What is spacetime? Window into Spacetime

Space and time seem like two completely different things.

Space is everything around us: left and right, front and back, above and below. Time is what a clock measures.

However, Albert Einstein discovered that space and time do not exist separately. Together they form a single whole: spacetime .

That sounds complicated, but actually, we notice something of it every day.

When you look at the sun, you do not see it as it is at that moment. The light from the sun takes about eight minutes to reach the Earth. So you are looking back eight minutes in time.

With stars, that difference is much greater. We see a star a thousand light-years away as it was a thousand years ago.

The further we look into space, the further back we look in time.

But Einstein discovered something much stranger.

Time does not pass at the same speed for everyone. The faster something moves, the slower time passes for that moving object relative to someone who is left behind.

At normal speeds, we hardly notice it. Only when speeds approach the speed of light does the difference become enormous.

And something extraordinary happens in the light.

For us, light can take millions or even billions of years to travel before it reaches us.

But according to the theory of relativity, no time passes along the path that light travels.

So for us, there are enormous distances and enormous periods of time.

But in the light, time disappears from the story.

That turns our conventional view of the universe upside down. Space and time turn out not to be an unchanging backdrop against which everything takes place. They are connected to movement and to the way we perceive the universe.

And perhaps that is just the beginning.

For in the quantum world there exists a phenomenon that is at least as strange: quantum entanglement .

Two entangled particles can be millions of kilometers apart and still form a single shared quantum state.

This raises a fascinating question:

If time loses its ordinary meaning in light, could distance lose its ordinary meaning in entangled particles?

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