Date: May 6, 2010
Title: Warp Drive Part 2
Podcaster: Renata & Damian Handzy
Description: This podcast takes off where the 365 DOA podcast for January 9, 2010 ended. There are many ways to understand and explain special relativity, and these two podcasts cover those explanations that the podcasters feel have the most impact on non-scientists. And to paraphrase Neil deGrasse Tyson, if you cannot explain science to non-scientists, it’s not your audience who has the problem. The conclusion of this podcast is possibly the single most important point that one of us (Damian) ever learned in the course of his scientific education.
Bio: Renata and Damian Handzy live in NJ with their three children, Matthew, Stephen and Sofia. Renata is an early-childhood educator and Damian is a nuclear physicist by training but has been employed in financial risk management for over 15 years. Both of them believe strongly that education is a lifelong endeavor and enjoy sharing their passion for understanding the world around us with others.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Mr. Thomas — Dedicated to my students: may they fly to work with jet-packs, and may some teach math to their students in their school on the moon.
Additional sponsorship for this episode of 365 Days of Astronomy has been provided by Kylie Sturgess and the Token Skeptic podcast, a weekly show about superstition, science and why we believe – at www.tokenskeptic.org.
Transcript:
Damian: OK, ok, I’ve waited long enough since our last podcast for you to explain this to me, so I want to make sure I get it. If I’m in a car driving at the speed of light with the headlights on, then I observe the beam of light coming out of my car to be traveling away from me at the speed of light.
Renia: yes, that’s right. The beam of light from your headlights appears to move away from you at the speed of light.
Damian: Good – at least I’ve got that right. Now, if you’re standing there as I drive past you at the speed of light, you’re telling me that you see both me in my car and the beam of light moving at the speed of light?!? You notice no difference in our speeds – we’re in a neck and neck tie.
Renia: that’s right.
Damian: That makes absolutely no sense. Is the beam of light moving away from me or not?
Renia: that’s a good question, and you’re posing it as if there is an absolute frame of reference that speed can be measured against. That’s the way most people think about time, space and speeds: that there is a “special” reference frame.
Damian: right, right, I understand that speeds are relative – that two difference people can measure two different speeds for the same object. And I know that it seems to me right now that you’re not moving at all but that compared to the sun you’re moving pretty fast and compared to the center of the galaxy you’re moving even faster. I get that. How does that help me understand that the beam of light doesn’t leave my car?!
Renia: The beam of light does appear to move away from your car for you. For me, both objects – the car you’re in and the beam of light – appear to move at the exact same speed, the speed of light, so they’re not moving apart.
Damian: Well, why doesn’t it appear to you that the beam of light comes out of my car at twice the speed of light? I mean, this makes no sense.
Renia: Oooooohhhh, tttthhhhat’s the issue you’re having. OK, that’s because you’re basing your expectations on the assumption that your experiences at sssssllllooooooowwwww speeds should naturally extend to all speeds. Your everyday experience – that speeds add linearly – is reinforced over and over again in your daily life. So when you encounter a situation at high speeds, where things don’t work the same way, you have a hard time accepting the reality of the situation.
Damian: but why should speeds not add linearly at all speeds? I mean, what causes that?
Renia: let me pose the question a slightly different way: why should speeds add linearly in any situation? Instead of being surprised that speeds don’t add linearly when we approach the speed of light, maybe we should be surprised that we can use the linear approximation so accurately at our mundane everyday slow speeds in the first place.
Damian: Oh, I get it, you’re trying to get me to view the whole problem from another perspective – instead of thinking that relativity is weird, maybe I should think that what we experience every day is weird. No dice.
Renia: OK, let me go through the ideas that Einstein went through as he thought about this.
Damian: You think I’m going to follow what Einstein was thinking?
Renia: Just listen. Let’s say that we’re both walking slowly in an airport to our gate at 2mph as we pass someone sitting on the side. You happen to step onto one of those people mover conveyor belt things that is moving at 2mph and you continue walking as you had been. In this case, the person sitting on the side sees you moving at 6mph and she sees me moving at 2mph. Right?
Damian: sure.
Renia: Ok, but it will seem to me that you’re moving at 2mph.
Damian: yup. Everybody knows this.
Renia: Be patient. Now, both she and I will see you get to the end of the conveyor belt in 1/2 the time it will take me, since you’re moving 2 times as fast. Right?
Damian: sure.
Renia: Good. Now, we agree on this because we know that the distance is fixed for both of us – it’s the length of the conveyor belt. Our speeds can be different, and the amount of time to cover that distance for us is different by the same factor of 2.
Damian: What does this have to do with relativity?
Renia: well, what Einstein supposed – and at this point it is nothing more than a wild supposition – is: “what if distance isn’t the thing that remains constant for two different observers when light travels, but rather speed is.” What if, no matter what happens to either observer, or how fast they’re moving, what if two different observers always measure the same speed for light?
Damian: So he just made up the notion that light always travels at the same speed and presto it happens that way!?
Renia: of course not. He had some good reasons to have this hunch. But let’s keep going with it. If you accept that light is always traveling at the same speed, then that has implications for how speeds add up. They obviously don’t add linearly because if they did, you could easily get a total speed more than the speed of light. It also means that distance and time are measured differently for the different observers.
Damian: I don’t like where this is going, but I’m Ok so far because there is that really big capital IF in front of everything you’re saying.
Renia: Right. So when you work the math out, starting with the very simple fact that you have to measure the same speed for light even if you’re moving, then you actually end up with something called the Lorentz Transformation that tells you how much differently two observers will measure distances, time and even mass.
Damian: wait a minute – you said that mass also changes? What’s up with that?
Renia: yes, mass also increases as you speed up. In fact, this is a good way to understand why quote-un-quote nothing can move faster than light.
Damian: huh?
Renia: You remember F=ma, right? Well, think of the mass as a number that relates how much force you have to apply to an object to get it to accelerate by an amount a. The bigger the mass, the more you have to push to speed the thing up. Well, since relativity says that the mass increases as you speed up, that means that mass gets bigger and bigger the closer you get to the speed of light. So lets say it took only a certain force to speed it up by 10 mph. After you did that, the mass has increased because of relativity, so to speed it up by another 10 mph you have to apply an even bigger force. The mass gets so big as the object’s speed approached the speed of light that you’d literally have to apply an infinite force to accelerate it to the actual speed of light.
Damian: Wow – that’s cool. You’re telling me that the fact that mass increases as you speed up ensures that nothing with mass can get to the speed of light. Wait a minute – there’s still that capital IF in front of everything you said, you know.
Renia: Yes, yes, I know. So we have a formula that says IF (capital IF) the speed of light is always measured to be the same number, regardless of how fast the observer is moving, then that means that two different observers will measure time, distance and mass differently – all according to the specific formula. I know it’s crazy. But what do you say about the fact that when we do the experiments and we find that everything works EXACTLY the way these crazy formulas say they work? And these crazy formulas only work if the speed of light really is a constant number regardless of how fast the observer moves.
Damian: So you’re saying that since the universe behaves according to the formulas, then that means that the assumptions leading to the formulas have to be true.
Renia: You’re raising a subtle but very good point. Not only is no other explanation that anyone has come up with consistent with these facts, but we now use relativity in a plethora of engineering and technical devices. None of these could possibly work if relativity weren’t true, and if it didn’t work precisely as the equations say.
Damian: Ya, that point you made in the last podcast about GPS devices using relativity to correct their clocks really hit me kinda hard. It’s just so unbelievable, that’s all. Why is it this way?!?
Renia: honey, you have to stop asking why and start accepting reality. Maybe there is no answer to your hunt for a more satisfying explanation. But you really can’t argue with reality. At some point, you have to accept that nature works this way whether you understand it, or not whether you accept it or not, and whether you like it … or not.
End of podcast:
365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.