What is dark energy?
If I had 3 wishes ... a proper answer to this would be a possible third.
I’d better start by declaring I’m no specialist, just curious, but here is what I’ve gleaned from my reading.
Dark energy was first proposed in the late 90’s when two teams independently discovered from studying very distant supernovae that they were a little bit brighter than expected, so a little bit closer than we would expect.
To unpack this will take a while. Firstly, they were all type 1a supernovae, so have a known, standard luminosity. Secondly, the distance was found from their red-shift, so well understood and a completely Independent technique. Thirdly, the effect was only present for the most distant supernovae (those further back in time.) This left one conclusion: the rate of expansion of the universe was not falling (as expected if gravitational attraction is the only force acting) but was accelerating.
It has been shown from studies of the cosmic microwave background radiation (CMBR) such as the WMAP satellite that this “dark energy” constitutes about 72% of all the mass-energy in the universe.
This leaves us with a slight problem... the total contribution of ‘known’ matter is 4.6%. Everything we can possibly account for is less than 1/20th of the cosmos.
As to what it is, we frankly have no idea, but you can read about some of the leading possibilities here.
p.s. if you find out let me know!!!
Dark energy is an unknown form of energy that is causing the expansion rate of the universe to increase.
Like the other person who responded, I am not an astrophysicist, astronomer, or cosmologist. I am an electrical engineer who briefly worked on the space shuttle a long time ago and I love all things that pertain to space.
Here is a link to the Wikipedia Dark Energy page.
The basic concept is:
Before about 1980 it was generally accepted and expected that the expanding universe was in the process of slowing down its expansion. However, during the period between 1980 and 1998, computer models and instruments were developed that could measure the rate of expansion like never before; these models and instruments repeatedly predicted or measured that the rate of expansion was increasing. This caused cosmologist Michael Turner to coin the name Dark Energy.
Not even the worlds most prominent scientists can tell you what Dark Energy is or how it works but they can tell you how strong it is. Please read the reference for more information.