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Comment by j9461701 | Hacker News Reader

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.

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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.

what

One of Euclid's axioms is that parallel lines do not intersect. This is true on a plane, so Euclidean's axioms describe planar geometry. In non-euclidian geometry you relax this requirement, giving rise to things like hyperbolic spaces and elliptical spaces. Not sure what OP is going on about though, as this doesn't seem particularly on topic.

https://en.wikipedia.org/wiki/Non-Euclidean_geometry

Space is non-euclidean under the influence of gravity. It's definitely on topic.

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.

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.

> 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.

Actually, that axiom made even the ancients uncomfortable. There were lots of attempts over the centuries to "prove" or "disprove" it.

The fact that violating it can still produce a self-consistent geometry was what was stunning.

i have a question about conservation of momentum. what about losses due to friction and/or heat?

I could imagine through some interesting device a way to have thrust in one direction with the "conservation" occurring as heat radiating in all of the other directions -- is this not compatible with conservation of momentum or am i a crackpot who doesnt understand the basics (the more likely case, i am sure)

How would that heat radiate?

Electromagnetic radiation has momentum - it's small, but not zero. If you're emitting a bunch of photons (e.g. infrared photons from blackbody radiation of a hot object) more to one side than the other, then the remainder of that device will have some thrust. But that does not violate conservation of momentum, as the momentum gained by the device will equal the momentum of these photons; and the total momentum of the whole system (the device plus all the photons radiated) will be constant.

Thank you!

Crackpot who doesn't understand the basics (not to be rude). Unlike energy, momentum is a vector quantity. A system can't disperse momentum "in all directions" because the net effect will cancel out. A bomb that has net momentum 0 still has net momentum 0 after it's been exploded.

Thank you!

It is entirely possible that it’s just a gap in our understanding that does not violate existing “laws.”

What’s that quote about sufficiently advanced science being indistinguishable from magic?

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