Host: Now back to you, Dr. Eddington. How would you describe your expanding universe theory?
Eddington: In my 1933 book, I have a short description of the expanding universe. Let me read it:
“For a model of the universe let us represent [Einstein’s] spherical space by a rubber balloon. Our three dimensions of length, breadth and thickness ought all to lie in the skin of the balloon…Imagine the galaxies to be embedded in the rubber. Now let the balloon be steadily inflated. That’s the expanding universe.”
In other words, the universe is exhibiting a “General Uniform Expansion.”” Please see Figure 20 for several analogies, in order to see what I am talking about.
Dingle: Those are nice, simple analogies, but when you analyze Eddington’s General Uniform Expansion concept from the point of view of observers on each expanding galaxy, you arrive at impossible anomalies. Please see Figure 21.
Host: Dr. Eddington, I know that you were concerned that the systematically expanding speed of the material galaxies might eventually exceed the speed of light. How did you reconcile this problem?
Eddington: Oh, that was fairly simple. We merely changed our theory from an expansion of matter through space (which is subject to the speed limit of Special Relativity), to Professor Georges Lemaitre’s theory that the space itself in Einstein’s spherical universe was actually doing the expanding. In Lemaitre’s theory, galactic redshifts were eventually renamed “Cosmic Redshifts,” and the material galaxies were considered to be dragged along in all different directions by the general uniform expansion of space. Space, of course, is nothing and therefore it is not subject to the speed limit of light or Special Relativity. Pretty clever, huh?
Host: Wasn’t that “expansion of space concept” just an expanding universe with a different name?
Eddington: I guess you might look at it that way.
Host: Didn’t Einstein or someone else around this time invent a new curved Special Relativity redshift expansion correlation to take the place of Hubble’s linear magnitude of redshift to estimated distance of galaxies correlation?
Eddington: Oh yes. That was imagined and invented so that the constantly increasing Doppler velocities of the expanding material galaxies could never reach or exceed the speed of light, as is required by Special Relativity. Please see Figure 22.
Host: Wasn’t that a rather artificial and unscientific solution for your dilemma?
Eddington: Well, I guess so, but we had to do something to keep the expanding universe theory from contradicting Einstein’s Special Theory of Relativity, and vice-versa.
Hubble: I would like to comment on this subject. The new curved special relativity expansion-velocity correlation line was not only arbitrary and unscientific, but it also contradicted any possible inference that my observed linear correlation of increasing magnitudes of redshift to estimated distances of galaxies indicated a systematic linear increase in galactic velocity. In other words, it destroyed any inference that the universe as a whole was rapidly expanding.
Dingle: I agree. Eddington and his relativistic and expansionist colleagues were, in effect, trying to eat their cake (the linearly expanding universe) and keep it, too (with Special Relativity). But with a curved correlation of expansion they can’t have it both ways! Special Relativity appears to be the expanding universe’s Achilles heel, and vice-versa.
Host: Dr. Eddington, there are many people who would say that your 1933 book convinced the world that the universe was expanding.
Eddington: Thank you for the compliment, and my 1933 book did become a best seller. I am especially proud of the fact that today the expanding universe is considered to be an established fact of nature and a scientific law. But I also had a lot of help in promoting my theory. For example, there was Dr. Einstein who helped immensely.
Host: Dr. Einstein, what did you interpret the observed galactic redshifts to mean?
Einstein: Vell, by late 1931, the evidence for an expanding finite spherical universe had become overwhelming, so I was forced to abandon my 1917 static finite spherical universe theory and change it to an expanding finite spherical universe theory.
About that time, I wrote an addendum to my book, Relativity, which included the following excerpts. Please let me read them to you.
“Hubble showed, by a special investigation of the [galaxies], that the spectral lines emitted show a redshift which increased regularly with the distance of the [galaxies]. This can be interpreted in regard to our present knowledge only in the sense of Doppler’s principle, as an expansion motion of the system of stars in the large…
“the interpretation of the galactic line-shift discovered by Hubble as an expansion…can hardly be doubted from a theoretical point of view…”
At this point, I got together with Willem de Sitter and we jointly created a new expanding model of the finite spherical universe. Please see Figure 10.
But I was particularly disappointed in my artificial cosmological constant force which I felt had let me down. I felt that it was the worst mistake that I had ever made in my life. If it hadn’t been for that ugly concept I might have discovered the Expanding Universe on my own.
Hubble: Excuse me, Dr. Einstein, but I never stated or implied that my linear law of redshifts indicated an expansion of the universe. On the contrary, after my extensive studies on the subject during the middle 1930s, my conclusion was exactly the opposite.
Host: Dr. Einstein, I have a question. Since your modified 1931 expanding finite spherical universe theory contained flat Euclidean space, wasn’t this a contradiction to your 1916 General Theory of Relativity, which was founded on non-Euclidean curved space? And wasn’t it also a contradiction to your finite spherical universe itself, which was based on the curvature of space concept of General Relativity?
Einstein: Vell, I guess so, but what was I to do? The expanding universe theory was based on Hubble’s observed linear Doppler correlation of increasing galactic velocities proportional to estimated distances, and curved space would destroy this linear relationship.
Shame on you, young man! I was hoping that no one would notice that my theories contradicted each other.
Host: Dr. Eddington, was the 1931 Einstein-de Sitter universe the only model of the expanding finite spherical universe that was invented?
Eddington: Oh no. There were literally dozens of other expanding and contracting models. The first ones were created by Friedmann around 1922 – 24. He invented numerous models that all began with a Big Bang. Then there was Lemaitre’s 1927 model of the expansion of the space in Einstein’s 1917 finite spherical model. De Sitter created his own model in 1917 that didn’t have any matter in it. After 1929 dozens of different models were created. Please see Figure 23 which illustrates some of these imaginative models. I even created my own model of the expanding finite spherical universe in 1933 which is illustrated in Figure 24.
Host: Dr. Hubble, you just stated that during the late 1930s you did not believe that the universe was expanding. What did you interpret galactic redshifts to indicate?
Hubble: After the so-called “velocity-distance relation” had been formulated by Eddington and others, during the early 1930s, Humason’s observations of faint galaxies began to accumulate. It was then that our much earlier…[Doppler velocity] tentative interpretation began to fade, and we became more and more skeptical. Let me read from my 1937 book:
“Each million light-years of distance added a hundred miles per second to the ‘velocity’ of each galaxy. As Humason swept farther and farther out into space he reported ‘velocities’ of 5,000 miles per second, then 10,000 then 15,000. Finally, near the absolute limit of our [Mount Wilson] spectrograph Humason recorded red-shifts of 13 and 14 per cent [of the speed of light], ‘velocities’ of about 25,000 miles per second—around the earth in a second, out to the moon in 10 seconds, out to the sun in just over an hour. Red-shifts continued to increase beyond the range of our spectrograph, and, for the faintest [galaxies] that could be photographed—the ‘velocities’ were presumably about 50,000 miles per second. These enormous quantities we were asked to accept as measuring a general recession of the galaxies, an expansion of the universe itself.
“Another reason for our skepticism was that ‘the familiar interpretation of red-shifts [as Doppler velocity indicators] seems to imply a strange and dubious universe, very young and very small.’ On the other hand, the plausible and, in a sense, familiar conception of a universe extending indefinitely in space and time, a universe vastly greater than the observable region, seemed to imply that red-shifts were not primarily velocity-shifts.”
Newton: I would agree with that logic. This whole idea of a finite spherical universe in the shape of the skin of a balloon, let alone a universe that is expanding at enormous speeds, sounds to me like what you would now call: science fiction.
Hubble: I concluded that perhaps the [galaxies] are all receding in this peculiar manner. But the notion is rather startling.
Host: Please go on, Dr. Hubble. believe that the universe was expanding. What did you interpret galactic redshifts to indicate?
Hubble: Let me continue reading from my 1937 book:
“The cautious observer naturally examines other possibilities before accepting the proposition of an expanding universe even as a working hypothesis. He recalls the alternative [interpretation] of the law of red-shifts—that light loses energy in proportion to the distance it travels through space. The law of red-shifts, in this form, sounds quite plausible. Intergalactic space, we believe, cannot be entirely empty. There must be a gravitational field through which the light-quanta travel for many millions of years before they reach the observer, and there may be some interaction between the [light] quanta and the surrounding medium. The problem invites speculation, but no satisfactory, detailed solution has been found. Light may lose energy during its journey through space, but if so, we do not yet know how the loss can be explained.”
Let me now continue with my speculations as to how light might lose energy as it propagates over millions of light years through space. And I quote:
“As light streams in from the remote [galaxies] in all direction, each million years of the light-paths subtracts the same fraction of energy from the light quanta. We may not know [exactly] how the reduction is accomplished, but we do know that the action is everywhere uniform.
“The observer seems to face a dilemma. The familiar interpretation of red-shifts leads to rather startling conclusions. These conclusions can be avoided by an assumption which sounds plausible, but which finds no place in our present body of knowledge. If the source [of the galactic redshifts] lies in the intervening space, the [exact] explanation of red-shifts is unknown but the [galaxies] are sensibly stationary.”
Host: Dr. Eddington, didn’t you at some point also explore the alternative possibility that galactic redshifts might be produced by the loss of light energy over the enormous intervening space through which light must travel?
Eddington: Yes. In my 1933 book I stated that, and I quote:
“The reddening signifies lower frequency of the light-waves and (in accordance with quantum theory) lower energy; so that if for any cause a light-quantum loses some of its energy in traveling to reach us, the reddening is accounted for without assuming any velocity of the source.
“If the loss occurs during the passage of the light from the [galaxy] to the observer, we should expect it to be proportional to the distance; thus the red-shift, misinterpreted as a velocity, should be proportional to the distance—which is the law actually found.”
My colleague Fred Zwicky came up with all kinds of ideas for how such loss of energy could occur, including: gravitational drag on photons, collisions of photons with material particles and other rays, countless absorption and re-emission processes, etc., all of which could subtract energy from photons of light. De Sitter and other scientists mentioned other possibilities.
But in the end, I went with the Doppler interpretation because it was a known and confirmed scientific phenomenon, whereas the loss of light energy over the distance traveled would involve a new, unknown and unconfirmed phenomenon of nature.
Host: Dr. Eddington, how sure were you that your interpretations were correct, and that the universe was really expanding?
Eddington: Oh, I was very sure. But I know what you are referring to. Toward the end of my 1933 book I did state (and I quote):
“…the theory of the expanding universe is in some respects so preposterous that we naturally hesitate to commit ourselves to it. It contains elements apparently so incredible that I feel almost an indignation that anyone should believe in it—except myself.”
Host: At this point, perhaps we should take a short intermission.