Time, Space and the Universe: How Gravity Changes Time

1. Introduction

For a long time, people thought time and space were separate and fixed. One second was one second everywhere, and one metre was one metre everywhere.

Albert Einstein changed this idea completely. He showed that time and space are not separate. They are joined together into one thing called Spacetime.

We do not live only 3 dimensions . We live in 4 dimensions: 3 dimensions of space (length, width, height) + 1 dimension of time.

2. What is Spacetime?

Imagine spacetime as a soft rubber sheet. If you put a heavy ball on it, the sheet bends down.

In the same way, planets, stars, and black holes bend spacetime. The heavier the object, the more it bends spacetime around it.

This bending is what we feel as gravity. Gravity is not a force pulling us. It is the curvature of spacetime.

Objects move in a straight line in spacetime, but because spacetime is curved, their path looks curved to us. This is why Earth orbits the Sun.

3. The Speed of Light: The Most Important Rule

The speed of light in a vacuum is constant for all observers:

c = 299,792,458 metres per second

This is a very important point and a common mistake:

Mistake: People think light slows down near a heavy object, like a car slowing down on a hill.

Correction: The local speed of light never changes. If you are standing near a heavy object and you measure the speed of light passing you, you will always measure it as c.

But from far away, it looks like light slows down. This is called the coordinate speed of light. It appears slower because time itself is running slower near the heavy object, and space is also curved. So light takes a longer path and more time to reach us.

Scientists call this the Shapiro Time Delay. When radar signals pass near the Sun, they take slightly longer to return because spacetime is curved there.

So: Light does not slow down in its own frame. Time slows down, and that makes light appear to slow down from a distance.

4. Relation Between Time and Space

Time and space affect each other.

a) Special Relativity - Speed Affects Time

If you move very fast, close to the speed of light, time runs slower for you than for a person standing still. This is called Time Dilation.

Formula:

t = t ÷√1- v^2÷c^2

Conclusion :

Light always travels as (c) locally, but near a heavy object, time slows down and space curves, so light appears to take longer and its path bends.