How many states of matter are there?
At school, the answer we are taught is three: solid, liquid, gas.
Elsewhere you will find four. Five. Seven. Or “many more”.
All of these answers are correct. All that remains is to understand why.
The answers going around
Three. Solid, liquid, gas. These are the states we observe every day: ice, water, steam.
Four. Add plasma: a gas whose atoms have lost electrons, and which conducts electricity. This is the most common answer among scientists, because these are the four states that exist naturally in abundance in the universe — the stars are made of plasma.1
Five. Add the Bose-Einstein condensate, predicted in the 1920s and produced in the laboratory in 1995 by cooling atoms to within a hair’s breadth of absolute zero. They then stop behaving like separate atoms and start acting as one.2
Seven. Then add the quark-gluon plasma, produced at very high energy, in which even the particles of the nucleus come apart; and the fermionic condensate.3
The latter was produced in the early 2000s in the laboratory of the American physicist Deborah Jin. The method is worth describing, because it is astonishing: first a gas of potassium atoms is cooled by evaporation — exactly as a cup of tea cools because the fastest molecules escape, except that here the process is pushed to the very limits of cold. Then a magnetic field is adjusted to set, at will, the way the atoms attract or repel one another.4
A knob that sets the force between atoms: that is the tool. It is this fine tuning that makes the new state appear.
Many more. If you count everything else matter can do: liquid crystals, to which we return below; the matter of neutron stars, so compressed that a teaspoonful would weigh about a billion tonnes. This list is not closed.5
There is no official count
This is the important point.
These answers do not contradict one another. They answer different questions, which nobody ever bothers to ask.
- What we come across in everyday life? Three or four.
- What exists naturally, in abundance, in the universe? Four.
- What we know how to make in the laboratory? Seven, or more.
- Every distinct form that matter can take? Nobody knows, and the list keeps getting longer.
There is no authority that settles the matter. The word “planet”, by contrast, was defined by a vote of astronomers in 2006. Our page on the Solar System (1.5) tells that story. Nobody has ever voted on the number of states of matter.6
What ought to be surprising
This mechanism turns up everywhere on this site.
- How many languages are there in the world? The answer varies by a factor of two, depending on what one calls a language (2.4).
- How many people live in towns? It depends on the threshold at which each country calls a group of houses a “town” (2.6).
- How many countries? How many centres of agriculture? How many scripts invented independently? How many planets? Each time, several answers, and each time for the same reason.
One might have thought that this vagueness was peculiar to human affairs — languages, towns, borders — and that physics, for its part, would give clear-cut answers.
It does not.
This is not because physicists are sloppy. It is because counting always means deciding what counts. Someone has to make that decision — in physics as elsewhere.
The right answer to “how many states of matter are there?” is therefore not a number.
It is a question: how far do we want to go?
A kind of matter that refuses its box
There may be one right before our eyes.
Liquid crystals are neither quite liquid nor quite solid. They are liquids — they flow — but their long, thin molecules keep a common orientation, like matches all laid the same way. This alignment gives them some of the optical properties that crystals have. Their name sums up their problem exactly: they have a little of both, and they fit into neither box.7
They are found in many screens — computers, televisions, phones. The abbreviation sometimes seen on devices, “LCD”, stands for “liquid-crystal display”. Not all screens contain them: other technologies exist, and you may well be reading these lines on one of them. But most homes surely have one.8
So this is not some remote laboratory object. It is an everyday object that forced physicists to admit that their boxes had blurred edges.
Note 1
Much of this is astrophysical plasma […] and that is contained within stars including the Sun. In plasma, some of the electrons separate and become free from neutral atoms […]. […] For one, unlike gas, plasma can conduct electricity.
U.S. Department of Energy, Office of Science, “DOE Explains...Plasma”, 18 March 2024
Note 2
Ich behaupte, daß in diesem Falle eine mit der Gesamtdichte stets wachsende Zahl von Molekülen in den 1. Quantenzustand (Zustand ohne kinetische Energie) übergeht, während die übrigen Moleküle sich gemäß dem Parameterwert λ = 1 verteilen. Die Behauptung geht also dahin, daß etwas Ähnliches eintritt wie beim isothermen Komprimieren eines Dampfes über das Sättigungsvolumen. Es tritt eine Scheidung ein; ein Teil »kondensiert«, der Rest bleibt ein »gesättigtes ideales Gas« […].
I maintain that in this case a number of molecules, always increasing with the total density, passes into the first quantum state (the state without kinetic energy), while the remaining molecules distribute themselves according to the parameter value λ = 1. The claim is thus that something similar happens as when a vapour is compressed isothermally beyond the saturation volume. A separation occurs; one part ‘condenses’, the rest remains a ‘saturated ideal gas’ […].
Bose, Satyendra Nath, “Plancks Gesetz und Lichtquantenhypothese”, Zeitschrift für Physik, vol. 26, 1924 ; Einstein, Albert, “Quantentheorie des einatomigen idealen Gases”, Académie prussienne des sciences, 1924-1925
A Bose-Einstein condensate was produced in a vapor of rubidium-87 atoms that was confined by magnetic fields and evaporatively cooled. The condensate fraction first appeared near a temperature of 170 nanokelvin and a number density of 2.5 x 10(12) per cubic centimeter and could be preserved for more than 15 seconds.
Anderson, Mike H. et al., “Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor”, Science, vol. 269, 1995, p. 198-201
Note 3
We conclude from the available empirical evidence that an equilibrated, but strongly coupled Quark Gluon Plasma has been made in such collisions. […] Concurrently, Collins and Perry and others[4] realized that the asymptotic freedom property of Quantum Chromodynamics (QCD) implies the existence of an ultra-dense form of matter with deconfined quarks and gluons, called later the Quark-Gluon Plasma (QGP)[5].
Gyulassy, Miklos and McLerran, Larry, “New Forms of QCD Matter Discovered at RHIC”, Nuclear Physics A, vol. 750, 2005, p. 30-63
Note 4
We have observed condensation of fermionic atom pairs in the BCS-BEC crossover regime.
Regal, Cindy A., Greiner, Markus and Jin, Deborah S., “Observation of Resonance Condensation of Fermionic Atom Pairs”, Physical Review Letters, vol. 92, 040403, 2004
A trapped gas of fermionic 40K atoms is evaporatively cooled to quantum degeneracy
Regal, Cindy A., Greiner, Markus and Jin, Deborah S., “Observation of Resonance Condensation of Fermionic Atom Pairs”, Physical Review Letters, vol. 92, 040403, 2004
a magnetic-field Feshbach resonance is used to control the atom-atom interactions
Regal, Cindy A., Greiner, Markus and Jin, Deborah S., “Observation of Resonance Condensation of Fermionic Atom Pairs”, Physical Review Letters, vol. 92, 040403, 2004
Note 5
Matter within a neutron star is so dense that a teaspoonful would weigh about a billion tons on Earth.
NASA, Goddard Space Flight Center (Francis Reddy, texte), “NASA’s Swift Catches an Anti-glitch from a Neutron Star”, Scientific Visualization Studio, 29 May 2013
Note 6
The first half of the Closing Ceremony of the 2006 International Astronomical Union (IAU) General Assembly has just concluded. The results of the Resolution votes are outlined here. […] Resolution 5A: "Definition of Planet" was not counted but was passed with a great majority.
Union astronomique internationale, “IAU 2006 General Assembly: Result of the IAU Resolution Votes”, communiqué de presse iau0603, Prague, 24 August 2006
Note 7
Nematic liquid crystals formed by organic substances show a strong optical anisotropy. The anisotropy is due to a partial parallel orientation of the elongated molecules. Optically the liquids behave like uniaxial crystals with the axis parallel to the preferred orientation.
Brown, Glenn H. (ed.), Basic Studies of Liquid Crystals as Related to Electro-Optical and Other Devices, final report for the Air Force Office of Scientific Research, Liquid Crystal Institute, Kent State University, January 1972
Note 8
In the beginning, liquid-crystal displays (LCDs) were limited to niche applications such as small-size displays for digital watches, pocket calculators, and small handheld devices. That all changed with the development of the notebook computer industry.
Kawamoto, Hirohisa, “The History of Liquid-Crystal Displays”, Proceedings of the IEEE, vol. 90, no. 4, 2002, p. 460-500
Notes and sources
- ↑
Passage plasma: a gas whose atoms have lost electrons, and which conducts electricity […] the stars are made of plasma
Much of this is astrophysical plasma […] and that is contained within stars including the Sun. In plasma, some of the electrons separate and become free from neutral atoms […]. […] For one, unlike gas, plasma can conduct electricity.
Source U.S. Department of Energy, Office of Science, “DOE Explains...Plasma”, 18 March 2024, 1st paragraph (plasma in stars), 2nd paragraph (freed electrons) and paragraph on the gas–plasma analogy (conductivity).
Open access open the source · checked on 27 October 2026
- ↑
Passage the Bose-Einstein condensate, predicted in the 1920s
Ich behaupte, daß in diesem Falle eine mit der Gesamtdichte stets wachsende Zahl von Molekülen in den 1. Quantenzustand (Zustand ohne kinetische Energie) übergeht, während die übrigen Moleküle sich gemäß dem Parameterwert λ = 1 verteilen. Die Behauptung geht also dahin, daß etwas Ähnliches eintritt wie beim isothermen Komprimieren eines Dampfes über das Sättigungsvolumen. Es tritt eine Scheidung ein; ein Teil »kondensiert«, der Rest bleibt ein »gesättigtes ideales Gas« […].
Editors’ translation I maintain that in this case a number of molecules, always increasing with the total density, passes into the first quantum state (the state without kinetic energy), while the remaining molecules distribute themselves according to the parameter value λ = 1. The claim is thus that something similar happens as when a vapour is compressed isothermally beyond the saturation volume. A separation occurs; one part ‘condenses’, the rest remains a ‘saturated ideal gas’ […].
Source Bose, Satyendra Nath, “Plancks Gesetz und Lichtquantenhypothese”, Zeitschrift für Physik, vol. 26, 1924 ; Einstein, Albert, “Quantentheorie des einatomigen idealen Gases”, Académie prussienne des sciences, 1924-1925, “Zweite Abhandlung”, session of 8 January 1925, § 6 (“Das gesättigte ideale Gas”), p. 4 of the 1925 Sitzungsberichte.
Public domain open the source · checked on 27 October 2026
Passage produced in the laboratory in 1995 by cooling atoms to within a hair’s breadth of absolute zero
A Bose-Einstein condensate was produced in a vapor of rubidium-87 atoms that was confined by magnetic fields and evaporatively cooled. The condensate fraction first appeared near a temperature of 170 nanokelvin and a number density of 2.5 x 10(12) per cubic centimeter and could be preserved for more than 15 seconds.
Source Anderson, Mike H. et al., “Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor”, Science, vol. 269, 1995, p. 198-201, abstract.
Paywalled · checked on 25 October 2026
- ↑
Passage the quark-gluon plasma, produced at very high energy, in which even the particles of the nucleus come apart
We conclude from the available empirical evidence that an equilibrated, but strongly coupled Quark Gluon Plasma has been made in such collisions. […] Concurrently, Collins and Perry and others[4] realized that the asymptotic freedom property of Quantum Chromodynamics (QCD) implies the existence of an ultra-dense form of matter with deconfined quarks and gluons, called later the Quark-Gluon Plasma (QGP)[5].
Source Gyulassy, Miklos and McLerran, Larry, “New Forms of QCD Matter Discovered at RHIC”, Nuclear Physics A, vol. 750, 2005, p. 30-63, abstract, then section 1 “Introduction”, first paragraph.
Open access open the source · checked on 24 October 2026
- ↑
Passage The latter was produced in the early 2000s in the laboratory of the American physicist Deborah Jin.
We have observed condensation of fermionic atom pairs in the BCS-BEC crossover regime.
Source Regal, Cindy A., Greiner, Markus and Jin, Deborah S., “Observation of Resonance Condensation of Fermionic Atom Pairs”, Physical Review Letters, vol. 92, 040403, 2004, abstract of the article.
Open access open the source · checked on 9 September 2026
Passage first a gas of potassium atoms is cooled by evaporation
A trapped gas of fermionic 40K atoms is evaporatively cooled to quantum degeneracy
Source Regal, Cindy A., Greiner, Markus and Jin, Deborah S., “Observation of Resonance Condensation of Fermionic Atom Pairs”, Physical Review Letters, vol. 92, 040403, 2004, abstract of the article.
Open access open the source · checked on 9 September 2026
Passage Then a magnetic field is adjusted to set, at will, the way the atoms attract or repel one another.
a magnetic-field Feshbach resonance is used to control the atom-atom interactions
Source Regal, Cindy A., Greiner, Markus and Jin, Deborah S., “Observation of Resonance Condensation of Fermionic Atom Pairs”, Physical Review Letters, vol. 92, 040403, 2004, abstract of the article.
Open access open the source · checked on 9 September 2026
- ↑
Passage the matter of neutron stars, so compressed that a teaspoonful would weigh about a billion tonnes
Matter within a neutron star is so dense that a teaspoonful would weigh about a billion tons on Earth.
Source NASA, Goddard Space Flight Center (Francis Reddy, texte), “NASA’s Swift Catches an Anti-glitch from a Neutron Star”, Scientific Visualization Studio, 29 May 2013, text presenting the visualisation.
Open access open the source · checked on 25 October 2026
- ↑
Passage The word “planet”, by contrast, was defined by a vote of astronomers in 2006.
The first half of the Closing Ceremony of the 2006 International Astronomical Union (IAU) General Assembly has just concluded. The results of the Resolution votes are outlined here. […] Resolution 5A: "Definition of Planet" was not counted but was passed with a great majority.
Source Union astronomique internationale, “IAU 2006 General Assembly: Result of the IAU Resolution Votes”, communiqué de presse iau0603, Prague, 24 August 2006, official IAU press release iau0603 (Prague, 24 August 2006): lead paragraph, then result of the vote on Resolution 5A (later B5).
Open access open the source · checked on 25 October 2026
- ↑
Passage They are liquids — they flow — but their long, thin molecules keep a common orientation […] This alignment gives them some of the optical properties that crystals have.
Nematic liquid crystals formed by organic substances show a strong optical anisotropy. The anisotropy is due to a partial parallel orientation of the elongated molecules. Optically the liquids behave like uniaxial crystals with the axis parallel to the preferred orientation.
Source Brown, Glenn H. (ed.), Basic Studies of Liquid Crystals as Related to Electro-Optical and Other Devices, final report for the Air Force Office of Scientific Research, Liquid Crystal Institute, Kent State University, January 1972, section III (“Theoretical Studies”, by A. Saupe), subsection I (“Deformation of Nematic Liquid Crystals by Polarized Light”), opening of the text written by A. Saupe, 1st sentence onwards.
Open access open the source · checked on 27 October 2026
- ↑
Passage They are found in many screens […] The abbreviation sometimes seen on devices, “LCD”, stands for “liquid-crystal display”.
In the beginning, liquid-crystal displays (LCDs) were limited to niche applications such as small-size displays for digital watches, pocket calculators, and small handheld devices. That all changed with the development of the notebook computer industry.
Source Kawamoto, Hirohisa, “The History of Liquid-Crystal Displays”, Proceedings of the IEEE, vol. 90, no. 4, 2002, p. 460-500, abstract, fifth and sixth sentences.
Paywalled · checked on 25 October 2026
Bibliography
11
- Anderson, Mike H. et al., “Observation of Bose-Einstein Condensation in a Dilute Atomic Vapor”, Science, vol. 269, 1995, p. 198-201, paywalled (the first Bose-Einstein condensate produced in the laboratory).
- Bose, Satyendra Nath, “Plancks Gesetz und Lichtquantenhypothese”, Zeitschrift für Physik, vol. 26, 1924 ; Einstein, Albert, “Quantentheorie des einatomigen idealen Gases”, Académie prussienne des sciences, 1924-1925, public domain (the theoretical prediction).
- Brown, Glenn H. (ed.), Basic Studies of Liquid Crystals as Related to Electro-Optical and Other Devices, final report for the Air Force Office of Scientific Research, Liquid Crystal Institute, Kent State University, January 1972, open access. https://apps.dtic.mil/sti/pdfs/AD0736882.pdf
- Chen, Francis F., Introduction to Plasma Physics and Controlled Fusion, Springer, 2016, chap. 1, in libraries (plasma as the most abundant state of the visible universe).
- de Gennes, Pierre-Gilles and Prost, Jacques, The Physics of Liquid Crystals, Oxford University Press, 1993, in libraries (liquid crystals, neither solid nor liquid; the common orientation of the molecules).
- Gyulassy, Miklos and McLerran, Larry, “New Forms of QCD Matter Discovered at RHIC”, Nuclear Physics A, vol. 750, 2005, p. 30-63, open access (the quark-gluon plasma). https://doi.org/10.1016/j.nuclphysa.2004.10.034
- Kawamoto, Hirohisa, “The History of Liquid-Crystal Displays”, Proceedings of the IEEE, vol. 90, no. 4, 2002, p. 460-500, paywalled (liquid-crystal displays).
- NASA, Goddard Space Flight Center (Francis Reddy, texte), “NASA’s Swift Catches an Anti-glitch from a Neutron Star”, Scientific Visualization Studio, 29 May 2013, open access (the density of neutron-star matter: a teaspoonful would weigh about a billion tonnes). https://svs.gsfc.nasa.gov/11260/
- Regal, Cindy A., Greiner, Markus and Jin, Deborah S., “Observation of Resonance Condensation of Fermionic Atom Pairs”, Physical Review Letters, vol. 92, 040403, 2004, open access (the first fermionic condensate: evaporative cooling of a potassium gas, then tuning of the interactions by magnetic resonance). https://doi.org/10.1103/PhysRevLett.92.040403
- U.S. Department of Energy, Office of Science, “DOE Explains...Plasma”, 18 March 2024, open access. https://www.energy.gov/science/doe-explainsplasma
- Union astronomique internationale, “IAU 2006 General Assembly: Result of the IAU Resolution Votes”, communiqué de presse iau0603, Prague, 24 August 2006, open access (the vote on the word “planet”; see Entry 1.5). https://www.iau.org/news/pressreleases/detail/iau0603/
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