# Everything is normally light. It is dark waves that travel and cause darkness - how?

In an alternative universe with alternative physics; light, by default, is everywhere at all times. Rays of 'dark' from a dark sun, are initially the only way to dispel the light. This provides day and night on a planet orbiting the dark sun.

When the 'sun' is in the sky, it radiates dark and produces night. When the 'sun' sets, day reappears and it is possible to see.

Eventually some inhabitants of this universe learn to use technology to make sources of dark. This means that they can sleep even if the sun is not visible, by creating dark in their bedroom for example.

Question

How can I explain a physics that lets you see by default when there is no radiation, but where darkness is caused by rays of dark emanating from a star?

• An important detail of this question that has been ignored by respondents thus far (probably because it's impossible) is the specification of "no radiation". Sight, as a sense, is dependent on radiation (or something analogous, like sound) bouncing off things and then being interpreted by the sense. If radiation isn't involved, it's not, meaningfully, "sight". Jan 9 at 22:04
• What is the meaning of the word "light" in this world? It obviously does not mean "electromagnetic radiation". And how can you reconcile the requirement for no radiation, when the very next sentence says that rays of dark are emanating from a star? (For fun: the English word "ray" ultimately comes from the Latin word "radius", which is of course the base of the word "radiation". In Roman Latin, the word "radiatio" meant "glittering, shining, luster".) Jan 9 at 22:45
• light, by default, is everywhere - how much? enough to barely see? enough to see well? enough to blind everyone? enough to cook everyone? enough to immediatelly turn everything into searing plasma? it's an interesting idea, but it won't work in any physics system that's comparable to ours. i'm afraid you'll have to use handwavium. (also: a species evolving in such a world would neccessarily have the ability to sleep even without darkness) Jan 10 at 6:30
• A lot of the answers here seem convinced that no physics that deviates from our physics could be internally consistent. The history of science shows us that there are plenty of internally consistent alternatives that we don't live in. To take an easy example; MSSM. Indeed, if there was only one internally consistent physics, we wouldn't need particle colliders at all, we could all just go do the maths. Jan 10 at 9:57
• You could sit in the bright spot that is the "shade" of a large tree (no matter the time of day). With that in mind, can people see that shade-light from afar, or does the "darkness" from the dark-sun eat up the light in transit? Similarly, do darksunglasses allow you to filter out the "dark" and see everything? Jan 10 at 14:00

In your universe eyes work by emitting a spectral band of sub-atomic particles that interact with and or bounce off objects and return to the eye where they are detected. The 'sun' emits an intense flux of anti-particles so when it is in the sky, the particles and anti-particles annihalate, nothing gets back to the eye and you can't see anything.

Artificial 'lights' are just artificial sources of those same anti-particles.

• I like the idea of eyes emitting light. That's definitely one possibility Jan 9 at 23:54
• Interestingly enough, there's this (obsolete, ancient) explanation of vision. en.wikipedia.org/wiki/Emission_theory_(vision) Jan 10 at 5:58
• This would mean that if a lot of creatures are looking at something, this thing is going to be very bright. Jan 10 at 18:30
• The problem with the anti-particle explanation is that objects would quickly "boil away" as antiparticles annihilated with regular particles, so the universe wouldn't exist. Jan 10 at 20:05
• Neutrinos and anti-neutrinos: Just make them interact more (and more like photons would). Their mass is very light, such that blue-energy neutrinos will be travelling at 90+% of the speed of light and way too light to annihilate electrons of baryons. The sun emits both kinds, and it's "light" washes out everything making it like being in very thick fog and you can't see anything, not actually "black" though. Jan 10 at 23:23

This may be cheating.

It's not that the sun produces darkness, but rather the people evolved for low-light environments and protect their delicate eyes from overexposure to radiation with a transparent film speckled with rapidly-expanding melanocytes. When any point on their field of vision is exposed to bright light, that point's corresponding melanocyte expands, darkening it.

We have something similar, but less efficient - our pupils constrict in response to light, darkening our entire field of vision at once to protect our retinas. This is why it is harder to see in a bright glare, even if we are not looking directly at the light itself. This species has it better - they perceive the light itself as "rays of darkness", but they can see everything else just fine.

• Not cheating. OP likely wants different mechanics just for visible light, not for all radiation (which would have much broader consequences). Jan 10 at 13:01
• Welders use auto-darkening helmets (or goggles) for similar protection. Jan 10 at 20:52
• I had the same understanding. It sounds like eyes that can only see in darkness (very low light) and become blinded in lihht. From their perspective darkness and light would have the opposite roles. Shade would be where one has to go not leave to read something in a "better lighting". Jan 10 at 21:22

Luminiferous Aether!

https://en.wikipedia.org/wiki/Luminiferous_aether

Of course this conception would be different than the 19th century version. In your world the Aether occupies non-solid spaces and to a lesser degree liquid spaces. Aether emits visible spectrum radiation.

The rays emitted from the sun alter the emanations from the Aether such that its emissions are no longer visible light. Perhaps they push them more energetically into the ultraviolet, or less energetically into the infrared. I lke the latter because nights would be warm and dark. Either way, Aether emanations are no longer visible to beings like ourselves.

Persons with an artificial radiant source similar to that emitted by the star can also locally push aether emissions to the invisible.

• I was going to say vacuum energy but otherwise the same thing. Jan 10 at 15:40

## You don't

Light, and its nature, are deeply and inextricably linked to the physical laws that make our reality what it is. The four fundamental forces simply don't work the same way if the default is light everywhere. Also, light carries energy (which is why using a lens to focus it can light things on fire). Everything constantly being illuminated all the time means a tremendous output of free energy. But that's the least of your problems, because radiation not working the same implies chemistry and nuclear physics doesn't work the same either.

There is probably no such thing as 'planets' or 'stars' or 'people' or even 'atoms' in your universe.

That's not to say you can't tell a story in a world where this is true. But it does mean you can't really make it be hard sci-fi. Your best bet is to gloss over it with as little explanation as possible.

• Yes but I did specify "In an alternative universe with alternative physics". We don't need to have the same fundamental forces. Maybe, instead of dark matter, this universe has light matter which always emits light except in the presence of a dark-emitting star. That is what I'm hoping to achieve Jan 9 at 23:48
• There are degrees between hard sci-fi and the complete lack of internal consistency of magical realism. It's not unreasonable to want to find a pseudo-physics that will keep the narrative flowing, even if it has to be a bit fast and loose to account for the fact that this is so far from our own physics that it's hard to second guess how it will behave. Jan 10 at 9:51
• @chasly-supportsMonica - If you're going with radically different physics then you can have them behave whichever way you want. There's nothing "realistic" about it to begin with, so why try to mimic our world? Heck, you can even make maths behave differently, because the fundamental laws and axioms of logics are also kinda... arbitrary. You can totally make working systems with different laws. Just make sure to think a bit about the implications of what you're laying down, so that you don't run into any glaringly obvious contradictions. The nuances can always be handwaved away. Jan 10 at 10:46
• @Vilx- I understand different physics, but how can you make maths behave differently? Jan 10 at 13:47
• This does not answer the question, nor does it provide a suitable frame challenge. The OP has stated that in another universe, sight may happen everywhere except where some radiation reaches. If you can't answer how that can happen, you haven't answered at all. Jan 10 at 14:17

Interesting premise. I don't see anyway to explain a visible light spectrum without radiation. Perhaps you can have both though. If in your alternate universe you have photons emitting from some other source, like a Higgs field for light, so that it is emanating everywhere constantly, you could have "dark" created by additional radiation that is perfectly out of phase creating phase cancellation.

I'll use audio as an example (I'm a hobbyist audio engineer). If you have two sine waves at the same frequency and amplitude, you'll hear them at whatever frequency they happen to be. But line up perfectly out of phase, you literally cannot hear either.

This could also lead to some other odd effects, for instance you could produce an out of phase light at, say 600nm and cancel out your ability to see green.

• > This could also lead to some other odd effects, for instance you could produce an out of phase light at, say 600nm and cancel out your ability to see green. That could be a very interesting tactic for hiding things subtly... make a green thing, make it so people can't see green in that space, and disguise the fact you're doing so.... Could have some interesting results if you use a color most people won't bring with them somehow to notice. Jan 10 at 18:05
• @coppereyecat note that not being able to see something isn't the same as making it invisible (let alone see-through). but i'm also not sure how this "out-of-phase light cancelling all green" would work - it's not like everything's equally green, so you will be overcompensating in some parts. which means no more complete destructive interference... Jan 10 at 23:30
• @somebody True. I wasn't thinking in terms of "oh gee we can't see this object because it's green", but maybe in terms of a tool used to conceal a secret door or something like that. Alternatively, a secret message that couldn't be read as long as the cancelling effect was present. Something like that. Jan 11 at 16:19

In our universe, every object constantly emits electromagnetic radiation (eg light) according to its temperature. This is called black-body radiation. When an object is very hot, for example it is lava or has just come out of a furnace, it glows. That is black-body radiation at work. Your body is warm and therefore emits EM radiation at a frequency below that at which humans can see, but infra-red equipment can see it, and that's how night-vision goggles can work. Low-temperature objects emit low-frequency red light, ("red-hot") and as they get hotter they also emit the higher frequencies until finally they emit all visible frequencies, and therefore glow white-hot.

So anyway, in your universe either the constants of physics are different such that everything glows in visible light, or the people can see different frequencies such that everything glows in visible light, unless the object is very cold.

The stars are a source of cold, therefore putting out the lights. The people who have developed dark-making technologies have actually just developed cold-making technologies.

Instead of emitting energy like in our universe, the stars in your universe emit anti-energy that cancels out energy, thereby making things cold. But then if the stars are constantly sucking out all the energy, how is there any left? In our universe things cool because they dissipate energy. Energy can never increase due to conservation of energy. In your universe, energy can never decrease due to anti-conservation of energy. Anti-energy causes energy to build, therefore thank goodness for the stars that cool things once per planet's turn.

• Or more likely, stars warm thing and push them out of the visible spectrum the other way. The problem is, they would fade not vanish - black body radiation is a curve not a point, there will always be some radiation at any given lower frequencies. To an extent that hits cold too, but not extreme cold Jan 10 at 14:39

In a universe with "alternative physics" you are seeking to explain the science which underpin this behaviour. But as this science is fictional, it will defy any rational explanation unless you were to set the action within OUR universe, but with some special conditions which might make it illusory - such as how the planet's inhabitants' eyes have evolved. The song title "Blinded by the Light" comes to mind.

A real example of this is how ancient civilizations once believed that the Earth was at the centre of the universe and that the sun would orbit the earth. This model worked as far as their limited ancient observations could tell, but of course this was later revealed by science to be false. Those who made the earliest claims that the model was wrong, such as Copernicus and Gallileo were declared heretics and this, of itself, could make the basis of a good story.

'Science Fiction' is mainly about the narrative, not the physics, so you primarily need to consider how this "alternative physics" directs your narrative, rather than how your narrative is going to explain the alternative physics.

By way of example, I would refer you to the plot for the Movie "Upside Down" where two estranged lovers live on two conjoined worlds with opposing gravitational fields. https://www.imdb.com/title/tt1374992/plotsummary

The physics is clearly impossible in our universe, but the author concentrates on the seemingly impossible odds that face these two lovers which are consequent upon this gravitational anomaly, rather than trying to explain how the physics works. The opposing gravity is used as an allegory for the political and cultural differences between the two worlds, of which one is a world of wealth and the other is a world of poverty. Their love is an extension of the "forbidden love" story which breaks the laws of man... and the laws of science. This Sci-Fi storyline echoes other great love stories of forbidden love, such as Romeo and Juliet / West Side Story, Cleopatra and Mark Anthony or Wuthering Heights, and simply accepts that the physics exists, without too much explanation.

This odd universe affords some opportunities for comic relief where the main protagonist attempts to overcome the physics by using anti-gravity "weights" tied to his person and in his pockets to stop him 'floating away', in order to reunite with his love. Again, not too much explanation is required, and the audience readily accepts that this is simply how the universe works for the plot to progress.

I include these examples to help you think about your universe where the traditional forces of energy appear to be switched. Where a rational explanation appears to be beyond our understanding, you must decide whether it is simply illusory, or if it is real, how does the physics drive your narrative? What are the particular difficulties that the planet's inhabitants will face because of this? Does the arrow of time always flow forwards? Does gravity work in the same direction as ours? How will the protagonists live in this environment? Do they heretically oppose it, or do they discover something more fundamental at work? Is there a conspiracy to hide the "truth"? You don't need to answer them here, but these questions are all about character and story development rather than the "alternative physics".

You might also check out the plot for "Dark City", a world with no sun. https://en.wikipedia.org/wiki/Dark_City_(1998_film)

This cannot be done using conventional physics. If you are willing to bend the laws of physics until they snap, there are some options.

# A black hole sun is easy

The real universe is filled with "light", but it is so dark and redshifted that only special instruments can see it: the cosmic background radiation. Perhaps our universe is younger than our real universe, so it is smaller and the radiation shines brighter, and creatures evolved to see by the light of the background radiation.

Moreover, the background radiation in our fantasy universe does not consist of photons, but another elemental particle that could only be formed in the extreme conditions of the big bang.

Stars are perfectly normal, and emit perfectly normal photons, but our creatures cannot see photons. They evolved to see only the special particle in the background radiation, perhaps because they emerged on the back side of a tidally locked planet or before their sun ignited. To them, the sun is black, casting a shadow but generating heat. It would look like a "black hole sun", but would not be an effective source of night.

# Antiphotons (sort of)

If we want more effective darkness, we need two further changes to the laws of physics: the exotic particle that makes up the background radiation is actually an antiphoton, and regular photons only interact with antimatter while antiphotons only interact with regular matter. This has no parallels in real life, but real life has stranger phenomena, such as particles that could be interpreted to look different when you rotate them 360 degrees. "It's quantum physics" could be a valid handwave here.

(Note that real world antiparticles are regular particles with an opposite electric charge and opposite quarks, and photons have neither, so antiphotons either don't exist or are technically just photons. Perhaps our fantasy "photons" are baryonic particles instead?)

Changing the background radiation to antiphotons allows the sunlight, consisting of invisible photons, to annihilate the cosmic background radiation, consisting of visible antiphotons, creating darkness and emitting neutrinos or other non-interacting particles. Any excess photons from the sun will pass through the planet without interacting with it, explaining why the sun does not generate heat and why the species did not evolve to see sunlight.

The sun will not cast "rays" of darkness, but will extinguish the light across the entire sky. On the opposite side of the sun, there is a large glowing circle that does not fully cover its half of the skydome and is brightest in its center, fading to darkness along the edges. The brightest time of the day would be when the sun is directly underneath and the glow is directly overhead, but at that time the horizon would be dark.

And every once in a great while, the sun could reflect off a more distant planet and create an "eclipse".

The brightness of the sun matters. The sun is always going to be brighter than the background radiation and thus fill space with more particles (otherwise it would overheat and blow up) but particles are small and the incoming antiphotons may survive the flak barrage of photons from the sun and make it to the observer. There is a balance where few antiphotons from the direction of the sun survive but most antiphotons from the opposite direction survive, but it would only generate pleasing results on a narrow band of planets, with most others being eternally bright or fully dark.

As a side effect, because the photons emitted during fusion now no longer interact with solar matter, the sun will be slightly smaller, slightly hotter, have a slightly shorter lifespan, lack a measurable solar wind and be slightly more likely to implode into a black hole at the end of its lifespan.

• I really like the idea of visible cosmic background radiation and the star providing only non-visible heat. I'm going to think this through and then maybe accept this answer and/or make a new question to build on it and check the feasibility. Jan 10 at 13:19

Similar to echolocation/radar, your inhabitants emit light and perceive it as it bounces back from objects. Just like echolocation (or even picking out auditory speech) requires relatively quiet to be effective, people cannot properly see with so much visual noise. In fact, when the Sun is up their brains perceive nothing with so much background "noise".

How can I explain a physics that lets you see by default when there is no radiation, but where darkness is caused by rays of dark emanating from a star?

You need to think about more than physics. The terms "light" and "dark" confuse this issue a bit. Those terms were invented long before we understood how light actually worked. They're treated as opposites, but they're two completely different types of thing (one's a physical entity and the other is a description of how much sensory input the speaker is receiving). Replace those with the more-accurate terms "I can see" and "I can't see" and more solutions become apparent. The concepts of light and dark have more to do with biology than with physics.

A universe naturally filled with light is easy enough to handwave away. However, your "dark" sun also radiates light. It's not the same light, though. The sun's light and the universe's background light are completely different wavelengths. Your sun is called a "dark sun" because your species' eyes cannot see the particular color of light that your star emits (similar to how our eyes can't see into the infrared or ultraviolet). You know the sun is there because it obscures a section of the sky, but it looks like a big blank spot.

Your eyes can't consciously see your sun's light but they're extremely sensitive to it. Your brain interprets this wavelength of light as a "glow". Your eyes are more sensitive to the glow than they are to the normal background light, so the glow overwhelms your senses and will drown out the useful light. You don't perceive the glow directly, but by overwhelming the receptors in your eyes it attenuates the apparent brightness of visible light, similar to how stars disappear during the day. When the sun's light is bright enough, the glow will completely saturate your vision and you won't be able to detect any of the useful background light. You're completely unable to see anything at this point, and you call this state "darkness".

This state of "darkness" isn't a complete absence of light, it's merely the inability to perceive any light in the range our eyes happened to be tuned for. Some might say that's being a bit of a language lawyer, but it's literally the definition of what we humans define as "dark". Even in the dark, there's still light present. What we perceive as "dark" may not be dark at all to something like a mantis shrimp whose eyes are built differently.

Eventually some inhabitants of this universe learn to use technology to make sources of dark. This means that they can sleep even if the sun is not visible, by creating dark in their bedroom for example.

Man-made sources of "darkness" are easy. Build a light source that generates the same wavelength of light as your sun. Your example use case seems wildly impractical, though. A simple eye mask would do the same thing.

You could make it work if you willing to add a fictional extra property to particles in physics. When matter and antimatter collide they annihilate each other and release pure energy (as photons). This happens because matter and anti-matter have opposite charge.

Light is made of photons however and photons have a charge of zero. Because photons have a charge of zero (and negative zero is still zero) photons cannot be annihilated in the same way that matter and antimatter do.

Seeing as existence should have a net energy sum of zero anyway, and there are several mathematical physics equations which suggest the existence of negative energy, and matter/anti-matter annihilation doesn't decrease energy (just splits it into photons), you could claim there is an additional property of particles (lets call it phase) which dictates whether a particle has positive or negative energy.

Your dark stars emit photons with negative energy for some reason (so negative phase photons) and every time a negative phase photon hits a normal positive phase photon they erase each other - completely eliminating the energy of both photons. This means that your dark stars will erase normal light.

With the logic above, make all matter on your world radioactive enough to emit light. When the sun is up the amount of negative phase photons it emits overwhelms the amount of light released by your radioactive matter, when the sun is down there are too few negative phase photons to suppress the illumination of your radioactive matter. Similarly, if you underground and thus in an area shielded from the negative phase photons, the area will be lit up even during the day.

Measure of Darkness

Negative cancels positive (e.g. electric charges, amplitudes of waves etc.).

In our universe, light has positive lumens and darkness means 0 lumen. In your universe, maybe there is a light with negative lumens. Your sun or other devices emit a light with negative lumens which cancels the light of positive lumens.

The idea is that if darkness is emitted, there should be some measure of darkness as well.

Also there should be sensors to detect and measure darkness.

• Negative lumens would be like negative miles. If you go visit a friend one mile away, you can walk one mile there and one mile back... but you still walked two miles. Jan 10 at 13:04
• If you carry something one mile up, it will gain potential energy. If you bring it one mile back to earth, its potential energy will be Zero. May be you are very much tired and exhausted all your energy, but potential energy will be Zero. In this scenario, darkness is cancelling light. There should some kind of measurement of darkness. Jan 10 at 14:37
• @imtaar note that potential energy is not energy (which can be neither increased nor decreased) Jan 10 at 23:34
• In Physics, if an object moves one mile and then moves back to the same point, the total Displacement is Zero. Similarly total work done on an object by a conservative force moving in a closed loop W = F•s = 0 Jan 11 at 7:32

How is this In your universe for practical purposes don’t exist individal atoms, the smallest building block is an atom pair. Where the first atoms is analogous to ours (hydrogen, oxygen….) and every single atom is paired via strong atomic force with another, slightly unstable atom, long halflife, but during fission, emmits gama radiation.

Now eyes of all the beings in your universe have evolved to be sensitive to this radiation and are thus percieving all the world to be bright.

The fusion of the sun however is affected by this secondary atom. Instead of generating light and heat during fusion, the other element absorbs this extra energy and emmits a pair of virtual anti gama photons, most immediately recombine or transition to other particle due to large gravity, some however are expelled and fly towards your world, where they interfere with the naturaly generated gama photons making it “dark” as the human eyes don’t see this virtual anti photon.

• Interesting. In effect, everything on the planet is radioactive and the star somehow suppresses the radioactivity. Jan 9 at 23:59

How about instead of seeing using light, the inhabitants “see” the gravity of objects with extremely sensitive “eyes”? Almost everything has mass, so almost everything is visible in gravity. Far away things, and small things, are felt/seen less strongly.

If the mechanism of gravity-sight is through detecting tiny changes in the force pulling you in a direction, there could be some fun consequences like acceleration distorting your vision. Objects could be made invisible/dark by placing equally sized objects exactly on the other side of you. A “dark star” wouldn’t need to emit anything - it could be sized, shaped, and located in such a way that it cancels out the gravity of nearby objects in a way that renders gravity-sight too distorted or noisy to see anything. Granted, we’d have to be talking some very specifically shaped and located objects.

A potential fun consequence: you could sneak up in front of someone, providing an accomplice of equal mass, shape, and motion was sneaking up behind them at the same time.

But the natural world is sufficiently asymmetrical that the gravitational pull of multiple objects around you would hardly ever cancel out, and if it did you could just move slightly to recreate enough asymmetry to see them again. The technology to create darkness would therefore be the technology to precisely mirror objects around a target. Want to sleep in perfect darkness? Go inside a sphere with a perfect inverse-square-scaled model of the universe embossed on its inner surface.

I think the necessary sensitivity of gravity-sight would require magical handwaving.

Let us consider light. In this (the OP's) universe, let light be a massless particle with energy but no charge... much like in our own universe.

However, let us also consider anti-light. In this universe, anti-light is also a massless particle with energy but no charge. However, it is also the antiparticle of light.

When a particle of light and a particle of anti-light meet, they cancel one-another: When a particle of light meets a particle of anti-light, their energies are summed. If they had equal energy, then there would be zero result. If one particle had more energy, then the energy of the other would reduce the energy of the greater to the sum of the two.

As an example, say that we have two particles, a light particle with +5 energy and an anti-light particle with -6 energy. When they collide, an anti-light particle with -1 energy will continue on in the same direction as the original -6 anti-light particle.

Let us also consider optical temperature. In this universe, let optical temperature be a measurable property which is expressed as a signed real number, ranging from some negative value, through zero to some positive value. As optical temperature decreases, the particles vibrate less in one dimension and below zero, begin to vibrate more in a dimension at right-angles to the first. However, as objects lose thermal energy and physical temperature, their optical temperature tends toward the positive, not toward zero.

Now, let us consider the optical temperature of the universe and the objects within it. Let the universe's background optical temperature approach some value +n. In places which are warmer, the optical temperature will be lower, not higher.

If we carry this trend onwards, at some point, hotter objects will attain zero, then negative optical temperature, until they reach the value -n.

Now, let us consider the phenomenon of black-body radiation. Objects with a non-zero optical temperature emit radiation. Positive optical temperature objects emit positive light. Negative optical temperature objects emit negative anti-light. The further from zero the value, the more energetic the emissions, positive or negative.

Now we need to consider the structure of the universe. The universe is mostly empty space. Cold inert matter which is far from stars will have an optical temperature which approaches +n. Such matter will emit light. Planets which are closer to stars will be warmer, having a positive optical temperature considerably less than +n. They will not emit as much light, and like black-body radiation in our own universe will appear to be a different colour.

Stars, on the other hand, are much more energetic, and have negative optical temperatures approaching -n. They will emit anti-light, which will cancel out the positive light emitted from the less energetic parts of the universe with positive optical temperature.

So, why have I said that cold and light are positive, while hot and anti-light are negative? Because of what sentient creatures see and describe. The sentient creatures on a particular world in this universe can only see light, not anti-light.

That means that they will see the light from all the cold things reflecting off the warmer things, but they won't see the anti-light from the hot things at all. In fact, being close to something hot enough will mean that the anti-light that the hot thing emits will cancel out the light from all the cold things nearby... and will therefore cause darkness.

An interesting side-effect of this light/anti-light duality is that there may exist species which can only see anti-light, and they would consider stars to be bright, and the rest of the universe to be dark.

Additionally, there may exist species which can see and distinguish between both light and anti-light. Everything would likely be visible to such a species, but light and anti-light would be different colours in a way that those that can see only light or only anti-light wouldn't recognise.

The planet is not orbiting one star but a binary pair - one light star, the other the dark star. Day time is when the planet is predominantly influenced by the light star & likewise for night, the planet is influenced by the dark star.

The dark star produces photons that are out of phase with the photons produced by the light start. When the out of phase photons interact with the light photons they cancel each other out & darkness ensues. Additionally, the light receptor cells in peoples eyes only detect normal phased photons, not out of phase photons.

I believe that this universe will be the same as the universe where the light works as normal. Just label dark as light and vice versa.

Imagine that there is an antiphoton that makes things dark. Then:

1. Light is now the absence of antiphoton energy, which means:
2. Things interact with darkness now. This includes plants and your eyes. Since your eyes interact with darkness, then
3. You will perceive dark things as more prominent. Your color perception will be based on how dark is the darkness on a certain wavelength, if we invert the color scheme, then:
4. Darkness will be basically light in our sense.

This also means that people will sleep at day and awake at night.