I'm only asking this because every time I want to explain the basic difference between Newtonian mechanics and Einstein's relativity to someone, I am compelled to say the word spacetime, and whoever is listening to me tends to get a bunch of question marks over their head. :lol: My question is simply, if someone asks me what spacetime is, what should I say? It really isn't something that can be explained nor understood easily. Or am I wrong? I just want a definition of spacetime in layman's terms is all -- assuming there is even one. Thanks.

Space-time, as I understand it, is simply the normal x,y,z dimension we are accustomed to with time being not so much the fourth dimension but the perception of the other 3 dimensions. To explain this there are two examples that are easy enough to understand. 1) The stars we see in the sky including our sun are a shadow of what they actually are. That is to say the light we see coming from them was emitted long before it got to our eyes. Light takes roughly 8 minutes to reach us from our sun, so the sun we see is where it was 8 minutes ago. Some stars are billions of light years away. The space we see is defined by the objects in it, and the space that far away is the space as it was billions of years ago. 2) Perhaps the better example, is our perception of time as the change we see in light. If you were to travel faster than the speed of light you would essentially travel "back in time." Time is a constant it will always move forward. It cannot be changed, but we would "catch up" to the light that once left us. Seeing the light we already saw would appear as time "rewinding," so to speak. Time is still moving forward but our perception of it is reversed.

Does that make sense?