While contemplating the twin paradox the thought occured to me that every observer should see the universe as being the same size, and the same age. If we consider a set of twins in which one twin flies off in a spaceship at near light speed, and then returns some time later, the two brothers will have aged differently. But if upon returning the brothers should run an experiment to estimate the size and age of the universe the results for each of them should be identical. In other words the size and age of the universe should be the same for both brothers, no matter what the differences in their ages may be. Even if the difference is a billion years. Indeed if we send out a hundred spaceships at different speeds, upon returning they should all agree upon the size and age of the universe. Thus shouldn't the size and age of the universe be the same for all observers? If this weren't true then two observers standing side by side could see the universe as being of two different sizes, and two different ages. Which should be impossible. But if all observers see the universe as being the same age, then shouldn't we be able to set up a universal calendar upon which every observer could agree? In which case one twin when departing in his spaceship could tell his brother that he would be back on such and such a date, and they would be in complete agreement as to when that date is, simply by using the universe as a calendar. They may not know what age they would personally be on that date, but they would agree on when that date is. Do all observers see the universe as being the same size, and the same age? And can't this fact be used to create a universal calendar/clock?