
'Impossible' EmDrive Space Thruster May Really Be Impossible - jackfoxy
https://www.space.com/40682-em-drive-impossible-space-thruster-test.html
======
daotoad
Disappointing, but not really surprising.

Yes the _actual_ laws of physics can't be broken. We don't know those. We know
an approximation of them based on centuries of careful observation and
analysis. That approximation is incredibly good, too. It lets us make
microchips with 7nm features, synthesize high atomic weight elements, and
build spacecraft that have traversed the solar system. Even so, there are
things we know we don't know and there are bound to be things we don't know we
don't know.

It would be nice if the EmDrive turned out to be a ground breaking
demonstration of a hole in our model. We could probably squeeze a century of
amazing science out of it. Not to mention the potential practical
applications.

But groundbreaking new discoveries that shake the foundations of a developed
scientific theory are incredibly rare. So, as awesome as it could be if it
were right, the odds were always against it.

~~~
WJW
It is also much more likely for such a discovery to appear at the edge of our
knowledge where our understanding of the rules is at least a bit fuzzy (like
near black holes and whatnot). Something like EmDrive, which is in a regime
that has been exhaustively tested, would be like discovering that Bin Laden
was hiding in the Oval Office all along.

~~~
marcosdumay
> It is also much more likely for such a discovery to appear at the edge of
> our knowledge

This instantly reminds me of the Casimir Effect. Yes, it's way more likely for
problems to appear at the edges of our knowledge. But discoveries within the
noise of experiments people run every day are not unheard of.

I would also expect any such discovery coming from public science made by
somebody wondering why their instruments are off, not by for-profit research
looking for patents. But that's not unheard of either.

~~~
Florin_Andrei
> _discoveries within the noise of experiments people run every day are not
> unheard of._

That's also at the edge of the parameter space we're familiar with.

~~~
marcosdumay
This one is on the edge of low noise measurement of torque. In fact, the
entire exercise pushed the edge way lower than it was.

------
DanielBMarkham
I've been curiously watching this story although, like many other folks, I
realized that the chances were greater than 99% that it wouldn't work out.

What saddened me is the glee that some scientists and students took with
dismantling all of these home experimenters. It was shameful to watch. What
could have been a great opportunity for many to learn more about science and
experimentation turned into a bunch of jackasses mocking a bunch of interested
laymen. Not exactly the public image you want for your field of study.

~~~
SubiculumCode
Agreed. Science is hard, especially without funding...but amateurs do
contribute to science. This is most noted in astronomy.

~~~
DanielBMarkham
When I was 17, I took independent math study at my high school. (I had ran out
of math classes to take by doubling up on them) The math department lead
mentored me.

One day I asked "Why is 1/0 undefined? You guys said you couldn't take the
square root of a negative number, but when push came to shove, you just
invented new stuff. Why not do that with 1/0?"

He did not laugh at me or mock me. He looked earnestly at me and said "Why
don't you try doing that. See what happens."

I spent the next week or two trying to set up another number system. When I
ran into trouble, I did a bunch of research at the library.

When I came back the following week or two? I was able to give him a mini
lecture on why it didn't work.

Curiosity, humility, ignorance, and passion is the beating heart of science.
The more we make it into some modern priesthood, pro football team, or rock
band, the more the general public doesn't want anything to do with it.

~~~
flubert
[https://en.wikipedia.org/wiki/Riemann_sphere](https://en.wikipedia.org/wiki/Riemann_sphere)

~~~
DanielBMarkham
Yep. That's where I ended up. What a great way to get an introduction to a
really neat concept.

------
gaze
Of course it is. Nearly every physicist knew this was quackery from day one.
It should of course be tested properly, but nobody should be surprised.

~~~
Pyxl101
Why is it impossible? Is it the _amount_ of thrust that's generated that's
impossible, or the mere concept of generating thrust from electromagnetic
waves?

The reason that I'm asking is because light has momentum. If I shine a beam of
light out the back of my spacecraft, then I will accelerate in the opposite
direction. Not a lot, just a little.

Was EmDrive impossible because it was claimed to generate way more thrust than
could be explained from the energy levels involved? (Edit: It looks like an
additional reason it's impossible is because the EmDrive was claimed _not_ to
emit radiation, and rather keep it bouncing around in the cavity. Thanks for
the replies and explanations!)

Imagine that I attach a 1 megawatt laser in the 630 nm spectrum to my
spacecraft. From some rough calculations based on (1), it looks like the laser
will generate about 0.003 newtons of thrust (equal to the weight of 0.2 pounds
on Earth), which is very little thrust, and impractical for accelerating a
spacecraft over regular time scales.

(1) Momentum of a laser beam:
[http://umdberg.pbworks.com/w/page/50455623/Momentum%20of%20a...](http://umdberg.pbworks.com/w/page/50455623/Momentum%20of%20a%20laser%20beam)

~~~
roywiggins
Any reactionless drive better than a photon drive is probably a perpetual
motion machine.

[https://arxiv.org/abs/1506.00494](https://arxiv.org/abs/1506.00494)

~~~
mojomark
Again, this is incorrect interpretation of the cited paper.

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bitL
Pity, I really hoped we hacked the rounding error of the Universe :-/

------
alan
Hmm, could we use interactions with the Earth's magnetic field for thrust when
in LEO? With the Sun's magnetic field? It would be slow going.

~~~
ben_w
Yes, sort of, but that’s mainly useful for torque rather than thrust as thrust
relies on (if I’m getting this right) field _gradients_ rather than absolute
field strength. It’s not nothing, but it might as well be.

I back-of-enveloped a launch system with a very big magnet on the ground,
supplying a much steeper gradient to push against, and it was still crazy
expensive.

(I wonder if it would be useful for skyhooks?)

------
roywiggins
It would have been a perpetual motion machine of the first kind (you could get
an unlimited amount of energy out of it):
[https://arxiv.org/abs/1506.00494](https://arxiv.org/abs/1506.00494)

The evidence for it was no better than the evidence for any other perpetual
motion machine, there was nothing that made it special other than not claiming
to be a perpetual motion machine (despite being one).

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searine
I wanted to believe it could be true, but that's the beauty of science.

Test. Test and re-test. If the conclusion isn't want you want it to be, refine
the accuracy of your test and increase sample size. If you test is already at
maximum resolution, then tough tacos buddy.

~~~
tabtab
Re: _" I wanted to believe it could be true"_

Indeed. Star Trek dreams shatnered, I mean shattered. Sorry, no visiting green
Orion space-babes. Live long and cuss.

And, wouldn't somebody typically check electrical interaction with Earth's
magnetic field? It's a factor already known about.

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jwilk
The paper discussed on HN:

[https://news.ycombinator.com/item?id=17096175](https://news.ycombinator.com/item?id=17096175)

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ballenf
The measured thrust was evidently interactions of electrical cabling with the
Earth's magnetic field as per the new study.

~~~
yummybear
Wasn’t that just a theory - has it been conclusively proofed it was the
cabling?

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larkeith
Unsurprising, but still unfortunate.

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nategri
Yes, the laws of physics are rarely to be messed with. Doesn't mean we should
stop trying, as long as we stay grounded.

~~~
the-pigeon
We still can't bridge classical mechanics and quantum mechanics so obviously
we are missing at least one huge piece of the puzzle.

~~~
marcosdumay
What problems with bridging them do you have in mind? I thought this was
entirely solved.

~~~
21
Einstein theory of gravity is still considered classic (since it's not
quantified).

