by Prasad Ganti

As I listened to a science lecture on a Saturday morning, “Science on Saturdays” at the Princeton Plasma Physics Lab, the title was related to interaction of plasma with the surfaces. It made me think when the speaker made a point that most of the matter in our Universe is not solids or liquids, but gas and plasma instead. This contrasts with what we find in our daily lives on our Earth.

The three dominant states of matter we experience on the Earth are solid, liquid and gas. Solids are the rocky surface on which we stand and live. Liquids like water are so crucial for life on Earth. The colorless and odorless gas called air is what we breathe. We ourselves are made of solid bone and water. We are married to our solid smartphones and liquid alcohol and perfume. The foods we eat are made of solids and liquids, but not of gases or plasma. Yet the solids and liquids do not figure in the list of prominent entities in the Universe. How strange!

Plasma is found only in stars as they possess very high pressures and temperatures. The gases in such conditions exist in ionized state in which the electrons are stripped off from the central nucleus. On the Earth, nuclear fusion reactors contain Plasma. This is only an experiment to harness the nuclear energy by trying to bottle the Sun on Earth.

How does gas and plasma come into the picture across the Universe ? The Universe consists of billions of galaxies. Each galaxy consisting of billions of stars. Stars consist mainly of Hydrogen and Helium in a plasma form. Then there is interstellar gas and dust which could be remnants of a dead star and can lead to the birth of new stars. Some of the stars may be having one or more planets. Some of them could be rocky planets, and some gas giants. Our own solar system consists of inner planets up to Mars which have solid surfaces and the outer gas giants starting from Jupiter. The gas giants Jupiter, Saturn, Uranus, and Neptune are much bigger compared to the inner rocky planets.

Of all the known hundred or so chemical elements we know so far, only two of them dominate the Universe. Hydrogen and Helium. Rest of the elements are trivial. The Universe was formed with mostly Hydrogen and some Helium. The composition of the elements did not change substantially in the last thirteen billion years or so. Later elements like Lithium, Boron, carbon etc. got formed, but still their quantities do not have an impact on the overall composition of the Universe.

A strange thing is that Hydrogen in the gaseous form is found only in trace quantities on the Earth. Helium is still rarer. Almost all helium on the planet is a by-product of natural gas extraction process which releases this inert gas produced by slow radioactive decay of terrestrial rock. It was detected in 1868 by French astronomer Jules Janssen during a total solar eclipse while analyzing the spectrum from Sunlight. This new element was named as Helium after the Greek name for Sun which is Helios. Bottomline is that whatever dominates the Earth is trivial in the Universe. Likewise, whatever dominates the Universe is trivial on Earth.

What do other intense astronomical objects like neutron stars and black holes contain ? Neutron stars are very dense matter. At those levels, there are no chemical elements. Black holes do not contain solids, liquids or gases in their native form. These objects are gravitational extremities and do not contain matter as we know it on Earth.

Muddying the waters is the fact that the normal matter, which is dominated by Hydrogen and Helium, is only a minor piece of the overall cosmic puzzle. Universe is supposed to be dominated by dark matter and dark energy. Dark matter and energy make much of the Universe unknown. And it is fair to say that Hydrogen and Helium dominate only the known part of our Universe.

Earth itself is very insignificant in the Universe. Given its size in our own Solar system, given the size of our Solar system in the Milky Way, given the position of Milky Way in the local cluster of galaxies etc. And now we know that whatever is found on Earth is insignificant as well, not just its size. The big picture is really big indeed.