If you read some of the threads on this board you will find a lot quite a few discussions on these topics.<br /><br />In a nutshell:<br />Dark matter is matter that can only be observed or inferred by its gravitational effect. It might be strange quark matter, ordinary matter we cannot observe, or gravitational shadows of mass in this universe or an adjacent brane universe. Pick any two.<br /><br />Dark energy is the born-again cosmological constant invoked originally to explain a static universe. Dark energy is used to explain why the expansion of the universe might be accelerating. The pressure of the universe should be zero given that gravity cancels mass, so dark energy is thought to inject a negative pressure causing the expansion to speed up. The loss of gravitons from our universe to an adjacent brane universe has been posited as a possible source. Other sources invoke vaccuum energy and even white holes. I'm sure I'm leaving out an important one but I can't think of it at the moment. All the negative pressure...<br /><br />The expanding universe has been known since the days of Hubble (guy not the space craft) looking at red shifts of distant galaxies. By extrapolating everything flying apart back in time there came a theory described as the Big Bang. <br /><br />The best guess for what started the Big Bang is a supercooled Higgs field caught on a potential plataue when a microscopic early irregular universe cooled. The super cooled Higgs field infused space with a constant negative pressure. There are two key differences between a supercooled Higgs field and a cosmological constant:<br />1) Higgs field does not vary with time,<br />2) the energy and negative energy is 10**100 times larger than the cosmologicl constant.<br />I think this is called Guth's theory, I might be wrong. The gun powder for the Big Bang.<br /><br />