
EmDrive study officially published - babak_ap
http://arc.aiaa.org/doi/full/10.2514/1.B36120
======
mrob
Recent previous discussion:

[https://news.ycombinator.com/item?id=12992536](https://news.ycombinator.com/item?id=12992536)

~~~
dang
Since there's obvious appetite to discuss this, we've merged the comments here
instead of burying the current (re)post as a dupe like we normally would.

A couple more posts about this:

[https://news.ycombinator.com/item?id=12994541](https://news.ycombinator.com/item?id=12994541)

[https://news.ycombinator.com/item?id=12994400](https://news.ycombinator.com/item?id=12994400)

------
jtchang
This is pretty good news if only that we will get more research into this
phenomenon.

In 1933 von Neumann basically published a proof against the idea of any
hidden-variable theory. It took 30 years but Bell then discredited it.

My guess is that a lot of this will get revisited. The outcome of this in the
next 10-20 years might be really cheap probes (via reusable launch vehicles
like SpaceX is making) that need no propellent to continue onto their merry
way for a long time. The current way of doing this would be using solar sails
or something along those lines which is not exactly compact.

Having a way to push your little probe along (even at a little bit of
acceleration) without having to carry a lot of heavy propellant is a big deal.
Maybe just some solar panels to generate the energy needed.

~~~
lomnakkus
> This is pretty good news if only that we will get more research into this
> phenomenon.

Or maybe it's just a waste of time/money? (I'm not being facetious for the
sake of it. See cjensen's comment[1])

[1]
[https://news.ycombinator.com/item?id=12995341](https://news.ycombinator.com/item?id=12995341)

~~~
caconym_
Nothing in that comment is news, but if we've reached a point where we're
_completely_ unwilling to accept that experiments could show us something new
before theorists predict and explain it, then we should hang up our science
hats and go home.

Skepticism is warranted, but the team behind this study seems to be proceeding
with a healthy dose of it, and AFAIK they have not made any inappropriate
claims. The results so far are interesting, the experiments do not seem
terribly expensive, and I see no reason why they shouldn't be followed to
their conclusion (which will probably be the discovery of a mundane
explanation for the phenomenon that's been observed).

~~~
Retra
Are you actually worried that all of the world's scientists are completely
unimaginative and incompetent? I don't understand why you'd escalate it this
way just because _this_ topic comes up. That certainly doesn't sound like a
reliable frame of mind in which to be.

~~~
caconym_
You seem to be looking at my comment through a radically different lens than I
was when I wrote it. You know it was in reply to another comment, right?

------
Animats
It's so frustrating. One micronewton per kilowatt. All that power going in,
and so little force coming out. All it takes is some tiny noise effect to get
that much force. The effect is so weak and they're so near the noise
threshold.

Quotes: "Components get warmer and the geometry changes slightly due to
thermal expansion". "The thermal signal in the vacuum runs was slightly larger
than the magnitude of the impulsive signal." "As the aluminum heat sink got
warmer, its thermal expansion dominated the shifting center of gravity (CG) of
the test article mounted on the torsion pendulum. This CG shift caused the
balanced neutral point baseline of the torsion pendulum to shift with the same
polarity as the impulsive signal when the test article was mounted in the
forward or reverse thrust direction." "The seventh error is outgassing, which
has the potential for a false positive from vaporization of surface molecules
of the dielectric insert or other nonmetallic surfaces."

~~~
gwern
> It's so frustrating. One micronewton per kilowatt. All that power going in,
> and so little force coming out. All it takes is some tiny noise effect to
> get that much force. The effect is so weak and they're so near the noise
> threshold.

Yep. Reminds me of psi. You can set up mechanical radiation-decay powered RNGs
with pre-set runs of numbers in pre-registered double-blind experiments with
remote audit logs analyzed carefully with permutation tests and randomness
test suites, and all of the huge effects claimed by regular people and
psychics go away... but you still get on net a _slight_ excess of bit flips in
the psi direction. Is psi real? Seems highly unlikely. But what could possibly
be left - publication bias, fraud, or what? No one knows. At some point,
effects become subtle enough that you just can't believe studies finding it on
net - there's some sort of epistemological 'noise threshold' where stuff is
happening but you don't know why or can come up with causal explanations.

~~~
austinjp
> you still get on net a slight excess of bit flips in the psi direction.

Is that "net" extracted from all published experiments, i.e. in some meta
syntheses? And is statistically significance calculated in each individual
experiment?

> Is psi real? Seems highly unlikely. But what could possibly be left -
> publication bias, fraud, or what? No one knows.

Publication bias toward positive results should be detectable via methods such
as funnel plots.

If you've looked into these aspects it would make interesting reading.

~~~
gwern
> Is that "net" extracted from all published experiments, i.e. in some meta
> syntheses? And is statistically significance calculated in each individual
> experiment?

You can find excesses in both individual experiments and meta-analyses, IIRC.

> Publication bias toward positive results should be detectable via methods
> such as funnel plots.

Funnel plots have notoriously low statistical power, it would require only a
little publication bias to produce excesses, and asymmetry in a funnel plot
can be due to other reasons.

~~~
austinjp
Thanks for these comments, will make for interesting investigations.

------
gfodor
There seems to be a meme around the EmDrive where "it works" and "conservation
of momentum is upheld" are mutually exclusive. Couldn't it be the case that
there is some local phenomenon happening that we do not understand that still
manages to maintain conservation of momentum? Isn't assuming that momentum
conservation is violated a conjecture on the underlying physics of the device,
which we don't know?

~~~
akiselev
It's a little more complicated than conservation of momentum, which is just a
subset of conservation of energy useful for intuition about the non quantum
world. If you're converting energy into massive particles or photons for
propulsion you can still have a "massless" drive while maintaining
conservation of momentum because what you're really conserving is the total
energy of the system. Research has previously shown that it is possible to
create particles but it requires ungodly amounts of energy and a specially
designed apparatus that separates the resulting particle and antiparticle
using quantum effects before they can annihilate each other. There is even
some research into using a vibrating "quantum mirror" that forces virtual
photons to become real using only energy from quantum fluctuations but that's
even more complicated and difficult to engineer.

Either the EM drive has a unique combination of features that allows efficient
creation and separation of particles using electricity, some other unknown
quantum effects are present that can convert energy to momentum without an
opposite reaction on another particle/field, or there is still a hidden error.
Given the scientific knowledge we have today, it's extremely likely to be the
latter but that doesn't preclude the possibility that we have discovered
something novel.

~~~
cynicalkane
Really annoying to see false expertise pop up again and again.

> conservation of momentum, which is just a subset of conservation of energy

This is false. Momentum and energy are two different things, even with mass-
energy equivalence. In particular, momentum is a vector while energy is a
scalar, and their mass-energy equivalent units (impulse vs energy) are also
different.

Also: pair production doesn't necessarily require some amazing quantum device
to keep the pair separate.

> There is even some research into using a vibrating "quantum mirror" that
> forces virtual photons to become real using only energy from quantum
> fluctuations but that's even more complicated and difficult to engineer.

This is true if you consider conservation of energy to be an engineering
problem. Under no scientific theory can you pluck energy from the vacuum.

~~~
pdonis
_> Momentum and energy are two different things, even with mass-energy
equivalence. In particular, momentum is a vector while energy is a scalar, and
their mass-energy equivalent units (impulse vs energy) are also different._

None of this is correct when you take relativity into account. In relativity,
momentum and energy are both parts of a 4-vector, and that 4-vector is
conserved. And in natural units, in which c = 1, energy and momentum have the
same units. Particle physicists use these units all the time.

~~~
cynicalkane
Yes, I know how the 4-dimensional momentum vector in relativity works.

I'm not aware of a physical view for which energy and momentum are the same
for the purposes of something like the EmDrive. In particular, you cannot
completely turn one into the other by a choice of coordinates, and you cannot
mix them by any physical process. And I could be wrong, but I'm 99% sure you
need both energy and momentum conservation to get 4-momentum conservation.

No matter your view, conserving the spacelike components of 4-momentum is not
"a subset of the conservation of energy". And the truth/falsehood of this view
has nothing to do with the "non quantum world". Relativity was an extension of
classical electrodynamics before it was anything else.

~~~
akiselev
_> And I could be wrong, but I'm 99% sure you need both energy and momentum
conservation to get 4-momentum conservation._

I'm almost certain you're wrong. The most mathematically precise definition I
remember for conservation of 4-momentum only requires that the interaction is
invariant to spacetime translations. I don't see how that requires you to
conserve both separately from the whole.

 _> No matter your view, conserving the spacelike components of 4-momentum is
not "a subset of the conservation of energy". And the truth/falsehood of this
view has nothing to do with the "non quantum world". Relativity was an
extension of classical electrodynamics before it was anything else._

That was a poor choice of words on my part. I meant that an understanding of
conservation of momentum based in classical mechanics is rather meaningless
when talking about a drive that might use energy to create particles. What
matters is that the total energy of the system is conserved and I stand by my
choice of "subset" because momentum is _not independently conserved._ Calling
conservation of momentum a subset of conservation of energy is not even close
to calling energy the same thing as momentum and I have absolutely no clue
where you got that idea.

~~~
cynicalkane
There's a confusion here which you still don't get. Momentum is not
4-momentum. Conservation of latter implies the former but the reverse is not
necessarily true. And nothing in the above is a "subset of conservation of
energy"\--that's absurd.

Actually, I'm not 99% sure, I'm 100% sure. It's very easy to imagine a
relativistic system where momentum is conserved but energy isn't. Imagine if
the universe was made of inelastic billiard balls, with no internal "heat", so
every collision just lost energy. But momentum is still conserved.

~~~
pdonis
_> It's very easy to imagine a relativistic system where momentum is conserved
but energy isn't. Imagine if the universe was made of inelastic billiard
balls, with no internal "heat", so every collision just lost energy._

This won't work. Let's suppose we have just two billiard balls, and that
3-momentum is conserved in the center of mass frame (in which it is by
definition zero), but energy in this frame decreases at each collision.
(Ignore the fact that this obviously implies that the 4-momentum of the system
is not conserved, even though it is undergoing no external interactions.) Now
transform into any other inertial frame. You will find that 3-momentum is not
conserved either; it has a different nonzero value after a collision than
before.

~~~
cynicalkane
This is a bizarre comment. If we forget about energy, this is equivalent to
saying 3-momentum is not conserved in inelastic collisions _in real life_.
Which is false.

~~~
pdonis
_> this is equivalent to saying 3-momentum is not conserved in inelastic
collisions in real life._

No, it's not. In real life, energy is conserved, so the energy that is lost
from kinetic energy in inelastic collisions needs to go somewhere. And
whatever receives that energy will also have momentum (even if it doesn't in
the center of mass frame, it will in other frames), so it has to be included
in the accounting of momentum conservation as well as energy conservation. A
relativistic theory that conserves energy as well as 3-momentum (i.e.,
standard relativity theory) will still conserve both energy and 3-momentum
when you change frames, even in inelastic collisions. (In the simplest case,
the lost kinetic energy goes into increasing the rest mass of the two billiard
balls, by increasing their temperature.)

What you hypothesized was something different: a hypothetical relativistic
theory (which obviously does not match our actual world) in which energy is
not conserved but 3-momentum is. In such a hypothetical theory, inelastic
collisions could take place without the lost kinetic energy going anywhere: it
simply disappears. I am simply explaining why such a relativistic theory is
not possible: if energy is not conserved, 3-momentum cannot be conserved
either (except in one particular frame, the center of mass frame, but that
violates the principle of relativity so it is not allowed in a relativistic
theory).

~~~
cynicalkane
No, the 4-momentum is conserved _as a vector_ given a reference frame, which
means all 4 parts are conserved, which means 3-momentum is conserved. It
doesn't "go somewhere".

You seem to be obsessed about conservation of the magnitude of 4-momentum
under Lorentz transformations. It's the whole vector I'm talking about, not
the magnitude. and change-of-frame is not a necessary part of conservation
laws.

The claim that you can observe conversation in one frame but not another is
absurd. The laws are affine; they hold in any frame or none.

~~~
pdonis
_> the 4-momentum is conserved_

In standard relativity, yes. But not in your hypothetical "relativistic system
where momentum is conserved but energy isn't". You said such a system was easy
to imagine. I simply pointed out that, easy to imagine or not, such a system
doesn't work. Nothing that I said about 3-momentum being conserved in one
frame but not another applies to standard relativity where the 4-momentum is
conserved. It only applies to the hypothetical system that you claimed was
easy to imagine. I don't understand why you keep talking as though my comments
about 3-momentum being conserved in one frame but not another referred to
standard relativity.

 _> It doesn't "go somewhere"._

By "go somewhere" I simply meant energy can get transferred from one part of
the system to another. I didn't mean that total energy wasn't conserved (in
standard relativity).

 _> change-of-frame is not a necessary part of conservation laws._

It is in a relativistic theory, since the principle of relativity requires
that the laws of physics, including conservation laws, must hold in all
frames.

 _> The claim that you can observe conversation in one frame but not another
is absurd._

For standard relativity, of course it is. But not for your hypothetical
system.

 _> The laws are affine; they hold in any frame or none._

This seems to contradict what you said earlier in the same post, that "change
of frame is not a necessary part of conservation laws".

~~~
cynicalkane
You seem confused by how conservation works, and intent on misunderstanding
it.

All I can say is that momentum conservation is Lorentz invariant in my system,
and hence cannot depend on choice of reference frame. The conserved quantity
is not invariant, and conserved quantities do not need to be Lorentz
invariant, and fact almost always are not. If this confuses you, sorry, but I
cannot follow your reasoning anymore.

~~~
pdonis
_> All I can say is that momentum conservation is Lorentz invariant in my
system_

If by "my system" you mean your hypothetical theory where energy is not
conserved but 3-momentum is, I strongly suspect you have not done the math.
See below.

 _> The conserved quantity is not invariant, and conserved quantities do not
need to buslye Lorentz invariant, and fact almost always are not. If this
confuses you, sorry, but I cannot follow your reasoning anymore._

I understand what you are saying here, but it does not refute what I was
saying. You are saying that, for example, in standard relativity, energy is
conserved--in a given frame, it stays the same through any series of events--
but it is not frame invariant; changing frames changes the energy. I agree
with that.

What I am saying is something different: in your hypothetical relativistic
theory in which energy is not conserved, then 3-momentum cannot be conserved
in any frame other than one particular one (which in my example was the center
of mass frame). I am not saying the numerical value of the 3-momentum has to
be the same in all frames. I am saying that in all frames but one, the
numerical value of the 3-momentum, as evaluated in that frame, is different
after an inelastic collision than before, i.e., 3-momentum is not conserved in
that frame.

Here is the math backing up that assertion. Suppose 3-momentum is conserved in
the center of mass frame. In that frame the 3-momentum is zero. We assume that
our system consists of just two billiard balls, each with the same rest mass
m. Before the collision, one ball has speed v and the other has speed -v (we
can restrict ourselves to one spatial direction). After the collision, one
ball has speed w and the other has speed -w, where w < v (because the
collision is inelastic). So 3-momentum is zero before and after the collision
in this frame, and energy is not conserved--it is smaller after the collision.

Now transform to any other frame. Call the relative velocity of the Lorentz
transformation u. Then, in this frame, the speeds of the two balls before the
collision are (I am using units where c = 1)

v+' = (u + v)/(1 + uv)

v-' = (u - v)/(1 - uv)

and the speeds after the collision are

w+' = (u + w)/(1 + uw)

w-' = (u - w)/(1 - uw)

Now we evaluate the 3-momentum in this frame. Before the collision, it is

m ( v+'/sqrt(1 - (v+')^2) + v-'/sqrt(1 - (v-')^2) )

After the collision, it is

m ( w+'/sqrt(1 - (w+')^2) + w-'/sqrt(1 - (w-')^2) )

Substituting and straightforward algebra simplifies these to

before = 2mu/sqrt[(1-u^2)(1-v^2)]

after = 2mu/sqrt[(1-u^2)(1-w^2)]

These are obviously not equal, hence 3-momentum is not conserved in this
frame. (In standard relativity, where energy is conserved, 3-momentum would be
conserved as well; as I mentioned before, the simplest way for that to happen
would be for the two billiard balls to heat up, increasing their rest mass.
More complicated ways would involve other particles, or the billiard balls
emitting radiation, or something like that.)

~~~
pdonis
Just to clean up one item: I did assume in the above that the rest mass of the
billiard balls was unchanged in the inelastic collision. But we can drop that
assumption and still prove that, if energy is not conserved in the center of
mass frame, 3-momentum cannot be conserved in any frame other than the center
of mass frame. Suppose the rest mass of the balls after the collision is M
(instead of m). Then we have for the 3-momentum before (P0') and after (P1')
the collision, in a frame with velocity u relative to the center of mass
frame:

P0' = 2mu/sqrt[(1-u^2)(1-v^2)]

P1' = 2Mu/sqrt[(1-u^2)(1-w^2)]

But we can simplify this by writing down the total energy before (E0) and
after (E1) the collision, in the center of mass frame:

E0 = 2m/sqrt(1-v^2)

E1 = 2M/sqrt(1-w^2)

So we can see that

P0' = E0 (u/sqrt(1-u^2))

P1' = E1 (u/sqrt(1-u^2))

Hence, if E0 > E1, we must also have P0' > P1. In other words, the only reason
we happen to have P0 = P1 in the center of mass frame is that being in that
frame is equivalent to having u = 0 in the above formulas.

(It is also straightforward to show that if energy is not conserved in the
center of mass frame, it is not conserved in any frame. So the Lorentz
invariance of the two conservation laws, energy and momentum, cannot be
separated--they are inseparably linked.)

------
michwill
Interesting what are the fundamental reasons for the thrust. It's certainly
not throwing photons. Hypotheses:

* Flawed study. It actually throws something (like, cavity material slowly ablating) or repels of Eddy currents in surroundings;

* It repels of Earth (and the force has either gravitational or magnetic nature); then it's not suitable for deep space propulsion

* A sort of ether actually exists, and it throws that. Though, then there would be some anisotropy showing ether wind; in this case it is suitable to be used in deep space

~~~
politician
If you read through their conclusions, they suggest that there may be a
quantum vacuum capable of transmitting oscillations and this vacuum is what
this this device pushes off of leaving a wake behind.

~~~
gus_massa
[Disclaimer: I think it's a measurement error.]

Just ignore the theoretical explanations. Just imagine that it's something
they wrote to avoid the crackpot tag. That explanation doesn't make any sense.
Also avoid all the other theoretical explanations, they are also very sloppy.

Just concentrate in the experiments, that is the less sloppy part of these
reports.

If they discovered something new, then they can make a working prototype and
improve it until it's clear that they are measuring something really new and
it's not an experimental error or a misattributed force. They can make
foolproof instructions so anyone can make a version in a good enough lab and
reproduce the experiment, or sell an experimental setup in Ebay. Then it will
"confirmed".

There has been a many famous experiments that were later debunked, like:

* cold fussion [https://en.wikipedia.org/wiki/Cold_fusion](https://en.wikipedia.org/wiki/Cold_fusion) , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment.

* arsenic in DNA [https://en.wikipedia.org/wiki/GFAJ-1](https://en.wikipedia.org/wiki/GFAJ-1) , they had also some kind of theoretical excuse, but it was wrong and it was impossible to reproduce the experiment.

If you want success cases, my favorites are:

* the asymmetric disintegration of cobalt in a magnetic field [https://en.wikipedia.org/wiki/Wu_experiment](https://en.wikipedia.org/wiki/Wu_experiment) , I guess they had some wrong explanation, but the correct explanation was discovered like 20 years later

* high temperature superconductivity [https://en.wikipedia.org/wiki/High-temperature_superconducti...](https://en.wikipedia.org/wiki/High-temperature_superconductivity) IIRC they have some explanation or practical rules, but the correct explanation was discovered like 20 years later

Just concentrate in the experiments, and wait 20 years for a good explanation.

~~~
542458
> They can make foolproof instructions so anyone can make a version in a good
> enough lab and reproduce the experiment,

Is that not what this is? Roger Shawyer invented it, but NASA, NWPU and the
Dresden University of Technology have all built and verified their own
versions to work.

~~~
beevai142
The TU Dresden people did not "verify" that the device works --- instead, they
identified many spurious error sources, and recognized that the final results
were essentially null on the level of measurement accuracy, and unable to say
whether there's thrust or not.

[http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083](http://arc.aiaa.org/doi/pdf/10.2514/6.2015-4083)
[https://tu-dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/...](https://tu-
dresden.de/ing/maschinenwesen/ilr/rfs/ressourcen/dateien/forschung/folder-2007-08-21-5231434330/ag_raumfahrtantriebe/JPC
---Direct-Thrust-Measurements-of-an-EM-Drive-and-Evaluation-of-Possible-Side-
Effects.pdf?lang=en)

~~~
542458
Oops, you're right. Thanks for the correction!

------
chopin
There is an elaborate analysis of potential error sources, which I appreciate
highly. However, I would have preferred a more rigorous quantitative analysis.

The offered explanation model is highly fascinating. I'd appreciate if
somebody would chime in with a more understandable version or resources
thereto.

------
caconym_
A while back I read an interesting but possibly also batshit crazy article
that proposed an explanation possibly involving something like quantization of
inertia, and/or generation of extremely long-wavelength photons, wavelengths
on the order of the size of the universe.

Does anyone know what I'm talking about? IIRC it was based on some theoretical
work that was done before EmDrive was a thing, and it seemed less hand-wavey
to me than simply "conservation of momentum is wrong" or "we're using the
quantum vacuum as a tractive medium which is supposed to be impossible but
whatever" explanations.

I'm not saying this explanation is right (or wrong, or that the thrust
observed in these experiments is or isn't caused by "new physics"); I'm just
curious whether anyone knows what I'm talking about and can provide some more
context.

edit, found it: [https://www.technologyreview.com/s/601299/the-curious-
link-b...](https://www.technologyreview.com/s/601299/the-curious-link-between-
the-fly-by-anomaly-and-the-impossible-emdrive-thruster/)

Any thoughts?

~~~
kybernetikos
I think you're talking about McCulloch's quantisation of inertia theory.
[http://www.ptep-online.com/index_files/2015/PP-40-15.PDF](http://www.ptep-
online.com/index_files/2015/PP-40-15.PDF) which I believe was originally
inspired by the rotation of galaxies.

~~~
caconym_
Yup, that's it. I found the article I read, edited my post to include it.

------
jayajay
If anyone's lazy, I highly suggest at least reading parts 9 and 10. One of the
interesting takeaways here is that Q __* -thrust is 2 orders of magnitude
stronger than Photon-thrusters, and about 1-2 orders of magnitude lower than
Ion-thrusters.

 __* A Q-thruster is a thruster which pushes off of the zero point
fluctuations in vacuum, which is still not understood.

~~~
lisivka
But if you will try to discuss pilot-wave and walking droplets here (they are
mentioned in part 10), you will receive lot of downvotes here.

Quote:

Although the idea of a pilot wave or realist interpretation of quantum
mechanics is not the dominant view of physics today (which favors the
Copenhagen interpretation), it has seen a strong resurgence of interest over
the last decade based on some experimental work pioneered by Couder and Fort
[13]. Couder and Fort discovered that bouncing a millimeter-sized droplet on a
vibrating shallow fluid bath at just the right resonance frequency created a
scenario where the bouncing droplet created a wave pattern on the shallow bath
that also seemed to guide the droplet along its way. To Couder and Fort, this
seemed very similar to the pilot-wave concept just discussed and, in
subsequent testing by Couder and others, this macroscopic classical system was
able to exhibit characteristics thought to be restricted to the quantum realm.
To date, this hydrodynamic pilot-wave analog system has been able to duplicate
the double slit experiment findings, tunneling, quantized orbits, and numerous
other quantum phenomena. Bush put together two thorough review papers
chronicling the experimental work being done in this domain by numerous
universities [14,15].

~~~
amluto
> But if you will try to discuss pilot-wave and walking droplets here (they
> are mentioned in part 10), you will receive lot of downvotes here.

If you try to claim, without evidence, that pilot waves predict different
behavior than standard quantum mechanics, you might deserve that downvote.

Pilot waves are a mathematical framework, they may be useful mathematical
tricks in some cases, but they don't predict new behavior AFAIK.

I've been to talks about Couder et al's work, and the authors _don 't_ argue
that pilot waves are validated as descriptions of the universe by their work.
They do demonstrate a novel macroscopic system that observes the laws of
classical mechanics, and under certain circumstances, behavior emerges that is
nicely described by the pilot wave equations. This does _not_ mean that pilot
waves are somehow a more fundamentally correct description of what's really
going on.

~~~
kobeya
This is actually incorrect. Pilot wave theory gives a deterministic
explanation of phenomenon that the standard model treats as frequentist random
events. Only if you assume no knowledge of the underlying hidden variables
does the model reduce to the same as the frequentist standard model.

This is exactly analogous to statistical mechanics (e.g. the ideal gas law)
arising from classical Newtonian mechanics when you assume no specific
knowledge about gas particles (individual positions or velocities), just
aggregate mass and energy.

An experiment that "proves" an extension of pilot wave theory might be, e.g.,
observing that decay rates of radioactive isotopes are affected by being in a
quantum corral or something like that. An experiment that shows there is a
more fundamental, and influenceable process underlying phenomenon that the
standard interpretation treats as frequentist.

For this reason it could be easily argued that theoretical physicists should
be spending more time on pilot wave theory since it is this sort of theory
from which future advances would come, vs the standard interpretation which
puts up a semantic stop sign and says "proceed no further".

~~~
amluto
> This is actually incorrect. Pilot wave theory gives a deterministic
> explanation of phenomenon that the standard model treats as frequentist
> random events.

That's a remarkably incorrect statement. Let's see:

* The "standard model" is a quantum field theory and has essentially nothing to do with this discussion.

* Standard quantum mechanism says _nothing_ about frequentist vs Bayesian interpretations of anything.

* Standard quantum mechanism is a deterministic theory, too. Take a look at the Schrödinger equation: it's deterministic.

Determinism is tricky. Suppose you have a particle doing its thing (going
through double slits or whatever) and then you measure its position. In
standard QM, you have two choices: you use the Born rule (or a fancier version
-- I like the POVM formalism) and get a distribution of outcomes and a new
post-measurement wavefunction, or you can include the measurement apparatus in
your system and you end up with many worlds. In PWT, I think you have two
similar choices. You can start with a distribution of your (hidden) initial
condition and get an resulting distribution over the outcomes (which will be
the same as the Born rule distribution if you calculate it correctly). If you
do this, you still need to model decoherence, and I believe it looks at least
as artificial as the standard QM case. Alternatively, you could presumably add
degrees of freedom and more hidden variables to describe the measurement
apparatus and you end up with an IMO extremely messy version of many worlds.

<aside>My personal view is that standard QM with many worlds is the best
theory we have. If you start with the many worlds hypothesis and assume that
it's totally impractical to devise an experiment that actually detects
coherence between large-scale states, you can ignore this coherence, average
it out, recover the Born rule, etc, as an approximation. IOW I think that
decoherence is a limitation of our ability to build crazy experiments rather
than a fundamental property of the universe.</aside>

------
acqq
[http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-v...](http://blogs.discovermagazine.com/outthere/2014/08/06/nasa-
validate-imposible-space-drive-word/)

About the previous tests of the same team:

"The testing was done by five NASA employees in a lab devoted to exploring
unorthodox propulsion ideas. The team leader is a researcher named Harold
“Sonny” White, himself a proponent of ideas about faster-than-light warp
drives that most of his colleagues have classified as physically impossible.
The lead author is one of White’s Eagleworks teammates, David A. Brady.
Calling this group “NASA”—as almost every popular news story has done—is a
gross oversimplification."

~~~
SubiculumCode
They fund it, no?

~~~
acqq
Would it be better if NASA wouldn't have less then 10 people, out of their
18,000 employees (0.05%), working on testing nevertheless such claims which
almost surely don't work?

Maybe, if that 0.05% is used against NASA by claiming it doesn't do its job
how it should.

~~~
binarycoffee
Interestingly, NASA used to have a group working on such projects.

[https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physic...](https://en.wikipedia.org/wiki/Breakthrough_Propulsion_Physics_Program)

And I believe they actually did a serious job, which is probably why they
never found any warp-drive ;-)

------
snarfy
If you pressurize a sealed cavity with a gas, it's not going to move due to
the internal pressure regardless of what shape you make it. If you sum all of
the collisions of the gas atoms along with the container, the sum momentum
will be zero. Momentum is mass x velocity.

Contrast this with pressure created via light. Velocities with light don't add
that way. Instead there is a red/blue shift in the frequency.

I can't put my finger on how this could work, but it seems there is a
discontinuity here between the speed of light being constant in all reference
frames and summing velocities to calculate momentum.

Maybe with light, only energy conservation matters and momentum can be changed
via redshift/blueshift relative to the container.

~~~
lisivka
You know that everything around us is both matter and wave at same time (wave-
particle duality). Right? I.e. small bit of matter surrounded with wave. (See
any of walking droplets videos to develop intuition).

Unlike regular matter, waves are propagating through space, by contraction and
expanding of a field. Because of particle-wave duality, when matter is moving,
EM field around matter expands and contracts at high frequency. Right?

EM radiation in form of radio-waves can interact with these surrounding waves
because of interference. Right?

IMHO, interference between radio-waves and surrounding waves may cause effect
similar to used in acoustic levitation.

~~~
lisivka
These anonymous downvotes are frustrating. I cannot guess what caused them, so
I cannot learn on my mistakes.

~~~
Jach
I downvoted for basically the same reason as 'danbruc -- the comment contains
inaccuracies (as far as I understand physics, IANAP) that don't become
accurate just by appending "Right?" to them. I don't really read that "Right?"
as condescension like 'humbledrone but more as a verbal tick. I hear it from
others and even suffer from it myself sometimes, the idea is that a "Right?"
pause offers the other party in the conversation a chance to interrupt and
correct you, because you're not entirely certain of your own assertions. But
that doesn't work so well in written communication except maybe with instant
messaging.

I gave you an upvote for persisting in getting corrections/tips from people
like 'danbruc and 'lutusp though. Since you were interested in simulation you
might enjoy this article (or others on his site) from an actual physicist:
[http://oyhus.no/QuantumMechanicsForProgrammers.html](http://oyhus.no/QuantumMechanicsForProgrammers.html)

~~~
lisivka
Can you enumerate these inaccuracies, please?

PS.

I enjoyed articles about
[https://en.wikipedia.org/wiki/Amplituhedron](https://en.wikipedia.org/wiki/Amplituhedron)
.

------
mrob
Any chance this thing is using dark matter as reaction mass? We're confident
that dark matter exists because it's the only thing that perfectly explains
the evidence from gravitational lensing of colliding galaxies (eg.
[https://en.wikipedia.org/wiki/Bullet_Cluster](https://en.wikipedia.org/wiki/Bullet_Cluster)
). Finding a way to interact with dark matter sounds much more plausible than
breaking thermodynamics.

~~~
dozzie
Please read where the "dark matter" term came from. It's not a faerie dust
that facilitates magic use. It's just a hypothetical matter in the universe
that we can't observe, because for some yet-unknown reason it doesn't emit
light. There's no reason it can't be just regular matter.

~~~
mtpro
Not only does it not emit light, it does not interact with electromagnetic
waves in any way.

~~~
JoeAltmaier
And it doesn't obscure light - doesn't leave a shadow. No, its not regular
matter at all. Its definitely something strange.

~~~
rebolek
If it is something at all and not only a flaw in our theories.

~~~
Zigurd
Calling it "inexplicable gravity thing that makes galaxies work" does not
exude confidence.

------
daveguy
One thing that bothers me about this paper:

The measurement error is stated to be +/\- 6 micro-Newtons. However, the
difference between force measured _at the same power_ is 30-40 micro-Newtons
and the "measurement error" is listed as the +/\- error. So if the measurement
error is that low then the additional variation is unreliability of the effect
itself _or_ a miscalculation of the measurement error.

------
s_kilk
Can someone smarter than I explain the impact of this?

~~~
anchpop
It's a machine that seems to produce a miniscule amount of thrust without a
propellant. The laws of physics as we know them require that momentum always
be conserved, but this thing seems to move without pushing on anything, which
should be completely impossible.

Most likely what's happening here is a thermal effect or the machine pushing
off the earth's magnetic field. Keep in mind that these things are very
difficult to measure due to the tiny amount of thrust they may or may not
produce. According to this study 1.2mN was measured, which is about the same
amount of force as gravity exerts on 6-7 grains of rice (according to my back-
of-the napkin calculation).

If this were real it would be absolutely huge, and destroy just about all of
modern physics. It isn't just that we believe in conservation of momentum
because we don't know of any way to break it, the equations we're using to
describe things don't work without it.

This paper has a number of flaws. For example, the test really needed to be
performed inside of a vaccuum to have any credibility at all, and whether that
was the case was not made clear.

TL;DR It's most likely bunk, unfortunately, but it would be very revolutionary
if true

~~~
gus_massa
The 6-7 grains of rice is an interesting comparison, but they actually they
didn't get 1.2mN, they got 1.2mN/kW and they only tested the device with 40W,
60W and 80W and they got
[http://arc.aiaa.org/action/showPopup?citid=citart1&id=t3&doi...](http://arc.aiaa.org/action/showPopup?citid=citart1&id=t3&doi=10.2514%2F1.B36120&area=aop)
so they only measure a force of ~70uN, that is like 1/25 of a grain of rice,
that's probably like a few grains of salt.

And then they use a "aggressive slope-filtering level" method (whatever it
means) to get 124uN, that is still very small, like 1/10 of a grain of rice.

~~~
walrus01
The results would be a great deal clearer if they could test it in a high
vacuum at 2 to 4 kW. Measuring 3-4 millinewtons reliably is a lot easier to
believe than a newton force equivalent to a tiny fraction of 1 grain of rice.

------
chriskanan
How much evidence is needed to motivate testing it in space? It seems that
would settle the dispute regarding whether it works or not. Considering how
inexpensive cubesats are to launch, it seems like it could be launched for
about $100k, not including the additional R&D.

~~~
bobwaycott
I could be mistaken, but I believe someone is lunching such a test next year.

Edit: Cannae Inc. intends to launch a test with a small satellite. 2017 is so
far a guess for launch based on a quick search.

------
binarycoffee
Several comments have hinted at the possibility that this would be a over-
unity device but as I couldn't find a specific demonstration, here is one that
does not involve any fancy physics.

Let's assume we have a spacecraft powered by an energy source with total
energy `E` and mass `m`. The EM-drive produces a constant thrust `F` at a
constant power `P`.

Kinetic energy of the S/C after time `t`:

    
    
        Ek = 0.5 * F^2 * t^2 / m
    

If `t` is the time at which the energy in the source is exhausted, then the
ratio of kinetic energy developed to the expended energy (E = t * P) is:

    
    
        Ek/E = 0.5 * F^2 / P^2 * (E/m)
    

So this basically says that we have a over-unity device whenever the energy
source has a specific energy above:

    
    
        E/m > 2P/F ~ 1.6 10^6 J/kg
    

which is certainly not achievable in practice, but in theory is totally fine
being still well below c^2 (which by the way justifies a-posteriori the
neglect of relativistic corrections in the above).

------
anotheryou
Can't we put one in a cube sat and give it a go? (or: why can't we?)

~~~
trothamel
I'd think power is a problem. This produces a very slight acceleration with a
kilowatt of power, while it looks like a 3U (triple stack) cubesat might
produce ~14 watts.

~~~
lobster_johnson
Cannae is launching its thruster experiment in a 6U cubesat next year:
[http://www.popularmechanics.com/science/energy/a22678/em-
dri...](http://www.popularmechanics.com/science/energy/a22678/em-drive-cannae-
cubesat-reactionless/).

~~~
anotheryou
Cool! Any chance a 6U could stay up for month with conventional thrusters? Or
will it be proven to work or at least be better than other thrusters once and
for all?

------
ctoth
Thanks for submitting this, love to see feedback from the physicists who hang
out around here!

~~~
debunkit
There was a very elaborate experiment in Germany regarding this.

They concluded that the force is excerted by coupling the RF-energy from the
outside.

If the system is fully self-contained (driven by a battery physically
connected to the cavity) there is no thrust to be measured.

It's very sad to see NASA being involved in such shitty research.

~~~
_benedict
The linked paper draws no such conclusion:

"The nature of the signals observed is still unclear."

They are, clearly, taking the tack of eliminating all sources of measurement
error. But they haven't yet achieved that, and as yet a force remains. It
seems perfectly reasonable to assume it _will_ be attributed to measurement
error, but that is not yet the case:

" Next steps include better magnetic shielding.... We believe that this is a
good education project to track down measurement errors..."

~~~
debunkit
Yes, and the is the point.

NASA would have had the means to eliminate most of those sources of errors. I
wouldn't call these measurement errors though -> the measurement is fine -
your setup is the source of error.

But they decided not to follow such a line of research.

And yes, they are right "We believe that this is a good education project to
track down measurement errors".

The measurement error being the "thrust" that is due to your experimental
setup.

But let them waste some more money, time and reputation and build this in
space so they can find out it does not actually work.

~~~
raverbashing
Did you create this account only to comment on this story? (just curious)

> NASA would have had the means to eliminate most of those sources of errors.

Yes. NASA as a whole yes. One group researching something that may or may not
bear fruit no.

So it's natural they try to eliminate easier errors first. But (as an example)
it's one thing to have a good vacuum, another one to have an _excellent_
vacuum for testing. So first you test on the good vacuum.

~~~
debunkit
> Did you create this account only to comment on this story? (just curious)

Yes i did, usually i just let certain topics pass by me and never comment
here.

RF-cavities though are the very core to my line of research, so my acceptance
for bs is very low in this regard.

If one wants to convince me of a thrust effect: build a prototype where the
power source (a battery for example) and the RF-source are strapped onto the
cavity, put the whole setup in a vacuum of your choice (i heard NASA has very
nice and !large! facilities) and show me a sustained increase in impulse (just
let it rotate for a while)

~~~
ncallaway
> If one wants to convince me of a thrust effect: build a prototype where the
> power source (a battery for example) and the RF-source are strapped onto the
> cavity, put the whole setup in a vacuum of your choice (i heard NASA has
> very nice and !large! facilities) and show me a sustained increase in
> impulse (just let it rotate for a while)

Okay, but they aren't trying to convince _you_ yet.

They're trying to convince _themselves_ that it's worth spending the resources
you describe.

~~~
elcritch
Excellent point. They do mention performing an experiment with large angular
displacement and a larger vacuum.

> To definitively rule out any residual concerns about thermal error sources,
> future test campaigns could employ a test apparatus capable of measuring
> small torques over much larger angular displacements. For example, a
> Cavendish balance approach properly designed to allow very large rotation
> angles such as 90, 180, or even 360 deg will not be susceptible to this type
> of thermal false positive.

------
imdsm
> Although this test campaign was not focused on optimizing performance and
> was more an exercise in existence proof, it is still useful to put the
> observed thrust-to-power figure of 1.2mN/kW1.2 mN/kW in context. The current
> state-of–the-art thrust to power for a Hall thruster is on the order of
> 60mN/kW60 mN/kW. This is an order of magnitude higher than the test article
> evaluated during the course of this vacuum campaign; however, for missions
> with very large delta-v requirements, having a propellant consumption rate
> of zero could offset the higher power requirements. The 1.2mN/kW1.2 mN/kW
> performance parameter is over two orders of magnitude higher than other
> forms of “zero-propellant” propulsion, such as light sails, laser
> propulsion, and photon rockets having thrust-to-power levels in the
> 3.33–6.67μN/kW3.33–6.67 μN/kW (or 0.0033–0.0067mN/kW0.0033–0.0067 mN/kW)
> range.

Read More:
[http://arc.aiaa.org/doi/full/10.2514/1.B36120#_i36](http://arc.aiaa.org/doi/full/10.2514/1.B36120#_i36)

------
tbrownaw
_If the vacuum is indeed mutable and degradable as was explored, then it might
be possible to do /extract work on/from the vacuum, and thereby be possible to
push off of the quantum vacuum and preserve the laws of conservation of energy
and conservation of momentum. It is proposed that the tapered RF test article
pushes off of quantum vacuum fluctuations, and the thruster generates a
volumetric body force and moves in one direction while a wake is established
in the quantum vacuum that moves in the other direction._

...well, at least it's better than calculating the theoretical produced thrust
by ignoring the axial component of the radiation pressure against the side
walls. Which is how tapered resonant cavities like this were supposed to
produce thrust when I was in high school.

But, leaving a wake in the vacuum should require that the vacuum exists in
some particular reference frame. How's that supposed to work?

Or since the paragraphs immediately before that one discussed the vacuum
behaving differently when there's stuff in it, are they just saying that
_something_ is being exhausted out the back (which should be visible by some
sort of effect on the vacuum?) even if they have no idea what that something
might be?

------
recycle
Open Source Projects / Experiments that might be relevant to the discussion:

[https://hackaday.io/project/5596-em-
drive](https://hackaday.io/project/5596-em-drive)
[https://hackaday.io/project/10166-flying-an-
emdrive](https://hackaday.io/project/10166-flying-an-emdrive)

------
gigatexal
For the uninitiated how good or bad is 1.2mN/kw?

~~~
sonium
To put into proportions: The radio isotope thermoelectric generator (RTG) of
the Voyager spacecraft wheighs 37kg. So let's say we can build a spacecraft
using this and the EM drive weighing a total of 50kg. The RTG produces 157W of
power. This translates to a change in speed 30cm per day.

Bonus question: The power of the RTG halfes avery 87.7 years. What is the
asymptotic speed the spacecraft will reach?

~~~
photogrammetry
Asking this is like asking how long it should take for a sperm cell to swim
across the Atlantic Ocean.

The EMD is simply not applicable to scales where RTGs are used, much as a 5MW
maritime diesel turbine is not applicable to swimming motions of a biological
cell. The power density of Voyager is a hundred times lower than what an EMD
ship would need.

------
pmcollins
Doesn't a standard microwave (or any other) transmitter produce a tiny force
due to radiation pressure?

I understand that this is different because the radiation bounces around an
enclosed chamber and so momentum wouldn't be conserved, but if the issue is to
create propellant-free propulsion, doesn't that already exist (even though
it's not practical)?

~~~
ribble
> Doesn't a standard microwave (or any other) transmitter produce a tiny force
> due to radiation pressure?

pressure against what?

~~~
pmcollins
[https://en.wikipedia.org/wiki/Radiation_pressure#Radiation_p...](https://en.wikipedia.org/wiki/Radiation_pressure#Radiation_pressure_by_emission)

~~~
ribble
this article includes a grey body that the force is acting upon.

the difference with the EM drive's method of propulsion is, that while the
article you posted describes a force reacting upon an external, "grey body,"
as is acceptable with the copenhagen interpretation of quantum mechanics, the
EM drive force exhibits a characteristic betrayed by a theoretical pilot wave,
which indicates a non-copenhagen interpretation of quantum mechanics, but
rather a bohmann version of quantum mechanics, in which the force can act upon
itself.

run-on sentence alert.

------
tombone12
Goddamit, I wanted to get to the comment about the superoptimizer, not this
mass hallucination over crap sience :(

------
thearn4
Some criticism on reddit:

[https://www.reddit.com/r/science/comments/5dqy9b/em_drive_is...](https://www.reddit.com/r/science/comments/5dqy9b/em_drive_is_shown_to_work_measurement_of/da6n92f/)

------
nepotism2016
For those who dig this stuff...I strongly recommend you watch BBC Horizon
episode Project greenglow

[http://www.dailymotion.com/video/x40a65t](http://www.dailymotion.com/video/x40a65t)

------
walrus01
1.2 millinewtons per kW is not a lot - the size of a 12kW solar array for a
large satellite is quite considerable... Space based nuclear reactors anyone?
No cosmos-954 incidents, hopefully.

------
microcolonel
For those who wish to see the abstract page without enabling cookies.
[http://archive.is/zuVaz](http://archive.is/zuVaz)

------
petters
If this holds up I am prepared to believe in almost anything – like the
universe being a simulation and this is a deterministic round-off error.

Conservation of momentum is pretty fundamental.

------
sabujp
I don't understand how the 1.2mN/kW is better than the hall thruster that
achieves 60mN/kW ? Isn't it better to achieve higher mN per kW than lower?

~~~
mabbo
Every other thruster works by pushing something small at very high speeds in
the opposite direction of the direction you wish to move in. Hall thrusters
are pushing small ions at near the speed of light or something, right?

This thruster pushes nothing. It just achieves thrust with only energy. No
refueling ever, solar/nuclear energy into movement until you have no more
energy.

This violates certain physical laws, but there it is being measured anyways.

~~~
sbierwagen
Hall-effect thrusters throw ions at 15 to 30 Km/s, or 0.0001c.

There is one other thruster that doesn't need a tank of reaction mass: a
photon rocket-- moving yourself around only using radiation pressure. Exhaust
speed really is c, but generated thrust is tiny, since photons are pretty
light. The resonant cavity thruster is more interesting than a photon rocket,
since its thrust is much higher.

------
Odenwaelder
The laws of physics prevailed, despite the LHC and other experiments. As
awesome as it sounds, I find it hard to believe that this finding is something
relevant.

------
cjensen
For those new to this, the emdrive is very likely bogus.

1\. It violates Conservation of Momentum. If the phenomena is real, a large
number of basic Physics principles would need to be discarded.

2\. It was designed based on certain principles. Those principles have been
shown to be wrong. But it works anyway because _reasons_?

3\. The results of each experiment are suspiciously close to the limits of
measurement.

There are two choices here: (a) experimental error or (b) profound alteration
to fundamental physics. Occam's Razor applies. Also, "extraordinary claims
require extraordinary evidence" and this evidence is far from extraordinary.

That this is being published in a journal which does not cover basic physics
is not helping.

~~~
arcanus
Agree with everything you write except,

> That this is being published in a journal which does not cover basic physics
> is not helping

AIAA is an extremely reputable journal and society. All the members are
extremely familiar with conservation of momentum.

The observation of superluminal photons (later disproved) was published in
reputable journals as well.

No scientist took either result very seriously. However, the observation of
anomalous results is a result worth of publication and communication to other
scientists and engineers.

As a practicing scientist, I can assure you that peer-review does not mean
something is 'correct', but that is it not provably false, and that the
results may be important to the community.

~~~
noobermin
The hope is that this gives the idea some legitimacy, which will encourage
others to test the idea too. It's like a win-win situation, if you test it and
you discredit the effect, that's a free paper. If you verify it or add your
own little spin, you'll go down in the history books along with this team.

------
Symmetry
So 1.2 mN/kW. By comparison the ion engine on the Dawn probe puts out 34 mN/kW
(236mN / 6.9 kW). But of course that's for an effectively infinite exhaust
velocity rather than just 42 km/s.

------
philip142au
When the super-conducting version work it will change the world.

------
smcameron
If real, you could build a perpetual motion machine with it. Therefore it's
not real.

~~~
eridius
Could you? How? Perpetual motion machines must put out at least as much energy
as they take in. AIUI the EmDrive requires external power (such as solar
panels) and produces a rather tiny amount of force. This does not sound to me
like it's anywhere even remotely close to putting out as much energy as it
takes in.

~~~
DennisP
It's because there's no such thing as absolute velocity, so your thrust can't
vary with velocity, it has to be a constant for given input energy. Kinetic
energy is the square of velocity, so as you keep accelerating at a constant
rate, you'll eventually get to some velocity at which the energy you get out
is higher than the energy you put in, assuming your reactionless drive is more
efficient than a photon rocket.

Not that it matters. If it works, it already violates conservation of momentum
as we currently understand it. That's just as fundamental as conservation of
energy.

~~~
sampo
Hmm, relativistic velocity under constant acceleration is

    
    
        v(t) = a t / sqrt(1 + a^2 t^2)
    

and relativistic kinetic energy is

    
    
        Ek = m c^2 / sqrt(1 - v^2/c^2) - m c^2
    

Leave out the constant -mc^ and for simplicity put m=1, v=1, c=1, and we get

    
    
        Ek = (1 - t^2/(1+t^2))^(-1/2)
    

which is linear in larger values of t, not square.

Proof:

    
    
        d/dt Ek = t sqrt(1 / (1 + t^2))
                = sqrt(t^2 / (1 + t^2))
    

which is always < 1.

~~~
DennisP
So at the extreme efficiencies Shawyer claimed, overunity was at decidedly
nonrelativistic velocity. It'd be interesting to calculate a maximum drive
efficiency before you get overunity.

I've seen claims that the max is the efficiency of a photon rocket, but I
haven't seen it backed up with math.

------
revelation
Sounds like Polywater:

[https://en.wikipedia.org/wiki/Polywater](https://en.wikipedia.org/wiki/Polywater)

------
maverick_iceman
As I said earlier this is bogus. We might as well try to prove virgin birth.

~~~
photogrammetry
[https://en.wikipedia.org/wiki/Parthenogenesis](https://en.wikipedia.org/wiki/Parthenogenesis)

------
sergj
I was pretty sure there was a seperate study where they debunct it? Gonna look
for the link...

------
fitzwatermellow
SPR's Roger Shawyer Explaining The Basic Science behind #EmDrive:

[https://www.youtube.com/watch?v=wBtk6xWDrwY](https://www.youtube.com/watch?v=wBtk6xWDrwY)

~~~
jasonwatkinspdx
Since many people may be jumping into this topic without context/awareness:
Shawyer's explanations simply do not hold up. Even the minority of folks that
know physics and think the emdrive is real agree that Shawyer's proposals are
invalid. Further, he's been at this for years, repeatedly making grandiose
claims and failing to deliver on them. Take anything he says with a huge grain
of salt.

