96% of Our Universe is Missing - What Can the Matter Be?

 It's an embarrassment of gargantuan proportions that lies at the heart of modern physics, a kind of cosmic elephant in the room. Put simply, physicists realize that when we look out 13.7 billion light years across the visible universe with our telescopes, whether at visible,

infrared, gamma ray or x-ray wavelengths, we are only seeing a tiny proportion of all that there is. Modern physics and its key theories of Newtonian and quantum mechanics and general relativity, which has successfully provided us with everything from iPods to GPS systems simply doesn't have a clue as to what makes up 96% of the universe.

The best estimates of cosmologists and physicists reveal that the universe is constituted of 4% of normal baryonic matter, consisting of the things we see with our eyes and detectors. This is made of atoms and their constituent parts --

and includes stars, planets and intergalactic dust. Einstein said that mass and energy are equivalent, and since the late 1990s astronomers and cosmologists have found that a staggering 73% of the universe is made of something called Dark Energy, which reveals itself and an anti-gravitational force. The expanding universe it turns out, as first revealed by Edwin Hubble isn't just expanding at a linear rate, the expansion is accelerating.

One day in the far and distant future, cosmologists will no longer see galaxies outside our own cluster -- they'll simply be over the horizon, too far away for light to have had enough time to travel to the Earth. For now though, we have little idea as to what Dark Energy actually is.

We may have rather more success in identifying Dark Matter, first postulated by astronomer Fritz Zwicky in 1934, to account for evidence of "missing mass" in the orbital velocities of galaxies in clusters. Subsequently, other observations have indicated the presence of dark matter in the universe,

including the rotational speeds of galaxies, gravitational lensing of background objects by galaxy clusters such as the Bullet Cluster, and the temperature distribution of hot gas in galaxies and clusters of galaxies. It is believed that most Dark Matter, by its very nature does not consist of atoms, it doesn't interact with electromagnetic radiation, and therefore we cannot detect it with our telescopes.

There are many possibilities as to what Dark Matter may be, and these include:

-- Normal matter which has so far eluded our gaze, such as dark galaxies, brown dwarfs, planetary material (rock, dust, etc.), or black holes. Some of these could be MACHOs (Massive Astrophysical Compact Halo Objects), which would explain the distribution of Dark Matter in galaxy halos.

-- Massive standard model neutrinos.

-- Massive exotica. These can be divided into two possible classes, the first consisting of either axions (a hypothetical elementary particle), additional neutrinos, supersymmetric particles, or a host of others. Their properties are constrained by the theory which predicts them, but by virtue of their mass, they solve the dark matter problem if they exist in the correct abundance.

Particles in the second class are generally classed in loose groups. Their properties are not specified, but they are merely required to be massive and have other properties such that they would so far have eluded discovery in the many experiments which have looked for new particles. These include WIMPS (Weakly Interacting Massive Particles), CHAMPs (Charged Massive Particles), and a host of others.

Whatever Dark Matter turns out to be, and there are many experiments being conducted around the globe to detect it including at the Large Hadron Collider at CERN and in subterranean laboratories, we are likely to have an answer as to what this fundamental constituent of the universe is, long before that for Dark Energy.

For whichever way you look at it - it's an embarrassment for modern physics to only know what 4% of the universe is actually made of!

• tags:
• DarkEnergy
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• DarkMatter
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• LHC
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• CERN

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