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# Tag Archives: theory of relativity

## Time Dilation problem – Special Relativity

With what speed will a clock have to be moving in order to run at a rate that is one half the rate of a clock at rest?

Posted by Mona

Using the formula for Relativistic Time (according to Special Theory of Relativity)

$T=\frac{T_{0}}{\sqrt{1-\frac{v^{2}}{c^{2}}}}$

√[1 – (v²/c²)] = ½ → v² = (3/4)c²

v = [√3/2]*c = .866c

## Time Travel, Relativity

I’ve just watched “Faster than the speed of light” programme on ITV. There is one assumption that these people always have that I have never understood. Why does travelling faster than the speed of light have to mean “time travel”??. The only reasoning i ever hear is that “You would arrive before you left”. This just doesn’t make sense to me. Why is light any different to sound? In theory, you can make a sound then travel faster than the speed of sound to hear your own voice in another location.
If they mean Einstein’s theory about time slowing down as you reach the speed of light, why not say that? Why state that “it’s impossible to go faster because you “would arrive before you departed”? Do you know what I mean??

Thanks
Russell

According to Einstein’s assumptions in the theory of relativity, the velocity of light in vacuum is a constant and no particle can travel faster than light. The theory of relativity is based on this central concept. So, if we imagine to travel faster than light, time will reverse (As per theoretical results) and we may go back in time. That is why travel with or above the speed of light is referred to as “Time Travel”.

Light is an electromagnetic wave and is different from sound as it is a mechanical wave which requires a medium to travel. Sound cannot travel through vacuum.

## Was Einstein Wrong?

Was Einstein Wrong? What is the neutrino particle which traveled faster than light?

As we know it now; Neutrino is a neutral subatomic particle with a mass close to zero and half-integral spin, rarely reacting with normal matter.

Three types of neutrinos are known –

Einstein’s theory of relativity suggested that no particle can travel faster than light in vacuum.

If neutrino travels, there is something wrong and we have to make necessary amendments

Further Reference

TWIN PARADOX is a paradoxical situation coming in while explaining the theory of relativity. “Time dilation” is one of the important consequences of relativity. It says that if a body is moving with relativistic speeds, time will dialate for it. That is, a duration of 1 second for him will be more than that for a person at rest or moving at ordinary speeds.

The relativistic time is given by the equation,

So, if we imagine twin brothers, one at rest at earth and other going on a relativistic interstellar trip (certainly he has to go out of solar system as the velocity of light is very much more than escape velocity of solar system, and further, he will reach the sun in just 8 minutes if traveled with the speed of light)

Let us take that his speed is 0.9 times the speed of light in vacuum. Then 1 second for him is equal to 27 s (approximately) for his brother on earth. So, if he returns after one year of space programme, he will be older by 1 year, but his brother who was at home will be older by 27 years or more; if alive.

You are welcome to think of the possibilities of a relativistic travel and the related issues here.

## What are Tachyons?

What are Tachyons?

This question was posted by Vimal Raj.

Tachyons are hypothetical particles which always travel faster than light.

The idea is that, if there is a particle which travels with a speed less than the speed of light, it will never cross the speed of light. But if there are some partricles which originally travel faster than light, it will never come to a speed less than that of light. Such hypiothetical particles are called tachyons.
They are not discovered.They may or may not exist. It’s just a matter of logic.

## A Question From Relativity

“my question is on relativity.Let us say two persons,one is standing still and other is moving with uniform velocity in a straight line(in +ve x direction),both are carrying  a clock synchronized previously.For the moving person he is at rest and the other guy is moving away from him in the opposite direction(negative x direction).Both of them feel that clock of the other guy is moving slowly.let us say the moving guy never stops and he calls the other in telephone at some point of time and asks the
time in his clock.But he will find that clock with him,is actually faster.how can that happen?”

Please note that the theory of relativity can  be applied only for velocities compared to that of light in vacuum (3 lakh km/s). The situation will be very much different when we travel at such velocities. So far we are able to accelerate only subatomic particles to this speeds (LHC).

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