Iggy

Fantastic to hear. Perhaps I was being too pedantic in my criticism. That's been going around I hear.

I see. I should have said 'leggett inequalities' perhaps. The one sentence summary, and not the many sentences that preceded it, were your only concern, and all you were replying to. Your pedantic incessant writing is exhausting. Look at the quoted material and the post history and figure out the context! The relativity of simultaneity does matter when choosing between non-local theories. "instantaneous" (which is by one account different from "simultaneous" ) is non-local. Nobody here is talking about anything other.

The point you made is "But still, what's "really" happening is that space is expanding." You're treating a coordinate choice as an aspect of reality and you aught to know better. I gave the source already to refute it. "Is space expanding or are galaxies moving through space?" is a question that can only be answered "it is a coordinate choice" between different relativistic models. Please don't start talking Newtonian approximations again.

Yes it does and yes it did, but the portion I quoted started "A 2007 experiment ruled out a large class of non-Bohmian non-local hidden variable theories.[23]" If you don't understand that sentence to mean "non-local hidden variable theories" (as it so plainly says) being ruled out then I don't know what I could say to make it more clear to you.

The article was referring to non-local hidden variables. It said explicitly.

That is non controversial. We're talking about two different things.

The dichotomy isn't between Newtonian and Relativistic. A de Sitter universe in static coordinates vs. a de Sitter universe in comoving coordinates are neither Newtonian. Yet, in one the receding galaxies move through space and in the other you have metric expansion. Neither is a Newtonian expectation. "What is really happening is that space is expanding" can't be right because in other valid coordinate systems space could well be static. Galaxies move through space, and GR is perfectly able to solve that too. Coordinate choice. Neither is "really" correct. Relative to the perspective they both are.

Researching I find... A 2007 experiment ruled out a large class of non-Bohmian non-local hidden variable theories.[23] If the hidden variables can communicate with each other faster than light, Bell's inequality can easily be violated. Once one particle is measured, it can communicate the necessary correlations to the other particle. Since in relativity the notion of simultaneity is not absolute, this is unattractive. One idea is to replace instantaneous communication with a process that travels backwards in time along the past Light cone. This is the idea behind a transactional interpretation of quantum mechanics, which interprets the statistical emergence of a quantum history as a gradual coming to agreement between histories that go both forward and backward in time.[24] Bell's Inequality -- theoretical challenges So it sounds, if Bell's inequalities are true, that the paradox of the OP has yet been considered sufficient to rule out some interpretations of QM. Huh....

No. The expansion of space is a description of the metric on which the gravity-inclusive model of the universe is the most simply described. The FLRW metric expands by way of a scale factor in a Friedmann universe which is an exact solution of general relativity which is a theory that takes gravity well into account. Neither gravity, nor your inaccurately phrased notion of "modifying gravity" necessitates that one stop speaking in terms of expanding space. The two are 100% non-mutually exclusive. The expansion of space is not an "extra effect". It just means the expansion (ie getting larger) of space (ie distance). It isn't a force. It is a description of a metric.

I don't follow what you mean, but I suspect my use of the word 'predict' could be the trouble. How about this: An observer in one frame sees A measure spin up and B measure spin down and concludes (from the distance and the time it took the information to reach him) that A made the observation first. He says "in my frame A collapsed the wave"). Another frame also sees A measure up and B measure spin down, but concludes on the same basis that it was rather B who made the observation first and collapsed the wave. If both frames are essentially two ways of describing the same thing the QM should offer no difference in observables between the two 'scenarios'. Who collapses the wave shouldn't matter. And I believe C couldn't know if A actually looked at the entangled pair until the information arrived via light from that event.

I don't know much QM -- does it matter who collapses the wave -- where the disentanglement happens first? One frame could say A looked first and found spin up and predict that if C looks he would find spin down, and another frame could say C looked first and found spin down and predict that if A looks he'll see spin up. Either way, the observables are the same, right? Two ways of describing the same thing?

Sometimes a mythical magical being is just a mythical magical being.

Extremely well said

I'm sure that's fun to say, but the cosmological constant first appeared 81 years before it's value was known in 1998. It was a part of the first three models ever to be made of the universe with general relativity. Einstein said specifically that the constant arrived naturally from the derivation and it would be the measurements of the motion of the cosmos that will tell us if its value is zero or not. Anyone who thought the term had to be added after '98 must first have been under the false impression that the term had ever been prematurely removed. That would have been against the counsel of quantum mechanics and Einstein.

Well said. I anticipated your objection, HA!

Yes, the metric expansion of space is one valid way of looking at it. Your link describes it well. Another valid set of coordinates and associated way of measuring and looking at the cosmos, is what Ned Wright calls, in his tutorial, special relativity coordinates in which galaxies move through space. Both are valid as the link I already gave says so clearly and goes on to say exactly what I said... "the only means by which expansion occurs is gravity and momentum". Boo yeah Boosh Bomb goes the dynamite! Do we have to start another thread on this too?

That is a coordinate choice. Are galaxies really moving away from us or is space just expanding? This depends on how you measure things, or your choice of coordinates. In one view, the spatial positions of galaxies are changing, and this causes the redshift. In another view, the galaxies are at fixed coordinates, but the distance between fixed points increases with time, and this causes the redshift. General relativity explains how to transform from one view to the other, and the observable effects like the redshift are the same in both views. Part 3 of the tutorial shows space-time diagrams for the Universe drawn in both ways. In the absence of the cosmological constant, an object released at rest with respect to us does not then fly away from us to join the Hubble flow. Instead, it falls toward us, and then joins the Hubble flow on the other side of the sky, as discussed by Davis, Lineweaver & Webb (2003, AJP, 71, 358). In what are arguably the most reasonable coordinates, the cosmic time t and the distance D(t) measured entirely at the cosmic time t, the acceleration is given by g = -GM(r<D)/D2 where M(r<D) is the mass contained within radius D. This gives g = -(4*pi/3)*G*(rho(t)+3P(t)/c2)*D(t). The 3P/c2 term is a general relativistic correction to the otherwise Newtonian dynamics. Galaxies all move under the influence of this acceleration and their initial position and velocity. In other words, F = ma and gravity provides the force. Nothing extra or weird is needed. Also see the Relativity FAQ answer to this question.

The distance between A and B is measured in Rindler coordinates (or, you might say 'freefall coordinates') as is the distance between B and C. A (near the black hole) collapses the wave, which B learns a certain time later. The time between the collapse by A and the observation of the collapse by B, as measured by B, is the distance in Rindler coordinates divided by the speed of light. The time between B being informed of the wave collapsing and C's observation from B that the wave has collapsed is again 'the distance divided by the speed of light' time later.

I do ramble

No, there is no "gravity that keeps the Milky Way and Andromeda from moving away from each other". They are moving towards each other. The only thing that affect's a galaxies motion (in any reference frame) is gravity and momentum (the cosmological constant is part of gravity for those who were about to object). The relative gravity and inertia of the Milky way and Andromeda galaxy tell us that it should be moving towards us, and it is. Nothing keeps them from moving away from each other and they aren't so kept. The expansion of space is confused with the acceleration of expansion of space which is mistakenly left out of "gravity". Expansion is caused only by inertia. Things that once had a velocity away from each other, continue to have such an inertial velocity. What caused the initial velocity nobody knows. Whatever the Andromeda's initial velocity was... it wasn't a sufficient escape velocity from earth. Expansion, on this scale, only refers to the initial distance and time for which the Andromeda coasted away from us before gravity's acceleration turned the velocity negative.

Ok, if you want to start a thread on the topic we could bicker.

I'm afraid you don't know what the shell theorem is. It means that you can disregard anything outside the sphere and only consider the mass of what is inside. It means, for example, if you want to know the gravitational force of the earth on a person you don't have to consider the rest of the universe pulling up on that person. That all cancels. The same applies to any planet or any arbitrary sphere.

The Shell theorem allows one to mark off any arbitrary sphere and consider the gravitational force toward the center.

In a homogeneous medium the gravitational force toward the center of a sphere is proportional to distance. The universe is well approximated as homogenous at large scales.

I wouldn't grant him the premise. There are no Aeons in Christianity. It's a Gnostic idea. Different gnostic schools had different numbers of aeons, so one could have any number they liked. The Christians who survive today are the descendants of the Irenaeus and Tertullian schools -- people who weren't counting aeons, but pointing out what a schizophrenic exercise it was to name them and count them. Christians decided that aeons were too insane an idea for them a long time ago, and that's saying something.