KnowSoda
SciencePhysics
Relativity: fun facts and quiz
The essentials in 7 ideas, with fun facts, an illustrated story and a quiz to see how much you know.
The essentials
Albert Einstein
In 1905, while working at a patent office in Bern, Albert Einstein published papers that changed physics, including special relativity.
Key fact
1905 is known as Einstein’s “miracle year”.
The Cosmic Speed Limit
Relativity says nothing can travel faster than light in a vacuum, about 300,000 km per second, and light’s speed is the same for everyone who measures it.
Key fact
Light’s speed doesn’t change, even if you chase it.
Time Slows Down
Moving clocks tick more slowly. The effect is tiny at everyday speeds, but astronauts on the space station age very slightly less than people on Earth.
Key fact
After six months in orbit, astronauts are a few thousandths of a second younger.
E = mc²
Einstein’s most famous equation says mass and energy are two forms of the same thing. Because c² is enormous, a little mass holds a huge amount of energy.
Key fact
The Sun turns about 4 million tonnes of mass into energy every second.
Gravity Bends Space
In 1915, Einstein’s general relativity described gravity as the bending of space and time by mass. Heavy objects curve spacetime, and other things follow the curves.
Key fact
A 1919 solar eclipse showed starlight bending around the Sun, as predicted.
Relativity in Your Pocket
GPS satellite clocks run fast by about 38 microseconds a day compared with ours, because of relativity. Without correcting for it, GPS positions would drift about 10 km a day.
Key fact
Your phone’s map depends on Einstein.
Black Holes
A black hole is where gravity is so strong that not even light can escape. The first image of one, in the galaxy M87, was released in 2019.
Key fact
The edge of a black hole is called the event horizon.
Fun facts
In 1952, Einstein was offered the presidency of Israel. He turned it down.
The Large Hadron Collider pushes protons to 99.999999% of light speed, yet they can never quite reach it.
In 1971, atomic clocks flown around the world came back slightly out of step with clocks left on the ground, just as relativity predicted.
Turn the mass of a paperclip, about 1 gram, entirely into energy and you’d match the Hiroshima bomb.
Gravity can bend light so much that one distant galaxy shows up several times around a nearer one. It’s called gravitational lensing.
Atomic clocks are so precise they can detect time running faster when raised just 30 cm higher.
In 2015, detectors on Earth picked up gravitational waves from two colliding black holes for the first time.
Story: Lights All Askew
Lights All Askew
May 1919. Astronomer Arthur Eddington sails to the island of Príncipe, off Africa, to photograph stars near the Sun during an eclipse.
Clouds nearly ruin it, but a few plates come out. The stars look shifted, by just the amount Einstein’s theory predicted.
“Lights all askew in the heavens,” ran one headline. Almost overnight, Einstein became the world’s most famous scientist.
True or false?
Tap your answer to see if you got it, and why.
-
Question 1 of 10
Einstein published several ground-breaking papers in a single year.
Show the answer
True. His “miracle year”.
-
Question 2 of 10
Nothing with mass can reach the speed of light.
Show the answer
True. It would take infinite energy.
-
Question 3 of 10
Astronauts on the space station age slightly more slowly.
Show the answer
True. By a tiny fraction of a second.
-
Question 4 of 10
E = mc² links mass and energy.
Show the answer
True. E is energy, m is mass, c is the speed of light.
-
Question 5 of 10
General relativity describes gravity as curved spacetime.
Show the answer
True. Mass tells spacetime how to curve.
-
Question 6 of 10
GPS has to correct for relativity.
Show the answer
True. Or it would drift by kilometres every day.
-
Question 7 of 10
Light cannot escape from a black hole.
Show the answer
True. Not once it crosses the event horizon.
-
Question 8 of 10
Einstein worked out relativity while working as a pilot.
Show the answer
False. He was a patent clerk.
-
Question 9 of 10
A fast enough spaceship could overtake light.
Show the answer
False. Light speed is the universe’s limit.
-
Question 10 of 10
Time passes at exactly the same rate for everyone, everywhere.
Show the answer
False. Speed and gravity change how fast clocks tick.
Keep going in the app
KnowSoda learns what you know and brings back what you’re about to forget. Relativity has 6 more ideas at the Advanced and Expert levels.
Sources
- NASA — Einstein’s theories of relativity
- Nobel Prize — Physics 2017 (gravitational waves) and Einstein’s biography
- Event Horizon Telescope — First image of a black hole (2019)
- Ashby (2003), “Relativity in the Global Positioning System”, Living Reviews in Relativity
- LIGO Caltech — Gravitational waves detected 100 years after Einstein’s prediction
- NIST — Einstein’s time dilation apparent when obeying the speed limit (2010)
