Question

How time is not absolute?

Answer 1

Hello friend.

To understand why Time is not absolute, we must first understand some points:

♦ The great physicist James Clerk Maxwell unified Electricity and Magnetism into a single field Electromagnetism.

He showed that electromagnetic waves (including light), are just disturbances in the electromagnetic fields.

He also proved that these waves must travel at a fixed speed through vacuum. And their speed must be the same, no matter who-so-ever measured it. This speed is 299792458 m/s

• One thing: At that time, scientists thought that light waves propagated through an invisible medium, called the 'Ether'

→ Now, according to Newton's Laws, Time is absolute. So, it is not possible that all observers measure the same speed of light.

• For example, suppose observer A is stationary on Earth, while observer B is moving towards our source of light, the Sun. Now, thinking logically by Newton's Laws, we see that B is directly moving towards the light, while A is stationary. So, B should have measured a greater speed of light.

• Consider another example: You are travelling on a bike on the road. Now, if someone is travelling alongside you in the same direction, your relative velocity would be less. But if someone is moving in opposite direction to you, your relative velocity would be more. Thus, it would appear that a person coming towards you was always faster than a person going in the same direction as you.
This argument is true.

But the interesting thing is that this logic doesn't hold for light waves.

As I said before, James Maxwell proved that electromagnetic waves must travel at a fixed speed. Plus, we experimentally verified it.

• We measured the speed of light of sun in two cases:
1) When Earth was directly moving towards the Sun
2) When Earth was not directly moving towards the Sun.

We might think that the speed measured in first case would be greater than the speed measured in second case.

But to our surprise, we found them to be exactly same.

Something is not right.

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♦ Now, the person to explain this was Albert Einstein, when he presented his Special Theory of Relativity in 1905.

→ What he said that was James Maxwell had been correct. He said that the anomalies could be explained if we were ready to give up the concept of 'Absolute Time'

The simplest explanation is as follows:

For electromagnetic waves, the speed is constant. Plus, the distance it travels is also constant.

Now, speed = distance/time

To have speed as constant, time must be a variable. That means, time must not be absolute.

→ Think of it like this: Suppose I am moving towards the Sun.
I am directly moving towards sun, and Earth is not. Now, both should measure the same speed of light. And, as I am moving towards the source of light, then my relative velocity (w.r.t sun) must be more.

Speed = Distance/Time

Now, our relative velocity is more. The distance is constant. In order to keep the speed of light constant, the value of time must increase to nullify the effect of increase in relative velocity.

In other words, 1 second for me would be longer than 1 second on Earth. In that way, both I and Earth measure the same speed of light.

→ Now, an interesting thing:
From our above arguments, it comes out that as I move faster, time must flow slower for me.

Now, suppose that I am traveling near the speed of light with respect to Earth.

But now, by Maxwell's equations, I must still measure the speed of light to be 299792458 m/s. So, time must slow down heavily for me.


So, if I was travelling exactly at the speed of light with respect to Earth, some strange things would happen.

I still must measure the speed of light to be constant.

Time must stop for me. That is 1 second for me would be infinite seconds on Earth. It would seem to Earthlings that Time ceased to exist for me.


→ From these ideas, we must now get a fairly clear idea that Time is not absolute, but relative to each observer.


Hope my explanation was good and understandable.