DARK ENERGY IS THE MAJORITY OF THE UNIVERSE
I hope to describe astronomers' most recent definitions of dark energy. To me it is one of the most fascinating concepts in astronomy. There is a description of dark energy at science@nasa. The following is my summary of the website's definition.
Scientists don't know what dark energy is, but they know how much of it there is. Dark energy makes up approximately 70% of the universe. (I question how scientists can be certain of measuring the whole universe.) The matter we can observe, including all the matter on earth that we know of, makes up less than 5% of the universe. Dark matter, which I hope to describe in a future post, makes up around 25% of the universe. (Again, I wonder how scientists can claim to know what makes up the universe.)

According to science@nasa, "Albert Einstein was the first person to realize that empty space is not the same as nothingness. Space has amazing properties, many of which are just beginning to be understood. The first property of space that Einstein discovered is that it is possible for more space to come into existence. One version of Einstein's gravity theory makes a second prediction: "empty space" can possess its own energy. This energy would not be diluted as space expands, because it is a property of space itself; as more space came into existence, more of this energy-of-space would come into existence as well. As a result, this form of energy would cause the universe to expand faster and faster as time passes. Unfortunately, no one understands why space should contain the observed amount of energy and not, say, much more or much less."


According to the aforementioned article at science@nasa, scientists do not have an absolute value of the total energy in the universe. Rather, they measure differences in energy that they can observe. Scientists are not able to predict the magnitude of the energy in the universe.