Time Dilation

Look at the image carefully what does this say....

What is time dilation? What is the time dilation equation in special relativity? Read to know all about this special relativistic phenomenon.
time is not constant everywhere it varies...

The premier theories that dominate classical as well as gravitational mechanics are the special and general theories of relativity. Both were formulated by Albert Einstein in 1905 and 1915 respectively. The special theory deals with motion with respect to inertial frames of reference, while the latter deals with accelerated frames. One phenomenon that is described by both theories is time dilation or the slowing down of time. In this article I'll present an explanation of time dilation for dummies or laymen interested in physics. The equation presented here will only deal with the one related to inertial reference frames.

What is Time Dilation?

Let me first state the principle of time dilation that arises from an analysis of the motion of an object moving at a constant velocity, with respect to an inertial reference frame. Here it is. When an object moves at a constant velocity with respect to any inertial reference frame, a clock attached with the object will move slower than a clock which is fixed to the reference frame. The faster an object moves, slower will be its clock with respect to the reference frame clock. By clock attached to an object, I do not mean an actual clock. The change in the time variable associated with the object itself slows down! This is indeed one of the most astounding relativistic phenomena, besides Lorentz contraction, which you will study in advanced physics.

The Time Dilation Equation

This phenomenon can be described quantitatively by the following time dilation equation. Consider a spaceship moving at a high but constant speed with respect to a stationary reference frame. Let Δt' be the time associated with the spaceship travel, v its velocity and let Δt be the interval of time variable change related to the reference frame. Then the equation states that:

Δt' = Δt / √(1 - v2 / c2)

Here c is the velocity of light (3 x 108 meters per second). Work out the proof of the equation to know it in more detail. If you observe the above equation carefully, you will see that higher the velocity (v) is, longer will be the time interval (Δt')! So effectively, time has slowed down for every one on the spaceship, with respect to the inertial reference frame. However, the inhabitants on the spaceship will see time changing at its usual rate.

Gravitational Time Dilation

A phenomenon similar to special relativity time dilation occurs when an object is in a gravitational potential. The closer an object is to a gravitation potential, greater is the hold of gravity, and slower its clocks will be! So a clock kept at the sea level, will move slower compared to a clock placed on Mount Everest! It is not possible to discuss the equation for time dilation here, as it is different for every spacetime geometry. This phenomenon has been experimentally verified by physicists using the Mössbauer spectrometer.

The phenomenon of time dilation arises due to the very nature of spacetime and as a consequence of the basic postulates of special theory of relativity. The phenomenon of muon decay where it lives longer due to its high speed motion is conclusive evidence for time dilation. The phenomenon in its most crude form can be explained as 'Faster an object moves, slower does its clock move!'. Similarly, the closer you get to the surface of earth, slower is your clock running and the higher you go, faster is the clock going to move. Of course, the change in time is too small to be felt but it does exist. All this is a result of the 'local' nature of time.

Ring Nebula's structure Revealed by HUBBLE

The Ring Nebula in Lyra lies 2,300 light years from Earth. It is estimated to have been expanding for about 1,600 years.

Quantum Entanglement - Explained

Quantum entanglement is a quantum mechanical phenomenon in which the quantum states of two or more objects have to be described with reference to each other, even though the individual objects may be spatially separated.

This leads to correlations between observable physical properties of the systems.

For example, it is possible to prepare two particles in a single quantum state such that when one is observed to be spin-up, the other one will always be observed to be spin-down and vice versa, this despite the fact that it is impossible to predict, according to quantum mechanics, which set of measurements will be observed.

As a result, measurements performed on one system seem to be instantaneously influencing other systems entangled with it.

But quantum entanglement does not enable the transmission of classical information faster than the speed of light. Quantum entanglement has applications in the emerging technologies of quantum computing and quantum cryptography, and has been used to realize quantum teleportation experimentally.

At the same time, it prompts some of the more philosophically oriented discussions concerning quantum theory.

The correlations predicted by quantum mechanics, and observed in experiment, reject the principle of local realism, which is that information about the state of a system should only be mediated by interactions in its immediate surroundings.

Different views of what is actually occurring in the process of quantum entanglement can be related to different interpretations of quantum mechanics.

What Caused the Big Bang?

For almost one hundred years, we have known that the universe is expanding. We have traced this expansion back in time, through to the very beginning when the universe occupied an infinitesimal point in space. This was the state of the universe at time t=0, over 13 billion years ago.

It is from this starting point that everything we are familiar with came into existence: protons, neutrons, stars, galaxies - even space and time itself are here. At time t=0, this point began an unprecedented inflation, in this instant time and space were born. This event has become known as the Big Bang.

The big bang is our current, most accepted theory for how the universe began. It was inspired by the discovery that the universe is expanding.

It was an unusual and highly counter intuitive event. It was not an explosion, it did not occur inside anything, rather, everything that we are familiar with: left, right, up, down, cause and effect, the stage for all physical laws, was getting larger.

We possess a natural curiosity of the world around us. We want to know how and why things are the way they are.

This curiousity has served us well because it carries significant survival benefits. If we see an event and ask ourselves why it happened or what caused it, we are more likely to spot a threat before it becomes dangerous in the future.

Our curiosity gives us the ability to look beyond the present moment. From it, we have evolved an urge to look for causes, it is an inseparable part of our biology. Because of this, we really can't help ourselves when we attempt to find a cause for creation, it is second nature for us to ask, 'What Caused the Big Bang?'

Any answer to this problem must begin with a key realization: both time and space are contained within the universe and came into existence only AFTER the Big Bang occurred. The cause of the universe must not include them, they are not available to us. It must come from outside our experience.

In this realm, the solution, whatever it is, will seem very strange to us, and it will almost certainly make no sense to our brains because here, it is possible to have an event with no cause. There is no time, there is no before in which the Big Bang could have occurred, there simply is no cause and effect.

We must somehow come up with a solution that exists outside time and space.

GOD MADE IT HAPPEN

For many "God caused the big bang" is a perfectly reasonable response. This seems to help many cope with the unsatisfying prospect of an event without a cause.

The problem of course is that one is then immediately forced to ask, "From where did the creator come?"

If the answer is "he always existed" then we have a situation, from a causality standpoint, that is no more satisfying than a universe that springs forth from nothing. A creator that has always existed is an entity that somehow exists without a cause.

So this answer doesn't solve the causality issue whatsoever.

THIS UNIVERSE IS ONE OF MANY

Further, the idea of cyclical universes doesn't solve it either.

For reasons having to do with entropy and the second law of thermodynamics the process of an ever cycling universe - one that continually expands and contracts - cannot be perfectly efficient. This means that each successive expansion will take a little longer than the previous one.

If each previous universe is, say, half as long as the one that succeeds it, and the one before that half as long, this infinite sum does eventually converge to a universe with zero length with no obvious past and we are back again to at least one big bang starting for no obvious reason.

OUR BIOLOGY BETRAYS US

The real problem with this question of what caused the big bang is ultimately a biological one; our brains have evolved to assume that everything has a cause, we can't imagine any event ever not having one.

But 100 years ago, we couldn't imagine that our galaxy was only one in an ocean of one hundred billion. 200 years ago, we couldn't imagine that the stars were more than 13,000 light years away. 500 years ago, we couldn't imagine that the Earth revolved around the Sun. If our past enquiries into the universe are any guide, the truth of the cosmos is always more than we have imagined.

The answer to the cause of the universe will almost certainly be something strange and, by definition, wholly beyond our experience. Our occluded brains must always be open the answer, especially when asking questions that push the limits of our capacity to understand.