
The EmDrive just won't die - bookofjoe
https://www.popularmechanics.com/space/rockets/a33917439/emdrive-wont-die/
======
eloff
If nothing else, the EmDrive has been a great exercise in how hard it is to
control all variables in a sensitive experiment where the measured effect is
small.

It actually blows my mind how well the LIGO folks have accomplished this to be
able to detect gravitational waves.

I really like the effort going into this, despite a positive result being
impossible to our knowledge. Those are the high risk high reward experiments
with the potential to discover new physics. I still expect it to be
experimental error, but there's always that remote chance we'll learn
something we didn't expect about the universe.

~~~
choeger
Well, maybe they _didn 't_. How would we ever know?

The problem with LIGO is that is not making the expected number of
discoveries, it has, as far as I know, one signal that correlated to something
visible with other means, and it is so expensive that there won't be
independent confirmation soon.

Don't get me wrong, experiments like LIGO are massive achievements. But from
an outsider point of view, that very scale and effort seems to be problematic
when it comes to reproducing the results of experiments if there are no
immediately useful predictions.

~~~
ncallaway
> that very scale and effort seems to be problematic when it comes to
> reproducing the results of experiments

First of all, LIGO is 2 observatories so every result out of LIGO was observed
by at least two locations.

There is also an independent project called Virgo which is making
gravitational wave observations, and the results are being correlated with
LIGO. They have made a number of overlapping observations, which further moves
us towards reproducibility.

Future observatories are also planned (like LISA), which will be another
opportunity to further validate events.

~~~
Strilanc
Additionally, one of the gravitational wave observations was corroborated by
immediate follow-up observations with normal telescopes [1].

[1]: [https://www.as.arizona.edu/discovery-optical-counterpart-
gra...](https://www.as.arizona.edu/discovery-optical-counterpart-
gravitational-wave-event)

------
mdorazio
And it shouldn't die until the anomalous effect is adequately explained.
That's how good experimental science works, regardless of current theories -
if you see an effect you can't explain, you test it until you can explain it.
There's a very high chance the tiny force is attributable to something
mundane, but it's still worth finding out what that thing is.

~~~
trhway
i think we're wrong putting so much effort on understanding and proving it on
Earth (where it can never practically be used anyway). Just put it into space
and turn it on - whatever the nature of the effect if it is present - great,
lets use it, and understand it with time, if there is no effect - well, we're
done here.

~~~
bjo590
My understanding is running this experiment in space would cost >$10m, a very
pricey experiment when the expected outcome is negative.

~~~
macintux
It sure seems like collectively the world has wasted more than $10m of
attention on this concept by now.

~~~
ohyeshedid
Unrelated to the thread topic:

We live in an attention economy. If you read a story, or watch a video, it
doesn't matter if you agree or disagree with the content; you're still
traffic.

Just viewing content on most of the internet boosts it's signal, and creates
value for someone; much less engaging further by commenting, up/down voting,
or sharing it. It's a pretty ugly system.

~~~
dcolkitt
The most surefire way to acquire massive wealth in the 21st century is to get
convince people to pay as much attention to your app's notifications as they
would an incoming phone call.

------
dvh
> This is a technology which could transform space travel and see craft
> lifting silently off from launchpads

Not with 12 millinewtons per kilowatt! In space, sure but not from launchpad.

~~~
treespace88
With a cold fusion reactor attached, with some gravity shielding it should be
viable.

~~~
dilyevsky
Why not just teleport to where you want to be?

~~~
ed25519FUUU
I was thinking rocket roller skates.

------
wcoenen
If you could produce a constant force (and therefore constant acceleration)
for a constant power use, then both speed and the total energy spent would
rise linearly with time. This is in conflict with the fact that kinetic energy
goes up with the square of speed. In other words, if this works as described
you can create energy out of nothing by sticking the drive on the outside of a
rotating system and using it as a generator.

~~~
aaronblohowiak
Please forgive my ignorance. If you are floating in a vacuum, how do you know
what kinetic energy you have? isn't that all with respect to some other
object?

I believe the trick here is that constant-acceleration with constant power use
is due to the (puzzling) particulars that there's no ejection mass

~~~
wcoenen
Kinetic energy is relative to some inertial reference frame. You can pick any
reference frame you want and each will give you different numbers, but
conservation laws should still hold in each.

Addition of kinetic energy is pretty unintuitive in this regard, e.g. when
throwing a ball, the "work" done by your muscles depends on the reference
frame that you pick to analyze the event.

------
e40
_Many physicists had dismissed the revolutionary space drive as simply fake
science._

The use of "fake" here really bugs me. Fake implies lies and I don't think
that's at all present here.

~~~
pfdietz
It looks like an example of pathological science.

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

------
Izkata
> The sticking point is the law of conservation of momentum, which says that
> inside a closed system momentum remains constant.

...wait...

> The current design is calculated to provide a thrust of about .012 Newtons
> (equal to the weight of a paperclip, or a raisin) for one kilowatt of power,
> similar to the drives used to maneuver satellites.

It requires power input. Doesn't that mean this _isn 't_ a closed system?

~~~
molyss
I have a similar question. How can a system be truly closed ? It’s always
interacting with the stars and galaxies through their gravitational fields.
Similarly, and closer to your question) the spent energy can only be Generated
through a chemical or nuclear reaction (both of which should lead to a loss of
mass, which will be impacted by the gravitational fields, making it a non-
closed system), or by gathering energy from outside The system (solar panels
or other technologies), thus making it a non-closed system

What am I missing here ?

~~~
samus
It can often be considered closed for the purposes of the phenomenon that we
want to describe. To be specific, masses like galaxies, stars and planets
accelerate all parts of our tiny rocket the same way. Yes, there are
differences, but they are usually so small that they can be neglected. Our
rocket works mostly the same no matter how it is oriented to these sources of
gravity. Of course, as it gets closer to such masses, these forces (called
tidal forces) start to matter and will eventually rip it apart, given that it
doesn't burn up or collide first.

Rockets, differently to balloons, do not depend on an interaction with a
gravitic field for their operation. They work by ejecting reaction mass
opposite to the flight direction and relying on Newton's third law of motion.
Most of the time, the energy to eject the reaction mass is generated by
combustion, but it doesn't really matter. Rockets can also be driven by the
reaction mass's pressure inside its tank.

In general, any system can be turned into a closed system by including all
sources of force in the description. Of course, the more forces are included
in our model, the less useful it gets. Therefore, physicists and engineers
must decide which forces can be ignored. Else, even experiments would become
useless because without a model, the experience gained from experiments cannot
be generalized.

------
Aeolun
Can’t we just shoot one of these into space and see if it moves? We’d need
only a few days to generate any appreciable thrust and prove or disprove the
theory.

~~~
linkdd
Sending stuff to space isn't cheap.

~~~
grugagag
It’s certainly cheaper than funding the research and the cost to send stuff to
space has gone down and continues to go down

~~~
throwaway2048
You seem pretty confident of this, share your numbers.

~~~
grugagag
I cant find the numbers for the EmDrive research for the past 20 years but my
guess is that it wasn’t cheap at all. Comparing that to sending a few pounds
into orbit as a proof of concept is probably peanuts. I don’t have numbers and
its all speculation on my part. If you do have numbers please share them

------
walrus01
The best thing I can see to come out of this is some sort of standardized,
more easily replicated test apparatus for precise measurements of very small
thrust in vacuum chambers.

Such as for testing things that do actually produce thrust, built into low
cost satellites, such as very small ion and hall effect thrusters.

------
eximius
I feel like at this point it'd be easier to send it to space and toss it out
the airlock with a battery and just... See if it goes anywhere

~~~
roywiggins
You can generate thrust in Earth orbit with electricity by pushing off the
planet's magnetic field, so it's not quite a perfect test.

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

------
pengaru
Seems strange to not see a single mention of the "Quantum Vacuum" in an entire
popularmechanics article about the EmDrive AKA Q-Thrusters.

Sonny White of the Eagleworks lab discusses this subject in a Breakthrough
Discuss 2018 [0] talk. Has everything he says in that talk been since
disproven or something?

[0]
[https://www.youtube.com/watch?v=o-hjS7pdXGU](https://www.youtube.com/watch?v=o-hjS7pdXGU)

~~~
ComputerGuru
Wikipedia link for those that don’t like to watch videos:
[https://en.m.wikipedia.org/wiki/Vacuum_state](https://en.m.wikipedia.org/wiki/Vacuum_state)

------
waterheater
Wrote an article on the EmDrive some years back and have a little more insight
on it than the average bear.

Good to see the Dresden group is still plunking away after all these years.
Other than Eagleworks and a group in China, they were early leaders on
verifying the concept.

The law of conservation of momentum was created before quantum mechanics was
discovered. Let's assume there's a base medium in which all energy (that is,
mass) is embedded. Furthermore, let's assume there's a way to interface with
this medium. The EmDrive works if one allows mass (that is, energy) to be
transferred into this base medium. Momentum is conserved because the
mass/energy is transferred to the all-encompassing medium. This medium is the
same medium which enables quantum entanglement.

In theory, the quantum vacuum and surrounding phenomena provides that medium.
Frankly, I feel the classical interpretation of CoM is insufficient to explain
the workings of the EmDrive. The article uses the phrase "a physics
violation," but a more accurate statement is "a high-school level physics
violation."

How big of a deal is the EmDrive? It's an EM-wave-to-thrust device. Take a
moment and consider the significance of such a device. Satellites could remain
in space effectively forever, because solar panels continuously source the
"propellant". Build one strong enough to counter Earth's gravity, and you get
the hovercraft. As long as you have access to electricity, you can generate
thrust.

The article also mentions Salvatore Pais and his patents. His story took off
after one particular Hacker News post and a comment on that post. You can read
the full comment at the link below, but here's the most important points:

"Whether or not the named inventor was a crank, and whether or not the
invention was equally frivolous, this was a patent prosecuted by a Navy
attorney, vouched for by the Navy CTO, and pushed through under atypical
circumstances, in a public forum.

What's even more intriguing is that, if the Navy wanted, it could obtain the
patent under a secrecy order that would keep it from the public's eyes until
it was declassified.

Knowing all this, now ask yourself why this impossible sounding patent issued
in a public forum with high-level brass support under tax payer dollars."

[https://news.ycombinator.com/item?id=19763445](https://news.ycombinator.com/item?id=19763445)

My gut tells me the EmDrive works. Time will tell, of course.

~~~
Strilanc
> _if one allows mass (that is, energy) to be transferred into this base
> medium. Momentum is conserved because the mass /energy is transferred to the
> all-encompassing medium. This medium is the same medium which enables
> quantum entanglement._

What are you talking about? Entanglement is not mediated by a medium. If it
was, it would have speed of light limitations.

This is like saying there's an unknown type of matter that enables statistical
correlations to exist. It's mixing together incompatible concepts.
Correlations just don't behave that way. Neither does entanglement.

~~~
waterheater
>Entanglement is not mediated by a medium. If it was, it would have speed of
light limitations.

This medium is that in which all energy is embedded. Two particles becoming
entangled does mean they're highly correlated with each other. But what
enables this correlation? I don't see this question as answered, because wave
function collapse is actively disputed.

While my view of quantum entanglement is limited, I don't fully understand how
entangled particles can be strongly correlated but can't transmit information
FTL. Is it correct to say that two separate entangled particles are now one-
and-the-same? I suppose you then get into a philosophical question of whether
all parts of a system can ever observe the exact same thing at the exact same
time. If this statement is false, then information must be transmitted, no?

>unknown type of matter that enables statistical correlations to exist

Matter and energy are one and the same. Why can't other types of energy exist
which we don't fully understand? For example, how does dark "matter" work? We
only have incomplete theories thus far, and I know of no paper that discusses
physical manipulation of dark matter.

The ether as a concept existed because people didn't understand the vacuum of
space. But perhaps the zero-point field is a more accurate rendition of what
etherians were trying to communicate.

~~~
Strilanc
> _Is it correct to say that two separate entangled particles are now one-and-
> the-same?_

It's not. If they were literally the same then swapping them should have no
effect, and you shouldn't be able to distinguish whether you applied effects
to one qubit or the other. But often this is not the case. For example, the
state |00> \+ |01> \- |10> \+ |11> is a maximally entangled state but applying
the swap operation to it produces a different state. And if I give that state
to you, and you secretly apply a bit flip to one of the qubits before giving
it back to me, I can do measurements that determine which one you flipped
over.

There are some entangled states where the swap operation has no effect, but
there are no states where all possible operations on both qubits become
identical. They're never literally the same.

~~~
waterheater
So, the entangled particles remain independent but highly correlated, that one
can be used to determine information about the other (and vice versa)?

Am I correct in reading that the broader scientific community doesn't fully
understand the mechanism which enables this correlation?

------
api
"Yup, the Earthlings are still using warp drives to heat food. We will revisit
this solar system in 25 of their planet's revolutions to check for further
progress."

------
Lerc
This is an interesting counterpoint to scientific discoveries that found
utilization some time after the discovery happened. For each of those
discoveries, there were always those standing on the sidelines going "Yeah,
but what is it good for?" The world has been changed many times over by such
discoveries that found later application.

The EmDrive sits on the other side of the fence. We know what it would be good
for so there are critics who dismiss it precisely for that reason citing
wishful thinking.

I do wonder if the curious force measurements would be much less contentious
if people didn't know what it could be used for. The focus would be purely on
"Why is it doing that?"

------
tomrod
How is the test of this not just to put one in space and see if it moves in a
controlled manner?

------
est
LENR and emdrive used to be my favorite topics on reddit. Right or wrong, you
can learn many amazing stuff which wont be found on other subs.

------
causality0
Even if it did work I don't think the EmDrive would be revolutionary. A
vehicle equipped with it still has to generate energy. It terms of how useful
it is you've just moved the payload requirement from the fuel tank to the
generator module. Going by these experiments the EmDrive doesn't have a hope
of ever matching the mass efficiency of an ion drive.

~~~
akiselev
That's the irony of it all. Power plants capable of powering an EmDrive that's
practically useful for manned flight can be summed up with one word: nuclear.
With the exception of the (lovely but insane) Project Orion, all of the
nuclear propulsion designs like NERVA and the nuclear lightbulb generate a
ridiculous amount of heat that we have trouble handling here on Earth, let
alone in vacuum without convection - most nuclear plants are built with access
to large natural or artificial bodies of water as a heat sink.

The future of manned space flight is almost certainly nuclear and it looks
like tiny cabins attached to giant passive heatsinks or spacecraft that
constantly have to accelerate just to dump all the waste heat and avoid
cooking its inhabitants.

~~~
bjo590
> Project Orion

Here is some declassified test footage of Project Orion. I don't believe any
of the test crafts used nuclear explosions, but you'll get the idea from this
footage (on why it's a terrible idea that could only exist in the 40s or 50s)

[https://www.youtube.com/watch?v=Q8Sv5y6iHUM](https://www.youtube.com/watch?v=Q8Sv5y6iHUM)

~~~
damoe
I love the top comment on the video, "External combustion engine."

------
bob1029
What is stopping us from producing a larger scale model with 10~100x the
performance? Presumably the effect should scale in some fashion with the
dimensions & power levels. I would expect a larger magnitude effect could make
it easier to identify the cause(s).

~~~
mNovak
Would require a military grade klystron to generate 10+kW of S-band energy,
for starters. In a vacuum setting, I'm not sure how you'll sink all the
resulting heat to avoid melting the thing.

I think even then it's very challenging to measure ~100mN thrust

------
rurban
I thought that Tajmar already debunked it in August. But no, they postponed
their results to February. But then it will be dead for sure.

------
SubiculumCode
I wish science articles would stop making the front page of HN. So few
experts, for many opinions.

------
danschumann
I always figured it was based on a rounding error in the simulation.

------
nynx
I really, really wish that there was something to the emdrive/mach effect
drive/etc, but alas, physical theories do not exist to make our lives better.

~~~
ocdtrekkie
Many of those physical theories aren't all that old though. While I agree it's
pretty unlikely, it's possible that they can be overthrown with more research.

~~~
j9461701
The physical theories that prevent the EmDrive (conservation of momentum) are
centuries old, and utterly fundamental to our university of reality on every
scale from black holes merging to atoms radiating. A violation of this
principle would involve _radically_ altering the very foundations of modern
physics, on a level more profound than anything that has ever happened in the
history of the field.

~~~
mokus
What about the idea that parallel lines do not intersect and that there is
exactly one line through a point parallel to another given line? These were
thousands of years old and well accepted until pretty recently.

~~~
samus
Our daily lives are not greatly impacted by this assumption not being true.
Unless we look at the horizon or at a map, it is easy to forget that we live
on a globe. And without atomic clocks it is very hard to measure the curvature
of spacetime.

~~~
Dylan16807
And slight flaws in the conservation of momentum wouldn't affect our current
daily lives either.

But this would still be an extremely useful effect if it does exist, for
devices designed to focus it. Look at how an electric field's influence on
semiconductors has almost no relevance to anything except when harnessed _just
right_.

------
james412
> McCulloch says that the thrust appears to be between one and four
> micronewtons—exactly the amount his theory predicts

Somehow I thought physics was meant to be a little more precise than this

~~~
spacedcowboy
Physics is precise. The uncertainty is due to error-bars in measurements. Any
measurement has error bars for systematic, random and absolute errors, then
there is the combinative error as multiple types of measurement are combined
together.

It’s more of a worry, tbh, if you _don’t_ see an error estimate in a result...

~~~
matthewdgreen
I think the objection is that those are large error bars compared to the force
measured. And that even a modest source of experimental error could put this
at zero real output.

ETA: and since “non-zero real output” implies that virtually all of our
physics is incorrect, and needs to be rebuilt from the ground up, the bar for
measurement error needs to be exceptionally small.

------
jiggawatts
For the people in this thread gleefully calculating the absurd energies
required to achieve miniscule thrusts, please remember two things:

1) The version in the lab and the device that would actually be used for
satellite production are very different. The lab version is _not designed for
efficiency_. It's designed to be easy to manufacture and test, using simple,
well-characterised technologies. For one, a production design would use a
superconducting cavity for much better efficiencies, easily 100 to 10,000x
better.

2) Miniscule propellentless thrusts are still useful with solar power.
Satellite stationkeeping is largely limited by the finite propellent capacity
onboard. Even Xenon plasma thrusters, the most efficient currently available,
run out of fuel eventually.

Now, I'm not saying the EmDrive _works_ , I'm just pointing out that it's a
distraction talking about the efficiency or utility of a "benchtop
experiment".

~~~
Dylan16807
I dunno about 1, it sounds like the extreme inefficiency makes it extremely
hard to get numbers stable enough to do a test with.

------
jackcosgrove
I don't think human spaceflight will ever be a significant factor in our
history. We evolved for this planet, and there is little reason to send humans
through space when we can send robots. When we discover another earth-like
planet, we will send robots there that can replicate human life, and the two
civilizations will communicate with each other but it's unlikely any person
will ever travel between the two. As to how robotic interstellar travel is
fuelled, we'll probably use converted asteroids with thrusters built into
them.

