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Tag Archives: relativity

But what is the Universe expanding into? [Q&A]

It is probably the most common question astronomers encounter: “Fine, you say that the Universe is expanding. OK, I buy that. But what is it expanding into?” There is really no good way to answer this because the correct answer, that it is not expanding into anything, that there is no outside to the Universe, […]

superluminal expansion [Q&A]

Atul of Canara College asks, is it true that the Universe is expanding at a speed greater than light speed? And if so, does that not conflict with Relativity? Yes, but no. And no. Yes, the Universe is expanding, but there is no single speed that characterizes that expansion. However, two objects separated by a […]

the 4th dimension [Q&A]

Gautham of Poornaprajna College asks, what is the definition of time in 4-dimensional space? Typically, when people speak of the 4th dimension, they are talking of a spatial dimension. Any point in the 3-D space we are used to can be represented by 3 coordinates, say (x,y,z), with unit vectors all perpendicular to each other. […]