Years ago, eight to be exact, I found myself at a wedding party. Somehow I never found the appeal in those, so imagine my excitement when I heard Mum hurry towards me and inform me that there was a theoretical physicist amongst the guests, and she knows him through a mutual contact. Being the restless, naïve and oblivious kid that I was, albeit with a big interest in what happens in space, I was introduced to him. He was a Ph. D. student, working in several aspects of gravity and general relativity, and hence, of course space (spacetime, since now I know better)! Here is how the conversation went (at least how I remember it):
* small talk *
(Because I was nervous just as, a fan is, of a celebrity. Scientists were celebrities to me always, yes)
Me: What do you do Dada?
(for those of you not familiar with this local word, it is a respectful way to address a senior)
Him: I study how gravity works in the grand scheme of things, from the very small of particles(?) to the biggest of stars (galaxies, clusters, the whole universe)
Me: * speechless for a full 28 seconds and then * THAT IS AWESOME!!! I want to study space too when I grow up!
Him: That is very good, what are you interested in? Astronomy or Astrophysics?
Me: * dread landing on my face * ASTROPHYSICS. Wait, no, ASTRONOMY. Oh nonono, what is Cosmology Dada? It's the same right?
At this point I managed to put him in the identical position that I found myself in last night, at, no points for guessing, a wedding party! There was this distant cousin of mine, about a couple of years younger than what I am referencing to myself above. This kid, which I have to say was much much smarter than me, asks me: "Dada, I want to know more about the universe, what should I study when I grow up: Astrophysics or Cosmology?"
Thanks to my Dada eight years ago, I was able to answer her question! What follows is my explanation of the broad differences and similarities of each, based on what I had learnt all those years ago, added to my meagre experience since...
Say your look up in the sky with your bare eyes, and you see some object, any object, perhaps a bird, or a plastic bag floating around, or a satellite, or a plane, or a human falling down, maybe a meteor, or an asteroid, or a planet, maybe a star, maybe constellations, and gas clouds, and supernovae, and clusters, and super-clusters, and filaments, and whatever else there is. Chances are, they are merely spots, rather flecks, in the background. A far away floating plastic bag, might appear the same as a low orbit satellite reflecting off the sun. Or a planet, might appear to be a star, because on the sky, they are merely "points of light". So how can one know which is which? Well, you may take a pair of binoculars, which may help you differentiate between a plastic bag, and a bird. Or you may get your hands on an amateur telescope and be able to tell the planets and stars apart. Now what? You yearn for a more powerful instrument, but you are broke. Does that mean the end of human exploration into the unknown? What saves us, is collaboration: thousands, if not millions, of people donate to buy a better instrument, which is then shared by a select number of not-dumb-at-all humans. These people, are Astronomers, and what they do is merely look at objects, and try to come up with insanely ingenious (and often ridiculous, to the uninitiated) ways to tell them apart: this can range anywhere between knowing what their shapes are, to how brightly they glow, and also how fast they are moving with respect to us. This, is, Astronomy.
They say looks don't matter. To some, it really doesn't. To some, it very much does. And there are yet others, who claim to cherish "inner beauty" above all else. The intersection of this final class of sentient terrestrials and those of Astronomers, often end up calling themselves Astrophysicists. They are not content with merely how a certain speck in the sky looks, but why does it look that way, how did it come to look that way, and what makes it up on the inside, often suggesting techniques to literally look into the anatomy of such heavenly objects (again insanely ingenious and ridiculous). To put it simply, these creatures believe that the laws of Nature hold the same everywhere as they do in our puny laboratories. They aim to explain exotic, distant and oftentimes magical phenomena via simplistic verifiable principles that they believe Nature demonstrates the same at home as they do on (and in) a distant object. So if you're bored solving inclined plane problems on Earth, this might be a good direction to get some adventure. That, pretty much sums up Astrophysics.
Then come the "purists" (I claim to neither assign negative, nor positive connotations to this word in the present context; that is for you to decide)
Are these people scientists?
Or are they philosophers?
Wizards maybe,
or just plain crazy.
Some folks think BIG. They don't care about the little things. Stars and planets are but mere dust to them. Talk to them about galaxies, and they go, "boooring". Ask them about black holes, neutron stars, pulsars and quasars, they simply shrug, chuckle and walk away. Yes these human beings are called Cosmologists. They worry about the stage where all is played on. The background, the large scale structure to the chaos. Clusters of galaxies, to super-clusters, to super-super-clusters, to massive voids and filaments are what interest them, up until to the edge of what we can "see". Questions Cosmology tries to answer often coincide with what Religion and Spirituality have been asking since millennia:
Why do we exist?
Where did we come from?
Why are things the way they are?
What are we made of, like really?
When will it all end, if at all, and into what?
Is anything real?
The origin of the Universe, what happened to it as a "baby", how it evolved, why does it look like it does today, its ultimate fate, and what came before and what may come after it, are some of the musings that Cosmologists like to partake in. The result is wonderful notions about our existence, rooted in deep logical and mathematical arguments. That is mere mathematical philosophy you might exclaim! Isn't physics an experimental subject? As is almost all Science? Yes. So has Cosmology been, lately. The advent of technology, and money, has enabled us to do things which were unthinkable about a century ago. We have measured the baby "light" of our Universe to exquisite precision. We have seen how the first stars came to be. We know the entire Universe is expanding at an accelerated rate, and all that we see around us is a mere fraction of dark "stuff" out there. Cosmology is no longer a hobby of retired theoretical physicists and astronomers. It involves experimentation, computation, observation and analysis at tremendous scales today. So if you ever wonder one night what the point of everything is, give Cosmology a try.
I forgot about Astrology. You should too.