Home » Posts tagged 'time dilation'

Tag Archives: time dilation

Time dilation and Length contraction

Is time dilation and length contraction hypothetical or is it really an observable fact.

for example,consider a rectangular sheet in a spacecraft moving at some high velocity.

Would an observer in the spacecraft be ever able to see the sheet as a square due to length contraction along its breadth(if the velocity is so so adjusted).
Would a stationary observer in the earth be able to observe the same.
In other words who experiences length contraction?

Also who experiences time dilation?


relativityAsked Ajmal

What is twin paradox?

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,

timedilation.gif (113×68)

Twin Paradox - Relativity

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.

This is the TWIN Paradox.


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

Time Dilation in Relativity

Manishankar asks: “When we match the speed of light,it is said that time drags..does that mean we become old a little slower?If so,how?”

An interesting question based on Relativity (Time dilation and the Twin Paradox)

Yes, this is similar to the twin paradox, but with a few changes:

Two brothers set off from earth to make a round trip of 30 light years in total.

The first brother, say Albert, has a ship that travels at 10% the speed of light so his journey will take him 300 years and, due to time dilation, earth will have aged around 301 years by the time he (or his descendants) gets back.

The second brother, Carl, has a ship that travels at 99.99% the speed of light so his journey will take 30.03 years, however the earth will have aged over 2119 years on his return.

While, to Carl, his journey has been far quicker, he will arrive back to earth over 1800 years after his brothers ship returned.

Therefore, are we not best to be onboard Alberts ship even though his journey will take ten times longer? Unless we are intent on a one-way trip, travelling close to the speed of light would slow us down if our goal was to return to earth.

Yes, the twin paradox is the basis of the question, however, this time, both twins go on exactly the same journey, but somehow the one travelling slower gets back to earth faster. I’m just trying to find out at what point during the journey the twin travelling slower overtakes the one travelling faster?

I appreciate your time and hope that you can clear things up for me

(Andy posted this Question)


I cannot give a clear and final answer here, but we can discuss things over here.

If we are travelling with a 10% the speed of light means we will be going at at speed of 30000000 m/s. If we assume the safe level of acceleration, about 30 m/s2 then we can calculate the time required to accelerate to the speed given starting from rest. This comes to 1 million seconds (around 12 days).

In these 12 days it will travel a distance 15000000000 km which is 1171875 times the diameter of earth and about 100 times the orbital radius of earth around sun.

Thereafter, it goes with constant speed (but where?)


It’s nice to think deep and wide problems like this. I invite visitors to add to this discussion and take this as an opportunity to understand relativity and time travel better.

Hits so far @ AskPhysics

  • 2,266,383 hits

Subscribe to AskPhysics via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

Join 4,339 other subscribers

March 2021

Schrodinger’s Cat in Daily Life

%d bloggers like this: