Ep. 606: Time Dilation – Skipping Through Time
Description
Have you ever wanted to be a time traveler? Good news! You’re time traveling right now. Into the future at one second per second. Too long? Don’t want to wait? Good news, Einstein’s got you covered. Today, let’s talk about the weird world of time dilation.
Show Notes
What’s Up: Mercury at Sunset and Nova in Cassiopeia (CosmoQuest)
Harvard Science Center (Harvard)
What is relativity? Einstein’s mind-bending theory explained (NBC Mach)
How “Fast” is the Speed of Light? (NASA)
The Theory Behind the Equation (PBS)
Buck Rogers in the 25th Century (IMDb)
How does relativity theory resolve the Twin Paradox? (Scientific American)
Landmark NASA Twins Study Reveals Space Travel’s Effects on the Human Body (Space.com)
International Space Station (NASA)
Speed and Velocity (Math is Fun)
COMIC: Gravity Wells (xkcd)
How to Make Your Own Gravity Well (Saint Mary’s University)
Interstellar (IMDb)
The Expanse (IMDb)
How Fast Do Spacecraft Travel in The Expanse? (Wired)
Momentum (The Physics Classroom)
Transcript
Transcriptions provided by GMR Transcription Services
Fraser Cain: Astronomy Cast Episode 606: Time Dilation. Welcome to Astronomy Cast, our weekly facts-based journey through the cosmos. Where we help you understand not only what we know, but how we know what we know.
I’m Fraser Cain, publisher of Universe Today. And with me as always is Dr. Pamela Gay. A senior scientist for the Planetary Science Institute and the director of CosmoQuest. Hey, Pamela, how you doing?
Dr. Pamela Gay: I’m doing well. It is a glorious spring day. And while the stars don’t shine as many hours each night, it is great to have Mercery over on the horizon. Have you gotten out to go look at it yet?
Fraser Cain: I thought we went through this. I can’t see Mercury. I have no view to the East and I have no view to the West. Mercury is – I’m just gonna have to take it on faith that Mercery even exists.
Dr. Pamela Gay: Okay. I understand. I am going to have to go to a field somewhere.
Fraser Cain: Yeah.
Dr. Pamela Gay: Because I, too, have no horizon. But I have access to cornfields that don’t yet have much corn in them.
Fraser Cain: The only time I’ve ever seen Mercery I was in Australia. That’s it. And you have the benefit that the ecliptic sort of rise is straight overhead in Australia. So, you know, as opposed to things here being very low down to the horizon.
Dr. Pamela Gay: Right.
Fraser Cain: But yeah. And so, someone was like, “Oh, yeah. And there’s Mercery.” And I was just like, “This is the first time I’ve ever seen Mercery.” Too great.
Dr. Pamela Gay: I think I have seen it from the roof of a building at Harvard. The Science Center in Harvard Yard – or just outside Harvard Yard – has a small telescope on its roof that I used to work with. And light pollution always makes it questionable if you know what you’re actually looking at. Because there just aren’t enough stars. But I think I’ve seen it, but now that I live someplace darker, I’m gonna try again.
Fraser Cain: All right. So, if people wanna see Mercery and they do have, oh, I dunno, a horizon …where and when should they look?
Dr. Pamela Gay: So, if you go out right now it is located between the very, very bright Venus and the super-thin crescent moon. The moon’s getting higher and higher, and thicker and thicker each day. But it remains above Venus in the West/Northwest. So, go out –
Fraser Cain: Just after sunset.
Dr. Pamela Gay: Yeah.
Fraser Cain: Okay.
Dr. Pamela Gay: Venus will pop out brightest and then look up.
Fraser Cain: Have you ever wanted to be a time traveler? Well, good news. You’re time traveling right now into the future at one second per second. Taking too long? Don’t wanna wait? Good news. Einstein’s got you covered. Today, let’s talk about the weird world of time dilation. All right, Pamela. Time dilation. What?
Dr. Pamela Gay: So, one of my favorite things that was like this breakthrough understanding for me with relativity. Was the understanding that no matter who you are and what you’re doing the speed of light will appear exactly the same. And in order for that to happen, how you perceive time has to change.
So, the way to think about this is what we’re used to in day-to-day life is …if I’m standing on side of the road in front of my house. And a car zips by, it appears to zip by at 30 miles per hour if they’re following the law. Now, if I’m going down the road at 30 miles per hour, the car in front of me – in theory, if they’re following the law – should appear to be moving zero miles per hour relative to me.
Fraser Cain: Right.
Dr. Pamela Gay: And so, we’re used to seeing everything with relative speeds. The faster I’m going, I’ll see people on the side of the road appearing to go in reverse. People around me, I see their motions relative to my own. So, it seems like using that human experience that the faster I go, I should eventually be able to catch up to those photons and perceive them as moving side by side with me.
But the reality is that while some outside observer might somehow perceive me and those light particles going at almost the same speed. I will never go as fast as the light. I will never see that. I will always see light. At the exact same speed relative to me.
Fraser Cain: And that is such – I mean, when you think about Einstein’s ability to perceive the world in a fascinating way. To have this thought experiment that you’re traveling almost at the speed of light. And then you shine a flashlight, and you watch the flashlight. And in your mind, you be like, “Well, do I see the photons speeding away –
Dr. Pamela Gay: Right.
Fraser Cain: – just a little faster than me or do I see the photons speeding away at the speed of light?” And the only way – if you see them at the speed of light – is if time itself is changing.
Dr. Pamela Gay: And so, this brings up that bizarre reality that Buck Rogers in the 21st century is actually a possible outcome of someone orbiting at a high enough velocity. Now, the fact that orbital mechanics doesn’t allow you to zip around the planet that fast. Let’s say instead they put themselves in this massive orbit at super high speeds.
Fraser Cain: Yeah.
Dr. Pamela Gay: That’s more realistic. Orbit around the sun instead. But …well, good ole Buck Rogers perception of time will slow.
Fraser Cain: Okay. So, then you talk about this idea of speed. So, let’s break down time dilation. And I mean, I wanna ask why is time dilation? But I know the answer. And the answer is because. Right? Relativity. Because that’s how the universe works. So, let’s proceed right past ‘why’ and go straight to ‘how.’ How time dilation? And there’s sort of two factors. Two ways that you can get time dilation. And the one is the speed.
So, let’s break this down in some examples. And now you’re providing this example. The twin paradox is the classic o
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