Em drives

[kamaz]

Stop - MOND* does not model galaxy behavior correctly. Thats exactly the fallacy.

This is a misrepresentation of MOND. MOND has been fitted to galaxy rotation, yes, but then has been used to make accurate, ex-ante predictions related to galaxy evolution: 1, 2. If a theory makes an ex-ante prediction which is later positively verified, then it is generally accepted to be a sound theory.

Meanwhile, DM fails its ex-ante tests on galactic scale, each and every one of them. Heck, it even failed on the Bullet cluster: 1, 2.

Yes, LCDM works on extra-galactic scales, and can be fitted ex-post to work on galactic scales, so you can decide against modifications of inertia using Occam's razor. Problem is, the universe does not obey Occam's razor. If it did, there would be no tau neutrinos for example.

So as it stands, there's exactly zero basis to dismiss MiHsC a priori. Whether MiHsC is true is another matter, but it at least appears to be testable.

Next, it should be observed that your dismissal of MiHsC as Harry Potter stuff shows your incorrect use of Occam's razor. As it happens, MiHsC makes one assumption, and does away with Dark Matter, Dark Energy and explains em-drive to boot. So the MiHsC cosmology is objectively simpler then LCDM + (em-drive handwavium of your choice). Go figure.

Further, the invisible pink unicorn cosmology which you have proposed here is even simpler then MiHsC, because it also makes one assumption (everything is caused by invisible pink unicorns) and proceeds to explain everything, including the mood swings of my girlfriend. So that's the one which should be declared correct by your own criteria!

Now some question for you: If you can't see a mass, but can sense its gravity, does this mass exist or not?

That depends if my mass detector operates in a regime in which it is known to operate correctly. If yes, then the mass exists. If no, then the mass may, or may not, exist.

 

[Urwumpe]

Problem is, the universe does not obey Occam's razor.

If there could be any single sentence, to summarize why I can't agree with you, there it is. You can claim the invention.

The universe does not give a damn about any human model to explain it. MOND? Lambda-CDM? Intelligent design? Does it matter?

But you mistake the observed entity (universe) for the observer. Occams Razor does not exist to make the universe work. It exists as name tag for a large number of logical definitions, that all aim to find the most precise explanation of the universe.The universe would also be the same, regardless what you use for explaining it. Take unicorns. I can't just float one meter above ground by claiming to ride invisible unicorns. The universe does not care.

But what does not chance is, that any explanation of the universe should be absolutely functional, limited to just what is needed to explain it and what can be proven, and not add towers and columns to the building for decorating it.



Also you cite MOND proponents complaining that their pet theory had been beaten by its own argumentations and predictions, while Lambda CDM needed no modifications (OK, hardly impressive since you can simply claim to have more CDM locally - it requires a lot of math to prove that this kind of local CDM model is correct or not). What do you expect of them? They celebrate that the relativistic version of MOND needs only 20% of the CDM that Lambda CDM predicts there, while completely missing that MOND only exists to have a theory, that does not rely on CDM, since CDM can only indirectly be observed. I would call that an epic fail. In a few years, MOND proponents will celebrate to only need 99.999% of the CDM that Lambda-CDM uses.

I can tell you: Lambda-CDM has the better chances to prevail for a while and I strongly doubt, that any kind of MOND has any chance to replace it. Another theory will do so. A theory that we both can't even yet imagine in our wildest fantasies.

 

[kamaz]

From the chief MOND proponent himself:

The philosophy of science matters deeply here. One aspect of that is objectivity. One way we’re suppose to remain objective is through a priori predictions. I “grew up” with dark matter and remain more comfortable with it than with MOND. But it was MOND that predicted what I observed in low surface brightness galaxies, not CDM. Reporting that was simply a matter of intellectual honesty. [...]

MOND was obviously wrong and not worth considering. It required the direct shock of having it crop up in my own work to make me reconsider. My sin seems to have been taking successful predictions seriously rather than falling prey to the temptation of cognitive dissonance: to simply reject the evidence that didn’t fit with my pre-existing world view. Certainly that would have been easier, and better for my career. But if we do that, why bother doing science at all? [...]

 

[kamaz]

Thanks! I finally have a suitable forum avatar!

 

[RisingFury]

I thought this appropriate

 

[meson800]

CDM is preferred to MOND if CDM fails

1, 21, 2

LCDM

MiHsC

I looked at those URLs, but they mostly just talked about arguments for/against these alphabet soup of theories.

Is there a nice source to actually read about each of these theories?

 

[kamaz]

LCDM is the current standard cosmological model so any source will do starting from wiki http://en.wikipedia.org/wiki/Lambda-CDM_model

Introduction to MOND: [ame="http://en.wikipedia.org/wiki/Modified_Newtonian_dynamics"]Modified Newtonian dynamics - Wikipedia, the free encyclopedia[/ame] http://astroweb.case.edu/ssm/mond/ and http://www.scholarpedia.org/article/The_MOND_paradigm_of_modified_dynamics

Basic problem is this: galaxies rotate differently then they should under Newton's laws. To explain discrepancy, CDM introduces mass that we can't see (Dark Matter), while MOND modifies Newton's laws instead (thus eliminating, or at least reducing, the need for Dark Matter).

MiHsC is one guy's invention and he has a website here: http://physicsfromtheedge.blogspot.com/2014/01/mihsc-101.html . MiHsC is interesting because it appears he can derive both MOND and em-drive from his theory.

 

[Urwumpe]

Basic problem is this: galaxies rotate differently then they should under Newton's laws. To explain discrepancy, CDM introduces mass that we can't see (Dark Matter), ...

Exactly that tiny correction: The galaxies rotate differently then they should according to the visible mass distribution. That must not mean that the missing mass is only some obscure dark matter - the introduction of infrared astronomy meant that a lot of previously unaccounted mass was suddenly discovered, something that was previously invisible. Still not enough to explain the difference, but exactly that introduced the key question: How much right now invisible mass must be needed to account for difference?

The motion of galaxies in their clusters was until some years ago also unknown, today it has some huge error bars. But that motion also confirms that the galaxies are much heavier than by the observable matter, and the Lambda-CDM predictions fit well to the masses of the galaxies.

The real critical problem with Lambda-CDM is not dark matter actually. Its dark energy. It is the more mystical entity, that is far more ambundant than dark matter to explain what we see - but we still have no clue, what dark energy actually could be.

 

[Face]

This paper demonstrates how the postulated EM-Drive performance would not only violate the third law, but make it a free energy device, too. Given that even I can understand that, my opinion about the device wanders into "it's BS" area again.

IMO, either relativity, thermodynamics, or EM drive theory (or theories) is wrong. I think it is the later one.

 

[kamaz]

This paper demonstrates how the postulated EM-Drive performance would not only violate the third law, but make it a free energy device, too.

It's a straw man.

Experimenters including Shawyer himself claim that acceleration decreases as velocity increases ( http://emdrive.com/faq.html - Q7 ). Thus there is no violation of conservation of energy.

The REAL problem here is that dependence of acceleration on velocity requires either existence of an absolute reference frame (aether) or MOND.

https://www.reddit.com/r/EmDrive/comments/38cm2i/discussion_the_kinetic_energy_problem/

 

[Face]

Experimenters including Shawyer himself claim that acceleration decreases as velocity increases ( http://emdrive.com/faq.html - Q7 ). Thus there is no violation of conservation of energy.

The REAL problem here is that dependence of acceleration on velocity requires either existence of an absolute reference frame (aether) or MOND.

No evidence to this claim has been shown. And if we are into straws now, it sure feels like this is the one EMdrive theory supporters claw to: relativity is wrong, there must be an aether, despite countless experiments showing different evidence.

Of course this is possible, but the probability for it is very small, judging by how many experiments have been done - peer-reviewed and verified - that shows evidence that our theories of thermodynamics and relativity hold. Showing non-existence of anything is hard, so aether theorists may have a revival. :facepalm:

At first I thought this is exciting news, but now I am starting to see the crackpot nature of this stuff. I thought it would be cool to see this experiment in space to verify it, but now I can see how that would unfold: the experiment would yield no evidence for in-space propulsion, and immediately all supporters would jump on it and explain how the experiment was done wrong, how the experimenters are "government puppets" or somesuch, how we only need to tweak it some more to see something.

Perpetual motion machines all over again. Thanks, but no, thanks, and have a nice day. :tiphat:

 

[jedidia]

Experimenters including Shawyer himself claim that acceleration decreases as velocity increases ( http://emdrive.com/faq.html - Q7 ). Thus there is no violation of conservation of energy.

To be fair, his explanation sounds an awful lot like "the device will require more energy at higher velocities because otherwise it would be a perpetual motion machine". Like he knows that that is impossible, and the drive therefore must behave this way, although there is no clear reason why other than it's impossible to be otherwise.

 

[RisingFury]

It's a straw man.

Experimenters including Shawyer himself claim that acceleration decreases as velocity increases ( http://emdrive.com/faq.html - Q7 ). Thus there is no violation of conservation of energy.

Ooooo, that smells like a big pile right there!

The device doesn't know it's moving and it doesn't care it's moving. From its point of view, it's just doing its thing, providing thrust. And moving relative to WHAT?


If the device wasn't on shaky legs before, it is now...

 

[kamaz]

No evidence to this claim has been shown.

Untrue. Look at this video and observe that angular velocity of the rig is constant: https://www.youtube.com/watch?v=57q3_aRiUXs

---------- Post added at 02:07 PM ---------- Previous post was at 01:56 PM ----------

The device doesn't know it's moving and it doesn't care it's moving. From its point of view, it's just doing its thing, providing thrust. And moving relative to WHAT?

Precisely! That's why I said that the claimed behavior would require existence of an absolute reference frame. In other words, the paper Face posted is barking up the wrong tree. Conservation of energy is not the problem here, aether is.

---------- Post added at 02:11 PM ---------- Previous post was at 02:07 PM ----------

No evidence to this claim has been shown. And if we are into straws now, it sure feels like this is the one EMdrive theory supporters claw to: relativity is wrong, there must be an aether, despite countless experiments showing different evidence.

You are committing a philosophical error. Saying if em-drive works then relativity must be wrong is like saying if varistors work then Ohm's law must be wrong, and, conversely, varistors cannot exist and are a fraud:

 

[jedidia]

Conservation of energy is not the problem here, aether is.

Which is kind of on a similar level on the "the universe works completely different than past observations indicate" scale, no?

 

[meson800]

Experimenters including Shawyer himself claim that acceleration decreases as velocity increases ( http://emdrive.com/faq.html - Q7 ). Thus there is no violation of conservation of energy.

The REAL problem here is that dependence of acceleration on velocity requires either existence of an absolute reference frame (aether) or MOND.

Which frame does acceleration decrease in? If it's the frame of an external observer, then of course acceleration decreases as velocity increases, because relativity.

So I assume Shawyer is claiming acceleration decrease in the EM-drive frame? It's not clear which frame he's referring to on his website.

 

[kamaz]

Which is kind of on a similar level on the "the universe works completely different than past observations indicate" scale, no?

IF em-drive works, then there must be some way of accommodating it theoretically without throwing out entire physics.

Again, see the varistor example: you need band theory of solids to explain why it works and does not actually violate Ohm's law. But if you limit yourself to 19th century physics, then such device is literally impossible.

 

[Urwumpe]

IF em-drive works, then there must be some way of accommodating it theoretically without throwing out entire physics.

Again, see the varistor example: you need band theory of solids to explain why it works and does not actually violate Ohm's law. But if you limit yourself to 19th century physics, then such device is literally impossible.

There is one tiny problem with that analogy though - the Varistor does not violate Ohms laws. Ohm would have been terribly confused by a Varistor at first, but he would have been able to work with it.

You declare it to be impossible according to 19th century physics. Which is wrong. It did not exist for 19th century physics. But we still use the same Kirchhoff laws and Ohms law for describing the properties of Varistors, Transistors and other devices that are pretty exotic to school book electrics.

Please stop this kind of argumentation. The emDrive does not get better by making other things worse. Can ANY experimenter claim that he has a theory of the emDrive, that his experiment confirms? Currently, its absolutely not the case - their predictions (if any at all) and their measurements differ chaotically. As long as there is not even just a simple systematic difference between experiment and theory, it is maybe just a feedhorn with too much power.

 

[RisingFury]

Precisely! That's why I said that the claimed behavior would require existence of an absolute reference frame. In other words, the paper Face posted is barking up the wrong tree. Conservation of energy is not the problem here, aether is.

The conservation of energy is the problem!

The energy is measured relative to the frame in which the device was initially stationary... That's the problem! The device would need to produce less and less thrust relative to that frame and it can't do that.

But you don't need to measure energy relative to the initial frame, you can measure it relative to a frame in which the device is already moving. In that case, the energy in the device changes differently with time and the acceleration decreases differently.

So we're talking about two initial frames, one moving relative to the other which would see the device as decreasing its thrust purely because of its velocity.

You would see that at velocities not approaching the speed of light yet.

 

[kamaz]

Recall the equation given by McCulloch ( http://www.ptep-online.com/index_files/2015/PP-40-15.PDF )

and observe that the force is linearly dependent on on the Q-factor of the cavity.

If f0 is the resonance frequency of the cavity, and Q0 is the quality factor of the cavity at frequency f0, then the dependence of quality factor on operation frequency can be crudely approximated as

Q(f) = Q0*cos((f-f0)/fb*pi/2) for f0-fb < f < f0+fb
Q(f) = 0 otherwise

where 2*fb is system bandwidth.

Assuming that the on-board magnetron operates at frequency f0, then, for an observer standing on a parking lot next the em-driven spacecraft, the system operates at a reasonance frequency, and the Q-factor of the cavity is Q0, yielding a force F0. This force accelerates the spacecraft away from the observer with acceleration a0=F0/m, where m is the mass of the spacecraft.

Having accelerated, the spacecraft is now moving with with velocity v away from the observer still left on the parking lot. This means that the photons inside the cavity are now red-shifted with respect to the obsever, and have frequency fs instead of f0. Alternatively, one can say that the observer on the parking lot will see a frequency deviation of the on-board magnetron by:

fs - f0 = z * f0

where z is redshift:

z = sqrt( (1+v/c)/(1-v/c) ) - 1

or, for non-relativistic velocities, z = v/c.

This means that the Q-factor of the system for an Earth-bound observer is now:

Q(fs) = Q0*cos((fs-f0)/fb*pi/2)=Q0*cos((z*f0/fb*pi/2)=Q0*cos((v/c*f0/fb*pi/2)

And, the acceleration of the spacecraft as seen by observer left on the parking lot is:

as/a0 = cos(z * f0/fb * pi/2) = cos( v/c * f0/fb * pi/2 )

where a0 was the initial acceleration at v=0.

Note that as/a0 drops to zero as z*f0 approaches fb. So the maximum velocity of the spacecraft is

v_max = fb/f0 * c

Assuming a cavity with f0 = 1GHz and fb = 10kHz, v_max = 3km/s.