Hacker News Reader

Comment by mdorazio | Hacker News Reader

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.

View on HN

Imagine 10k years in the future. 2 aliens arrive on earth, and examine the rubble. "Hey, check it out. They were right on the cusp of developing stardrive". "Weird, what happened? Nuclear war? Climate change?" "Nah, looks like they just couldn't work the math out, so they gave up."

To some extent yes, but at some point the amount of effort might not outweigh the benefits.

There are limits to how much time and effort it is worth to debunk a perpetual motion device (a term usually reserved for something that violates the conservation of energy but the conservation of momentum is close enough, or perhaps even equivalent under special relativity).

Does it violate the conservation of energy though? I don't think that was proposed.

It claims to provide thrust without propellant, which is a violation of the conservation of momentum. Since momentum and energy are conserved in much the same way this is already bad enough, however in special relativity the 4-momentum mixes momentum and energy (or rest-mass) and I believe that a well chosen Lorentz boost could turn a violation of the conservation of momentum into a violation of the conservation of energy.

Seems like it violates conservation of energy just because kinetic energy is proportional to the square of velocity, and thrust has to be constant for a given input energy since there's no preferred reference frame. Thus the faster you go, the more kinetic energy you get for the same input energy.

Unless there are physics involved we aren't aware of.

Chances of that are very slim.

But investigating this might uncover what is causing the confusion. Some other external force unknown to us might be at play.

Technically yes, but as I've been trying to get across; violating the conservation of momentum isn't just 'new physics' it shakes the whole foundation of modern physics. The very definition of momentum ensures it is conserved by the (classical) equations of motion, to be otherwise is patently absurd.

Your comment seems like it would rule out a photon rocket , which proves too much. I think the resolution is that the faster you go, the heavier you are and the more thrust you need to increase your dv.

A photon rocket still has a preferred reference frame where the total momentum is 0.

Don't forget that photons still have momentum, even if they don't have mass.

So you can calculate, for a given thrust/energy ratio, what velocity you have to exceed to get more energy out than you put in. For relativistic effects to make enough difference to matter, that velocity would have to be pretty close to c. That translates to an extremely low thrust.

(I've been told that for a photon rocket, the threshold velocity is c, implying that a reactionless drive won't violate conservation of energy as long as it's no better than a photon rocket. I haven't done that math myself though.)

I agree with you in principle but the benefits here go beyond disproving one device. The engineering and experimental design required to disprove this design will no doubt have applications beyond the EM drive.

Right. Just like the pioneer anomaly it warrants investigation just in case if there is something going on we haven’t predicted. Even if it is eventually explained by a mundane process it’s still probably worth the refinement of techniques used to detect why it’s happening. If for no other reason there’s the risk of more film flam technologies making similar claims with no way to disprove them.

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.

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

$10m seems … relatively cheap for anything in space?

It seems cheap relative to pretty much anything these days. People pay that much for rare cars, a rich person could snap their fingers and make it happen. I hate to tell people how to spend their money but I wish someone pitched it as an experiment to Elon Musk or Bezos. Just like you said - put it in space, switch it on. Either it works or it doesn't, should be obvious straight away, no?

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

Putting another $10m to follow it would be chasing good money after bad, and fall into the sunk cost fallacy.

Since nothing has been proven or disproven yet, we’re really in no different position that before all the experiments began. Might as well spend that money now to end it.

It fits so far out of our theoretical models that it's unfair to say it isn't proven or disproven. There are virtually infinite hypothesis that are neither proven nor disproven experimentally, but because theory states it's impossible we don't consider them worth testing.

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.

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.

Getting a dollar from a million people is a different thing to getting a million dollars from one person.

That's about what Bezos makes in 60 seconds.

We could probable even go fund that

Make it happen!

Orbit is actually a very dynamic and variable place. The Earth’s gravitational fields varies due to asymmetric mass distribution of the continental shelves, mountain ranges and features below the crust. Our atmosphere has an affect on satellites at even thousands of km altitude. The magnetic field is constantly shifting and can affect the orbits of metallic satellites. Then there’s the solar wind. This is why a lot of satellites need station keeping thrusters. Decent thrust would be observable, but very small rates of thrust that are hard to measure at all in the lab could be swamped by these effects and just as hard to measure in orbit, if not more so.

Exactly, rocket science is pretty easy to a physicist but rocket engineering is absolutely not.

Reply on news.ycombinator.com