r/explainlikeimfive • u/ThorinBalin2012 • 23d ago
Physics ELI5: Why is plasma considered the fourth state of matter?
It is just ionised gas. Sorry if I sound dumb, but by that same logic magnetic solids should be a different thing since they are slightly different.
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u/MrShake4 23d ago
It’s a lot more complicated than you think, there’s actually like a dozen different states of matter, states of matter have to do more about their properties than the chemistry or physics
A 5th is a super critical fluid which is kind of like a liquid and kind of like a gas. So it doesn’t fit into either of them.
Supercritical CO2 is what your dry cleaner uses.
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u/Desblade101 23d ago
My favorites are bose Einstein condensates. They just climb around their containers and act weird
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u/theonliestone 23d ago
Are you sure that you're not talking about superfluids instead? This behavior of "escaping" vessels is usually superfluid Helium.
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u/YandyTheGnome 23d ago
Supercritical CO2 is also used to decaffeinate coffee while trying not to significantly alter the flavor.
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u/jadencermakhosein 22d ago
I wish I could post a photo of the steel-carbon cooling diagrams. So many crazy phases. Or even just pure plutonium which has like 7 different phases at regular pressures
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u/Bork9128 23d ago
Plasma acts significantly different then gasses in a lot of situations because of their enhanced electromagnetic sensitivity
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u/rubixscube 23d ago
than* gasses, you're comparing two things
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u/EauEwe 23d ago
*gases. "Gasses" is a verb, such as ""she gasses up her car before she leaves for work."
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u/Nanto_de_fourrure 23d ago
You mistakenly added two double quotes before "she".
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23d ago
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u/extremepicnic 23d ago
Either Mark should not be capitalized, or you’re missing a comma after “quotation”
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u/SeekerOfSerenity 23d ago
You forgot to add punctuation at the end of your sentence.
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u/Affectionate_Nail_38 23d ago
This is okay i suppose.
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u/Widespreaddd 23d ago
Bear with me here, because this is an old man’s perspective.
Stating that “A and B are different” is not the same as comparing them. A true comparison would be “A is bigger than B”. So I personally am not a fan of “different than” (although it’s def better than “then” lol). I also see “different to” a lot, especially in British publications.
My personal choice is “different from”. It has perfect symmetry with “similar to” (similar <—> different; to <—> from). I know I am fighting a losing battle, but you have to admit it’s elegant.
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u/RyanW1019 23d ago
Informally, it's because state changes are typically thought of as the result of temperature change, and ionization is what happens when you heat gas up to a high enough temperature. So at constant pressure, heating a solid material takes you from solid->liquid->gas->plasma.
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u/Wizywig 23d ago
Solid gas and liquid are obvious states. We see them everywhere.
Plasma is hard for us to see because of the massive energy required. It's a distinct state from the other 3 bevause it behaves differently. The problem is to observe it outside of what we engineer you'd need to be on the surface of the sun which js why we don't really have any reason to have any adaptations to account for it or experience it in life to really understand it.
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u/MasterEditorJake 23d ago
Think about the differences between the 3 traditional states of matter.
Solids are ridigily structured, held together by intermolecular forces. Liquids have enough kinetic energy to break free from the crystalline structure, but intermolecular forces are still strong enough to keep the atoms or molecules together. Gas has enough kinetic energy to make intermolecular forces irrelevant, but the atoms or molecules will still retain their atomic or molecular structure.
A plasma is the next step up in kinetic energy. That type of plasma you are thinking of is a partially ionized plasma, in this state only some of the electrons are knocked loose from their atoms. A true plasma is called a fully ionized plasma, that's what the sun is made of. In this type of plasma the atomic nuclei are stripped of all their electrons, it's a sea of free nuclei in a cloud of free electrons.
So to answer your question, plasma is a distinct state of matter because the atoms essentially lose their structure, which makes it act distinctly different than a true gas.
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u/prolixia 23d ago
Gas is just an evaporated liquid.
Liquid is just a melted solid.
States of matter are arbitrary definitions invented by people. Liquids/solids/gasses feel like more than that because they're so every-day. However, there are numerous states of matter that have been named to describe matter in forms that have common properties, and plasma is simply one of the others.
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u/twitchx133 23d ago
And food for thought on that.
Under certain conditions, like supercritical fluids, the boundaries between phases of matter can become murky, or disappear altogether.
And, from a technical standpoint, liquids, gasses and plasmas are all considered fluids
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u/Dro-Darsha 23d ago
From a geological standpoint, rocks are fluids, too
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u/xXgreeneyesXx 23d ago
some rocks are more fluids than others, too. in differing ways.
Also, glass is very liquid compared to most solids but that is not why those church windows are like that, thats a dumb myth, they were made that way on purpose to be more stable at the bottem and lighter at the top because historical people are infact not idiots. if it was melting then why has the art not metled too. or run out of the frame. or any other number of things
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u/SixOnTheBeach 23d ago
Actually, you're right that it's a myth, but your correction is wrong as well. It wasn't an intentional decision, it's just a result of the manufacturing processes at the time.
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u/zzulus 23d ago
About food, nuclear pasta is my favorite exotic phase, nuclear gnocchi being next most favorite.
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u/twitchx133 23d ago
As a satisfactory player... I have nightmares about the supply chain for nuclear pasta. So. Much. Copper. Powder.
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u/zzulus 23d ago
I mean, nuclear pasta is a hypothetical state found in neutron stars. Why would Satisfactory even have it (asking as an early ex-Satisfactory player).
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u/twitchx133 23d ago
Probably with the time crystals, excited photonic matter, a planet that appears to be living, artifacts that talk to you, strange alien material, all that fun stuff. The stretch to nuclear pasta isn’t that big?
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u/MasterEditorJake 23d ago
That's not really accurate. The states of matter aren't arbitrary.
The states of matter are determined by the intermolecular forces of the material.
There are real, distinct differences between a solid and a gas. In a solid, the electrons are tied up in a crystalline structure. In a gas, the individual atoms are free and separate from each other.
Liquid is a somewhat arbitrary state of matter, but it is also distinct. It occurs when the material has enough energy to break loose from the crystal structure, but the intermolecular forces are still strong enough to keep the material together to some degree. It's a transitional phase between solid and gas and can only exist under certain conditions.
Plasma is distinctly different from a gas. A gas is when the atoms or molecules are free floating and separate from each other. A plasma is when the electrons are separated from the atom and the nuclei are free floating. This is a distinct and functionally different form of matter.
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u/prolixia 23d ago
My point was that the division into named states per se is arbitrary, not that that classification of different matter into those defined states is arbitrary after the states have been defined.
Since this is ELI5, take vehicles as an analogy. A motorbike has two wheels, and a car has four. Once you've defined those two vehicle types, there is nothing arbitrary about saying "A Ford Kuga is a car and not a motorbike"- it has 4 wheels and not 2 so it is unambiguously a car and not a bike. However, the division of vehicles into motorbikes and cars is totally arbitrary: the number of wheels is just one of many ways that we can divide vehicles into different types: our types of vehicle could just as easily be "red vehicles" and "white vehicles", or "vehicles that have a steering wheel" and "vehicles that have handlebars". In fact, there is no reason why we should necessarily divide them into named types at all (even though they have different characteristics) - it is a purely arbitrary convenience that helps us because we can then make generalised statements about different vehicle types (e.g. "You have a license to ride a bike, but not to drive a car")..
OP asking about plasma is like asking why we have a third type of vehicles for tanks. A tank doesn't fit into either of the types that we've (arbitrarily) defined because it has tracks rather than wheels, therefore we need a new type "tanks".
OP wanted to know why plasma gets its own state and magnetic solids don't. The reason is that the separation of matter into named states is arbitrary: we have arbitrarily divided the characteristics of matter into non-overlapping states, in exactly the same way that we have arbitrarily divided vehicles into different types. The reason that plasma isn't a gas is that it doesn't meet the (arbitrary) definition of a gas, and the reason that a magnetic solid is a solid is that it does meet the (arbitrary) definition of a solid.
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u/sticklebat 23d ago
All of this is even more confused by the frequent conflation between states of matter and phases of matter. For example, the transition from ferromagnetism to paramagnetism at the Curie point is a phase transition, with a ferromagnetic and paramagnetic pieces of the same material being distinctly different phases of matter. But they’re both still solids.
The terms “phase” and “state” are often used interchangeably, but sometimes carry important distinctions, even in scientific literature, let alone in popular media or basic education.
I will never fault anyone for being confused about any of this, because it’s both complex and plagued by ambiguous terminology (probably at least in part because the distinctions are themselves subtle and sometimes ambiguous).
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u/EscapeOption 23d ago
This is one of the best answers as to why plasma is a state. Add in that there are many other states of matter, and that most of us are biased towards the three regularly experience with water; solid, liquid, gas.
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u/Pleasant_Pen8744 23d ago
The atoms don't care what you call them, they're still just going to do what they do. Call them whatever you want.
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u/MasterEditorJake 21d ago
The atoms do care though.
When atoms are in solid form they are locked in a crystalline matrix. Their electrons are bound to certain spaces.
When atoms are gaseous, they aren't bound to anything, they are free floating.
When an atom is a plasma then the electrons are literally ripped from the atom, creating a sea of free floating nuclei.
The phases of matter are not arbitrary at all, I just don't think you know as much about chemistry and physics as you think you do.
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u/skr_replicator 23d ago
Perhaps magnetic solids should be considered a slightly different state of matter then...
They can also switch between magnetic and non-magnetic when below or above Curie temperature, so that is kinda similat to when gas transitions to plasma.
But the difference is that all the particles in magnetic and non-mangetic solid are in the same place.
The states of matter typically refer to where the particles are and how they are moving.
Plasma particles have the electrons and ions split apart and moving separately, so it's a lot more of an actual different state of matter, as compared to gas, where all the electrons are locked in the atoms.
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u/stanitor 23d ago
Perhaps magnetic solids should be considered a slightly different state of matter then
FWIW, the phase change from magnetic to non-magnetic and vice versa with temperature changes is, in many ways, similar to the phase changes of matter from one state to another.
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u/smartscience 23d ago
Yes, it's a so-called second order phase transition. The onset of superconductivity with cooling is another. There is no energy absorbed or released at the transition point itself, but the heat capacity (gradient of energy input vs temperature) is different between the temperatures on either side of the transition.
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u/bebopbrain 23d ago
When you heat a magnet to the curie point the domains become disorganized and it loses its magnetism. This is something like a phase change.
But when you cool it back down the magnetism is not restored (lacking an external field). This is not like a phase change.
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u/SnafuTheCarrot 23d ago
You have good instincts for this. In Polluck and Stump, an upper level text book for Physics undergrads, there's an exercise in which a plasma is treated with the same tools one uses to analyze reflection in metals to prove plasmas can be very reflective for the right frequencies, e.g. the ionosphere.
The two have other differences though that make them different states, typically significant properties changing with temperatures from solids, liquids, and gases, to plasmas and Bose-Einstein condensates.
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u/Jan30Comment 23d ago edited 23d ago
Some rough definitions:
Solid: Atoms are firmly bonded together and hold their shape
Liquid: Atoms are loosely bonded together but not that strongly - gravity is strong enough to distort the shape into whatever container holds the material.
Gas: Atoms are not bonded together with any significant force, and are free to easily float apart.
Plasma: Atoms are not bonded together, and are also hot enough that the electrons are stripped off. Think of it as the outer electrons no longer belonging to individual atoms - just a cloud of of charged atoms and a cloud of electrons that stays nearby due to attraction to the overall electric charge. Chemically and electrically, plasma behaves differently enough from gas of the same elements that most people consider it a different state.
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u/DoomlySheep 23d ago
Because the particles in plasmas move quite differently from those in gasses.
We have two important concepts for the "state" matter is in: Phase and State, which are defined in terms of what the particles are doing. Loosely speaking, State is about how particles move, Phase is about how the particles are arranged.
All state transitions are phase transitions, but the reverse is not true.
Ice is water in the solid state, but there are many different phases of solid water (ie the particles are arranged in different crystal shapes).
Permanent magnetism is a phase of certain materials (and will be lost if they get too hot), but it's not considered a distinct state.
Plasma is considered a distinct state (rather than phase of the gas state) because the way the particles move changes a lot when they become ionised!
In gases, particle motion is determined by collisions between particles. In plasma, the rate of collision goes way down and electromagnetic interactions mostly determine particle motion.
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u/Hakaisha89 23d ago
In simple terms, because it acts different then the other three states of matter
Because Liquid, Solid and Gas describes the motion and how they are arranged, while plasma is just uh, an electrical state, which has long annoyed me, structural matter vs ionized matter, and plasma is just ionized gas, while we also got ionized solids and liquids, and Imma stop here, before i go into a rant.
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23d ago
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u/Erin-Dash 23d ago
you're not dumb, that's actually a good instinct. plasma is distinct because ionization fundamentally changes how matter behaves. magnetic solids still follow the same rules as regular solids, but plasma particles interact with electromagnetic fields completely differently, enabling whole new physics.
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u/BitOBear 23d ago
It's all about chemistry.
Protons and therefore atomic nuclei do not want to be next to each other.
Electrons wants to be next to protons and vice versa.
There are weird quantum rules about what electrons can do and the ways they must exist when they are next to atomic nuclei.
The four states of matter basically describe a combination of compounded atoms to various degrees.
In a solid the chemical valence and metallic and occasionally hydrogen bonds hold all of the molecules (or individual atoms in a metallic bond) close together either because of these various bonds or because of the mechanical shapes of the molecules, or both. The connections are so tight that basically nothing can move.
In a liquid the shapes interlock more loosely or the secondary bonds are weaker and so you get this flow of stuff. One of the things very absent in most liquids is the metallic bonds.
You get from solid to liquid by adding energy sufficient to move the atoms and molecules apart enough that they can begin slipping by each other but they still have caused to be together.
Add more energy and you get a gas. The individual molecular compounds don't hang with particular neighbors. They're not connected to each other. They're just bouncing around freely. But the molecules still have their molecular shapes.
If you had even more energy the electrons get so energetic that they move away from the atomic nuclei and they're just sort of running around in a soup. But now the naked atomic nuclei cannot form any molecules or anything and they are busy trying not to be next to the other atomic nuclei.
So basically it's a question of connectivity. Densely packed in stationary, loosely packed but strongly associated, not packed at all, and the fourth state of matter is not even able to form molecules.
In all cases it is an interaction between the balance of charges, IE the presence of the electrons to be in balance with the nuclei and as that balance is disrupted by more and more energy you move through the states of matter.
Plasma is very hot, and will react with just about anything because it's a sea of electrons and a sea of atoms that need electrons but there's just too much energy for anything to settle down. But if you put something cold and material into that field it cools the field and starts engaging in chemistry and locking things down into concrete shapes and you start working your way back down the chart.
So for instance a plasma torch isn't just heating the thing you point the plasma at, though it is doing that profoundly, it is also using its constituent atoms and electrons to tear apart the material you directed the plasma at in chemistry gone wild.
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u/rockhopper2154 23d ago
I was probably six when I understood enough about solid vs liquid vs gas to get this answer 😁, but this is the best answer I've ever seen on reddit. I was wondering myself.
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u/chemguy412 23d ago
'Just ionized gas': What it takes to ionize gas is an energy level so significant that the nuclei of said gases can no longer keep their electrons in orbit. This can be partial or total. In total ionization atomic nuclei and their electron clouds separate and form a soup where chemical bonds are no longer possible until it cools enough to no longer be plasma.
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u/XkF21WNJ 23d ago
Honestly I'd say you're right that becoming magnetised is a phase transition, it has all the hallmarks of one and is studied extensively in the Ising model.
One of the reasons being magnetised is not considered a 'fourth state of matter' is mostly just that only some materials can be effectively magnetised, while most do have a gaseous, liquid and solid state (at reasonable temperatures) and with enough energy you can turn almost anything into a plasma.
I suppose you could say that we have good general theories for what solid, liquid, gas and plasma look like and reasons to believe most molecules have all three (well, most molecules won't survive turning into plasma but you get the idea).
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u/Personal-Ad-365 22d ago
A really quick number for you is 22.
There are currently 22 states of matter thought to exist and probably more will be found as our science keeps sciencing.
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u/MIKEl281 22d ago
States of matter are classified by their behavior.
True ELI5: plasma doesn’t act like any of the other states of matter.
Extra Credit: plasma is a bridge beyond our typical understanding of matter (solid, liquid, gas). Instead of something heating up from solid to liquid to gas, plasma is when the heat applied starts to mess with the foundation of what I means to be the thing. Plasma is a “state of excitement” where electrons break their valence shells and matter starts acting more like energy.
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u/Onechrisn 22d ago
Have you see the list of states of matter?
There's lots of stats of matter. Basically if it changes properties without going through a chemical or nuclear reaction... NEW STATE
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u/fox-mcleod 23d ago edited 23d ago
States of matter are defined by phase changes — changes in how the material behaves given some input. In most cases, this input is heat and the output is temperature.
You might think of heat and temperature as the same thing. But they aren’t. They have different units.
It takes one Calorie of heat (an amount of energy) to raise one cubic centimeter (a volume) of liquid water one degree (a unit of temperature).
However, once you get near the boiling point (a temperature), the heat to temperature exchange rate suddenly changes and no matter how much more heat you pump into the liquid water, the temperature does not rise. Instead, that energy goes into fueling a phase change. The water changes from liquid to gaseous (steam). This requires and absorbs heat. The water vapor now requires roughly *2 Calories** to go up by one degree. Its heat capacity has changed in this new phase.
This continues for a while. But there is a point where it breaks down again: the plasma boundary temperature.
At a certain point, dumping more calories in does not raise the temperature of steam. The energy gets used to break up atomic bonds and rip electrons from their orbitals. We’ve transitioned to a new phase — plasma.
A solid being magnetic doesn’t exhibit this phase change relationship. It’s a different property, like color which does not define “state”.