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Everything posted by Markus Hanke

Requirement for two "nows" to grasp the idea of Simultaneity
Markus Hanke replied to tar's topic in Relativity
That’s not true  relativity of simultaneity is explicitly about distant simultaneity, ie events and observers at different spatial coordinates. Within the mathematical treatment, this spatial separation as well as the finite propagation speed of light are explicitly accounted for within the necessary Lorentz transformation. 
Mass is what usually comes to mind first  but it’s important to realise that other forms of energy also have gravitational effects. Examples are pressure, stresses and strains within materials; electromagnetic fields; and even the gravitational field itself acts (at least in some sense) as its own source. Hence, gravity is a lot richer and more complicated than the simplified picture most of us are taught in school.

I think you are missing the point entirely throughout this discussion  quantum object “are” neither waves nor particles, nor are they both or neither. You are attempting to shoehorn something that isn’t classical into a classical category. The point is that quantum objects sometimes exhibit particlelike behaviour, and sometimes wavelike behaviour, depending on the relationship between the object and the observer; this is called contextuality. It is meaningless to say that a quantum object “is” something or “has” certain properties, unless within the context of interaction with another system. These aspects are relational in nature, not ontic. A limited analogy (!) in the classical world would be electromagnetic fields  sometimes you see magnetic fields, sometimes electrical ones, and sometimes a mix  depending on the relationship between observer and source. But the underlying entity is the electromagnetic field, which “is” neither of these. Waveparticle duality is similar, except that now you are in the quantum world, so you have to also consider counterfactual definiteness.

Apologies if that was how it came across, that wasn’t the intention. Of course there are other aspects  besides noncommutative observables there is superposition of states, and the violation of Bell’s theorem which implies there are correlations which are stronger than classically allowed. I don’t think these things are wholly independent though. Of course. But we are talking about observables of the theory, which these are not.

Question: Does the Double Slit Experiment prove Free Will?
Markus Hanke replied to 22675728's topic in Quantum Theory
No sentience is required either. An observer in the QM sense is simply an external physical system interacting with the setup. 
Question: Does the Double Slit Experiment prove Free Will?
Markus Hanke replied to 22675728's topic in Quantum Theory
So long as the relationship between emitter and observer remains the same, the particles are subject to the same probability distribution. You don’t need human involvement. You can just set this up and let it run without a human observer being present; the result is the same. 
That’s right...nonetheless there is a clear conceptual cut at the end of the inflationary epoch. Inflation itself is a bit speculative; we don’t have a GUT, just a bunch of candidate models; and we don’t have a model of quantum gravity that would describe physics at the Planck epoch either (again just some candidate models). So everything prior to the electroweak epoch is either speculative, or unknown.

Actually, it’s domain only starts at 10^(32)s, which is the end of the inflationary epoch. What happened before is speculative at best, and, once you get to the Planck epoch, simply unknown.

I think clarification is in order. Firstly, I was the one who posted this, not iNow. Secondly, I said only that ‘the world is essentially quantum’  a statement I do stand by. What I meant by this, in the context of the discussion, is that there is no ontological difference between the macroscopic and the microscopic world; what is different is only the degree by which these domains are subject to decoherence; the larger the system, the more quickly it will generally decohere. This is why you don’t normally observe interference effects in the macro world. Classical mechanics is thus an effective description in the macro domain. But do remember that there is no law forbidding such effects  if you can find a way to delay decoherence for long enough, even macro objects would in principle exhibit such behaviour, at least for a short time. This is an engineering problem, not one of fundamental physics. I don’t believe that this is really in contention. None of this implies that ‘everything is quantised’, which clearly it is not. Even in standard QM the spectrum of hermitian operators is continuous until you impose boundary conditions on your evolution equation  it’s only this that yields discreteness of observables. Quantumness does not necessarily equal discreteness; it means primarily that there are pairs of observables that do not commute. And yes, I fully agree that quantisation of spacetime is very much under debate. I did not mean to imply otherwise.

Is spatial distance just a classical concept?
Markus Hanke replied to geordief's topic in Modern and Theoretical Physics
It should also be mentioned that the spacetime interval of Special Relativity is a crucial building block of quantum field theory. You couldn’t have the Standard Model without SR. 
Fundamentally, the world is quantum, irrespective of the size of the system you are looking at. The problem is just that superposition of states can persist only as long as no observation takes place, which means as long as the system does not interact with its environment (‘decoherence’). And the larger the size of a system, the harder it is to keep it isolated, and thus the more rapidly it decoheres. That’s the only reason why you never see quantum effects in the macroscopic world. There is no sharp ontological boundary between quantum and classical  the distinction is a relational one.

The Schrödinger's cat thought experiment proves there is no God
Markus Hanke replied to VenusPrincess's topic in Religion
Seems to me that this is a bit off topic for this thread...? Anyway, I don’t think anyone doubts the existence of NDEs, they are a well documented phenomenon. The question is why you feel the need to give them a supernatural interpretation? It seems clear that such experiences would feel very powerful, and I’m sure they have a deep impact on the experiencer  but that doesn’t mean they are of supernatural origin. 
Question: Does the Double Slit Experiment prove Free Will?
Markus Hanke replied to 22675728's topic in Quantum Theory
You don’t need to use light, you can use any type of quantum object (electrons, protons,...), or even something as large as a C60 molecule. The result is always the same  you get individual local hits on the screen (particle), and many such dots will over time produce an interference pattern. This is true also if the emitter only produces one such object at a time. 
To me entanglement is a correlation between measurement outcomes, due to nonseparability of the system. Note that nonseparability does not equal nonlocality. Also note that it is meaningless to talk of ‘correlation’ in a quantum system unless there’s an observer there who measures both parts, and compares results (remember counterfactual definiteness)  thus entanglement is a relationship between parts as much as a relationship of a system with its environment. Lastly, an entangled system seems to me a good example of where reductionism arguably becomes problematic, because knowledge of the system does not imply knowledge of the parts. You need to know the correlation plus at least one measurement outcome on one part.

The equivalence principle and weightlessness.
Markus Hanke replied to geordief's topic in Relativity
The metric which describes largescale spacetime of the universe does not resemble a ‘gravity well’. 
The equivalence principle and weightlessness.
Markus Hanke replied to geordief's topic in Relativity
Yes, indeed. That’s an example of tidal gravity. As a general rule of thumb, “local” means a region in the order of ~1/g, so near Earth’s surface for example it would be a box no larger than ~10cm. But of course it depends on your required level of accuracy. I think the recent spread of FET has more to do with the algorithms on social media platforms such as YouTube, than with understandings of gravity. 
How can Space, the volume of the Universe, be bent?
Markus Hanke replied to Conscious Energy's topic in General Philosophy
It is not constant, it is invariant. That’s a really important difference! The other thing is that this invariance is a local statement. If you send EM radiation through a larger region of curved spacetime, and you naively calculate the speed using your own clocks and rulers, you will come out with a smaller value  this is called Shapiro delay, and is one of the classic tests of GR. Nonetheless, the speed remains at exactly c at each point of the trajectory taken. That’s because what changes is the relationship between events in spacetime  not Maxwell’s equations. 
The equivalence principle and weightlessness.
Markus Hanke replied to geordief's topic in Relativity
Yes indeed. There wouldn’t be any purely local way to tell, but you can construct some scheme that relies on outside references, or on longerlasting measurements (to detect tidal forces). 
I don’t know if there is any objective definition of the term. Personally I would use it only in cases where there are demonstrable neurological differences (as the term itself implies), such as is the case for for autism, or Down Syndrom; the profiles here are often spiky, meaning they have large variations between traits. A single outlier on an otherwise typical profile doesn’t qualify, in my opinion.