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New tests cast doubt on 'impossible' EmDrive

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pallidin
20 hours ago, Waspie_Dwarf said:

This IS a controlled environment. What do you think would be more controlled than a laboratory? Space?

Now don't get uneccessarilly testy, Waspie... geeze.

I know the lab was a controlled environment, but I said a more controlled environment; refining the controls from what was learned or speculated. That's a valid comment.

There is nothing wrong with what I had said.

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Tom the Photon
On 25/05/2018 at 8:15 PM, pallidin said:

Now don't get uneccessarilly testy, Waspie... geeze.

I know the lab was a controlled environment, but I said a more controlled environment; refining the controls from what was learned or speculated. That's a valid comment.

There is nothing wrong with what I had said.

Much as I hate to agree with Waspie, this time he’s absolutely correct.

Some things are potentially possible, which is why the jury’s out on many issues like dark matter, multiverses, God, etc.  There’s no real harm in thinking about such ideas, even if little is to be gained from them.

Other things in science are simply not possible.  Perpetual motion machines do not exist.  Stone pyramids do not channel energy from distant stars.  Star patterns in the night sky do not determine our fates. 

An EM drive cannot work, as the idea violates conservation of momentum – a fundamental principle of the Universe.

Momentum is the most fundamental property of everything in the Universe, linking as it does mass, distance and time.  If two objects interact through a force they can exchange momentum.  As the forces on each object are the same magnitude, and the duration of the force is the same for both objects, the change in momentum of each is necessarily the same size.  No momentum is ever created or destroyed.

So why is there still any lingering hope that EM drives might work?  First of all it’s a brilliant dream – to travel through the Universe, explore stars and planets, find other lifeforms, mine asteroids of solid diamond, etc.  Furthermore the language used to describe EM drives is unintelligible to the layperson, leaving them to be swayed by whichever author they are reading at the time.

We’re not helped by diagrams like this (from Wikipedia):

220px-Emdrive_schematic.svg.png

 

On first inspection this seems plausible: with uniform pressure throughout the cavity, the force on the bigger window is indeed greater than that on the smaller one.  So why can’t it produce thrust?

I’m tempted to leave this post there, to see the quality of replies, and maybe offer a prize for the best answer…

…but instead here’s why!

Look at the slanted edges.  Picture microwave photons striking these vertically on the diagram.  Which way will they rebound?  They will reflect to the right, transferring momentum – and therefore force – to the left.  Do a little bit of maths and the extra force all these collisions create is equal to the difference between the two windows.  So: no net force, EM drive doesn’t move, QED.

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Tom the Photon
On 25/05/2018 at 9:15 AM, Srh25 said:

I thought this site was for dreamers of the unexplained, not some person bashing people for their creative idea's with his\her "apparently" extensive science knowledge. I would much rather read the idea's people throw out positively and discuss the possibilities. Not negative crap, quoting other's, then trying to bully your facts on them to make yourself seem smarter. I rarely post, but I read here a lot, and I would like for more positive comments after people's idea's. Instead of just trying to put them down with your idea of what's right or wrong. Be open people, I love all the different theories and idea's on all news\subjects here.

I totally agree with you: there's a lot of supercilious posting, pseudo-intellectual meanderings and pompous put-downs here.  There are a handful of cabals who cheer each other on, voting up even the most banal messages, revelling in their supposed intelligence and superiority.  I hope I don't come across like that - I always try to explain my contributions as carefully as possible.

But this topic isn't unexplained.  It's basic physics which is easy to understand (see my previous post).  Let's save our dreams and imaginations for the huge number of currently unexplainable topics still out there!

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bison

It's difficult to know what to make of the EM drive at this point. Even this latest refutation of its working is somewhat tentative. They propose to refine their test apparatus before firmly concluding that there is no unexplained directional force.

I agree that the laws of motion are very unlikely to be breakable. It occurs to me, though, that some unconsidered physical mechanism may be at work. Dr. Harold White, at NASA has discerned that a simple electrical charge may be able to warp space slightly. It's not inconceivable that some variant of this proposed electrical interaction with space-time is at work here.

Perhaps this is not very likely, but if we hope to progress beyond our current technical abilities, we will have to think along unusual, obscure, unlikely lines.  Powered, sustained flight was once considered by the experts of the day to be not merely unlikely, but impossible. We see what came of that. 

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Tom the Photon
3 hours ago, bison said:

It's difficult to know what to make of the EM drive at this point. Even this latest refutation of its working is somewhat tentative. They propose to refine their test apparatus before firmly concluding that there is no unexplained directional force.

I agree that the laws of motion are very unlikely to be breakable. It occurs to me, though, that some unconsidered physical mechanism may be at work. Dr. Harold White, at NASA has discerned that a simple electrical charge may be able to warp space slightly. It's not inconceivable that some variant of this proposed electrical interaction with space-time is at work here.

Perhaps this is not very likely, but if we hope to progress beyond our current technical abilities, we will have to think along unusual, obscure, unlikely lines.  Powered, sustained flight was once considered by the experts of the day to be not merely unlikely, but impossible. We see what came of that. 

Powered, sustained flight doesn't break any laws of physics!  It was just a matter of building engines light and powerful enough to achieve the speed to generate enough lift to overcome the weight of those engines plus wings and a load.  

 Dr White's work requires the existence of an entirely new form of matter that has never been detected.  This matter must have exactly the right properties to warp space-time around itself, notably it must have negative mass.  (This is totally different to antimatter which has positive mass but opposite charge.)  So much of the research and thinking in this field is speculative conjecture that I'm not optimistic they'll achieve anything soon.

I'm all for new ideas, as long as scientists and other proponents of novel concepts are honest about the limitations of their work and avoid sensational claims.

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bison

Lord Kelvin declared in 1895 that heavier than air flying machines were 'impossible'.  Being a very good physicist, he surely based that pronouncement on the laws of physics, as they were understood at that time. Note that he didn't say they were unworkable given current technical limitations. His statement is an unqualified 'impossible'. Eight years later, the Wright brothers performed the impossible.

Dr. White assures us that his test apparatus contains no exotic matter. He has explained why he believes that a simple electrical charge, contained in a ring of capacitors, may be able to warp space to a very slight, but still measurable degree. Dr. White reports some intriguing results, not only in his own experiments, but those of an independent laboratory, as well. He is reported to be improving his experiment, so as to better differentiate between results indicating a true space warp, and those due to experimental noise.  

  

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Tom the Photon
On 04/06/2018 at 9:43 PM, bison said:

Lord Kelvin declared in 1895 that heavier than air flying machines were 'impossible'.  Being a very good physicist, he surely based that pronouncement on the laws of physics, as they were understood at that time. Note that he didn't say they were unworkable given current technical limitations. His statement is an unqualified 'impossible'. Eight years later, the Wright brothers performed the impossible.

Dr. White assures us that his test apparatus contains no exotic matter. He has explained why he believes that a simple electrical charge, contained in a ring of capacitors, may be able to warp space to a very slight, but still measurable degree. Dr. White reports some intriguing results, not only in his own experiments, but those of an independent laboratory, as well. He is reported to be improving his experiment, so as to better differentiate between results indicating a true space warp, and those due to experimental noise.  

  

Didn't Kelvin also famously state words to the extent that "there is nothing more to be discovered in science" weeks before X-rays and radioactivity were discovered?

Thanks for the update on Dr White - I'll make time to read his work in depth and won't comment again unless I think I understand it.

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