Â鶹´«Ã½

If the universe originated at the big bang 13 billion years ago, how can there be stars that are 30 billion light years away?

Sarah Bloxham,

via email

Why do our knuckles and joints make a popping sound when cracked? Does it do us any good or harm?

Noah Horne,

Patrick Space Force Base, Florida, US

To answer this question – or ask a new one – email lastword@newscientist.com.

Questions should be scientific enquiries about everyday phenomena, and both questions and answers should be concise. We reserve the right to edit items for clarity and style. Please include a postal address, daytime telephone number and email address.

Â鶹´«Ã½ retains total editorial control over the published content and reserves all rights to reuse question and answer material that has been submitted by readers in any medium or in any format.

Terms and conditions apply.