Filling In The Empty Space

What seems to be a large amount of space with nothing in it is actually full of dark energy.  The vast universe is full of celestial bodies and objects and dark matter but dark energy accounts for about 73% of the rest.  With so much in existence, how do we know so little about it and why?  Such a peculiar idea that something of such quantity can even exist.

 (pie chart comparing dark energy to the rest of the universe, image from http://opentheory.net/)

Albert Einstein (once again) was one of the first to speculate that the "empty" space outside our world was not actually empty, but instead there is something rather than nothing.  This existing dark energy has a great affect on the universe.  Alternate to the assumption that the universe is expanding and slowing down, dark energy is theorized to cause the universe to expand but instead be speeding up!  This can be a consequence of the increase in space.  As more volume is created with the expanding universe, there is an increase in dark energy causing an increase in acceleration of expansion.  Seems unreal considering that if it is creating virtually an infinite amount of dark energy, how fast could the universe actually be expanding?  Perhaps faster than the speed of light?  Only furthering studies on dark energy could answer these questions; after all, our knowledge on dark energy is more unknown than it is known.

Of course, as with many physics topics, that is just one theory of dark energy.  Another is that there are virtual particles that are said to "pop" or appear in and out of existence in space.  This assumption seems quite strange in that it doesn't explain how a particle can just appear.

The cosmological constant (often distinguished by the capital form of the Greek letter lambda) is another term used in the theory of dark energy.  This constant is the fundamental energy of space, homogeneously filling in the "emptiness".  It has been estimated to have a density value of ten to the negative 27 power (g/cm^3).  Through thermodynamic discussion, the cosmological constant has a negative value of pressure equating to the energy density (rho).  A consequence of this is the acceleration of expansion.  Expanding changes the volume, causing a negative pressure, since for an isochoric (or isovolumetric) system work = - pressure * change in volume.  The energy is equal to rho * volume and therefore pressure = - rho or vice versa. 

Dark energy is an amazing substance that hopefully can be used in the future to benefit mankind.  Just as we use the knowledge of gravity to understand how many things work, maybe we can harness the idea of this somewhat new concept to extend our comprehension of our universe.

 (picture to show vast amount of "empty" space, image from http://www.windows2universe.org/earth/earth.html)