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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

#51

Post by Animats »

ngoldbaum wrote: post #29
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 reminds me of the story behind the "discovery" of cold fusion in the 80s. Sure, Pons & Fleischman may have thought they measured something, but in the end the whole effect could be attributed to careless experimental design and procedure. See this paper: http://pus.sagepub.com/content/5/2/121.short (unfortunately behind a paywall)

That was taken very seriously at the time. I went to a well-attended talk at Stanford by a Stanford physicist who was trying to replicate the Pons/Fleischman experiment. When they first set up the apparatus, they had radiation detectors with alarms, in case it started generating a dangerous level of neutrons. After some initial tests where not much happened, they moved the radiation alarm gear back a bit.

Total measured neutron output, best case, appeared to be twice background. That's small enough that people moving around (people are mostly water) was enough to cause such variation. So they moved the experiment to a "neutron cube", a big box built of lead bricks where few background neutrons penetrated. Then there was no significant difference in neutron levels between "off" and "on".

They also tried heat generation measurement. Because you have to put power into the Pons/Fleischman apparatus to get anything to happen (it's not self-sustaining) it's a difficult experiment to do accurately. It requires water jackets, insulation, and lots of measurements. They were unable to detect any heat output above measurement noise.

Re: What we know about the EmDrive and Cannae Drive

#52

Post by Steuard »

dicroce wrote: post #21
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…

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

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).

Re: What we know about the EmDrive and Cannae Drive

#53

Post by SEJeff »

Steuard wrote: post #17
creamyhorror wrote: post #9

Earlier quoted context omitted.

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 c…

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,…

For the longest time, everyone thought that the earth was flat as well until this heretic said, nope it is flat.

Challenging group think and being skeptical is part of being a proper scientist. Perhaps they end up learning something entirely new from all of this.

Re: What we know about the EmDrive and Cannae Drive

#54

Post by Steuard »

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...

Yes, it would be more precise if I had prepended "local" every time I said "conservation of momentum" above. With that clarification, I'm happy to stand by what I've said.

Re: What we know about the EmDrive and Cannae Drive

#55

Post by rasz_pl »

wbhart wrote: post #24

Comparing the Chinese results with the American results, it seems that raising the wattage by a factor of 50 raises the thrust by a factor of 15000. That's somewhat hard to believe. On the other hand, the linked pdf from the Chinese team suggests that at just 3 times the wattage of the American group, they got 1500 times the thrust. I think there is some confusion somewhere.

1 non linear

2 mianzi http://en.wikipedia.org/wiki/Face_(sociological_concept) & http://www.sciencedirect.com/science/article/pii/S0262407912...

Re: What we know about the EmDrive and Cannae Drive

#56

Post by MCRed »

I've some direct experience with a similar situation. I can speak to the issue of "why hasn't spaceX or other major company experimented with this".

During the "Cold Fusion" era, when Pons & Fleishman had claimed to develop room temperature fusion, I worked for a major US lab doing superconductor research. (We invented the first superconductors that operated at liquid nitrogen temperatures-- Y1B2C3O)

While fusion isn't our area of investigation we, being physicists, were curious. We managed to get our hands on a pre-print of the Pons & Fleishman study and did our own experiments.

We kept this very hush hush. We didn't want it getting out that we were doing the experiments or people would claim that we replicated them.

So, I believe that SpaceX and other companies are experimenting with this, and if they found good results (as the eagle works tests imply they would) they would continue to do so, but in secret.)

We eventually published our paper because we constructed a novel experiment that disproved the P&F observation, from our perspective.

None-the-less, true to our fears, this was later reported by "Mondo 2000" (The "arse technica" crossed with WIRED of the day) that we had "confirmed cold fusion is real!!1!1". The letter to the editor I wrote and got our most eminent physicist to sign was never printed by the magazine (IIRC).

When you get to the fringes-- that's where the action is-- but it's also where you can have confusing or odd results.

And even 30 years ago the media was not trustworthy enough to reveal these results to. Our paper was published in a journal, and yet the media still mis represented the results.

Re: What we know about the EmDrive and Cannae Drive

#57

Post by marze »

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…

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).

Re: What we know about the EmDrive and Cannae Drive

#58

Post by mahranch »

astrodust wrote: post #42
higherpurpose wrote: post #27

Earlier quoted context omitted.

I think even if it proves real, it would still take around 50 years to put in flying cars and such. But perhaps a bit less for using it in satellites. Still it's not too long on the humanity scale of time.

Why would it take fifty years? This isn' the 1800s where it takes a half century for flush toilets to catch on. We're in an era where things go from laboratory to ubiquitous inside of a decade.

This is less like flush toilets and more like computers. It took nearly 50 years for the first computers to sit in consumer's home offices. It took time for the technology to be miniaturized and cheap enough to make its way to consumer electronics.

Or even cell phones. We were using radio signals in hand held devices for nearly 50 years before a vast majority of consumers were walking around with phones in their pockets in the mid to late 90s. Sure, there were early adopters in the late 80s and early 90s, but the technology was still expensive. And the technology (like walkie talkies) had existed for decades before...

Re: What we know about the EmDrive and Cannae Drive

#59

Post by teraflop »

SEJeff wrote: post #53
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,…

For the longest time, everyone thought that the earth was flat as well until this heretic said, nope it is flat. Challenging group think and being skeptical is part of being a proper scientist. Perhaps they end up learning something entirely new from all of this.

Which "heretic" would you be referring to? Pythagoras? He was persecuted, but not for believing in a spherical earth.

Re: What we know about the EmDrive and Cannae Drive

#60

Post by mrfusion »

DennisP wrote: post #47
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…

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 i…

I'm not understanding this argument. Wouldn't the same amount of thrust get you less and less delta velocity as your velocity increases?
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