Thursday, April 09, 2015

Gravity Fan Club

(Edit: In honour and memory of the real rock star of modern times - Stephen Hawking)


No, I’m not talking about the movie. I’m referring to the actual gravity. The force that makes your feet stick to earth. And as of now, I suppose I’m the only member of this fan club (in my age group at least :) ). Wanna join?

Back when I was a kid, there’d be days when all the friends in the street would discuss seriously about stuff we’d read in our mythologies, about our gods and demigods. (Guess we'd be labelled as 'saffronised' now). We’d discuss the mechanisms of the Pushpakavimana – Ravana’s flying city, piloted by thought. Yeah – you could just think in your mind about your destination and the Pushpakavimana would go on autopilot and steer you through. You’d be free to lounge about in the pool, drink madira and party with the apsaras. We believed wholeheartedly that there was technology back then to fly this way, and somewhere along the way, something cataclysmic occurred, and we perished, only to be reborn, all that knowledge lost...or at least out of grasp. Today we are almost there. We need many more generations; many cycles of incremental evolutions to completely harness our thoughts...but for now, artificial intelligence is good enough. (I still believe in this, laugh all you want).

Anyway, one thing that really fascinated us was that in the place where Brahma sat writing our destinies, 1 day for Him was equivalent to thousands and thousands of years for humans. Or, for the divine entities of lower order, like the regular Devas, 1 earth year = 1 Deva day or something like that.

It remained a fairy tale, until the day I began to enjoy theory of relativity (way after I was done with classroom imprisonment). And no, I don’t do equations. I’m not wired to imagine that way – for example, a line or a slope can be represented by an equation. Not my cup of tea.

So here’s the deal. First, we need to understand the concepts or space and time. For this, we should approach the two from a very literal perspective. Imagine an empty room. Just four walls, the ceiling and the floor. Now, bring in furniture. The sofa against the wall. The TV in front of the sofa. A coffee table in between the two. If you imagine the room as the space given to you, there are objects at specific locations within that space. In nerdy terms, we call the location of the objects as coordinates. Space has dimensions – length, height and width.

Now let’s consider the tricky business of time. By time, we can imagine only one thing – a clock showing the minutes and seconds. But what exactly is this concept of time? We perceive a passage of time when some event occurs in the space around us – an event that changes the state of an object; that change causes another object to change its state and so on. That became too nerdy? Well, imagine the earth as one big room – that’s our space for the time being okay? We perceive the passage of time because of a series changes around us – for one, the sun rises, rather the position of earth is such that we are able to see the sun over the horizon. This is a change in state of the earth – it has changed its position. Because this has been such a constant event over millions of years, our bodies have evolved to be in sync with the rising sun. So the next event is triggered. Millions of living bodies change the internal rhythm so that we can all ‘wake up’. The earth’s position keeps changing – this is observable by the change in position of the sun in the sky – and this in turn is perceived as ‘time’ by us. Somewhere along the discovery path, human race calibrated time. But here is the thing about time – unlike space, time has no dimensions.
So in essence, space and time always coexist. Time becomes irrelevant without space – imagine an empty room, no windows, no doors, just a dark cube. Imagine sitting in this room. You wouldn’t know whether it’s day or night; you wouldn’t have any clue for how long you’ve been sitting – because there is nothing to indicate how much time has elapsed.  To indicate this coexisting space and time relationship, a mathematical (uggg)  model was worked out – famously known as space-time continuum.

Now that we got the two lovebirds sorted out, let’s tackle gravity. In the simplest sense, gravity is the force of attraction between two objects. The greater the mass of the object, greater is its gravitational pull. That’s what Newton figured out with the falling apple. That’s the era of classical physics. Gravity is much more than objects dropping to earth. This is where Einstein’s theory of general relativity plays an important role.
Courtesy - Wikipedia

Imagine a plastic sheet stretched tautly on a frame. Now, take a heavy ball and place it in the centre of this sheet. What do you observe? There is a dip in the sheet right? Take smaller, lighter balls and place them on the outer edges of the sheet. What happens? Without you applying any force, these balls accelerate and roll towards the heavy ball in the centre of the sheet. That’s the way our galaxy is. The taut sheet is space – vacuum. In the middle of that space is the heavy mass of the sun. As in the sheet, this mass causes a dip in space. So how come none of the planets are accelerating towards the sun, and falling into it? It’s because the planets themselves are moving at such high speeds, that the velocity keeps them in orbit. Assuming the planets were stationary, what would cause them to roll towards the sun, like the little balls in our experiment? What force causes anything to fall from a higher height to a lower height? Gravity. How do we know there is a dip in space? It is, after all vacuum? Simple. A straight beam of light shows curvature, in what is known as gravitational lensing effect. In very plain terms, Einstein in his general theory of relativity said this space-time distortion caused by heavy masses is perceived as gravity.

Now, because space-time is a duo of sorts, it’s not just space that is ‘dimpled’ by gravity. Time also is ‘pulled down’. This is known as gravitational time dilation, and it’s super fascinating. In other words, time ‘becomes’ slower when we are closer to a massive body like the earth, when compared to being far away. So time for someone who is on land is slower when compared to someone who is orbiting the earth. In other words, greater the mass of the object, greater is its gravitational potential – closer you are to that object, slower is the time.

Now imagine a mass that’s a million times greater than the earth’s. Obviously, time is even more slower on such a mass when compared to earth. Do such objects exist? Of course. The biggest, badass supermassive blackhole in the middle of our galaxy is Saggitarius A* - apparently has the mass of 4 million suns. Imagine how slowwwww time would be if you are in the vicinity of this.

So coming back to my childhood fascination – Brahma’s 1 day = thousands and thousands of years on earth – it is no fairy tale at all. It is all true. Proven.    

It is comforting, especially when you have lost a loved know...on a restless night, if you look out of the window and spot a star...they’re out there.

© Sumana Khan – 2015
(PS: If you enjoyed this post, you may also like my take on the boson ) 


  1. If they taught relativity like would be getting A s..instead we had a ma'am who said that relativity can be understood by seeing an aeroplane in the sky..and the amount of Tamil and English she mixed in the copious amounts of time she had in class led me dreaming into my own space-time the way you ended this one..I know its your feeling, but couldn't help feeling "now why didn't I think of that before".. Beautiful sumana..

    1. 'seeing an aeroplane' hahahahahaha! well the space-time equations stopped working in my abstract algebra classes too. it was like sitting at the edge of a blackhole.

  2. So much of it was OHT for me i.e over-head-transmission being a very visual person. But I am somewhat like a dog with a bone.. just won't let go :) Will understand these someday.. Waiting for that Aha moment.. :)