With a powered-by-phlebotinum (ergo very handy, very powerful) rifle, I am able to shoot high-energy beams which, in turn, can pulverize anything in their path in a considerable radius. The beams can travel very far in open air, and pierce every material known to man. They transmit mostly kinetic energy, but carry heat also.

At the present moment, for plot reasons, I'm shooting down a thick steel floor. I imagine that my beam will carve an hole into it, of the size of the beam itself.

To be precise, I'm shooting at an inclination of 30° from the ground, the beam is around 70 centimeters (27 inches) diameter, and I expect it to travel into layers of steel for about 200 meters before emerging on the other side. The beam is automatically focused, meaning it retains its width no matter the distance from the gun; also it can be emitted in a single, continuous pulse.

While I'm very sure that this will be enough to create a tunnel in the floor, I'm not sure how will the steel around the beam react. Will it overheat, and if so, for how long? Will it melt? I'm asking because I hope to use the hole created as a tunnel of sorts.

Extra informations: Feel free to suggest other characteristic for the beam, if you think they would suit the task better. Also, for the sake of the question, assume that the gun doesn't suffer from recoil, power shortage or overheating.

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    $\begingroup$ Do the magic beams transmit kinetic energy, heat energy, momentum, something else, or some mixture? $\endgroup$
    – user535733
    Commented Oct 22, 2018 at 19:26
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    $\begingroup$ I'd go with 'something else' involving force fields. Using anything subject to the laws of thermodynamics will wet-blanket anything you want to achieve. Kinetic energy for the first layer of steel alone will impart a big enough kick to splatter the human. Using super-duper-heat, the gaseous vaporized solids would be poisonous to breathe, and terminally hot. It may be an hour until the sides of the tunnel have cooled enough to touch. $\endgroup$
    – user535733
    Commented Oct 22, 2018 at 19:35
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    $\begingroup$ I'd like to suggest a more sub-atomic approach- the kinetic and/or thermal energies involved would wipe out anyone close enough to hold the weapon or observe the effects. Consider a simple field-based 'projector' of an unknown energy that causes weak EM forces to be suppressed...atoms simply fly apart on a subatomic level, little or no heat or impact required... (stand back anyway) $\endgroup$
    – Joe
    Commented Oct 22, 2018 at 19:44
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    $\begingroup$ If you're digging a tunnel, why vaporize the whole thing? Why not simply cut out a cylindrical piece and let it fall freely? That will drastically reduce the amount of material you're worried about, and the knock-on effects of cutting. $\endgroup$
    – Cadence
    Commented Oct 22, 2018 at 21:31
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    $\begingroup$ Well, since it's phlebotinium, there's a danger that you might bleed out. $\endgroup$
    – Spencer
    Commented Oct 22, 2018 at 22:41

3 Answers 3


"Kinetic energy" means energy of a moving object, e.g. a bullet fired from conventional gun, or a railgun projectile. Both of these guns will make the projectile hot. Hitting steel at 30 degrees will likely deflect the projectile, this is why tank armor is angled.

If you change angle to 90 degrees, you can find videos on youtube of railgun hitting various targets. Many of of them have multiple plates of armor with space between them. If you hit solid 200 meters of steel, I suspect you will make a crater rather than a deep narrow hole. B/c energy of the impact will evaporate steel in front of the projectile, and that gas has nowhere to go (projectile does make a hole, but it also plugs it).

Of you go for pure energy-beam weapon (e.g. a laser), you will not get a clean 200m hole either. B/c energy acts by evaporating steel, and that vapor will absorb energy of the beam. You might eventually get an explosion a bit under the surface, again forming a crater. If you keep the beam up for a few seconds, a series of explosions will make a hole through all 200 meters, but it will be a lot wider than 70cm, and very jaggged.

If you really want clean long hole, go for thinner beam that traces the circle, so vapor can come out while the beam is elsewhere. It will still take a few seconds to make the hole.

Edit: I just realized a neutron beam fits your description of a beam with kinetic energy. I suspect its effects will be somewhere between laser and railgun.


People near the openings will have trouble breathing, and the tunnel will be really hot for a while

In order for the beam to cut through the thick steel it will certainly need to heat it to get the steel out (otherwise it'll just shatter the 200 m plate. Most Steel grades melt at about 2,500 F and vaporize at about 5,000 F.

Breathing vaporized metals is not good for your lungs (see nuclear explosions).

Melting or vaporizing this column of metal will require a lot of heat, and the 200 m thick plate can hold a lot of heat. It will retain that heat until it has time to dissipate. For reference, Iron has a heat of vaporization of about 6000 kJ/kg, and a 27 inch column of steel 200 m (73.8 m^3) tall will weigh almost 600,000 kg. That's 3.6 billion kJ, about the equivalent of 86 tonnes of oil.


How fast is this beam penetrating the 200m of steel? If it's over a long enough period of time it might work more or less as you want (except you probably don't want it taking hours to days...)

If it's more-or-less instantaneous, speed-of-proverbial-bullet kind of thing, the steel and air around your hole is going to get fantastically hot as your beam continues to heat the steel vapor (soon to be plasma) that is produced that in turn heats the surrounding material. There's a bigger problem though: you're going to create a enormous explosion of superheated plasma right in your face as steel and air expands from the preposterous amount of power you're dumping into such a small area. The gun won't survive long enough to get through a fraction of the steel.

If you want a nice clean fast hole through 200m of steel kind of device, you're probably better off doing some hand waving about matter displacement or molecular binding nullifier or some such. Or don't explain it at all and just chalk it up to science-as-indistinguishable-from-magic (such as Iain M Banks did with his Lazy Gun.)

  • $\begingroup$ I'll probably have to do that, so thanks for saying out loud that it can get very hand-waving. $\endgroup$
    – Liquid
    Commented Oct 22, 2018 at 22:10
  • $\begingroup$ And yep, it should be fast, we're talking of under 10 minutes. $\endgroup$
    – Liquid
    Commented Oct 22, 2018 at 22:18
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    $\begingroup$ Just for kicks (and reality check) I figured how much energy you would require to vaporize a 70 cm hole through 200 m of steel. With 100% efficiency (i.e all energy going into heating the steel to vaporization and absolutely nothing beyond that), it would take 4.48 x 10^12 joules. Over 10 minutes that would be 750 megawatts. Basically the full output power of a large fossil fuel / small nuclear plant in a very small place. $\endgroup$
    – Gene
    Commented Oct 22, 2018 at 22:33

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