Hacker News Reader

Comment by rtpg | Hacker News Reader

The EmDrive website (http://www.emdrive.com/) has papers.

Quickly flipping through this paper[0], I think it explains the principles.

http://www.emdrive.com/FeasibilityStudytechnicalreportissue2...

The theory is simply wrong, it neglects the electromagnetic pressure between the electromagnetic field and the tapered wall of the waveguide, it should produce the missing force component for a net force of 0.

It's impossible to arrive at a non-zero net Force with classical electrodynamics. It's theoretically proven that it conserves momentum.

Very possible reasons for measuring non-zero force:

> Systematic measurement errors.

> Leaking EM field carrying momentum.

> Energy channel from outside carrying momentum (failing measurements including battery mentioned in comments)

Unlikely explanation: All currently used theories of electrodynamics are wrong.

But explaining non-zero force from classical ED is simply impossible.

Also note that breaking conservation of momentum + relativity means that conservation of energy is broken as well.

edit: typo

edit 2:

I mean the theoretical approach presented in the paper makes obvious mistakes. I'm not arguing that breaking conservation of momentum is impossible (although I think it's really unlikely), I argue that even if it would happen it couldn't be described by classical electrodynamics (or even QED). We would have to come up with better laws for electrodynamics.

This is exactly the kind of comment I would expect to read shortly before some presumed law of the universe were broken. Reminds me of the "maybe in thousands of years people will fly" newspaper comment the same year the Wright brothers flew.

I'm not treating it lightly that conservation of energy etc. would be broken. I'm just saying... it's a law until it's discovered that it's not. Or rather, that the law is only applicable within certain conditions, or needs some asterisks on it.

I think the issue is that if it were possible to break conservation laws using such setups, we would have seen nature doing it by now.

Perhaps we have: https://en.wikipedia.org/wiki/Flyby_anomaly

Maybe that's how the universe came into existence at all, is "breaking the law" of conservation of energy? I'm not even arguing this, I'm just saying maybe we haven't been looking at things the right way or the proof will be obvious after we know about a new effect.

There were decades of manned flight prior to Wright bros.

Also, there were birds flying all over the place so it was obvious to everyone that it was possible...

There were a fuckton of people who thought heavier than air flight was not possible until it was done. Not sure how they reconciled birds, but that was a common opinion even among scientists at the time

That's not what the comment addresses. Could the current theory be wrong? Sure. But any explanation within the current theory is someone doing math incorrectly.

The fact that several teams of very highly qualified physicists bothered to look at it makes me believe the physics involved is non-obvious and can't be written off with a simple "the theory is simply wrong". Dismissing it out of hand does a disservice to all those people.

That's not to say it'll prove to be true, I doubt it will, but this is something that has so much potential it's worth investigating the tiny possibility that it's real, and "all currently used theories of electrodynamics are wrong", just in case.

Worryingly, the 2015 paper didn't seem to have anything about measuring the mass of the device before and after the experiment.

An old radar technician asked me to take a look... apparently "boiling" waveguides are a thing when it comes to high-power RF.

If the waveguide boils at a certain rate at certain power levels, then it should be possible to estimate how much force this would produce. If that force is on the same order, then it's likely the reason for what we're seeing.

> Dismissing it out of hand does a disservice to all those people.

Or maybe they all know its impossible, but continue because they are perfectly happy with the amount of funding thrown at them. Not saying it's true, but it's the other side of the coin.

> Or maybe they all know its impossible

How could they know? That's the point of the scientific method isn't it, experimentation and valuing observation over preconceptions?

Has anyone bothered to write your counterargument in more detail?

I think I understand your argument but I wonder if anyone's really done the calculation... though I suppose the conservation of momentum itself a theoretical proof that the "other forces" have to cancel out.

Is it possible that classic electrodynamics are not wrong, but there's some other fundamental thing in play here? I'd be a bit surprised, given that this just seems to be such a simple setup, but maybe? One can dream....

Reply on news.ycombinator.com