Most of us may feel that we are familiar with the concept of Time. Yet, our understanding of the concept of Time is quite limited. I say this because we tend to understand or see the same by measuring Time Intervals between events using clocks and the predefined concept of Hours, minutes and seconds. So with all this inside your mind, how would you define Time? Let’s find out!

### Perception of Time: What are we actually measuring?

Let us take Time in reference to Past, Present and Future. We all experience the present at any given point.Let us take this as an example I’m typing this and you are reading this in the Present. Yet when you finish reading this you can conveniently say that It is the past. Such is the nature of Time. Confused? Well read on! Not? Well you still have to read!

There are various theories related to Time and the nature of each one of them makes it really tough to determine what actually is Time. Moving on..the simplest way to define Time would be… “Time is a measure in which events can be ordered from the past through the present into the future, and also the measure of durations of events and the intervals between them. Time is often referred to as the fourth dimension, along with the three spatial dimensions.” Let me take the liberty of introducing you to the concept of Light Cones. The below is a representation of the Light Cone:A simple description of the light cone for better understanding is “A light cone is the path that a flash of light, emanating from a single event (localized to a single point in space and a single moment in time) and traveling in all directions, would take through space time.”

Think of dropping a pebble into a pond, and the circular pattern the resulting wave makes. Now take a photo every second, and stack these one on top of another, and you have a “cone” of sounds waves. The oldest image of the wave is also the biggest, and furthest back in time.A light cone is not a physical object, nor is it made of light, it is a path that a mass-less object would take whilst traveling at the speed of light. It’s more like an imaginary boundary causally separating two regions of Space. The concept of light cone provides a fair insight on how objects would behave in Space-Time warps. So what is Space-Time Relativity? Let’s find out!

### Space-Time Relativity:

Einstein’s Theory of General Relativity has changed many ways including the concept of “Present ism”, which meant nothing but the Present is the only thing that exists. “Present ism” theories can wait for another edition. The theory of General relativity and Special relativity easily explains how motion and gravity are related to the fundamental nature of Space and Time.

“Einstein’s theory of general relativity predicted that the space-time around Earth would be not only warped but also twisted by the planet’s rotation. Gravity Probe B showed this to be correct.” In 1905, Albert Einstein determined that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum was independent of the motion of all observers. This was the theory of special relativity. It introduced a new framework for all of physics and proposed new concepts of space and time. Einstein then spent 10 years trying to include acceleration in the theory and published his theory of general relativity in 1915. In it, he determined that massive objects cause a distortion in space-time, which is felt as gravity.

This is where the concept of Space-Time Continuum comes into light, based on his theory of Special Relativity Einstein found out that Space and Time are interwoven into a single continuum known as Space-Time. According to Einstein’s mathematics, Space is restricted to 3 Dimensions and there exists a 4th Dimension which happens to be Time. There are many recent theories that presume existence of extra dimensions that we do not perceive, once again we’ll leave this for another edition. Space-Time can be thought of as a grid or a fabric, now presume the presence of mass in this grid or fabric of Space-Time! What would it do? Well it would distort Space-Time, just as shown above.

### Time-Dilation:

Time Dilation is based on the theory of Relativity, it is nothing but the difference of time elapsed between two events as measured by observers either moving relative to each other or situated away from gravitational masses. Time in the moving system will run slower as compared to a stationary observer. There is a factor by which time runs slower and it is,

The above equation is a reciprocal of the Lorentz contraction. As per the contraction the effects are negligible for small velocities but as the velocity is nearing the speed of light the effects increase asymptotically. You can observe the same in the graph provided below!

I will explain the above in a much simpler way by using the following example, Consider a person A who is our observer and person B who is in motion relative to person A. Both person A and B have a watch. Now the concept of Time Dilation here is, in the case of person B the time runs slower as compared to the person A, this difference may be negligible and insignificant because of the velocity at which person B is traveling yet it is measurable provided you have accurate atomic clocks and the velocity is comparatively closer to the speed of light. The following info graphic will make this clear.

At the velocities people currently travel the effect of time dilation is small, but measurable with accurate instruments. Since time dilation affects the rate at which time passes, the total discrepancy between stationary and moving clocks increases throughout the voyage. Several Russian cosmonauts have spent a year or more in Earth orbit on the space station Mir. Their orbital velocity, about 7700 meters per second, is only 0.0000257 times the speed of light, yielding a time dilation factor of 1.00000000033; each second on board Mir, 1.00000000033 seconds pass on Earth. For every second you age on Earth, the cosmonaut in orbit ages 3 nanoseconds less. This doesn’t seem like much, but it adds up; after a year the cosmonaut’s watch will be 3.8 seconds behind your earthbound timepiece.

You don’t even have to go into orbit to measure time dilation. Modern-day atomic clocks are so accurate that when synchronizing clocks between different observatories, the effect of time dilation due to transporting the reference clock on an airline flight must be taken into account.

### GPS : Time Dilation in our daily lives

In order for your car’s GPS navigation to operate as precisely as it does, satellites have to take relativistic effects into account. This is for the reason that even though satellites are not moving at anything near the speed of light, they are still going very fast. So, there’s a relativistic time dilation combined with the influence of Earths micro gravity, the atomic clocks on GPS satellites tick approximately 7 microseconds slowly each day relative to stationary gravity less observer. But, the story doesn’t end there. Further, the satellites are in orbits high above the Earth, where the curvature of space-time due to the Earth’s mass is less, the clocks on the satellites appear to be ticking faster than identical clocks on the ground. So the clocks in each GPS satellite should get ahead of ground-based clocks by 45 microseconds per day.

The combination of these two relativistic effects means that the clocks on-board each satellite should tick faster than identical clocks on the ground by about 38 microseconds per day (45-7=38). This sounds small, but the difference is very real: if no relativistic effects were taken care for, Over the course of a day this will build up to an error of approximately 10 km which renders the system utterly useless. So the ground stations have to constantly monitor the system and update the clocks on the satellites to counteract the fact they run fast and ensure that the world continues to run smoothly.

I guess we have discussed too much of raw data and information to take on in a single edition but such is the nature of these topics. Ponder on this topic and see what you make out of it. Watch this space on the next edition as we introduce you to “ Black Holes” and their phenomena. Until then, see if you can make some observations related to Time Dilation.

**Citations: **

##### C-Ship Einstein’s Theory of general and special Relativity,

##### How Relativity contradicts Presentism, Faculty of Philosophy, St. Oxford Metaphysics and Relativity, University of St. Andrews,

Wow simply wow…. I thought some professional wrote the article but here at the end I see mr. suryavanshi… Such examples such explanation…!!!

I mean no offense in saying I thought a professional wrote the article…I meant to say u r not a professional astronomer bt yet u were as brilliant as one…

Thank you very much tahir for your feedback. But it’s not just me behind the articles. It’s always team Astrosoc India.