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Questions about Nasa's space drive answered

wired.co.uk

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Re: Questions about Nasa's space drive answered

#101

Post by gus_massa »

chton wrote: post #87
gus_massa wrote: post #80

Short version: Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. With this definition using a red LED Laser powered by a 1.5V battery in the back of the spacecraft is a "no reaction mass" thruster. The problem is that the momentum / energy ratio has theoretical limitations, and they are getting too much momentum. Long version (based on a previous comment http…

While it's true that most reactionless drives break some of the most basic physical laws, that's not the case for all of them. An Alcubierre drive is a good example of a propulsion method that works within the current laws, yet does not emit anything. The idea that the designs they tested (and EmDrive) would be reactionless is exactly why everybody is so baffled and excited by this. If they are, they must have some w…

Alcubierre drive is not a thruster, you can't attach it to a spaceship to move it. It's something like: "If you put a spaceship inside this, and it stabilizes the gravity field using that, then it will travel faster than light in an external reference frame." It travels at a constant speed, so it doesn't need to emit particles to change the momentum. (On the other side, it uses exotic matter that no one has ever seen, so it may be impossible to construct.)

When you say "reactionless" you mean that the device doesn't emit anything and it breaks the momentum conservation law? The previous experiments tried to give some theoretical explanations, but usually they were equivalent to emitting photons or gravitons. The conservation of momentum is a very fundamental law. It's possible to change the physics laws, but you need to have very good experimental evidence. (Hey! I believe in the Higgs boson!) This is like the faster than light neutrinos. It's very exiting if it were true, but the easier explanation is an experimental error.

Re: Questions about Nasa's space drive answered

#102

Post by JulianMorrison » 

  A superconducting version of the EmDrive, would, in principle, generate thousands of times more thrust. And because it does not require energy just to hold things up (just as a chair does not require power to keep you off the ground), in theory you could have a hoverboard which does not require energy to float in the air.
If they have just solved flying cars and hoverboards, I think we can officially declare this to be the future already.

Re: Questions about Nasa's space drive answered

#103

Post by gambiting »

tobinfricke wrote: post #89
baq wrote: post #68

Earlier quoted context omitted.

they found 91 mmN of thrust and they claim their detector is sensitive to about 10mmN. that's almost an order of magnitude. this doesn't mean that it sounds too good to be true. edit: fixed units - dont have easy access to micro, thanks for pointing that out.

"u" is an acceptable replacement for "µ". I've never seen "milimili" (mm) before. You can spell it out, like "91 micronewtons". You can also use exponential notation like 91e-6 N or 91x10^(-6) N. To be fancy you can copy-and-paste unicode characters and write 91×10⁻⁶ N.

I've seen "mm" used very frequently as millimetres. 1cm/2=5mm.

Re: Questions about Nasa's space drive answered

#104

Post by antocv »

tobinfricke wrote: post #32
didgeoridoo wrote: post #2

Deep breaths. Probably experimental error. Extraordinary claims require extraordinary proof... God DAMN this is exciting.

I'd say that it's about on par with the faster-than-light neutrinos caper (tiny effect, violates known physics, probably result of experimental error, ...). Both would be very exciting if actually confirmed, but I personally found/find the chances too slim to (yet) get excited.

Wasnt the faster-than-light neutrino myster solved? It was an optical cable not plugged in all the way.

Re: Questions about Nasa's space drive answered

#105

Post by [deleted] »

tobinfricke wrote: post #32
didgeoridoo wrote: post #2

Deep breaths. Probably experimental error. Extraordinary claims require extraordinary proof... God DAMN this is exciting.

I'd say that it's about on par with the faster-than-light neutrinos caper (tiny effect, violates known physics, probably result of experimental error, ...). Both would be very exciting if actually confirmed, but I personally found/find the chances too slim to (yet) get excited.

[deleted]

Re: Questions about Nasa's space drive answered

#106

Post by idlewords »

readerrrr wrote: post #51
tobinfricke wrote: post #41

Here are two nice posts by physicist John Baez with some reasons to be skeptical about the "reactionless drive": https://plus.google.com/117663015413546257905/posts/WfFtJ8bY... https://plus.google.com/117663015413546257905/posts/C7vx2G85...

He seems to be makings some mistakes as well. He says: This is baloney too - but now it's graduate-level baloney. "Quantum vacuum virtual plasma" is something you'd say if you failed a course in quantum field theory and then smoked too much weed. There's no such thing as "virtual plasma". If you want to report experimental results that seem to violate the known laws of physics, fine. But it doesn't help your credibil…

Are you trying to suggest here that Baez isn't aware of the existence of virtual particles? He's done lots of work in quantum field theory.

Re: Questions about Nasa's space drive answered

#108

Post by jdmichal »

happyscrappy wrote: post #65
ColinWright wrote: post #23

Earlier quoted context omitted.

> ... we still can't make up our > minds as to how wings work, ... Interestingly, I recently spoke to an aerodynamicist and mentioned this, and I was severely lectured. In the follow-up he mellowed a little, but I suspect the "we" in your statement refers to laypersons who don't have advanced training in aeronautics, and yet claim to understand about flow pressure, Bernoulli, etc. I've been convinced that the people…

Does Feynman's "if you can't explain it to a laymen in a few paragraphs then you don't truly understand it" no longer hold?

That particular version of a quote is listed on Wikiquotes as unsourced, and therefore unreliable. [1] However, he did say, "I couldn't do it. I couldn't reduce it to the freshman level. That means we don't really understand it." [2]

[1] http://en.wikiquote.org/wiki/Talk:Richard_Feynman#Unsourced

[2] http://en.wikiquote.org/wiki/Talk:Richard_Feynman#Teaching_q...

Re: Questions about Nasa's space drive answered

#109

Post by ethbro »

chton wrote: post #87
gus_massa wrote: post #80

Short version: Unless they believe the machine breaks some of the fundamental physics laws, the device must emit something. With this definition using a red LED Laser powered by a 1.5V battery in the back of the spacecraft is a "no reaction mass" thruster. The problem is that the momentum / energy ratio has theoretical limitations, and they are getting too much momentum. Long version (based on a previous comment http…

While it's true that most reactionless drives break some of the most basic physical laws, that's not the case for all of them. An Alcubierre drive is a good example of a propulsion method that works within the current laws, yet does not emit anything. The idea that the designs they tested (and EmDrive) would be reactionless is exactly why everybody is so baffled and excited by this. If they are, they must have some w…

I think it's fair to place Alcubierre drive and something that's been physically built and tested in two very different camps.

I understand this thread was about the theory, but from an engineering perspective that's a substantial distinction.

Re: Questions about Nasa's space drive answered

#110

Post by DanBC »

tobinfricke wrote: post #45
DanBC wrote: post #35

Earlier quoted context omitted.

For various values of "we". http://www.grc.nasa.gov/WWW/K-12/airplane/lift1.html > There are many explanations for the generation of lift found in encyclopedias, in basic physics textbooks, and on Web sites. Unfortunately, many of the explanations are misleading and incorrect. Theories on the generation of lift have become a source of great controversy and a topic for heated arguments. There are lots of bits of scien…

By "we", I mean humanity as a whole. Nobody would contest that there are a lot of widespread misconceptions about how an airplane - or, for that matter, anything - works. A nice blog post on the topic is Sean Carroll's article, "The Laws Underlying The Physics of Everyday Life Are Completely Understood" ( http://blogs.discovermagazine.com/cosmicvariance/2010/09/23/... ).

https://www.youtube.com/watch?v=MO0r930Sn_8

Feynman: "Magnets repel each other."

Interviewer: "What I want to know is what's going on ..."

Feynman: "Magnets repel each other."

Interviewer: "...between those two bits of metal."

Feynman: "Magnets repel each other."

Interviewer: "Well then, but what does that mean? Or why are they doing that? Or how are they doing it?"

Feynman: "Ah, [pause] uh you're asking ..."

Interviewer: "I must say that's a perfectly reasonable question to ask"

Feynman: "Of course! It's a perfectly reasonable question."

See also his quote about quantum mechanics - "There was a time when the newspapers said that only twelve men understood the theory of relativity. I do not believe there ever was such a time. There might have been a time when only one man did, because he was the only guy who caught on, before he wrote his paper. But after people read the paper a lot of people understood the theory of relativity in some way or other, certainly more than twelve. On the other hand, I think I can safely say that nobody understands quantum mechanics."

https://en.wikiquote.org/wiki/Talk:Richard_Feynman#.22If_you...

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