Listen & Learn: Time Dilation

Learn how motion can slow down time

Pre-listening vocabulary

• thought experiment: an experiment that someone thinks about but doesn’t test
• universal: the same for everyone
• relative: different when compared to different things
• observer: a person or thing that can measure results
• outrun: to run faster than someone else
• constant: never changing
• variable: a value in a math equation that can change

Listening activity

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Gapfill exercise

When Albert Einstein was a teenager, he wondered what would happen if a human could run enough to chase a beam of light. This thought experiment led to his 1905 theory of special relativity. Einstein’s theory showed that time was not universal. People could experience time differently if they were moving very fast. This effect is called time dilation. Einstein used a few scientific to support his theory. The first was that speed is relative. Two trains travelling at the same speed in the same stand still relative to each other. However, experiments before Einstein had already proved that the speed of light is always 300,000 kilometres per . This is true no matter how fast the observer moves. Even if a person could chase a beam of light, the light would always outrun them by the same speed. Einstein realized that because the speed of light was constant, another variable had to change. This variable was time. Since Einstein published his theory, experiments have shown that run slower at high speeds.

Comprehension questions

See answers below

1. As a teenager, Einstein wondered what would happen if a human could chase
   a. a beam of light
   b. a train
   c. a clock
   
2. Einstein’s 1905 theory is called
   a. general relativity
   b. special relativity
   c. universal relativity
   
3. The speed of light is
   a. constant
   b. variable
   c. relative

Discussion/essay questions

1. Most scientists think that time travel to the past is probably not possible. However, time dilation means that time travel to the future would be possible if we could move very fast. What would you do if you could time travel? Do you think it would be more interesting to travel to the past or the future?

Transcript

When Albert Einstein was a teenager, he wondered what would happen if a human could run fast enough to chase a beam of light. This thought experiment led to his 1905 theory of special relativity. Einstein’s theory showed that time was not universal. People could experience time differently if they were moving very fast. This effect is called time dilation. Einstein used a few scientific laws to support his theory. The first was that speed is relative. Two trains travelling at the same speed in the same direction stand still relative to each other. However, experiments before Einstein had already proved that the speed of light is always 300,000 kilometres per second. This is true no matter how fast the observer moves. Even if a person could chase a beam of light, the light would always outrun them by the same speed. Einstein realized that because the speed of light was constant, another variable had to change. This variable was time. Since Einstein published his theory, experiments have shown that clocks run slower at high speeds.

Answers to comprehension questions

1a 2b 3a