
Redditor disputes recent emdrive paper conclusion in /r/physics - SwellJoe
https://np.reddit.com/r/Physics/comments/5ewj86/so_nasas_em_drive_paper_is_officially_published/dafqhw2/
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snowwrestler
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.

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ninkendo
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.

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snowwrestler
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).

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

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imode
can I ask why this redditor in particular matters?

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SwellJoe
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.

