Beyond our Cosmic Horizon.

Geraint Lewis' blog site is one of my favourites. He doesn't like to Tweet, he likes to write about the Universe. His latest blog covered the simple concept of a changeover from a matter dominated universe to an energy dominated Universe.

The Universe contains a constant amount of matter but - because it is expanding - the density of matter is contracting. "However", says Geraint, "The energy density of the other major component in the Universe, namely dark energy, remains constant even though the Universe expands."

So, we are now in a changeover period between a 'Matter dominated Universe' and a 'Dark Energy dominated Universe'. That density transition is more than halfway completed, with Dark Energy now measured at 73% and baryonic matter plus dark matter now totalling only 27%. Eventually, the Universe will be effectively totally dominated by Dark Matter.

This is an amazingly simple concept, yet it is the result of many exquisite measurements and calculations made by a lot of very clever astronomers. 

Geraint speculates that it may be more than just a coincidence that we are living in that changeover period - right now.

As for the future - in about 10 Gyr, when the Universe is dominated totally by Dark Energy - it will expand to the point where, apart from the Local Group of galaxies (if it still exists a group), the rest of the Universe will be beyond our cosmic horizon and astronomers will all be out of business.

Beyond that and into the far distant future, he says: "If, however, dark energy is phantom energy, then the Milky Way will be ripped apart, then individual stars, and then individual atoms, an event known as the big rip."

We live in a Universe where we can actually see what was going on in its distant past and we can investigate events just after the Big Bang, as the Cosmic Microwave Background images show us. 

Only a century ago, we did not understand the Universe, yet now we do and we can begin to predict scenarios for its long term future. Living in an enlightened world like this may not always continue, after the last galaxies disappear beyond the cosmic horizon and are forgotton about. We live in a very fortunate era. 

Now that's cool!