主题：三体里描述的星际发动机出现了 -- 北纬42度
- 复 这个意思是
家园 2.5kw的微波，基本上就是个比较大的微波炉啊 也就是说，可以一边煮方便面（也就是论文图里的“负载”），一边星际航行。。。
- 复 这个意思是
家园 还是算一下 光子能量 E=hv (miu)
光子动量 p=E/c
功率 = 单位时间辐射总能量 I=sum(E)， sum :单位时间辐射所有光子
单位时间辐射总动量 P=sum(E/c) = I/c
=单位时间航天器单位时间获得总动量=d(mv)/dt = ma = F = 压力
那么
F =I/c = 2500W / c
= （2500 牛*米/秒）/（3.0*10E9 米/秒)
< 1E-6 牛 = 1微牛
哪里算错了？
- 复 这个意思是
家园 我也怀疑，不过 我也怀疑，不过是这样想的
根据动量守恒，航天器所获得的动量和离开它的光子的动量应该是相同的（假设理想情况下无热量散失）。
那么离开它的光子动量可以传递给航天器的压力可以类比于光压。我记得太阳的光压是很小的，难道2500 W的微波功率是很高的亮度？初级物理知识就可以估算一下推力上限，不过现在没有时间。
当然我也就这么一想，没有计算，也许有明显的遗漏。
- 复 这个意思是
家园 以俺有限的知识，看得云里雾里 为什么微波辐射会获得推进力呢？原理是什么呢？
这个推进力大小受不受航天器运行速度的影响呢？不会是在低速下推进力大，高速下就不行了吧？
如果是真的靠谱，那就了不得了。谢谢小木的分析。
家园 微波源输出2500W的功率时, 推力在720mN 推力似乎是小点啊，不过总是一个好的开端
建议尽快搞出实验样机，放到太阳系里跑一跑
家园 P=Fv 这說明速度高嗎?
家园 我看了下论文，产生一个电磁压强梯度能明白 但是搞不懂真空中如何能推进宇航器，动量总要守恒阿？
家园 看wikipedia，好像物理界也有这个怀疑 http://en.wikipedia.org/wiki/EmDrive
注意analysis那部分
analysis
Any claim of a reactionless drive is treated with skepticism by the physics community, since reactionless drives violate the well-established principle of the conservation of momentum, which has enormous experimental support. Shawyer claims that his drive does not violate the conservation of momentum.[11]
Since there are no known phenomena that do not conserve energy, any calculation based on standard physical theory that predicts a violation of energy conservation almost certainly is in error. This is a non-controversial and fundamental fact regarding the mathematical structure of the theories, regardless of whether the theories themselves are or are not correct descriptions of the physical world. Accordingly, the results reported regarding the EmDrive, if true, would demonstrate that existing physical theory (or its application in engineering) is incorrect or incomplete.
The EmDrive has been compared to the previous Dean Drive, in that an oscillatory motion is set up so that it has a different effect in each direction of the stroke, in the hope that momentum transfer will differ in each direction, except in this case the oscillations are said to be electromagnetic.
Conservation of momentum is also required and maintained in Maxwell's equations, Newtonian mechanics, Special relativity and quantum mechanics (and their combination, quantum electrodynamics), so this claim cannot be valid unless these well-established physical theories are false or can be otherwise explained in terms within these existing theories.
Shawyer's calculations[12] may be in error.[4] He may have incorrectly identified the forces on the sides of the waveguide. If an error is present, it is most likely that the 'thrust' is eliminated and the drive then cannot accelerate. Despite some criticism, Shawyer has released to the public a video purportedly demonstrating that his device works.
Any dispute will be settled when independent observations are able to conclude whether or not the machine works in the way it is claimed.
