• Question: what is the link between time and space if there is one

    Asked by dillonlancaster to Cesar on 14 Jun 2011.
    • Photo: Cesar Lopez-Monsalvo

      Cesar Lopez-Monsalvo answered on 14 Jun 2011:

      I really like this question and I will try my best to answer it, or at least I will try to give an answer which is not horribly confusing.

      Space and time are two aspects of a single thing: SPACETIME. Before I tell you what spacetime is, I will explain something that happens in science every so often. When we try to understand how things work in nature, we developed theories that explain a lot of phenomena. At some point, scientist in history have been very confident that they had understood everything there is except for a few “minor” things around. That is the context in which Einstein’s theory of relativity came to be. There were around the time (1905) a number of unexplained things which didn’t fit into the ideas of old and respected scientists. One of those things was that the speed of light seemed to be the same for every observer in the universe. No matter how fast the observer is moving, the speed of light is always the same…even if you are moving at 99% of the speed of light, you will see the light moving away from you as if you were standing still. That give Einstein some clues to “re-think” the way we talk about space and time. His ideas eventually connected everything through gravity (in a very far from obvious way). This is what relativity is about.

      Relativity is one of our fundamental theories about nature. It really works! Here, space and time are combined together in a four-dimensional object which we call SPACETIME. In our every day experience, space and time seem to be two different things, but when gravity is strong (say if you compress the Earth to the size of an egg and move about 1 cm away from it), space and time become blurred into one another. In fact, if you cross the EVENT HORIZON of a black hole (ask me what those are) then space acquires properties of time and time properties of space! In that case the centre of the black hole is no longer a place that you can point at, but an event in your future!! That is why once you are inside a black hole you cannot escape hitting its centre, just as you cannot avoid walking into your future. This is an extreme case of course.

      So, short answer: the link is the speed of light, but in that case you are talking about one single object: spacetime

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