Last week, I read “Astrophysics for People in a Hurry”. I enjoyed the read but, overall, thought that there was too much information and too little explanation. The book is short but, advertised “for People in a Hurry”, I didn’t think it was accessible for a person with no scientific background. I would have enjoyed the chapters to be slightly longer and a bit more in depth. Nevertheless, I did learn quite a few things:
The 3 most important things I learned in “Astrophysics for People in a Hurry”:
Does antimatter exist? If so, what is it?
Yes, it does exist and, as the name suggests, antimatter is the opposite of matter. You’re probably telling yourself: “yes, I could have guessed that, but, what does ‘the opposite of matter’ mean?”. Well, antimatter particles are identical to their matter counterparts except that they carry the opposite charge and spin. For example, anti-electrons (or positrons) are just like electrons but instead, have a positive charge. The magical thing though is that encounters between particles and antiparticles lead to their mutual annihilation. So, a universe with equal amounts of matter and antimatter is equal to no universe at all. But, why is the observable universe composed of almost only matter, instead of an equal mixture of matter and antimatter?
Scientists presume that there was one extra matter particle for every billion matter-antimatter pairs during the Big Bang. Since there was slightly more matter than antimatter, the matter that hadn’t been annihilated into energy became the universe that we see today. If matter wouldn’t have outnumbered antimatter, we wouldn’t be here. This, however, is just a theory. The asymmetry of matter and antimatter is one of the great unsolved problems in physics.
What is the cosmic background radiation?
You might think that a large part of the universe is just dark – that there is nothing there. But, a sensitive radio telescope can detect a faint background noise coming from every direction in the universe. The strange thing is that this radiation isn’t associated with any stars, galaxies or other objects. It’s been called the cosmic background radiation (or CBR) and scientists believe that it is “the afterglow of the Big Bang”.
Initially, when the universe was born, the heat from its creation made it too hot for electrons and protons to coalesce into atoms. The matter in the universe was in a state known as plasma. This plasma was emitting light, but, the light couldn’t travel very far because it kept bouncing off electrons. So, if you would have been around at the time, you wouldn’t have been able to see anything. You would be in a white-hot fog of plasma.
After about 400 000 years, the universe had expanded enough – and therefore cooled down enough – for electrons to combine with nuclei to form atoms. Because there were no more free electrons to redirect the light, the universe was, for the first time, transparent. In fact, the universe wasn’t black as we know it today. It was orange.
From that moment onwards, the light was able to propagate through the universe forever. The CBR is basically the leftover of this light emitted during the Big Bang.
But, why can’t we see the CBR? Why isn’t everything orange as it once was? As the universe expanded, the wavelength of the light emitted by the Big Bang stretched out too. Consequently, its frequency has gone from the visible to the microwave part of the spectrum. So, you can’t see the CBR with your eyes.
What is dark matter ?
A few months ago, I read about how Hubble discovered that the universe is expanding. In the process, I learned about dark energy (you can read about it here). In short, dark energy is a mysterious force that drives the accelerating expansion of the universe. I’ve now also been introduced to dark matter.
Dark matter is known as ‘the missing mass of the universe’. It is thought to account for approximately 80% of the matter in it. We’ve never actually been able to observe dark matter but, without it, a variety of astrophysical observations can’t be explained. For example, many galaxies would not have formed or would not move as they do if they did not contain a large amount of unseen matter. Just like the asymmetry of matter and antimatter, dark matter is one of the great mysteries of physics.
Painting by Peter Doig