What does actually mean by the saying that Einstein united space and time?
It means what it says. In classical physics, space and time were not related, but what Einstein figure out is that they ARE related --- in fact they are both aspects of the same thing. I guess I'm not sure what exactly you are asking.
Yah - it's not clear what is being asked here is it?
There is "what do we mean by "unified", and what do we mean by "Einstein did it" for example? There are also several ways in which the meaning can be unclear.
Perhaps if you (sreerajt) were to tell us what you currently understand this to mean, we can clear up any misunderstandings?
Basically, and without going into epistomology too much:
If A and B are usually though to be distinct concepts, we can say they have been unified when someone demonstrates that they are each aspects of the same, encompassing, concept. The three blind men and the elephant springs to mind... their rope, snake, and wall concepts of the elephant would be unified by realizing that each is but an aspect of the overall organism.
eg. someone unfamiliar with coins may think of "heads" and "tails" as being separate things. We could unify these two concepts directly, by producing a coin and showing them, or indirectly, say - by demonstrating by careful experiment that the two concepts are related to each other in that particular way consistent with being two sides of a coin.
This is what Einstein is famous for doing with the classical concepts of "space" and "time".
Does that answer your question?
sorry for that... What are the old and new concepts about space and time?
It was mainly Hermann Minkowski:
It means what it says, it is not a figurative statement, you read it literally; space & time are "united". From now on you can call it "outer spacetime"
It's a bit of a hurdle to understand it though,
The concept of three-dimensional space and time are combined into a single four-dimensional spacetime.
Pre Einstein, we thought that space and time were completely separate things, and that space was relative and time was absolute. What does that mean? Imagine you are on a train going past me. As you pass, I let off a banger. A minute later, I set off another one. According to me, both bangers exploded at the same place. According to you, one banger went off next to you, and one some distance behind. Neither of us is wrong, we just have different perspectives. However, we will both agree that the bangers went off one minute apart. Anyone who says different is wrong. That's the difference between 'relative' space and 'absolute' time.
Over the second half of the 19th century, experimental and theoretical developments began to undermine that view. Einstein was the first to realise that the new developments implied that time was also relative (or, at least, the first to realise it and put all the maths together under one logical roof). You, on the train, do not agree with me, on the ground, that the bangers went off in the same place, nor that they went off one minute apart.
In fact, it was Minkowski who first re-wrote Einstein's equations as implying that time was just another dimension, similar to the three spatial ones. So, arguably, it was Minkowski who unified space and time. But Einstein paved the way, and he also took Minkowski's ideas and built on them, creating a way to describe gravity that is based on that unification.
That's a short history, anyway. Hope it answers your question.
Thanks Ibix .. that was a nice one....
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