Friday, November 21, 2008

Space, time and relativity - Part 1

I should have probably called it space-time and relativity, but, even 'Space, time and relativity' should be ok :-) 

For people who are new to the subject, I'd like to give a small intro before before we discuss the details...

According to Sir Isaac Newton, space is absolute. i.e., irrespective of the observer, space exists. 

To make this statement more clear, consider two places - Chennai and Bangalore.  Also consider the following dialog

Dialog #1
Me: What is the distance between Chennai and Bangalore?
Newton: 350 kms
Me: Thanks a ton.

Life becomes more complicated with Einstein...

Dialog #2
Me: What is the distance between Chennai and Bangalore?
Einstein: For whom?
Me: Holy crap!

In a Newtonian world, space is absolute. For Newton, distance between Chennai and Bangalore is same irrespective of who measures it. 

It is not so for Einstein. For him, Space and Time are relative. For an observer who is travelling at a good speed, the distance will appear less! The difference in the distance observed between a stationary and mobile observer will be more as one of the observers travels closer to speed of light (300,000 kms per sec)

Einstein published this result in 'Special Theory of Relativity'. This was a direct inference of his result that ‘Speed of light is constant irrespective of the speed of the observer’ 

For people who are not surprised by my previous paragraph, I would like to explain it further. 

Consider that a train is moving towards you at 50 kms/hour. The first thing you should do is to get off the track (he he)

Joke apart, consider you are feeling suicidal (which you shouldn’t) and standing on the track with train approaching you at 50 kmph. You’ll see that the train is approaching you at 50 kmph. 

If you are anxious to meet Mr. Yama Dharmaraj, you can choose to run towards the train, at say 10 kmph (the best I can do :-) ), the train will appear to come to you at 60 kmph. 

Suppose a dog starts chasing you, and you start running away from the train at 20 kmph, it will appear that the train is approaching you at  30 kmph. 

So far so good. Now, since you understand this, you got happy and jumped off the track and the dog got ran over by the train. Lets get back to Physics.

Now, you decide to chase light. Mr. Light Bheem is traveling at 300,000 km/sec. You decide to get on your super vehicle, and chase it at 100,000 km/sec [The fastest rocket on earth travels at less than 3 km/sec - You can now guess how fast light is!]

Since you are chasing Mr. Light Bheem at 100,000 km/sec, you expect his speed to be 200,000 km/sec (300,000 – 100,000). When you measure the speed of Mr. Light Bheem, you find that his speed is still 300,000 km/sec!!!! 

You get frustrated and increase your speed to 200,000 km/sec. And then you measure light’s speed – It is still 300,000 km/sec. You finally decide to give up and go back to railway track. You measure the speed for light for one last time after stopping your super vehicle. It is still 300,000 km/sec.

So, whatever the speed of the observer might be, the speed of light is Holy Constant. 

This observation led Einstein to derive that space and time are not absolute. 

I’ll explain more on Einstein’s conclusion next time… I have to step out now. 

Comments are welcome!

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