[THEORYCRAFT] Can a mirror made with the Silent Illusion spell reflect an image?

[Deathtongue]

If I create an image of a bedroom mirror using as spell like Silent Image and someone looks into it: what would they see?

It seems like a simple enough question, until you actually explore the implications.

Let's say that our illusory mirror wouldn't show anything. It would be a solid block of metal/glass that would not, outside of the illusionist's parameters, not only not show what was in front of it but would completely block what was behind it. This implies quite a few things. Note that most of these observations would apply to sound waves as well.

It's pretty much impossible to have a convincing illusion unless you're in an extremely static environment with unobservant N/PCs. Illusions will look immersion-ruiningly different depending on what time of the day they were cast. Or if you just turn your back to a campfire. This is more of a game balance problem than a logic problem, but it renders spells like Disguise Image completely useless and only boring and obvious illusions like Simulacrum available.
There's actually a very serious question as to whether you can actually see illusions at all. If illusions can't reflect light, then how are they getting to your eyes? They could be projected into your mind, but A) it doesn't solve the above problems and B) it raises further questions such as to whether, say, a self-driving car could see the illusions. Or whether someone who was blind since birth could in fact see the illusion.
Because illusions
If Illusion spells are not affected by light, they also block all forms of electromagnetic radiation. If you claim that illusions don't block light for... reasons, that means that anyone would be able to see through the mirror and thus couldn't see the mirror at all.
There's also the possibility that illusions perfectly absorb light but the illusion adjusts so that it doesn't show any absorption. So either you can generate waste heat way in excess of effects you could get with Fireball, or if any light that would've otherwise been absorbed gets destroyed with no further effect on reality you have a way to completely make things like radiant damage and electricity damage nonfunctional.


However.

Once you go with the interpretation that spells like Silent Image can in fact reflect light there are a ton of awesome things that a wizard with a doctorate in particle physics can do with them. Such as Solar sails. Or even if your DM won't let you create light outside of the visible spectrum, it's still actually pretty simple to filter or even convert light to any of its other forms the electromagnetic spectrum. So: enjoy having access to X-rays. So, with enough patience, Kugelblitz black holes. The interpretation of 'Illusions otherwise interact normally with physics' prevents your game from collapsing but it also opens up the serious possibility of your 11th-level wizard having access to technologies the game never intended you to have. Such as antimatter power plants.

[Unoriginal]

If I create an image of a bedroom mirror using as spell like Silent Image and someone looks into it: what would they see?

It seems like a simple enough question, until you actually explore the implications.

Let's say that our illusory mirror wouldn't show anything. It would be a solid block of metal/glass that would not, outside of the illusionist's parameters, not only not show what was in front of it but would completely block what was behind it. This implies quite a few things. Note that most of these observations would apply to sound waves as well.

It's pretty much impossible to have a convincing illusion unless you're in an extremely static environment with unobservant N/PCs. Illusions will look immersion-ruiningly different depending on what time of the day they were cast. Or if you just turn your back to a campfire. This is more of a game balance problem than a logic problem, but it renders spells like Disguise Image completely useless and only boring and obvious illusions like Simulacrum available.
There's actually a very serious question as to whether you can actually see illusions at all. If illusions can't reflect light, then how are they getting to your eyes? They could be projected into your mind, but A) it doesn't solve the above problems and B) it raises further questions such as to whether, say, a self-driving car could see the illusions. Or whether someone who was blind since birth could in fact see the illusion.
Because illusions
If Illusion spells are not affected by light, they also block all forms of electromagnetic radiation. If you claim that illusions don't block light for... reasons, that means that anyone would be able to see through the mirror and thus couldn't see the mirror at all.
There's also the possibility that illusions perfectly absorb light but the illusion adjusts so that it doesn't show any absorption. So either you can generate waste heat way in excess of effects you could get with Fireball, or if any light that would've otherwise been absorbed gets destroyed with no further effect on reality you have a way to completely make things like radiant damage and electricity damage nonfunctional.


However.

Once you go with the interpretation that spells like Silent Image can in fact reflect light there are a ton of awesome things that a wizard with a doctorate in particle physics can do with them. Such as Solar sails. Or even if your DM won't let you create light outside of the visible spectrum, it's still actually pretty simple to filter or even convert light to any of its other forms the electromagnetic spectrum. So: enjoy having access to X-rays. So, with enough patience, Kugelblitz black holes. The interpretation of 'Illusions otherwise interact normally with physics' prevents your game from collapsing but it also opens up the serious possibility of your 11th-level wizard having access to technologies the game never intended you to have. Such as antimatter power plants.

1) Yes, it is possible to make an illusion of a reflective surface.

2) There is no such thing as X-rays or particle physics in D&D 5e

3)The interpretation of "illusions otherwise interact normally with physics" is incorrect on a fundamental level, because a) nothing in 5e interacts with real-life physics b) by definition, if one thing does not follows the laws of physics, then nothing does. You can't say "the laws of physics do not work for X, but if then you apply Y physical principle you get this awesome result". It's either all or nothing (and the 5e writers wisely decided for "nothing").


So yes you can make a mirror with Silent Image, no you can't get solar sails or Kugelblitz black holes or antimatter power plants.

And an 11th level wizard will never havr access to technologies except the ones they're intended to have.

[JackPhoenix]

2) There is no such thing as X-rays

Ring of X-Ray Vision says hi.

[clash]

Silent image wouldn't truly reflect. It was just have an illusion of the reflection. So if you're making it move to match what's in front of it then it would appear to reflect. Minor illusion on the other hand could not be used for a convincing reflection because the "reflection" in the mirror wouldn't change. Programmed illusion could be used to make a functional mirror without your intervention.

[Willowhelm]

Silent image wouldn't truly reflect. It was just have an illusion of the reflection. So if you're making it move to match what's in front of it then it would appear to reflect. Minor illusion on the other hand could not be used for a convincing reflection because the "reflection" in the mirror wouldn't change. Programmed illusion could be used to make a functional mirror without your intervention.

How does a 5 minute scripted performance (programmed illusion) work like a mirror?

[Unoriginal]

Ring of X-Ray Vision says hi.

Ah, right, X-rays do exist, they have just nothing to do with real-life X-rays beside the name, as seeing them means you can see through matter as if it was transparent, and as if regular light went through. And seeing them more than once per day is tiring.

They're probably on the same light spectrum as dark light (which allows people with dark vision to see in places where there is no regular light).

[JackPhoenix]

Ah, right, X-rays do exist, they have just nothing to do with real-life X-rays beside the name, as seeing them means you can see through matter as if it was transparent, and as if regular light went through. And seeing them more than once per day is tiring.

They're probably on the same light spectrum as dark light (which allows people with dark vision to see in places where there is no regular light).

Hence the blue color. Just because something in game uses real-life term in its name doesn't mean it's got anything in common with the real-life thing.

[Jervis]

1) Yes, it is possible to make an illusion of a reflective surface.

2) There is no such thing as X-rays or particle physics in D&D 5e

3)The interpretation of "illusions otherwise interact normally with physics" is incorrect on a fundamental level, because a) nothing in 5e interacts with real-life physics b) by definition, if one thing does not follows the laws of physics, then nothing does. You can't say "the laws of physics do not work for X, but if then you apply Y physical principle you get this awesome result". It's either all or nothing (and the 5e writers wisely decided for "nothing").


So yes you can make a mirror with Silent Image, no you can't get solar sails or Kugelblitz black holes or antimatter power plants.

And an 11th level wizard will never havr access to technologies except the ones they're intended to have.

I don’t think the logic of magic existing means physics doesn’t exist hold up. Animate object still makes perpetual motion machines.

[Deathtongue]

So yes you can make a mirror with Silent Image, no you can't get solar sails or Kugelblitz black holes or antimatter power plants.

And an 11th level wizard will never havr access to technologies except the ones they're intended to have.

I'm sorry, but 'your plan wouldn't work because I said so' doesn't leave me much to argue with.

Even 'it's inapplicable to 99% of D&D settings because even the settings that lean into the sci-fi such as Spelljammer don't care about non-Newtonian physics' or 'Most DMs don't even know where UV and Infrared are on the electromagnetic spectrum, let alone microwave, so it's just adding confusion' gives me something to work with.

So let's try this: if a player announced that they were using a combination of their character abilities to build one castle out of concrete and one out of solid hematite -- would you have the castles operate largely the same in a siege? Why or why not?

[Unoriginal]

I don’t think the logic of magic existing means physics doesn’t exist hold up.

Dragons can fly. Giants can stand without worrying about the square-cube law. Faster-Than-Light vehicles exist. Matter in the Material Plane comes from the Planes of Fire, Air, Water and Earth. It is possible to produce heatless light. It is possible to see in total darkness.

Nothing in the D&D world works according to real-life physics.



Animate object still makes perpetual motion machines

That would require perpetual Animated Objects. Or at least one perpetual Animated Object.

[bid]

If I create an image of a bedroom mirror using as spell like Silent Image and someone looks into it: what would they see?
There's the physical layer-of-paint theory. You cannot paint a mirror, therefore there can be no reflecting surface.
But the paint cannot vanish is you disbelieve it.

There's the mind-bending theory. It's just a spoon floating in the air saying "I'm a mirror, I'm a mirror." Of course you will see what you expect!
Until you look at at your hand and see something unexpected, which the mirror of your mind didn't replicate. Then you realize the truth... there is no spoon.


So no, physics has nothing to do with illusions. A true mirror that vanishes makes no sense.

[Witty Username]

We need to first answer if illusions can block light, and this question has some complicated break points with the natural world.
The most obvious answer is it depends whether the illusion is believed. Since this is a given that falsified illusions can be seen through.
But this opens up a bunch of nonsense with illusions and light sources. A torch with an illusionary metal box around it can both illuminate the room and fail to illuminate the room based on whether a given subject is fooled by the illusion. To prevent this the illusion would have to allow light to pass through it, but then most illusions become much more obvious, unless we accept the rules in play are not physics in even fundamental ways.

[Deathtongue]

Silent image wouldn't truly reflect. It was just have an illusion of the reflection. So if you're making it move to match what's in front of it then it would appear to reflect.If it just appears to reflect then where does the light go?


If the mirror doesn't interact with light at all, you wouldn't be able to see it in the first place. There's a word for materials that don't absorb light: transparent.
If the mirror absorbs the light but doesn't reflect it it will create massive amounts of heat. As in, with a 1st-level spell you can lay waste to entire cities at a speed that not even Meteor Swarm can match if you're positioned correctly.
If the mirror destroys and visible recreates light like it 'should' with no transfer in energy (not even kinetic energy), then not only you have just invented the most powerful anti-radiation/anti-EMF technology ever but you have also have a way to create neutron stars and even black holes.


The fourth possibility is that the mirror doesn't exist in the real world and it's just a projection of our mind. Or some cosmic intelligence from the Shadowlands or whatever not really making a mirror but projecting mind particles to perfectly recreate the behavior of one. Such possibilities are obviously contradictory and will not be discussed.

[Deathtongue]

But this opens up a bunch of nonsense with illusions and light sources. A torch with an illusionary metal box around it can both illuminate the room and fail to illuminate the room based on whether a given subject is fooled by the illusion. To prevent this the illusion would have to allow light to pass through it, but then most illusions become much more obvious, unless we accept the rules in play are not physics in even fundamental ways.I don't think 'physics not covered explicitly by the rules are not in play unless the DM says so' is an acceptable answer. It's lazy and boring.

[Segev]

It creates an image of an object. It will look how the real thing would look in the place you put it, so yes, an image of a mirror reflects things.

No, your wizard doesn't have a Ph.D. in particle physics.

[Unoriginal]

I'm sorry, but 'your plan wouldn't work because I said so' doesn't leave me much to argue with.

Even 'it's inapplicable to 99% of D&D settings because even the settings that lean into the sci-fi such as Spelljammer don't care about non-Newtonian physics' or 'Most DMs don't even know where UV and Infrared are on the electromagnetic spectrum, let alone microwave, so it's just adding confusion' gives me something to work with.

Deathtongue, I says that not to be a jerk, so I apologize if it comes out like this, but this is 5e. This is not the edition for semi-game-rule-logic semi-real-life-physical-phenomenon shenanigans to obtain results like the Peasant Railgun or other similar concept.

Your OP is more likely to work out on the 3.X subforum.



So let's try this: if a player announced that they were using a combination of their character abilities to build one castle out of concrete and one out of solid hematite -- would you have the castles operate largely the same in a siege? Why or why not?

A player would not announce such a thing, because there is no combination of abilities that would let them build a castle out of solid hematite. Wish could arguably do it, but it wouldn't be a combination of abilities.

Assuming the player used Wish to create an hematite castle, then it wouldn't have the same characteristics as a concrete castle.


It creates an image of an object. It will look how the real thing would look in the place you put it, so yes, an image of a mirror reflects things.

Indeed. Otherwise it would be impossible for an illusionist to create an image of, say, a knight in shining armor, or anything containing water.

[Willowhelm]

I don't think 'physics not covered explicitly by the rules are not in play unless the DM says so' is an acceptable answer. It's lazy and boring.

The thing is that you’re coming at this fresh as a wondrous new idea to have fun with.

They’re coming at this as something that has been discussed to death a million times before.

They’re short cutting to the final answer and you want to explore the route.

In your campaigns, in your worlds, it works how you want it to. The consequences of that are left for you to extrapolate (with help if people want) but there is no correct answer.

Dnd magic and dnd physics are entirely broken and inconsistent. Pointing out the holes can be fun but at the end of the day it isn’t really relevant because the game doesn’t run on any rules other than the (extremely vague) books and the players interpretations (including the DM as a collaborative player not a omniscient physics engine).

In my game? You want a mirror to check your teeth - go nuts. You want a mirror formed in a precise way to act as a solar furnace - eh… maybe. You want a mirror to act as a solar furnace in order to melt the chain on the drawbridge and crush the guard… pushing it. Maybe the first time because it’s a cool new idea.

You want to bring down the entire Golden Gate Bridge using a cantrip? No. You want to claim your adventurer has real world phd physics knowledge and the entire campaign world isn’t drastically different… nope.

But that’s my table.

[Unoriginal]

I don't think 'physics not covered explicitly by the rules are not in play unless the DM says so' is an acceptable answer. It's lazy and boring.

The alternative would be to write the interaction of every single real-life physical laws with every single fantastical phenomenon in 5e.

For starter: how come that the illusion of a mirror, which is made solely of light, does not generate enough heat to hurt an humanoid even slightly?

Producing the light needed to make a mirror hologram requires a lot of energy. If we're assuming that the Illusionist is projecting this light, then a lot of heat (or infrared light) would be generated as well.



They’re short cutting to the final answer and you want to explore the route.


Yeah, I think you've hit the nail on the head, Willowhelm.



In your campaigns, in your worlds, it works how you want it to.

Indeed.

Ergo, an 11th level wizard will never have access to technologies except the ones they're intended to have, even if it's the DM who intended them to have it.

[Bohandas]

2) There is no such thing as X-rays or particle physics in D&D 5e

https://www.5esrd.com/gamemastering/magic-items/magic-rings/#Ring_of_X-ray_Vision

[bid]

For starter: how come that the illusion of a mirror, which is made solely of light, does not generate enough heat to hurt an humanoid even slightly?

Producing the light needed to make a mirror hologram requires a lot of energy. If we're assuming that the Illusionist is projecting this light, then a lot of heat (or infrared light) would be generated as well.
Absolutely not.

Sunlight is enough to make an object visible, therefore your illusion shouldn't generate more heat than sunlight does. Even if the spell was as inefficient as an ICE / heat engine, 3 times that heat is nothing.

[Segev]

Most illusion spells that create images explicitly call out that they do not generate light. They aren't "light" that is emitting. They're images that interact with light in such a way that they can be illuminated. Whether they also cast shadows on things other than themselves is up to your DM, as well as how that interacts with "becoming faint" to some observers but not others when they're discovered to be illusions.

Personally, I advocate for them to interact with light as if they were solid. If they "become faint," that observer can see what's beyond them, but still is in the image's shadow. Creatures who can see into the lighting conditions of that shadow and for whom the image is faint can see things in the image's shadow, but the shadow persists.

That is not at all the only way to run it, however.

[Unoriginal]

Absolutely not.

Sunlight is enough to make an object visible, therefore your illusion shouldn't generate more heat than sunlight does.

Unless I'm mistaken, it is more complicated like that.

A real object is made visible by absorbing the light of the sunlight and reflecting a percentage of the light spectrum.

To project the same percentage of the light spectrum, however, results in a a lot more heat than what the reflected light of the sun would.

Now I'm not saying it should do tons of damage, but it still should be something hot enough to hurt.

I could be mistaken, however.

[Segev]

Unless I'm mistaken, it is more complicated like that.

A real object is made visible by absorbing the light of the sunlight and reflecting a percentage of the light spectrum.

To project the same percentage of the light spectrum, however, results in a a lot more heat than what the reflected light of the sun would.

Now I'm not saying it should do tons of damage, but it still should be something hot enough to hurt.

I could be mistaken, however.

1) That isn't how silent image works; it specifically cannot generate/emit light. (But obviously, it can be illuinated by it, and thus - if you assume reflecting light is a thing - reflect it.)

2) The light spell emits light as bright as a torch with no heat at all. So magical sources of light need not emit heat.

[Willowhelm]

1) That isn't how silent image works; it specifically cannot generate/emit light. (But obviously, it can be illuinated by it, and thus - if you assume reflecting light is a thing - reflect it.)

2) The light spell emits light as bright as a torch with no heat at all. So magical sources of light need not emit heat.

I believe you’re agreeing with the point being made. “Real world” Physics does not align with magic/dnd physics.

[Segev]

I believe you’re agreeing with the point being made. “Real world” Physics does not align with magic/dnd physics.

In general, it does at the "classical physics" level. That is, absent magic, things you see in D&D-world will seem to function much like things you see in the real world, as long as you stick to "normal" things. Anything you need a special material for in a chemistry experiment in the real world is not guaranteed to behave the same way in D&D-world. Quantum mechanics probably don't work in D&D. But the physics are "close enough" that everyday life seems the same. Even if dragons can fly.

Whether a magnifying glass can burn things is up to the DM. Whether an illusory one can do the same is also up to the DM, and need not be "yes" even if the real magnifying glass really can. I probably would allow it on the grounds that it's no more powerful than prestidigitation starting a fire, myself, and it aligns with my feeling that images of objects interact with light and vision the same way the real ones would (as a general rule).

[Unoriginal]

1) That isn't how silent image works; it specifically cannot generate/emit light. (But obviously, it can be illuinated by it, and thus - if you assume reflecting light is a thing - reflect it.)

Fair, but if the light the illusion is made off isn't produced by the spell, then it must be the caster is bending the already existing light in order to reflect the right color.

Ex: the caster makes it appears there is a sheet of red paper, but in fact it is just the sunlight that gets bent in a specific pattern so that only a part of the light spectrum is reflected into the viewer's eyes, with the optical nerves registering the stimulus the brain will then translates into "red".

However, an Illusionist is also perfectly capable of creating the Silent Image of a red sheet of paper while in a deep-underground cave with no source of light of any sort. And if the Illusionist has Darkvision, they would see this red sheet of paper in black-and-white.




2) The light spell emits light as bright as a torch with no heat at all. So magical sources of light need not emit heat.

Indeed. Which breaks physics in half


I believe you’re agreeing with the point being made. “Real world” Physics does not align with magic/dnd physics.

Indeed.


In general, it does at the "classical physics" level. That is, absent magic, things you see in D&D-world will seem to function much like things you see in the real world, as long as you stick to "normal" things. Anything you need a special material for in a chemistry experiment in the real world is not guaranteed to behave the same way in D&D-world. Quantum mechanics probably don't work in D&D. But the physics are "close enough" that everyday life seems the same. Even if dragons can fly.

Whether a magnifying glass can burn things is up to the DM. Whether an illusory one can do the same is also up to the DM, and need not be "yes" even if the real magnifying glass really can. I probably would allow it on the grounds that it's no more powerful than prestidigitation starting a fire, myself, and it aligns with my feeling that images of objects interact with light and vision the same way the real ones would (as a general rule).


We've debated and disagreed on this point several times, I think.

The key word is "seems" the same. DnD physics share superficial similarities with real life physics on some obvious places, but digging any deeper than this skin-deep seemingliness reveals that nothing actually works the same in terms of physical mechanics, even if sometime the end results are close enough.

[Segev]

Fair, but if the light the illusion is made off isn't produced by the spell, then it must be the caster is bending the already existing light in order to reflect the right color.

Ex: the caster makes it appears there is a sheet of red paper, but in fact it is just the sunlight that gets bent in a specific pattern so that only a part of the light spectrum is reflected into the viewer's eyes, with the optical nerves registering the stimulus the brain will then translates into "red".

However, an Illusionist is also perfectly capable of creating the Silent Image of a red sheet of paper while in a deep-underground cave with no source of light of any sort. And if the Illusionist has Darkvision, they would see this red sheet of paper in black-and-white.I mean, yes? They create an image of a red sheet of paper. It looks like a red sheet of paper would to anybody who could see a red sheet of paper under the lighting conditions present.


We've debated and disagreed on this point several times, I think.

The key word is "seems" the same. DnD physics share superficial similarities with real life physics on some obvious places, but digging any deeper than this skin-deep seemingliness reveals that nothing actually works the same in terms of physical mechanics, even if sometime the end results are close enough.Generally speaking, they have to be the same at the "easily observed" level. How they work "under the hood" is going to be, well, magical by IRL standards.

[4koboldsinacoat]

Indeed. Which breaks physics in half




An LED can produce as much light as a torch and cause negligible heating of objects.

Illusions in DND seem to work as:

1) The illusion is entirely in the mind if creatures who see it, the light reaches their retinas and they simply misinterpret it unless they make an investigation check.

2) They act as a physical object which absorbs/reflects light, but does not interact with matter or other particles. This doesn't mean they can absorb infinite energy, light strong enough to cause physical damage is modeled in 5e by effects such as the sunbeam spell, which passes through illusions, so you can't use illusions as particle shields or what have you.

The second option does have some problems in the case of putting an illusory box around a torch, as the light level of the surroundings would hinge on whether a creature saw through the illusion, so I personally prefer the first , mental, option.

[Deathtongue]

Deathtongue, I says that not to be a jerk, so I apologize if it comes out like this, but this is 5e. This is not the edition for semi-game-rule-logic semi-real-life-physical-phenomenon shenanigans to obtain results like the Peasant Railgun or other similar concept.
Why not? Is it because it's gamebreaking if taken to obvious extremes? Is it because most players aren't chemists/physicists/etc. and it puts too much control of the narrative in the hands of one or two players? Is it because it's immersion-ruining if wizards are talking about Maxwell Equations or even differential calculus?

That gives us something to talk about. 'It doesn't/shouldn't work because D&D just doesn't work like that' forecloses any discussion.

Okay. Great.

So what if D&D DID work like that? It's not even out-of-genre for it to do so. 'Scientist with real-world knowledge humiliates wizards even when they have actual power' is a trope going at least as far back as A Connecticut Yankee in King Arthur's Court -- why couldn't a PC play Hank Morgan? Or one of those industrialist-scientists in Legend of Korra?

Hell, to ground things more in the D&D idiom: what if you are at a table where you're playing Spelljammer and the premise of the game is that you're a naturally evolved species who had to discover their technology on their own warring against an uplifted species who was gifted technology by a patron they can use, maintain, and replicate but can't further refine?


A player would not announce such a thing, because there is no combination of abilities that would let them build a castle out of solid hematite.
Once you found a sufficient deposit of hematite (literally an easier task than finding an iron mine) you can use Transmute Rock from Xanathar's Guide to Everything to turn it into transportable mud. Apply the hematite-mud to scaffolding. Cast 'Dispel Magic'. You now have a structure of solid hematite without having to pulverize it, debase it, or use other materials to connect the bricks.


In general, it does at the "classical physics" level. That is, absent magic, things you see in D&D-world will seem to function much like things you see in the real world, as long as you stick to "normal" things. Anything you need a special material for in a chemistry experiment in the real world is not guaranteed to behave the same way in D&D-world. Quantum mechanics probably don't work in D&D.
I'm sorry, this is completely incoherent. Quantum mechanics ARE the real world. It's not some special magical dimension that some versions of our reality may or may not have. Newtonian physics cannot work without quantum mechanics to lay down some ground rules. We don't need to know what they all are and we probably never will, but it does need to exist.

You can handwave it away or replace it with some other internal physical law (which I don't recommend, Runequest takes that approach and its setting is incomprehensible) but you can't just say 'it doesn't apply'. You may as well say that hydraulics or friction doesn't apply in D&D. Or gravity for that matter, since terminal velocity is the same in D&D regardless of location.


Absolutely not.

Sunlight is enough to make an object visible, therefore your illusion shouldn't generate more heat than sunlight does. Even if the spell was as inefficient as an ICE / heat engine, 3 times that heat is nothing.
It doesn't need to generate heat (though because certain illusions can create light, they literally have to create heat as well -- though some illusions also explicitly create heat as well!), reflection and focusing can be enough. Otherwise it'd be impossible to light kindling with a magnifying glass.

[Unoriginal]

An LED can produce as much light as a torch and cause negligible heating of objects.

Negligible by which standards?

For example, a sufficiently-advanced heat detector can detect a LED/objects heated by the LED. No heat detector would ever be able to detect a Light spell.

Or you can technically use a magnifying glass and a LED to burn a leaf, but you cannot use a magnifying glass and a Light spell to do the same.

The Light spell demonstrates that real-world physics do not apply.



Illusions in DND seem to work as:

1) The illusion is entirely in the mind if creatures who see it, the light reaches their retinas and they simply misinterpret it unless they make an investigation check.

2) They act as a physical object which absorbs/reflects light, but does not interact with matter or other particles. This doesn't mean they can absorb infinite energy, light strong enough to cause physical damage is modeled in 5e by effects such as the sunbeam spell, which passes through illusions, so you can't use illusions as particle shields or what have you.

The second option does have some problems in the case of putting an illusory box around a torch, as the light level of the surroundings would hinge on whether a creature saw through the illusion, so I personally prefer the first , mental, option.

Illusions which are mental only are explicitly stated as such. Spells like Silent Image are not mental.

[Segev]

I'm sorry, this is completely incoherent.It's quite coherent. There's even a term for it; unfortunately, I don't remember it despite some smart forumite here introducing it to me ... I think last week.


Quantum mechanics ARE the real world. It's not some special magical dimension that some versions of our reality may or may not have. Newtonian physics cannot work without quantum mechanics to lay down some ground rules. We don't need to know what they all are and we probably never will, but it does need to exist.YEs and no. Yes, they're the underlying reality...kind-of. We may be wrong about them in some very fundamental ways; we know that they don't mesh with the other major unseen-but-definitely-our-reality thing: relativity. The resolution of those models is currently one of the holy grails of physics.

Newtonian physics works perfectly well without quantum mechanics. In fact, quantum mechanics proves Newtonian Physics is NOT how the world works; it's just an approximation of how the world works. There are a number of "underlying models" that can reduce at large scale to Newtonian physics as a good approximation.


You can handwave it away or replace it with some other internal physical law (which I don't recommend, Runequest takes that approach and its setting is incomprehensible) but you can't just say 'it doesn't apply'. You may as well say that hydraulics or friction doesn't apply in D&D. Or gravity for that matter, since terminal velocity is the same in D&D regardless of location.Again, false. If we extend Newtonian physics down to small scale, or up to grand scale, we get behaviors that are radically different from those that quantum mechanics predict or that relativity predict, but we don't break "classical scale" anything.

I could write a pulpy sci-fi space adventure that runs on pure Newtonian physics, where there's no relativisitic time dilation and no relativistic shift to velocities that forces relative velocity to gradually asymptotically approach c rather than continuing linearly forever. i.e., we could just keep accelerating a rocket at 9.8 m/s2 forever, and it would eventually be going arbitrarily fast, and time on the space ship and on Earth and at the destination all move at the same speed. This would be a perfectly coherent narrative, and in fact tends to be how most sci-fi is depicted even though time dilations should cause all sorts of odd effects between far-flung star systems.

Similarly, I can have a fantasy setting where Newtonian physics works just fine at the human scale, but the ways it "breaks down" at other scales, or in the presence of other rules/energies/whatever, are very different from how they do on Earth IRL.


It doesn't need to generate heat (though because certain illusions can create light, they literally have to create heat as well -- though some illusions also explicitly create heat as well!), reflection and focusing can be enough. Otherwise it'd be impossible to light kindling with a magnifying glass.The bolded part is either self-contradictory, or is relying on an assumption I am not able to infer properly. Can you please clarify what you mean by it?

The reason kindling lights with a magnifying glass has to do with the kind of energy that light represents. Infrared light agitates matter to produce heat. It is not "heat" by itself. The sun has a LOT of infrared light. Get a light source that lacks the appropriate wavelengths to agitate matter, and you won't get heat.

In D&D magical physics, the reason why a magnifying glass turns light into heat could have something to do with what radiant damage is. Fire and radiant are two different things, though the latter does seem to transform into the former pretty easily.

[Chronos]

You don't have to go to the level of theoretical particle physics to do crazy things with mirrors. Plain ordinary classical optics will do fine. With a set of mirrors, lenses, and other mundane objects that fit into a 5' cube, I could make an image of a window looking out on a vast landscape. Distant trees and even mountains, as viewed through that mirror-window, would look just as they do through a real window looking at a real landscape. Does this mean that a Minor Illusion of that optics-box can do the same thing? Suddenly I'm using a cantrip to make an illusion of an entire kingdom.

Or even simpler, with almost no knowledge of optics required: I want to see around a corner, without poking my head around the corner and exposing myself to whatever might be beyond. Can I make an illusion of a mirror to look around the corner? How about a simple periscope or the like?

Personally, I rule that an illusion can have what appears to be reflections in it, so you can get things like a glint of light off of the edge of an illusory sword, but the reflections aren't faithful enough to act as a mirror. Does this mean that illusions aren't perfect replicas of the things they mimic? Yes. But we already knew that, because it's possible for an Investigation check to reveal an illusion. Maybe imperfect reflections are one of the cues you can (potentially) pick up by investigating.

Another trick: In a D&D world, it's possible to have things, even non-illusory things, that are transparent from one side but opaque from the other (such as the boundary of a Tiny Hut). This, also, is a violation of our world's physics. But given that such things can exist in a D&D world, can you make an illusion of them? An illusion of a wall that's opaque on one side but transparent on the other would have all sorts of uses.

[Deathtongue]

An LED can produce as much light as a torch and cause negligible heating of objects.

Illusions in DND seem to work as:

1) The illusion is entirely in the mind if creatures who see it, the light reaches their retinas and they simply misinterpret it unless they make an investigation check.

2) They act as a physical object which absorbs/reflects light, but does not interact with matter or other particles. This doesn't mean they can absorb infinite energy, light strong enough to cause physical damage is modeled in 5e by effects such as the sunbeam spell, which passes through illusions, so you can't use illusions as particle shields or what have you.If they DON'T absorb infinite energy then where does the remainder go? You still have to explain what happens to the leftover light the illusion can't interact with -- which leads to the four possibilities I outlined earlier.


The second option does have some problems in the case of putting an illusory box around a torch, as the light level of the surroundings would hinge on whether a creature saw through the illusion, so I personally prefer the first , mental, option.The first interpretation doesn't work and can't work. To give two examples why it doesn't:

A) I have a telescope I can see the American flag with when the moon is at its proper rotation. A wizard teleports to the moon in that exact spot and uses Major Image to create a permanent copy of the flag right on top of it. Do I see this second flag through the telescope?

B) Going with the previous example: let's say I'm a high-level wizard, make it to the same spot, then cast Project Image. I then cast Plane Shift twice to put me back on Earth without losing my concentration. I then peer through the Project Image. Do I see the second flag through this method?

The second interpretation is just straight-up ignoring the rules. There are certain illusions where that could hold simply because they foreclose the possibility (such as Minor Illusion), but illusions can specifically create and interact with things like sound waves, heat (i.e. kinetic energy), light, and even particles of sufficient quantity so that you can smell them. And those are just effects we unquestionably call illusions like Major Image.

[4koboldsinacoat]

Negligible by which standards?

For example, a sufficiently-advanced heat detector can detect a LED/objects heated by the LED. No heat detector would ever be able to detect a Light spell.

Or you can technically use a magnifying glass and a LED to burn a leaf, but you cannot use a magnifying glass and a Light spell to do the same.

The Light spell demonstrates that real-world physics do not apply.

There are as many rules in 5th edition for heat transfer via the light spell as there are for heat transfer via nonmagical sources of light, so it's heat transfer is anywhere from none (violates physics) to not enough to bother making a rule for it (does not necessarily violate physics).

Burning a leaf with a magnifying glass and a light spell is possible if your dm says it's possible, though lighting a fire with a flashlight is very difficult and requires a very good lens.

[Unoriginal]

Why not? Is it because it's gamebreaking if taken to obvious extremes? Is it because most players aren't chemists/physicists/etc. and it puts too much control of the narrative in the hands of one or two players? Is it because it's immersion-ruining if wizards are talking about Maxwell Equations or even differential calculus?

Among other things. There is also "the reality of the setting has rules that make such real-life concepts not applicable", to name one of said things.

But yeah, trying to break the game isn't a constructive endeavor, especially when there are many people at the table who'd rather have the game work and are putting in effort to make the game work.


'It doesn't/shouldn't work because D&D just doesn't work like that' forecloses any discussion.

Indeed. That is the goal.



So what if D&D DID work like that? It's not even out-of-genre for it to do so. 'Scientist with real-world knowledge humiliates wizards even when they have actual power' is a trope going at least as far back as A Connecticut Yankee in King Arthur's Court -- why couldn't a PC play Hank Morgan? Or one of those industrialist-scientists in Legend of Korra?

For the same reason that a PC cannot actually be Harry Potter or Gandalf or Luke Skywalker or Korra.

D&D is its own genre, its own setting, with its own rules. Yes, there are technological genuises with mysterious contraptions, and mad scientists, and airships, and exploding barrels. But they do not work like anything in real life, for obvious reasons.

You can make someone who want to humiliate Merlin by blowing up his wizard tower. If you happen to be the D&D world of Oerth, though, real-life explosive would be inert, while on Toril Gong himself would get rid of it.




Hell, to ground things more in the D&D idiom: what if you are at a table where you're playing Spelljammer and the premise of the game is that you're a naturally evolved species who had to discover their technology on their own warring against an uplifted species who was gifted technology by a patron they can use, maintain, and replicate but can't further refine?

Spelljammer technology and the principles behind it are not the same as our world's, so that wouldn't change what I'm talking about.



Once you found a sufficient deposit of hematite (literally an easier task than finding an iron mine) you can use Transmute Rock from Xanathar's Guide to Everything to turn it into transportable mud. Apply the hematite-mud to scaffolding. Cast 'Dispel Magic'. You now have a structure of solid hematite without having to pulverize it, debase it, or use other materials to connect the bricks.

But:

1) Hematite is not a stone, it is an iron oxide. Therefore, it is not affected by Transmute Rock.

2) If we apply real-life physical laws, even if you could liquefy hematite using D&D magic (with an hypothetical Transmute Oxide spell or similar), it would be more than improbable for the castle structure to endure its own weight and the tension created by its shape, as hematite is a brittle mineral with a rating of 5.5–6.5 on the Mohs scale.



I'm sorry, this is completely incoherent. Quantum mechanics ARE the real world. It's not some special magical dimension that some versions of our reality may or may not have. Newtonian physics cannot work without quantum mechanics to lay down some ground rules. We don't need to know what they all are and we probably never will, but it does need to exist.[QUOTE=Deathtongue;25463492]

Exactly. And since D&D world does not follow quantum mechanics, well...

[QUOTE=Deathtongue;25463492]
It doesn't need to generate heat (though because certain illusions can create light, they literally have to create heat as well -- though some illusions also explicitly create heat as well!), reflection and focusing can be enough. Otherwise it'd be impossible to light kindling with a magnifying glass.

Illusions that create light but not heat exist.

[Deathtongue]

You don't have to go to the level of theoretical particle physics to do crazy things with mirrors. Plain ordinary classical optics will do fine. With a set of mirrors, lenses, and other mundane objects that fit into a 5' cube, I could make an image of a window looking out on a vast landscape. Distant trees and even mountains, as viewed through that mirror-window, would look just as they do through a real window looking at a real landscape. Does this mean that a Minor Illusion of that optics-box can do the same thing? Suddenly I'm using a cantrip to make an illusion of an entire kingdom.I mean, I don't see why you wouldn't be able to? It's a very in-genre use of illusions. Or non-illusion spells like Shape Water for instance, once you realize all of the fun things you can do with optics once you have color-changing ice.


Personally, I rule that an illusion can have what appears to be reflections in it, so you can get things like a glint of light off of the edge of an illusory sword, but the reflections aren't faithful enough to act as a mirror. Why not? Are you proposing that mirrors from illusions have a maximum refractive index? If so, among other things that A) won't stop the more fantastical uses of reflected/absorbed light and B) still makes the two-way mirror you describe later a trivial trick. Mostly because the only interpretation of illusions that can't be used to create true two-way mirrors is the 'it's all in your mind' interpretation.

[PhoenixPhyre]

Illusions that create light but not heat exist.

And not just illusions. Continual flame, for example. Which explicitly does not produce heat.


A flame, equivalent in brightness to a torch, springs forth from an object that you touch. The effect looks like a regular flame, but it creates no heat and doesn't use oxygen. A continual flame can be covered or hidden but not smothered or quenched.

Note that it doesn't use oxygen, cannot be quenched, and doesn't run out of fuel. Or even consume the fuel, because it can be cast on an object that cannot burn. And yes, that's an enormous energy conservation violation right there. As well as violating a bunch of other real-world physical laws. Which is ok, because D&D does not use real-world physics in any way. The gross-level observables act similarly (enough so it fades into the background), but the only consistent set of laws that govern D&D worlds are not in any way compatible with the fundamental principles of real-world physics. And not just spells, the entire makeup of the universe is incompatible. When properties like Law and Goodness (or Chaos and Evil) are measurable physical principles and you can have creatures made up of literal Lawful Evilness, and those beings can interact with the normal world without issue, you know the fundamentals are utterly different.

It's convenient that the surface level looks like the surface, non-physicist/chemist/scientist understanding most people have of our world. But don't mistake that (anyone) for the underlying model being the same.

[4koboldsinacoat]

If they DON'T absorb infinite energy then where does the remainder go? You still have to explain what happens to the leftover light the illusion can't interact with -- which leads to the four possibilities I outlined earlier.

The second option does have some problems in the case of putting an illusory box around a torch, as the light level of the surroundings would hinge on whether a creature saw through the illusion, so I personally prefer the first , mental, option.

The first interpretation doesn't work and can't work. To give two examples why it doesn't:

A) I have a telescope I can see the American flag with when the moon is at its proper rotation. A wizard teleports to the moon in that exact spot and uses Major Image to create a permanent copy of the flag right on top of it. Do I see this second flag through the telescope?

B) Going with the previous example: let's say I'm a high-level wizard, make it to the same spot, then cast Project Image. I then cast Plane Shift twice to put me back on Earth without losing my concentration. I then peer through the Project Image. Do I see the second flag through this method?

The second interpretation is just straight-up ignoring the rules. There are certain illusions where that could hold simply because they foreclose the possibility (such as Minor Illusion), but illusions can specifically create and interact with things like sound waves, heat (i.e. kinetic energy), light, and even particles of sufficient quantity so that you can smell them. And those are just effects we unquestionably call illusions like Major Image.

The energy that would be absorbed by an illusion if they interact with light is not infinite, normal objects don't heat dramatically in sunlight, and heat much less in torchlight. An illusion which mimicked the reflective properties of an object would absorb an identical amount of power as the object it is mimicking, which is generally not enough to matter in game.

As for how it would maintain thermal equilibrium, ie where the power they absorb goes, there are many explanations that don't have any in game repercussions

1) Illusions give off black body radiation. This is how normal object stay at constant temperature when exposed to light, and is generally imperceptible.

2) Illusions reflect all light, but they red/blueshift light the object they mimic wouldn't reflect to either the the wavelength they would reflect or nonvisible wavelengths.

3) Illusions planeshifts excess light to the shadow plane/ethereal plane/wherever stuff that is cleaned via prestidigitation goes.

4) Illusions don't emit energy they absorb, this means they won't heat anything that touches them, since that would require releasing energy. The power can be destroyed when the illusion ends (big violation of physics, but so is a lot of magic), or transfered to another plane, as in 3).

As for the purely or partially mental view of illusions, I fail to see why it wouldn't work in your scenario, the illusion would be seen in both cases.

In A), you would see the second flag, because the illusion is magical phenomena that causes anyone who detects the area to hallucinate the sight, smell, sound, etc. of a second flag, as appropriate to how they would detect the area.

In B) the wizard would see the second flag with or without project image for the same reason.

[Segev]

You don't have to go to the level of theoretical particle physics to do crazy things with mirrors. Plain ordinary classical optics will do fine. With a set of mirrors, lenses, and other mundane objects that fit into a 5' cube, I could make an image of a window looking out on a vast landscape. Distant trees and even mountains, as viewed through that mirror-window, would look just as they do through a real window looking at a real landscape. Does this mean that a Minor Illusion of that optics-box can do the same thing? Suddenly I'm using a cantrip to make an illusion of an entire kingdom.Sure, why not? You've made a very detailed diorama. I might require you to give me an Intelligence (something artistic) check for the artistry of composing it and getting it all just right.


Or even simpler, with almost no knowledge of optics required: I want to see around a corner, without poking my head around the corner and exposing myself to whatever might be beyond. Can I make an illusion of a mirror to look around the corner? How about a simple periscope or the like?Absolutely!


Personally, I rule that an illusion can have what appears to be reflections in it, so you can get things like a glint of light off of the edge of an illusory sword, but the reflections aren't faithful enough to act as a mirror. Does this mean that illusions aren't perfect replicas of the things they mimic? Yes. But we already knew that, because it's possible for an Investigation check to reveal an illusion. Maybe imperfect reflections are one of the cues you can (potentially) pick up by investigating.A valid ruling, but one I find lackluster because it starts getting into questions about other kinds of light interaction with the illusion. Remember, it can't create / emit light, so if it isn't acting like an object under illumination, it must somehow be visible without interacting with light at all, which gets into weird questions like whether you can make an illusion of a treasure chest in pitch darkness and have even those without darkvision see it in full color.

So, while you can rule this way, I would not, and would argue against it.


Another trick: In a D&D world, it's possible to have things, even non-illusory things, that are transparent from one side but opaque from the other (such as the boundary of a Tiny Hut). This, also, is a violation of our world's physics. But given that such things can exist in a D&D world, can you make an illusion of them? An illusion of a wall that's opaque on one side but transparent on the other would have all sorts of uses.As long as you're using silent image or other ones that say they can do phenomena, probably!


If they DON'T absorb infinite energy then where does the remainder go? You still have to explain what happens to the leftover light the illusion can't interact with -- which leads to the four possibilities I outlined earlier.Your keyboard does not absorb infinite light IRL. Where does the remainder go?


A) I have a telescope I can see the American flag with when the moon is at its proper rotation. A wizard teleports to the moon in that exact spot and uses Major Image to create a permanent copy of the flag right on top of it. Do I see this second flag through the telescope?I am having trouble following the conversation, but to just answer this question with how I would rule it, of course you see the second flag. You can see the illusion as long as you could see a real thing where it is.


B) Going with the previous example: let's say I'm a high-level wizard, make it to the same spot, then cast Project Image. I then cast Plane Shift twice to put me back on Earth without losing my concentration. I then peer through the Project Image. Do I see the second flag through this method?Again, yes, unless I'm missing something here.

[Deathtongue]

Among other things. There is also "the reality of the setting has rules that make such real-life concepts not applicable", to name one of said things.

But yeah, trying to break the game isn't a constructive endeavor, especially when there are many people at the table who'd rather have the game work and are putting in effort to make the game work.

We don't need to go into game-breaking extremes to show that it's a question that needs to be answered. For example, I want to look down a shaft in a mine that I know has been booby-trapped by kobolds. I am safely around the corner. I then cast Silent Image to create an illusion of a mirror tilted at an angle so I can look down the hall.

What do I see? Why or why not? I'll accept 'because the rules say this', 'because physics say this', 'because genre conventions say this', or even 'because illusions are already gamebreakingly powerful even if you don't deconstruct their physical properties, it's purely an arbitrary game balance decision'. But I'm afraid I cannot accept 'the reality of the setting has rules that make such real-life concepts not applicable' because A) that's lazy and boring and B) what if I am playing in a setting where the DM declares is like reality unless otherwise noted.



Yes, there are technological genuises with mysterious contraptions, and mad scientists, and airships, and exploding barrels. But they do not work like anything in real life, for obvious reasons.No, the reasons are not obvious at all. They're only obvious if you accept the logic of 'what the DM says, is in-game reality'. Which becomes circular when a DM, like most DMs, declare that the setting operates like reality unless otherwise noted.


You can make someone who want to humiliate Merlin by blowing up his wizard tower. If you happen to be the D&D world of Oerth, though, real-life explosive would be inert, while on Toril Gong himself would get rid of it.The setting of Oerth is explicitly nonsense that operates by consensus reality, it is not worth discussing its metaphysics. As far as Toril goes: why would I need to use a chemical explosive to destroy Merlin's tower? Why couldn't I use hydraulic pressure or a steam explosion or an arc flash? Is Gond going to explicitly detect my evil scientist thoughts and intervene to stop me from creating a magnetic explosion with electromagnets while still allowing compasses to work properly? Hell, Toril is also a planet in Spelljammer. And so is the City of Sigil. Will Gond intervene to stop my experiments with dynamite in my contained lab? Or will the Lady of Pain intervene on his behalf?

I mean, you could always just go 'Gond / Lady of Pain / etc. are just an avatar of the DM who will change their personality, memories, motivations, and abilities just to thwart any form of science more complex than a pulley' but... why? What do you GAIN from that interpretation?


But:

1) Hematite is not a stone, it is an iron oxide. Therefore, it is not affected by Transmute Rock.I could attack this assertion through a geological perspective, but first here's some trivia you might be interested in since we're talking about how illusions can break the game: Page 229 of the PHB, Creation Spell: "You can also use this spell to create mineral objects such as stone, crystal, or metal."

5E D&D explicitly defines metals as minerals. The definition of a rock is an object primarily composed of one or more minerals. There exist rocks that are made of one mineral, such as dolomite. Therefore: Transmute Rock works on Hematite.

Your interpretation of what a rock/stone is would make Transmute Rock not work on limestone, the most rockiest rock that ever rocked.

Now, my interpretation of Transmute Rock would, without DM intervention, result in a 40' cube of nonmagical knights finding their armor turned to mud -- to this I say, so? Assuming that it's even a game balance problem at the point of the game where it's available, I as the DM or player can just go 'Transmute Rock only works on stone that wasn't chemically processed in the past 10,000 or whatever years'. Or just go 'lol no'. Certainly beats making up my own geology from scratch and claiming why my interpretation should supersede real-world chemistry, rather than just saying that I'm going to Rule Zero it.


2) If we apply real-life physical laws, even if you could liquefy hematite using D&D magic (with an hypothetical Transmute Oxide spell or similar), it would be more than improbable for the castle structure to endure its own weight and the tension created by its shape, as hematite is a brittle mineral with a rating of 5.5–6.5 on the Mohs scale.Making something like the Tower of Zot or even Storm's End is structurally impossible without some other kind of BS magic, but at this point it's just another engineering problem. Don't even need magic at that point. You can mix in another type of mud of a rock with a lower hardness rating. You can introduce air bubbles to make it weigh less and be less vulnerable to torsion. You could even just use some other kind of support or even scaffolding that absorbs the impact from things like wind and weight. Or you could do something boring like just make your castle walls four stories high instead of twelve. Or your castle is just a giant Dwarf Fortress-style mountain stronghold that has a lot of tunnels and rooms in it.


Exactly. And since D&D world does not follow quantum mechanics, well...
Okay, so why do natural effects at the macrocosmic scale such as optics and electrical circuits work at all in D&D? And if you claim that they don't, what is your reasoning? Are you trying to tell me that mirrors operate like they do in the real world but the photons that compose the light doesn't?

[Unoriginal]

Okay, so why do natural effects at the macrocosmic scale such as optics and electrical circuits work at all in D&D? And if you claim that they don't, what is your reasoning? Are you trying to tell me that mirrors operate like they do in the real world but the photons that compose the light doesn't?

Mirrors operate in a way that is superficially similar to how they work in real life, most of the time. However, 5e-reality-mirrors do not actually operate as real-life mirrors, as evidenced by all the weird things that can happen with them, such as spontaneously transform into portals to other places, spawn evil reflections bound on killing the onlookers, or similar effects.

[Deathtongue]

And not just illusions. Continual flame, for example. Which explicitly does not produce heat.So why should we extrapolate 'Continual Flame somehow produces light without imparting kinetic energy' to 'light from illusions does not create kinetic energy', especially when there are illusions that explicitly create kinetic energy in the form of sound and heat? Why is Continual Flame used as precedent for how illusions should work unless otherwise noted and not, say, Major Image?


Your keyboard does not absorb infinite light IRL. Where does the remainder go?At lower levels of light, it gets reflected so that I can see it. But after a certain point, the light imparts so much kinetic energy that my keyboard catches on fire. Now, I (generally) don't have to worry about my plastic keyboard catching on fire from too much sunlight in the real world... unless it a bunch of mirrors/lens exposed to light themselves were focused on it. We don't even have to get too fantastical. In the real world, light from a sun reflected through a fishbowl or a Christmas tree ornament could set my keyboard on fire.

And as a high-level wizard, I can make happen so long as I understand the science.



Absolutely not.

Sunlight is enough to make an object visible, therefore your illusion shouldn't generate more heat than sunlight does. Even if the spell was as inefficient as an ICE / heat engine, 3 times that heat is nothing.
It doesn't need to generate heat (though because certain illusions can create light, they literally have to create heat as well -- though some illusions also explicitly create heat as well!), reflection and focusing can be enough.


As for how it would maintain thermal equilibrium, ie where the power they absorb goes, there are many explanations that don't have any in game repercussions

They only don't have in-game repercussions if you don't try to extrapolate from them. Which, fair enough, most tables don't want to do that kind of navel-gazing. But if you ARE playing something like Halo or Uplift where the protagonists' superior scientific knowledge of things everyone takes for granted, they're ramifications worth exploring.

1) It's questionable if illusions can even give off black body radiation. If you rule that illusions don't actually absorb light, it's reflected and/or destroyed, because most illusions don't have enough physicality to have, you know, resting mass then what in the illusion is actually giving off black body radiation? Also, what happens to the excess? If the black body radiation is proportional to the incoming light, then you can totally pull a Kefka. If it's destroyed... well... see #3.

2) You say that illusions change the frequency of light? Thanks for giving me a way to destroy the city with my microwave lasers and/or gamma ray bursts. If you're saying that illusions transmute the frequency of light to the visible spectrum without relying on pesky things like harmonics, you just gave me a way to make my entire party immune to electrical, radiant, and arguably thunder damage.

Also, what's the nature of this red/blueshift? Because you may have just given my wizard the ability to time travel with a 1st-level spell if you're using the 'the light just becomes this frequency'. More of the 'I am the kind of Batman Wizard that Batman Wizards fear, and they don't fear actual gods' kind of time travel than the gateway to another world kind of time travel.

3) That doesn't really meaningfully hinder our Hank Morgan Wizard. It just requires him to take more time to find out where the energy goes and why it goes that way. And if the DM rules that the kinetic energy is just dispersed evenly throughout the Shadow Plane's atmosphere, you just gave me a way to turn the Shadow Plane into Venus and/or a way to kill stars with no one noticing. Depending on if you're ruling if the Shadow Plane is ACTUALLY infinite or if it's more like one of those one-biome planets we see in Star Trek. This is true even if you rule that the energy doesn't go anywhere, it just destroys the excess above a certain level.

4) In addition to the problems posed by 3), if illusions don't emit energy they absorb, then how does someone see them at all?

[Deathtongue]

Mirrors operate in a way that is superficially similar to how they work in real life, most of the time. However, 5e-reality-mirrors do not actually operate as real-life mirrors, as evidenced by all the weird things that can happen with them, such as spontaneously transform into portals to other places, spawn evil reflections bound on killing the onlookers, or similar effects.Those are exceptions brought about explicitly by the rules, though. It's like claiming that there's no standard, nonmagical way wave propagation works in D&D because the Silence spell exists.

[PhoenixPhyre]

So why should we extrapolate 'Continual Flame somehow produces light without imparting kinetic energy' to 'light from illusions does not create kinetic energy', especially when there are illusions that explicitly create kinetic energy in the form of sound and heat? Why is Continual Flame used as precedent for how illusions should work unless otherwise noted and not, say, Major Image?


I'm not. I'm stating that the proposition "D&D physical law works like real-world physical law in its details except where explicitly overridden" cannot be true. It's flat false. So any kind of reasoning from real-world physics beyond the very most surface (and even then it's sketchy) fails on its face and is invalid.

And further, you can't reason from a specific rule. You can't extrapolate "how illusions work" from any other spell. No matter what. Each spell stands alone unless it specifically and explicitly calls out to another spell or absolutely requires another spell to function, and then only interacts to the minimum degree necessary.

Major image tells you everything about major image that's not contained in the general rules for spells...and nothing about any other spell (except as noted above). It teaches you nothing about minor image or silent image or any other illusion. Illusions, taken as a whole, have no general rules other than those common to all spells. Note: this is not 3e, where category tags (creature types/subtypes, spell schools, etc) had independent mechanical weight. In 5e, they're just empty tags. Spells (or creatures) that use them inherit no mechanical properties from those tags whatsoever--they exist solely to facilitate interaction with other mechanical elements that reference things by tag.

[JackPhoenix]

So why should we extrapolate 'Continual Flame somehow produces light without imparting kinetic energy' to 'light from illusions does not create kinetic energy', especially when there are illusions that explicitly create kinetic energy in the form of sound and heat? Why is Continual Flame used as precedent for how illusions should work unless otherwise noted and not, say, Major Image?

At lower levels of light, it gets reflected so that I can see it. But after a certain point, the light imparts so much kinetic energy that my keyboard catches on fire. Now, I (generally) don't have to worry about my plastic keyboard catching on fire from too much sunlight in the real world... unless it a bunch of mirrors/lens exposed to light themselves were focused on it. We don't even have to get too fantastical. In the real world, light from a sun reflected through a fishbowl or a Christmas tree ornament could set my keyboard on fire.

What's this "kinetic energy" you speak of? I don't see it anywhere in the books. Is it in any way related to positive or negative energy? Or perhaps cold energy, which is a thing instead of a lack of a thing in D&D?

[PhoenixPhyre]

What's this "kinetic energy" you speak of? I don't see it anywhere in the books. Is it in any way related to positive or negative energy? Or perhaps cold energy, which is a thing instead of a lack of a thing in D&D?

This.

If you interpret anything in D&D using the models and theories of modern science, catgirls die horrible deaths. Ok, really what happens is you get incoherent, inconsistent nonsense. The whole system breaks down because D&D itself, at its core assumptions, is incompatible with modern science.

It actually fits relatively well if you take about a 12th century European alchemist/"natural philosopher" mindset. Pre-Newton, so Aristotelean mechanics for physics, alchemy for chemistry, and assorted weirdness for biology. And then beat your brain with an "it doesn't work the way you think it does" stick for a while, especially if your natural mindset is more attuned to modern science.

[greenstone]

For example, I want to look down a shaft in a mine that I know has been booby-trapped by kobolds. I am safely around the corner. I then cast Silent Image to create an illusion of a mirror tilted at an angle so I can look down the hall.

What do I see? Why or why not?

I believe that an illusion is fundamentally the same as a painting or sculpture. The illusionist produces all the shapes and colours and smells and behaviour.

You can't include something in an illusion that you don't know. If you have no idea what a wurtzlefrog is then you can't create an illusion of it, just the same as you can't create a painting of it.

So, in your mirror, you would see whatever you put in the mirror. :-)

It certainly won't be what's actually in the shaft, because you don't know what's in the shaft.

[Willowhelm]

I don't think 'physics not covered explicitly by the rules are not in play unless the DM says so' is an acceptable answer. It's lazy and boring.

Just to go back to the original thing here rather than all the random side tracks about different physical interactions.

I think you're missing the point here. It isn't, as you say 'physics not covered explicitly by the rules are not in play unless the DM says so'

It is that the behaviour covered explicitly by the rules actively prevents the possibility of physics working "as it should". (Even without magic). The rules are not a simulation.

Eg. Gravity, forces, and acceleration don't work like they should. You fall at terminal velocity instantly? Or you fall any vertical distance in one round? There's a maximum damage an object will do, even if it falls from orbit?! And a PC can survive?!

Light doesn't work as it should. A candle outside of it's radius of light is invisible. It's brightness doesn't drop of proportionally to the cube of the distance. It just goes Bright, low, none with hard boundaries. (See the unending threads about different ways to adjust and interpret the darkness rules). See the ridiculously long thread about create bonfire (https://forums.giantitp.com/showthread.php?645419-Create-Bonfire-does-it-produce-light-Heat)!?

Space isn't even euclidian! (5ft squares with diagonals costing the same movement)

You can draw and fire 20 arrows at 20 different targets in 6 seconds. (I think that's the right ballpark, i haven't checked the current optimized number of attacks). You can run at insane speeds but also only travel 20(ish) miles a day. How does that work?

If you want a grand unified theory of how dnd physics works then you will see that it looks nothing like "real world" physics.

Bring in magic and it just gets even dafter.

How does time stop even work? It stops creatures but not objects? Everywhere? In what frame of reference? Whaaaa?

Sure... that's time stop. The problem (as this thread demonstrates) is that that same utter brokenness is present in every facet of dnd if you just start extrapolating from what you're presented. Just about every cantrip would fundamentally change what we know about physics if it existed in the real world.

It's fine to fall back to how things "really" work when you're filling in the gaps in a game and trying to make a reasonable ruling as a DM. (Although some might call that lazy and boring).

When you try to take a description of something in dnd and extrapolate it based on real world physics... you're playing a losing game. The two things don't actually mix. There's no foundation to build on.

Do you want to find every place where dnd rules explicitly break real world physics? There are too many! Search this forum for "physics" and you've got days and days of reading material with threads just like this.

So what do you want this thread to be about? The question of the OP has been asked and answered.

[Segev]

In the real world, light from a sun reflected through a fishbowl or a Christmas tree ornament could set my keyboard on fire.

And as a high-level wizard, I can make happen so long as I understand the science.

You can use prestidigitation to create a small fire, too. I don't think being able to do so with minor illusion and the sun is going to be a problem.

[JackPhoenix]

Space isn't even euclidian! (5ft squares with diagonals costing the same movement)

Eh, I think this one gets a pass. DMG aknowledges it's inaccurate, but done for simplicity. "The Player's Handbook presents a simple method for counting movement and measuring range on a grid: count every square as 5 feet, even if you're moving diagonally. Though this is fast in play, it breaks the laws of geometry and is inaccurate over long distances."
Also, playing on a grid isn't even the default assumption.

[bid]

Unless I'm mistaken, it is more complicated like that.

A real object is made visible by absorbing the light of the sunlight and reflecting a percentage of the light spectrum.

To project the same percentage of the light spectrum, however, results in a a lot more heat than what the reflected light of the sun would.

Now I'm not saying it should do tons of damage, but it still should be something hot enough to hurt.

I could be mistaken, however.
Take an apple, put it in the shade. Notice it's red enough. Notice it's somewhat cold.
Whatever physical effect happens on the skin of the apple, magic can replicate just as well.

A LED screen is hot because it works by stopping the "wrong" color from leaving and the whole backlight is not 100% efficient.


If they DON'T absorb infinite energy then where does the remainder go? You still have to explain what happens to the leftover light the illusion can't interact with -- which leads to the four possibilities I outlined earlier.
A wall doesn't "absorb infinite energy" but we know "where the remainder goes."


The reason kindling lights with a magnifying glass has to do with the kind of energy that light represents. Infrared light agitates matter to produce heat. It is not "heat" by itself. The sun has a LOT of infrared light. Get a light source that lacks the appropriate wavelengths to agitate matter, and you won't get heat.
Actually, it's temperature-based. No matter how strong your magnifying glass is, you cannot use moonlight to start a fire (https://what-if.xkcd.com/145/).


I understand playing heroic deeds doesn't need more than real-world common sense because anything else is magic. I shoudn't be disappointed at how this thread is based on fantasy physics.
But when I see people pretending some PhD can macgyver his way to build a railgun cannon, I can't stop thinking that no self-respecting physics major would believe Silent Image can melt steel better than jet fuel.:smallyuk:

[4koboldsinacoat]

1) It's questionable if illusions can even give off black body radiation. If you rule that illusions don't actually absorb light, it's reflected and/or destroyed, because most illusions don't have enough physicality to have, you know, resting mass then what in the illusion is actually giving off black body radiation? Also, what happens to the excess? If the black body radiation is proportional to the incoming light, then you can totally pull a Kefka. If it's destroyed... well... see #3.

2) You say that illusions change the frequency of light? Thanks for giving me a way to destroy the city with my microwave lasers and/or gamma ray bursts. If you're saying that illusions transmute the frequency of light to the visible spectrum without relying on pesky things like harmonics, you just gave me a way to make my entire party immune to electrical, radiant, and arguably thunder damage.

Also, what's the nature of this red/blueshift? Because you may have just given my wizard the ability to time travel with a 1st-level spell if you're using the 'the light just becomes this frequency'. More of the 'I am the kind of Batman Wizard that Batman Wizards fear, and they don't fear actual gods' kind of time travel than the gateway to another world kind of time travel.

3) That doesn't really meaningfully hinder our Hank Morgan Wizard. It just requires him to take more time to find out where the energy goes and why it goes that way. And if the DM rules that the kinetic energy is just dispersed evenly throughout the Shadow Plane's atmosphere, you just gave me a way to turn the Shadow Plane into Venus and/or a way to kill stars with no one noticing. Depending on if you're ruling if the Shadow Plane is ACTUALLY infinite or if it's more like one of those one-biome planets we see in Star Trek. This is true even if you rule that the energy doesn't go anywhere, it just destroys the excess above a certain level.

4) In addition to the problems posed by 3), if illusions don't emit energy they absorb, then how does someone see them at all?


1) You cannot destroy a city with the energy absorbed by an illusion, a 10 ft cube silent image will absorb at most the light energy that would pass through that cube. That isn't nearly enough energy to destroy a city unless the light is strong enough to do so already. As for how an illusion would give off black body radiation, if it can reflect light, there is no reason to contain reflected light to the visible spectrum.

2) Again, there isn't enough energy passing through an illusion to destroy a city, and blueshifting the light that passes through it won't change that. You would get a dental x ray at most. Additionally, the ability to change the frequency of light won't let you time travel.

3) The energy absorbed by a well lit illusion is again, bounded by the amount of light passing through the illusion. This means that the shadow plane can survive casting an illusion about aswell as it can survive a lot torch, which it presumably can. As for star killing, the illusion isn't absorbing energy the star isn't already emitting, so it will not affect the stars lifetime.

4) If an illusion only reflects/reemits relevant visible light and absorbs the rest without a mechanism to reemit it, then it would be visible but otherwise unable to transfer energy

[Witty Username]

I don't think 'physics not covered explicitly by the rules are not in play unless the DM says so' is an acceptable answer. It's lazy and boring.

That is not my meaning. What I mean is the rules of illusions are incompatible with physics in basic ways.

Take an illusion of a black window curtain, in the real world this would either block all light or be partially transparent, Illusions by the rules are both at the same time. In the solar sail example, assuming the illusion is reflective, this would mean to individuals that believe the illusion the vessel would move faster than individuals looking at the same vessel at the same time (assuming you found a way for an illusion to impart force, a whole other thing). Can by real world physics, can an object have two different velocities in the same relative context, or be in two places at once? Kinda, Quantum mechanics has some principles that can allow this, but not often to the scale or reliability of illusions like Silent Image.

Which is the rub, can an illusion reflect light? The answer is Yes and No, not even necessarily it depends, but Yes and No at the same time if we are dealing with multiple observers. This is a very difficult state to resolve in real world physics already without the mental state of the observer being taken in as a factor.

It is not about real world physics not being covered by the rules, but the rules given do not allow real world physics to function.

[Mastikator]

I don’t think the logic of magic existing means physics doesn’t exist hold up. Animate object still makes perpetual motion machines.

1) Magic works according to grammar, not physics.
2) Completely independently of magic, D&D does not have Newtonian physics, it works on Aristotelian physics. IE there are 4 elements, no such thing as atoms, heavy objects fall faster, darkness is not the absence of light but rather a real thing that you can attack with magic missile. :smallamused:

[DeadMech]

2) You say that illusions change the frequency of light? Thanks for giving me a way to destroy the city with my microwave lasers and/or gamma ray bursts. If you're saying that illusions transmute the frequency of light to the visible spectrum without relying on pesky things like harmonics, you just gave me a way to make my entire party immune to electrical, radiant, and arguably thunder damage.

Yeah about the time anyone says that at my table they will be told firmly no. And that if they continue bringing the subject up they will find themselves magically transported to a reality where they are no longer a part of my table.