You can see back as far as the Big Bang, approximately 14 billion years ago, so all matter in the <i>visible</i> Universe is within 14 billion light years of the Earth.   However, the space the Universe occupies is only <i>really</i> finite if it&#x27;s positively curved.   If it&#x27;s flat or negatively curved, the space it occupies is infinite, and if its density is constant, it must contain an infinite amount of matter even though we only see part of it.   The Big Bang is a singularity - a point with infinite density.   It&#x27;s hard to get your head around intuitively, but it all makes sense mathematically.   (The maths is pretty hard, and rarely covered at undergraduate level.)<p>The simplest model in rough agreement with observations is called the Einstein-de Sitter Model, and it&#x27;s flat with a zero cosmological constant.   See <a href="http:&#x2F;&#x2F;www.britannica.com&#x2F;science&#x2F;cosmology-astronomy&#x2F;Relativistic-cosmologies#ref1069808" rel="nofollow">http:&#x2F;&#x2F;www.britannica.com&#x2F;science&#x2F;cosmology-astronomy&#x2F;Relati...</a><p>More general models are covered here: <a href="https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Friedmann%E2%80%93Lema%C3%AEtre%E2%80%93Robertson%E2%80%93Walker_metric#Solutions" rel="nofollow">https:&#x2F;&#x2F;en.wikipedia.org&#x2F;wiki&#x2F;Friedmann%E2%80%93Lema%C3%AEtr...</a>