What came before the Big Bang?
If the universe began billions of years ago with the Big Bang, what preceded it? According to the late renowned physicist Stephen William Hawking, PhD: Nothing. However, no one can know for sure; any events that happened before the universe came into existence are without “observational consequence,” as Hawking put it, and therefore, we “may as well cut them out of the theory, and say that time began at the Big Bang.”
What is dark matter?
Everything and everyone is made up of “baryonic matter:” protons, neutrons and electrons. Until about 30 years ago, astronomers thought that the universe followed the same rules – it was entirely baryonic matter. Over the last few decades, however, scientists have found that only 5 percent of the universe is composed of baryonic matter – and they can’t even detect the other 95 percent. Scientists believe that some 25 percent consists of dark matter – but nobody can say definitively what dark matter actually is or what it’s made of yet.
What is dark energy?
The other 70 percent of the universe is thought to be comprised of dark energy. What scientists do know about dark energy is that it has a gravitationally repulsive effect (which is to say, the opposite of gravitational pull) and that it’s responsible for the expansion of the universe. But what exactly is dark energy continues to elude scientists, leaving NASA scratching their heads and wondering if Einstein got his theory of gravity wrong.