Hi
I’ve been studying pharmacy/medical sciences for all my adult life when i stumbled upon “a brief history of time” by stephen hawking
Anyway,for a person who hasn’t studied physics much..how does “spacetime” exist? I mean einstein abandoned the idea of absolute time
But what is spacetime? And how does time exist as a physical dimension? I mean it’s just something we measure as it passes
How does all this exist?
In: 3
Think of the movement of a ball, bouncing all around a closed box. How many dimensions do you need to be able to fully describe its motion inside the box? And what even *is* a dimension?
We can think of a dimension as an ‘index’ of a quantity. For example; let’s say something like ‘I have ten’. Just ‘ten’. The question immediately then becomes ‘okay… ten *what?* That *what* can be considered the dimension of the quantity. Without dimensions, quantities are just disembodied numbers with no meaning.
Okay, so for normal Euclidean space inside this box, I need a dimension that quantifies up and down position, I need a dimension for left and right position, and I need a dimension for forward and back position. With those three dimensions, I can fully describe the ball’s location inside the box. But remember; the ball is *moving.*
An stationary object’s position is completely time-independent. A static position doesn’t ‘occur over ten seconds.’ It just *is* a position. You don’t need to measure the passage of time to describe a thing’s location. But you *do* need to track time for **movement**. Movement is a *transient* phenomenon – that is to say, it occurs over an amount of time. The balls position inside the box is dependent on time, because it is moving; one second, it’s somewhere, another second, it’s somewhere else. How is a ball meant to bounce without the passage of time?
In this manner, time is the fourth dimension we use to fully quantify the behaviour of the ball. We have three *spatial* dimensions that fully describe its position, and we have one *temporal* dimension that describes how that position changes with the flow of time.
In the universe, all things move, and time never stops flowing forward. All things are moving through space, and all things are moving through time as well. For this reason, we consider space and time to be an inseparable entity; four-dimensional spacetime. We need these four dimensions because they are the number required to fully describe an object’s position, at any point in time.
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