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Comment Re:Perpetual motion machine of the first type (Score 1) 404

Noether's theorem is a direct consequence of empirical properties of space-time: space-time homegeneity and isotropy. It is just as fundamental result as relativity, maybe even more so.

Well... Noether's theorem is a mathematical theorem, so there's nothing emperical about it. Those bits about homogeneity are in relativity: there are no position or direction dependent terms. If you apply Noether's theorem, you get that in relativity, momentum is conserved, meaning under the rules of relativity, the EM drive is impossible.

IOW, the homogeniety terms are in relativity, Noether's theorem tells you the consequences of that.

Comment Re:Vs. Ion Drive [Re:points of interest] (Score 1) 404

If it's so wimpy, why not use ion drives?

People do because ion drives actually work :)

A key difference between EM and ion drives is that ion drives spew radiation to produce thrust while the EM drive allegedly doesn't. While that may be interesting from a physics perspective, it's not a practical issue from a space travel perspective because spewing radiation (ions) is not a significant problem.

Spewing ions is a problem: they're reaction mass and they have to be carried. If you have reaction mass, you end up on the wrong end of an exponential in the rocket equation.

EMD titillates (or teases) physicists because of the perpetual-motion-machine-like qualities

I don't think it titillates physicists any more than a huge pile of horseshit titillates them.

Comment Re:points of interest (Score 2) 404

I think people don't really get the difference in scale between 1mn and 1kw, so why having the two together makes things so hard.

1mn is of course the weight exerted by 0.1g. That's about half a grain of rice. To get that, you require 1kw. Think about the things that take pr process 1kw of power, e.g. an electric bar fire, a very high end PC, a mid-size UPS and so on and so forth.

They're all large, heavy things, which require considerable cooling to dump that much heat.

So the question is how do you transport 1kW from one place to another. The awnser is of course, wires. Consider the size of the wires, interaction with the earth's magnetic field, thermal expansion of the equipment and so on.

And you've got to figure out the half grain of rice's worth of force from all that.

Comment Re:points of interest (Score 1) 404

"Zero, since it doesn't actually provide thrust."

That in itself would violate Newton's Laws of Motion, wouldn't it? Specifically, that would be Newton's Third Law, for every action, there is an equal and opposing reaction. If you're emitting something, even inside of a closed cavity, THERE MUST BE INITIAL THRUST/PUSH OFF OF THE EMITTING MATERIAL, NO MATTER HOW SMALL, EITHER POSITIVE OR NEGATIVE.

Back to school with you.

Comment Re:Perpetual motion machine of the first type (Score 1) 404

I'm not a physicist, so I can't speak to whether his explanation makes sense.

It doesn't. Firstly, Noether's theorem applies to relativity and proves that conservation of momentum happens in relativity. So, it's impossible for this device to work merely using the theory of relativity. There was an error in his maths and I think someone actually found it.

Comment Re:Reference devices? (Score 2) 178

They probably mean that they will support hardware specific to that phone. In the past they have always provided APIs that anyone can use for things like the fingerprint sensor and camera features. Maybe they are planning to allow some stuff that is unique to their phones and not supported elsewhere.

My guess would be it is related to VR and 3D mapping.

Comment Shame on you, and whoever modded you up (Score 5, Informative) 111

You are comparing apples to oranges. Progress is a spacecraft, not a rocket. Falcon 9 is a rocket, not a spacecraft. They cannot be directly compared, because they aren't even the same class of thing! SpaceX's equivalent of Progress is the Dragon capsule.

The Soyuz ROCKET , specifically the newest version (called Soyuz-2, has a payload of 8200 kg to LEO and 3250 kg to GTO. It's still not nearly so powerful as Falcon 9, even the reusable configuration (I believe the numbers you quoted omit the F9's grid fins, landing legs, and reserved fuel for recovery), but it's far more than one ninth as powerful.


Comment Re:So what would you use? (Score 4, Insightful) 371

Unless you like staying up all night tracking down errors in pointer arithmetic.

Lumping C and C++ together generally means you haven't looked at how dramatically the C++ language has changed recently, especially if you talk about pointer arithmetic. If you're using modern C++ and are still worrying about pointer arithmetic (i.e. you're not abstracting it away), you're probably doing it wrong.

The nice thing about C++ is that, quite often, those abstractions either cost nothing at all, or at worst, far less than interpreted languages. Also, having used modern C++ for a few years now, I think garbage collection is vastly overrated compared to reference counted pointers and simple RAII. C++ is still harder to use than Java or C# in many subtle ways, but basic memory management is no longer one of those persistent thorns.

Efficient compilation? Yeah, sadly, that's not C++, and likely never will be. There are some newer alternatives that have these features and compile quite efficiency, since they don't come with the baggage of backwards compatibility, but I'm not sure how much traction they're going to gain in practical measurements outside of some niche locations. Their biggest downside? Yeah, they're not backwards compatible with billions of lines of C or C++ code out in the wild.

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