# Einstein's twin paradox explained - Amber Stuver

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TEDEd Animation

## Let’s Begin…

On their 20th birthday, identical twin astronauts volunteer for an experiment. Terra will remain on Earth, while Stella will board a spaceship. Stella’s ship will travel to visit a star that is 10 light-years away, then return to Earth. As they prepare to part ways, the twins wonder what will happen when they’re reunited. Who will be older? Amber Stuver investigates the “Twin Paradox.”

## There are several different ways to prove that the “Twin Paradox” isn’t really a paradox at all. In this explanation, we focused on the arrival time of light signals from both twins. Besides measuring the time interval of these signals, Terra and Stella could measure changes in the properties of the light they receive. Let’s assume that Terra and Stella send each other a light signal of the same color (wavelength) and they are sending this light constantly (not yearly as described in the animation). a. What change in the color of light (change in wavelength) would Terra measure while Stella is moving toward the destination star? (It is helpful to remember that the speed of light is the same regardless of the speed of it source.) b. During that same time, what change in color (change in wavelength) of light would Stella measure coming from Terra? c. What do these changes mean for how time is passing where the light was emitted? d. How can you use just information about the change in the wavelength of the received light (not the arrival time of light) to prove that the “Twin Paradox” isn’t a paradox at all?

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## Meet The Creators

• Educator Amber L. Stuver
• Director AIM Creative Studios, Rui Almeida
• Narrator Bethany Cutmore-Scott
• Producer Tom Knight
• Sound Designer André Aires
• Animation Mulligan Studio, Ricardo Coelho
• Composer André Aires
• Storyboard Artist Rui Almeida
• Illustrator Rui Almeida
• Character Designer Rui Almeida
• 3D Animator Hélder Vasconcelos
• Music AIM Creative Studios
• Director of Production Gerta Xhelo
• Editorial Producer Alex Rosenthal
• Associate Producer Bethany Cutmore-Scott
• Script Editor Alex Gendler
• Fact-Checker Brian Gutierrez