13 ms·

This is not worth getting excited about. Really. Extraordinary claims require extraordinary evidence. These drives would violate conservation of momentum.[0] C

by Steuard 11y ago

This is not worth getting excited about. Really. Extraordinary claims require extraordinary evidence. These drives would violate conservation of momentum.[0] Conservation of momentum is built in to the known laws of physics at an extraordinarily deep level. It is obviously not impossible that our known laws are wrong, but the alternative would be to somehow produce a radically different set of physical laws that nevertheless reproduce every test of existing theory to high precision (as much as 14 digits of accuracy in some cases). And you probably also need to explain why the existing theory worked so very well if its bedrock foundation doesn't describe our universe. So really, don't get excited. And don't send these folks money that could do real good elsewhere until they give at least some small reason to expect that it's not a wild goose chase. (Edit to add: I wish this were real, too. With all my heart. But it's not a realistic wish.) [Re-edited to cut some less-appropriate phrasing.] [0] Yes, I know the EmDrive site FAQ (http://emdrive.com/faq.html http://emdrive.com/faq.html) claims that it doesn't violate conservation of momentum. The explanation of why it doesn't actually indicates that it does: "The electromagnetic wave momentum is built up in the resonating cavity, and is transferred to the end walls upon reflection." But the wave's momentum has to come from somewhere, too. So either this is just equivalent to a photon drive (propelled by shooting light out the back), or their device is pulling momentum out of nowhere.

Tossrock 11y ago
Why isn't it worth getting excited about? I get excited about lunch. It costs me nothing to follow the progress on low-probability, high impact technological advancements (see: space elevators, commercial fusion power, etc)
- Steuard 11y ago
  I guess this is really the point: space elevators and commercial fusion are many, many orders of magnitude more likely to pan out than this is. Both of those are engineering challenges, and materials science challenges. They may be insurmountable ones, or they may not. But neither one would unconditionally require changes to the bedrock principles of physics. Human beings are not good at distinguishing between levels of "very low probability". Getting excited about space elevators is awesome, even though we're awfully unlikely to see them in our lifetimes and they might never pan out. But these drive theories are pretty literally too good to be true.
  - Dylan16807 11y ago
    Well here's the thing. We could put a fully-functioning fast food restaurant on the moon by 2020. It's an engineering challenge and 100% surmountable. But we won't. It's more likely that we've fundamentally misunderstood physics than we would actually put in the effort to do that.
    - titanomachy 11y ago
      But the economic consequences of, say, commercial fusion would be enormous. Whoever mastered it would stand to become the wealthiest nation/corporation/person on the planet. Can't say the same for a Jack-in-a-box on the Sea of Tranquility.
    - Steuard 11y ago
      I can't begin to tell you how much more likely I would consider a lunar McDonald's publicity stunt than a demonstration that "momentum isn't conserved after all". The first is so implausible as to be laughable. But the second makes the first look mundane. The future behavior of large groups of people is enormously more complicated and less understood than quantum field theory and the standard model.
      - Dylan16807 11y ago
        I'm not really talking about this specific thing. (Though are you sure it even requires momentum to not be conserved?) I'm just trying to say that our knowledge is incomplete enough that I would very solidly bet on certain "impossible" things being more likely than certain "possible" things. So sure people are bad at judging highly unlikely things, but even possible/impossible is not a reliable criterion. (As long as you don't cheat with hindsight.)
kowdermeister 11y ago
> Extraordinary claims require extraordinary evidence So what do you call a second, replicated experimental setup conducted in vacuum, if not extraordinary?
- scott_s 11y ago
  I want to be pithy and say "N=2", but it's not even that. As the experimental controls get stricter, the effect becomes more negligible. That hurts the likelihood, not helps it.
yohui 11y ago
> And don't send these folks money that could do real good elsewhere until they give at least some small reason to expect that it's not a wild goose chase. Is it even possible to give them money? I wasn't aware that NASA accepts earmarked donations, or contributions from private individuals in general.
- Steuard 11y ago
  In the back of my mind, I suppose I'm hoping that some administrator involved with the NASA budget is reading my comment. (Just for instance, I would say that the possibility that we could find life on Europa or the other outer moons is many, many orders of magnitude higher than the possibility that these drives turn out to be even a little bit worthwhile.)
  - pavlov 11y ago
    Are you serious? If you had the power, you would actively prevent NASA from doing these experiments and trying to falsify the claims? I could somehow understand that if the experiments cost a billion dollars. But they don't. Any Europa mission is in no way related to nor threatened by these drive tests.
    - Steuard 11y ago
      Yes, actually. Every dollar that NASA spends has the potential to accomplish something for humanity. To my eye, even the vast potential benefits of this technology are more than washed out by the tremendously low probability that it will turn out to be real. I absolutely do not want NASA to give money to every person who comes to their door claiming to have a recipe for a warp drive. There has to be some threshold of viability, or else all of the folks with home-brewed theories of everything who spam my inbox (I'm a theoretical physicist) could secure their own grants. I honestly have no idea what about this project put it over that threshold, but it seems to imply that the threshold is too low. I want NASA to spend some money on speculative ideas! But surely there are speculative ideas out there that don't require us to rewrite all the laws of physics. Let's fund those.
Glyptodon 11y ago
Even if something disproves the functionality of these things it's still likely to be quite interesting. I think there's room to be excited either way.
- XorNot 11y ago
  The FTL neutrino was a fiber-optic cable from a frequency generator that was slightly loose. So no, it could still be something really stupid, and not exciting. Beyond the fact I wish someone from that team had sent a video into FailArmy on YouTube.
creamyhorror 11y ago
According to physicist Harold White, leader of the NASA Eagleworks team, it can't simply be a "photon rocket": The NASASpaceflight.com group has given consideration to whether the experimental measurements of thrust force were the result of an artifact. Despite considerable effort within the NASASpaceflight.com forum to dismiss the reported thrust as an artifact, the EM Drive results have yet to be falsified. After consistent reports of thrust measurements from EM Drive experiments in the US, UK, and China – at thrust levels several thousand times in excess of a photon rocket, and now under hard vacuum conditions – the question of where the thrust is coming from deserves serious inquiry. And also, a quote from the paper he co-authored in mid-2014 (http://ntrs.nasa.gov/search.jsp?R=20140006052 http://ntrs.nasa.gov/search.jsp?R=20140006052): Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma. Future test plans include independent verification and validation at other test facilities. i.e. "Something weird and exciting may be going on and let's all verify it and figure it out" edit 2: io9 has a handy pop-sci summary of the EmDrive: http://io9.com/new-test-suggests-nasas-impossible-em-drive-will-work-1701188933 http://io9.com/new-test-suggests-nasas-impossible-em-drive-w... vvvv edit: Yes, it's very probably a minor phenomenon that's occurring (barring an outright error), and not new physics. But it's a somewhat consistent phenomenon (in separate China & US experiments) associated with this particular test setup, so hopefully we'll learn something of decent interest in the coming years. The skeptical crowd should do its important job and scrutinise the research, and in the meantime, we (and the admittedly enthusiastic Dr White) can hope :)
- InclinedPlane 11y ago
  Realize that this is the exact same level of verification as superliminal neutrinos, except at a vastly decreased level of rigor. At this point the overwhelmingly likely explanation is that there is some phenomenon at work which we don't understand or haven't properly accounted for, not that there is new physics afoot.
  - lotsofmangos 11y ago
waterlesscloud 11y ago
"But I also wish that I could cure cancer with a single magical kiss, and that I had my very own pet dragon" This kind of condescending response doesn't do science or scientists any good. It's actually actively harmful. Don't do it.
- SeanLuke 11y ago
  Nonsense. These devices are on the far extreme end of the "requires extraordinary evidence" spectrum. Until this extraordinary evidence is provided, they are well within the prior probability category of providing pet dragons.
  - jotm 11y ago
    If the evidence is out of the ordinary, no one will believe it anyway. /s
- Steuard 11y ago
  Fair point, and thanks for calling me on it. In retrospect, accurate or not, that sentence grew out of feelings of frustration more than a desire to teach, which is always a bad sign. I've rephrased it. (I really do have much the same feeling about the magical cancer-curing kiss, though. Oh, how I wish...)
dicroce 11y ago
What about this well known, tested and well accepted effect: http://en.wikipedia.org/wiki/Casimir_effect http://en.wikipedia.org/wiki/Casimir_effect I'm not sure this working implies what you think it does.
- Steuard 11y ago
  I'm not sure what you're getting at, either. The Casimir effect is real, absolutely. I think it was an exercise in one of my quantum field theory classes. In particular, the Casimir effect is something that you can compute entirely within the structure of existing physics, and it doesn't violate any conservation laws. Now, if you suggest that I can somehow extract the Casimir energy without having put the same energy into the system first, I'll start arguing about violations of the laws of physics (in much the same way that I have above).
  - btilly 11y ago
    ...and if you did, then you'd be on shaky ground. Extracting energy from the zero-point energy all around us no more violates conservation of energy than extracting energy from E=mc^2 does. And we can no more figure out how to do so than Einstein could figure out how to do so a century ago. Heck, simply finding an efficient way to store lots of energy that way would be a nice trick as well! We know of no reason why you can't beat any existing battery technology by many orders of magnitude! The trick is that we cannot think of any plausible way to do these things. And once you open up the window of, "This would be amazing if we could, and we can't prove you can't," then you've got something of great interest to cranks who convince themselves that they have done so. So you'd be on safe grounds promptly excusing yourself from any conversation where someone is trying to convince you that it has been done. But dismissing them with a general wave of the hand and appeal to conservation laws makes you as wrong as they are.
    - pdonis 11y ago
      > Extracting energy from the zero-point energy all around us Which can't be done because it's the zero point energy--i.e., it's the state with the lowest possible energy. If there were a lower energy state possible, we would be calling that the "zero-point". > We know of no reason why you can't beat any existing battery technology by many orders of magnitude! We know more than that: we know how to store orders of magnitude more energy than existing battery technology. Just use rest mass to store it: equal quantities of matter and antimatter. The problem, of course, is how to do that safely.
DennisP 11y ago
Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps increasing linearly, while kinetic energy increases quadratically. At some point you start getting more energy out than you put in. For some reason, this disturbs a lot of people more than violating conservation of momentum. The alternative is that there really is absolute velocity, so the basic assumption of relativity is false. But that makes it a pretty big coincidence that atomic bombs work. Still can't say I mind them checking just to be sure.
- avian 11y ago
  > Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps increasing linearly, while kinetic energy increases quadratically. At some point you start getting more energy out than you put in. Can you explain why photonic rockets are not breaking conservation of energy using this reasoning? They have the same property you describe, but are considered feasible as far as I understand (if unpractical to implement).
  - DennisP 11y ago
    Because a photon rocket is throwing stuff out the back like any other rocket. It doesn't really matter that it's just photons due to mass-energy equivalence.
- mrfusion 11y ago
  I'm not understanding this argument. Wouldn't the same amount of thrust get you less and less delta velocity as your velocity increases?
  - DennisP 11y ago
    Velocity compared to what? You have an infinite number of velocities, depending on what you compare to. But you can only have one acceleration at any given time. So how can your acceleration depend on your velocity?
marze 11y ago
Compared to making a feature film, the budget required to check this out very carefully isn't much. Worth it, even if it has 1 in 10000 odds (my guess).
jdjdps 11y ago
I get really tired of these ignorant psuedo sceptic responses. It's so obviously a straw man attack it makes me cringe. Why are you so set on assuming that it is violating conservation of momentum? No one of import is claiming this. My god, authority must always be right! All who move beyond appeals to authority when constructing arguments must be decried as beyond the fringe! Heathens! Infidels! Traitors! Expell them from within the walls of science, from the walls of Freedom. Yeah muh Science/freedom/nationalism/whatever makes me feel safe by allowing me to feel like I belong and satisfies a psychological need to construct a them and us world. Ffs. Grow up. Seriously hacker news. Grow up. Please, please humanity, grow up. Arrrrgggghhhh. I cant even. - Edited to remove swear words
- GhotiFish 11y ago
  I got the same response when I informed /r/science that "No, no one in the OPERA Experiment actually believes that neutrinos are actually going faster than light and breaking special relativity, they're asking for input on what went wrong with their observations" I got a tirade of responses just like yours informing me that I'm a biggot, childish, close minded, backwards thinking, co-dependent on authority, cretin who will be the responsible for the downfall of humanity. ect. ect. ect. I believe I got down to -45 karma on that post, my lowest score ever, and I wasn't being aggressive or hauty or anything. I was just saying "they're just looking for explanations on their observations, there's no way it's actually happening." I never got an apology for that, strangely enough.
- Steuard 11y ago
  I honestly don't even know where to begin in responding to this. You've called me (or my words) "ignorant" and "pseudo-skeptic", you've suggested that I have relied on appeal to authority in making my arguments, and you've implied that I'm motivated by an ignorant "us vs. them" mentality. You've told me to "grow up". All of that seems like pure personal attack, rather than any sort of robust engagement with ideas. The only actual point of science that I can find here is your claim that "No one of import is claiming" that these drives violate conservation of momentum. In my original comment, I explicitly addressed this: the EmDrive FAQ's own attempt to explain how their drive doesn't violate momentum conservation seems to imply a violation of momentum conservation. Maybe I'm mistaken about that somehow: if so, I'd very much appreciate knowing how! (At the very least, I find it perhaps telling that the site's authors don't understand that their attempted answer is no answer at all.) As for the personal attacks, I'll just give one piece of context for the "ignorant" bit. I'm a tenured professor with a Ph.D. in theoretical high energy physics from the University of Chicago. That doesn't give me any special magical authority to declare truth about the universe, but it does mean that I've got a pretty solid base of knowledge for my statements and (I hope) decent judgement about how confident to be in my beliefs about questions in my area of expertise. I work on crazy theories that might or might not wind up describing our world at all, so I'm very aware of both the vastness of our ignorance and the importance of pushing at its boundaries in bold and unconventional ways. And with all that background, I think these drive ideas sound entirely unreasonable. If you've got equally solid reasons to believe otherwise, more power to you, and I'd love to hear them.
madaxe_again 11y ago
Please do explain dark energy, given that all of physics is known and in the can? Nothing is ever cut and dry, or proved - just commonly accepted and proved within our current paradigm - there's plenty to suggest that we've got the nature of reality fundamentally wrong.
- pdonis 11y ago
  > there's plenty to suggest that we've got the nature of reality fundamentally wrong How does dark energy show that? It's either a cosmological constant, or a quantum field with a particular equation of state. Both possibilities are covered by our current theories. Also, both possibilities obey local energy and momentum conservation, so even when we discover exactly what kind of stuff dark energy is and why its density is what it is, those conservation laws won't change. We certainly don't know everything, but we do know some things.
madaxe_again 11y ago
Also, as everybody knows, it is impossible that the earth could be orbiting the sun rather than vice versa - all books on the subject confirm it, and this would totally defy the theological principle, which is certainly impossible. Only hereticks waste their time thinking of such stupid ideas as a heliocentric solar system. They should spend their time productively, and cut up some cats for their humours.

by Steuard 11y ago

Tossrock 11y ago

Why isn't it worth getting excited about? I get excited about lunch. It costs me nothing to follow the progress on low-probability, high impact technological advancements (see: space elevators, commercial fusion power, etc)

Steuard 11y ago
I guess this is really the point: space elevators and commercial fusion are many, many orders of magnitude more likely to pan out than this is. Both of those are engineering challenges, and materials science challenges. They may be insurmountable ones, or they may not. But neither one would unconditionally require changes to the bedrock principles of physics. Human beings are not good at distinguishing between levels of "very low probability". Getting excited about space elevators is awesome, even though we're awfully unlikely to see them in our lifetimes and they might never pan out. But these drive theories are pretty literally too good to be true.
- Dylan16807 11y ago
  Well here's the thing. We could put a fully-functioning fast food restaurant on the moon by 2020. It's an engineering challenge and 100% surmountable. But we won't. It's more likely that we've fundamentally misunderstood physics than we would actually put in the effort to do that.
  - titanomachy 11y ago
    But the economic consequences of, say, commercial fusion would be enormous. Whoever mastered it would stand to become the wealthiest nation/corporation/person on the planet. Can't say the same for a Jack-in-a-box on the Sea of Tranquility.
  - Steuard 11y ago
    I can't begin to tell you how much more likely I would consider a lunar McDonald's publicity stunt than a demonstration that "momentum isn't conserved after all". The first is so implausible as to be laughable. But the second makes the first look mundane. The future behavior of large groups of people is enormously more complicated and less understood than quantum field theory and the standard model.
    - Dylan16807 11y ago
      I'm not really talking about this specific thing. (Though are you sure it even requires momentum to not be conserved?) I'm just trying to say that our knowledge is incomplete enough that I would very solidly bet on certain "impossible" things being more likely than certain "possible" things. So sure people are bad at judging highly unlikely things, but even possible/impossible is not a reliable criterion. (As long as you don't cheat with hindsight.)

kowdermeister 11y ago

> Extraordinary claims require extraordinary evidence So what do you call a second, replicated experimental setup conducted in vacuum, if not extraordinary?

scott_s 11y ago
I want to be pithy and say "N=2", but it's not even that. As the experimental controls get stricter, the effect becomes more negligible. That hurts the likelihood, not helps it.

yohui 11y ago

> And don't send these folks money that could do real good elsewhere until they give at least some small reason to expect that it's not a wild goose chase. Is it even possible to give them money? I wasn't aware that NASA accepts earmarked donations, or contributions from private individuals in general.

Steuard 11y ago
In the back of my mind, I suppose I'm hoping that some administrator involved with the NASA budget is reading my comment. (Just for instance, I would say that the possibility that we could find life on Europa or the other outer moons is many, many orders of magnitude higher than the possibility that these drives turn out to be even a little bit worthwhile.)
- pavlov 11y ago
  Are you serious? If you had the power, you would actively prevent NASA from doing these experiments and trying to falsify the claims? I could somehow understand that if the experiments cost a billion dollars. But they don't. Any Europa mission is in no way related to nor threatened by these drive tests.
  - Steuard 11y ago
    Yes, actually. Every dollar that NASA spends has the potential to accomplish something for humanity. To my eye, even the vast potential benefits of this technology are more than washed out by the tremendously low probability that it will turn out to be real. I absolutely do not want NASA to give money to every person who comes to their door claiming to have a recipe for a warp drive. There has to be some threshold of viability, or else all of the folks with home-brewed theories of everything who spam my inbox (I'm a theoretical physicist) could secure their own grants. I honestly have no idea what about this project put it over that threshold, but it seems to imply that the threshold is too low. I want NASA to spend some money on speculative ideas! But surely there are speculative ideas out there that don't require us to rewrite all the laws of physics. Let's fund those.

Glyptodon 11y ago

Even if something disproves the functionality of these things it's still likely to be quite interesting. I think there's room to be excited either way.

XorNot 11y ago
The FTL neutrino was a fiber-optic cable from a frequency generator that was slightly loose. So no, it could still be something really stupid, and not exciting. Beyond the fact I wish someone from that team had sent a video into FailArmy on YouTube.

creamyhorror 11y ago

According to physicist Harold White, leader of the NASA Eagleworks team, it can't simply be a "photon rocket": The NASASpaceflight.com group has given consideration to whether the experimental measurements of thrust force were the result of an artifact. Despite considerable effort within the NASASpaceflight.com forum to dismiss the reported thrust as an artifact, the EM Drive results have yet to be falsified. After consistent reports of thrust measurements from EM Drive experiments in the US, UK, and China – at thrust levels several thousand times in excess of a photon rocket, and now under hard vacuum conditions – the question of where the thrust is coming from deserves serious inquiry. And also, a quote from the paper he co-authored in mid-2014 (http://ntrs.nasa.gov/search.jsp?R=20140006052 http://ntrs.nasa.gov/search.jsp?R=20140006052): Test results indicate that the RF resonant cavity thruster design, which is unique as an electric propulsion device, is producing a force that is not attributable to any classical electromagnetic phenomenon and therefore is potentially demonstrating an interaction with the quantum vacuum virtual plasma. Future test plans include independent verification and validation at other test facilities. i.e. "Something weird and exciting may be going on and let's all verify it and figure it out" edit 2: io9 has a handy pop-sci summary of the EmDrive: http://io9.com/new-test-suggests-nasas-impossible-em-drive-will-work-1701188933 http://io9.com/new-test-suggests-nasas-impossible-em-drive-w... vvvv edit: Yes, it's very probably a minor phenomenon that's occurring (barring an outright error), and not new physics. But it's a somewhat consistent phenomenon (in separate China & US experiments) associated with this particular test setup, so hopefully we'll learn something of decent interest in the coming years. The skeptical crowd should do its important job and scrutinise the research, and in the meantime, we (and the admittedly enthusiastic Dr White) can hope :)

InclinedPlane 11y ago
Realize that this is the exact same level of verification as superliminal neutrinos, except at a vastly decreased level of rigor. At this point the overwhelmingly likely explanation is that there is some phenomenon at work which we don't understand or haven't properly accounted for, not that there is new physics afoot.
- lotsofmangos 11y ago

waterlesscloud 11y ago

"But I also wish that I could cure cancer with a single magical kiss, and that I had my very own pet dragon" This kind of condescending response doesn't do science or scientists any good. It's actually actively harmful. Don't do it.

SeanLuke 11y ago
Nonsense. These devices are on the far extreme end of the "requires extraordinary evidence" spectrum. Until this extraordinary evidence is provided, they are well within the prior probability category of providing pet dragons.
- jotm 11y ago
  If the evidence is out of the ordinary, no one will believe it anyway. /s
Steuard 11y ago
Fair point, and thanks for calling me on it. In retrospect, accurate or not, that sentence grew out of feelings of frustration more than a desire to teach, which is always a bad sign. I've rephrased it. (I really do have much the same feeling about the magical cancer-curing kiss, though. Oh, how I wish...)

dicroce 11y ago

What about this well known, tested and well accepted effect: http://en.wikipedia.org/wiki/Casimir_effect http://en.wikipedia.org/wiki/Casimir_effect I'm not sure this working implies what you think it does.

Steuard 11y ago
I'm not sure what you're getting at, either. The Casimir effect is real, absolutely. I think it was an exercise in one of my quantum field theory classes. In particular, the Casimir effect is something that you can compute entirely within the structure of existing physics, and it doesn't violate any conservation laws. Now, if you suggest that I can somehow extract the Casimir energy without having put the same energy into the system first, I'll start arguing about violations of the laws of physics (in much the same way that I have above).
- btilly 11y ago
  ...and if you did, then you'd be on shaky ground. Extracting energy from the zero-point energy all around us no more violates conservation of energy than extracting energy from E=mc^2 does. And we can no more figure out how to do so than Einstein could figure out how to do so a century ago. Heck, simply finding an efficient way to store lots of energy that way would be a nice trick as well! We know of no reason why you can't beat any existing battery technology by many orders of magnitude! The trick is that we cannot think of any plausible way to do these things. And once you open up the window of, "This would be amazing if we could, and we can't prove you can't," then you've got something of great interest to cranks who convince themselves that they have done so. So you'd be on safe grounds promptly excusing yourself from any conversation where someone is trying to convince you that it has been done. But dismissing them with a general wave of the hand and appeal to conservation laws makes you as wrong as they are.
  - pdonis 11y ago
    > Extracting energy from the zero-point energy all around us Which can't be done because it's the zero point energy--i.e., it's the state with the lowest possible energy. If there were a lower energy state possible, we would be calling that the "zero-point". > We know of no reason why you can't beat any existing battery technology by many orders of magnitude! We know more than that: we know how to store orders of magnitude more energy than existing battery technology. Just use rest mass to store it: equal quantities of matter and antimatter. The problem, of course, is how to do that safely.

DennisP 11y ago

Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps increasing linearly, while kinetic energy increases quadratically. At some point you start getting more energy out than you put in. For some reason, this disturbs a lot of people more than violating conservation of momentum. The alternative is that there really is absolute velocity, so the basic assumption of relativity is false. But that makes it a pretty big coincidence that atomic bombs work. Still can't say I mind them checking just to be sure.

avian 11y ago
> Also conservation of energy. Thrust can't vary by velocity because there's no such thing as absolute velocity. So your velocity (relative to whatever) keeps increasing linearly, while kinetic energy increases quadratically. At some point you start getting more energy out than you put in. Can you explain why photonic rockets are not breaking conservation of energy using this reasoning? They have the same property you describe, but are considered feasible as far as I understand (if unpractical to implement).
- DennisP 11y ago
  Because a photon rocket is throwing stuff out the back like any other rocket. It doesn't really matter that it's just photons due to mass-energy equivalence.
mrfusion 11y ago
I'm not understanding this argument. Wouldn't the same amount of thrust get you less and less delta velocity as your velocity increases?
- DennisP 11y ago
  Velocity compared to what? You have an infinite number of velocities, depending on what you compare to. But you can only have one acceleration at any given time. So how can your acceleration depend on your velocity?

marze 11y ago

Compared to making a feature film, the budget required to check this out very carefully isn't much. Worth it, even if it has 1 in 10000 odds (my guess).

jdjdps 11y ago

I get really tired of these ignorant psuedo sceptic responses. It's so obviously a straw man attack it makes me cringe. Why are you so set on assuming that it is violating conservation of momentum? No one of import is claiming this. My god, authority must always be right! All who move beyond appeals to authority when constructing arguments must be decried as beyond the fringe! Heathens! Infidels! Traitors! Expell them from within the walls of science, from the walls of Freedom. Yeah muh Science/freedom/nationalism/whatever makes me feel safe by allowing me to feel like I belong and satisfies a psychological need to construct a them and us world. Ffs. Grow up. Seriously hacker news. Grow up. Please, please humanity, grow up. Arrrrgggghhhh. I cant even. - Edited to remove swear words

GhotiFish 11y ago
I got the same response when I informed /r/science that "No, no one in the OPERA Experiment actually believes that neutrinos are actually going faster than light and breaking special relativity, they're asking for input on what went wrong with their observations" I got a tirade of responses just like yours informing me that I'm a biggot, childish, close minded, backwards thinking, co-dependent on authority, cretin who will be the responsible for the downfall of humanity. ect. ect. ect. I believe I got down to -45 karma on that post, my lowest score ever, and I wasn't being aggressive or hauty or anything. I was just saying "they're just looking for explanations on their observations, there's no way it's actually happening." I never got an apology for that, strangely enough.
Steuard 11y ago
I honestly don't even know where to begin in responding to this. You've called me (or my words) "ignorant" and "pseudo-skeptic", you've suggested that I have relied on appeal to authority in making my arguments, and you've implied that I'm motivated by an ignorant "us vs. them" mentality. You've told me to "grow up". All of that seems like pure personal attack, rather than any sort of robust engagement with ideas. The only actual point of science that I can find here is your claim that "No one of import is claiming" that these drives violate conservation of momentum. In my original comment, I explicitly addressed this: the EmDrive FAQ's own attempt to explain how their drive doesn't violate momentum conservation seems to imply a violation of momentum conservation. Maybe I'm mistaken about that somehow: if so, I'd very much appreciate knowing how! (At the very least, I find it perhaps telling that the site's authors don't understand that their attempted answer is no answer at all.) As for the personal attacks, I'll just give one piece of context for the "ignorant" bit. I'm a tenured professor with a Ph.D. in theoretical high energy physics from the University of Chicago. That doesn't give me any special magical authority to declare truth about the universe, but it does mean that I've got a pretty solid base of knowledge for my statements and (I hope) decent judgement about how confident to be in my beliefs about questions in my area of expertise. I work on crazy theories that might or might not wind up describing our world at all, so I'm very aware of both the vastness of our ignorance and the importance of pushing at its boundaries in bold and unconventional ways. And with all that background, I think these drive ideas sound entirely unreasonable. If you've got equally solid reasons to believe otherwise, more power to you, and I'd love to hear them.

madaxe_again 11y ago

Please do explain dark energy, given that all of physics is known and in the can? Nothing is ever cut and dry, or proved - just commonly accepted and proved within our current paradigm - there's plenty to suggest that we've got the nature of reality fundamentally wrong.

pdonis 11y ago
> there's plenty to suggest that we've got the nature of reality fundamentally wrong How does dark energy show that? It's either a cosmological constant, or a quantum field with a particular equation of state. Both possibilities are covered by our current theories. Also, both possibilities obey local energy and momentum conservation, so even when we discover exactly what kind of stuff dark energy is and why its density is what it is, those conservation laws won't change. We certainly don't know everything, but we do know some things.

madaxe_again 11y ago

Also, as everybody knows, it is impossible that the earth could be orbiting the sun rather than vice versa - all books on the subject confirm it, and this would totally defy the theological principle, which is certainly impossible. Only hereticks waste their time thinking of such stupid ideas as a heliocentric solar system. They should spend their time productively, and cut up some cats for their humours.