The 'impossible' EmDrive could reach Pluto in 18 months? • Hacker News Board

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

#91

Post by gus_massa » Mon, Jul 27, 2015, 11:40 AM UTC

api wrote: post #26

saalweachter wrote: post #11

Earlier quoted context omitted.

Smaller effect size as studies improve is the classic sign of a non-event. ESP and the like went through similar cycles - impressive early studies followed by a series of more rigorous studies with diminishing effects until people got bored and moved on to the next big thing.

In this case different tests have occurred at different power levels. Has anyone normalized the results? Of course with only a couple replications its early for a meta study.

Someone compiled here a list of experiments: http://forum.nasaspaceflight.com/index.php?topic=36313.msg13...

I think that the best metric is to compare this with the maximal Force/Power ratio that is consistent with a "massless" thruster and special relativity, (i.e. a laser beam, photon thruster, ...). In this case the Force/Power ratio is at most 1/c, that is 0.0033 uN/W = 0.0033 mN/KW.

The results in the table vary from 3x to 200000x the theoretical maximum if we assume that this doesn't break the conservation of momentum, special relativity and quantum mechanics.

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

#92

Post by mdpopescu » Mon, Jul 27, 2015, 12:07 PM UTC

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…

http://amasci.com/weird/end.html

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

#93

Post by avian » Mon, Jul 27, 2015, 12:46 PM UTC

nickff wrote: post #85

avian wrote: post #82

Earlier quoted context omitted.

> we still have basically no understanding of what [light] actually is. Finding the true nature and, whether it exists or not, is the domain of philosophy. Science builds models. And we do have at this point extremely good models of electromagnetism which can correctly predict results of all experiments done so far. Whether these models reveal some fundamental truth or not is a matter of opinion (or perhaps religion)…

I think you misunderstand my point. Model-building is only one aspect of science, and happens to be the most prevalent in some (though not all) of today's mathematical and statistical based studies of physics (which are often criticized as an exercise in curve-fitting). One example is how string theorists are making a valiant (though perhaps errant) effort to understand matter; they are not simply modelling well char…

I guess you can say that ariving at Maxwell equations or QED is an exercise in curve-fitting in some sense. In the end, it is the simplest set of rules that matches a set of observations.

Similarly, the current model of the sun is the simplest model that explains some observations (neutrino flux, the fact that some stars seem similar spectroscopically, our knowledge from other branches of science, etc.).

I see no fundamental difference between these two.

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

#94

Post by jdmichal » Mon, Jul 27, 2015, 1:01 PM UTC

eropple wrote: post #22

jdmichal wrote: post #17

Earlier quoted context omitted.

While your comment doesn't add much to this discussion, I won't turn down a chance to educate. Conventional microwave ovens only have two states: on and off. (I won't rule out the possibility of some exotic build having multiple powers, but the ones you interact with on a normal basis don't.) So, power levels cannot change the output level of the magnetron. Instead, the power levels control what percentage of time th…

> I won't rule out the possibility of some exotic build having multiple powers, but the ones you interact with on a normal basis don't. Mine does, and it cost $120. http://www.amazon.com/Panasonic-Countertop-Microwave-Technol... (I don't find that it actually makes a difference when using it, though.)

Cool. This is still unusual for a consumer microwave, at least for the current moment. But I'm glad to see some manufacturers including it. Hopefully my post will be antiquated in the near future!

And, as mentioned by others, you really won't see a difference on the higher power settings, because there really isn't much of a difference. 10 seconds of almost-high output or 9 seconds of high output... On lower power, you should notice much bigger differences though.

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

#95

Post by jdmichal » Mon, Jul 27, 2015, 1:07 PM UTC

PhantomGremlin wrote: post #47

eropple wrote: post #22

Earlier quoted context omitted.

> I won't rule out the possibility of some exotic build having multiple powers, but the ones you interact with on a normal basis don't. Mine does, and it cost $120. http://www.amazon.com/Panasonic-Countertop-Microwave-Technol... (I don't find that it actually makes a difference when using it, though.)

I have a Panasonic and it makes a difference. (or maybe it's just confirmation bias?) Where the Panasonic shines is at lower power settings. E.g. if you defrost at 30% power for 3 minutes you get much more pleasant results than using the typical microwave. In a typical microwave the thinner areas actually start cooking rather than simply defrosting when operating at 30% power.

I would expect it to make a bigger difference at low power settings, so I don't think it's confirmation bias at all. 10 seconds of almost-high output compared to 9 seconds of high output won't see much difference. However, 10 seconds of low output vs 2 seconds of high will see a big difference. Same amount of energy, but delivered over a 5x longer time period.

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

#96

Post by TheLoneWolfling » Mon, Jul 27, 2015, 1:08 PM UTC

Filligree wrote: post #67

dev-da0 wrote: post #63

Earlier quoted context omitted.

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.

It's not an ISP of infinity.

You're forgetting mass-energy equivalence. energy / thrust is a specific impulse, once you work in the factor of c^2 (that being the minimum amount of mass you need to burn to get the energy to produce the thrust.)

In this case, for instance, they are saying they think it produced 20 uN with an input of 700w. That works out to an effective specific impulse of 2.5x10^9m/s as an upper limit (yes, this is tachyonic. One of the problems with this drive is that it throws conservation of energy and momentum out the window...), assuming we could convert mass to energy directly. (If you're using D-T fusion, it's a specific impulse of ~9.7x10^6m/s instead as an upper limit, assuming 339.72 TJ/kg. Other reactions are lower.)

If you're assuming solar panels or some other external power source, then the only real difference between this and a laser is that this produces a constant factor more thrust per energy input. Sure, it's reactionless - but, effectively, so is a neutrino source, for instance. All that means is that you don't need to be as careful as to which direction you burn in.

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

#97

Post by Analog24 » Mon, Jul 27, 2015, 2:27 PM UTC

nickff wrote: post #85

avian wrote: post #82

Earlier quoted context omitted.

> we still have basically no understanding of what [light] actually is. Finding the true nature and, whether it exists or not, is the domain of philosophy. Science builds models. And we do have at this point extremely good models of electromagnetism which can correctly predict results of all experiments done so far. Whether these models reveal some fundamental truth or not is a matter of opinion (or perhaps religion)…

I think you misunderstand my point. Model-building is only one aspect of science, and happens to be the most prevalent in some (though not all) of today's mathematical and statistical based studies of physics (which are often criticized as an exercise in curve-fitting). One example is how string theorists are making a valiant (though perhaps errant) effort to understand matter; they are not simply modelling well char…

"we cannot say that we understand all there is to know about electromagnetic phenomena because we can make a few simple predictions"

This is quite an understatement. QED, which is the underlying theory of EM, is the most accurate scientific theory ever. Full stop. It's theoretical predictions match experimentally measured observables out to ten decimal places. By your standards we don't really understand any physical phenomena. To bring up your analogy with the sun: our understanding of QED is like saying that we know the exact chemical composition of the sun to an accuracy of one part in ten billion. I think we would be justified in stating that we understand the sun in those circumstances.

On a related note, QED does provide a lot of context for what "light"(photons) is(are). It's the gauge boson (read: mediating particle) of the electromagnetic force. In my mind it doesn't get much more elegant than that.

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

#98

Post by Analog24 » Mon, Jul 27, 2015, 2:31 PM UTC

eevilspock wrote: post #64

nickff wrote: post #59

Earlier quoted context omitted.

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.

I think it was implied that "truths" meant scientific truths, which are well defined as anything that can be verified beyond statistical doubt with experimental evidence.

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

#99

Post by eropple » Mon, Jul 27, 2015, 2:58 PM UTC

PhantomGremlin wrote: post #47

eropple wrote: post #22

Earlier quoted context omitted.

> I won't rule out the possibility of some exotic build having multiple powers, but the ones you interact with on a normal basis don't. Mine does, and it cost $120. http://www.amazon.com/Panasonic-Countertop-Microwave-Technol... (I don't find that it actually makes a difference when using it, though.)

I have a Panasonic and it makes a difference. (or maybe it's just confirmation bias?) Where the Panasonic shines is at lower power settings. E.g. if you defrost at 30% power for 3 minutes you get much more pleasant results than using the typical microwave. In a typical microwave the thinner areas actually start cooking rather than simply defrosting when operating at 30% power.

Fair enough! I don't do a lot of defrosting in mine. Usually that's in the 'fridge.

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

#100

Post by zamalek » Mon, Jul 27, 2015, 2:58 PM UTC

Anjin wrote: post #55

Animats wrote: post #44

Earlier quoted context omitted.

"Every time this gets tested—presumably more and more carefully—the measured force gets smaller." Uh oh. That's a classic sign of a bogus effect. It's like physicists at Stanford trying to replicate the Pons-Fleischmann cold fusion experiment. At first, they were enthusiastic, and expected big results. They started out with the apparatus surrounded with radiation alarms in case it generated dangerous amounts of neutr…

No it is because the Chinese test dumped kilowatts of energy into the test item but the NASA test used only miniscule power. The guy you replied to presented the facts in a misleading way.

I'm slightly more skeptical about EmDrive than optimistic, however, you are right: if someone has to distort the truth in order to make a point it might be time that they question their standpoint on a matter. This looks like a lot of opinions about science. Which is a logical contradiction. An opinion has absolutely no sway in determining whether or not the device works. Opinions have nothing to do with science.

The device will either be shown to work or not to work with additional experiments and nothing anyone says regarding how it can or can't work will change that.