Host: Let us begin with you, Sir Isaac. How big do you believe the universe is, and what is its shape?
Newton: Well, after I discovered that all bodies of matter attract each other with a force that is proportionate to their mass, I soon applied this law of gravity to all of the stars and other celestial bodies that we see with our telescopes. In 1692, I wrote a letter to a colleague of mine, Richard Bentley, and told him that the universe must be infinite in size.
Host: Why did you believe that?
Newton: For several reasons. First, if the universe was finite, then all of the matter on the outside would be attracted toward the middle by the force of gravity and the result would be one great spherical mass at the center, which we do not currently observe.
Secondly, if the universe was finite then we would have to answer Bruno’s age-old question: what lies beyond the finite universe? There is no possible answer for this question.
On the other hand, if all matter is evenly scattered throughout an infinite space, then some of it would be attracted by the force of gravity into one mass, and some of it into another mass, and so on. Therefore, the universe would end up as an infinite number of great masses scattered at great distances apart throughout all that infinite space. And, I might add, this scenario is exactly what we currently do observe.
Host: Dr. Einstein, what do you think about Newton’s infinite universe?
Einstein: Vell, in 1917 I thought that the universe could be infinite in time, and it didn’t appear to be moving so I thought that it was a static universe. But I found a couple of criticisms of Isaac’s infinite universe that led me to believe that it should not be infinite in space.
Host: What were those criticisms?
Einstein: Probably the most important one was, that when we pointed our telescopes to the heavens in 1916 the number of stars appeared to thin out to nothing after awhile in all directions, so we couldn’t find any of the great masses that Isaac was talking about.
Host: How did you attempt to solve this problem?
Einstein: Ah ha, with mathematics of course. In 1917, I found the answer in the Spacetime geometry of my General Theory of Relativity: The Universe must be finite and spherical. Please see Figure 6. But in order to keep the finite mass uniform and to keep my spherical universe from collapsing toward the center like Isaac suggested that it might, I had to imagine and invent a new force that would oppose gravity. I called this new theoretical force the cosmological constant force. It’s amazing what you can do with a good imagination and mathematics, don’t you think?
Host: But Dr. Einstein, how did you answer Bruno’s impossible question: what lies beyond your finite spherical universe?
Einstein: Ah yes, that little detail. Hmm. Vell, I try not to think about that too much.
Host: How has your new finite spherical universe been received by the scientific community?
Einstein: Vell, not too many people knew about it at first, but my mathematical friends thought it was pretty clever. A finite spherical or cylindrical universe resulted in a perfectly uniform mathematical field of matter where all motions and accelerations were mathematically completely relative or the same. I needed this result in order to make my General Theory theoretically work perfectly. In other words, so that all accelerations were perfectly equivalent.
Oh yes, there were a couple of guys, one a Russian named Friedmann and the other a Belgian cleric named Lemaitre, who during the 1920s tried to tinker with it. They claimed that my finite spherical universe was mathematically unstable and that it could either collapse or expand forever. But I ignored both of them pretty much, and I didn’t hear many other criticisms for awhile.
Host: Why did you ignore them?
Einstein: Because, during the period between 1917 and 1924 there was no convincing observational evidence that contradicted my concept of a static Finite Spherical Universe. Most of our relatively small telescopes during this period could not see much beyond the Milky Way mass of stars, and the Milky Way appeared to be finite, somewhat spherical in shape, and it appeared to have boundaries at the point where there were no more stars. So naturally I thought that the Milky Way mass of stars was the entire universe.
As for the mysterious spiral nebulae or clouds which some astronomers reported, it could not then be determined whether they were just clouds of gas within the Milky Way system or something that lay beyond it.
Even after 1925, when Hubble discovered that many of these nebulae were actually independent island universes or galaxies of stars, there was no observational evidence that my static mathematical spherical universe might be collapsing or expanding. As my colleague George McVittie once stated: “the [typical] galaxy shows no sign of being in motion; the direction in which it lies never changes; its angular diameter does not alter, and so on.”
Host: Dr. Hubble, about this time didn’t you receive a new much more powerful telescope?
Hubble: Yes. It was 100 inches across; the largest telescope in the world in 1920. After it became operational on Mount Wilson we pointed it at some of these mysterious distant objects called nebulae. When we pointed it at the nearby Andromeda spiral nebula we could clearly see that Andromeda was not just a cloud of dust inside of the Milky Way system, but rather it was composed of many distant stars. In other words, it was a separate galaxy of stars just like the Milky Way Galaxy. Once we were able to estimate its distance from Earth to be about 2 million light years away, we were sure about our conclusion. That was in 1925.
By the way, a “light year” is the distance that light travels through empty space at the velocity of 300,000 kilometers per second during one year.
Thereafter, during the late 1920s, we discovered quite a few more galaxies in the neighborhood of the Milky Way Galaxy. It soon dawned upon us that these were the great masses of matter scattered throughout seemingly infinite space that Isaac Newton had been talking about in 1692, and which Einstein’s much smaller telescopes had failed to detect in 1917.
Host: Dr. Einstein, what did you do when you read about Hubble’s discoveries of galaxies?
Einstein: Nothing. I was just as amazed as everyone else.
Host: Was that all that you discovered about galaxies, Dr. Hubble?
Hubble: No, not by a long shot. Over the next four years after 1925 my assistant, Milton Humeson, and I discovered more and more galaxies farther and farther out into endless space. But all of these galaxies taken together had a very unique and puzzling feature. The magnitude of the redshifts observed from each of the most distant galaxies were exactly proportional to their estimated distance from the Earth. And this trend continued out into space as far as we could observe. In 1929, Humason and I called this strange phenomenon the “law of redshifts.” Please see Figure 7.