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Message: <blockquote data-quote="freyar" data-source="post: 6682388" data-attributes="member: 40227">I almost put in "ask me anything except about the EM drive" in the OP but decided not to. <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f609.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=";)" title="Wink    ;)"  data-smilie="2"data-shortname=";)" />  Anyway, like Umbran, I am skeptical on general grounds, as follows: this violates one of the oldest principles of physics, that of conservation of momentum, which is another way of saying Newton's laws.  Before I'm willing to believe that could happen, I'd need very very good experimental evidence ("extraordinary claims require extraordinary evidence" in the words of Carl Sagan).  I think it's worth saying that the experimental groups who've looked at this haven't yet felt their evidence was strong enough for submission to peer review yet as far as I can tell (certainly the most recent group has not).  Another good discussion of the results on this can be found here: <a href="http://io9.com/no-german-scientists-have-not-confirmed-the-impossibl-1720573809" target="_blank">http://io9.com/no-german-scientists-have-not-confirmed-the-impossibl-1720573809</a>The problem with the EM drive is that the predicted thrust is so small as to be nearly unmeasurable with current techniques. While there have been measured "thrusts," those thrusts also behave in ways consistent with a heating effect (see the link I gave; apparently the measuring devices don't work well at the temperatures reached by the apparatus).  Furthermore, there is no credible theoretical work to motivate testing the drive in the first place.  I think it's instructive to compare to another recent episode when an experiment possibly indicated a violation of a important physical law: a few years ago, the OPERA experiment, which was timing the flight of neutrinos over hundreds of kilometers, found them arriving something like 60 nanoseconds faster than the speed of light would allow.  In that case, the experiment's press release was a touch more cautious --- inviting the physics community to find problems with their experiment rather than saying their results warranted further investigation --- but just a touch.  The reception by the physics community was also very cautious, but the consensus was that there was less of an obvious problem (both the recent EM drive experiments have been criticized for not analyzing the effects of heating on the apparatus).  In the case of the OPERA experiment, there were a number of theory papers, either showing that FTL travel wouldn't look like what OPERA saw or trying to figure out a way neutrinos could move FTL, even though it would be fair to say that everyone would have been shocked if the OPERA results stood up.  In the end, the problem was a faulty cable connection.  And, in the end, these EM drive results are probably due to something like a faulty cable or more likely measuring devices that can't take the heat.  But the EM drive experiments haven't given as much a reason to be interested as OPERA did.Back to more normal physics tomorrow.... <img src="https://cdn.jsdelivr.net/joypixels/assets/8.0/png/unicode/64/1f609.png" class="smilie smilie--emoji" loading="lazy" width="64" height="64" alt=";)" title="Wink    ;)"  data-smilie="2"data-shortname=";)" /></blockquote>

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