Where is dark matter and dark energy supposed to exist?

We've seen the *effects* of what Dark Matter and Dark Energy do... But what the material or energy itself is made of or from - we don't know yet (Hence the term, "Dark.") Think of the planets we discovered in the mid-90's - we couldn't see *the planet itself*, but we could see the effect it's gravity had on its parent star. Dark Matter and Dark Energy are similar - we can see their effects - but not truly what's causing those effects.

The reason it's called dark is that not only can we not see it, but we don't know what it is. There are theories explaining why they might be dark, however. One theory for dark matter is that it's an elusive particle like the neutrino, that can pass through solid matter but still has mass. In that case, it interacts only gravitationally, and would be difficult or impossible for us to detect. Another is that dark matter exists as compact objects such as black holes, neutron stars, also difficult to detect. Dark matter appears to clump near galaxy clusters, or rather galaxy clusters clump within dark matter halos. Dark energy is though to be a property of space itself, however, like the Casimir effect. So it can't be seen, but its force can be felt over huge volumes of space. Over small volumes of space, like individual solar systems or even galaxies, its force is comparatively tiny.

After publishing his General Theory of Relativity in 1915, Einstein explored the consequences of his gravitational field equation. G = 8πT In a paper titled 'Kosmologische Betrachtungen zur allgemeinen Relativitatsctheorie' (Cosmological Considerations on the General Theory of Relativity) published in 1917, Einstein found that to model a steady state universe, which was the then favoured model, he had to bastardise his field equation into the parameterised form: - G(μν) - λg(μν) = -κ(T(μν) - ½g(μν)T) Where the constant(?) 'λ' is the cosmological constant or a 'fudge factor' that Einstein introduced to make his field equation work for a steady state universe. When Edwin Hubble discovered, in 1925, that the universe was expanding, Einstein commented that this constant was the greatest blunder of his life. It seems that Einstein ignored the implications, implicit, within his field equation that the universe is expanding! However, a modern interpretation of this constant is that it represents a repulsive aspect to the gravitational force. The repulse force could be viewed as anti-gravity! Wikipedia, the free encyclopaedia comments, 'In 1998, observations of type Ia supernovae ("one-A") by the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory and the High-z Supernova Search Team suggested that the expansion of the universe is accelerating'. this acceleration is attributed to the presence of 'dark energy'. However, Wikipedia, the free encyclopaedia further comments, 'The simplest explanation for dark energy is that it is simply the "cost of having space": that is, a volume of space has some intrinsic, fundamental energy. This is the cosmological constant, sometimes called Lambda (hence Lambda-CDM model) after the Greek letter λ, the symbol used to mathematically represent this quantity. Since energy and mass are related by E = mc², Einstein's theory of general relativity predicts that it will have a gravitational effect. It is sometimes called a vacuum energy because it is the energy density of empty vacuum.....The cosmological constant has negative pressure equal to its energy density and so causes the expansion of the universe to accelerate.'