Monday, December 1, 2014

The ultimate speed limit - Light, and why is it so

The movie Interstellar reinvigorated my childhood curiosity about the natural world.  Questions and wonder overwhelmed me.  My favorite subject during school and college was Physics.  I still love it and regularly read the new findings.  Interstellar got me thinking on many of the phenomena we don't observe; like what makes certain materials transparent and others opaque.  Why is the speed of light limited to ~3,00,000 km/s, what does empty space exactly consist of etc. etc.  A lot of thoughts came rushing.

I picked up a random one, why does light have a speed limit, what is the constraining factor?  I tried reading online and asked questions in science forums (like StackExchange).  Upon reading multiple sources, the response left me in awe.  Something amazing happened when stuff travelled through space.
A short answer to the question is:  The speed limit is not that of light, but the medium in which it is travelling.  This implies that ~3,00,000 km/s is the speed limit of the vacuum through which light travels. 

Long answer; all I thought I new about space and vacuum was inadequate.  To explain, let me draw an analogy with a compute memory hard disk.  Those of us in Computer Science would know that there is nothing like empty memory.  When we buy a hard disk of 1 terabyte space, the memory is not actually empty.  It has some junk data that is de-referenced.  Or in other words, when we delete a file from our computer, it is de-referenced from the objects in the system.  No memory location can point to the deleted area, but the data still resides there (Even after it is deleted from Recycle Bin, in Windows' parlance).  This is a security concern, as anybody with a physical access to the hard disk can extract the data.  Anti-Virus companies came up with a solution of shredding the memory.  This process basically overwrites the memory location with junk data, so the deleted data is lost permanently.  The important point here is that memory has to contain something if it has to exist, or there is nothing like empty memory.

This logic applies to vacuum as well.  Nothing can be empty in the universe.  Even space which seems empty  is a plasma of annihilating particles.  And this plasma has certain properties, one of which is the maximum speed of any form of energy travelling through it (remember, matter is a form of condensed energy).  This is what limits the speed of light.

Let me draw another analogy; let's say you are travelling from Pune to Mumbai, an average distance of 150 km.  You are travelling at a speed of 600 km/hr.  Assuming there's no traffic, you should reach your destination in 15 min.  But there are toll booths in between, which limit your minimum time.  If there are total 3 toll booths and each take up 5 minutes, then at any speed you won't be able to reach your destination before 15 min.  Similarly, there are electromagnetic doorways in vacuum space, which restrict the speed of any form of energy travelling through it.  Even though I can travel at infinite speed between these doorways, I will have to wait at the next door way until it opens.  I got goose bumps even typing this.


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What this means that in a parallel universe, there might exist such pockets where space and time geometry is such that it allows faster than light travel, without worm holes.  Scientists are exploring such possibilities.

This is a very naive explanation to a very complex phenomenon.  But that's the challenge, if I can't explain something in simple terms that a layman does not understand then it means that I myself do not understand the concept clearly.  It's wonderful exploring how complex the mundane phenomena around us are. 
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