Size of the *observable* universe Everybody should know that General Relativity allows distances to expand faster than the speed of light, and indeed it predicts that in many circumstances they will do so. This is hardly news, Friedman figured out the standard expansion cosmology model in 1921 (long before Hubble found a pattern of expansion in the redshifts) simply on the basis of vintage 1915 General Relativity. Already in that 1921 model many of the distances increase at rates faster than light. It is so-to-speak typical. No object is going anywhere, i.e. approaching a destination. It's dynamic geometry, not ordinary motion. Newcomers frequently show up puzzled by the usual estimate of the size of the observable (the stuff that we have already received light from). It may help them to focus on an example which contains the essentials of what I think confuses them. EXAMPLE: REDSHIFT Z = 1090. The Cosmic Microwave Background. Microwave background radiation started life as orangish light in a hot fog, around 380,000 years after start of expansion. And its wavelengths are now longer by a factor of about 1090. The original mix of visible and infrared wavelengths have been extended by the same factor that largescale distances have increased during the intervening years while the light was in transit. One way you can really focus in on this is to google "wright calculator" and put in 1090 for the redshift and see what you get. It would be a big help if everybody had some experience with the standard cosmo model which is built into that calculator. This is at the heart of cosmology. It implements Friedman's 1921 model, with modern parameters determined from millions of datapoints of observation. The model has been amazingly successful. You should get some hands-on experience with it. If you do that, put in z = 1090 and press "general" to get it to compute, it will tell you how far the crud was then, when it emitted the orangish light. And it will tell you how far the same stuff is now, today, as we are receiving the light in its present microwave form. The distance then, it will tell you, was only 42 million lightyears (look where it says "angular size distance"). And the distance now, if it could be measured today by the concerted efforts of a chain of observers using standard radar ranging, would be 46 billion lightyears (that is where it says "comoving distance".). In other words the distance to the crud has increased by a factor of around 1090. And neither that matter nor our matter (what became us) has moved significantly. The light has taken 13.7 billion years to get here. The matter that emitted it is 46 billion lightyears farther now than on the day the light was emitted. I'm rounding off: 46 billion - 42 million = 46 billion. The little distance makes virtually no difference.