted While anti-matter does have the highest energy density possible, E=mc^2, anti-matter is the MOST reactive substance. It will literally react with any matter releasing 2mc^2 energy (the 2 being because there's an equal amount of matter reacting) which is a lot. It's a really dangerous choice for a power source.What would you like continued? $\endgroup$
    – Schwern
    Mar 12, 2017 at 19:30
  • $\begingroup$ Cancer and burned out electronics in a wide area at best. Michael Bay at worst. $\endgroup$ Mar 12, 2017 at 19:31
  • $\begingroup$ @RedactedRedacted "What are three things I don't want to have happen in a movie theater, Alex." What? $\endgroup$
    – Schwern
    Mar 12, 2017 at 19:36
  • $\begingroup$ What do you mean b...... AHHHHH that joke hurts! $\endgroup$ Mar 12, 2017 at 19:39

No, entanglement doesn’t work that way.

You can't put energy in “here” and get it out “there” without some conventional means to convey the energy through space.

If you are introducing wormholes etc. into your story's universe, use that to carry energy to remote locations.

That should, in fact, be clear from the question you linked to. If your technobabble (partially measure the entanglement and use out the conservation of energy to transport energy from one place to another while preserving the entangled state) is meant to be a unique idea, then no, that's not a sentence with real-science meaning.


Not the way you're describing, but the effect you're after can be produced with a "quantum Maxwell's demon".


A standard heat engine works by extracting energy from the difference between two heat reservoirs, a hot side and a cold side. When the engine has extracted all the work it can, both sides are at the same temperature.

But the temperature is not zero Kelvin, so all the particles of (gas) are still moving, and they move at random speeds. There is energy in the system, but it is unusable.

Maxwell's (classical) demon knows which particles are moving fast, and which are moving slowly, and opens and closes a particle-sized gate between the two reservoirs to allow only the fast moving ones through in one direction, and only the slow moving ones through in the other direction. The result is that now there is a temperature difference between the sides, and work can be done by the heat engine.

This is, of course, impossible.

The problem is that bits of information have a minimum energy, and the demon's knowledge has to be greater than or equal to the energy the heat engine can extract after the demon tries to recharge it.

However, there is a quantum loophole: in A quantum-mechanical Maxwell's demon, the information is removed from the heat reservoirs by… well, the paper uses the word ‘entangled’, but a) I'm not a quantum physicist, and b) I have a cold and my brain's not running at full tilt anyway. I can't really give you a proper summary, just the link to the paper.

That said, I'm sure I've read this is "controversial", and even if it isn't, the data transfer requirements for anything remotely interesting are absurd:

1.1×1025 bits – entropy increase of 1 mole (18.02 g) of water, on vaporizing at 100 °C at standard pressure;

— Citation: Wikipedia: Orders of magnitude (data)

  • $\begingroup$ I wonder if it's really this? A heat engine using information as the working fluid. But it still doesn't violate the laws of thermodynamics. So… imagine you still have the hot end and cold end, but the link between them can be a communications channel rather than a pipe of some kind. $\endgroup$
    – JDługosz
    Mar 12, 2017 at 23:52
  • $\begingroup$ I read the paper you refer to. This is a heat engine undergoing a Carnot cycle. It has absolutely nothing to do with “teleporting” energy! The mention of entanglement in the paper is at the end, in a section proving why the efficiency is limited to a factor that's lower than a conventional heat engine, analysing where the entropy goes in detail. This heat engine uses hot and cold resovoirs so it’s not getting work from equilibrium — it does not violate the laws of thermodynamics. I really don’t see how this addresses the Question in any way. $\endgroup$
    – JDługosz
    Mar 13, 2017 at 8:48
  • $\begingroup$ @JDługosz Hang on, what? Information and energy are related because of entropy. The abstract even says "in apparent (but not actual) contradiction to the second law of thermodynamics". I'll grant my physics isn't at this level (or close), but I got the concept from an article that summarised as "the place where the entropy goes up is where the other half of the entangled pair is, so it's good enough." $\endgroup$
    – BenRW
    Mar 13, 2017 at 14:25
  • $\begingroup$ Searching for the stem “entang” to be sure to find all variations, it's only used once in the paper. That's in §3 in a discussion on the thermodynamic efficiency. This leads up to “When is the cost of quantum measurement realized? When decoherence occurs.” I think it was “not apparent” 20 years ago when this was written, and they were exploring the relationship between thermodynamics and information. Now it's more widely understood that information is linked with entropy. $\endgroup$
    – JDługosz
    Mar 13, 2017 at 14:41
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    $\begingroup$ @JDługosz I appreciate the suggestion, but I don't think I can; my understanding is mixed-up and confused still. I'd be knowingly spouting BS, instead of just unwittingly. $\endgroup$
    – BenRW
    Mar 19, 2017 at 21:14

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