A Bend in the Road
Narrator (April Hobart, CXC): There are many things around us that bend. Straws bend. Rivers bend. But did you know that light also bends? Actually, it's not light itself that bends, but rather the path that it takes. While this may sound strange, many of us witness this every day when we put on our eyeglasses or insert our contact lenses. These objects are especially shaped to bend incoming light so that it focuses properly on the retina of the eye, allowing those of us with poor vision to see more clearly.
It's possible to find examples of how light's path is bent at the end of the day as well. If you've ever looked at the horizon when the Sun is setting, you may have noticed that the Sun looks more oval than round. What you're witnessing is the Sun's image being distorted. With eyeglasses or contact lenses, it is a piece of glass or plastic that alters the path of light. However, in the case of the sunset, it's the Earth's atmosphere that acts as a lens. The thicker the atmosphere, the more the light from the Sun is bent. That's why the Sun looks more flattened as it gets closer and closer to the horizon, because the light has to travel through more of our atmosphere. The result is that the Sun can look like it's oval shaped, even though we know it always remains a sphere, as it sits some 93 million miles away from us in space.
Speaking of space, the path of light can be also bent on much larger scales involving some of the largest objects in the Universe. In the early part of the 20th century, Albert Einstein predicted that very massive objects could actually bend space, and if this were true, then light traveling through that space would follow along the curved path. And, as with most things, Einstein was right. Today, we see many examples of this phenomenon that scientists call "gravitational lensing." When the light from very distant galaxies passes through, say, a massive cluster of galaxies, that cluster can act as a lens. The result is that the images from the galaxies are magnified and distorted into elongated and arched shapes. Scientists have used gravitational lensing to study the effects of the most mysterious substance known as dark matter among many other things.
So remember the next time you are driving along and notice a bend in the road, think of how light's path is often curved as well. This bending of light provides more than just improved vision or optical illusions here on Earth. Instead, it’s the fact that light's path can be bent that allows us to get information about objects that lie billions of light years away from us and helps us learn more about the very nature of the Universe itself.