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I'm writing a story where in the future bullets have become obsolete as batteries have become cheap and very energy dense, so much that making defensive lasers that are able to vaporize bullets before they touch you its plausible. So the question is, is this even possible? How much energy you could pack in something the size of a cellphone battery? Given a lot more space, say the size of a car, could you change the course of the bullet so the vapor doesn't hit you?

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    $\begingroup$ If you solve the storage of antimatter, E=MC2 is the formula. Your battlefield will smell of plasma instead of gunpowder. $\endgroup$ – Alexander Jun 18 '18 at 17:37
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    $\begingroup$ How far out of the edge of the theoretically possible technologies do you want us to go with the technology here? Because if we go the limit the answer is really "sure whatever you like". There are even pieces of tech I can think of that exceed mass/energy equivalency. $\endgroup$ – Ash Jun 18 '18 at 17:41
  • $\begingroup$ @Ash, what kind of device could do that? $\endgroup$ – Gryphon Jun 18 '18 at 18:16
  • $\begingroup$ @Gryphon Peter Hamilton calls them Niling D-Sinks I've seen a couple of other treatments that amount to the same thing; basically you create a pocket universe and stuff it with energy. In theory it can hold as much as you like at mass/energy density without weighing any more than the interface device that gives you access to the pocket. $\endgroup$ – Ash Jun 18 '18 at 18:22
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    $\begingroup$ @Gryphon In terms of artifice yes, the mathematical practicalities are there, mostly anyway. That's why I asked how far down the rabbit hole the OP wanted us to go because once we start getting out towards the edges of current mathematical theory there's some really weird technology to be considered. $\endgroup$ – Ash Jun 18 '18 at 18:40
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A 'box' of perfect mirror containing photons in a vacuum might be your best bet here, since you're using the energy to produce a laser anyway you can instead just open up a pinhole in the 'box' to extract the energy. such a system can approach E=MC^2 though you won't need nearly that much for the desired application. unlike antimatter suggested by alexander (though good on him for pointing it out) this doesn't produce harmful and hard to harness gamma rays.

the specific energy by mass of such a system is as previously stated E=MC^2, they specific energy by volume is just slightly less than the swartzchild radius.

that being said this is very much overkill for the application given and if your civilisation has energy storage this good they have much better options available to them than bullets and well war. the enthalpy of vaporisation of lead is 178 KJ/mol or 860J/gram in other words even if someone threw a tonne of bullets at you it would take only 9 micrograms worth or energy about 860MJ to get rid of them all meaning you need no where near ideal energy storage to do it.

Finally if you did do this I am afraid the lead oxide fumes will immediately kill everyone on the battle field from exposure and if this technology is available then bullet have been made obsolete last century. other than that this technology is totally viable.

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    $\begingroup$ I love this idea, I think I will use it thanks $\endgroup$ – Eric Jun 18 '18 at 21:24
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    $\begingroup$ Just a note on your suggested application for vaporizing bullets, if you vaporize a tonne of lead heading towards you, you end up with a tonne of vaporized lead coming towards you a little less coherently, which is still going to kill you. $\endgroup$ – Gryphon Jun 19 '18 at 20:49
  • $\begingroup$ @Gryphon No this isn't actually a problem, gases do not retain their velocity for long when travelling through other gases especially if they aren't properly formatted like in a vortex ring. this is beacuse as they spread out they increase greatly in cross section capturing more air slowing down and then spreading out futher. this is why you can't do any damage with a blank round and why you can't blow so much as a piece of paper from accross the room. done in vacuum its a different story but in atmosphere I could easily fire as much gas as i wanted your way and do no damage (within reason). $\endgroup$ – Ummdustry Jun 20 '18 at 11:31

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