Saturday, May 27, 2023

Five Cosmological Theories of How It All Ends, And How They Are All Incomprehensibly Mysterious


The cosmological theory of the Big Crunch predicts that eventually the Universe will collapse upon itself, because the expansion of the Universe initiated at the Big Bang will begin to slow down through the force of gravity on matter until the Universe collapses back into something like a black hole, although this would be far in the future, probably tens of billions of years.

Deciding the plausibility of this theory depends on measuring the expansion rate of the Universe.  In the late 1990s, some cosmologists determined that far from slowing down, the expansion of the Universe was actually speeding up, which seemed to show that the Universe would be eternally expanding, and thus the Big Crunch theory must be false.


If the expansion of the Universe is accelerating, that suggests that the Universe will end in Heat Death.  Here "heat" means not "warmth" but rather the "disordered motion of particles or energy"--entropy.  According to the Second Law of Thermodynamics, in any isolated system, the total entropy or state of disorder must increase.  If the Universe can be considered an isolated system, then it must evolve towards increasing disorder or decay, in which no organized structures can exist.  Most cosmologists consider this Heat Death the most likely fate of the Universe.

The problem with this theory of Heat Death, however, is that it depends upon some ideas that are so deeply mysterious that no one can understand them.  For example, dark energy is a hypothetical form of energy permeating all of space that tends to accelerate the expansion of the Universe.  If dark energy keeps a constant density as the Universe expands, then we get Heat Death.

But while dark energy is believed by some cosmologists to constitute about 70% of the total energy in the observable universe, dark energy is invisible and undetectable in laboratory experiments.  If it is real, it must arise from a new kind of physics that no one understands today.  As Mack says, dark energy is "a sure sign of some new physics beyond our current understanding" (2020, 106).


While the evolution of dark energy as a cosmological constant keeps a constant density as the Universe expands leading eventually to Heat Death, with "phantom dark energy," the density increases, and we get the Big Rip, in which everything in the Universe--even spacetime itself--is progressively torn apart.  First, the clusters of star galaxies begin to drift apart and then dissipate.  Next, the Earth drifts away from the Sun, and the Moon drifts away from the Earth.  Every structure begins to strain from the expanding space within it.  Planets explode.  Then atoms and molecules unravel from the expanding space within all matter.  Even the nuclei at the centers of atoms are torn apart.  But maybe we shouldn't worry about this because it is estimated that the earliest possible Big Rip is somewhere around 200 billion years in the future (Mack 2020, 114-15).

When Robert Caldwell and his colleagues first wrote about this in 1999, they explained their term "phantom dark energy":  "A phantom is something which is apparent to the sight or other senses but has no corporeal existence--an appropriate description for a form of energy necessarily described by unorthodox physics" (Caldwell 2002, 23).  In other words, no one understands what this means or whether it has any real "corporeal existence," because it is beyond comprehension through the established laws of physics.


                            Paul Sutter on False Vacuum Decay and the End of the Universe

Like Paul Sutter, Katie Mack explains the possibility of the Universe ending through vacuum decay by considering the Higgs field that permeates the Universe.  The Higgs field is a field of energy that is accompanied by a fundamental particle known as the Higgs boson, which interacts with other particles, and through this interaction, these particles gain mass.  Without the Higgs field, particles would not have the mass required to attract one another, which supports the physical structure of the Universe as we know it.

In 2012, the Higgs boson was detected at the Large Hadron Collider.  In 2013, the Higgs effect was proven at the LHC.

The value of a field can change depending upon its potential.  You can imagine the potential of the Higgs field as a pebble rolling down a slope into a valley, and the shape of that slope represents the potential.  Just as a pebble will roll to the bottom of a valley, the Higgs field will seek the lowest-energy state, where the potential is at its lowest value, which is its vacuum state.  The problem, however, is that the bottom might not really be the bottom.  There might be another vacuum state at a lower part of the potential that will be its true vacuum state.  Look at it this way:

Mack explains: "Each valley in the potential is a possible state of the Universe.  If our Higgs field lives in the higher valley (the false vacuum), it could transition to the other state (the true vacuum" via a high-energy event (marked 'fluctuations' on the diagram) or via quantum tunneling.  If we live in a false vacuum universe, a transition of the Higgs field to the true vacuum would be catastrophic" (Mack 2020, 143).

And by "catastrophic," she means that everything in the Universe would be annihilated.  It would start with the formation of a tiny bubble of true vacuum.  The world within that bubble would be governed by a physics with laws different from those that govern our Universe.  As that bubble expanded at the speed of light, the forces that previously held particles together in atoms and nuclei would no longer function, and consequently would be dissolved.

Mack reassures us: "it's for the best that you don't see it coming."
". . . if you happen to be standing nearby when the bubble appears, you won't notice it.  Something coming at you at the speed of light is invisible--any little glint warning you of its approach arrives at the same time as the thing itself.  There is no possible way to see it coming, or even to know that anything has gone wrong.  If it approaches you from below, there will be a couple of nanoseconds during which your feet no longer exist while your brain still thinks it is looking at them.  Fortunately, the process is also entirely painless: at no point will your nerve impulses be able to catch up with your disintegration by the bubble.  It's a mercy, really."

She also observes:

"In fact, it's entirely possible that, as we sit here now, calmly drinking our tea, vacuum decay has already occurred.  Maybe we're lucky and the bubble is beyond our cosmic horizon, swallowing up galaxies we would never have known.  Or maybe it is, cosmically speaking, right next door, quietly approaching with relativistic stealth, destined to catch us unawares, between breaths" (2020, 145-46).

Even without fully understanding what this all means, it's easy enough to see that the plausibility of this theory of how the Universe could be destroyed by a false vacuum decay depends on the claim that our Higgs field is indeed in a false vacuum or a "metastable state"--somewhat stable but not fully so.  

As she often does, Mack contradicts herself on this point.  On the one hand, she says that "the best data we have" confirms this claim that our Higgs field is in a false vacuum (143).  On the other hand, she says there are good reasons to doubt this.

"If we conclude that our vacuum really is unstable, this may be incompatible with the theory of cosmic inflation [in the first nanoseconds after the Big Bang].  The quantum fluctuations during inflation, or the ambient heat afterward, seem like they should have been sufficient to trigger vacuum decay in the first moments of the cosmos, negating our very existence.  Clearly, that didn't happen.  Which suggests either we don't understand the early universe, or vacuum decay was never possible at all."

"Whether or not you trust early universe theories, taking vacuum decay seriously depends on placing a great deal of trust in the Standard Model of particle physics, which we know cannot be the whole story.  Dark matter, dark energy, and the incompatibility of quantum mechanics and general relativity all point to there being something more to the universe than what we can currently write down.  Whatever comes along to replace the Standard Model might, by the by, save us from even having to vaguely worry about a wayward bubble of quantum death" (154-55).

But then there's still at least one more cosmological theory of how the Universe might end.


According to a "bouncing" or "cyclic" cosmology, the Universe began as a bounce from a pre-Big Bang universe to our current universe, which will in turn come to an end, but will then be bounced into a new universe.  One version of this cosmology is the ekpyrotic scenario.  "Ekpyrotic" comes from the Greek for "conflagration," which is associated with the ancient Stoic cosmology in which the universe goes through an eternal cycle of fiery birth, death, and fiery rebirth. 

The ekpyrotic Universe is grounded in the idea of "braneworld" from superstring theory.  String theory is a theoretical framework for physics in which the particles of particle physics are replaced by one-dimensional strings. But some string theorists have said that these strings could be multidimensional.  A multidimensional string is called a "brane"--short for "membrane."

The ekpyrotic theorist can say that our Universe lives on a three-dimensional brane within a larger space of multiple branes.  When two branes collide, this produces a new universe--that's the "bounce"--and this can become an eternal cycle of collisions and bounces.  This is a kind of multiverse theory insofar as the multiple branes can be understood as multiple universes.

There are many problems with this theory, however.  The most obvious is that there is no observational evidence for string theory or multiverse theory, because--as I have indicated in a previous post--looking for hypothetical strings and other universes reaches beyond the range of human observational experience, and therefore these hypothetical realities are in principle untestable and unfalsifiable.

Moreover, cyclic cosmology faces a fundamental problem shared with all other cosmological theories to explain the end of the Universe--physicists cannot reach any agreement on any of the theories.  Mack admits this: "Unfortunately, despite decades of hard work and extraordinary calculations, we haven't yet settled on a theory that's broadly accepted by the physics community" (161).


Mack reports that even though they cannot agree on any one theory of how the Universe will end, physicists do agree that the Universe must somehow come to an end eventually, even if the end is far off in the cosmic future.  So, then they must wonder what this tells us about the ultimate meaning and purpose of life.

Mack has interviewed many physicists and asked them about this: What does it mean to us if the Universe must end?  Hiranya Peiris summed up her answer in one word: "sad."

"It's very depressing," she said.  "I don't know what else to say about it.  I give talks where I mention that this is probably the fate of the universe, and people have cried" (206).

Mack likes to quote from one of the earliest papers on vacuum decay by Sidney Coleman and Frank De Luccia.  Once the true vacuum bubble forms, everything inside it will collapse gravitationally within microseconds (154).  Then they wrote:

"This is disheartening.  The possibility that we are living in a false vacuum has never been a cheering one to contemplate.  Vacuum decay is the ultimate ecological catastrophe; in a new vacuum there are new constants of nature; after vacuum decay, not only is life as we know it impossible, so is chemistry as we know it.  However, one could always draw stoic comfort from the possibility that perhaps in the course of time the new vacuum would sustain, if not life as we know it, at least some structures capable of knowing joy.  This possibility has now been eliminated" (Coleman and De Luccia 1980, 3314).

Surely, this must be what Leo Strauss saw as the "most terrible truth" of evolutionary science as taught by Lucretius: "nothing lovable is eternal or sempiternal or deathless, or that the eternal is not lovable."  And yet while most human beings would be crushed by this terrible truth, Strauss argued, those few human beings who can live the intellectual life of philosophy or science--devoted to Reason rather than Revelation--can bear this truth, because for them the intellectual understanding of the nature of reality, including the terrible truths of nature, is in itself deeply satisfying.

Mack and many of her colleagues in physics and cosmology seem to partly agree with Strauss about this.  They agree with him that understanding the nature of the Universe--including how it must end--is satisfying.  

Mack concludes her book by reporting an interview with a scientist who says that contemplating the end of the Universe in Heat Death isn't depressing or boring for her but "cold and beautiful."  "Even if we can do nothing to change it, that knowledge . . . even if that knowledge goes away, if all humans die, that knowledge right now is incredible. . . . I am delighted that we get to live at a time in the universe when we can see dark energy and not be ripped apart by it.  But that means the whole point is that you understand it, and then you enjoy it, and then . . . 'so long and thanks for all the fish.'  Cool."

As the last word for her book, Mack repeats that word: Cool.

But even if understanding that the Universe and everything in it must die is cool for scientists like herself, is it cool for everyone else?  Strauss thought not.  He thought that for thousands of years philosophers and scientists understood the need to hide such terrible truths by writing esoterically to avoid harming that great multitude of human beings who would be crushed by learning such truths, and who needed the comforting belief in the religious conception of the Universe as divinely created by a Creator who loved and cared for human beings.

Clearly, scientists like Mack think Strauss is wrong about this.  They accept the claim of the modern Lucretian Enlightenment that scientists and philosophers should openly share their understanding of nature with the general public, even when that understanding might seem at first deeply disturbing.  This is evident with someone like Mack who writes about science for a popular audience, and who often writes in a comic tone about the inevitable end of the Universe.  Evidently, she assumes that she can convince her readers, including those who are not devoted to the life of science, that understanding the terrible truths of modern science is cool.

But then when Mack and her colleagues say that "the whole point is that you understand it," we might wonder--do they really understand it?  After all, she repeatedly admits that the dominant components of the cosmos--such as dark matter and dark energy--are "beyond our current understanding" and "completely mysterious"--and "in that sense we don't understand at all" (106, 180-81).  So here she contradicts herself by both affirming and denying that scientists really understand the nature of the Universe.

She could resolve the contradiction by saying that by "understanding" she means the Socratic understanding of one's ignorance.  As scientists probe ever deeper and farther into nature, they discover the limits of human observational experience of the Universe.  And so, for example, we can infer the reality of phenomena like dark matter and dark energy; but since we cannot directly observe or detect them, we cannot fully understand them or explain them.  This illustrates how the evolutionary adaptation of the human mind gives us a reliable but fallible understanding of the world.

As long as the human mind faces such fundamental mysteries of nature that cannot be dispelled by reason alone, those of us who appeal to Reason as the ultimate authority cannot refute those who appeal to Revelation as the ultimate authority for understanding the nature of reality.  And so, for example, an atheistic scientist like Mack cannot refute a Christian scientist like Deborah Haarsma who argues that the scientific understanding of the Universe cannot refute the religious understanding of why the Universe is so fine-tuned for human life.

This leaves an opening for appealing to Revelation to explain how the Universe will end.  That will be the topic for the next post.


Coleman, Sidney, and Frank De Luccia. 1980. "Gravitational Effects on and of Vacuum Decay." Physical Review D 21: 3305-3315.

Mack, Katie. 2020. The End of Everything (Astrophysically Speaking). New York: Scribner.


1 comment:

Roger Sweeny said...

The idea of "the heat death of the universe" is pretty much as old as the development of the entropy concept and the realization that since heat always moves from hotter to colder, eventually the entire universe will be lifeless, at a uniform low temperature.

William Thomson said as early as 1852, "There is at present in the material world a universal tendency to the dissipation of mechanical energy... Any restoration of mechanical energy, without more than an equivalent of dissipation, is impossible... Within a finite period of time past, the earth must have been, and within a finite period of time to come the earth must again be, unfit for the habitation of man." ("On a Universal Tendency in Nature to the Dissipation of Mechanical Energy", The Philosophical Magazine, 1852) Thomson was a biggie in Victorian science. So much so that he was "ennobled" as Lord Kelvin, which is how most people know him today.

My impression (which may be completely wrong) is that for forty years, few people noticed or cared about the potential "heat death of the universe" but that toward the end of Victoria's reign, it was one of many things leading to a loss of optimism and a vague feeling that things weren't as good as people had supposed.