How much is the universe expanding every second (Earth second)?
If you could be a bit simple in the answer that would be good.
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As Stefan has mentioned in his comment, there are already several questions on this issue. However I'd guess from the way you have phrased your question that the existing answers might be a bit technical so I'll attempt a simpler explanation.
Suppose you draw a line that measures out some distance, $d$, then as shown above the Hubble expansion means that the end of the line is moving away from you at a speed $v$ given by:
$$ v = H \space d $$
where $H$ is Hubble's constant. So your question "how much is the universe expanding every second" doesn't have a simple answer because the speed of expansion depends on the length of your line, $d$.
You may have heard that the size of the observable universe is 13.7 billion light years. What we could do is take this distance and find out what speed it's travelling at. If we feed in $d$ as 13.7 billion light years into our equation above (and assuming that $H$ has remained constant during that time) we get the speed, $v$, about equal to the speed of light. So we calculate that the edge of the observable universe is travelling away from us at about the speed of light. See this question for a more technical explanation of why the answer is about the speed of light but not exactly equal to it.
You could try a different calculation and ask how fast your drive to work is expanding. Actually it isn't expanding, or at least not due to Hubble expansion, since the expansion of the universe only overrides other forces at huge distances but let's ignore this for now. Suppose you drive 10km to work, then your office is receding from you at a speed of:
$$\begin{align} v &= H \times 10,000 \\ &= 2.3 \times 10^{-14} m/s \end{align} $$
John Rennie
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