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All of these questions are related to the pretty deep math of General Relativity and Quantum Mechanics, but I'll try to answer them at an easier level.

The mass of a particle increases as it approaches the speed of light because the energy can't go into increasing the speed very much (otherwise you would exceed the speed of light), and so the energy goes into increasing the mass. Only the mass increases, the size (to an outside observer) actually decreases in the direction the particle is traveling.

Light does not have mass. Under General Relativity, you don't need to have mass to be affected by gravity. Only things with no mass can travel at the speed of light.

Quantum Mechanics says that things can be both particles and waves at the same time. It is not only light -- electrons were shown to behave like waves quite a few years ago (one of the "proofs" of quantum mechanics). This has nothing to do with the previous questions.

Dr. Eric Christian

This site from Zona Land does an excellent job of explaining the water ice to liguid water phase change.

Dr. Ed Tedesco
(December 2004)

A neutron star is about 10¹⁵ times as dense as normal matter, or the radius is 10^-5 smaller. So the Earth would be about 64 meters in radius.

If the universe is about 20 billion light years in radius (the age of the universe), and its density is about 8 x 10^-30 gms/cm³ (the critical density to close the universe), then to get the universe to the density of water, you would compact it to about 4 light years in radius, and it would be .00004 light years (4 x 10¹¹ meters) in radius at neutron star densities. This is nearly three times the distance from the Earth to the Sun.

Under high pressures, fluids undergo a phase change and become compressible.

Dr. Eric Christian

Do physicists now talk of "five states of matter" or is it still three? Also, is this concept of discrete "states of matter" still favored or is there a paradigm shift to more of a continuum where unlimited transitional states of matter can be found or created?

I wanted to make sure that I had the correct latest information on this interesting question, as I am working in space plasma physics, a field a little more distant from Bose-Einstein Condensates (BEC). On this website we mostly only answer questions in our area of expertise, i.e. astrophysics and space physics. Therefore, I asked Karsten Pohl, a colleague who is involved in condensed matter physics for some help on the BEC.

As far as my colleague and I know, there is no really practical application for these condensates in sight so far. However, high tech applications in research itself are a likely possibility, such as building lasers with highly monochromatic radiation for the use in atomic spectroscopy, because the condensate is so cold. Also one could think of building waveguides on an atomic scale. Whether that would lead to an application, e.g. in communication technology, remains to be seen.

The expansion of the number of states of matter to 4 or 5 is not a universally agreed upon concept, although I found it mentioned in many places. I found a well written and fairly comprehensive description of plasma as the 4th and the BEC as the 5th state of matter on the website of the Singapore Science Center. A few words of caution should be said about the additional states of matter.

Firstly, the transition from an ordinary neutral gas to a plasma is distinctly different from any of the transitions between the original 3 states. The phase transition occurs at specific combinations of pressure and temperature. While the transition to a plasma is also a function of temperature and pressure (ionization into plasma needs higher temperatures, because the electrons must be knocked out of the atoms), there is a rather gradual transition over a wide temperature range, over which the constituents of ordinary neutral gas and plasma coexist (mixed together in the same volume), contrary to an abrupt transition from solid to liquid or liquid to gas.

Secondly, I have found a note in a German encyclopedia of physics from 1980 that the 5th state of matter should be a gas of nucleons and electrons, i.e. the bare nuclei of the plasma further broken up into pieces at even higher temperature. The more modern take on the 5th state of matter puts it at the opposite end of the spectrum, namely the BEC at extremely cold temperatures. Contrary to the transition to plasma the transition into a BEC is much more defined again, thus much closer to a traditional phase transition between states of matter. In summary, the last word of authority on states of matter has not been spoken yet.

Dr. Eberhard Moebius
(October 2004)