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- Understanding the Cosmos A Spacetime Odyssey Episode 10: Exploring Gravitational Fields
Understanding the Cosmos A Spacetime Odyssey Episode 10: Exploring Gravitational Fields
Discover the fascinating world of gravitational fields in the cosmos as discussed in episode 10 of Cosmos: A Spacetime Odyssey. Learn how Earth itself acts as a giant magnet with force fields extending into space, and how migrating birds navigate using familiar landmarks and senses.
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Video Transcript
The compass needle that people wondered at for a thousand years was not reacting to some
faraway magnetic North Pole.
It was detecting a continuous force field that stretched all the way there.
Earth itself is a giant magnet, and like any other magnet, its lines of force extend far
out into the space surrounding it.
They're everywhere, all around us.
They've always been, but nobody had ever noticed them before.
Nobody human, that is.
Birds are the last living descendants of the dinosaurs.
Pigeons and other birds are remarkably good at finding their way around.
They can migrate thousands of miles without getting lost.
How?
Partly by recognizing them.
Recognizing familiar landmarks, rivers, mountains, stars, even certain smells can serve as signposts
for migrating birds.
But birds also have an inner compass.
They can actually sense the Earth's magnetic field.
Their brains process magnetic data in much the same way ours process visual data.
By sensing the direction of the field, birds can tell north from south.
That's one way North American birds know which way to go when they head south for the
winter.
The field is stronger near the poles than it is at the equator, a fact that birds use
to figure out their latitude.
There are also small irregularities in the field, locations where the field is a little
weaker or stronger.
Just like a distinctive mountain or river, these magnetic anomalies can serve as landmarks.
For thousands of years, humans have used carrier pigeons to send messages to distant locations.
It was a crucial method of communication as recently as World War II.
When you think about it, we've been using magnetic fields to communicate for a long
time.
We just didn't know it.
