https://bigthink.com/starts-with-a-bang/...ulational/
EXCERPT: . . . In plain English, the contents of your Universe determine how spacetime is curved. You can then take the spacetime curvature and use it to predict how every quanta of matter and energy will move through and evolve in your Universe...
[...] What we don’t measure, though, is spacetime itself. We can measure distances and we can measure time intervals, but those are only indirect probes of the underlying spacetime. We can measure anything that interacts with us — our bodies, our instruments, our detectors, etc. — but an interaction only occurs when two quanta occupy the same point in spacetime: when they meet at an “event.”
We can measure every one of the effects that curved spacetime has on the matter and energy in the Universe, including:
But that doesn’t mean that spacetime itself isn’t a physically real entity. If you have actors acting out a play, you’d justifiably call the location where the play took place “their stage,” even if it was simply a field, a platform, bare ground, etc. Even if the play took place in the weightlessness of space, you’d simply note that they were using their freely-falling reference frame as a stage.
In the physical Universe, at least as we understand it, you cannot have quanta or interactions between them without the spacetime for them to exist in. Wherever spacetime exists, so do the laws of physics, and so do the fundamental quantum fields that underpin all of nature. In a sense, “nothingness” is the vacuum of empty spacetime, and talking about what occurs in the absence of spacetime is as nonsensical — at least from a physics perspective — as talking about a “where” that’s outside of the boundaries of space or a “when” that’s outside of the boundaries of time. Such a thing may exist, but we have no physical conception of it... (MORE - missing details)
EXCERPT: . . . In plain English, the contents of your Universe determine how spacetime is curved. You can then take the spacetime curvature and use it to predict how every quanta of matter and energy will move through and evolve in your Universe...
[...] What we don’t measure, though, is spacetime itself. We can measure distances and we can measure time intervals, but those are only indirect probes of the underlying spacetime. We can measure anything that interacts with us — our bodies, our instruments, our detectors, etc. — but an interaction only occurs when two quanta occupy the same point in spacetime: when they meet at an “event.”
We can measure every one of the effects that curved spacetime has on the matter and energy in the Universe, including:
- the redshifting of radiation due to the Universe’s expansion,
- the bending of light due to the presence of foreground masses,
- the effects of frame-dragging on a rotating body,
- the additional precession of orbits due to gravitational effects that go beyond what Newton predicted,
- how light gains energy when it falls deeper into a gravitational field and loses energy when it climbs out of it,
But that doesn’t mean that spacetime itself isn’t a physically real entity. If you have actors acting out a play, you’d justifiably call the location where the play took place “their stage,” even if it was simply a field, a platform, bare ground, etc. Even if the play took place in the weightlessness of space, you’d simply note that they were using their freely-falling reference frame as a stage.
In the physical Universe, at least as we understand it, you cannot have quanta or interactions between them without the spacetime for them to exist in. Wherever spacetime exists, so do the laws of physics, and so do the fundamental quantum fields that underpin all of nature. In a sense, “nothingness” is the vacuum of empty spacetime, and talking about what occurs in the absence of spacetime is as nonsensical — at least from a physics perspective — as talking about a “where” that’s outside of the boundaries of space or a “when” that’s outside of the boundaries of time. Such a thing may exist, but we have no physical conception of it... (MORE - missing details)