by Steve Z.
Dark matter and dark energy are hypotheses to explain why the Universe is not behaving in the way we think it should be, suggesting that some other force is at work. In the 1990s we were quite certain of one thing about the Universe; it might have enough energy density to stop its expansion and recollapse, or maybe it had so little energy density that it would never stop expanding but gravity is certain to slow down the expansion over time.
In 1998, the Hubble telescope, while observing distant supernovae, revealed something inexplicable. Instead of slowing down, the expansion of the Universe was speeding up. So the expansion of the Universe was not slowing down because of gravity as everybody thought. Nobody knew what was causing this or why but there was something else at work here. The physicists called it dark energy.
Many people tried to explain dark energy, such as Albert Einstein, who was the first person to realise space was not just “nothing”; it has many amazing qualities we are just beginning to understand. Einstein found out that it is possible for more space to come into existence. Einstein then predicted that empty space could have its own energy that cannot be diluted as space expands. Therefore, according to Einstein’s theory, as more space comes into existence, more of this “energy-of-space” will just appear. This would account for the Universe expanding at such a rate. Unfortunately, no one knows why this should be there, much less why it would have the exact right value to cause the Universe’s expansion.
What is dark matter? We pretty much don’t know anything about dark matter, apart from a few things.
1. It is dark and is not in the form of stars and planets that we can see.
2. It is not in the form of dark clouds of normal matter; matter made up of particles called baryons. We know this because we can detect normal baryon clouds by the radiation passing through them.
3. Dark matter is not antimatter (the opposite of matter) as we do not see the unique gamma rays produced when antimatter annihilates with matter.
Right now, scientists do not know much about dark matter and dark energy. But, over time, we may begin discovering more properties of dark matter and dark energy that might help us piece together this giant jigsaw puzzle. For now, dark matter and dark energy are just obscure and vague theories which we cannot explain.
Thank you, Steve. If you have an article you would like to contribute then send it to me at my school address.
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