This is the third in a series of posts prompted by Stephen Wolfram’s lengthy paper “How Did We Get Here? The Tangled History of the Second Law of Thermodynamics” (click here for it on ArXiv). The Second Law of Thermodynamics says, in brief, that the universe is Doomed, which leads to questions of how we can be so lucky as to not have reached Doom yet.
In post #2 of this series (click here for it) we finished with William Thomson, Lord Kelvin, discussing in 1852 how the universe was Doomed because heat flows from hot to cold. Lord Kelvin writes that at one time “the earth must have been… unfit for the habitation of man” and that in the future “the earth must again be” unfit. Later in 1852, Kelvin’s colleague, the Glasgow engineering professor William John Macquorn Rankine (now you know where the temperature units of Kelvin and Rankine come from), provided a synopsis of what Kelvin was saying (and of what we learned in post #2):
The experimental evidence is every day accumulating, of a law which has long been conjectured to exist, — that all the different kinds of physical energy in the universe are mutually convertible…. Professor William Thomson has pointed out the fact, that there exists (at least in the present state of the known world) a predominating tendency to the conversion of all the other forms of physical energy into heat, and to the uniform diffusion of all heat throughout all matter…. until all matter shall have acquired the same temperature.
There is, consequently, Professor Thomson concludes, so far as we understand the present condition of the universe, a tendency towards a state in which all physical energy will be in the state of heat, and that heat so diffused that all matter will be at the same temperature; so that there will be an end of all physical phænomena.
The end of all physical phenomena is what is often called the “heat death” of the universe. Scientific reasoning thus says that the universe is Doomed to thermal equilibrium (recall the term from post #2). In an 1854 paper, Kelvin wrote, “the end of this world as a habitation for man, or for any living creature or plant at present existing in it, is mechanically inevitable”.
But thermodynamics did not just point to an end; it also pointed to a beginning. In that same 1854 paper, Kelvin also wrote, “purely mechanical reasoning shows a time when the earth must have been tenantless; and teaches us that our own bodies, as well as all living plants and animals, and all fossil organic remains, are organized forms of matter to which science can point no antecedent except the Will of a Creator”.
In other words, the study of heat flow pointed to a universe that changes over time; it pointed to an evolving universe; it pointed to a universe in which we inhabit a moment in which conditions are favorable to life, sandwiched between a past of unknown length that was not favorable to life, and a future of indefinite length which will not be favorable to life.
This was a weird, maybe even repugnant idea to science. The normal scientific view had been that the universe is stable and unchanging. Aristotle imagined the universe to be cyclic and eternal, with no beginning and no end. So did lots of people. Aristotle’s universe was possible because it was Earth-centered, with the heavens that circled above it being made of an indestructible substance not found on Earth, all driven by the love of a single unchanging god who reason said must exist. The sun rose, the sun set; it drove the water cycle and the whole cycle of life — eternally.
This idea of an unchanging universe had been challenged by Copernicus’s idea that the Earth circles the sun, and by the Newtonian physics that followed. If Earth, Mars, and Venus all circle the sun, that means the Earth is a planet. It also means that the planets are in some sense other earths. Earth is not inherently indestructible. If planets are earths, that means that not all the universe is inherently indestructible, cyclic, and eternal (and maybe none of it is).
Nevertheless, well into the twentieth century, scientists were still expecting the universe to be eternal. In an interview in the 1960s, Fr. Georges Lemaître, who first developed what we now call the “Big Bang” theory for the origin of the universe, talked about how, in the 1920s,
we expected the universe to be static. We expected that nothing would change. It was an a priori idea that applied to the whole universe…. For which there was no experiment.
This attitude can be seen in the words of the astronomer Arthur Eddington from the early 1930s, around the same time that Lemaître proposed his theory:
[Going back in time] we come to a time when the matter and energy of the universe had the maximum possible organization. To go back further is impossible. We have come to an abrupt end of space-time — only we generally call it the ‘beginning’. I have no ‘philosophical axe to grind’ in this discussion. Philosophically, the notion of a beginning of the present order is repugnant to me. I am simply stating the dilemma to which our present fundamental conception of physical law leads us. I see no way around it [“The End of the World: from the Standpoint of Mathematical Physics,” Nature, 127, 450].
Eddington, who seems to be talking about thermodynamics here more than any “Big Bang”, was the British astronomer who led an expedition to use a solar eclipse to test Einstein’s relativity theory by measuring whether the light from stars that passed near the sun was deflected by the warping of space and time caused by the sun. Lemaître studied under Eddington.
So, given that the idea of an evolving universe was repugnant to Eddington in the twentieth century, you can imagine that Kelvin’s ideas would create quite the stir in the middle of the nineteenth century. Wolfram in his paper gives this quotation from Hermann von Helmholtz:
[The study of heat] has conducted us to a universal law of nature, which radiates light into the distant nights of the beginning and of the end of the history of the universe. To our own human race it permits a long but not an endless existence; it threatens it with a day of judgment, the dawn of which is still happily obscured. As each of us singly must endure the thought of his death, the human race must endure the same.
Helmholtz seems to be referencing both Genesis 1 and Matthew 25:31-46 here — the Beginning and the Last Judgment. The chemist Josef Loschmidt in 1876 spoke of “the terroristic nimbus of the Second Law… a nimbus which makes that Second Law appear as the annihilating principle of all life in the universe”. Doom. Judgment. Science was going all biblical on us in the nineteenth century!
So, how to rescue the universe from the Doom implied by science and its blasted Second Law of Thermodynamics? How do we get back to those nice cycles, with no beginning and no end?
Answer: We bring in a random multiverse!
That will be subject of the last post in this series!
CLICK HERE for all posts in this series.
