Why is the universe depicted as a cone [1]?

Given this links to a Penrose’s Hawking Points based diagram, i am constantly wondering why the universe - or its history is always depicted as a cone.<p>It’s hard to get my head around it since if there was a big bang, you’d expect a spherical visualization.<p>Plus I am aware of WMAP and even if the reality is a, b or c - it all goes back to the theory of a flat universe, thus space time.<p>Since everything we see - on earth and through instruments in space - has three dimensions it is hard to understand gravity by showing a warped plane by spheres. That works when showing the earth and its moon but is hard to follow once you add a galaxy, a cluster, etc…<p>Does anyone know of any good explanations and above all visual models that might make this more comprehensible?<p>Cheers and thanks!

2010, but interesting.<p><i>“Who will be around then to be bored by this apparent overpowering eventual tedium?” A thought occurred. If, by then, only massless particles are present (the rest having decayed), Penrose reasoned that eternity will pass in a flash since no proper time elapses at all for these voyagers along space-time light-cones.</i><p>Edit: the review of Penrose&#x27;s book is by Julian Barbour, who concludes with his own thought:<p><i>Despite his great attraction to conformal geometry, Penrose still accords length a real physical role. But in fact we only ever observe angles, never lengths as such. Do we really need them?</i><p>Or, as Pauli said, &quot;Your idea is crazy, but is it crazy enough?&quot;