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Earlier I studied about the three states of matter-gaseous,liquid ans solid. Then, I came to know about Plasma and Bose-Einstein Condensate. Now, scientists are trying to explain superconductivity as a state of matter. But, I would like to know on what factors does scientists rely to decide whether a particular state is a state of matter?

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In general a state of matter is distinguished from other states by a phase transition, which can be accompanied by a changing symmetry. Superconductivity is such a state and since 50 years described in such a way, so not a new explanation. Maybe you can be a bit more specific, at the moment the answer spans several chapters in many statistical physics/condensed matter textbooks. –  Alexander Nov 22 '13 at 12:00
    
@Alexander Can you please tell about how to make this question more specific? I think this question is getting not much attention as it is a broad one as you said. –  Rajath Krishna R Nov 22 '13 at 13:16
    
@Alexander Alexander gave the generic answer for your generic question. A phase of matter is separated from an other one by a phase transition. So, a plasma is not a phase of matter, whereas gas (no interaction), liquid (interaction), solid (interaction + space ordering / lattice) are. Quantum condensates are a bit more tricky to classify, and this question is to a large extend not resolved. Maybe you could try to check on Wikipedia the pages about Bose-Einstein and superconducting condensates, and come back with more explicit questions about them. Have fun learning more about that. –  FraSchelle Nov 25 '13 at 13:49
    
(to be continued) Also, you could try to obtain more information on the internet between first and second order phase transition. Classical phases of matter are separated from each other by a first order phase transition. But classical phases are just gas - liquid - solid, so it is not a big issue to learn about that. On the other hand, the quantum condensates are usually separated to the non-condensed-phase by a second order phase transition (say, because once more time reality is much more complicated). There is (still) no generic mechanism characterising quantum condensate. –  FraSchelle Nov 25 '13 at 13:52
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The wiki article on states of matter should clear up your questions.

In physics, a state of matter is one of the distinct forms that different phases of matter take on. Four states of matter are observable in everyday life: solid, liquid, gas, and plasma. Many other states are known such as Bose–Einstein condensates and neutron-degenerate matter but these only occur in extreme situations such as ultra cold or ultra dense matter. Other states, such as quark-gluon plasmas, are believed to be possible but remain theoretical for now. For a complete list of all exotic states of matter, see the list of states of matter.

Historically, the distinction is made based on qualitative differences in properties. Matter in the solid state maintains a fixed volume and shape, with component particles (atoms, molecules or ions) close together and fixed into place. Matter in the liquid state maintains a fixed volume, but has a variable shape that adapts to fit its container. Its particles are still close together but move freely. Matter in the gaseous state has both variable volume and shape, adapting both to fit its container. Its particles are neither close together nor fixed in place. Matter in the plasma state has variable volume and shape, but as well as neutral atoms, it contains a significant number of ions and electrons, both of which can move around freely. Plasma is the most common form of visible matter in the universe.

Read on in the link provided.

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