<img src="https://d5nxst8fruw4z.cloudfront.net/atrk.gif?account=iA1Pi1a8Dy00ym" style="display:none" height="1" width="1" alt="" />
Skip Navigation
We experienced a service interruption from 9:00 AM to 10:00 AM. PT. We apologize for any inconvenience this may have caused. (Posted: Tuesday 02/21/2017)
You are viewing an older version of this Concept. Go to the latest version.

Special Theory of Relativity

Interpret motion between different objects that are moving at constant speeds relative to each other.

Atoms Practice
Estimated9 minsto complete
Practice Special Theory of Relativity
This indicates how strong in your memory this concept is
Estimated9 minsto complete
Practice Now
Turn In
Twin Paradox

Twin Paradox

Credit: Gareth Williams
Source: http://www.flickr.com/photos/gareth1953/6012290797
License: CC BY-NC 3.0

One of the many thought experiments in physics, the twin paradox discusses what would happen when one of two twins goes on a trip at relativistic speeds.

Amazing But True

  • Imagine the following: Billy and Jimmy are identical twins. One day Billy jumps into a space ship and travels off at very high speeds; assume Billy travels at a speed that is 80% the speed of light towards an object that is 8 light years away. According to Jimmy, it will take Billy 20 years to make the round trip. If we calculate the time that will elapse on the ships clocks during this trip it will be

\begin{align*}t^{\prime} &= \frac{t}{\gamma}\\ t^{\prime} &= \frac{(0.6)}{(20 \ \text{years})} = 12 \ \text{years} \end{align*}

  • Therefore, when Jimmy returns he will have aged only 12 years while his twin Billy will have aged 20 years.
  • The paradox is a result of each twin seeing the other traveling. Therefore, Billy and Jimmy should find the other twin to have aged more slowly. This paradox is resolved when it is realized that there is no symmetry in the problem because only one of the twins, Billy, undergoes acceleration and deceleration.
  • Learn more about the twin paradox below: 


Show What You Know

Using the information provided above, answer the following questions.

  1. If Billy traveled at only 10% the speed of light for the trip described, how long would time elapse for Jimmy?
  2. How much time would elapse for the twin that is on the ship? (Assume he was able to live that long).
  3. Why are the previous answers so close? Is something wrong with relativity?

Notes/Highlights Having trouble? Report an issue.

Color Highlighted Text Notes
Please to create your own Highlights / Notes
Show More

Image Attributions

  1. [1]^ Credit: Gareth Williams; Source: http://www.flickr.com/photos/gareth1953/6012290797; License: CC BY-NC 3.0

Explore More

Sign in to explore more, including practice questions and solutions for Special Theory of Relativity.
Please wait...
Please wait...