Redditor disputes recent emdrive paper conclusion in /r/physics | Hacker News Reader

physics

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36 pointsSwellJoe6 comments

The entire Reddit comment depends on the idea that such a "tailing-off" shape in the graph could only be caused by thermal contraction. This is just another way of saying that the experimental results don't seem to match existing theory, which is something we already knew.

When an experimental result doesn't make sense, you can't disprove it by pointing at part of it and saying "hey that doesn't make sense." Yeah, we know it doesn't.

In general I'm tired of people typing dismissive comments into social media and then high-fiving. Oh you're a physicist who thinks the error is obvious? Here's what I don't see: you risking your own grant money to prove it.

I'm not saying that the emdrive works--it almost certainly doesn't--I'm saying that science gets done in the lab, not web forums.

The redditor is not saying it can only be caused by thermal expansion, only that thermal expansion is a simpler explanation that doesn't require any new physics.

Sure, you can't thoroughly disprove it by saying it doesn't make sense, but what the redditor is doing is coming up with an explanation that fits the data that makes a lot more sense.

Actually all he is saying is that the post-power tail-off matches what one would expect from thermal contraction. He does not address whether the onset of force matches what one would see from thermal expansion (because it does not--note how it is not a smooth curve like the tail-off).

It's still a good idea to add thermal sensors though to discard his explanation.

can I ask why this redditor in particular matters?

I'm not a physicist, so my opinion matters even less, but from what I can tell, the explanation he gives fits known physics, while the explanation given in the paper requires a new understanding of physics. I found it really interesting, and thought folks here might, since there was a lot of conversation here when it was posted, but I don't remember this particular angle being discussed.

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