The First Quantum Cosmologist

By Sean Carroll | August 21, 2008 11:20 am

Many of you scoffed last week when I mentioned that Lucretius had been a pioneer in statistical mechanics. (Not out loud, but inwardly, there was scoffing.) But it’s true. Check out this passage from De Rerum Natura, in which Lucretius proposes that the universe arises as a quantum fluctuation:

For surely the atoms did not hold council, assigning order to each, flexing their keen minds with questions of place and motion and who goes where.

But shuffled and jumbled in many ways, in the course of endless time they are buffeted, driven along, chancing upon all motions, combinations.

At last they fall into such an arrangement as would create this universe…

Lucretius, along with Democritus and Epicurus, was an early champion of atomism — the idea that the tremendous variety of substances we see around us arise from different combinations of a few kinds of underlying particles. He was also a materialist, believing that the atoms obeyed laws, not that they received external guidance. So a problem arose: how could all of that regular atomic motion give rise to the complexity we see around us? In response, Lucretius (actually Epicurus — see below) invented the “swerve” — an occasional, unpredictable deviation from regular atomic behavior. And then, he points out, if you wait long enough you will swerve your way into the universe.

It’s a good idea, and one that has been re-invented since then. Boltzmann, another famous atomist, hit upon the same basic scenario. Here is Boltzmann in 1897:

There must then be in the universe, which is in thermal equilibrium as a whole and therefore dead, here and there relatively small regions of the size of our galaxy (which we call worlds), which during the relatively short time of eons deviate significantly from thermal equilibrium. Among these worlds the state probability increases as often as it decreases. For the universe as a whole the two directions of time are indistinguishable, just as in space there is no up or down.

However, just as at a certain place on the earth’s surface we can call “down” the direction toward the centre of the earth, so a living being that finds itself in such a world at a certain period of time can define the time direction as going from less probable to more probable states (the former will be the “past” and the latter the “future”) and by virtue of this definition he will find that this small region, isolated from the rest of the universe, is “initially” always in an improbable state.

Boltzmann imagines the universe as a whole (or what we would call the “multiverse”) is in thermal equilibrium, about which he knew a lot more than Lucretius. But he also understood that the Second Law was only statistical, not absolute. Eventually there would be statistical fluctuations that took the thermal gas and turned them into something that looks like our universe (which, as far as Boltzmann knew, was just the galaxy).

We are now smart enough to know that this kind of scenario doesn’t work, at least in its unmodified form. The problem is that fluctuations are rare, and large fluctuations are much more rare; a universe-size fluctuation would be rare indeed. Who needs 100 billion galaxies when one will do? Or even just one observer? This objection was forcefully put forward by none other than Sir Arthur Eddington in 1931:

A universe containing mathematical physicists [which is obviously the correct anthropic criterion — ed.] will at any assigned date be in the state of maximum disorganization which is not inconsistent with the existence of such creatures.

These days, we throw away the rest of the mathematical physicist and focus exclusively on the cognitive capacities thereof, and call the resulting thermodynamic monstrosity a Boltzmann Brain. The conclusion of this argument is: the universe we see around us is not eternal in time and bounded in phase space. Because if it is, over the long term we really would just see statistical fluctuations, and we would most likely be lonely brains. So either the universe is not eternal — so that it doesn’t have time to fluctuate ergodically throughout phase space — or its set of states is not bounded — so that it evolves forever, but doesn’t sample every possible configuration.

Sorry about that, Lucretius. You’ll be happy to know that we’re still struggling with these same issues. Except that you’re dead and famously railed against the irrationality of belief in life after death. So probably you don’t care.

CATEGORIZED UNDER: Science, Time
  • Lucretius

    I’m dead?!?!?!

    That does explain a lot. But…how am I posting, then?

    Dang…I hate being wrong

  • http://dienekes.blogspot.com Dienekes

    In response, Lucretius invented the “swerve” — an occasional, unpredictable deviation from regular atomic behavior. And then, he points out, if you wait long enough you will swerve your way into the universe.

    Lucretius did not invent the swerve; Epicurus did. In Epicurean physics, atoms move in straight lines unless they bounce off each other or become entangled to each other. But, Epicurus wondered, if the natural motion of the atoms is straight, why don’t they move parallel to each other but in many different directions, thus allowing them to form composite bodies? His answer to this question was that they occasionally randomly deviate from the straight path.

    http://www.iep.utm.edu/e/epicur.htm

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    You’re right; my mistake. Lucretius, as far as I know, was the first to try to explain the whole universe this way.

    Note that Boltzmann, despite not knowing about quantum mechanics, did not have to resort to a “swerve” to get statistical fluctuations. That’s because, post-Newton, we know about phase space and the equivalence of inertial trajectories. The Greeks and Romans thought that different kinds of matter had different kinds of “natural” motion.

  • wdjohns

    Nay, we scoff neither outwardly, nor inwardly lol!

  • http://vacua.blogspot.com Jim Harrison

    Lucretius and Epicurus believed that the natural motion of atoms was downwards so that if that’s all there was to it, they would continue on forever without colliding:

    “while the first bodies are being carried downwards by their own weight in a straight line through the void, at times quite uncertain and uncertain places, they swerve a little from their course…For if they were not apt to incline, all would fall downwards like raindrops through the profound void, no collision would take place and no blow would be caused amongst the first beginnings: thus nature would never have produced anything.” (II, 217-224 De Rerum Natura)

    Lucretius invoked the swerve (clinamen) not only to explain the creation of things but also to account for the freedom of the will.

    Factoid: Karl Marx’s doctoral dissertation was about the swerve.

  • cecil kirksey

    Sean:
    You edited the Boltzmann quote some. But any comments on his vision about the apparent size of the universe and galaxy? Did his use of the term “galaxy” mean the same as it does today? (Assuming that that is a correct translation of course.) Do you know when it was generally accepted that galaxies, as we now understand the term, were first recognized as a collection of stars independent from our Milky Way Galaxy? It would seem that Boltzmann at least conjectured this as early as 1897.

  • http://blogs.discovermagazine.com/cosmicvariance/sean/ Sean

    How did I edit the Boltzmann quote?

    The fact that some nebulae were distinct galaxies was a hot, controversial topic in 1920 (see the Shapley-Curtis Debate), finally resolved by Hubble in the mid-20’s. Long after Boltzmann. I don’t know what the state of speculation was during Boltzmann’s time.

  • http://dienekes.blogspot.com Dienekes

    Lucretius, as far as I know, was the first to try to explain the whole universe this way.

    The word translated as “this universe” is “concretam rem” (=concrete thing). Lucretius is not speaking of the whole universe which consists of an infinity of atoms and void, some of them free, others conjoined in worlds or other objects, but rather of the “world” which is formed by the confluence of atoms moving in random directions and is maintained by such confluence.

  • CarlN

    This is whole thing just an other argument for creation from nothing. Why has not reality reached thermal equilibrium long ago? Like an infinite time ago?

    :-)

  • The Last Quantum Cosmologist

    Over the last 10 years, theory and observation have led to a view of the universe as being infinitely large in both space and [future] time. I don’t think that people have yet understood the implications of this; the main one being that what would have seemed wild speculation 10 years ago is suddenly respectable science. Hence we have the gang of know-nothings scoffing at talk of Boltzmann Brains, not realizing that such things are *certain* to exist in our universe if it is really infinite as above…..

  • The Last Quantum Cosmologist

    “This is whole thing just an other argument for creation from nothing. ”

    I agree. But then we have to explain why “nothing” created “everything” in a state of ultra-low entropy……

  • CarlN

    Hi LQC, there is no reason to assume that “everything” was created with low entropy.

  • http://uslhc.us/blogs/?author=9 Seth Zenz

    I scoff.

    You may not be completely serious about your narrative, but in general the ancient philosophers get a lot more credit as scientists than they deserve. They considered, using the methods of philosophy, questions we would today consider scientific. Without a program for systematically comparing their ideas with real observations and refining them, the ones who happened to be right about these physical questions are no more praiseworthy than the ones who happened to be wrong.

    A modern scientist living two thousand years ago would have looked at the available evidence, set an upper bound for the size of atoms, and concluded, that while they could exist, there was no reason to believe they did.

    (Appreciating Lucretius for his philosophy, and even for his philosophical work on what would become the underpinnings of science—stuff like materialism—is fair enough.)

  • Thomas R.

    Conc. Epicurus: I guess he even had an idea about counterintiutive properties of random processes, e.g. like those of random walks which one could easily show with a balance and randomly distributed weights on it. Something like that might have bridged the apparent gap between the cosmological and lifestyle parts in his philosophy.

  • Fermi-Walker Public Transport

    The idea that the Milky Way galaxy was not the whole universe, but one amongst many was starting to be considered by 1890’s. Larger and better telescopes, such as Lord Rosse’s 72 inch reflector, were beginning to show detail in some of what were previously blurry objects. Most astronomers thought that these objects, which we now know to be spiral galaxies, were actually solar systems in the making since they roughly resembled what was expected from the Laplace-Kant theory of solar system formation. Some though took the bolder step and imagined that they were actually galaxies independent of our Milky Way.

  • Fermi-Walker Public Transport

    A pretty good book on the history of cosmological thinking from the mid-19th Century to Hubble is “Man Discovers the Galaxies” by Berendzen, Hart and Seeley.

  • http://dienekes.blogspot.com Dienekes

    Without a program for systematically comparing their ideas with real observations and refining them, the ones who happened to be right about these physical questions are no more praiseworthy than the ones who happened to be wrong.

    A scientist may propose a theory before it is technically possible to test it. When Democritus proposed that the Milky Way was composed of stars, there were no telescopes powerful enough to see the stars, does that make him not a scientist? The invariance of the speed of light was proposed as a theory before other scientists tested it. General relativity emerged as a theory before it could be tested empirically. The Higgs boson emerged as a theory before it could be tested empirically. A theory is scientific if it can be tested empiricially; whether or not it can be tested at the time it is proposed in no way diminishes the achievement of its creator.

  • T.R.

    Walter Benjamin discussed in his “Passagenwerk” Blanqui’s Essay:
    http://classiques.uqac.ca/classiques/blanqui_louis_auguste/eternite_par_les_astres/eternite_.html
    as crucial for understanding an often ignored general public impact then of 19th century cosmology.

  • http://atomakaikeno.wordpress.com/ Sarkaflias

    Epicurus’ Letter to Herodotus is an epitome of the lost 37 volumes On Nature.
    In the paragraph 60-63 of this letter, Epicurus represents some details of the atomic theory corresponding to the quantum principle of superposition.
    Generally Epicurean school has a very robust physical theory because they refined
    the original democritean atomic theory.

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  • http://voicesofreason.info Neil B. ?

    Just in general terms, I have long been impressed with what the ancient thinkers could imagine, and accomplish.

  • http://vacua.blogspot.com Jim Harrison

    Since nobody made the point, I will. Lucretius was not only an insightful thinker, he was also a wonderful poet. It takes some talent to write a great poem about atoms and void.

  • http://atomakaikeno.wordpress.com/ Sarkaflias

    Yes, but the key element of theories of ancient thinkers was the absolute, radical materialistic monism. They achieved such theories using the tool of monism without any metaphysical entities.
    In epicurean/democritean/atomic terms “void” is also “being” like atoms. Void exist the same like the atoms. There is not “zero”, or “not being” in monism. Everything that exist is one thing, “one being”, and this is the matter.
    In modern terms, there is no absolute void but “quantum void”, in “quantum void” particles produced all the time by the living “one being”.

  • http://uslhc.us/blogs/?author=9 Seth Zenz

    Hi Dienekes,

    Of course a theory can be proposed before it can be tested empirically. I think theories do become less useful the further in the future that testing is, and several of your example theories were proposed virtually hand-in-hand with corresponding experiments. The Higgs boson was testable much longer ago than you might think–it’s just that the searches for the Higgs boson at a few GeV came up negative. And of course, Einstein himself predicted how to test General Relativity using the 1919 solar eclipse, only four years after he published the theory, and the test worked out well.

    But the larger issue, and the reason that the ancient atomists weren’t really scientists, is that (as far as I understand it) they had no concept that their ideas needed to be tested. Are their ideas important philosophical building blocks of science? Yes. But were they scientists? No.

  • http://dienekes.blogspot.com Dienekes

    I think theories do become less useful the further in the future that testing is

    That is true only from the viewpoint of the time when theories are proposed. They are not immediately useful; they may be appealing because of their simplicity or elegance, but you can’t accept them fully.

    It is the empirical evidence that decides whether such theories are _accepted_ as scientific explanations. Theories are right or wrong whether or not they are recognized as such or not. It doesn’t make one iota of difference whether they are recognized as such during or shortly after their originator’s lifetime. In fact, the larger the intervening time, the more visionary they appear to be.

    The Higgs boson was testable much longer ago than you might think–it’s just that the searches for the Higgs boson at a few GeV came up negative.

    Democritus’ theory was also testable when the first magnifying glasses appeared. Eventually one of them was powerful enough, and someone pointed it to the heavens, and the theory was confirmed.

  • http://uslhc.us/blogs/?author=9 Seth Zenz

    But as I said, Dienekes, Democritus didn’t think he needed to test it. And he didn’t believe it because his previous observations made him suspect it explained the data better than the alternative hypothesis. So he believed something that turned out to be true, but as far as I’m aware, it was for the wrong reasons. How visionary is that, really?

  • yo

    He applied logic to nature, as far as i am concerned
    he was a scientist.

  • http://dienekes.blogspot.com Dienekes

    But as I said, Dienekes, Democritus didn’t think he needed to test it.

    There was no way to test it back then. Should Democritus have conceived of the telescope too?

    Your notion that the atomists (especially Democritus) did not see the need to test their theories is not based on any evidence. Their works abound with empirical justifications for their theories.

    You’d have a point if Democritus’ theory on the Galaxy was just a wild guess. If someone makes 1,000 wild guesses, then one of them may turn out to be true, but that doesn’t make him a visionary.

    However, Democritus didn’t get it right about the Galaxy by a wild guess. His idea was a natural consequence of his physical theory.

    Scientists extrapolate their theories beyond what can be tested at the time. They proposed the idea of a “black hole” long before anyone thought of a way to “observe” one.

  • http://bigganpuri.wordpress.com Khan Muhammad

    Very interesting. One of my favorite posts in Cosmic Variance.

    I tried to read the foreward of “The Difference Between the Democritean and Epicurean Philosophy of Nature” (Doctoral Dissertation of Karl Marx) few months earlier but understood nothing.
    Today, I’ve got something more objective to think of. Finally, I am starting to understand the materialism of Karl Marx.

  • Randy

    A “neither world” is both existant and not at the same time. Quantum flux particle acceleration = matter. Quantum flux particle accelerators can be a very big thing when pumping energy into the void.

    A state of being only occurs where there is a significant quantum flux in the quantum void or vacuum.

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Random samplings from a universe of ideas.

About Sean Carroll

Sean Carroll is a Senior Research Associate in the Department of Physics at the California Institute of Technology. His research interests include theoretical aspects of cosmology, field theory, and gravitation. His most recent book is The Particle at the End of the Universe, about the Large Hadron Collider and the search for the Higgs boson. Here are some of his favorite blog posts, home page, and email: carroll [at] cosmicvariance.com .

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