What does the “emdrive” claim to do? How does it violate almost all of known physics? What were the problems with the experiments? I discuss these questions and more in today’s Ask a Spaceman!
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EPISODE TRANSCRIPT (AUTO-GENERATED)
What if you could fly around space without needing to fly around space? Like, without any rockets, you just have a box sitting in the middle of your spacecraft, and away you go. Nothing comes out of the box, but your spaceship just moves. Sounds like science fiction, and, well, as we'll see in this episode, it is. I'm talking about the EmDrive, also known as the electromagnetic drive, the RF resonant cavity, the Q drive.
Some people even call it the impossible drive because it is. The concept was first introduced back in 02/2001, but the media world went nuts back in 2016 and again in 2019 as various groups around the world claimed to build them, test them, and get positive results. But before I go too far, I need to describe what it is. It's a closed metal cavity that's narrower on one end than the other, and it's designed to be pumped full of microwave radiation or really whatever radiation you feel like at the time. And, well, that makes a rocket engine.
I mean, it's literally a fancier version of putting your microwave oven inside a rocket and waiting for something to happen while you cook your frozen burrito. It doesn't sound all that exciting until you start to dig into what it would actually mean. It's a big deal because rockets need thrust. They need a propellant. They need to push something out out of the back end to make them go forward, and they they can push anything out.
It could be, it could be gas. It could be exhaust. It could be chunks of dirt. It can even be radiation, like, just whatever. You chuck it out the back and your rocket goes forward, and this works through conservation and momentum.
You have a bunch of stuff inside your rocket and this stuff goes one way and the rocket goes the other. In fact and and all rockets work this way. If you've heard of ion drives, they work this way. You know, the fancy stuff that SpaceX is building, that works this way. Just this is just how rockets work.
But the em drive has no thrust. It has no exhaust. Nothing comes out. It is a closed cavity. It is a microwave oven, but it provides thrust to the spaceship.
You just need this fancy metal box and some sort of energy source, doesn't matter what, and you're good to go. You can have in the middle of the spaceship, it could be in the front, it could be down in the basement, duct tape to the side. It doesn't matter. You just turn it on in a way you go. It's nicknamed the impossible drive because it shouldn't work.
But like I said, some groups claim that they were able to measure, like, to build this, have a special cavity, and it's and it's, like I said, it's it's like conical shaped. It's it's shorter. It's smaller on one end than the other. Fill it with radiation, and they say they were able to measure a tiny bit of thrust. Not not a lot.
We're talking not enough thrust to, say, push a piece of paper, but not zero. So what's going on? I mean, it's been twenty years from the time this was introduced to the time that this podcast was recorded. Twenty years since this idea first came on, groups around the world have attempted to work on it, have developed it, have tested it, and they keep saying, like, every couple years, there's where I'll say, hey. We did it.
Here's the m drive. We got it to work. We have motion, thrust without, you know, thrust, without exhaust. Is physics as we know breaking down, or is something else going on? At the time back in 2016 and again in 2019, many scientists, including yours truly, took the science media to task for their reporting on the EmDrive Because the reporting of the m drive described it as controversial, which it is, but they also described it as a big debate.
Like, there was one group of physicists that were trying to build m drives and show how they would work and another group of physicists who were saying, you know, wagging their fingers saying, oh, you you don't understand conservation of momentum. There's no way this could work. And that there was this, like, fiery debate going on in the physics community about about the nature. Yeah. Blah blah blah blah blah.
I'm not even going to read the headlines out loud. I thought I would. I thought I'd read through some of the headlines that are reporting on the M drive or were reporting on the M drive back in the day, but I don't want to because I don't wanna give myself or you an aneurysm because it totally misrepresented what was going on. It made it appear like there was this big debate among physicists or that these people were developing the EmDrive, and they were going rogue and fighting the power against the status quo of scientists who didn't have enough imagination to see past their century old theories. And, also, the headlines completely misunderstood physics.
You were tossing words around that the writers of the headlines obviously didn't understand what those words meant, misunderstood physics, both theoretical and experimental, didn't understand the meaning of statistical significance, didn't understand sources of uncertainty, didn't understand what it means to actually write a paper, didn't understand what some of these people were saying. Because some of the people and I'm not gonna name any names in this because why bother? Some of the people developing end drives were going in some very odd directions, and we'll get into the physics of it or the claimed physics. But the short version is either you need to break conservation of momentum in order to get this thing to work, or you need to appeal to brand new physics. And no matter what direction the people who, let's call them m drive aficionados go in, it gets just to get real murky and real mumbo jumbo, real hand wavy, and then the journalist just swallowed it up.
And then when, you know, like, real physicists would show up and say, well, that's not how it works. You know, we can't do this. Like, that's actually forbidden. It made it seem like there was an active healthy debate in the community, and that there was an old guard of physicists who didn't want to give up onto their precious closely held theories, and then new physicists, new engineers who are bucking the trend. These were the millennials, you know, going after those boomer scientists and their their conservation of momentum that's so twentieth century.
Like, this is this modern era. That's what it the headlines made it feel like. Nobody thought the EmDrive would work. No serious physicist thought it would work. We, and I'm gonna include myself, perhaps unfairly in the club of serious physicists, we thought it was dumb.
We thought it was a waste of time. We thought it won't work because the people developing the EmDrive are not understanding physics. And if you don't understand the physics that you're claiming to fight against, good luck trying to come up with something new. I will explain all this in the episode. Don't worry.
It just made me mad because it painted it's like it's like when the news media comes on and it tries to paint the picture that there's a massive debate among climatologists about climate change or global warming. There isn't. There are all the scientists who think that global warming is happening based on the evidence, and then there's, like, the three fringe weirdos who just happen to have PhDs or tenured positions, and and that's it. But there is actually no debate or discussion about whether the fact that the Earth's climate is getting warmer. There's just no debate about that anymore.
There may have been debate about it fifty years ago, but that was fifty years ago. And so now there's no debate, and then there's just oh, sorry. I could go on. It made me upset. And it painted it painted scientists as uncreative, as unwilling, as curmudgeons.
Okay. Maybe the curmudgeons part is fair. But it it painted scientists as, you know, just holding it like dogmatists. That's how it made science to be. And then then these people developing the EmDrive were were the ones, the radical new ones with the new ideas who are getting come up with new physics and tear down centuries of tradition, and they're just these stuffy ivory tower intellects.
Do scientists need to be creative? Yes. Can new results come out of nowhere outside of established mainstream research? Yes. Must we be prepared to shape the foundations of physics as we know it?
Absolutely. But do we also need to be skeptical? Yes. Do we also need to ramp up that skepticism when results that come out that are supposedly huge deals? Yes.
Do we also need to make sure we understand why scientists believe certain things strongly? Yes. Can experiments be done incorrectly? Yes. Can experimental results be understood?
Yes. Are we allowed to dismiss ideas as nontenable? Yes. Here's the thing about the EmDrive. It can't work.
It can't work. At the end of that sentence, there's technically a little asterisk. And when you go down to the footnotes, you see at following the asterisk after I say it can't work, I have to say according to everything we currently know about physics. Is there that you might think there's an opportunity? What if everything we know about physics is wrong and the EmDrive is simply the first experimental evidence we have that modern physics is breaking down?
Fair point. It's true. We don't know everything there is to know about the universe. Welcome to modern physics, all of science. We don't know everything there is.
Half this series is about stuff we don't fully understand or wish we understood. And our understanding of the universe constantly changes and evolves and updates. Like, the other half of this series is describing how our thoughts have evolved and changed and updated. The worldview in 1850, the physical worldview in 1850 was vastly different than the physical worldview of 1950. Compare 1850 to 1950.
Eighteen '50, you don't have electromagnetism. You don't have relativity, special, or general. You don't have quantum mechanics. You don't have quantum field theory. You don't even know about the nuclear force or the weak nuclear force.
You don't know about cosmology and the big bang. You don't know spectroscopy. You don't know the structure of atoms. You don't know chemistry. Like like, there's a lot that changed, but then some things haven't changed.
There are some things that we know really, really well. There are some things that we knew in 1850 that we still knew in 1950 and likely aren't going to change by the time we hit 2050. Some parts of physics have become so well tested and so well understood that to break them would require complete rewriting of every single known law of physics, everything we know about the universe. Like, there are some foundations that we figured out a long time ago and have stuck. Things like conservation of momentum.
Conservation of momentum is the idea that, well, momentum is conserved. Momentum, if you'll, recall, I don't think I've ever given a mathematical definition of momentum in this show, is mass times the velocity. It's the oomph that an object has. The more mass or the more velocity you have, the more oomph you have. And if you have more of both and double the oomph.
The cool thing about momentum is that it's this very curious physical property that if you have, say, an isolated system and you add up all the momenta of all the different objects in the system and then let them interact, you close your eyes for a while, you go take a nap, eat a sandwich, you come back, and then you measure all the momenta again, Some objects will be slower, some will be faster. They'll have mixed up their momentum. But if you add it all up at the beginning and then add it all up at the end, they'll be the same. Momentum stays the same. That's what it means for momentum to be conserved.
And so the conservation of momentum is the principle that says momentum is conserved. Momentum stays the same throughout the universe, the total momentum. Conservation momentum was first proposed by Descartes. Talk about intellectual ancestry. And it was laid out mathematically by Newton.
In fact, Newton's second law, the whole force equals mass times acceleration thing, is actually a restatement of conservation of momentum. Newton didn't really realize it right away, but, eventually, he did. You can't have f equals m a without conservation of momentum. So to say force equals mass times acceleration, you're actually saying momentum is conserved. And momentum conservation was a part of physics all through the eighteen hundreds, '17 hundreds.
Like, ever since Newton and Descartes figured it out, it was there, tested, and observed again and again and again, even with the development of thermodynamics. Guess what's at the heart of thermodynamics conservation momentum? Even through the development of electromagnetism. Guess what's at the heart of electromagnetism? Conservation momentum.
And then in the early nineteen hundreds, the brilliant mathematician, Emmy Noether, proved, and proved is a word you rarely hear on this show because in science, nothing is really proven. We just do inference. We gather information. We gather evidence to make cases. But Emmy Noether proved something because you can do that with mathematics.
You can prove statements to be true based on certain assumptions. She proved something remarkable. She proved that you can keep this show going with Patreon. That's right. Over a hundred years ago, Emmy Noether proved that if you go to patreon.com/pmsutter, you can keep this show going and that I will be grateful.
That was fantastic of her. How far reaching. She also proved that conservation momentum is a consequence of asymmetry in nature. The fact that you can do the same physics experiment and get the same result in different places. Like, if you have some physics experiment, who cares what it is, and you pick it up and move it to somewhere else.
Once you take into account the changes in your environment, like, say, different air pressure or different gravitational strength, you know, whatever, do you you account for those differences, you will get the same result. You pick up your science experiment, physics experiment, take it to the other end of the Milky Way. Once you account for things like air pressure and gravitational field, you will get the same result. Take it to the other end of the observable universe, account for air pressure, gravitational blah blah blah. You will get the same result.
There's a fundamental symmetry in nature, a spatial symmetry. And Emmy Noether was able to prove that this spatial symmetry leads directly to conservation of momentum. There's also a symmetry in time, and that leads to conservation of energy, and then there's other symmetries that lead to other laws that we bake into our physical theories. Absolutely powerful insight shows a deep and fundamental connection that if you develop a physical theory or if you observe in nature a certain spatial symmetry, then conservation of momentum is a direct mathematical consequence of that. So if you were to break conservation of momentum and, of course, you can break conservation of momentum in certain systems.
You can construct scenarios where conservation momentum is broken, or at least you have to understand conservation momentum at a different level. Like, if I have two balls that stick together, obviously, if I just add up the momentum at the beginning and then they smash into each other and stick and add up the momentum at the end, conservation momentum will not hold unless I look at it atom by atom in detailed view, then I will see that the momentum has just been transferred into other kinds of motions, and then everything's kosher again. But if you want to break conservation momentum momentum at a big level, like with the m drive, you need to prove that this symmetry is not respected in our universe at some level. And conservation momentum isn't just baked into basically every theory of modern physics. Conservation momentum is modern physics.
Modern physics is a fancy way of expressing conservation momentum in this fundamental symmetry. Newton's laws, special relativity, general relativity, quantum field theory, thermodynamics, electromagnetism, the whole deal is just restating conservation momentum over and over and over again. Conservation momentum is one of the most central cornerstone far reaching concepts in all of physics, and it has been for hundreds of years. If you break conservation of momentum, you have broken all of physics and you have to rebuild and reexplain all of physics. This means that conservation momentum has been tested just a little bit.
Every single day, multiple experiments around the world routinely test conservation momentum, either directly because they're trying to directly test some physical theory that includes conservation of momentum or indirectly where they just assume conservation of momentum and then because they're actually investigating something else and they get those results. Nowhere in no shape, in no form, in hundreds of years of experimentation has anyone found a single variation or a single exception to the conservation momentum. Nobody until EmDrive. If the m drive were to work, it would violate the conservation of momentum because you would have a box sitting there not moving, and then you turn it on, nothing leaves, and then it starts moving. The momentum at the end does not equal the momentum at the beginning.
Conservation momentum has been broken in a big way, and that this would be the first experimentally verified breaking of the conservation of momentum. That's why so many scientists took one look at the explanation of the m or just the description of the m drive of, hey, we're gonna turn on a bunch of microwaves inside a cavity, and none of the microwaves will escape, and then this thing is gonna be pushed around. Almost every single physicist looked at that and said, pass. No. No.
Mm-mm. Because it breaks conservation of momentum. There's no controversy. There's no argument. There's no debate.
Yes. Violating conservation of momentum could be a real thing that we could someday uncover, but physicists aren't really interested in it because it's so incredibly unlikely. It's probably just a massive waste of time and money. We have already tested conservation of momentum in all sorts of crazy exotic scenarios. It's baked into physics.
It's baked into your cell phone. It's there. We tested all we've already tested it. It had passed every single test we throw at it. Conservation momentum, yeah, could be wrong, but it's not gonna be proven wrong by the EmDrive.
That's why I think it was irresponsible for the media to cover the EmDrive the way it did. It ignored real actual physics as we understand it and pretended that the EmDrive even had a shot at working. Yes. It's important to keep an open mind. Absolutely.
It's important to know and recognize that our physical theories can be broken down, and that can be they can be reshaped and restated. And that someday, we could discover some strong piece of evidence that would lead us to think that our understanding of conservation of momentum and spatial symmetry in our universe is flawed or incomplete? Absolutely. Is that gonna happen tomorrow? Probably not.
A lot of the EmDrive aficionados, sidestepped this issue because it was such a gross violation of conservation momentum, and they knew it. You can't just go around saying, well, it just violated well, maybe we don't understand momentum. Like, physicists around the world say, yes. We do. So some m drive aficionados say, well, maybe it's something else.
Maybe it's not violating conservation momentum. Maybe it's some new physics that we haven't understood before. I mean, yes. It violates conservation momentum, but it's because conservation of momentum is violated in certain special physical scenarios, and then here's how. And this is where the mumbo jumbo came in.
I've seen explanations like, there's the quantum field plasma that is interacting with the radiation in the cavity. There's no such thing. The quantum field is not a plasma. Like, that's not how it works. It doesn't interact with radiation that way.
Some people say, well, there's the the the vacuum energy, and then this the the radiation in the cavity is pushing against the vacuum energy, but the vacuum energy doesn't permit anything to push off of it because it's not like a substance. It's not a wall. It just very, very quickly became mumbo jumbo. Like, once it was proposed and people started working on it, physicists say, like, explain to me how this works. How exactly is momentum conservation violated?
And then there had to be excuses, like explanations, and all the explanations made no sense. And then the science journalists just repeated what the EmDrive aficionados were saying and putting them in headlines, putting in articles as if it made it was just word salad. You know, quantum this, vacuum that, self interaction, blah blah. Yeah. Just just it was like watching Star Trek.
Like, how are we gonna defeat those Romulans? I know. We'll use the EmDrive. It can push against the the quantum vacuum plasma, and it'll accelerate them. But, you know, it it sounded like so it was just like writers in a room like, hey.
This is cool words we found out Wikipedia. None of the explanations for how the EmDrive could work make any sense whatsoever. But still, EmDrive aficionados persists and says, well, we it works. It works. Some groups claim to get results.
Some groups claim to get measurements of a force of thrust out of these out of these ovens. Sorry. I keep calling it oven. I know that's a little bit derogatory, but I just can't help myself. And to dig into this, we need to go into the wonderful world of experimental physics.
Here's a little advice for the real world kid. Nothing is as it seems. Cause and effect are never clearly connected, and nature hates it when you tester and will actively fight against you. Yes. Groups around the world over the past few years, like in 2016 and again, 2019, have claimed to get various versions of the EmDrive working.
Most of those groups make the claim but never actually publish, so so we can just toss those out. Every once in a while, like in 2016, a paper did come out claiming to show experimental results of an EmDrive. Even though and then and you could just hand wave. Like, yes, there's all the mumbo jumbo conservation of angular of momentum. Oh oh, well, I don't know how it works, but it works.
So now we need to rewrite physics. Okay. One issue is uncertainty. I saw I read the results. I read the papers.
I combed through it. You know, I skipped through all the mumbo jumbo. When I looked at the data, I looked at the results, and the results have uncertainty. There's two kinds of uncertainty when you try to publish results. One is called statistical uncertainty.
The is the other is called systematic uncertainty. Statistical uncertainty is due to the fact you only have so much data. You only have so many data points. You're trying to make a measure something, and so you you just don't know everything you would like to know, and so you have to have a little bit of uncertainty. If you take more data, if you do run experiments longer, you can bring those uncertainty levels down.
Okay. The other kind of uncertainty is called systematic uncertainty, and this is due to the fact that other things can come in and contaminate your results. Like in the case of the m drive, you're trying to measure this very, very tiny thrust. You've got this box, this cavity. You turn it on, and you're trying to see if the box moves.
But it could be moving because of some weird thing that violates conservation of momentum, or it could be moving because, I don't know, you walk by it, you know, because because Ed leans on it. Come on, Ed. It could be weird electromagnetic interactions. It could be not completely closed. One part of it could be heating, then the other, like, maybe your air conditioner is blowing on it.
So you gotta work really, really hard to get a nice controlled experiment and also understand the sources of your systematic uncertainty. It's very, very hard to estimate uncertainty in general, both statistical and especially systematic. It's really hard to get a sense of how well you know something. Like, we've measured a thrust because it's greater than zero. How do you know it wasn't just noise?
How do you know it wasn't something else? That's the job of a typical experimental paper is to convince the world that what you're measuring is what you actually measure. What you claim to measure is what you actually measure. The results that I have seen are far from convincing. I looked at those results claiming to see a thrust.
I saw large uncertainties large enough to make it this just look like noise. I if I were the referee on the paper, I would not accept. I would say you've just these uncertainties are way too large. Run your experiment for another year and get back to me. What claimed to be a result of thrust was, to me, honestly, it looked like they had just measured noise where things were just so barely above zero, it wasn't even worth talking about.
There was no statistical significance to the effects at all. That's what I've seen published, results that do not look statistically significant, especially when you account for systematic uncertainties and the fact that they may not be understanding their uncertainties very well. Because then they measure like, yeah. We measured this much thrust, plus or minus, you know, like like, let's say, just as an example, we've measured 10 micronewtons of thrust, plus or minus eight micronewtons. Well, that's basically zero.
That is not statistically different from measuring no thrust at all. I immediately wondered when I read these papers, why haven't they run the experiment just a few months longer to bring the air bars down? I'm not claiming that the authors of the papers are trying to lie in their results, but cherry picking is a very real thing and pernicious thing in science, and it has been demonstrated before where scientists will keep running experiments again and again and again and again, knocking anything until out of random chance you get one that looks nice, and then you publish on that claiming a result. This has happened in science, unfortunately. I don't know if it has happened with these results.
Like, oh, we're just gonna run this m drive thing here. And oh oh oh, look. Look. Look. Look.
We got it. We got it. Like, save this one. Screenshot that. Stick it in the paper.
We got a result, folks. Happens to all of us. I don't know if they did that. I don't know why they didn't just run their experiment longer to get smaller uncertainties and get more data, but I'm not them. And then there's the issue of replication.
Some groups would take these results and try to replicate it. And either they get nothing at all, as in fail to replicate, or they find a mistake in the original analysis that can explain the results. One example, another group tried to replicate an m drive and found that, say, microwaves were leaking from the cavity could explain the results, vibrations could, explain the results, The interactions between the cables in the Earth's magnetic field. This is such a tiny force that the m drive, aficionados are claiming that basically anything can give this amount of force. If you just wait long enough, eventually, your box is gonna jiggle in a certain direction that is gonna look favorable, and then you can publish it, whether it's even plugged in or not.
The original groups still claim the results are valid and are still trying to build them drives. Their explanations for how the work how the m drive could work show that they clearly don't understand physics, like pushing off vacuum fluctuations or using the quantum vacuum plasma. None of these are things. None of them have an explanation of how or why conservation momentum could be broken. In general, the EmDrive makes me mad and sad.
Mad and sad. Yes. Physics could be written rewritten any day now, but not today. Not with the m drive. Nobody thought it would work.
Nobody has shown that it does work. There is no controversy. There is no debate. There is no argument. We don't have any evidence of anything interesting happening with em drives, which is exactly what we expected.
There's nothing about the design of the em drive that shows that it could work. There has been no explanation for how it could work, of how momentum conservation could be violated, new physics or not. There has been no statistically significant result. There has been no replication of results from non m drive aficionados. There's nothing here, which is exactly what we thought would have, and all the physicists said, no.
This isn't gonna work because you can't have thrust without and you have in in my view, it's a waste of time, money, and attention, and it hurts the broader understanding of science because people the science journalists just make it look like you can just make up words and violate physics and that things that we've understood for hundreds of years, can just be turned over in a moment. It can't. It's just PM drive just isn't interesting. I'd like to thank Mitchell l by email for the question that led to today's episode. And, of course, I'd like to thank my top Patreon contributors.
Before but before we do, go to my website, pmcenter.com/book, or search How to Die in Space on Amazon. Go ahead and leave a review if you've bought the book. If you like it, leave a review. That helps get the word out. I really appreciate it.
But you can also buy it at Barnes and Noble. It's also available as an audiobook. That's how to die in space. It it was a fun book to write. I would like to thank my top Patreon contributors.
That's patreon.com/pmsutter, Matthew k, Justin z, Justin g, Kevin o, Duncan m, Corey d, Barbara k, Chris c, Robert m, Nate h, Andrew f, Chris l, Cameronell, Nalia, Aaron s, Kirk t, Tom b, Scott m, Billy t, and Rob h, and all the other fine space cadets for making this show possible. Of course, you can please, please, please, keep sending me questions. Ask a spaceman@Gmail.com. Hashtag ask a space space man social media at paul matt sutter. You know what to do.
It's your questions that keep this show going. Honestly, your questions are more important than the Patreon contributions. I'm grateful for all of it, and I will see you next time for more complete knowledge of time and space.