Are We Alone? (02:45)
Will, Lindsay, and Sian will be given tools to understand if humans are alone in the universe. The first step is to find out what makes life possible.
Scale of the Galaxy (02:44)
Will, Lindsay, and Sian use sand, a scale, and a calculator to guess how many stars there are in the Milky Way and find a way to visualize it.
Galileo Galilei (02:03)
Galilei pointed his telescope towards the Milky Way and realized it is made out of stars.
Stars in the Milky Way (03:45)
Will, Lindsay, and Sian estimate that there are one billion stars in the galaxy. Science estimates the number at 300 billion.
Giordano Bruno (01:44)
The volunteers ponder what an alien life form would need to live. In 1584, Bruno proposed the stars were surrounded by planets; he was burned at the stake.
Planet and Stars to Scale (03:09)
Will, Lindsay, and Sian use small spheres and a spotlight to replicate the layout of a solar system.
Planet Osiris (02:12)
As a planet orbits between its star and Earth, astronomers hypothesized it would fractionally decrease the amount of starlight reaching Earth. In 1999, Charbonneau was the first person to see a planet pass in front of another star.
First Planet Spotted (02:00)
The volunteers use a telescope and light meter to understand how scientists learned it is possible detect planets outside our solar system.
Kepler Telescope (03:57)
The volunteers figure out the significance of each planet dimming the starlight to a different degree. Knowing where to look is the first step in detecting intelligent life.
Goldilocks Zone (02:30)
The volunteers consider what could make other planets suitable for life. The possibility of liquid water is determined by how close a planet is to its star.
Generating Heat Through Friction (03:48)
Will, Lindsay, and Sian use ice cubes and an iron bar to begin to understand how liquid water could be present on a planet far from a star.
Moon Orbiting the Gas Giant (02:59)
The volunteers discuss how liquid water could be present on a planet outside the Goldilocks Zone. Europa follows an elliptical path around Jupiter.
High Probability of Alien Life (01:29)
It is likely that there are places water based life could exist besides Earth. There could be other advanced civilizations in the Milky Way.
Sound of the Universe (01:54)
The volunteers hear signals from deep space. Astronomers may use this data to discover extraterrestrial life. Everything in the galaxy emits radio waves.
Listening to Space (02:04)
The volunteers use an equalizer and megaphone to simulate a message from deep space in an attempt to figure out how could be possible to hear an alien broadcast through white noise.
Giuseppe Cocconi and Philip Morrison (03:06)
Scientists in the 1950s proposed that intelligent aliens would use the hydrogen line frequency to communicate. The volunteers figure out how to eliminate background noise to hear the simulated alien broadcast.
The Great Filter (03:45)
Astronomers have been listening for alien signals for 30 years. Enrico Fermi believed that contact would have been made long ago if aliens existed.
Fragility of Life (03:44)
According to the Great Filter theory, advanced life occurs so rarely that humans are unlikely to make contact with extraterrestrial life.
Conclusion: Are We Alone? (03:07)
Hawking summarizes what is known about the possibility of extraterrestrial life. The volunteers reflect on what they have learned.
Credits: Genius By Stephen Hawking: Are We Alone? (00:19)
Credits: Genius By Stephen Hawking: Are We Alone?
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