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I've read comics in which someone with pyrokinetic powers was able to block bullets with a sheet of fire. I have three questions

  1. How hot would the fire have to be to melt a bullet passing through it? (fire is about 1 inch/ 2.54 cm thick)
  2. Would this be an effective defense, or just mitigate the fact that you still have a small lump of metal flying at you at a high velocity? (Would the aerodynamics change enough to matter) (The "Shield" is about 2 yards/ 1.8288 meters away from you)
  3. Would there be a temperature that would make guns unusable?
  4. Any other ideas for counter-gun pyrokinetic tricks are welcome.
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    $\begingroup$ One work around which I have seen used effectively, is to consider pyrokinesis to be telekinesis on a molecular scale, mechanically oxidizing burnable substances (including the air) and thus producing flame. When this is the mechanism the implements your pyrokinesis, it is an easy step to shift it from one class of invisible objects (molecules) to another (speeding bullets). As long as the psychic can't see what they are moving with their mind, they don't know that they can't move it psychically. $\endgroup$ – Henry Taylor Jul 27 '17 at 2:35
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    $\begingroup$ I don't think it would stop a bullet because although the fire could be more than hot enough to melt a bullet, the bullet would pass through an inch of space in a tiny fraction of a second and air only transfers heat to a bullet so fast. Also, the bullet could be molten metal and still end up hitting the person with pyrokinetic powers. What if they used their fire powers to melt a makeshift shield off of their surroundings? $\endgroup$ – Tom Jul 27 '17 at 2:37
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    $\begingroup$ 3 and 4: Blow up the magazine of the gun by exploding the bullets. $\endgroup$ – rytan451 Jul 27 '17 at 2:49
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    $\begingroup$ @John It would probably still be lethal, though less so, and it will be really hot. If you've ever stood under a large bucket of water being poured from high heights, you would know that droplets at high speeds can still be painful. And in this case, they would be hot. Really hot. $\endgroup$ – rytan451 Jul 27 '17 at 3:18
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    $\begingroup$ This question has a huge X Y problem. It is not asking how a pyrokynetic would block bullets, it is asking about a proposed solution. $\endgroup$ – Mindwin Jul 27 '17 at 10:47

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I may be put on a number of watch lists during my researching to answer this. :P

My criteria for making the bullet undamaging is this: if the bullet has been boiled into a vapor, it is no longer capable of damaging your pyrokinetic. This is a bit strict, but easier to calculate. You may want to lower the temperature to compensate.

A Beretta M9 has a muzzle velocity of 381 meters per second. This means that the bullet will be passing through the fire barrier in more than 66.6 microseconds, depending on the distance between the gun and the barrier. That is a very short time (emphasis on very) for the bullet to be rendered ineffective.

Rifles have a greater muzzle velocity, so their bullets would have a much shorter time to be vaporized.

BEGIN EDIT

I am assuming primarily conductive heat transfer over the time span required, and that the energy imparted by the firewall would be distributed constantly over the entire bullet. I admit that is somewhat of a stretch. The bullet starts at around $50 °C$ from the gunshot. Vaporized means that the entire bullet has reached $1749 °C$, which is the boiling point of lead. This means that the bullet must increase around $1700 °C$ in 66 microseconds. Given that amount of time, the lead must increase in temperature at $25757575.\overline{75} °C/s$.

The bullet is around 1 gram of lead (very approximate), so the amount of energy to increase the temperature of the bullet by 1700 °C is 21.76 Joules (ref). That's around 329697 watts of heat transfer needed throughout the 66 microseconds.

That much power requires extreme amounts of heat around the bullet. (I don't actually remember my line of thought after here, but I did calculate this.)

END EDIT

You'll need a temperature of around 3,000,000 Celsius (5,400,000 Fahrenheit) to vaporize an unjacketed lead bullet. That is more than five hundred times the surface temperature of the sun.

Chances are, with that much heat two yards away from your pyrokinetic, getting shot would be the least of his concerns.

A quick message to your pyrokinetic:

Dear pyrokinetic, Please do not try to block bullets with fire. You'll probably burn yourself to death. Perhaps you may consider the saying "The best defense is a good offense"? If your enemies are unable to shoot you, you won't get shot.

Perhaps instead of blocking the bullets with fire, you may explode their cartridges in the magazine, or melt the firing mechanisms of their guns. Just try to keep at a good distance, and be aware of your surroundings.

Don't get shot.

Best regards,
A concerned citizen

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    $\begingroup$ More answers should include safety messages like this. Considering the temperatures involved, wouldn't be easier and not so overheated as to set fire to the shooter (preferably before they fire their weapons)? Good luck with the watch lists! $\endgroup$ – a4android Jul 27 '17 at 6:07
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    $\begingroup$ I like the use of "around" to describe a temperature of nearly 3 megakelvin ... given to a precision of 10mK. I would have written it as "about 3,000,000 C (5,300,000 F)" $\endgroup$ – Martin Bonner Jul 27 '17 at 10:50
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    $\begingroup$ I'd like to see your math. $\endgroup$ – Samuel Jul 27 '17 at 16:17
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    $\begingroup$ Note that at that temperature the air would turn to plasma and would start emitting x-ray radiation that would kill everybody. $\endgroup$ – ZeroOne Jul 28 '17 at 1:12
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    $\begingroup$ @Rytan451 Can you explain what went into your math? As it is right now, you made up a number and are getting a bunch of upvotes for no evidence at all. $\endgroup$ – BobTheAverage Jul 28 '17 at 14:17
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For another trick in using pyrokinesis to block bullets:

Depending on how long the sheet of fire can be maintained for, it could be used simply to obscure the view of the shooter.

It's pretty difficult to see through fire, especially with the addition of smoke, which in an enclosed space would cause the shooter's eyes to suffer as well (though that might also happen to your pyromancer - I would recommend goggles).

Alternatively, depending on how well the heat can be manipulated, it could be possible to conjure a mirage, in which heat bends light rays and creates a different picture than what is really there, which could be used to distort what the shooter sees and cause them to miss.

Whilst these techniques don't necessarily stop bullets in the air, it can stop them from being fired accurately, which is just as useful.

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    $\begingroup$ "though that might also happen to your pyromancer" People wielding super powers are usually somewhat more resistant to effects caused by their own ability, so that's easy to handwave. $\endgroup$ – Mast Jul 27 '17 at 10:52
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Pyrokinetic "sheet of fire" can not be fire at all. What it has to be is a region of space where thermal molecular velocity is increased by the kinetic's power, to the point where oxygen-nitrogen recombination occurs (which means that pyrokinesis is not environmentally friendly, as nitrogen oxides are responsible for acid rains).

The same effect is a defense against most kinds of projectiles: their macroscopic kinetic energy is neutralized, they can be heated or fractured until they disintegrate, and even the shock wave of an explosion - being kinetic energy of air molecules - can be diverted.

The possible limits are where does this energy go - we can somehow transmit it without physical contact, but it's best if we don't repeal the laws of thermodynamics - and how much of it can be transferred by the kinetic, and for how long. Also, how long does it take for the kinetic power to "lock" on the incoming bullet.

Since the power for a sheet of fire is above what can be generated by a human body, the energy must be supplied by something else (alien nanomachines, trans- dimensional demons...). Maybe that something else can take care of monitoring airspace and target acquisition.

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As user @rytan451 states, it's not really feasible to flat out vaporize the bullet (though I'd be curious to see the calculations he used to arrive at 3ish Mk). What you could do is super heat the air next to the bullet and use the expansion of the gas to deflect the trajectory slightly. For this to be effective however, your pyrokenetic would have to have superhuman reflexes and precision in order to intercept the bullet as it travels.

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    $\begingroup$ This was the solution I thought made the most sense. However, if you have the ability to deflect the bullet early, it means you have the ability to heat things right near the barrel of the gun substantially. As an easier solution, reach a few inches further, and make a fire which turns the trigger mechanism into a pile of goo. $\endgroup$ – Cort Ammon Jul 27 '17 at 16:24
  • $\begingroup$ @CortAmmon trigger mechanism, or the person holding the gun ;) (someone had already suggested disabling the gun however) $\endgroup$ – Aaron Jul 27 '17 at 17:53
  • $\begingroup$ As some point you do transition over from defense to offense =) $\endgroup$ – Cort Ammon Jul 27 '17 at 18:07
  • $\begingroup$ If the pyrokinetic abilities are psychic in nature, and the "superhuman reflexes and precision" above are precognitive in nature, than this makes perfect sense to me. $\endgroup$ – Ghotir Jul 27 '17 at 19:45
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Your pyrokinetic will be lucky if his assailant is only using lead bullets. Most ammo today is steel jacketed and there are much more durable materials being used to make armor piercing projectiles.

So, with that in mind, mayhaps we should look for a means of using your pyrokinetic's talents in more imaginative ways. And, as always, the devil is in the details.

For instance, if his assailant happens to be a sniper then your pyrokinetic may never even see it coming, so mounting any kind of defense would become a moot issue. So we must assume you're looking for a way to preserve the life of your pyrokinetic in situations where he has some prior warning of impending doom. Thus he has time to mount a formidable offense and should do so prior to his assailant firing his weapon. In this scenario your pyrokinetic can use his amazing talents to fry his arch nemesis to a crispy thin strip of bacon.

On the other hand, if your pyrokinetic hasn't the stomach for such violence then he could just warm his assailants weapon to a point where holding on to it long enough to take aim is out of the question. That always produces opportunities to lighten the mood for all observers when they see the assailant dancing around trying to find a way to cool his trigger finger.

Now, let us assume the weapon has already been dis-charged in your pyrokinetic's direction. As others have pointed out these projectiles are not walking. If your pyrokinetic hasn't already got a plan ready and begun its initiation, it isn't likely he is going to survive long enough to figure out what to do about the bullet, except maybe figuring out how to get it out from under his skin.

Likewise, if he knows the weapon is about to be discharged in his direction and he has time to flame on, simply trying to generate enough heat to melt the bullet isn't going to be the safest method of ensuring his survival. So let's assume your pyrokinetic has very precise control over his amazing ability and has had enough practice to use it effectively in concentrated bursts. As opposed to a wall of flame, your pyrokinetic should discharge an extremely intense beam of fire about twice the size of a standard bullet in circumference and thrust it in a trajectory that will ensure collision with the bullet at a force much greater than any bullet, irrespective of powder pack or material used, could resist. In this way he simply slows the bullet down very quickly until it drops at his feet, still smoking hot and glowing a bright orange/red, capping off the scene with a loud hiss and sizzle as the ground it has fallen on is damp.

Does that work for you?

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It would be very effective if you assume one thing:
Your pyrokineter is actually electro/air (apart from Firefly from DC pyros don't use any kind of fuel to burn and/or flamethrowers).
Mostly because it's easier to use nitrogen from the air and add a little of electricity to create plasma.
Plasma has the advantage that it can:

  1. cut through metal
  2. plasma can be magnetically charged and would push away Pb

So you would not only have to deal with smaller particles, but it would be easier for the field to push them in different directions.

Think of it as a bush that changes the trajectory of a bullet.

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What is pyrokinesis actually?

Is it a gathering of molecules from the surroundings (air, dust, etc) and then superheating and accelerating them?

If your hero can throw a fireball, could he also generate a mini-fireball that travels at similar speeds as a bullet? Could he generate a fire bullet fast enough and at the correct mass+velocity to counter the energy of the bullet?

You could stop the forward momentum, but the bullet would probably shatter and you would have fragments spreading out from the point of impact. If the fire bullet was a larger mass, then it could envelop the bullet and pretty much vaporize the fragments. That fire bullet would also probably "shatter" and dissipate back into the air after impact.

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The pyrokinetic does not need to destroy the bullet to not get hit.

The pyrokinetic could blow the bullet off course.

Flame is simply air so hot that it is incandescent. When you heat a gas it expands in volume. The faster you heat it, the faster it expands. Rapidly expanding gas is an explosion.

https://www.physicsforums.com/threads/how-much-does-air-expand-with-heat.267530/ PV = nRT; V is volume and T is temperature. So if pressure is stable an increase in temperature causes the same increase in volume. A candle flame is 900C. From 30C to 900C means a volume increase of 30x. An oxyacetylene torch is 3000C; from 30C to 3000C is 100x the volume. If you turn 1 cubic meter of gas into 100 cubic meters of gas in 1 second, that would make a 360 kph wind or 223 mph wind.

A sudden expansion of heated gas (flame!) in the path of a bullet could blow it off course. There is no question that wind can push a bullet off course. The deviation has to do with the mass of the bullet, the speed of the wind, and the flight time of the bullet (or how long the wind gets to push it). There are published tables for shooters. Here is one.

enter image description here

Multiplying the values for 20mph wind by 10, a 200mph wind could push a bullet this size 16 inches over 100 yards and farther over longer distances.

This would not always save the target. The deviation of the bullet would depend on the volume of gas heated, how hot it got, the speed and mass of the bullet and the distance of the shot. The pyrokinetic should practice. But a bullet does not need to miss by much to miss.

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  • $\begingroup$ That is a great strategy, and considering he could use subtle applications of heat to create convection to move the air couldn't he technically airbend? $\endgroup$ – Efialtes Mar 15 at 19:18
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I propose another theory in which to 'stop' the bullets with flames or pyrokinesis. Creating a wall of flame is pointless, as other before me have said, it would need to be very hot and very thick to vaporize a bullet.

So instead, create a vacume of air and oxygen within a circle of flames. If possible the barrier should stop the bullets momentum or drag it down lower. And if your pyrotechnic is skilled enough, they should be able to control the vacume of air and fold the flame within to change or divert the bullets.

As my Uncle once said, "Not everything can be solved with fire, but a damn lot can."enter image description here

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    $\begingroup$ How exactly can a vacuum act as a barrier? Vacuum exercises no drag, so it is even better than air for a moving bullet! $\endgroup$ – L.Dutch Mar 15 at 6:54
  • $\begingroup$ I think he means that the vacuum would act as space between the air so that the projectile hits the vacuum and speeds up and then suddenly hits a gaint wall of air slowing it down due to the sudden friction. $\endgroup$ – Efialtes Mar 15 at 19:16
  • $\begingroup$ @Efialtes That's not how it works. The bullet is under constant drag during flight. Taking away some of the drag doesn't speed the bullet up, it just doesn't slow it down. When it hits the air on the other side of the void it just resumes slowing down like it was before. $\endgroup$ – Corey Mar 15 at 23:58
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I'm in the group that think of pyrokinesis as a specialized form of telekinesis where the pyrokinetic energizes molecules to induce heat and ultimately fire. Take this far enough and I don't see why your pyrokinetic couldn't end up generating plasma. CERN has produced a type of plasma that reaches 5.5 TRILLION degrees celcius, which exceeds the above temperatures about 2 million times over. Your pyrokinetic could also have some degree of electro-magnetic influence as well, which would be a bit of a requirement for controlling plasma.

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You need to calculate Heat capacity of air and Heat capacity of lead going through it. Boiling point of lead is 1750 °C. So it is 1730 difference to make. Lets assume that bullet will only gain heat from Air it went through - so basically it has same volume (or very similar).
Air has higher mass heat capacity, but it depends on mass, not volume.
So we take volume heat capacity because of same volume of air and bullet. That is 0.00121 for Air and 1.44 for Lead.
Lead/Air*1730 = 2 058 842°C/K or 3 705 947 degrees Fahrenheit.

You shouldn't care about velocity, unless you think "only 10% of heat would be absorbed by bullet" - in that case you will need 10x higher temperature.
"Small lump of metal flying at you" - Unless you have 2000+ degrees around you, it will change back to metal. But more likely it would stay as hot steam for few seconds - just don't breathe it.

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    $\begingroup$ This answer assumes that the bullet and the air are left in the same space until their temperatures equalize. The bullet will take a microsecond to travel through the flames. $\endgroup$ – BobTheAverage Jul 29 '17 at 16:18
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Other answers have focused on the sheer amount of heat needed to vaporize the bullet, but I think (I don't really know -- ask someone who's good at physics) that your first obstacle to get over would be air displacement. It's worth considering that the vortex left in the wake of the bullet's path may effectively extinguish any flame nearby due to starvation.

Depending on your pyrokinetic's origin of ability (e.g. on their person v. at a remote location in their field of vision) combined with their level of detail and speed, the more effective defense (other than obscuring themselves with a smokescreen/the sheet of flames or distracting/frightening the attacker) may be to preempt the shot and cause an early ignition, although this would require considerable attention to detail so that the projectile is not aimed somewhere equally damaging.

Air temperature might also be taken into account -- is there any property of air buffering or flight physics that can be altered by a drastic change in temperature?

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