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Uncertain Propulsion Breakthroughs?

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Re: Uncertain Propulsion Breakthroughs?

#81

Post by mhneu »

DanielBMarkham wrote: post #75
euyyn wrote: post #47

Earlier quoted context omitted.

Except the neutrino paper then was a big lot of physicists asking colleagues to help them review, so as to find where the problem was. What I see here is just hype. The former, as opposed to the latter, is what gives confidence that the people involved are doing their darnest not to fool themselves. That what they're doing is actually science.

I don't know. I see a few universities looking into building their own setup. I see the Chinese filing patents, testing them in orbit. I see a 2017 microsat launch. I see a healthy debate continuing over on the reddit Emdrive board. That doesn't look like people trying to sell things to me. That looks like a lot of different people from different backgrounds playing around with an experimental setup that does somethi…

> With the emdrive, folks are saying If this works, it's by some model we do not yet understand.

A summary of the parent article is "The experimenters did not do the obvious control experiments [e.g. testing under a null load], thus there are currently no results at all."

Re: Uncertain Propulsion Breakthroughs?

#82

Post by mhneu »

freehunter wrote: post #36
cjensen wrote: post #35

Earlier quoted context omitted.

The "premise" for the em-drive has been determined to be a thorough misunderstanding of the physics involved, so you cannot rule out any potentially contributing force in the experiment. Yes you heard that right: guys who misunderstand physics go and design a reactionless thruster which, when measured in their shoddy experimental setup, produces a measurable thrust. If there really is a measurable thrust, then the La…

You sound very negative towards conducting more experiments on this, when the results have been unexpected every time it's been tested. You're displaying the kind of dogma that science has been fighting against since the dawn of time. Either it's true or it's not, but we can't tell until we test it. And so far, it's only been disproven in theory, not in practice. That's worth more experiments.

The only unexpected "results" happened in experiments with a lack of controls, so while nothing can be ruled out, it would not be surprising if all the data so far is explained by well known forces (like flow in the liquid supply lines.). It's on the previous experimenters to do proper controls.

Re: Uncertain Propulsion Breakthroughs?

#83

Post by mhneu »

bicubic wrote: post #77
cjensen wrote: post #44

Earlier quoted context omitted.

Occam's Razor says it is not true. If you read the linked article, it is saying, in the most polite and disinterested way possible, that it is not true although they allow, in the driest of terms, that it could be true. I expect if the same authors analyzed the Loch Ness monster or Big Foot, they would also disinterestedly point out the unlikelihood of either and point out the how awful the proofs put forth are while…

I don't expect the em-drive to work, but the parent post has a point. We've had repeated experiments yielding unexpected results. It's worth an inquiry; if nothing else, to thoroughly explain what went wrong so the same mistake is avoided in future experiments. Outright dismissing new ideas, no matter how far-fetched, is very much the antithesis of the scientific principle. You mustn't forget that everything we take…

Many possibilities of what went wrong are well-explained in the parent article, drawing on experience of other scientists that make low-force measurements. (E.g. forces on rig due to electrical current flow, or liquid flow.)

Unfortunately it seems likely we won't learn much by finding the possible sources of error - the sources are already well understood by people doing low force experiments.

Re: Uncertain Propulsion Breakthroughs?

#84

Post by zachrose »

madengr wrote: post #79
therein wrote: post #69

Earlier quoted context omitted.

Made me think of this. Maybe when they were doing the experiment, a gravitational wave happened and they somehow reflected it? > Thin superconducting films are predicted to be highly reflective mirrors for gravitational waves at microwave frequencies. The quantum mechanical non-localizability of the negatively charged Cooper pairs, which is protected from the localizing effect of decoherence by an energy gap, causes…

They were able to repeat it. Damn, I wish I could find it. I actually have it printed off somewhere. The issue is that distorting gravity has far more consequential effects due to generally relativity than just moving something. You are actually distorting time too.

> You are actually distorting time too.

That explains the significance of the floating hole-puncher confetti in the movie Primer.

Re: Uncertain Propulsion Breakthroughs?

#85

Post by sandworm101 »

JumpCrisscross wrote: post #29
sandworm101 wrote: post #24

Earlier quoted context omitted.

For the power required to generate minimal thrust, this will not be useful in low orbit. The solar panels required to power the drive would result in more drag than the truster might overcome. So no market. And this test flight will not result in a clearcut "it stays up" rather "it fell slower than expected". There will be much calculation and debate re drag, magnetics and gravitational anomolies, so small are the ex…

> For the power required to generate minimal thrust, this will not be useful in low orbit A recent paper [1] quotes this system's predicted efficiency at 1.2 mN/kW. Hall thrusters, a propellant-throwing electric engine, perform at 60 mN/kW. Non-propellant systems like light sails, laser propulsion and photon rockets perform around 0.0033 to 0.0067 mN/kW. If this works, and that's a big if, a 50x performance improveme…

But how big will the panels need be? And how much extra aerodynamic drag will they create in a low orbit?

Re: Uncertain Propulsion Breakthroughs?

#86

Post by naasking »

andrewflnr wrote: post #62
naasking wrote: post #61

Earlier quoted context omitted.

General relativity doesn't conserve energy in some spacetimes, so it's not unheard of.

I'm fairly certain GR conserves momentum, even if it doesn't conserve energy.

I thought so too until recently, but in GR energy and momentum are unified in an energy-momentum metric which is only locally conserved [1].

[1] https://en.wikipedia.org/wiki/Physical_theories_modified_by_...

Re: Uncertain Propulsion Breakthroughs?

#87

Post by Bluestrike2 »

cjensen wrote: post #35
dom0 wrote: post #30

Earlier quoted context omitted.

> If this works by impelling against the Earth's magnetic field That's a completely different premise than the em-drive has, though. It's supposed to not depend on an external field; developing a force between two magnets wouldn't exactly qualify as (non-)rocket science today.

The "premise" for the em-drive has been determined to be a thorough misunderstanding of the physics involved, so you cannot rule out any potentially contributing force in the experiment. Yes you heard that right: guys who misunderstand physics go and design a reactionless thruster which, when measured in their shoddy experimental setup, produces a measurable thrust. If there really is a measurable thrust, then the La…

But it's not dogma. Dogmatic principles are one "laid down by an authority as incontrovertibly true." 'Science'--with a capital 'S', denoting a specific authority--doesn't say that the laws of motion are accurate. Years of empirical research, with repeated and verifiable confirmations by other scientists, do. The laws of motion are held to be true not because scientific authorities say they are so, but because of the method by which they came to be able to say it.

It's a subtle distinction, but an incredibly important one. But that same subtlety can sometimes be lost when it's discussed by the general public. The policy debate over climate change is an excellent example. Speaking strictly in terms of the often quoted statement that "97 percent or more of actively publishing climate scientists agree," [0][1] it's clear how different individuals can read very different meanings into that statement. For the scientists themselves, while the statement is referring to scientists as individuals, it's based on the published research that informed their views. Amongst the general public, particularly those who don't accept anthropogenic climate change, the statement is understood as referring to the beliefs of the individuals. It's taken as an appeal to authority (and it doesn't help that many politicians and activists who want to take action often use it as such). The same statement is understood in two very different ways based on the reader's background and understanding of what the scientific method actually is.

Returning to the subject of the em-drive, the reason for skepticism is precisely because it flies in the face of our basic understanding of the physical world. The more well-founded a theory is, the greater the burden on any new findings that would seem to contradict it. That's as it should be. But if those new findings hold up under scrutiny and are verified, even a basic, fundamental law can and will be revised. That's how the scientific method works.

Personally, I'd love for the em-drive to be proven if only because it would represent such a fascinating shift in physics. To say nothing of potential applications. But I'm inherently skeptical. Not because of a dogmatic acceptance of the laws of motion, but because those laws are already so well-supported.

0. http://climate.nasa.gov/scientific-consensus/ 1. http://iopscience.iop.org/article/10.1088/1748-9326/11/4/048...

Re: Uncertain Propulsion Breakthroughs?

#88

Post by stale2002 »

samplonius wrote: post #72
stale2002 wrote: post #34

Earlier quoted context omitted.

This is what they are doing. They are sending something into space to demonstrate the effect. Let the experiments decide what is right or wrong.

So "space" is some magical place where measurement error does not exist? Low earth orbit isn't perfect either. You still have micro gravity. And the experiment requires a lot of power, and very sensitive instruments to measure the phenomenon. How do you get sensitive instruments which are expected to be operating near their error threshold into orbit without damaging them? Orbital experiments will have to be smaller,…

The experiment is pretty simple.

You put the engine in space, with solar panels, and you see if it stays there or falls back to earth.

There is no experimental error, or even measurement devices.

It is a space engine. Either it flys or it doesn't.

Over the course of a year, it will be obvious if it works or not. Because if it doesn't work it will fall to earth.

Re: Uncertain Propulsion Breakthroughs?

#89

Post by tunap »

pmezard wrote: post #71
alasdair_ wrote: post #18

Earlier quoted context omitted.

Quite a few medicines (especially antidepressants) state something like "we don't really know why this stuff works, only that it does."

From Wikipedia Paracetamol article ( https://en.wikipedia.org/wiki/Paracetamol#Mechanism_of_actio... ): "To date, the mechanism of action of paracetamol is not completely understood." and: "It is the most commonly used medication for pain and fever in both the United States and Europe." "Not completely understood" is not the same as "we have no idea why it works", but still I find it telling for such a popular produc…

9 years ago I heard a NPR interview with the scientist(s) who cracked the code on exactly how chlorine bleach kills bacteria. Something I assumed was known longer than I've been around using bleach to disinfect.

edit: link

http://www.npr.org/templates/story/story.php?storyId=9700789...

Re: Uncertain Propulsion Breakthroughs?

#90

Post by Nomentatus »

Remember that "tacking"* in sailboats (going upwind, using only the force of that wind) was held to be impossible, a violation of the laws of nature until people actually witnessed it, too. Severe violations of our expectations don't always break the actual math of a physics model.

*more properly said "beating to windward" https://en.wikipedia.org/wiki/Tacking_(sailing)

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