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First post, so I’d appreciate suggestions and help on how to make this question better.

Question

Suppose there’s a sorcerer with power over light. He can use these abilities to perform all the supernatural tricks you might expect: creating illusions, making things invisible, acting as a human torch, annoying foes with super bright flashes of light etc. Normal wizardy stuff.

I’m wondering what would happen if we extended the definition of “light” beyond just visible radiation and assumed that the real laws of physics still hold in his world (alongside magic).

Assumptions and Constraints

Say we make the following assumptions:

  1. He can generate electromagnetic radiation, shift it, focus it, or essentially manipulate beams of light like clay

  2. He can, to a limited extent, change the wavelength of existing light.

  3. He can, to a limited extent, change the intensity of existing light.

  4. The source of the light generated need not be from his body—just within line of sight.

  5. He can’t alter the properties of materials to change how they actually interact with light (i.e. changing their refractive index or absorption coefficient). He can only modify the light itself (i.e. bending it around things)

  6. He can (either magically or physically) protect himself from whatever light he emits. Just for simplicity.

  7. He can’t emit ultra-focused high powered lasers, or extremely high frequencies like X-rays and gamma-rays. Too ham.

  8. He has limited mana, and generating light tends to be more costly than simply moving or removing it. So there is some hand-wavey degree of conservation of energy going on…but I’m flexible on this.

  9. Physics acts normally until you directly manipulate it with magic

  10. The guy’s living sometime around 1900-1940, before the advent of computers. Again flexible on this.

Would it be possible to…

  • ...interfere with or attenuate radio waves nearby?
  • ...microwave his foes from several meters away? (What if his foes are wearing metal?)
  • ...act like an IR flashlight to spot-broil things from afar?

Tl;dr:

In general, what are some of the possibly absurd, overpowered, world-breaking, plot-hole-generating things that a light mage could do in the real world?

Thanks for your help and let me know if I’ve overlooked any of the rules!

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    $\begingroup$ You say your wizard has limited mana... Can you elaborate? How much energy can this mage create? How much light can they bend? $\endgroup$ – AngelPray Feb 25 '18 at 19:32
  • $\begingroup$ "Physics acts normally until you directly manipulate it with magic" - how does physics react then, if not normally? $\endgroup$ – Aify Feb 25 '18 at 19:34
  • $\begingroup$ @Aify i think what he means is the physics act normally apart from the obvious manipulation of light $\endgroup$ – Ajnatorix Zersolar Feb 25 '18 at 19:38
  • $\begingroup$ @AngelPray Great question. These are some of the parameters I'm trying to figure out--ie how much would be reasonable? I'm not picky and I'm okay with a bit of hand waving. $\endgroup$ – Useless Island Feb 25 '18 at 21:53
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    $\begingroup$ @JBH: You are absolutely wrong. Green light and a radio wave of the same frequency are exactly the same thing. All electromagnetic radiation is made up of photons; it's just that energy of each individual photon is directly proportional with the frequency of the radiation, so that gamma-ray photons are more energetic than X-ray photons, which are more energetic than ultraviolet photons, which are more energetic than visible photons, which are more energetic than infrared photons, which are more energetic than microwave photons, which are more energetic than radio frequency photons... $\endgroup$ – AlexP Feb 26 '18 at 4:47
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Your light mage can instantly incinerate whatever he wants... as long as the moon/sun is visible.

There are two cases here, but based on the manipulation of light rays (Rule 1) and the source requirement being line of sight (Rule 4), all he has to do is roughly focus (different from highly focused, its just that there's a lot of light from the sun) the rays from the source (sun/moon) onto any spot - even if that spot is a couple meters in diameter, possibly more, the mage should be able to incinerate everything in that spot.

Feel the warmth heat of the sun.

One one-billionth of the Sun's total energy output actually reaches the Earth. Of all the energy that does reach Earth, slightly less than 34 percent is reflected back to space by clouds. The Earth itself reflects another 66 percent back to space.

Consider the possibility where the mage manipulates any small percentage of the suns energy output to go towards the Earth; if he could point it inside a 3km * 3km area that would already be a tiny spot, equivalent to how we, as humans, hold magnifying glasses and set fire to ants and leaves. Except he's going to set fire to the entire area, way more quickly, relative to how much light he's redirecting.

Your mage is basically a god, able to instantly create stretches of scorched earth, or end life on Earth as we know it. He can evaporate any amount of water almost instantly, cause the oceans to boil, or a glacier to melt.

Of course, the mage might also cause the earth to warm up very very quickly and/or set fire to the atmosphere during the process depending on the duration this beam is held but... I don't know enough math to calculate that stuff. Maybe you can magic it away.

To the moon!

The second situation has to deal with the moon. Depending on how much light is reflected off the moon (eg: full moon vs half moon vs crescent moon) and your rules for "line of sight light source", its not impossible for your light mage to set fire to things using the moon as a reflector for the sun. I haven't done the math yet (and I don't plan to), so this possibility is up to story purposes. Theoretically, I think if you could focus it into a small enough spot, it would do the trick.

Esentially, your light mage would be unstoppable in the day time, and less powerful when the moon is out, and almost powerless during eclipses.

Another limitation would be the mana limitations. I don't know how much mana is used or stored by the caster, but you could set it up so that these absurd things are impossible depending on your mana rules - but that goes for every absurd thing, and if the point of your question is to figure out how to fix the broken stuff, what was the point of your question?

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    $\begingroup$ @ajnatorixzersolar I didn't do the math. But manipulating a large amount of light after it enters the atmosphere means changing the direction of the light by a lot. Alternatively, if you change it directly from the source, you only have to change the angle of the light wave by a little bit in order for it all to hit the same spot. Less mana required. $\endgroup$ – Aify Feb 25 '18 at 19:53
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    $\begingroup$ @UselessIsland There really isn't that much light to work with if you apply a distance limitation, and that would cause his powers to be even worse at night. I suggest using mana to limit his powers; the amount required to maintain more than a nanosecond of a light barrage on a large area, for example, could be enough to drain him. If you give him precise control, that would help the case as he would be able to use his mana sparingly and accurately in order to set small things on fire. $\endgroup$ – Aify Feb 25 '18 at 22:21
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    $\begingroup$ Relevant what-if.xkcd.com/145 . Moon won't work $\endgroup$ – AEonAX Feb 26 '18 at 11:45
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    $\begingroup$ @AEonAX That xkcd article is talking about using lenses, which are reversible and require no energy input. The wizard isn't necessarily constrained by the same limitations because he's expending energy (or mana, I guess) to deflect the moonlight. $\endgroup$ – el duderino Feb 26 '18 at 14:30
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    $\begingroup$ @AEonAX it's possible to start a fire with a LED flashlight whose emitter is quite cold, therefore this xkcd is wrong. I suspect it has to do with the assumption the radiation must be blackbody, which moonlight isn't. $\endgroup$ – peufeu Feb 26 '18 at 15:14

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