AaS! 72: How Does Gravity Make a Lens?
Ask a Spaceman!
Paul M. Sutter
4.8 • 853 Ratings
🗓️ 16 January 2018
⏱️ 35 minutes
🧾️ Download transcript
Summary
How does gravity bend the path of light? Does it seriously act like a lens or is that just a metaphor? What does it take, and how do we know? What can we learn from this strange physics? I discuss these questions and more in today’s Ask a Spaceman!
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Music by Jason Grady and Nick Bain. Thanks to WCBE Radio for hosting the recording session, Greg Mobius for producing, and Cathy Rinella for editing.
Hosted by Paul M. Sutter, astrophysicist at The Ohio State University, Chief Scientist at COSI Science Center, and the one and only Agent to the Stars (http://www.pmsutter.com).
Transcript
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| 0:00.0 | You're at a picnic and you see an ant crawling along the blanket over all the little hills and valleys because your blanket isn't perfectly flat. |
| 0:17.0 | The ant knows exactly where it wants to go. It sees the strawberry or the pickle sandwich, |
| 0:25.0 | or I'm not exactly sure about what you pack for a picnic, but you get the idea. The ant |
| 0:30.0 | thinks it's going in a straight line. It knows. It saw the strawberry in the distance, |
| 0:37.1 | and it's going to go right for it. No hesitation. But it's forced to follow the contours of the blanket. It has to go up, down, maybe sideways. |
| 0:49.7 | It's making a beeline for the food, but the blanket makes it follow an ant line. Get it? No, nobody? Okay. Well, you know what? Either way, good jokes or bad jokes, you should contribute to Patreon. Go to Patreon.com slash PM Sutter to learn how you can keep all this outreach going. Maybe if more people contributed to Patreon, I would be able to write better jokes. |
| 1:12.6 | But you know what? |
| 1:13.5 | This is all you're going to get. |
| 1:14.6 | Actually, I'm just kidding. |
| 1:15.7 | All of you are incredibly generous, and I appreciate all the support. |
| 1:18.7 | That's patreon.com slash BM Zutter. |
| 1:21.1 | The word of the day that we all need to come away from this episode with is geodesic. |
| 1:29.2 | Geodesic. |
| 1:30.2 | You may have heard that word before in other contexts. |
| 1:35.1 | Like if you think about airlines and flights and the path that a flight will take, |
| 1:42.9 | it connects one city to another. Say you're leaving from New York |
| 1:46.8 | and you want to go to Paris. A straight line in three dimensions, a straight line in three |
| 1:53.5 | dimensions would send you in a tunnel through the earth. That's not exactly feasible. So instead |
| 1:59.6 | we're going to stick to the surface of the earth and we're going to follow. We're just, we're going to set our compass heading. And the plane is going to one direction. It's not going to turn left. It's not going to turn right. It's going to go right to Paris. But then when I look at that in three dimensions, it's a curved path. because the plane has to follow the surface of the earth because it's not going to go off into space |
| 2:00.9 | and it's not going to because the plane has to follow the surface of |
| 2:17.9 | the earth because it's not going to go off into space and it's not going to start digging |
| 2:20.9 | through the rocks in the dirt in the ocean. It's going to follow a straight line, but the earth is |
... |
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