A controversial concept called the electromagnetic drive, or Emdrive for short has been called impossible. But one company believes the concept is viable and has worked for several years on building demonstration models. The Emdrive is a reactionless propulsion system that supposedly generates thrust by converting electrical energy via microwaves. If it works it could provide an almost endless supply of thrust for satellites and possibly other spacecraft. But no detectable energy emanates from the device, and most scientists say the Emdrive violates the well-established principle of the conservation of momentum. Satellite Propulsion Research, Ltd. (SPR), the company working on the drive now says researchers from China have confirmed the theory behind the Emdrive, and they should have a trial engine ready to test by the end of this year.
http://www.universetoday.com/2008/10/09/is-the-impossible-emdrive-possible/ (http://www.universetoday.com/2008/10/09/is-the-impossible-emdrive-possible/)
If you want, I can get an ex-director of Brookhaven Labs in NY to give his opinion on this.
Quote from: LMNO on October 10, 2008, 02:59:59 PM
If you want, I can get an ex-director of Brookhaven Labs in NY to give his opinion on this.
Sure, that would be cool.
My opinion of it is that its bunk.
Me too, but I sent him an email.
He often likes to talk about this kind of stuff... in a debunking way.
So, the comments of a man who's been studying phisics for over 50 years:
"About the EMdrive. It's utter bullshit. Don't buy stock. There is no recognized physical theory that supports such a device. It would indeed violate the law of conservation of momentum (or Newton's first law). The idea of a "reactionless" propulsion system is an oxymoron. You can't get thrust except by reaction against something thrown out the back of the device.
"The language of the article in the link is fishy. "milliNewtons of force" and "watts of power" are not commensurate. Watts is energy per unit time, force is energy required to go unit distance. The setup described reminds me of the old physics homework problem where you have someone inside a boxcar who tries to get it going on a track by running the length of the car and slamming into the front wall. As he starts running, the boxcar begins to move in the opposite direction in reaction to the thrust of his legs. When he hits the front wall, it stops the car. Microwaves inside a closed resonator are going to act the same way, no matter how you slice and dice them. (You can make the boxcar cone-shaped and pad it or make the surfaces out of rigid material, it won't help.)
"At the end of the article are links to a paper by the inventor and an "opposing paper" by a John Costello. I looked at them both. Costello is right."
So, there you have it. If he has time, I'll ask about the bubble-shaped universe.
Thats what I thought. Thanks for that. :)
No problem.
I should dig up his "how many dimensions are there?" riff.
Quote from: LMNO on October 13, 2008, 03:58:15 PM
No problem.
I should dig up his "how many dimensions are there?" riff.
This IS a certain relative of yours, is it not?
Or am I thinking of the wrong person?
Shawyer's paper isn't peer-reviewed, and [insert everything LMNO posted for emphasis].
Quote from: LMNO on October 13, 2008, 01:26:12 PM
So, the comments of a man who's been studying phisics for over 50 years:
"About the EMdrive. It's utter bullshit. Don't buy stock. There is no recognized physical theory that supports such a device. It would indeed violate the law of conservation of momentum (or Newton's first law). The idea of a "reactionless" propulsion system is an oxymoron. You can't get thrust except by reaction against something thrown out the back of the device.
"The language of the article in the link is fishy. "milliNewtons of force" and "watts of power" are not commensurate. Watts is energy per unit time, force is energy required to go unit distance. The setup described reminds me of the old physics homework problem where you have someone inside a boxcar who tries to get it going on a track by running the length of the car and slamming into the front wall. As he starts running, the boxcar begins to move in the opposite direction in reaction to the thrust of his legs. When he hits the front wall, it stops the car. Microwaves inside a closed resonator are going to act the same way, no matter how you slice and dice them. (You can make the boxcar cone-shaped and pad it or make the surfaces out of rigid material, it won't help.)
"At the end of the article are links to a paper by the inventor and an "opposing paper" by a John Costello. I looked at them both. Costello is right."
So, there you have it. If he has time, I'll ask about the bubble-shaped universe.
I think this analogy is flawed, in a boxcar you can also manipulate friction (depending on the design of the car ofcourse) by shifting your weight. Or are there limits to the design of a boxcar that i am not aware of?
to test this in real life try moving a skateboard while keeping both feet off the ground. it is doable.
ETA: i agree that the EMdrive is utter bullshit.
Regret:
The analogy is an analogy about a physics homework problem. You know, the ones in high school that try to teach about the basics of mechanical physics? "Ignore for friction" and all that?
Sheesh.
And don't get me started with your skateboard "experiment".
relax dude, i didn't mean to discredit the logic, i just have problems understanding what parts of an analogy should be ignored. Its one of my flaws.
There is also the possibility that they're not really telling us how it works, and have something completely different.
I'm not sure I follow. You mean they're offering a bogus explanation that violates Newton's first law, and keeping the "real" explanation a secret?
Why would they do that?
No idea, just brainstorming.
I keep reading this title as "Emodrives, in MY Universe?"
Quote from: Cain on February 09, 2009, 04:10:11 PM
I keep reading this title as "Emodrives, in MY Universe?"
Powered by cutting themselves and crying.
Unfortunately as a side effect the decay of this energy source creates emo albums and poetry with exceptionally long half lives, which can pollute the environment.
This gives a whole new meaning to "cutting the power".
Though the resistence of an EMO unit is much lower than most materials, thus providing an overall energy gain as it doesn't take much energy to get through any number of EMO's.
Sort of kind of on topic, a friend who was into some project involving von neumann probes once asked me if I had any ideas for liftoff from asteroids/small planetoids. I came up with this off the top of my head, and I'm sure that it's probably total nonworking BS, but I'm not sure that it IS total nonworking BS.
You have two metal parabolic dishes, one on the top of the launch pad and one on the bottom of the 'ship'. They line up perfectly. You make an imperfect vacuum seal (assuming that there's some level of atmosphere), just enough to put stress on both dishes. The dish on the launch pad contains a powerful rare-earth magnet, and to create more stress, a powerful electromagnet is turned on on the bottom of the 'ship' with the polarity pulling it towards the pad. At a certain point, a spark gap is turned on (the hall effect, iirc, for a small amount of lift), and shortly afterwards, the polarity is suddenly reversed on the electromagnet, getting: 1) a push from the magnet, 2) a slingshot effect from the pressure of both dishes, and 3) the hall effect using ionization for maintaining some level of lift.
This wouldn't work on anything with no atmosphere. I don't plan to do the math to work out whether or not it would work anywhere in particular.