AbstractDreamer

-1 for irrelevance. You quoted half a line and took it out of context to troll a response that has no context to my original text, with no intent other than to derail my topic with graffiti. I mean if you read my post you'd realise the expansion is present in the wavelength of a photon. And if the photon wavelength is the ruler, and the wavelength has expanded, then the ruler has expanded.

Exactly you're wrong and just trolling.

Define "closer"

Neither. As neither axes have any values other than zero. In this manifold, zero is the only value that can be taken. Everything has the value zero.

How exactly does the expansion of space result in the lengthening of the wavelength of a photon? So you have a tiny photon in superposition with regards to its position and momentum travelling through spacetime for 13 billion years. An excitation propagating through the EM quantum field. Presumably the field is stretched by expansion, but the photon at any moment is a point. So how do the properties of the photon get stretched when it is just a point in the field? Unless the photon isnt a point, and is a line? And if it is a line, then space expansion doesnt occur at any instant but rather over a period? If a volume experiences space expansion, how do you measure the increase in volume from inside the volume? I'm guessing you cant because any ruler you have will expand with the volume. I'm guessing from inside the volume, there is no measurable increase in volume. If a volume experiences space expansion, how do you measure the increase in volume from outside the volume? Assuming, for any observer outside the volume, in order to be able to measure a redshifted photon that exceeds the speed of light you have to be sufficiently far away in spacetime such that the observer and the volume do not share a valid local reference frame. If there is no valid local frame of reference, how do we measure its volume? If there is no increase in volume locally, and you cannot measure the volume from outside, how does space expansion increase volume and result in lower average energy density?

You're very wrong. Coordinates are sufficient for comparison. 2<3. Two is less than Three. You don't need any units of meters, seconds, degrees or apples, square roots or coloured pixels. Wrong again. The number of coloured pixels are the same in both, even if you use a metric of number of coloured pixels. Count them. There are 4 pixels in both. The difference between the pixels in both vertical and horiztonal direction are also the same. There are two pixels in the vertical direction for both, and 2 pixels in the horizontal directions for both. Your mistake is assuming the grid lines have significance. They dont. Only the numbers on the axes have meaning. Labelling with units is irrelevant. Which number is bigger? The number 2 or the number 3?

I'm asking which has bigger volume, not how big their volumes are according to some metric. You don't need a metric to compare volumes, if the coordinate systems are the same, which they are. The point is stretching axes doesn't change magnitude whatever metric you are using, and so space expansion doesn't change volume. Both objects are 2x2 square units, and internally consistent with that shape and magnitude - no matter how much an observer stretches the axes, inside the polygon you will never notice any difference. If you are arguing that space expansion increases volume, then you are saying the square has larger volume than the rectangle, because I changed the magnification and zoomed in significantly on the x-axis. So then your position is that the volume of each green polygon is a property of the observer and not the polygon. Space does not have to expand at all. That's the whole point of that paper. Cosmological redshift does not have to interpreted as due kinematic Doppler shift.

Here's a neat trick. Which green polygon has greater volume?

Wonderful answer thank you! I feel somewhat vindicated with posting this thread. This paper seems to answer my questions, at least to my level of comprehension. I disagree that they conclude Doppler redshift is more accurate than gravitation redshift. My understanding is that they conclude Doppler redshift interpretation is more natural. And by natural I assume they mean because its more simplistic to describe. "Within this frame, you would, by the equivalence principle, interpret their results as a Doppler shift. In so doing, you would be choosing to regard the Doppler family as the natural one, because this family is the one whose behavior is simplest to describe in your chosen frame" page 8 line 4 from the paper above. At this point, I have an issue with the free fall requirements of the Doppler shift model. That is, no gravitational difference between an observer and its neighbour along the path of the radiation, where any difference in observed frequency can be attributed as kinematic . Would a passing gravitational wave not break this local inertial frame between a pair of neighbours? Over 13 billions years, its hard to imagine how a photon avoids an encounter with a gravitational wave. On the other hand, a family of observers where each member is at rest relative to its neighbour seems more "natural" to me. That is, any difference in observed frequency of the photon can be attributed to gravitational redshift - a time dilation cause of redshift. More important than this choice of frame, is their conclusion that BOTH interpretations are valid. "There is no “fact of the matter” about the interpretation of the cosmological redshift: what one concludes depends on one’s coordinate system or method of calculation." page 8 line 17 "The common belief that the cosmological redshift can only be explained in terms of the stretching of space is based on conflating the properties of a specific coordinate system with properties of space itself. This confusion is precisely the opposite of the correct frame of mind in which to understand relativity." bit further down This validates my point entirely. The interpretation of cosmological redshift as Dopplershift or gravitational shift is a matter of choice, and not of facts. A choice of your arbitrary orientation of your coordinate system, something which I said even before I knew what I was talking about (or rather less that what I know now which is just marginally above zero). Space expansion is an ARTIFACT of the coordinate system where we CHOOSE zero gravitational causes to cosmological redshift. In other words if you choose to zerolise time dilation causes to cosmological redshift, then space expansion neatly explains superluminal recession speeds. So to address other points of evidence of space expansion as fact rather than choice: But I thought space expansion doesn't increase volume. Unless you are observing the volume from outside using a measurement reference that is independent of such expansion. If a cube 1m3 expands under space expansion, it's still 1m3 because your ruler also expands with the cube. So wouldn't you have to be outside of the universe to claim any part of it increased in volume? Or if you are inside the universe measuring another part of it, how do you know your ruler is not being stretched in order to conclude the volume being observed is increasing? Temperature is measurement of average energy in body/volume right? "Average" meaning over time. Even if space expansion "creates volume", how can we say the temperature decreases due to an increasing volume. Why can we not say "temperature decreases due to a slowing of time" (we are receiving less observables that measure temperature due to time slowing down)? If I measure 10 photons with a fixed energy propagating from a 1m3 volume over 1 second and we agree to calibrate this reading and call it 10 Hotness. If I then tell you I have two more experiments, one where I space expanded the volume to 2m3 the volume and another where I time diluted the volume to half the rate of time. In the space expansion experiment there are now less photons per volume. In the time dilated experiment there are now less photons per time. Both experiments would measure a decrease in temperature to 5 Hotness. But why would we assert that the decrease in temperature is due to only the volume changing? I don't see why time dilation necessarily contradicts BB or steady state. Both of which are conclusions from many other factors besides time dilation. I think its more important to build from the ground up and end up wherever we end up, rather than top down where we want either the BB or a steady state to be a reality and then railroad observations, interpretations and models to fit. Einstein did that when declaring "God does not play dice", and trying to make QM fit his deterministic belief of the universe. Ultimately, there is no evidence that excludes time dilation as a factor in cosmological redshift, either through gravitational time dilation or some other kind of mechanics that result in time dilation. And I don't know why we commonly accept cosmological redshift is fully attributed to kinematic Dopplershift.

First post that addresses my questions. +1 So time rescaling as it passes is equivalent to space expansion due to a scale factor at that time. But what determines how much of that change is attributed to which case? In other words, how much of a redshift measurement is due to space expansion and how much is due to time dilation? According to the FLRW metric, it is ALL due to space expansion and there is a zero, or at least a net-zero, time dilation effect. Take in the extreme case where there is no space expansion at all, and all the redshift is caused by time dilation, and the recessional velocity is caused by a dilation in time rather than by an expansion of space Why is this such an absurdity? Right, but that is just an artifact of orientation of your coordinate system. A neat trick to simplify a model. If you orientate the model to where certain dimensions on a manifold do not vary and other dimension do vary, that does not mean that the dimension that does not vary cannot vary in other models. So we orientate our redshift observations to one where the temporal dimension does not vary. That does not mean it cannot vary. The FLRW metric is orientated towards no allowance for time dilution in flat spacetime - of course it is not going to vary, its orientated that way! That does not mean there is no time dilution in flat spacetime. So we go back to my original questions. Where are the other interpretations / orientations - ones where time dilution can occur in flat spacetime? Why have we all towed the line fro 100 years with the one accepted orientation where there is no time dilation in flat spacetime? But more importantly... what are the limitations and consequences of such an orientation? What might we be missing because of this orientation?

I have no model to develop. I'm only asking questions that we've had for over 100 years since establishing the accepted model. There's a giant elephant in the room saying "Spacetime is a single manifold". There's another giant elephant in the room saying "Space is different from time because we have conditions in flat spacetime where only space expands and time does not dilute". There is a clear contradiction here.

But why do we allow space to expand and not allow time to dilute in flat spacetime?

But if there was a cosmological, non-relative motion sourced, time dilation effect, could the universal still be homogenous and isotropic wrt mass distribution? Ignoring a number of observations that could be argued as violations to homogeneity and also ignoring the violations of isotropy for now (https://en.wikipedia.org/wiki/Cosmological_principle), why or how does homogeneity and isotropy directly refute time dilation in flat space? What makes the premise of homogenous and isotropic mass distribution irrefutable and sacrosanct? Where is the evidence, other than ΛCDM model which is based (not solely) upon the FLRW metric and inherits the same premises? We cannot use models and equations to prove their premises, despite the models and equations matching many observations and predictions. The implications of the premise that space can expand but time does not dilate when spacetime is flat (not the premise of homogeneity) are enormous. And the only evidence we have is redshifted measurements of wavelengths that have been travelling cosmological distances and times. Why has so little scientific attention been paid towards a critical point in our progression of knowledge since 1922, such that there are NO viable alternative interpretations of what is a conflated and ambiguous observation. We have the Many Worlds and Copenhagen interpretations of observations in quantum phenomena. But we only have the space expanding interpretation of cosmological redshift and absolutely forbid any time dilation in flat space, when GR is screaming spacetime is continuum? Just seems like an enormous elephant in the room to me.

Yes the relationship between frequency and wavelength automatic. But wavelength is a measure of space, which we allow to expand as described by the FLRW metric, and frequency is a measure of time... which apparently cant expand (specifically in the case of cosmological redshift and not in the case of dilation). Why? Spacetime is a continuum. Why, in the case of interpreting cosmological redshift, is it not a continuum? If there are no viable alternatives, then it is the only viable interpretation. Which is rather surprising considering there is no evidence for space expansion other than cosmological redshift observations. We observe cosmological wavelengths redshifted in 1912, we theorise space can expand, we develop a model (FLRW) to match redshift observations based on that in 1922. We can use the model to match subsequent observations based on the same assumptions. But we cannot then go and claim the model and the mathematics proves space expands. In analogy: Newton observed an apple fall, he theorised gravity as a force, he developed models and maths to match his "falling" observations. We can use the model to match subsequent observations and make predictions rather accurately in most circumstances. But you cannot use Netwon's law to claim gravity is a force. Why is that? Why must there be no time dilation? What is it about cosmological redshift observations that says space expands but time does not dilute? If relative motion can dilate time, why should non-relative motion not? Why are we applying "classical reasoning" to cosmological redshift observations?

I'm not even really asking to justify the FLRW metric. It is perfectly justified - given its assumptions and premised. I'm asking to justify why space expansion is the only interpretation of cosmological redshift. You've said for me to suggest a different interpretation and then explicitly repeated it. Stop derailing my thread please.

That's the FLRW metric. One of it's premises is that space is expanding. After that assumption it then describes the expansion. But ill say it again, we can tear apart the FLRW equations all day, you can never use it to justify its own premise. So please, stop using the FLRW to justify that space is expanding. The FLRW describes how it expands. It does NOT justify it. We have to go back to observational evidence - cosmological redshift. It is very logical why cosmological redshift is interpreted as space expansion - it makes a lot of sense. But spacetime is not commonly sensible. And having a sensible interpretation does not mean that there are no alternatives.

I'm not suggesting anything. I'm asking questions. All of the answers so far have missed the real crux of my questions. "There is only one metric, the spacetime metric" and yet it is called space expansion and not spacetime expansion. Why?

Right. So.... why is the metric of space expanding and the metric of time NOT changing, in the specific case of the widely accepted interpretation of cosmological redshift.

It is used in the FLRW metric, AFTER the interpretation of space expansion. Space expansion is a premise of the FLRW metric You cant use a metric to justify its premises. Once we assume cosmological redshift is the observation resulting from space expansion, the FLRW metric ensues. Before that, it is meaningless to talk about the FLRW. I'm not asking about the GR used within FLRW, I'm asking about its premise that space is expanding. Show me where GR is used in the interpretation of cosmological redshift as something other than space expansion. If the equations assume space expansion exists in order to describe it, then they wont help question space expansion only reinforce and it. Where is the evidence for space expansion other than cosmological redshift? What are alternative interpretations of cosmological redshift other than space expansion?

Show me where. It is, but show me where cosmological redshift is interpreted as a decrease in frequency then. This is how the FLRW fits observations of cosmological redshift and interpretation of it as space expansion. You can't use a parametisation to prove it's assumptions.

"In physics, a redshift is an increase in the wavelength" https://en.wikipedia.org/wiki/Redshift "One interpretation of this effect (cosmological redshift) is the idea that space itself is expanding." https://en.wikipedia.org/wiki/Redshift "In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold" https://en.wikipedia.org/wiki/Spacetime Why do we use classical physics and not GR to interpret cosmological redshift as an increase in wavelength and not a decrease in frequency? Why do we allow the metric of space to expand, but not the metric of time, when interpreting cosmological redshift as space expansion? What are the other interpretations of cosmological redshift where something else is happening other than space expanding?

Yes, I had dark energy or space expansion phenomenon in mind. Perhaps "mechanics" is confusing the issue. I had in mind the concept of "micro" vs "macro", or "quantum" vs "classical" as in the OP, when thinking about categories of which there are only two and not three. The introduction of the word "mechanics" open up the number of categories to any number really.

Why do we only categorise only two perspectives of reality, "micro" and "macro". Is that because of the difference between QM and GR? If we can say decoherence makes observations lose their quantum properties (not sure if we can say this), can we also say a fully coherent observable is "beyond the limit of QM"? Why is there not three (or more) mechanics? If there was a third, I would guess it would lie beyond the macro mechanics, "super-macro" rather than beneath the micro, "sub-micro". It would have to describe phenomena that is beyond the limits of GR, such as the local referenced limit of speed and the apparent superluminal recession speeds at very large distances. Is it possible we need a third set of mechanics to describe observable physics at the super-macro scale, but still within our observable or future observable envelope. Or is the scale of all observations complete with just two mechanics?

What kind of oscillation do you mean? Do you mean a physical oscillation, that is, this EH boundary's location/position in space wobbles with some frequency? Or do you mean oscillation in the values of a BH's properties, such as mass, angular momentum and charge? If the position of the EH can "wobble", is it possible the wavelength of this is large enough to allow energy to escape? For example if you were a photon just within the EH, but moving with 99.99999% of your speed directly away from the point of singularity, such that your geodesic is almost parallel with the EH boundary (you are still falling in just very very slowly). If the boundary then wobbles sufficiently, is it possible to wobble "behind" you and momentarily wobble you outside the EH? While it is likely you will wobble back within the EH on the next phase, is it possible to permanently leave the EH in this way?

"... the photons instead increase in wavelength and redshift because of a global feature of the spacetime through which they are traveling. One interpretation of this effect is the idea that space itself is expanding." https://en.wikipedia.org/wiki/Redshift Wiki even states that space expansion is only ONE interpretation. I am guilty of entertaining another interpretation. Yet despite all your responses you have repeated failed to address the important points; either due to a failure to understand my point, or you are blinded by a desire to be right and steadfast refusal to be helpful.