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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

#61

Post by bjourne »

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.

The heretic, Galileo Galilei, claimed that the earth revolved around the sun instead of the sun revolving around the earth. That the earth is (almost) spherical was known since antiquity.

Re: What we know about the EmDrive and Cannae Drive

#62

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…

You'd never get more change in kinetic energy than the energy you put into it, right?

Re: What we know about the EmDrive and Cannae Drive

#63

Post by MCRed »

alextgordon wrote: post #48
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,…

Happens the other way too. In the 80s high-temperature superconductors were discovered, which were 'impossible' by previous understanding. The theory is still catching up to that.

I worked for the Texas Center for Superconductivity, where Paul Chu discovered superconductors that operated at liquid nitrogen temperatures, in the 1980s a year or so after his discovery.

We spent a great deal of time trying to figure out how the mechanism worked, and about half the team were theoreticians who would try and posit theories, or evaluate theories posited by other teams, and the the other half of the team spent time either testing the new theories, or experimenting to try and improve the results of previous experiments.

Y1B2C3O is not even a metal, but a ceramic crystal. This was kinda mind blowing at the time. It shouldn't even conduct.

IIRC the best theory at the time was that it was superconducting because of particular errors in the formation of the crystal due to the production process. But I left the lab in the early 1990s.

Re: What we know about the EmDrive and Cannae Drive

#64

Post by knodi123 »

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.

Interesting side note, it wasn't thought to be flat for as long as most people think. The roundness of earth is a pretty ancient piece of knowledge.

https://en.wikipedia.org/wiki/Myth_of_the_Flat_Earth

Re: What we know about the EmDrive and Cannae Drive

#65

Post by Tossrock »

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…

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)

Re: What we know about the EmDrive and Cannae Drive

#66

Post by avian »

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…

> 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).

Re: What we know about the EmDrive and Cannae Drive

#67

Post by Tossrock »

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.

It seems like an impossibly basic mistake, but confusing micro- and milli- newtons would make the math a lot more reasonable.

Re: What we know about the EmDrive and Cannae Drive

#68

Post by Steuard »

alextgordon wrote: post #48
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,…

Happens the other way too. In the 80s high-temperature superconductors were discovered, which were 'impossible' by previous understanding. The theory is still catching up to that.

And even low-Tc superconductors looked "impossible" under the physics of their day. No question about it! Science thrives on surprises: it's the very best part of what we do.

But maybe non-physicists don't have a sense of the range of meanings that "that isn't possible within current theory" can have. High-Tc might have been "impossible" under basic BCS superconductivity theory, but BCS theory itself taught us that it was possible to find novel theoretical mechanisms generating zero resistance, so needing a new one was surprising but not unprecedented. "Standard" low-Tc superconductivity appeared "impossible" under the usual models of materials' resistivity, but even that was merely a violation of a well-tested model when it was extended to a previously untested very-low-temperature regime. Resolving that apparent impossibility didn't require rewriting any fundamental principles, it just required very careful application of the existing theoretical framework.

These speculative new propulsion theories appear to violate the conservation laws underlying all of our existing models of physics, and in an experimental regime of size/temperature/etc. where (I believe) they have been very well-tested in the past. Any calculation within the framework of quantum field theory or general relativity will inevitably result in momentum being (locally) conserved: it's unavoidably built in to the formalism. So as I said to begin with, although it's obviously not truly impossible that some entirely different framework could turn out to be correct, that is an enormously bigger jump than any stage of the discovery and explanation of superconductivity.

Re: What we know about the EmDrive and Cannae Drive

#69

Post by lotsofmangos »

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.

Go read up on Eratosthenes. http://en.wikipedia.org/wiki/Eratosthenes

Re: What we know about the EmDrive and Cannae Drive

#70

Post by lotsofmangos »

InclinedPlane wrote: post #12
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…

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.

From a Bayesian perspective, it isn't. One experiment that is difficult to disprove does not carry the same weight as 5 different ones giving similar results.
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