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The 'impossible' EmDrive could reach Pluto in 18 months?

wired.co.uk

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Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#61

Post by ttctciyf »

cabinpark wrote: post #58
javert wrote: post #39

Earlier quoted context omitted.

Thanks, nice summary. > I think the last thing anyone wants to see here is "new physics". I really want to see new physics, because I want to see us get off this rock and far away. I think most people want to see new physics. I think that's why this topic is so popular. That said, I can understand physicists not wanting to see new physics. Wait. In a way, that sentence is crazy . In a way, physicists should want to s…

I'd love to see new physics! Every physicist I know loves new physics. But if you claim to violate the conversation of momentum, everyone is going to be skeptical and not believe it. We have hundreds of years of experiments and observations that support the law and have looked in many places from small to large and not seen violations. This is what makes people not believe it and thus physicists are going to assume y…

> Every physicist I know loves new physics.

If physicists don't want new physics, they should stop doing research!

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#62

Post by leni536 »

repsilat wrote: post #60
leni536 wrote: post #57

Conversation of momentum is strongly tied to the conservation of energy through relativity theory. If it actually works (I doubt it) it has really strong implications.

Conservation of momentum is a much bigger deal than conservation of energy. We already know of situations in which energy isn't conserved (like the energy of a photon decreasing when there is metric expansion where it is.) Conservation of momentum is a consequence of the translational symmetry of physics via Noether's theorem, so that's what we'd need to give up to hope to see it broken.

Much like conservation of energy is a consequence of time translation symmetry. If you mix spatial and time coordinates through relativity theory you can see that these are strongly coupled.

Your photon example works because there is no time translational symmetry in the case of metric expansion and it's a general relativity model. In general relativity there is no conservation of momentum either. It would be hard to even define since coordinate systems change from point to point. We can only say that the energy-momentum vector is going through parallel transport, which is like conservation in the local coordinate system.

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#63

Post by dev-da0 »

teraflop wrote: post #30
api wrote: post #25

Earlier quoted context omitted.

Why the assumption that if it works it must violate a conservation law? That's the last thing I would suggest after exhausting every other possibility, even weird ones like space time distortion thst would still operate within known conservation laws.

The whole reason the EmDrive is supposedly so revolutionary is that it's claimed to produce thrust without requiring any propellant. If conservation of momentum isn't going to be violated, something with mass-energy has to be carrying that momentum away from the spacecraft, and if it's not matter, it has to be radiation. But the claimed efficiency is about 5 orders of magnitude higher than radiation pressure could po…

Explanations aside, if in the slight chance it's workably better than ion thrusters for certain applications, that's great. If it turns out to be snake oil or a hoax, that would not be a huge surprise either.

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#64

Post by eevilspock »

nickff wrote: post #59
thaumaturgy wrote: post #56

Earlier quoted context omitted.

Oh! This is one of my favorite questions about scientific progress. People seem to regard scientific progress as this kind of wave function, where some theory comes along and then some other theory or discovery disproves the previous one and so on and so forth. But if you want to think of scientific progress that way, then you have to think of it as a dampened sine wave ( https://en.wikipedia.org/wiki/Damped_sine_wav…

I'm sorry, but your reasoning completely escapes me. The only things that are left are very big, and very small? In addition to this being an incredibly vague catchall (which misses all the possible discoveries of 'black swans', that is phenomena and occurrences we have never seen), your statement more importantly misses the fact that humans don't even understand what something as common and important as light (or el…

I agree. I also take issue with

> rapidly zeroing in on the truths of our reality

The truths? No, humans are as likely to arrive at the truths as ants an understanding of a microwave oven.

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#65

Post by jboggan »

foobarian wrote: post #3

I wonder how they rule out the effects of the Earth's magnetic field. I can see there being some small effect due to some kind of eddy currents pushing ions into one direction. Maybe they turn the apparatus at multiple angles and check the bias to north-south?

I seem to recall that they could not find any variance in the force by orienting the apparatus in different directions. Some good work has been put into finding the cause of this, and most of the easy and obvious errors have been tested and found to be unrelated to the effect.

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#66

Post by rndn »

thaumaturgy wrote: post #56
nickff wrote: post #51

Earlier quoted context omitted.

Photoelectric cells were invented before we understood the photoelectric effect, alcohol and preserves were used to store drinks and foodstuffs before we understood microbes, forging and annealing used before anyone had a theory on metallic crystal formation, and incandescence was used before anyone understood electromagnetic radiation; to name but a few examples. Why would it be surprising that someone invented a de…

Oh! This is one of my favorite questions about scientific progress. People seem to regard scientific progress as this kind of wave function, where some theory comes along and then some other theory or discovery disproves the previous one and so on and so forth. But if you want to think of scientific progress that way, then you have to think of it as a dampened sine wave ( https://en.wikipedia.org/wiki/Damped_sine_wav…

Actually, there is still the possibility that conservation/symmetry is also just an approximation of the actual fundamental laws. Lee Smolin argues that way in his book Time Reborn: https://santitafarella.wordpress.com/2013/06/04/lee-smolins-...

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#67

Post by Filligree »

dev-da0 wrote: post #63
teraflop wrote: post #30

Earlier quoted context omitted.

The whole reason the EmDrive is supposedly so revolutionary is that it's claimed to produce thrust without requiring any propellant. If conservation of momentum isn't going to be violated, something with mass-energy has to be carrying that momentum away from the spacecraft, and if it's not matter, it has to be radiation. But the claimed efficiency is about 5 orders of magnitude higher than radiation pressure could po…

Explanations aside, if in the slight chance it's workably better than ion thrusters for certain applications, that's great. If it turns out to be snake oil or a hoax, that would not be a huge surprise either.

An ISP of infinity would be quite a lot better than ion thrusters, yes, and that's what they're suggesting.

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#68

Post by rndn »

idlewords wrote: post #9
Niten wrote: post #7

It's good to see that someone finally got around to testing this in a vacuum. Here's the paper mentioned in this story: http://arc.aiaa.org/doi/abs/10.2514/6.2015-4083 High levels of skepticism are still warranted, as much as I would love for this to pan out. Every time this gets tested—presumably more and more carefully—the measured force gets smaller. The original test at Chinese Northwestern Polytechnical Universi…

From the abstract: "We identified the magnetic interaction of the power feeding lines going to and from the liquid metal contacts as the most important possible side-effect that is not characterized yet. Our test campaign cannot confirm or refute the claims of the EMDrive..." Given that this is a 700W microwave oven putting out a tiny amount of thrust, and that a positive finding would invalidate a basic conservation…

On the other hand, the current theory of the EmDrive predicted exactly that amount of thrust for the given configuration.

Re: The 'impossible' EmDrive could reach Pluto in 18 months?

#70

Post by javert »

thaumaturgy wrote: post #53
javert wrote: post #39

Earlier quoted context omitted.

Thanks, nice summary. > I think the last thing anyone wants to see here is "new physics". I really want to see new physics, because I want to see us get off this rock and far away. I think most people want to see new physics. I think that's why this topic is so popular. That said, I can understand physicists not wanting to see new physics. Wait. In a way, that sentence is crazy . In a way, physicists should want to s…

Laymen tend to underestimate the very vast body of research which supports current physical models. "New physics" would imply that something has been fundamentally wrong with physics for a long time, and that is unlikely.

I get that.
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