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Questions about Nasa's space drive answered

wired.co.uk

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Re: Questions about Nasa's space drive answered

#121

Post by gus_massa »

lukev wrote: post #93
gus_massa wrote: post #80

Short version: Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. With this definition using a red LED Laser powered by a 1.5V battery in the back of the spacecraft is a "no reaction mass" thruster. The problem is that the momentum / energy ratio has theoretical limitations, and they are getting too much momentum. Long version (based on a previous comment http…

> Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. I presume you're referring to the third law of motion, but if so, you've mischaracterized it. Nothing in the laws of motion state that engines must "emit" something. My car drives along quite efficiently without relying on any emission of mass. So does a sailboat. Of course, these are still third-law complia…

Actually, the conservation of momentum is local, so the car must emit some particles. The bottom of the tires emits (virtual) photons that are absorbed by the road. When you see it globally, the tires just push the road. (You can't go to the local mechanical shop and talk about virtual photons.)

In the middle of the space, where there is only vacuum around, you can't use the "virtual particle that get absorbed almost immediately" trick. So you need to emit some real particles (like a photon).

To explain this experiment, you can't push against the virtual particles, because they collapse and create some real particle (like a photon) to carry the momentum away and then you get the momentum/energy upper bound. (It's more complicated, particles appear and disappear, but the net effect is the same.)

Most of the "explanations" use virtual particles, but as an alternative explanation it's possible that this is pushing "dark matter". Perhaps this is a neutrino fan. (I'm not sure if neutrinos are technically dark matter, but they are "dark" enough and very abundant). It catches some neutrinos from the sun, change their direction a little, and then the neutrinos exit the chamber unnoticed. The change in the neutrinos direction gives the momentum to the thruster. I think that this doesn't break any theoretical law in an obvious way. The problem is that the dark mater is "dark" because it's very difficult to measure and to interact in any way. It's very difficult to change the direction of neutrinos, but at least it's an engineers' problem, not a physicists' problem. (In particular, neutrinos can travel through the earth.) The easier explanation is a measurement error.

Re: Questions about Nasa's space drive answered

#123

Post by lukev »

gus_massa wrote: post #121
lukev wrote: post #93

Earlier quoted context omitted.

> Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. I presume you're referring to the third law of motion, but if so, you've mischaracterized it. Nothing in the laws of motion state that engines must "emit" something. My car drives along quite efficiently without relying on any emission of mass. So does a sailboat. Of course, these are still third-law complia…

Actually, the conservation of momentum is local, so the car must emit some particles. The bottom of the tires emits (virtual) photons that are absorbed by the road. When you see it globally, the tires just push the road. (You can't go to the local mechanical shop and talk about virtual photons.) In the middle of the space, where there is only vacuum around, you can't use the "virtual particle that get absorbed almost…

Like I said, there would have to be some breakthrough physics here, like what "vacuum" actually means, or how dark dark matter is, etc.

I'm just pointing out that there are a number of logically possible solutions that don't involve violating the conservation of momentum, which may or may not be physically possible.

Re: Questions about Nasa's space drive answered

#124

Post by readerrrr »

idlewords wrote: post #106
readerrrr wrote: post #51

Earlier quoted context omitted.

He seems to be makings some mistakes as well. He says: This is baloney too - but now it's graduate-level baloney. "Quantum vacuum virtual plasma" is something you'd say if you failed a course in quantum field theory and then smoked too much weed. There's no such thing as "virtual plasma". If you want to report experimental results that seem to violate the known laws of physics, fine. But it doesn't help your credibil…

Are you trying to suggest here that Baez isn't aware of the existence of virtual particles? He's done lots of work in quantum field theory.

He dismissed the idea in a very arrogant way, just look at the wording, because someone used a incompatible word. Yet, the experiments gave a result; but he doesn't like that, and instead of using arguments he used ridicule, which doesn't show any credibility.

Re: Questions about Nasa's space drive answered

#125

Post by ElliotH »

servowire wrote: post #63
marcosdumay wrote: post #43

Earlier quoted context omitted.

At the paper. And it's crazy simple.

I can't find prototype diagrams with dimensions or something, did you find any? Please link? The paper is $25 .... mmm http://arc.aiaa.org/doi/abs/10.2514/6.2014-4029 This post has some more info https://plus.google.com/117663015413546257905/posts/WfFtJ8bY...

Here it is on scribd from some kind person http://www.scribd.com/doc/235868930/Anomalous-Thrust-Product...

Re: Questions about Nasa's space drive answered

#126

Post by gus_massa »

jliechti1 wrote: post #112
gus_massa wrote: post #101

Earlier quoted context omitted.

Alcubierre drive is not a thruster, you can't attach it to a spaceship to move it. It's something like: "If you put a spaceship inside this, and it stabilizes the gravity field using that, then it will travel faster than light in an external reference frame." It travels at a constant speed, so it doesn't need to emit particles to change the momentum. (On the other side, it uses exotic matter that no one has ever seen…

I asked a particle physicist to compare the validity of this to the faster than light neutrino claim that came up and his response was: "Although several people are drawing that comparison, they're really not in the same class. OPERA did an extremely thorough analysis of the faster than light neutrino result before they published. In the end it turned out to be a very subtle experimental error that cause the problems…

Just for the record: I agree.

I was just comparing that there was also a lot of excitement.

Re: Questions about Nasa's space drive answered

#127

Post by tobinfricke »

bane wrote: post #116
tobinfricke wrote: post #45

Earlier quoted context omitted.

By "we", I mean humanity as a whole. Nobody would contest that there are a lot of widespread misconceptions about how an airplane - or, for that matter, anything - works. A nice blog post on the topic is Sean Carroll's article, "The Laws Underlying The Physics of Everyday Life Are Completely Understood" ( http://blogs.discovermagazine.com/cosmicvariance/2010/09/23/... ).

One of the problems with this idea, that we have the physics "perfectly understood", is that even that statement isn't accurate. What we actually have are unbelievably precise models for how things work and people who understand those models at extremely deep levels. But even something we experience literally every moment of every day, like gravity or magnets, we haven't the foggiest idea of how it actually works. We…

All models are wrong. Some are useful.

But what is your point, really?

By "understand" in physics, we really mean that we can predict what will happen in a given experiment to any desired accuracy based on the established "laws of physics".

"But even something we experience literally every moment of every day, like gravity or magnets, we haven't the foggiest idea of how it actually works."

I think this does a deep disservice to how much we actually do know about how the universe works.

Re: Questions about Nasa's space drive answered

#128

Post by tobinfricke »

SamReidHughes wrote: post #91
tobinfricke wrote: post #84

Earlier quoted context omitted.

" We still can't make up our minds as to how wings work, so this isn't overly novel. Sure, we can explain the outcome, but whether it's Navier-Stokes or Bernoulli or something else, we can't make up our minds. " Time to trot out my favorite quote about how airplanes fly, from Stick and Rudder by Wolfgang Langewiesche, page 9, published 1944: »The main fact of all heavier-than-air flight is this: the wing keeps the ai…

Okay but there's a difference in the nature of the "pushing down" of a rocket, a plane, and a hovering helicopter, and in how much of an impulse is actually inflicted on an external mass.

Is there?

Re: Questions about Nasa's space drive answered

#129

Post by colanderman »

servowire wrote: post #63
marcosdumay wrote: post #43

Earlier quoted context omitted.

At the paper. And it's crazy simple.

I can't find prototype diagrams with dimensions or something, did you find any? Please link? The paper is $25 .... mmm http://arc.aiaa.org/doi/abs/10.2514/6.2014-4029 This post has some more info https://plus.google.com/117663015413546257905/posts/WfFtJ8bY...

Regarding the EmDrive…

OK, so, there's microwaves producing forces on either end of the cavity, and one end is bigger and…

wouldn't the forces be proportional to the area normal to either direction? i.e. one end may be smaller, it may even be a point (making the cavity a cone), but microwaves bounce off of the tapered neck of the cavity too.

Re: Questions about Nasa's space drive answered

#130

Post by crusso »

spingsprong wrote: post #48
tobinfricke wrote: post #41

Here are two nice posts by physicist John Baez with some reasons to be skeptical about the "reactionless drive": https://plus.google.com/117663015413546257905/posts/WfFtJ8bY... https://plus.google.com/117663015413546257905/posts/C7vx2G85...

"They're claiming to see a force one thousandth as big as the Chinese - probably because they are doing the experiment one thousand times more accurately. And still, some people are excited about this. " I think he's slipping from skepticism to cynicism here.

Disagree. He's being prudent and rational to hold these experiments to the same standards that we hold other more mundane ones.

Hoax phenomenon and devices always seem to fail in precisely the way that this one has. As you more carefully examine the test setups, suspicious conditions of the experiment persist (like the lack of using a vacuum in the vacuum chamber), and observed phenomenon continue to diminish as the accuracy of the test equipment improves.

And I use the word "fail" knowing full well that they claimed that they had positive results. If they couldn't use best practices in performance of the experiment like evacuating the vacuum chamber and they couldn't even show that their null device that wasn't designed to produce the same effect didn't work, then they have some serious problems.

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