Curvature versus Expansion: Both Relativistic Observations of Space

[Maartenn100]

But I start from the principle of relativity that since Einstein there is no absolute time and space anymore like according to the Newtonian worldview.

 Space is also relative. (and time)

There is no preferred reference frame for space.

So, the observation of 'space-expansion', seen from the point of view of an observer in a spaceship going at 0.99c of the speed of light towards Proxima Centauri, slowing down again, is 'the relativity of space' at work. This observer will see a so-called 'space-expansion' of the earlier contracted space/length in front of his spaceship, slowing down again. And this space-expansion is of the same kind of every other space-expansion we observe.

If space is relative, everything we observe about space is relative and depending on observers.

There are observers who 'see' zero space in the universe. Like a foton. 

So, if you say: 'space is expanding' (the universe is expanding),

in my opinion: it's your particular ruler that is expanding, given your clock and given your position in spacetime.

 

The metriek you use to calculate spacetimecoordinates is something conceptual.

4D-spacetime cannot be directly observed. The block universe is a conceptualised idea. More 'real' then our relativistic observations of space (and time), 

but a concept.

 

 

   

 

 

 

Edited March 25 by Maartenn100

[KJW]

9 hours ago, Maartenn100 said:

4D-spacetime cannot be directly observed.

That is not true. Although there are limitations on how much spacetime we can be directly observe, we can observe enough of it to know that it is real. Bear in mind that "to observe" means "to measure"... one doesn't need to be able to look at a four-dimensional block of spacetime directly with our eyes.

 

[KJW]

10 hours ago, Maartenn100 said:

the observation of 'space-expansion', seen from the point of view of an observer in a spaceship going at 0.99c of the speed of light towards Proxima Centauri

When cosmologists speak of the expansion of space, they are referring to a space that is constant in age from the big bang singularity along the spacetime trajectory field of the matter of the universe. This does not depend on the observer and is an invariant of the spacetime described by the Friedmann-Lemaître-Robertson-Walker (FLRW) metric. Different observers may have different notions of space according to special relativity, but these are not the notion of space that is cosmologically expanding.

 

Edited March 26 by KJW

[Maartenn100]

9 hours ago, KJW said:

That is not true. Although there are limitations on how much spacetime we can be directly observe, we can observe enough of it to know that it is real. Bear in mind that "to observe" means "to measure"... one doesn't need to be able to look at a four-dimensional block of spacetime directly with our eyes.

 

4D-spacetime is very real. Even more 'real' then our relative measurements of space and time. You can not measure spacetime distances. You need to calculatie them. What you measure are relative spacedistances and time. Spacetimemetriek is calculated. Not observed. 

Edited March 26 by Maartenn100

[Maartenn100]

My point is that the universe without observers has no such properties like relative time and space distances. 

Edited March 26 by Maartenn100

[KJW]

57 minutes ago, Maartenn100 said:

My point is that the universe without observers has no such properties like relative time and space distances. 

This is a moot point. Observers exist and what they observe of reality is an important aspect of science. But that doesn't mean that observers are intrinsically important to reality. Or maybe they are, if one has a penchant for solipsism.

 

2 hours ago, Maartenn100 said:

You can not measure spacetime distances.

One can measure spacetime distances. A clock measures spacetime distance in the time direction, and a ruler measures spacetime distance in a space direction. And if one arranges for a clock to travel at relativistic speeds (e.g. an unstable subatomic particle), then one can measure spacetime distances that are combinations of our time and space that are not accessible to ordinary clocks and rulers.

 

 

Edited March 26 by KJW

[Maartenn100]

The 4D spacetime can be conceptualized as a "block universe," an idea that stems from Einstein's theory of general relativity. In this model, the universe is viewed as a four-dimensional spatial structure, where time is akin to the spatial dimensions, and all moments in time—past, present, and future—exist simultaneously.

It's this spatial Block universe that can only be conceptualised. 

In the block universe, the future is as 'fixed' as the past; both are already "written" and exist within the four-dimensional space.  This concept is  abstract and can be difficult to grasp since our everyday experience of time is sequential—we experience time as flowing from the past to the future. Visualizing the block universe as a geometric figuren, is an abstract concept in our minds. More real then the relativistic observations of time and space. 

Edited March 26 by Maartenn100

[KJW]

I know what spacetime is, so I'm not seeing the point of what you are saying within the context of this thread.

 

[Maartenn100]

If there is simultaneity of all events in the block universe/spacetime, then there is no sequential order of events through time in the block universe. Then there is no timeduration in the block universe/spacetime. Then there is no time.

 

Only observers measure timeduration. And they disagree.

 

Edited March 26 by Maartenn100

[Mordred]

You will never learn physics if you pay attention to interpretations which the block universe  is.

We don't use the block universe  interpretation in actual physics. It's just an interpretation. Stick with the math involved would show

Edited March 26 by Mordred

[Maartenn100]

Your idea is to 'stick with the math'.

The current models of the expanding universe, such as the Friedmann-Lemaître-Robertson-Walker (FLRW) metric, are, as I understand it, solutions to the Einstein field equations that describe the entire universe as a whole. These models assume the cosmological principle, which states that the universe is homogeneous and isotropic on a large scale. This is an unproven assumption that is simply taken for granted. One cannot oversee the entire cosmos and confirm this cosmologicle principle. Within this unproven framework, observations of the expansion of space are seen as consistent for all observers, despite the relativity of individual time and space measurements.

New observations challenge the (unproven claim of) cosmological principle:

Newly discovered cosmic megastructure challenges theories of the universe | Space | The Guardian

 

So, the scientists do not 'stick with  the math' either.

Edited March 27 by Maartenn100

[Mordred]

Thats a poor excuse, one cam still stick to the math and model any form universe conditions by applying the correct math alterations provided one correctly performs the correct math operations.

I can easily adapt the FLRW metric to a form that does not require a homogeneous and isotropic dstribution as per the Cosmological principle or even adapt the metric for a rotating universe.

That's because I know the needed math steps. You don't learn those by simply studying pop media literature. 

Regardless if you study the arxiv and professional papers instead of paying attention to pop media you will learn that pop media literature makes mountains out of mole hills.

Pop media will always lead a reader astray. The cosmological Principle is quite secure by observational evidence a good example is the uniformity of the CMB. The scale however one must apply is per 100 Mpc. 

Edited March 27 by Mordred

[Maartenn100]

I follow simple logical deduction from true premises:

True premise: Space and time are no longer absolute as in the time of Newton. They are relative, since Einstein.
Valid logical conclusion: There is no preferred reference frame for space.
Supporting (thought) experiments: Observers can be conceived who measure a different space. (a photon, a hypothetical observer close to the speed of light approaching Proxima Centauri).

Valid conclusion: Every observation of space is relative. THUS ALSO the observation of expanding space, as an interpretation of the observation of the Doppler effect of light emitted from distant galaxies, by 'expansion of space' moving away from us.

True premises, logical reasoning, valid conclusion.

 

And there is not only no preferred reference frame for space where every observation of space is relative, so also the observation of expanding space.

 

There is also no preferred reference frame for time.

Therefore, (elapsed) time since the so-called Big Bang is also relative. Different observers with their own clocks will measure a different duration since the Big Bang. So, the so-called age of the universe depends on which clock? Which preference do you give to which reference frame for (elapsed) time since the so-called Big Bang?

[Mordred]

Your logic is not the same as my logic or Bob's logic. Logic means nothing. It's simply an aid. There is no preferred frame this is well established and if you understand the mathematics of GR with its application of invariant quantities you would understand the truth of that statement.

 

Let's use the following math statement on the Lorentz transforms

\[\mu \cdot \nu= \nu \cdot \mu)\]

This statement describes the  symmetric relations of the Lorentz transform. 

Edited March 27 by Mordred

[swansont]

22 hours ago, Maartenn100 said:

Therefore, (elapsed) time since the so-called Big Bang is also relative. Different observers with their own clocks will measure a different duration since the Big Bang. So, the so-called age of the universe depends on which clock? Which preference do you give to which reference frame for (elapsed) time since the so-called Big Bang?

We measure it with our clock, since we’re doing the measurement. Most clocks in galaxies run at about the same rate, unless you’re near a black hole or moving at a significant fraction of c. (it’s been estimated that the center of the earth is younger than the surface by ~2 years. A pittance compared to 4.5 billion years)

So what? We know this. We’re not comparing notes with any observers in other reference frames.

How, specifically, does this tie in with expansion? I don’t see how your conclusion follows.

[Markus Hanke]

16 hours ago, Maartenn100 said:

Valid conclusion: Every observation of space is relative. THUS ALSO the observation of expanding space, as an interpretation of the observation of the Doppler effect of light emitted from distant galaxies, by 'expansion of space' moving away from us.

I think you’re forgetting that these distant objects are not just moving away from us, but also from each other. Metric expansion happens for all distances, not just those centred on Earth (which would be exceedingly weird). Furthermore, there’s a precise relationship between distance and recession velocity, irrespective of which direction you look.

Be careful to place to much stock in a single observation - you have to remember that cosmological redshift is not the only data point available to us; there’s quite a number of different observations involved, and the Lambda-CDM model is currently (!) the one that best fits all the available data. It’s not just based on redshift.

[KJW]

21 hours ago, Maartenn100 said:

I follow simple logical deduction from true premises:

True premise: Space and time are no longer absolute as in the time of Newton. They are relative, since Einstein.
Valid logical conclusion: There is no preferred reference frame for space.
Supporting (thought) experiments: Observers can be conceived who measure a different space. (a photon, a hypothetical observer close to the speed of light approaching Proxima Centauri).

Valid conclusion: Every observation of space is relative. THUS ALSO the observation of expanding space, as an interpretation of the observation of the Doppler effect of light emitted from distant galaxies, by 'expansion of space' moving away from us.

True premises, logical reasoning, valid conclusion.

 

And there is not only no preferred reference frame for space where every observation of space is relative, so also the observation of expanding space.

 

There is also no preferred reference frame for time.

Therefore, (elapsed) time since the so-called Big Bang is also relative. Different observers with their own clocks will measure a different duration since the Big Bang. So, the so-called age of the universe depends on which clock? Which preference do you give to which reference frame for (elapsed) time since the so-called Big Bang?

This represents a misunderstanding of the nature of relativity. Different observers may obtain different values for a given measurement because the measurement as well as the description of the result of the measurement are from different perspectives. But the thing being measured is absolute. Reality can only make sense if the objects within it are absolute. Different observers may obtain different values for their measured results, but knowing how the different observers relate to each other allows one to determine how the different values for their measured results relate to each other. This only makes sense because of the absoluteness of what is being measured. In relativity, there are invariants that are the same for all observers. The time measured by a clock, and the distance measured by a ruler are invariants. The notions of time dilation and length contraction occur because the different observers are not measuring the same thing. Thus, the moving clock is measuring its own time, an invariant, but the non-moving clock is only measuring a projection of the moving clock onto the non-moving clock's notion of time. The time measured by the non-moving clock is also an invariant, but not the same invariant as the time measured by the moving clock. Similarly for the ruler.

 

 

[Maartenn100]

22 hours ago, swansont said:

We measure it with our clock, since we’re doing the measurement. Most clocks in galaxies run at about the same rate, unless you’re near a black hole or moving at a significant fraction of c. (it’s been estimated that the center of the earth is younger than the surface by ~2 years. A pittance compared to 4.5 billion years)

So what? We know this. We’re not comparing notes with any observers in other reference frames.

How, specifically, does this tie in with expansion? I don’t see how your conclusion follows.

Indeed: we measure with our clock. You say: 'Most clocks in galaxies run at about the same rate unless you're near a black hole or moving at a significant fraction of c'.

The distinction between a universe where time, or age, is relative, and one where the universe's age can be precisely defined, is critical. Even minor discrepancies in time measurements suggest significant differences in our understanding of the universe: one with a definite age versus one without a measurable timescale.

Edited March 28 by Maartenn100

[KJW]

23 hours ago, Maartenn100 said:

So, the so-called age of the universe depends on which clock? Which preference do you give to which reference frame for (elapsed) time since the so-called Big Bang?

One considers a spacetime trajectory from a point in the three-dimensional space defined by the big bang singularity to the corresponding point in the current space. The proper time of that trajectory is the invariant age of the universe at that point. Now consider all the spacetime trajectories from all the points of the three-dimensional space defined by the big bang singularity to all the corresponding points in the current space. Each spacetime trajectory to each point in the current space has its own proper time, giving each point in the current space its own age. If we create an arbitrary three-dimensional slice through spacetime, then the ages of the different points of the slice may differ. But we are interested in the particular three-dimensional slice such that all the points have the same age. That is, specifying the age of the universe defines it as a particular three-dimensional space. Because the proper times that define the three-dimensional space are invariant, so is the three-dimensional space.

The spacetime trajectories that define the age of the universe are the rest frames of the bulk of the matter that make up the universe. This leads to the identification of the frame of reference in which the cosmic microwave background radiation has zero dipolar anisotropy as the preferred global frame of reference of the universe. Special relativity remains locally valid as always, and general relativity is unaffected because this notion of "preferred global frame of reference" is about symmetries and broken symmetries of the spacetime, and not about the principle of relativity which is always true.

 

Edited March 28 by KJW

[Mordred]

The term for the observer your looking for is the commoving observer. This is an observer at the same influences of the global spacetime conditions. In essence the flat global metric. The flat spacetime of the LCDM parameters has no significant curvature term for any time dilation effects. 

 Subsequently the age of the universe is determined from the commoving observer. The formulas applies the Hubble parameter in its formula.

There is absolutely no point in using the observations of an observer in a traveling spacecraft, particularly using redshift. One simply has to realize how useless thar would become by recalling that as the spacecraft approaches a destination you blueshift while at the same time getting redshift from the crafts origin point.

Makes using observers on a spacecraft essential useless. Particularly once you start applying transverse Doppler for every angle not parallel to the travel direction.

In essence an observer in a spacecraft would get different redshift values at every single angle of measurement. Kind of pointless to use that to calculate expansion or age.

Edited March 28 by Mordred

[Maartenn100]

14 minutes ago, KJW said:

One considers a spacetime trajectory from a point in the three-dimensional space defined by the big bang singularity to the corresponding point in the current space. The proper time of that trajectory is the invariant age of the universe at that point. Now consider all the spacetime trajectories from all the points of the three-dimensional space defined by the big bang singularity to all the corresponding points in the current space. Each spacetime trajectory to each point in the current space has its own proper time, giving each point in the current space its own age. If we create an arbitrary three-dimensional slice through spacetime, then the ages of the different points of the slice may differ. But we are interested in the particular three-dimensional slice such that all the points have the same age. That is, specifying the age of the universe defines it as a particular three-dimensional space. Because the proper times that define the three-dimensional space are invariant, so is the three-dimensional space.

The spacetime trajectories that define the age of the universe are the rest frames of the bulk of the matter that make up the universe. This leads to the identification of the frame of reference in which the cosmic microwave background radiation has zero dipolar anisotropy as the preferred global frame of reference of the universe. Special relativity remains locally valid as always, and general relativity is unaffected because this notion of "preferred global frame of reference" is about symmetries and broken symmetries of the spacetime, and not about the principle of relativity which is always true.

 

But if you now travel close to a black hole for a few months and return to Earth, your perception of the elapsed time since the Big Bang will differ from that of other observers. Thus, your method of reckoning time violates the principle of relativity of time in my opinion.

[KJW]

13 minutes ago, Maartenn100 said:

But if you now travel close to a black hole for a few months and return to Earth, your perception of the elapsed time since the Big Bang will differ from that of other observers. Thus, your method of reckoning time violates the principle of relativity of time in my opinion.

What is your point? Are you concerned with the structure of spacetime or how we measure it?

 

[Maartenn100]

8 minutes ago, KJW said:

What is your point? Are you concerned with the structure of spacetime or how we measure it?

 

My point is that you can not make statements about the duration since the socalled big bang (the age of the universe), because different observers will disagree on this idea. And even if the differences are small, the fact that there is a difference makes a big difference for in what kind of universe we  live. A universe with a relative time where there can be no statements  about age or time or a universe with absolute time or space.

[swansont]

40 minutes ago, Maartenn100 said:

Indeed: we measure with our clock. You say: 'Most clocks in galaxies run at about the same rate unless you're near a black hole or moving at a significant fraction of c'.

The distinction between a universe where time, or age, is relative, and one where the universe's age can be precisely defined, is critical. Even minor discrepancies in time measurements suggest significant differences in our understanding of the universe: one with a definite age versus one without a measurable timescale.

But we (scientists) are aware of relativity, so there is no difference in understanding. It’s a given that the measurement was made with our clock. 

And this has no impact on expansion.

1 minute ago, Maartenn100 said:

My point is that you can not make statements about the duration since the socalled big bang (the age of the universe), because different observers will disagree on this idea. And even if the differences are small, the fact that there is a difference makes a big difference for in what kind of universe we  live. A universe with a relative time where there can be no statements  about age or time or a universe with absolute time or space.

You could make the same flawed argument about any measurement affected by relativity, and yet GPS (for example) still works. 

You are overstating the impact of relativity; it does not render things unknown. It merely makes measurements frame-dependent, but with a known transform between frames.

It's like saying that the fact that things can be written in both English and German means language has no meaning, as if one can’t translate between the two.

[Maartenn100]

In my opinion, what's common in general relativity theory and quantum theory = observers.

Einstein talked about observers and in quantum theory 'the observer effect' plays a role.

So, to unite both theories, we have to look at the world with observers versus the world without observers.

 

In my opinion:

 

in quantum theory 'everything is in superposition' when there are no observers.

In relativity in the block universe: everything happens simultaneously when there are no observers.

 

I think that the difference between a world with observers versus a world without observers is a world where events happen sequentially versus a world where

everything happens simultaneously.

When the scientist (and all other observers) isn't there, all the steps to execute the experiment are all together existing in spacetime simultaneously.

When there is a scientist, this is been observed as sequential order of events through time.

 

 

 

 

 

 

Edited March 28 by Maartenn100