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What we know about the EmDrive and Cannae Drive

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Re: What we know about the EmDrive and Cannae Drive

#161

Post by scott_s »

Intermernet wrote: post #157
scott_s wrote: post #95

Earlier quoted context omitted.

Steuard is too polite to point this out himself, so I will do it for him: he is a physics professor. That the amount of money is small is a measure of how incredibly unlikely he thinks any useful result would come from the experiments.

Steuard himself would hopefully point out that although being a physics professor grants his opinion a greater weight than those of us who are less informed, to claim that he is automatically correct would be fallacious. Politeness in this regard is preventing appeals to authority. I personally disagree. The money has been allocated to a section of NASA designed to research exactly this sort of theory. Pulling fundin…

I am not saying he is automatically correct. I am saying that one should consider his profession, expertise, his level of skepticism, and then reconsider priors.

Re: What we know about the EmDrive and Cannae Drive

#162

Post by [deleted] »

Confusion wrote: post #148
Retra wrote: post #134

Earlier quoted context omitted.

That is one of my arguments against homeopathy: We've got a world full of bright young medical students looking for cheap and easy research to do that will lead to positive results. If they haven't proven homeopathy effective, it's because it isn't.

There is no cheap and easy research in medicine when it comes to showing that some substance heals people, which is what if often comes down to, because the actual mechanism is unknown. You can't show something as simple as aspirine 'works' by setting up a lab experiment without test subjects. And as soon as you involve those, it becomes legally complex, expensive, time consuming and hard. You simply can't compare me…

[deleted]

Re: What we know about the EmDrive and Cannae Drive

#163

Post by Steuard »

jdjdps wrote: post #146
Steuard wrote: post #4

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 neve…

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 the…

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.

Re: What we know about the EmDrive and Cannae Drive

#164

Post by pdonis »

spott wrote: post #45
Steuard wrote: post #17

Earlier quoted context omitted.

Yes, sure, they've measured something surprising. I have no reason to doubt that. A few years ago, the enormously more respected folks at the OPERA experiment were willing to announce that they had seemingly detected neutrinos moving faster than light. Despite this coming from a large group of scientists with top-notch credentials, that was immediately doubted by almost the entire physics community, and sure enough,…

So, it is worth bringing up: GR doesn't require global conservation of momentum or energy.[0,1] I'm not saying anything about the experiment, but I think your statement that "conservation of momentum is more deeply embedded..." isn't quite so accurate. [0] http://www.preposterousuniverse.com/blog/2010/02/22/energy-i... [1] http://math.ucr.edu/home/baez/physics/Relativity/GR/energy_g...

> GR doesn't require global conservation of momentum or energy

That's not what the pages you linked to are saying. They are saying that there are solutions in GR where there is not any well-defined notion of total energy, as in "total energy of the universe". But GR certainly does require local energy and momentum conservation, which is what EmDrive would violate if it worked.

Re: What we know about the EmDrive and Cannae Drive

#165

Post by pdonis »

tonyhb wrote: post #105
Steuard wrote: post #17

Earlier quoted context omitted.

Yes, sure, they've measured something surprising. I have no reason to doubt that. A few years ago, the enormously more respected folks at the OPERA experiment were willing to announce that they had seemingly detected neutrinos moving faster than light. Despite this coming from a large group of scientists with top-notch credentials, that was immediately doubted by almost the entire physics community, and sure enough,…

This doesn't have to violate conservation of momentum to work. We don't understand how it works yet, which precludes us from saying that it violates our current understanding of physics. I'm no physicist but this guy[1] is, and his paper — which is based off of research with evidence backing it up in the 1970's — suggests that the EmDrive creates propulsion from Unruh radiation[2]. [1] http://physicsfromtheedge.blogs…

> the EmDrive creates propulsion from Unruh radiation

This would just be a standard photon rocket--the cavity would eject photons out one end and move in the other direction. AFAIK all the EmDrive experimenters are claiming that no radiation is coming out of the cavity.

Re: What we know about the EmDrive and Cannae Drive

#166

Post by pdonis »

jdjdps wrote: post #146
Steuard wrote: post #4

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 neve…

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 the…

> Why are you so set on assuming that it is violating conservation of momentum?

Because the EmDrive experimenters themselves are saying that thrust is being produced without any exhaust--i.e., momentum is being added to the cavity in one direction, without any compensating momentum being ejected in the other direction. That violates conservation of momentum.

> No one of import is claiming this.

Not directly, perhaps, but that is the clear implication of the results they are claiming. No exhaust, no momentum conservation. If they were saying "oh, we did see some radiation being ejected in the other direction", that would make a huge difference. But they're not.

> All who move beyond appeals to authority when constructing arguments must be decried as beyond the fringe!

It's you who are appealing to authority: you are saying there can't be violation of conservation of momentum, simply because the experimenters said there wasn't any. That's not how science works. You're supposed to question what they're saying; you're supposed to look at logical implications to see if what they're saying is all consistent. You're not supposed to just take them at their word.

Re: What we know about the EmDrive and Cannae Drive

#167

Post by pdonis »

madaxe_again wrote: post #149
Steuard wrote: post #4

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 neve…

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.

> 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.

Re: What we know about the EmDrive and Cannae Drive

#168

Post by pdonis »

btilly wrote: post #126
Steuard wrote: post #52

Earlier quoted context omitted.

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…

...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 y…

> 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.

Re: What we know about the EmDrive and Cannae Drive

#169

Post by issa »

Retra wrote: post #136
issa wrote: post #76

Earlier quoted context omitted.

This is exactly my attitude. I'm shocked that people don't think twice about spending money on frivolous or even harmful things, but balk at the idea of paying for pure research.

You don't want to shovel fuel into a crackpot industry. That actually prevents real science from being done.

This isn't an example of a "crackpot" theory. Everyone seems to agree that SOMETHING is happening. Even if the explanation is simply known-physics (which is overwhelmingly likely) there is still value in solving the mystery.

Re: What we know about the EmDrive and Cannae Drive

#170

Post by MertsA »

wnkrshm wrote: post #156
MertsA wrote: post #110

Earlier quoted context omitted.

What's more surprising is that every number I've seen for the higher power Chinese test was 750 milinewtons for 2.5kw of power. That's 300 micronewtons per watt of power.

Are you sure? 300 µN per W would equal a photon drive's efficiency, with 300MW = 1N.

Actually a photonic drive takes only 299.792458 MW to get a newton of thrust. You're units are off, the thrust per watt is equal to 1 / c which would come out to 3.3356 nanonewtons of force per watt.

As for the accuracy of the 750 millinewton figure, that's the only one I've seen for the Chinese results but again, that has to be an error, even if the EmDrive did pan out in the end that's just an unbelievably high amount of thrust. I would assume it's supposed to be micronewtons and that was lost in translation.

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