What, exactly, is space-time? – The Conversation

What, exactly, is space-time?

Published: August 24, 2025 8:22am EDT

Author

1. Daryl Janzen Observatory Manager and Instructor, Astronomy, University of Saskatchewan

Disclosure statement

Daryl Janzen does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

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University of Saskatchewan provides funding as a founding partner of The Conversation CA.

University of Saskatchewan provides funding as a member of The Conversation CA-FR.

Few ideas in modern science have reshaped our understanding of reality more profoundly than space-time — the interwoven fabric of space and time at the heart of Albert Einstein’s theory of relativity.

Space-time is frequently described as the “fabric of reality.” In some accounts, this fabric is referred to as a fixed, four-dimensional “block universe” — a complete map of all events, past, present and future.

In others, it’s a dynamic field that bends and curves in response to gravity. But what does it really mean to say that space-time exists? What kind of thing is it — is space-time structure, substance or metaphor?

The heart of modern physics

These questions aren’t just philosophical. They sit at the heart of how we interpret modern physics and quietly shape everything from how we understand general relativity to how we imagine time travel, multiverses and our origins.

These questions inform the emergence of space-time itself and radical new proposals that treat it as the universe’s memory. And yet the language we use to describe space-time is often vague, metaphorical and deeply inconsistent.

Read more: Why do metaphors of space help us understand time?

Austrian-British philosopher Ludwig Wittgenstein once warned that philosophical problems arise when “language goes on holiday.” Physics, it turns out, may be a prime example.

Over the last century, familiar words such as “time,” “exist” and “timeless” have been repurposed in technical contexts without examining what baggage they carry from everyday speech.

This has led to widespread confusion about what these terms actually mean.

Austrian-British philosopher Ludwig Wittgenstein once warned that philosophical problems arise when “language goes on holiday.” Physics, it turns out, may be a prime example.

Over the last century, familiar words such as “time,” “exist” and “timeless” have been repurposed in technical contexts without examining what baggage they carry from everyday speech.

This has led to widespread confusion about what these terms actually mean.

Continue/Read Original Article Here: What, exactly, is space-time?