KJW

The problem with this reply is that it depends on precisely what an "unplugged" or "on" detector does to the light, the term "detector" not being sufficiently specific. It may be useful to consider the following: Suppose one places a horizontally oriented polariser in one slit, and a vertically oriented polariser in the other slit. Then there is no interference pattern even though no which-slit detection has been performed. Each photon has which-slit information by virtue of its polarisation, which is sufficient to prevent the interference pattern even when the polarisation is not measured. The quantum states from both slits are orthogonal, and there is no interference between orthogonal states. Perhaps you should also explore quantum eraser experiments. I'm quite confident about what I said... or are you telling me you can mathematically predict quantum outcomes?

It wasn't on "The Science Forum" but on an Australian forum that hasn't been running for years. The thread was started and had run its course before I had even joined the forum. I had looked at a few posts in the thread, but I don't think I contributed to it. It was a running joke on the forum to mention this thread because of the size of it. As you can imagine, it covered every conceivable aspect of the question. I doubt that it came to any definite conclusion, though.

On another now defunct science forum, there was a thread that was quite notable among forum members for being the longest thread in the history of the forum. It was titled: "What colour is an orange in the dark?"

This thread is titled "The Observer Effect", so in order to meaningfully discuss the observer effect, one needs to distinguish between observers playing a passive role and observers playing an active role. An active role means that the conscious observer somehow affects the measurement of the quantum system so as to collapse the wavefunction. A passive role means that the quantum system affects the measuring device in a way that produces a macroscopic state that through perception affects the mind of the conscious observer. As conscious observers, we have a somewhat solipsistic subjective point of view that needs to be taken into consideration when considering an objective reality. I'm not applying any "old misguided" concept of observing. I'm certainly not suggesting that it is some kind of physical influence. Indeed, I said precisely the opposite. That is why I consider it important to distinguish between the active and passive role. I hadn't really considered whether or not the measuring apparatus is doing anything to the quantum system. Wavefunction collapse is ultimately about what the quantum system is doing to the measuring apparatus. In the many-worlds interpretation, there is no wavefunction collapse and that a superposition of quantum states leads to a superposition of measuring apparatus states which leads to a superposition of observer states. It is the superposition of observer states, entangled with the superposition of measuring apparatus states and quantum states that is the essence of the many-worlds interpretation. The role of the observer is then to answer the question: why do we not observe the superposition of observer states, measuring apparatus states, and quantum states? You've indicated that the many-worlds interpretation is not falsifiable. The reason it is not falsifiable is because the many worlds are not observable (if they were observable, there would be no question about existence). Therefore, it is about observation. At the heart of the matter is where we draw the line between objective reality and subjective observation. There is nothing in the mathematics that says that a measurement selects one eigenstate from the set of possible eigenstates. The mathematics only identifies the set of eigenstates. The selection of a particular eigenstate from the set of eigenstates is artificially imposed on the basis of observation. The mathematics ultimately implies the many-worlds interpretation, or as it was originally called, the "relative state formulation".

As one attempts to separate the quarks in a proton, the force between them increases. Thus, there comes a point where there is so much energy that one or more quark-antiquark pairs are created. This results in one or more mesons being released, leaving behind some form of baryon (not necessarily a proton).

Yes, the observer does have an important role, though it is a passive role. We don't need observers, we are observers. Without observers, the measuring devices would still do their thing, only there would no longer be any need for the Copenhagen interpretation. The Copenhagen interpretation suggests that it is physics that determine the particular eigenstate that we observe, whereas the many-worlds interpretation implies that it is not physics but the observer that determines the particular eigenstate that we observe, simply through the act of observation. Because the microscopic quantum state, the macroscopic state of the measurement device, all the observers observing the measurement device, and the world that contains all of these are in an entangled state. Considering Schrödinger's cat, the cat becomes entangled with the radioactive source, and when I open the box, I become entangled with the cat and the radioactive source. By becoming entangled with the cat, I no longer observe the cat state and the radioactive source state as a superposition of states. Any other observers who observe the cat becomes entangled with the same cat state as me, as well as becoming entangled with me, and therefore observes the same cat state and radioactive source state as me.

It's not really an interpretation of an interpretation, but more like saying that the notion of the splitting of realities is a strawman that should not be used to reject the many-worlds interpretation of quantum mechanics. In truth, all I am saying is that in the Born rule, all the eigenstates exist, and that it is merely a first-person perspective that gives rise to the observation of only a single eigenstate. Although I am saying that the many worlds is the ontological reality, and that the Copenhagen interpretation is the subjective observation of the many worlds, I am not claiming to fully understand the precise details of the many worlds.

That's the problem with the requirement of falsifiability: Reality is not obligated to reveal itself in its entirety. It may be that the many worlds actually do exist, but are unobservable because they are mathematically orthogonal to each other. By rejecting the many worlds on the grounds that they are not falsifiable, one then has a reality that is inexplicable. I personally don't interpret the many-worlds interpretation as a splitting of realities each time a quantum decision is made. Instead, I regard all the spacetimes as existing from the very beginning, at least conceptually (I don't think reality is as simple as multiple spacetimes).

When a pure quantum state is measured, it is decomposed into a complex-number weighted sum of eigenstates. However, only a single eigenstate is observed as the result of the measurement, and this is chosen randomly with a probability based on the complex-number weighting of the eigenstate. If a large number of identical pure quantum states are identically measured, then the various eigenstates will be observed with their respective probabilities. For example, in the double-slit experiment, each spot corresponds to a random position eigenstate, but the accumulation of spots is an interference pattern resulting from each quantum state passing through both slits. In the Copenhagen interpretation, the pure quantum state collapses randomly to a single eigenstate, and the other possible eigenstates simply vanish. But in the many-worlds interpretation, the different versions of the observer in the different worlds observe all of the possible eigenstates. And because all the eigenstates are mutually orthogonal to each other, there is no interference between them, and thus the observer can observe only a single eigenstate and not the other versions of the observer.

\[ y = \int f(x) dx \]

Also, in the animal world, brightly coloured means dangerous. This is called "aposematism".

Continuing from my previous post: This can be further developed by manipulating the arbitrary constant to obtain: (ds)² = exp(k (t' – t'0))² ((c dt')² – (dx')² – (dy')² – (dz')²) where t'0 is an arbitrarily chosen value of t' at which the metric is locally Minkowskian For the general case: dƒ(t')/dt' = a(ƒ(t')) 1/a(ƒ(t')) dƒ(t')/dt' = 1 Let F(t) be such that: dF–1(t)/dt = 1/a(t) Then: F–1(ƒ(t')) = t' – t'0 where t'0 is an arbitrarily chosen value of t' ƒ(t') = F(t' – t'0) dƒ(t')/dt' = dF(t' – t'0)/dt' = A(t' – t'0) (ds)² = A(t' – t'0)² ((c dt')² – (dx')² – (dy')² – (dz')²)

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Fractional distillation under a vacuum is all I can offer. Yes, fatty acids found in nature do tend to have an even number of carbon atoms because they are biosynthesised from two-carbon units (acetyl-CoA).

No, it doesn't. Only the time coordinates are involved in the coordinate transformation. If the original metric describes a flat three-dimensional space, then the transformed metric will be a scalar function multiple of the Minkowskian metric: guv = ƒ(t) ηuv Consider: (ds)² = (c dt)² – a(t)² ((dx)² + (dy)² + (dz)²) t = ƒ(t') ; x = x' ; y = y' ; z = z' dt = ∂t/∂t' dt' + ∂t/∂x' dx' + ∂t/∂y' dy' + ∂t/∂z' dz' = dƒ(t')/dt' dt' dx = ∂x/∂t' dt' + ∂x/∂x' dx' + ∂x/∂y' dy' + ∂x/∂z' dz' = dx' dy = ∂y/∂t' dt' + ∂y/∂x' dx' + ∂y/∂y' dy' + ∂y/∂z' dz' = dy' dz = ∂z/∂t' dt' + ∂z/∂x' dx' + ∂z/∂y' dy' + ∂z/∂z' dz' = dz' dƒ(t')/dt' = a(ƒ(t')) Solve for ƒ(t'), then let A(t') = dƒ(t')/dt' = a(ƒ(t')) Then: (ds)² = A(t')² ((c dt')² – (dx')² – (dy')² – (dz')²) .............................. For example, let a(t) = k t. Then: (ds)² = (c dt)² – (k t)² ((dx)² + (dy)² + (dz)²) dƒ(t')/dt' = k ƒ(t') ƒ(t') = exp(k t' + C) where C is an arbitrary constant. A(t') = k exp(k t' + C) (ds)² = (k exp(k t' + C))² ((c dt')² – (dx')² – (dy')² – (dz')²)

So? I don't think so. In fact, that the number of missing sequences is greater than the number of sequences is kind of what Cantor is proving. Although Cantor's diagonal method is only generating a single sequence missing from a list, because the number of sequences in a list is aleph-0, and the number of possible sequences is aleph-1, then the number of sequences missing from a list is also aleph-1. Cantor is proving that aleph-1 is greater than aleph-0.

I actually prefer the term "coordinate transformation" because that's what they are. I think the term "diffeomorphism" is a bit too esoteric for me. There are also "point transformations" which are conceptually distinct from coordinate transformations though mathematically identical, and it's not clear to me to which of these the term "diffeomorphism" actually refers. The OP enquired as to why it is only space that expands and not time. The answer is that the difference between time expanding with space and time not expanding with space is just a coordinate transformation, which means that there is no physical difference. However, as you correctly point out, the time coordinate of the time-expanding metric doesn't correspond to anything, in particular, not a co-moving clock, whereas the spatial coordinates actually do correspond to the co-moving cosmological fluid. No, it doesn't. Only the time coordinates are involved in the coordinate transformation. If the original metric describes a flat three-dimensional space, then the transformed metric will be a scalar function multiple of the Minkowskian metric: guv = ƒ(t) ηuv It depends on how the metric is used. For example, if one is describing light-like trajectories in spacetime, then they have a simple straight-line form.

Methane is a single carbon atom to which are attached four hydrogen atoms in a tetrahedral arrangement.

Except that when you place sx in line 1, you've created a new list, requiring a new application of Cantor's diagonal method, generating a new sequence that is not in the new list (nor in the old list). Given any list of sequences of binary digits, Cantor's diagonal method generates from that list a sequence of binary digits that: differs from the first sequence of that list in the first position, differs from the second sequence of that list in the second position, differs from the third sequence of that list in the third position, ... differs from the n-th sequence of that list in the n-th position, differs from the (n+1)-th sequence of that list in the (n+1)-th position, ... etc and therefore differs from every sequence of that list (that is, not in that list).

A metre is still a metre, and a second is still a second for the two observers at different elevation. Any disagreement between these two observers is the result of how these are compared, noting that the comparison is non-local. But on earth, the surrounding spacetime is approximately stationary and admits a Killing vector field, providing a natural frame of reference in which gravitational time dilation manifests itself as an apparent change in time with respect to elevation. But in spite of the naturalness of this frame of reference, it is still just some frame of reference no more special than other frames of reference in general relativity.

In relativity, we frequently see discussions of quantities that are different in different frames of reference. Less often do we see discussions of quantities that remain the same in different frames of reference (other than the speed of light in a vacuum). I think this leads to confusion about the nature of relativity. I think it is important to note that all observers measuring the same quantity will always obtain the same value regardless of their frame of reference. This means that regardless of the picture relativity seems to paint, relativity does present a truly consistent picture of reality. When it is said that observers in different frames of reference obtain different values for a given measurement, it is because they are actually measuring different things. For example, length contraction is the result of observers in different frames of reference measuring the proper distance between different points in spacetime. The measured width of a river will depend on whether it is measured perpendicularly across or obliquely across, and the same is true for the world-strip of a rod in spacetime. In the case of time dilation, one is comparing the proper time between one pair of points in spacetime with the proper time between another pair of points in spacetime, with some notion of simultaneity between the pairs of points justifying the comparison. But it is when one believes that the different measurements are the same measurement that one can have a confused picture of relativity.

Actually, one can perform a coordinate transformation on the FLRW metric to produce a metric in which time and space expand equally. The resultant metric is a scalar function multiple of the Minkowskian metric, and therefore FLRW spacetime is conformally flat, or as Markus Hanke said above, "a Petrov-type O spacetime". One advantage of such a coordinate system is that it simplifies light-like trajectories as well as the cosmological redshift.

You made a mistake with your arithmetic. You said γs=5/3 whereas it's γs=5/4

There was no need to repost the earlier post. It seems to me that you are not understanding the point I'm making. If the acoustic wave equation is only valid for a stationary medium, then that means a different equation applies to a moving medium. And a different equation for a moving medium means that the acoustic wave equation is not invariant to "A'rentz" transformations. You did make the mathematical error of failing to recognise where the analogy between light and sound fails. It's not a preferred frame of reference. It's two non-equivalent frames of reference. And they are non-equivalent because only the travelling twin accelerates.