Comment by pdonis | Hacker News Reader

Comment by pdonis | Hacker News Reader

Parent Full thread

> What you are doing here is saying - I will take my model of the world and check that their observations are consistent with what it predicts are physically possible.

Conservation of momentum has been confirmed by many, many experiments; it's not just a feature of my or anyone's "model" of the world.

> there might in fact be conventional exhaust escaping from the device in a manner they had not anticipated.

Yes, that's quite possible. But as far as I can tell, the experimenters are not even considering that possibility, or checking for it.

> I am very able to imagine a world where my model is innacurate

Sure, imagining a world in which momentum is not conserved is easy. But, as I said above, experiments have shown us that we do not live in such a world.

Of course it is logically possible that momentum is conserved almost all the time, instead of absolutely all the time, and these experiments just happened to be the first ones anyone ever ran that poked reality in a place where momentum was not quite conserved. But in Bayesian terms, my prior for that being the case is much, much lower than my prior for the experimenters having made a mistake somewhere. Experimenters make mistakes all the time; but nobody has yet discovered any violation of a conservation law.

'it's not just a feature of my or anyone's "model" of the world.'

This may just be semantics, but I dont see how you could argue that it isnt a feature of a model of the world. A neural representation of the world shared amongst a group of humans. Tested against reality in the best ways we can imagine. But it is still just a model, it is not actual reality. Are you really so sure about those priors? You are also have a very influential prior there which supposes that that if the device functions, it does so because it violates conservation of momentum. Surely you cant know this? Are there really no other explanations which fit more neatly with our current models?

> it is still just a model, it is not actual reality.

We have a model that includes conservation of momentum. But experiments have shown that reality also includes conservation of momentum--that that feature of the model is an accurate representation of reality.

> Are you really so sure about those priors?

Yes.

> You are also have a very influential prior there which supposes that that if the device functions, it does so because it violates conservation of momentum.

That isn't a prior; it's a hypothesis--the one the EmDrive proponents are claiming.

> Are there really no other explanations which fit more neatly with our current models?

"The experimenters have made a mistake somewhere" is another explanation which fits in more neatly with our current models. Their mistake could be that the device isn't actually producing thrust, or it could be that it's producing thrust because it's ejecting radiation out the back end which they aren't detecting. Either one of those invalidates the EmDrive proponents' claims.

I give up. I think you're wrong, you think I'm wrong. I dont have time to iron out all the mistakes you are making and Im sure you feel the same way.

Reply on news.ycombinator.com