The relativity of space (and not only of time)

[Maartenn100]

(additional thoughts to the Timescape model of scientist David Wiltshire )

Did you know that we, as observers of space and time, have not only our own particular clock ‘(time is relative) , but we also have our own particular idea of what ‘standing still’ in non-moving uncurved flat spaces, means from our location in space (and time).

In some sense, the flat Earthers are partly right…

We have a particular local idea of what ‘standing still’ in flat unmoving spaces means and that’s our reference point for for seeing curved rotating objects and expanded spaces elsewhere.

Wherever you are, you have a particular idea of straight uncurved spaces, that stands still.

And that idea determines what you will observe outhere in space, moving, rotating, expanding

And your local idea of a straight line that is not moving differs from the straight line that stands still of other observers with different clocks.

You have not only a different clock (time is relative)

you also have a differen ruler. (your local idea of unmoving eucledean space is relative)

Let me explain with a well known example:

You feel that you stand still in space on Earth, right? That’s your referenceframe right there, as an observer in space.

When you start escaping Earth with your spaceship and reach escape velocity, you will see the curved space of Earth more and more under you, relative to your timestretched new environment in space you are now entering with your spaceship.

You will see the Earth turning around more and more from your new point of view.

If you escape gravity of the solar system, you will see the Earth and moon wobbling together and moving in the solar system around the sun more and more from your new perspectives.

Because you have a new ‘idea’ of what ‘standing still’ means and a new idea of a flat space.

And: the duration of your actual moment is the same for you, wherever you are. It is not stretched in your experience as an observer of time. Even if there is grafvitational timestretch when you leave the fields of gravity, you experience the same actual moment duration. Your actual moment is not stretched or dilated in the fields of gravity. So, you will see rotating and curved objects all around you further away from you.

Your clock and your ruler are the standards for observing spaces further away from you. (f.e. intergalactic space).

Why is your clock always ticking ‘normal’ in your experience, wherever you are, even near the vicinity of a black hole of near to the speed of light? Because to every observer, the duration of the actual moment is the same, wherever he is.

The duration of the actual moment is the same, for every observer, wherever he of she is. Therefore: he will always measure ‘deformations of space’ elsewhere’. (expansions of spaces, curvatures of massive objects, rotations of massive curved objects, lengthcontraction, lengthstretch relative to him/her).

Outthere, there is spacetime. A 4D geometry where past, present and future events exist simultaneously. (Einstein)

But an observer exists only in the actual moment. That’s why he or she can only experience an unfolding of events, moment by moment. While in spacetime, all events exist simultaneously. Only living beings can exist in the actual moment. Objects are events existing simultaneously in spacetime in different moments in time.

An observer always has a local idea of a straight line, that is not moving. (a reference frame for spaces and massive objects). You have your own clock, and your personal measurement of the timeflow, locally, is connected to your local idea of a straight line, that is not moving.

Earth stands still, relative to you. Same clocks. Same timeflow. Locally, your idea of a eucledean space that is not moving is here on Earth.

That’s an inertial frame of reference for an observer.

In the world there are only these observers of time and space and no chosen coordinate systems. A reference frame randomly chosen by a mathematician is therefore something different from a physical observer with an actual moment experience who experiences the unfolding of the events moment by moment (and not simultaneously like in spacetime) in a 3D-world, with its own idea of standing still in unmoving straight spaces.

The Observer cannot be found in material reality. The observer is a blind spot. A blind spot while measuring. It’s not measurable, but it is deducibly present, which is reduced to a zero point in mathematics Introducing a vague term such as ‘observation’ into science could meet resistance within physics because it falls outside the domain of what is considered ‘material or measurable reality’. But this difference in perspective makes a world of difference with regard to what kind of explanations you get for the observed phenomena, such as the observed expansion of space. (see timestamp model with ‘expanded space’ as relativistic space, depending on our experience of time)

An observer always uses his own standards for space and time (his own frame of reference, as it is called) to measure a ‘length contraction’ or ‘time distortion’ elsewhere. Wherever he or she is.

Genesis of this world?

First there was spacetime. An invisible (pure non-material?) 4D geometry where all events exist or are accessible simultaneously. (people in near-death experiences talk about this timelessness experience and accessibility to all events simultaneously…).

Then the first observer came into being and he or she experienced a 3D-world from his of her perspective with a particular clock (a local duration) and a particular ruler (a local particular idea of eucledean spaces that stands still, locally).

Then he or she observed the curved and expanded spaces, rotating or not, elsewhere, with his or her clock and his or her ruler as the standard for these measurements.

So, no Big Bang needed.

Maarten Vergucht

24/12/2024

Antwerp, Belgium

[Markus Hanke]

The geodesic structure of any particular spacetime (thereby also expansion) follows from the connection and the metric, both of which are tensorial quantities - and thus these are not observer-dependent.

[Maartenn100]

But a reference frame is always required in order to talk about time and space coordinates; in that sense, the 'observer' is inevitably present.

[KJW]

44 minutes ago, Maartenn100 said:

But a reference frame is always required in order to talk about time and space coordinates; in that sense, the 'observer' is inevitably present.

Not everything is relative. For example, the "distance" between any two points along a given path in spacetime is invariant, the same for all observers, the same in all coordinate systems. Length contraction and time dilation occur because the "distance" measured in different frames of reference isn't between the same two points along the same path in spacetime.

 

Edited December 25, 2024 by KJW

[Maartenn100]

1 hour ago, KJW said:

Not everything is relative. For example, the "distance" between any two points along a given path in spacetime is invariant, the same for all observers, the same in all coordinate systems. Length contraction and time dilation occur because the "distance" measured in different frames of reference isn't between the same two points along the same path in spacetime.

 

Yes, that’s correct, but those spacetime distances are not directly visible. They can only be calculated. They do not belong to the immediately observable or measurable 3D reality of observers. It's an abstract distance. More absolute than our relative observable 3D observations of space and time. The true nature of these proper distances is conceptual. But more real, then our relativistic observations of space (and time).

Edited December 25, 2024 by Maartenn100

[Markus Hanke]

56 minutes ago, Maartenn100 said:

They do not belong to the immediately observable or measurable 3D reality of observers.

Actually yes, they do. The spacetime distance between two events - which is the geometric length of a world line connecting these events - is precisely the total amount of time physically accumulated on a clock carried by an observer tracing out this world line. You can directly measure and observe this, without needing any fancy equipment or calculations. All you need is a simple clock. The entire concept of spacetime is set up such that it connects to physically measurable and observable reality in this neat and direct way. That is what makes it so useful as a model.

[Maartenn100]

2 hours ago, Markus Hanke said:

Actually yes, they do. The spacetime distance between two events - which is the geometric length of a world line connecting these events - is precisely the total amount of time physically accumulated on a clock carried by an observer tracing out this world line. You can directly measure and observe this, without needing any fancy equipment or calculations. All you need is a simple clock. The entire concept of spacetime is set up such that it connects to physically measurable and observable reality in this neat and direct way. That is what makes it so useful as a model.

I think what I mean is: you cannot observe the 4D metric directly as one 4D geometry. As this manifold.  You can only observe and measure in 3D. This whole 4D geometry as a whole is not visible to us. It's an abstract geometry. You can't see the block universe. You can only see an unfolding of events moment by moment. You can't see the whole sequence at once. But in this 4D-geometry, all the events are accessible at once. as human observers, we perceive time in a sequential manner: one “now” after another. We don’t see the entire 4D structure at once; we only see slices of it in three dimensions, unfolding in what we call “the present moment.” 

Our senses are adapted to detect 3D space plus the passage of time. There’s no direct way to view or navigate the time dimension the way we do spatial dimensions. You can measure intervals and record events, allowing you to infer aspects of 4D geometry (such as proper time, spacelike separations, etc.), but you never literally “see” all four dimensions together.

Abstract Geometry vs. Physical Observation

The 4D metric (the mathematical description of spacetime distances) is an abstract object. It unifies space and time into a single geometric framework. Physically, you measure distances and durations in 3D space plus time. That’s why we say the 4D manifold is not directly visible: it’s a model capturing how these measurements fit together across all possible reference frames.

we can only observe and measure slices of reality in 3D, one moment at a time, even though the underlying spacetime structure may be “there” in four dimensions all at once.

I’d like to suggest a possible connection between the four-dimensional “block universe” of physics and those states sometimes described as timeless or eternal, especially in near-death experiences, deep meditation, or psychedelic journeys. In the relativistic block-universe view, spacetime is treated as a four-dimensional manifold where all events, past, present, and future, are laid out in a single, unchanging geometry. From our usual perspective, however, we perceive only one instant at a time, as though we’re watching individual frames of a film. We can never simultaneously witness the entire “reel.” That sequential flow is simply how our consciousness, anchored in a body, processes the dimension of time.

Yet individuals who have undergone especially profound experiences—such as near-death states, intense meditation, or psychedelic visions—often report something radically different: a vivid sensation that time has dissolved, a feeling of union with everything, and a sense that all events and information are equally accessible “at once.” Some describe this as seeing beyond the linear progression of moments into a realm that contains all possible points in time. Philosophically, it’s easy to see how this might echo the block-universe idea. If time is a dimension woven together with space, then in principle, past, present, and future could coexist in a single geometric structure, even though we only experience them sequentially in our day-to-day lives.

From this perspective, being embodied may act like a perceptual filter, limiting us to a 3D slice plus the passing of time. In extreme or altered states of consciousness, perhaps that filter loosens, letting us momentarily intuit something more akin to the four-dimensional reality underneath. Naturally, mainstream physics distinguishes between the mathematical framework of spacetime and the subjective realms of experience. Still, there is plenty of room in philosophy, metaphysics, and personal belief to explore whether these transcendent episodes are glimpses of the block universe or simply separate phenomena altogether. 

Edited December 25, 2024 by Maartenn100

[KJW]

3 hours ago, Maartenn100 said:

We can never simultaneously witness the entire “reel.”

Why do we need to witness the entire "reel" simultaneously? You also said:

7 hours ago, Maartenn100 said:

spacetime distances are not directly visible. They can only be calculated.

Even if that were true, so what? Why is it so important that things be directly visible? What is wrong with calculated results?

 

[Maartenn100]

2 hours ago, KJW said:

Why do we need to witness the entire "reel" simultaneously? You also said:

Even if that were true, so what? Why is it so important that things be directly visible? What is wrong with calculated results?

 

There is nothing morally wrong with it. But it tells you something about the true nature of it. Is it conceptual, this 4D geometry, or is it directly observable as a 4D manifold?

The fact is, the 4D geometry not directly accessible when we are in our bodies. As Einstein said, time is an illusion, created by our brain and senses. Once we are out of body (see NDE's, deep meditation, or deep mystical psychedelic experiences) we experience 'all at once', 'all information immediately accessible', etc. We will experience the block universe, in my opinion.

Edited December 25, 2024 by Maartenn100

[studiot]

1 hour ago, Maartenn100 said:

Abstract Geometry vs. Physical Observation

The 4D metric (the mathematical description of spacetime distances) is an abstract object. It unifies space and time into a single geometric framework. Physically, you measure distances and durations in 3D space plus time. That’s why we say the 4D manifold is not directly visible: it’s a model capturing how these measurements fit together across all possible reference frames.

Does it ?

and there is me thinking that four-vectors are something to do with abstract multidimensional spaces, which are algebraic, not geometric.

[Markus Hanke]

7 hours ago, Maartenn100 said:

As Einstein said, time is an illusion, created by our brain and senses.

Tbh, this doesn’t sound like something Einstein would have said.

14 hours ago, Maartenn100 said:

I think what I mean is: you cannot observe the 4D metric directly as one 4D geometry. As this manifold.

Well, a ‘manifold’ is fundamentally a mathematical model that’s intended to represent certain elements of reality, so no you can’t ‘observe’ it as such. But you have to remember that whatever observations you do make in the real world always involve time, no matter how short - so in that sense it is in fact impossible to perceive reality in anything less than (3+1)D, because any measurement of something that is spatially extended inevitably requires time as well.

[Maartenn100]

12 hours ago, studiot said:

Does it ?

and there is me thinking that four-vectors are something to do with abstract multidimensional spaces, which are algebraic, not geometric.

Certainly, one can view four-vectors as elements of an algebraic vector space equipped with a bilinear form (the Minkowski metric). From a pure math standpoint, that is an algebraic description of a set of vectors and their inner products. However, this algebraic structure also defines a specific kind of geometry—namely Minkowski geometry.

In other words, once you endow a vector space with a metric, you move from “just algebra” into the realm of geometry—because that metric tells you how to measure intervals between vectors. Minkowski’s great insight was that this geometric viewpoint (treating time and space as a unified four-dimensional manifold) elegantly explains the relativistic effects of length contraction and time dilation as straightforward geometric consequences of that metric, rather than mere algebraic manipulations.

So yes, four-vectors live in an “abstract multidimensional space,” but that metric is what allows us to interpret it geometrically. The geometry may differ from our usual Euclidean intuition—it’s a pseudo-Riemannian or Lorentzian geometry—but it is still very much a geometry.

4 hours ago, Markus Hanke said:

Tbh, this doesn’t sound like something Einstein would have said.

Well, a ‘manifold’ is fundamentally a mathematical model that’s intended to represent certain elements of reality, so no you can’t ‘observe’ it as such. But you have to remember that whatever observations you do make in the real world always involve time, no matter how short - so in that sense it is in fact impossible to perceive reality in anything less than (3+1)D, because any measurement of something that is spatially extended inevitably requires time as well.

Thanks for your comment. Let me clarify a couple of points:

First, regarding the idea that “Einstein said time is an illusion”:
The commonly cited phrase comes from a letter Einstein wrote after the death of a friend, where he remarked something along the lines of “For us believing physicists, the distinction between past, present, and future is only a stubbornly persistent illusion.” It’s often paraphrased or taken somewhat out of context. Einstein was referencing the notion that in a four-dimensional spacetime picture, all events exist “at once” in the block-universe sense, so the usual way we divide events into past, present, and future can be seen as partly a feature of human perception. While he did say something close to “time is an illusion,” it wasn’t meant as a casual denial of time’s physical reality but rather an expression of how relativity treats all of spacetime as one geometric whole.

Second, about “observing” the (3+1)-dimensional world:
I agree that every real measurement inherently involves time. We always observe phenomena through a window of duration, however brief. What I’m emphasizing is that although our measurements happen in (3+1) dimensions, we don’t get to see the entire 4D spacetime manifold “all at once.” Instead, we experience one slice of it at a time and infer the rest from theory and indirect measurement.
“Manifold,” as you say, is indeed a mathematical model. We can’t literally place it under a microscope. Yet it’s precisely that model (the 4D metric plus our experimental data) that unifies the separate measurements we take over time. This is why I referred to the 4D geometry as abstract and not directly visible in one go, because our sensory experience and measuring apparatus only ever sample events sequentially.

So yes, we inevitably measure and perceive reality in (3+1)D segments, but that doesn’t mean we can lay out the entire 4D manifold in one visual scene. The manifold remains a powerful conceptual framework allowing us to interpret our sequential observations in a consistent, relativistic whole.

[Markus Hanke]

1 hour ago, Maartenn100 said:

but that doesn’t mean we can lay out the entire 4D manifold in one visual scene

Of course not. But why would you want to do such a thing?

[swansont]

15 hours ago, Maartenn100 said:

There is nothing morally wrong with it. But it tells you something about the true nature of it. Is it conceptual, this 4D geometry, or is it directly observable as a 4D manifold?

The fact is, the 4D geometry not directly accessible when we are in our bodies. As Einstein said, time is an illusion, created by our brain and senses. Once we are out of body (see NDE's, deep meditation, or deep mystical psychedelic experiences) we experience 'all at once', 'all information immediately accessible', etc. We will experience the block universe, in my opinion.

!

Moderator Note

This is supposed to be a physics discussion, and there are rules for speculations. So morality and out-of-body are off-topic, and “in my opinion” is not an acceptable substitute for a model and evidence