Date: October 23, 2011
Title: Encore: Warp Drive
Podcaster: Renata and Damian Handzy
Link: This podcast originally aired on Jan. 9, 2010: http://365daysofastronomy.org/2010/01/09/january-9th-warp-drive/
Description: What are some of the astonishing and real things that happen as a spaceship were to approach the speed of light? This podcast goes over some of the amazing effects of Einstein’s Relativity along with some of the rock-solid evidence we have supporting relativity in case anyone ever says “well, that’s only a theory.” The podcast will cover: time dilation, twin paradox, length contraction, mass dilation, muon decay, atomic-clock flight, GPS systems, and red-shift, just to name a few topics.
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.
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Transcript:
Damian: You know all these exo-planets we keep hearing about – it’s a shame they’re so far away. I mean, it will take years, decades or even centuries to ever get a spaceship to one of those places. People will live their entire lives on the spaceship.
Renata: Well, not necessarily. If the spaceship can get going fast enough, relativity will actually contract the distance the ship has to travel and it will not seem to take that long to the astronauts.
Damian: What?? That makes no sense. If I travel at 50 miles per hour and I drive 50 miles, it takes me 1 hour. If an exo-planet is 10 light years away, and my rocket travels at just about the speed of light, it will take me 10 years to get there. That’s what it means to be 10 light years away, right?
Renata: You’re half right – it will take those astronauts ten years as measured by someone on Earth, but that’s not what the people on the rocket will measure. Remember, the faster the rocket goes, the slower the clocks on the rocket go. If the rocket moves fast enough, time will slow down dramatically and the astronauts might only experience a few weeks or so before arriving.
Damian: Wait. That means that if we could go really really really close to the speed of light that those astronauts would think that they traveled those 10 light years in just a few minutes?? For them, it would be like teleporting?
Renata: right.
Damian: so all those science fiction stories of hyperspace or warp drive or whatever they call it are actually real!
Renata: well, not exactly. You see, time back on earth doesn’t slow down. For all of them, ten full years passed by while the rocket was traveling to the exo-planet.
Damian: OK, hang on – if those astronauts, after they arrive send a message back home, that message would take another ten years to get to mission control. So for people on earth, the message would arrive 20 years after the rocket left. But for the people on the spaceship, they would think that it took a few minutes to get to the exo-planet plus 10 years to get the message back.
Renata: that’s right. The astronauts think they themselves traveled that 10 light-year distance in only a few minutes, but the message they send saying they arrived safely still takes 10 years to get back – as measured by them and as measured by the people on earth. Both groups – the people on the exo-planet and the people on earth – measure the same amount of time for the message to get back: 10 year, and that’s because those two groups of people aren’t moving with respect to each other while the message travels. You see, the message still takes 10 years – in other words, there really is no “subspace” channel like they use in Star Trek to send a message faster than light.
Damian: I bet you Steve Jobs will invent one.
Renata: what?
Damian: never mind – instead of sending the message the regular way, what if one of the astronauts got back in the spaceship and headed back to earth with the news that they got there safely, and she traveled just about at the speed of light back to earth. That trip would also seem like it only takes a few minutes, so the message would arrive right away!
Renata: (laughing) you’re half right again. For that astronaut who took the message and only for her would it seem that the trip took a few minutes. For everybody else watching the trip – the group of astronauts on the exo-planet AND the people back on Earth – that trip back would also take 10 years. Remember – for someone not moving time doesn’t slow down. You CAN NOT have faster than light communication. Your astronaut who took the round trip only experienced a few minutes from when she left Earth to when she got to the exo-planet, plus only a few minutes more to get back to earth. The astronauts she left behind on the exo-planet feel like it took minutes for them to get there but that she took 10 years to get back. And the people back on earth waited 20 years for her to get back. Those people would really be 20 years older but she’d only be a few minutes older. Get it?
Damian: I’m glad you understand it.
Renata: remember, relativity doesn’t just tell us that time slows down, distances decrease and mass increases as an object approaches light speed – it also tells us by exactly how much they change. And the coolest part, for me at least, is that all those things change in exactly the right ways to keep everything self-consistent for every observer – the time you measure times the velocity you measure is always the distance you measure. But those quantities will be different for different measurers, depending on their speed.
Damian: OK, so how fast do you have to go before you notice these things?
Renata: (surprised) that’s a really good question – it’s a highly non-linear relationship and you actually have to go really really fast to get the effects we’re talking about. But the effects start happening no matter how slowly you go.
Let’s say you’re going 10% the speed of light. That’s already fast enough to fly around the Earth in only 1.3 seconds. In that case, time slows down by only a factor of ½ of 1%. Not very exciting. Let’s speed up to 90% the speed of light. That’s fast enough to go around the earth 7 times in one second. At that speed, time slows down by a factor of 2.3. In other words, 1 day in the space ship would correspond to 2 days and 7 hours back on earth. Still not that exciting. Let’s go to “4 nines” – 99.99% the speed of light. At this speed, things slow down by a factor of 70. That means every day in the spaceship is like 70 days, or 2.3 months, back home.
Damian: Now we’re talkin’. What happens if we hit 6 nines – 99.9999% the speed of light?
Renata: At 6 nines, you’re looking at a slowing of time by a factor of 700. Each day in the spaceship is like almost 2 years back on early.
Damian: OK, so all this relatively theory sounds cool – how much of it is proven? I mean, it is still just a theory.
Renata: Don’t get me started on the word “theory.” We really shouldn’t call relativity a theory – we should call it a fact. It’s as well supported as the theory of gravity or the theory of electricity. Are those “just theories”?
Damian: OK, but it’s only been proven in the laboratory, right?
Renata: Not even close. For one, in 1971 they took 2 synchronized atomic clocks and put them on jet planes and flew them in opposite directions specifically to test relativity.
Damian: I thought you said relativity doesn’t apply at slow speed.
Renata: (annoyed) will you please pay attention: I said it applies at all speeds, but that relativity’s effects are really small unless the object is going really fast. At jet engine speeds, the effect is measured in nanoseconds and that’s why they used hyper accurate atomic clocks – to measure the tiny effect. And guess what – the two clocks were off from each other and from a control clock they left on the ground by the amount that relativity predicts.
Damian: Really?
Renata: Really. Then, there’s the curious story of the muon. Muons have a half-life of only one and a half microseconds, which means that half of them decay away in that short time. When cosmic rays hit the upper atmosphere, they create plenty of muons at high speed, which fly down to earth. If you ignore the whole time slowing down thing, you would estimate that the number of muons that reach the earth is only about 1/5 the number that we actually observe. WHY? Because time really slows down for the muons, and to them much less time has passed by before they hit the earth, so far fewer of them have decay than you would expected if relativity weren’t true.
Damian: That’s weird.
Renata: That’s reality. Time itself slows down. It’s not a faulty watch or some trick – time itself slows down. Another way to understand the muon phenomenon is that from their point of view relativity shrinks the distance from the upper atmosphere to the ground by the same factor of 5, so they cover the now shorter distance in less time than naïvely expected. Since less time has passed, fewer of them have decayed so more of them arrive at your detector on the ground.
Damian: My head hurts.
Renata: I haven’t given you the single most down-to-earth piece of evidence for relativity – your favorite device: the GPS.
Damian: What does relativity have to do with my GPS?
Renata: The GPS satellites that orbit the earth actually move pretty fast, and remember that they’re all synchronized. Well, if they didn’t take relativity into account, including the very real effects of time dilation, their synchronization would be totally off. In fact – they’d be off by a cumulative amount of about 3 miles per day. After just 1 month, they’d be off by over 100 miles. The fact that they work at all is proof positive – in your own car – that relativity is real and relevant.
Damian: (laughing) Speaking of cars, if I’m driving at the speed of light and turn on the headlights, isn’t it true that I wouldn’t see any light shining in front of my car ‘cause nothing can move faster than light?
Renata: Actually, every observer measures that light, in a vacuum, travels at the exact same speed, regardless of how fast that observer is moving. So you would actually see the light coming out of your headlights and moving away from you at the speed of light. And if I were standing outside your car watching this, I would measure both your car and the light from your headlights moving at the same speed – the speed of light.
Damian: whaaaaat? How can I see light moving away from me but you for you it doesn’t move away. It’s either moving away or it’s not.
Renata: Sorry, honey, we’re out of time for this podcast, so it’ll have to wait until next time…
End of podcast:
365 Days of Astronomy
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