Imagine you're aboard a spaceship, hurtling through space at nearly the speed of light. To you, everything feels normal—minutes tick by on your clock as usual. But what if I told you that, for someone watching from Earth, time on your spaceship is moving much slower? What seems like minutes to you could be hours or even days to them. This mind-bending phenomenon is called time dilation, a fascinating consequence of Einstein's theory of relativity. But how does it work, and why does time behave differently when you’re moving so fast? Let’s delve in and explore the science behind it.   . Time dilation is a concept from Einstein's theory of relativity that says time can pass at different rates depending on how fast you're moving or how close you are to a massive object. For example, if you travel very fast or are near a strong gravitational field, time will pass slower for you compared to someone who is moving slower or further from the massive object. Today we are going to only see about the object which travels very fast .

Lets begin,

Time dilation occurs when one observer (or object) is moving at a significant fraction of the speed of light relative to another observer. The faster an object moves, the slower time passes for it when compared to a stationary observer. This effect becomes especially noticeable at speeds close to the speed of light.

 Stationary Observer

   The person is stationary seating on chair, meaning they are not moving relative to their surroundings. For them, time is ticking normally. The clock next to them represents their perception of time which is one second feels like one second.

Moving Object (Spaceship traveling at 0.99999c)

   The spaceship  is moving extremely fast, nearly at the speed of light (0.99999 times the speed of light). According to special relativity, when objects move at speeds close to the speed of light, time slows down for them relative to as stationary observer .  Now here slowing of time compared to other means none other than time dilation.

Now we might think that why it happen -

So the reason behind time dilation is that  the speed of light is constant in all frames of reference, regardless of how fast an observer is moving. This idea is proposed by Einstein in his theory of special relativity. The Speed of Light is Always the Same One of the fundamental principles of special relativity is that the speed of light (c) (approximately 300,000 km/s), is the same for all observers, no matter how fast they are moving relative to one another. Even If you're moving at 0.999999999999999c the speed of light and your friend  is standing still, both of you would still measure the speed of light as  (c) . If the speed of light is constant for everyone, the way time and space behave must change for different observers. This is where time dilation comes in. For someone moving close to the speed of light, light still has to cover the same distance in a given time. Since light cannot travel faster than( c), time must slow down for the moving object to make the equations balance. At high speeds, events that happen simultaneously for a stationary observer may not happen simultaneously for someone moving at high velocity. This shift affects how time is experienced.

Now lets take the above image and solve the math 

∆ t' = is the time interval for the stationary observer.

∆ t = is the time interval for the moving observer.

 v =  is the velocity of the moving object (0.99999c)

c  = is the speed of light

The factor of time dilation is approximately 223.6. This means for every second that passes for the astronaut moving at 0.99999c, 223.6 seconds pass for the stationary observer. This happens due to the extreme velocity close to the speed of light, leading to significant time dilation effects.

The actual time ∆t experienced by the moving object (astronaut) could be any value in seconds, minutes, or hours. 

For clear picture lets solve more 

1. 1 second for spacecraft  =  223.6 seconds for stationary observer 

2. 1 minute for spacecraft  =  223.6 minute for stationary observer (3 hours ,43 minutes and two seconds )

3. 1 hour for spacecraft = 223.6 hours for stationary observer (9 days and 7hours  or  9.311 days )

4. 1 day for spacecraft =  223.6 days for stationary observer 

5. 1 week for spacecraft = 4.28 years or 1565.2 days for stationary observer 

6. 1 month for spacecraft = 18.38 years or 6708 days for stationary observer 

7. 1 year for spacecraft = 223.6 year for stationary observer

As demonstrated above we can understand that the astronomer 's age in spacecraft will grow by just 1 year where as stationary person 's age will grow by 223.6 year.  These shows us how drastically time slows for someone travelling at near speed of light compared to a stationary observer .