Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

nextbigfuture.com

Post reply on HN
Print view View original

31–38 of 38 posts

Re: New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

#31

Post by duckingtest »

witty_username wrote: post #26
duckingtest wrote: post #25

Earlier quoted context omitted.

How do you know that? Consider a pretty simple and obviously correct device: an electric engine with an internal rotating shaft + a solar panel to power it, floating in space. The faster it rotates, the higher its acceleration in the gravitational field.

The engine would spin, but it would have 0 velocity unless it sent out something as exhaust.

That's not how general relativity works. Spinning would increase its energy, hence increasing its gravitational pull, hence accelerating faster.

Re: New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

#33

Post by EvgeniyZh »

Pfhreak wrote: post #10

The file name is: Q-Thruster In-Vacuum Fall 2015 Test Report.pdf That hardly suggests that there's a new Emdrive paper, and the linked blog doesn't have sufficient detail about the paper to suggest that the paper is new either.

There is PDF file. You can read and check if it's new or not.

Re: New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

#34

Post by EvgeniyZh »

maverick_iceman wrote: post #12
StanislavPetrov wrote: post #8

Earlier quoted context omitted.

Its amazing to me how many people who purportedly believe in science act more like priests than scientists. Science is about drawing conclusions from empirical data, not ignoring empirical data that doesn't jive with your predetermined conclusions.

The science is pretty settled here. No such thing can exist by laws of physics. You might as well try making a perpetual motion machine or homeopathic medicine.

Scientific method say that if observation contradicts your theory, then your theory is wrong.

Re: New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

#35

Post by witty_username »

duckingtest wrote: post #31
witty_username wrote: post #26

Earlier quoted context omitted.

The engine would spin, but it would have 0 velocity unless it sent out something as exhaust.

That's not how general relativity works. Spinning would increase its energy, hence increasing its gravitational pull, hence accelerating faster.

But momentum conservation holds in GR.

I don't know GR, but approximately the Earth would also accelerate faster.

Re: New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

#36

Post by duckingtest »

witty_username wrote: post #35
duckingtest wrote: post #31

Earlier quoted context omitted.

That's not how general relativity works. Spinning would increase its energy, hence increasing its gravitational pull, hence accelerating faster.

But momentum conservation holds in GR. I don't know GR, but approximately the Earth would also accelerate faster.

Conservation of momentum only works because the gravitational field itself is supposed to have momentum. Similar to how momentum is conserved for an accelerating paddling boat only if you include the sea. Sea analogy is a good one I think, especially because the gravitational field interacts with itself, like water, contrary to electromagnetic fields.

Conservation laws in general are a quirky thing in GR, see: http://people.bu.edu/gorelik/ES_GG_Conservation_Laws.pdf

or http://www.preposterousuniverse.com/blog/2010/02/22/energy-i... for a shorter read

>but approximately the Earth would also accelerate faster.

Well yes, Earth has a stronger gravitational pull because of rotation. On smaller distances rotation effects become even more interesting:

https://en.wikipedia.org/wiki/Frame-dragging

Re: New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

#37

Post by gus_massa »

maverick_iceman wrote: post #12
StanislavPetrov wrote: post #8

Earlier quoted context omitted.

Its amazing to me how many people who purportedly believe in science act more like priests than scientists. Science is about drawing conclusions from empirical data, not ignoring empirical data that doesn't jive with your predetermined conclusions.

The science is pretty settled here. No such thing can exist by laws of physics. You might as well try making a perpetual motion machine or homeopathic medicine.

Actually, IF this were true and they really were breaking the conservation of momentum law, then by special relativity in most of the reference frames they must be breaking the conservation of energy law.

So if this were true then they could build a perpetual motion machine too. IIRC one possible design was to put two em-drives with opposite directions at the opposite sides of a carousel.

[Disclaimer: I think that this is an experimental error and that the conservation of momentum and energy laws are safe.]

Re: New NASA Emdrive paper shows force of 1.2 millinewtons per kilowatt in a Vacuum

#38

Post by gus_massa »

EvgeniyZh wrote: post #34
maverick_iceman wrote: post #12

Earlier quoted context omitted.

The science is pretty settled here. No such thing can exist by laws of physics. You might as well try making a perpetual motion machine or homeopathic medicine.

Scientific method say that if observation contradicts your theory, then your theory is wrong.

One of the more important things that you learn in a laboratory is that experimental science is hard. There are many source of experimental errors.

So it's not enough to have an experimental result, it's necessary to check very carefully the details to be convinced that it breaks the theory.

In this case, the problem is that they are measuring a very small force, and many things can cause small forces. So you must be sure that all the other possible small forces sources are under check and that the force you are measuring is created by the method you are trying to measure.

In this case, the most obvious candidates for errors are:

* Thermal: The device gets very hot, so there may be some thermal expansions and some thermal air currents.

* Electromagnetic: They use a lot of current, so the wires that connect the device may be acting as an electromagnet or something.

They try to bound this error, but it's very hard to estimated correctly how big each one of them are, and prove that they are smaller than the force they see in the experiment.

Post reply on HN