exchemist

Yes, there are two lengths, if you like. The point about relativity, which you seem not to have absorbed, is that measurements of length (and time) are not absolute. There is no single "true" value for them. Any measurement of them depends on the viewpoint (frame of reference) from which they are measured and all are equally "true". If you still can't grasp this I suggest going back to your books and reading carefully what relativity says. Nothing can inhabit two different reference frames at once. So you can't do QM (for example) from the viewpoint of two different reference frames at once either. Which means that relativity does not lead to a superposition of states, as you originally suggested.

I don't know where you are, but in the UK university lecturers are as poor as church mice. And you have to do decent research as well, as @CharonY points out. People do it for love of the subject rather than for financial reward. But I take your point that university students don't require such a large amount of sheer teaching expertise as schoolteachers do.

Incorrect. What you "know" is that, due to the relative motion between your 2 reference frames, you expect a difference in these measured lengths, depending on the reference frame choose to consider. You do not "know" 2 incompatible things, for the simple reason that you cannot be simultaneously in both reference frames at once. Rather obviously.

"Clearly", ballocks. If you change reference frames you start your QM analysis again, with the length ruler appropriate to that frame. You only have a superposition if you have 2 states that are mixed. But in either reference frame, you have only one state. This is why I keep telling you that you can't somehow stand outside these frames of reference when you apply your QM, and say "Look, there are 2 different states". I repeat: any application of physics has to assume some frame of reference, from which it takes its dimensional yardsticks. You cannot use two different ones at once.

You are not making much sense now. I have tried to explain to you why length contraction does not imply any superposition. Nothing is changed, as far as QM is concerned, by one spatial dimension appearing foreshortened in one frame of reference relative to another one. You can't do QM outside a frame of reference, any more than you can do any other physics outside one. A frame of reference is always presumed, either explicitly or implicitly. So in your example, you are in one or the other and your QM maths will come out the same in both, with, say, the x dimension a bit squashed in one compared to the other. That's all. From your other response it looks as if you are labouring under the misapprehension that there is some "intrinsic" or "real" length and that observations made from other frames of reference are an illusion or distortion. This is wrong. I think it is the source of your confusion.

The issue with that is that it will be >50% teaching and <50% science. I mean, you really need to have a skill at communicating, and be able to handle a room full of kids and so on. That's a skill that not everyone has, by any means, and it is quite exhausting. Also it is notoriously poorly paid. But handing on the torch of knowledge to the next generation can be very rewarding. No one forgets an inspirational teacher. Or a really crap one, come to think of it........

Hoho. But it's not a subject as such, to the extent that there are teachers employed to teach astronomy, so far as I know. But I'd be interested to hear what, um, Kevin has to say - and how he expresses himself.

So, um, Kevin, if you have no links with certain schools, are there some schools that you do have links with? I was not aware that astronomy featured in the UK school curriculum.

Far from it. Temperature is often quoted as an example of an emergent phenomenon, yet we know exactly how it arises. As I understand it, it is meaningless to speak of the temperature of an individual molecule, because temperature applies to an assembly of molecules, statistically large enough to form a Boltzmann distribution, in which the probabilities of each state the molecules can occupy is proportional to exp(-e/kT), T being the temperature. Other bulk properties of matter that arise from statistical distributions of atomic-scale entities - and there are lots of them - would be similar.

Thanks. That's informative. What they call the Breeding Blanket seems to be the crucial component. That has led me to this paper,https://nucleus-new.iaea.org/sites/fusionportal/Shared Documents/FEC 2016/fec2016-preprints/preprint0228.pdf according to which ITER will test a design for this blanket, which will then have to be scaled up and proved in something called DEMO, which is a reactor to be built only if and when ITER succeeds in achieving stable fusion. It seems to me it is going to take several further decades of development work before we have commercial fusion power. If we ever get there.

OK I understand. But they are not in 2 locations. Each observer sees them in only one location. Do not fall into the trap of thinking that one can somehow stand outside this scenario and see both at once, or that these observers are seeing two different "distortions" of some "true" version. A system always has to be analysed from one frame of reference or another. You can do QM in either reference frame and in neither of them will any superposition arise. But you can't do QM in some imaginary space that stands outside reality and can see both perspectives at once.

For each observer all lengths, along the direction of relative motion, are affected equally. If we call it the x direction and say it is foreshortened for one observer, compared to the other, then it means that wherever x appears in the wave equation x is shorter. So the probability cloud of the particle is foreshortened, etc. Hence it does not cause anything to "overlap" that was not overlapping before. Quantum superposition, however, does not in any case refer to particles physically overlapping one another. That requires another discussion.

I suppose that, to be fair, an initial Q factor of 10 to break even would start dropping as the power of the thing increased. I would expect the power absorbed by all the ancillary systems to become less, as a proportion of the total, as the power output increases. But I still miss any serious discussion of how a practical power extraction and generation system would be designed. Would it be by intercepting the neutrons in some moderator shell construction, surrounding the torus, that gets hot, and raising steam from that? Or would it be by intercepting radiant heat emitted by the plasma itself ? If the latter, how, given that the torus is surrounded by (I think?) superconducting magnets that have to kept very cold? Do you have any idea? It sounds to me like a difficult engineering challenge.

No, the link I provided was mainly focused on ITER and confirms the number for JET. So it's about tokamaks. But it does seem that the numbers for inertial confinement systems are even worse. Tell me, how does the heat exchange from this plasma to a steam boiler work? Has anyone produced a design yet for this? I don't think I've seen any steam pipes anywhere, wrapped around the torus, in any of the tokamak designs, but I don't pretend to have followed it all very closely. The torus seems to be festooned in magnets and cables in every picture I've seen.

Yes. And as far as I am aware, little to no work has yet been done on how to get the energy out of the plasma, once it exceeds break-even. So it seems to me there is a hell of along way to go. Here is one link that goes into it. https://whyy.org/segments/fusion-energy/ The energy you actually input to the plasma is only a fraction of the energy needed to drive all the systems at the facility. And then the energy output from the plasma goes through various lossy processes, including a Carnot efficiency factor (<50%) in the steam turbine or whatever heat engine is used to convert heat to electricity. According to this article, to break even and become a net provider of electricity to the grid, you will need a Q factor of around 10. With laser "inertial confinement" systems it is even worse, apparently. (The article also corroborates @Prometheus's figure of 0.01 (1%) for JET.)

On what basis do you welcome us? You've only just joined. And who is "we", please?

I'm not quite sure what you mean by "peer-reviewed" in this case. Peer review is a process carried out when a piece of research is written up and submitted for publication, to make sure the research is sound and properly explained. In your case, you haven't written up or otherwise dlsclosed the details of your device, as you don't want to put it into the public domain. So how can anyone review it? You seem, rather, to be inviting the people here to just agree with you that it is possible to have a reactionless thruster, when on the face of it it isn't. Obviously we are not going to do that. Hence the scepticism about your claims and the attempts to guess at what is really going on in your device. I don't see any way out of the dilemma. Nobody can review a black box. Which is why, instead, I have been trying to dispel some of the misconceptions you seem to have about the physics of the setup, without asking you to reveal too many details. I am willing to carry on with that, as there are some issues left dangling at the moment. If you want to abandon that discussion then fair enough, but I think the responses you are going to get anywhere else will be similar to those here.

@Aquatek, I've answered your 3 questions and explained that momentum is conserved in inelastic collisions. Are you intending to respond, to explain why you asked me those questions?

My use of the term "addendum", in the 4th post of this thread, was qualified to make clear it was not intended to signify something added algebraically. Let's not descend to word games.

Why not make it a dwarf-throwing contest, to get some of that true Antipodean flavour?

Shall we see how many posts we can generate on this fascinating topic? 😃 Exactly. But it's just not how I have generally thought about it, given that we tend to use algebraic expressions without units until we have a specific application for them.

As an addendum, in the form of a piece of explanatory text, rather than as part of the algebraic expression. This I think is how most people see them. But logically you must be right, I think.

Oh I'm not complaining about him. He was a good tutor and still remembers me when I show up for college functions. I remember once I was reading a book about electron spin resonance and querying something I didn't understand, which also baffled him, so he picked up the phone and just rang the author (a don at another college) - and got the answer on the spot! I thought that was pretty cool. By the way, nothing gay about him: he even tried to get my then girlfriend into bed, at one point....(it was the 70s)

Bye bye Theorist, Amber, Tyler Shaw, Spencer 666, TheBrokenSoul, Sustainer, James Blunt, etc., etc., etc. Until next time, eh? 😉

I remember one physical chemistry tutorial in which white rum (!) was broached at about 3pm and I staggered out of the door at 7, to get my gown for dinner, and really had to concentrate quite hard not to bump into either of the doorposts, thinking : "left a bit, right a bit, right a bit more, no right you fool, steady.........." etc. But that tutor was notorious. And it was the 70s: things will be more strait-laced now. He's still alive, amazingly, after all that liver abuse.