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"The EmDrive Just Won't Die"


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27 minutes ago, damerell said:

That seems completely extraordinary. We have no evidence whatsoever of causality violation - and, while this is a slightly pat argument, if _is_ possible, it's not just that it hasn't been done _yet_. To suppose it is possible for the sake of not recognising FTL is impossible is not sensible.

It's not about evidence, our mathematical model doesn't require global causality. We're not supposing to it is possible for the sake of anything, we just look at the current field theory and say "hey, there's nothing in there that really requires global causality". That's it. To suppose it's impossible, based on available theoretical work, is not sensible, because such a position is unsupported by the theories in question. This means, BTW, that we have no real evidence, experimental or theoretical, against causality violation, either. Absence of evidence is not evidence of absence.

How would evidence of such a phenomenon look like, anyway? Detecting a causality violation would be very difficult, just like detecting a closed timelike loop. How do you know it isn't happening "all the time" (whatever that even means in this context), and we just aren't equipped to perceive it? This is most definitely the case with relativistic effects, after all. Indeed, this is another category of counterintuitive spacetime shenanigans, although in that case they can be measured with two good clocks and a fast airplane.

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On 9/13/2020 at 5:31 AM, Dragon01 said:

A small waste is still a waste, it's wrong on principle, and harm may be small, but it's very much real.

CIA tested cat-bugging in the 60s.

The other thing to Space Exploration that pushes *anything* forward is Intelligence™.

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9 minutes ago, Dragon01 said:

Training it, as anyone who's ever been owned by a cat knows, is one of those problems that no amount of money could solve. :) 

Article claims the other way...

 

But yeah. Honestly I'm willing to bet they're in it for other stuff as well, it is an RF resonator after all. Could be a disguise for other stuff too.

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11 hours ago, damerell said:

If any leg of that triangle is going to give, I'd go for relativity, which does at least have a few problems around the edges like all this spooky dark matter whizzing about.

If GR is broken, so is Standard Model. Which means absolutely ALL of physics. That's not the weak link here.

And conditions for causality violation in GR are extraordinary. We had many decades between black holes being a purely math prediction of GR to actually discovering them, and in that time, you could have made the same argument you're making now that they're just a math artifact. Conditions for causality violations would have to at a minimum involve collisions of such objects, and we've only been able to detect these for a few years. Give it time.

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2 hours ago, DerekL1963 said:

Cats absolutely can be trained.  Problem is, most people suck at training animals.

anyone who says its hard to herd cats have never tried to make a tuna sandwhich in their presence. you cant open a can of anything without them showing up to investigate. 

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On 9/28/2020 at 5:22 AM, Nuke said:

you cant open a can of anything without them showing up to investigate. 

Investigators usually have the good sense not to disturb a scene. Meanwhile, I have an orange paw in my ham sandwich every morning.

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On 9/27/2020 at 3:13 PM, Dragon01 said:

It's not about evidence, our mathematical model doesn't require global causality. We're not supposing to it is possible for the sake of anything, we just look at the current field theory and say "hey, there's nothing in there that really requires global causality". That's it. To suppose it's impossible, based on available theoretical work, is not sensible, because such a position is unsupported by the theories in question. This means, BTW, that we have no real evidence, experimental or theoretical, against causality violation, either. Absence of evidence is not evidence of absence.

How would evidence of such a phenomenon look like, anyway? Detecting a causality violation would be very difficult, just like detecting a closed timelike loop. How do you know it isn't happening "all the time" (whatever that even means in this context), and we just aren't equipped to perceive it? This is most definitely the case with relativistic effects, after all. Indeed, this is another category of counterintuitive spacetime shenanigans, although in that case they can be measured with two good clocks and a fast airplane.

Maybe it's not formal evidence, but if causality violations were happening commonplace, I believe we'd see many more things that didn't make sense. And with so many physicists et al looking pretty closely at so many things, wouldn't it be likely that we'd notice?

Which may only relegate causal violations to "rare but possible" like "forbidden" transitions seen in physics (eg: how lasers work) but I think if they were common, we'd see it.

Lack of evidence is not evidence of absence, but it is a pretty strong indicator when so much effort is spent on observation.

The fact that the scientific method exists does support a causal universe. If acausality were truly discovered, we'd have to come up with a very, very good explanation as to why so many things appear causal in spite of that.

Now none of that is proof, but it shows that just because it is hard to prove something doesn't exist, it would still take extraordinary evidence to prove it did, or even to suspect it.

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4 hours ago, p1t1o said:

Maybe it's not formal evidence, but if causality violations were happening commonplace, I believe we'd see many more things that didn't make sense. And with so many physicists et al looking pretty closely at so many things, wouldn't it be likely that we'd notice?

Would we? In Quantum Field Theory, when we are evaluating particle interactions and have to add up al possible exchanges, we include FTL ones to get the right answers. We also include ones going back in time, and simply count them as antiparticles. If microscopic causality violations are simply part of particle dynamics and macroscopic ones require astrnomic events, but are localized phenomena even then, how are we suposed to detect it?

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Just now, K^2 said:

Would we? In Quantum Field Theory, when we are evaluating particle interactions and have to add up al possible exchanges, we include FTL ones to get the right answers. We also include ones going back in time, and simply count them as antiparticles. If microscopic causality violations are simply part of particle dynamics and macroscopic ones require astrnomic events, but are localized phenomena even then, how are we suposed to detect it?

 

There are MANY things we cannot detect or even see ithat exist.

The more we know, the more we will realize how little we know.

The universe has an awful lot of secrets.

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1 hour ago, K^2 said:

Would we? In Quantum Field Theory, when we are evaluating particle interactions and have to add up al possible exchanges, we include FTL ones to get the right answers. We also include ones going back in time, and simply count them as antiparticles. If microscopic causality violations are simply part of particle dynamics and macroscopic ones require astrnomic events, but are localized phenomena even then, how are we suposed to detect it?

I don't know much about QFT.  I know that in GR a particle cannot go FTL, but is that not really a problem in QFT?  -- If so, is this actually a particle that can be said to travel at L plus/times some number, or is this more in line with universal gravitation?

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2 hours ago, JoeSchmuckatelli said:

I don't know much about QFT.  I know that in GR a particle cannot go FTL, but is that not really a problem in QFT?  -- If so, is this actually a particle that can be said to travel at L plus/times some number, or is this more in line with universal gravitation?

Well, I've heard it postulated that there is only a single electron in the universe. It goes back and forth in time, and when it goes back, we see it as an antielectron, and when it goes forward, it looks like a normal electron. :) AFAIK, this is fully in agreement with QFT. 

Of course, this leaves us with the question of "why are there more electrons than positrons?", but other theories have problems answering that one, too, seeing as that is one of the major unsolved problems in modern cosmology.

7 hours ago, p1t1o said:

Now none of that is proof, but it shows that just because it is hard to prove something doesn't exist, it would still take extraordinary evidence to prove it did, or even to suspect it.

We have such evidence, up to you if you'd call it extraordinary (it certainly took some impressive experimental setups to get). We have a theory (QFT) that includes it as an integral component, a theory that agrees, for most part, with experimental results. That's evidence enough to suspect that this theory really has something in common with how the universe works, and as it happens, it includes FTL and time travel. :) 

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7 hours ago, JoeSchmuckatelli said:

I know that in GR a particle cannot go FTL, but is that not really a problem in QFT?  -- If so, is this actually a particle that can be said to travel at L plus/times some number, or is this more in line with universal gravitation?

Ooof, so that's a lot to unravel, actually. Part of it is that the word "time" means so many different things.

First, GR prohibits particles from traveling FTL locally. So if you take two objects close enough to each other that we can disregard space-time curvature, they can move at most with the speed of light relative to each other. Once you either increase the distance or start twisting space-time into a pretzel, you can actually change that. Again, case in point, expansion of the universe. Far-away galaxies are flying away from us at FTL speeds because space itself is stretching out between us at sufficient rate. And it's why we have FTL concepts like Alcubierre Drive in the first place.

In QFT, we treat space-time as flat. (Usually. There are field theories in curved space-time. Useful, for example, if you are talking about particle physics inside a neutron star.) So the causality violations in QFT are local, and it looks off the bat like an incompatibility between GR and QFT. And it sort of is, and is part of why Quantum Gravity is so flipping hard, but it's not actually a contradiction. General Relativity is a mean field theory. (Specifically it's a mean field approximation of a gauge field theory on the Poincare group.) That's a smarty-pants way of saying that GR inherently averages out motion of particles to a classical path.

You don't have to understand the full mind-melting madness of building a particle theory in curved space-time to gain some appreciation for how this works. Lets take the simplest particle represented as a field we all know. A photon. Light, or just electromagnetic radiation in general, is a great example, because we kind of have intuitive understanding of how light behaves. And it's also relatively easy to picture it as a wave, so that helps. First of all, just a touch of E&M. How does an electromagnetic wave propagate? When an electric field changes at a point, it induces a magnetic field around it. In turn, a change in magnetic field induces an electric field. So if you take a charged particle and start wiggling it, it results in an electric field nearby alternating, which causes the magnetic field to alternate, which causes the electric field further out to alternate, and so on. But the identity of the source doesn't really matter. Every point of space around the emitter results in its own spherical wave echo spreading in every direction.

So this is the kicker. What path does the electromagnetic wave take? It looks like it will take absolutely every possible path, as every point in space that gets excited by a wave produces its own spherical wave which excites all the nearby points of vacuum and so on. But we know from our every day experience that light doesn't normally just bend around to reach every corner of space. It appears to propagate out in straight lines, casting shadows. What gives? Well, you have to take into account interference. Electromagnetic wave has a phase. If the phases of two waves reaching the same point match, they add up. If they are exactly out of phase, they subtract from each other. As the wave is re-emitted by every point in space, the overall phase is related to the total distance traveled along the path. If we take all the possible paths, we get a random mixture of phases for all the possible distances, and an average of random selection of phases will add up to zero. So while light can be considered to take all possible paths, they all cancel each other out. Well, all except for a few special paths. This gets a touch mathy, and I don't know how to prove this in a straight forward way. The exact field of math is called Calculus of Variations. One of the results from it is that if you take a random path and slightly vary it, the length of the path will vary slightly, unless this path happens to be an extreme path. For light, in practice, it's always going to be the shortest path. When you take the shortest part between two points and make a slight deviation from it, the change in length is infinitesimal. What that means is that near the shortest path, there are infinitely many of tiny variations that all have the same phase. And that means that light traveling along the shortest path between any two points will not be canceled out. This is usually phrased differently: light always takes the shortest path between two points. The more general application of this principle to particle physics is known as Path Integral Formulation. In a more general representation of particles, instead of length of path the quantity we are interested in is called action, and if you ever wondered why Principle of Least Action exists, this is the root cause. A classical trajectory of a particle is a path along which action is stationary. And it's the reason why we have to consider particles as taking every possible path in space and time in QFT, and yet we arrive with a system where, when we take measurements, nothing goes at FTL speeds. There are a whole lot of caveats here, and I'm oversimplifying all over the place, but hopefully, it gives you some idea of why we can have QFT and GR and they say seemingly contradictory things, while being fundamentally derived from the same principles. QFT is the field theory over some fixed space-time structure, and GR is "averaged out" mean field theory of that space-time structure itself.

Does that mean that General Relativity will fall short in predicting certain phenomena? Yes, absolutely! GR fails miserably when you try to describe what happens to particles as they cross event horizon, for example. We have no formalism that can handle that exact case. And it's also why I'm cautious about claims regarding time travel and FTL. There's just enough gray area there to leave uncertainty. But there aren't any inherent problems with either that we know of yet.

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14 hours ago, K^2 said:

Does that mean that General Relativity will fall short in predicting certain phenomena? Yes, absolutely! GR fails miserably when you try to describe what happens to particles as they cross event horizon, for example. We have no formalism that can handle that exact case. And it's also why I'm cautious about claims regarding time travel and FTL. There's just enough gray area there to leave uncertainty. But there aren't any inherent problems with either that we know of yet.

If GR is correct, anything beyond the event horizon is non-falsifiable.  You might as well claim that any claims past the event horizon aren't scientific (or at least can only be so if GR is invalid in this case).

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46 minutes ago, wumpus said:

If GR is correct, anything beyond the event horizon is non-falsifiable.  You might as well claim that any claims past the event horizon aren't scientific (or at least can only be so if GR is invalid in this case).

I'm not sure that's actually strictly true. Certainly, if we treat black hole as static, immovable object, then yeah. No time-like curves lead out of the interior region. But hypothetically, if we start bending space-time with something even more extreme, it might be possible to make parts of the interior briefly accessible. And it might not require anything out of science fiction, either. For example, I'm not sure what will happen to a stellar black hole passing through ergosphere of a supermassive black hole with extreme angular momentum. Intuitively, I expect the event horizon of the former to shift and possibly even shrink, but I ain't doing the math on this one.

More relevant to what I was talking about, however, GR breaks down just outside the event horizon. Very, very close to it, but still on our side. And the particle dynamics there can be relevant to the way black holes emit Hawking radiation. So it's actually something physical, potentially measurable, and we are kind of guessing on, because we don't have the math to describe what actually happens there. Hawking himself suggested that whatever quantum soup is simmering just above the event horizon, it's probably key to squaring the fact that black holes emit radiation with cosmic censorship.

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It lives! 

Sorry... could not help myself.

Speaking regarding EM drive.

Seriously though, even if it's a fluke they just might learn something new they do not already know.

Compared to the complexities of politics and human ethics/laws, science is downright simple.

At least the rules do not shift back and forth nearly as much... not if it is GOOD science anyway.

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8 hours ago, Spacescifi said:

Compared to the complexities of politics and human ethics/laws, science is downright simple.

At least the rules do not shift back and forth nearly as much... not if it is GOOD science anyway.

It's clear that you never, ever had a good look into biology, nevermind studied it. :) Granted, the rules do not shift back and forth (usually), but we are discovering new ones all the time. Try working with that, no legislature could produce such a tangled, impenetrable mess that is a single human cell. Best of all, unlike legislatures, it works, and surprisingly smoothly, at that. 

Human-created systems are the ones that are simple. The real complexity starts when things have a few million years to evolve. Biology is layers upon layers of "temporary fixes" and incremental improvements, often to adapt to situations that are no longer even remotely relevant. Not only that, due to the way evolution works, the resulting mess is not only functional, but highly optimized for what it does. I'd say, human body is probably the most complex single system you can find on Earth.

Though physics is easy, too, compared to biology. There, you just have to wade through incomprehensible maths written in off-kilter notations, and be flexible enough to ditch any notions of intuitiveness and think purely in mathematical terms. Once you can do that, most physics is actually fairly straightforward, if a little mind-bending. :) 

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8 hours ago, Dragon01 said:

It's clear that you never, ever had a good look into biology, nevermind studied it. :) Granted, the rules do not shift back and forth (usually), but we are discovering new ones all the time. Try working with that, no legislature could produce such a tangled, impenetrable mess that is a single human cell. Best of all, unlike legislatures, it works, and surprisingly smoothly, at that. 

Human-created systems are the ones that are simple. The real complexity starts when things have a few million years to evolve. Biology is layers upon layers of "temporary fixes" and incremental improvements, often to adapt to situations that are no longer even remotely relevant. Not only that, due to the way evolution works, the resulting mess is not only functional, but highly optimized for what it does. I'd say, human body is probably the most complex single system you can find on Earth.

Though physics is easy, too, compared to biology. There, you just have to wade through incomprehensible maths written in off-kilter notations, and be flexible enough to ditch any notions of intuitiveness and think purely in mathematical terms. Once you can do that, most physics is actually fairly straightforward, if a little mind-bending. :) 

 

Have you heard of hyperbole? Exaggerating to make a point?

What I will say next is not hyperbole.

Does the universal laws really change or does man's understanding of them change or grow?

The universe does not adjust for man. Man must adjust to it, or otherwise attempt to bend the universe to his will.

 

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3 hours ago, Spacescifi said:

Does the universal laws really change or does man's understanding of them change or grow?

The universe does not adjust for man. Man must adjust to it, or otherwise attempt to bend the universe to his will.

Man's understanding of them grows, and it occasionally changes completely. Especially outside particle physics, where the models we have are pretty solid, and it's more likely that if a revolution happens as a results of those "small mathematical inconsistencies", it'll create a whole new field rather than upend the existing ones (just like relativity didn't really oust Newtonian mechanics, but opened up a whole new can of worms). Biology, OTOH, is pretty much in flux, with new discoveries sometimes upending our understanding of things we thought we've figured out quite well. Not even established theories are safe, see amyloid plaques in Alzheimer's disease. Underlying laws staying the same doesn't really help you much in such environment.

BTW, you'll do well to avoid hyperboles. If you need to exaggerate to make a point, you don't actually have a point. If you don't need to exaggerate, then don't, and the point will stand on its own. It's a dishonest rhetorical technique, typically a fare of snake oil peddlers such as real estate salesmen or politicians rather than serious debaters.

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2 minutes ago, Dragon01 said:

Man's understanding of them grows, and it occasionally changes completely. Especially outside particle physics, where the models we have are pretty solid, and it's more likely that if a revolution happens as a results of those "small mathematical inconsistencies", it'll create a whole new field rather than upend the existing ones (just like relativity didn't really oust Newtonian mechanics, but opened up a whole new can of worms). Biology, OTOH, is pretty much in flux, with new discoveries sometimes upending our understanding of things we thought we've figured out quite well. Not even established theories are safe, see amyloid plaques in Alzheimer's disease. Underlying laws staying the same doesn't really help you much in such environment.

BTW, you'll do well to avoid hyperboles. If you need to exaggerate to make a point, you don't actually have a point. If you don't need to exaggerate, then don't, and the point will stand on its own. It's a dishonest rhetorical technique, typically a fare of snake oil peddlers such as real estate salesmen or politicians rather than serious debaters.

Agree, biology I see as one of the breakthrough techs, like computers and steam engines changed the world. Ai is the other. 
Relativity is not very useful, its something you have to factor in for extreme accuracy.
On the other hand quantum effects are very useful as in mosfet transistors, see this as another growth area but less than neural nets at this time. 

 

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7 hours ago, Kerwood Floyd said:

I've read several times that GPS would not work well enough to be useful if they didn't take relativity into account.

Correct, but we don't really need to understand relativity to correct for it. Just measure that time on GPS satellites runs a little faster, observe that the difference is fairly consistent, and compensate for it.

Of course, the fact that we are actually using theoretical values predicted by General Relativity and it gives us the necessary precision is one of the proofs of the theory.

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1 hour ago, K^2 said:

Correct, but we don't really need to understand relativity to correct for it. Just measure that time on GPS satellites runs a little faster, observe that the difference is fairly consistent, and compensate for it.

Of course, the fact that we are actually using theoretical values predicted by General Relativity and it gives us the necessary precision is one of the proofs of the theory.

Yes it explained lots of weird stuff like the error with Mercury's orbit, how very short lived particles could reach the surface after getting created in the upper atmosphere, gravity lensing, later might end up as useful. 

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