There is a simple rule for a thing to be real. It must be measurable by everyone.
If someone claims they have a thing which only they can measure, everyone else should ignore the claim, even laugh at it.
Physics relies on evidence which is obtained by a measurement. Anything which cannot be measured is also a thing which cannot be claimed to be real. Forces can be measured even if not visible.
Real objects do not rely on a specific observer. Others must be able to observe it.
If one person gives a box to another person and they measure it with the same values (every measurement method has a margin of error), obviously they can agree this box is real. (A weight anomaly from the observer's altitude is not relevant because the thing has an attribute measurable by all.)
The crucial requirement for determining the reality of an object is whether it can be measured independently of a specific observer.
There is a multitude of mechanisms to measure point-to-point distances, with the result independent of the person using that mechanism.
Here on Earth, we have 2 position measurements available which are independent of a particular observer.
1) The GPS coordinates have the latitude and longitude planes referenced to the fixed point at the center of the Earth.
The elevation measurement is also referenced to the center of the Earth.
The latitude, longitude, elevation measurements can be made for any point on or around the globe, independent of one observer.
2) The celestial coordinate system has the declination and right ascension (RA) planes referenced to the fixed point at the center of the Earth.
Each observer does a coordinate system transformation for their current position on Earth's surface relative to that fixed point at the center of the Earth.
The distance measurement is also referenced to the center of the Earth.
The declination, RA, distance measurements can be made from any point around the globe, independent of one observer.
Using these 2 Earth-based techniques we can agree on what is measurable and real in our observable universe. If we cannot measure something independent of a particular observer then it cannot be verified as real.
Right now, the only way to observe or measure anything anywhere in the universe requires an observer on Earth. A space probe leaving Earth can still use the celestial coordinates by accounting for its position relative to Earth.
Probes in interstellar or intergalactic space making celestial position measurements will be challenged to use Earth as a reference for those measurements. Alternately a somewhat fixed point could be used.
A galactic coordinate system has been defined but the moving Sun is its center so it has a restricted basis..
The New Horizons probe traveling to Pluto took an image of Messier 7 for its first calibration of its LORRI camera. That observation required a known location for the probe to correctly observe that open cluster in distant space when far from Earth.
We cannot verify any claims of anything as real beyond our observable universe. This statement is simple logic.
The fabric of space is claimed to originate with the big bang. For a legitimate claim as being real, this fabric must be measurable independent of one observer.
To meet this requirement, a universal coordinate system is required, or one not using Earth as its reference. Its dimensional planes and a distance must be referenced to a specific fixed point in the universe.
Currently, it is impossible to determine limits on the size of the universe so it must be treated as having no limits (or infinte).
It is impossible to identify a fixed point within any space having no defined limits.
There is no fixed point in the universe to serve as this required reference for the defined dimensions.
If we ever, somehow, define the limits on a finite universe, then it becomes possible to identify a fixed point within that finite volume.
Until that time, it is impossible to define an observer independent coordinate system for the universe.
All measurements for cosmology require an observer to define the dimensions and their reference point in the observable universe.
Space-time is the moving observer's reference frame. When confined to that context, the observer's current position in space is the reference for the space-time dimensions. Space-time is explicitly an observer dependent coordinate system.
Relativity is a background independent theory meaning it has no reference to any physical coordinates in the background of the observer. Though relativity is the basis for popular cosmology, relativity has no role in verifying positions independent of an observer.
Therefore the fabric of space cannot be verified as real because it requires a particular observer who must use the Earth for measurements. This requirement for verifying a real thing is crucial.
Cosmology claims to explain the universe and this is possible now within only the observable universe simply because we are all on the Earth which is the basis for our measurements.
The claim of a fabric of space is reaching too far to justify. It cannot be measured beyond a reference to Earth.
The big bang is claimed to create the fabric of space which cannot be verified as real.
All cosmological claims based on a fabric of space have no real basis when that fabric cannot be verified as real.