What is space time fabric?
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Space time fabric is a misleading and confusing term used by science popularisers when presenting Einstein’s relativity to the general populace. It is really a term that shouldn’t be used due to the confusion it causes. Spacetime is not a fabric, and that should be obvious given the meaning of the word fabric.
What the science popularisers are trying to get across to you though is that space and time are part of one thing: spacetime, or in other words you need to consider time and space together. You can’t have time without space, and you can’t have space without time, they are dependent on each other.
Einstein showed us with his theory of relativity (both the special theory and the general theory) that time and space are even more closely linked than you might think. The special theory of relativity starts of with the postulate that the speed of light is constant and the same for all observers. The only way for this to be possible given relative motion is if time and space are relative, which is what the special theory of relativity tells us. A good way to understand the relation between time and space is through spacetime diagrams, which are covered in this excellent short introduction to special relativity:
“Fabric” is poetic phrasing often used to create analogies for introducing new physical concepts, specifically regarding gravity. With every analogy there comes unfortunate confusion, such as the idea that the fabric can “tear”.
Spacetime is not literally a fabric. And spacetime itself doesn’t even literally exist in the same way that you and I exist. It is purely a structural quality we use to describe gravitational fields.
In physics the mathematics is all we have to perfectly describe reality. When we start trying to describe it using the English language, things get fuzzy. But I doubt a mathematical equation would explain a lot to most people.
In general relativity, the path, the trajectory and object takes can be change depending on what is around the object, so we use the comparison to fabric to show paths changing through the use of curves which is easier to visualise. There is nothing “there” though.
Space time is sometimes referred to as “block time” or “block universe” . This is due to its description of space-time as an unchanging four-dimensional “block”, as opposed to the view of the world as a three-dimensional space modulated by the passage of time. Any point in time and space throughout the universe since the big bang can be referenced with coordinates with this model. We can visualise it as a literal block like a cube.
The more imaginative writer can easily extend ths visual metaphor to being some sort of fabric.
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